NATIONAL BUREAU OF STANDARDS REPORT

6246

Engineering Manual for Protective Construction

Part V

Heating and Air Conditioning

of Underground Installations

Revision by

B. A. Peavy

H. E. Robinson

R. S. Dill (Deceased)

Report to

Office of the Chief of Engineers

Department of the Army

li. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL KUKEAL' OF STANDARDS

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NATIONAL eUREAy OF STANOAIIOS REPORT

NBS PROJECT

1006-11-^831 December 19, 1958

NBS REPORT

6246

Engineering Manual for Protective Construction

Part V

Heating and Air Conditioning

of Underground Installations

B. A. Peavy

H. E. Robinson

R. S. Dill (Deceased)

Heat Transfer Section

Building Technology Division

Protective Structures Section

Protective Construction Branch

Office of the Chief of Engineers

Department of the Army

Revision by

To

or progress accounting documents

$ formally published It Is subiocted

Ing, reproduction, or open-Htflr?Jwre rmisslon Is obtained In writing iom

C. Such permission Is not needed,

ally prepared if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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PROTECTIVE CONSTRUCTION BRANCH

ENGINEERING MANUAL FOR PROTECTIVE CONSTRUCTION

PART V

HEATING AND AIR CONDITIONING OF UNDERGROUND INSTALLATIONS

TABLE OF CONTENTS

Chapter 1

Introduction

1“01 Purpose

1=02 Scope

1=03 Historical Background

1=0^ Structural Arrangements

1=05 Operating Conditions

Chapter 2

PPinciples and Design Objectives

2=01 Function oT Underground Installations

2=02 Design Criteria and Limitations

2=03 Air Conditioning Requirements

2=04 Air Conditions for Personnel Efficiency

2=05 Air Conditions for Material Preservation

2=06 Outside Air Requirements

2=07 Disaster Condition Air Supply

2=08 Combustion Air and Cooling Water Requirements,

Engines and Boilers

2=09 Kitchens and Lavatories

2=10 Climate

Chapter 3

Design Information and Data

3"01 Heating and Cooling Load Principles

3=02 Warm=Up Period

3“03 Operation at Steady Air Temperature

3“0b Cooling Loads

3“05 Dehumidification

3”06 Waste Heat Disposal

3“07 Air Conditioning Effect of Tunnels or Shafts

3“08 Evaporation from Pools or Damp Surfaces

Chapter b

Heat Absorption of Rock Around Underground Spaces

b=01 Principles

4—02 Procedure for Estimating Heat Transfer, Air to Rock

b“03 Equations for Heat Transfer, Air to Rock

4-=04- Heat Absorption of Underground Reservoirs
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Chapter 4- (Cont'd)

4=05 Heating and Cooling of Air by Tunnels and Shafts

4“06 Thermal Properties of Rock

4=07 Initial Underground Conditions

4-08 Thermal Properties of Materials and Structures

4-09 Vapor Permeability of Materials

4-

10 Underground Water

Appendix 4a Data Forms

Appendix 4b Heat Absorption of Rock Surrounding Underground

Spaces; Some Practical Aspects

Appendix 4c Problems Illustrating Use of Equations for

Underground Reservoirs

Chapter 5

Air Conditioning Processes and Systems

5“01 Sizes and Shapes of Underground Systems

5=02 Access Tunnels and Shafts

5“03 Simple Installation, Single Shaft

5“04 Simple Installation, Two or More Shafts

5=05 Simple Installation, Single Tunnel

5“06 Simple Installation, Tunnel and Shaft

5=07 Installations with Multiple Access Openings

5-

=08 Types of Inner Structures

5“09 Acoustical Treatments

7“10 Small Structures in Large Underground Chambers

5=11 Annular Spaces Used as Cold Air Plenum

5=12 Air Conditioning Processes for Larger Installations

5=13 Central Air Conditioning Systems

5=l4 Self-Contained Air Conditioners

5=15 Chilled Water Systems

5=16 The Ice Reservoir as a Heat Sink

Chapter 6

Equipment and Operation

6=01 Equipment Selection

6=02 Economy of Operation

6=03 Air Conditioning System Components

6=04 Tempering Coils

6-

05 Air Washers

6=06 Air Heating and Cooling Coils

6=07 Air Conditioning Units

6=08 Air Cleaners and Purifiers

6=09 Fans

6=10 Duct Systems

6=11 Steam and Hot Water Heating Systems

6=12 Ohemical or Sorbent-Type Dehumidifiers

6=13 Mechanical Dehumidifiers
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List of Figures

2=1 Oxygen depletion in unventilated occupied spaces

2=2 Carbon dioxide concentration in unventilated occupied

spaces

2=3 Temperature rise in occupied unventilated underground

spaces

2-h Temperature of water from non=thermal wells at depths

of 30 to 60 feet

2=5 Mean annual range of temperature for the world, F

^-1 Values of R, equation ^=05, for the cylinder

h=2 Values of R, equation 4=05, for the sphere

^=3 Equation ^=04; constant rock heat absorption rate,

condition for sphere

4=^- Equation 4=04, constant rock heat absorption rate,

condition for sphere

4=5 Equation 4=06; constant air temperature, condition

for cylinder

4=6 Equation 4=06; constant air temperature, condition

for sphere

4=7 Equation 4=07; for reservoir heat absorption at a constant rate

4=8 Equation 4=08; values of function 1(F)

4=9 Equations 4=11 and 4=12; values of parameters A and B

4=10 Surface heat transfer coefficients for tunnels or

shafts

4-11 Conductivity of rock

4=12 Annual earth temperature variation near Washington

4=13 Evaporation of water from flat saturated surfaces

Tables

2=1 Humidity tolerances of some materials

2=2 Minimum outdoor air requirements to remove body odors

2=3 ^Properties of chemicals for air revivification

2=4 Typical fuel, air and cooling water requirements for

power generating equipment

3“1 Cooling loads due to personnel

4=1 Heat transfer coefficients for underground structures
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References

1. "Guide**, handbook of the American Society of Heating

and Air-Conditioning Engineers, 62 Worth Street,

New York 13, N. Y.

2. "Air Conditioning and Refrigerating Data Book", handbook of the American Society of Refrigerating Engineers,

23^ 5th Avenue, New York 1, No Yo

3. "Deterioration of Materials", Greathouse and Wessel,

Reinhold Publishing COo, ^30 Park Avenue, New York, N. Y.

Report No. 301^A, Engineering Division, Industrial Test

Laboratory, Philadelphia Navy Yard.

5e "Personnel Shelters in Modern Warfare o’*

6 . Uo S. Naval Civil Engineering Research and Evaluation

Laboratory, Technical Memorandum M-017, July 1951-

7. "Underground Installations, Foreign", Office of the

Chief of Engineers, Contract W-49-129-59, October 31,

19^80

8 . "A Study of the Principles of Air Conditioning in Under-’

ground Installations"; Bertram Broberg, Report No.

122 ; 1/1112BF , 1 April 1955-, Royal Fortification Administration, Bureau of Fortification, Sweden.

9 . "The National Gallery in War-Time", F.I.G. Rawlings,

Nature Magazine, Vol. I5l, page 123, Jan. 30, 195-3*

10, "Some Physical Aspects of Storage of Works of Arts",

Rawlings, Journal Institute Heat, and Vent. Engineers,

19^3, 11, 175.

11. "Engineering Aspects of Wartime Storage of Art Treasures",

Fletcher, Journal, Inst. Heat, and Vent. Engineers, 195-3,

11 , 186 .

12, "A Factory in a Railway Tunnel", Mount. Journ. , Inst,

Heat, and Vent. Engineers,, 195-6, 12.355-.

13 . *‘Air Conditioning of Underground Areas", Wadsworth,

Journ, Inst. Heat, and Vent. Engineers, 195-6, 15-, 195-.

l5-. "Heating and Ventilating Plants in German Underground

Installation", Journ., Inst, Heat, and Vent, Engineers,

19^8 , 16 , kkh.
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References (Cont'd)

15 . "Conduction of Heat in Solids", Carslaw and Jaeger,

Oxford University Press, London, 19^7.

16 . "Measurements of Heat Losses from Slab Floors", National

Bureau of Standards, BMS Report 103, GP0»

17 . "Moisture Condensation in Building Walls", H. W. Woolley,

National Bureau of Standards, BMS Report 63 , GPO.

18 . "Evaporation of Water from Saturated Surfaces", Powell,

Trans. Inst, Chem. Engineers, Vol. 18 , p, 36 , 19^0.

19 . "Cooling of Shipboard Electronic Equipment", National

Bureau of Standards Report No, 4lh6 , May 1, 1955*

20. "The Industrial Environment and its Control", by J. M.

Dallavalle, Pitman Publishing Corp, , New York, N, Y,

21. "Mechanical and Electrical Engineering Handbook",

Construction Division, Public Buildings Service, General

Services Administration, January 19%

22. "Temperature of Water Available for Industrial Use in

the United States", by W. D. Collins (U, S. Geological

Survey, Water Supply Paper No. 520F) pp. 97“101,

23 . "Weather Elements", by T. A. Blair, Prentlce-Hall , Inc.,

New York, N. Y, , 19^2.

24. "Heat Transfer in Deep Underground Tunnels", by A. W.

Pratt and L, F, Daws, National Building Studies Research

Paper No. 26, H.M.S.O., London, 1958.
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Underground Installations: Heating and Air Conditioning

CHAPTER 1

Introduction

1=01 Purpose

The purpose of this Manual is to present in a practical

and convenient form all useful engineering data and infor^’

mation available on heating and air conditioning of underground installations. This program was initiated by the

Office of the Chief of Engineers in cooperation with the

National Bureau of Standards and included a literature survey, a mathematical analysis of heat transfer to rock, and

field investigations conducted in several existing underground installations. The conclusions and recommendations

herein are based upon the results of these approaches.

Having responsibility for establishing procedures and

criteria for designing underground constructions, the Office

of the Chief of Engineers undertook this program of investigation to develop some necessary data that were lacking, and

to investigate the applicability of commonly accepted

materials, equipment and design to underground installations.

The data gathered so far have been correlated into what

is considered an acceptable design procedure, although the

work is expected to be refined and extended by future

experience and experiment. As the advantages of underground

installations become more apparent, this Manual may attain a broad application, and it is hoped that information gained

in the use of underground installations will be brought to

the attention of this Office in order to supplement any

major contribution this Manual may make to heating, ventilating, and air conditioning.

Military structures, because of the destructiveness of

modern means of attack, and the possible increased potency

of future weapons, may be placed in mines or other excavations below ground. Circumstances in these types of installations are usually such that air temperature and humidity

must be controlled to maintain conditions within satisfactory limits for occupancy and preservation of equipment,

supplies, and materials. Structures subject to dampness

may have to be air conditioned for storage of perishable

goods, hygroscopic materials, or critical war material

susceptible to deterioration in moist surroundings.
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The omission of air conditioning systems in the initial

design of military structures built during the war can be

attributed in some instances to wartime restrictions imposed

on the use of this equipment. However, it has since been

realized that controlled air conditions are necessary for

efficient work with papers, delicate tools, or instruments,

as well as for material preservation, and therefore a variety

of heating, ventilating, and air conditioning equipment has

been installed in seacoast fortifications and in military

structures within the United States, While for the most

part the results have been satisfactory, there are cases in

which the measures taken either do not meet or greatly

exceed the minimum requirements. The principles and phe^

nomena involved are fairly well understood, but data are

lacking on which to base design and selection of equipment

sizes

1=02 Scope

The scope of this Manual includes system design,

capacity selection, and application of heating and air con”

ditioning equipment to underground spaces intended for

human occupancy, storage space, or other use. Underground

spaces may be utilized for protective structures, office or

tactical administrative use, signal centers, machine or

electrical equipment parts production or repair, storage of

equipment, munitions, or documents, etc., or storage of

food. The heating and air conditioning equipment for under=

ground structures may include steam, hot water, or warm air

heating systems, mechanical or absorptive=type air condi“

tioning systems, dehumidifiers, heat pumps and cooling

towers, or other means for disposing of waste heat, etc.

There may be need for segregation of the air conditioning

system into zones. Auxiliary equipment will include fans,

duct work, pumps, piping systems, and controls. An underground chamber may or may not have a liner or inner struc”

ture, insulated or uninsulated. Ground water may add to the

latent load or condensation on rock may reduce the latent

load in air conditioning processes.

Temperature, humidity, and other air conditions

required in underground installations may not be different

from those maintained in surface structures when the purposes are similar, but air conditioning processes used and

design procedures may be considerably different. The conditions peculiar to underground use are emphasized in this

Manual, and some data and information applicable to any

heating and air conditioning problem are included for convenience and completeness.
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Underground protective structures can be divided into

three broad functional classes based on the use of the space;

namely, storage, industrial, and military. The treatment of

the space, the air conditions required, and the type of air

conditioning equipment installed are different for the three

types of usage.

Underground storage space might be used for preserving

food above or below freezing temperatures, for general

storage of miscellaneous supplies and equipment, or for

storage of military material such as explosives, precision

machinery, or organic and fibrous materials that are hygroscopic. In such structures, accurate control of temperature

and humidity to the conditions best suited to the stored

goods would be of primary importance, whereas human comfort

and ventilation would be relatively unimportant and there

would seldom be any large amounts of heat generated in the

structure

An underground industrial site might be a machine shop,

a factory for precision instruments, explosives, or electronic equipment, a foundry or metallurgical plant, a fabrication plant, or any one of many other important industrial

activities. In such an installation, the particular industrial process in use would often determine the capacity of

the heating and air conditioning system required and would

frequently have an important bearing on the temperature and

humidity to be maintained. In some cases there would be a high heat release in the space, requiring a high rate of

ventilation or continuous air conditioning. Some processes

might release toxic gases that would require high ventilation rates. Human occupancy would always be involved but

might not be of high density. In installations having processes liberating large quantities of heat, gases, or vapors,

conditions under the attack phase might rapidly become crirical unless the processes could be stopped quickly.

A military installation might be a communications center,

a fortification, an air raid shelter, a staff headquarters, or

a research activity. In such structures, the human heat load

might frequently predominate, although the heat release of

equipment might also be high in some instances. Such military

sites would often need to remain in operation during attack

conditions. Vitiation of the air might become critical during

attack under high density occupancy. Greater attention would

have to be given to providing adequate facilities for maintaining full working capabilities during abnormal conditions

in this type of installation.
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Each of the broad classes of usage described, and some

of the special uses in each class, would require a different

kind and number of commercial services or utilities, different types of air conditioning and ventilating systems,

varying provisions for self-sufficiency under abnormal conditions, and oftentimes different optimum conditions of temperature and humidity under normal conditions.

1-03 Historical Background

Underground installations can be utilized more advantageously now than heretofore, chiefly because a variety of

heating and air conditioning equipment is readily available

and knowledge of its use has increased rapidly in reoent

years. In the past, underground spaces appear to have been

avoided for practical purposes, chiefly on account of dampness, or heat and dampness in combination. Few, if any,

underground spaces were air conditioned for personnel comfort or efficiency or for the preservation of equipment or

material prior to World War II. Some deep mines were cooled

by refrigeration but the objective was to permit survival

under conditions of heavy labor at low levels where valuable

minerals would be otherwise unattainable.

Early measures taken to prevent dampness within heavy

masonry structures included provision of small air passages

in the walls through which air circulated as a result of

natural draft or convection. They were intended to keep

the wall temperatures near to the room air temperatures and

thus preclude condensation. However, in many cases the

effect was not adequate and the resulting conditions were

often unsatisfactory

It is reported to be the practice in some salt mines to

pass the outside air introduced for ventilation through a worked-out portion of the mine. The air, if received hot

and humid, is cooled to a degree and dried by the residual

salt. In the working portion of the mine, the air is warmed

by the machinery and lights, with resultant lowering of the

relative humidity.

Applications of a similar scheme to underground spaces

other than salt mines are also recorded. Air is drawn

through unused underground spaces where it is cooled and

dried by contact with the rock. Then it is warmed to an

acceptable temperature and introduced into the occupied

spaces. The relative humidity falls when the air is warmed

and thus an unused tunnel or other underground space is a means of air conditioning. When this process has been
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employed in the past, the -anderground space used for conditioning the air has usually been large compared to the

occupied or conditioned space, and the limits of the

capacity of an unused tunnel or other space as an air

conditioner were not known.

Underground spaces were utilized in Norway, Sweden,

Germany, and Japan during World War II, chiefly as manufac-’

turing or processing plants. Much useful information on this

subject is contained in a report, "Underground Installations,

Foreign" (Ref. 7), but the report yields little design data

on heating and air conditioning. It appears that air conditioning was not considered justifiable for most underground

installations in a majority of these countries under the then

prevailing war-time conditions. Of the plants surveyed, only

7 percent had air conditioning, and only 47 percent had other

than natural ventilation. Heating was reported as provided

in 27 percent of the plants surveyed.

The paper, "The National Gallery in War Time" (Ref, 9),

is an account of the underground storage of paintings from

the British National Gallery. An existing site was selected

that provided space for the whole collection and afforded

200 to 300 feet of rock cover. The initial air conditions

were 47 F and 95 to 100 percent relative humidity. The

underground space, apparently an old mine, was large, so six

buildings were erected within it to contain the pictures.

Each small building was warmed by means of a forcedcirculation system, apparently utilizing electric heat. For

ventilation, small amounts of air from the space, at 47 F

and near saturation, were introduced into each building as

required. It was found that when the buildings were warmed

to 64 F, the interior relative humidity was near 57 percent,

which was considered satisfactory for long term storage of

the pictures. No cooling means or dehumidifying means was

required, and no dehumidification was provided, other than

that provided by the heating system in conjunction with the

enclosing, relatively cool chamber.

With this background of information, this program

was undertaken by the Office of the Chief of Engineers in

cooperation with the National Bureau of Standards.

l-04 Structural Arrangements

Some features of the structural arrangement of an

underground installation affect the ^ size and design of the

air conditioning equipment and system. Relevant definitions

are as follows:
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Bare Chamber: An underground chamber with no covering

on the rock walls or ceiling that will appreciably affect

heat transfer; walls painted to improve illumination of the

chamber are considered bare from the heat transfer standpoint. A chamber with a concrete floor poured on the underlying rock is considered a bare chamber.

Lined Chamber; An underground chamber with a wall

covering of concrete or another material, in contact with

the rock walls and ceiling, having thermal resistance

materially affecting heat transfer from the chamber to the

rock. Some liners may consist of insulating or acoustical

material and may contain a vapor barrier.

Internal Structure: A building or enclosure erected

within an underground chamber to house equipment or facilities. The internal structure reduces the heat transfer from

the occupied space to the rock (^=05) and influences the

dehumidification load (3“05)-

Annular Space; The space around an internal structure,

between it and the rock walls, floor, and ceiling of an

underground chamber.

I-05 Operating Conditions

An underground installation must be heated or air conditioned to accommodate the activity under various operating

conditions. Some of the probable operating conditions of an

underground space are as follows:

Standby: Facility ready for normal operation at short

notice; may be occupied by a skeleton force for maintenance;

air conditioned for maintenance of equipment and furniture.

Normal Operation, Maximum Capacity; Facility operating

at full or design capacity; occupied by full complement of

personnel; air conditioned for personnel efficiency ( 2 - 0^-)

and as required for operation of equipment.

Normal Operation, Partial Capacity: Facility operating

at less than full capacity, as when full output is not

required; air conditioned for personnel efficiency and

equipment operation in occupied parts; air conditioned for

equipment maintenance in other parts.

Alert Condition; Occupancy and activity the same as

Normal Operation, except for adjustments made in anticipation of attack.
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Attack Condition; Occupancy and activity the same as

Normal Operation, except for alterations necessitated by

attack.

Post Attack; Normal Operation to the extent permitted

by damage due to attack.

Emergency Condition; Outside services, including

power, water supply, and possibly sewage disposal system,

cut off; installation expected to continue performing its

mission, utilizing self-contained power source, water supply,

etc, ; outside air supply greatly reduced or cut off.

Disaster Condition; Installation inoperative due to

damage or exhaustion of supplies; occupants dependent on

stored food and water and, possibly, revivification of the

air for survival.
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CHAPTER 2

PRINCIPLES AND DESIGN OBJECTIVES

2-01 Function of Underground Installations

The design of the heating and air conditioning system

for an underground installation depends on the location,

function, size, and shape. These factors are likely to be

established by the agency requiring the space, or by some

higher authority, on a basis of anticipated needs.

Underground installations may serve as protective

structures for tactical administrative offices or communication centers; as shops or factories producing machine parts,

electronic equipment, chemical products or instruments, or

as storage space for machine parts, instruments, electronic

equipment, food, clothing, munitions, or other equipment.

Hospital wards, as well as domestic facilities, including

kitchens, lavatories, and berthing accommodations may be

required in conjunction with any of these other functions.

The heating and air conditioning system must maintain

conditions suitable for personnel efficiency (2-04) in working

spaces and for material preservation ( 2 - 05 ) in storage spaces,

as well as shops, offices, and other spaces were equipment is

utilized. These conditions must be maintained during the

standby, normal operating, and, so far as possible, during the

attack and post-attack conditions (1-05). Air conditioning or

revivification of the air must also be considered for a condition of extreme emergency or disaster (2=07).

2-02 Design Criteria and Limitations

The size, shape, and depth of cover chosen for an

underground installation may be influenced by function. A

storage space for clothing, food, etc., may be irregular in

shape and have a relatively shallow cover of earth and rock.

More important equipment or facilities essential to defense

may be installed in deeper workings. The chambers in deeper

workings are likely to be long and tunnel-like. The installation may occupy one or several stories and there may or may

not be an internal structure (l-04).

Location determines the climate and the geological formation (4-06) that will surround a proposed underground structure. Climate, in turn, governs the conditions of outside air

(2-10) available for ventilation, the prevalence of undergrouhd water (4-10), availability of water for equipment

cooling, and the initial earth or rock temperature (4-07).
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Floor area and volume of an occupied space depends upon

population, function, and internal load.

Environmental conditions, in particular air temperature,

humidity, purity, and, to a lesser extent, motion, must be

selected with reference to personnel efficiency (2-04-) or

endurance (2=07) and material preservation ( 2 “ 07 )

Outside or fresh air must be supplied, except under

emergency conditions, for personnel (2“06), for engines or

boilers ( 2 - 08 ), for kitchen and lavatories (2-09), and for

any special processes involved.

Air filters are usually recommended for all air to be

passed through conditioning coils, used in engines, or to

ventilate shops where delicate equipment is stored, made, or

repaired. Air purifiers are essential for all fresh or outdoor air if maximum security is required (6-08).

The initial temperature (^-07) , thermal conductivity,

and heat capacity of the surrounding rock (^-06) affect the

heating and cooling loads in an underground chamber (3“01).

2-03 Air Conditioning Requirements

For design purposes, an interior air condition of 75 F

and 50 percent relative humidity can be assumed in many

cases. This condition is within the practicable range

attainable with conventional equipment (6-01), and available

data show it to be suitable for personnel efficiency (2-OA)

and material preservation ( 2 - 05 ) under usual circumstances.

In general, air conditions for underground installations

should be similar to those selected for surface structures

utilized for the same or similar purposes. Fresh or outside

air supply (2-06) may be reduced, since comfort is not always

a prime objective. Since infiltration is unlikely in an

underground installation, the air supply and exhaust system

must be adequate to handle the air required at all times.

Flexibility of equipment is necessary to allow adjustments to cope with the range of operating conditions imposed

by circumstances ( 1 - 05 ) oi* to accommodate changes from design

conditions that may be shown desirable by experience.

Special air conditioners may be required for special

purposes, such as storage or work with unusual materials.
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2~0h Air Conditions for Personnel Efficiency

Experience has shown that personnel can sustain a considerable range of temperature (65 to 85 F) without serious

loss of efficiency, particularly if the humidity is controlled

and is adjusted downward when the temperature increases, or

vice versa. The condition 75 F and 50 percent relative

humidity may be assumed for design purposes, but other conditions in the comfort zone (Ref, 1) are also satisfactory

for many purposes. The comfort zone is defined as that area

on a psychrometric chart for which 50 percent or more of the

subjects were found to be comfortable during some tests con-- ducted by the American Society of Heating and Air Conditioning Engineers. The comfort conditions are still under

examination and new findings are in prospect, particularly

relating to effects of radiation. Changes in design criteria

are not likely to be extensive, however, so far as air conditioning underground installations are concerned.

The condition 75 F and 50 percent relative humidity is

warmer than the 68 or 70 F often recommended for indoor winter

temperature. However, in many occupied spaces, cooling rather

than heating will be required due to internal loads, and use

of the higher temperature reduces the size of the cooling

equipment. It is common experience that many people are more

comfortable at a DB temperature of 75 F winter and summer than

at a DB temperature of 70 F. The condition 75 F and 50 percent relative humidity is safely below that causing excessive

sweating, which can interfere with the performance of instrument makers, draftsmen, typists, and others working with

papers and office equipment.

Fresh or outside air must be supplied to occupied

spaces in proportion to the population (2-06).

2-05 Air Conditions for Material Preservation

Available data indicate that a humidity in the range

from ^-0 to 65 percent is satisfactory for the preservation

of most technically useful materials at substantially steady

temperature conditions, either in storage or in use as in

shops, offices, or communication centers.

An important exception is unprotected low carbon steel,

which requires a humidity of 15 percent or below for no damage,

or 30 percent or below for tolerable damage in 30 months. This

means that special low humidity may be required in instrument

shops where such steel is worked or stored without oil or rust

preventive treatment.
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Probably the most comprehensive information now available on the relation between humidity and deterioration of

materials is that gathered under the auspices of the U. S.

Navy and reported in Reference 3o The data in Table 2=1

were extracted from that source. The data in Table 2=1

indicate the necessity for a low humidity for the preser=

vation of unprotected carbon steel, but such steel, as in

the form of small arms, lubricated, can tolerate 65 percent

like most of the other items listed. An upper humidity

limit for tinned cans was not found but such cans probably

can withstand at least 50 percent relative humidity.

During the tests on which the data in Table 2=1 are

based, only the humidity and not the temperature was con=

trolled. The tests were conducted in enclosures exposed to

the weather and the inside temperatures closely followed the

weather. This probably approximates the condition within a

ship in storage, which was the point of interest in this

investigation. As a result of the tests and other considerations, a humidity of 35 percent was chosen for the interior

of many ships placed in storage following World War II. This

35 percent is considerably below the demonstrated tolerance

of many materials but it affords a factor of safety against

equipment failure and against sharp temperature changes that

might cause condensation on some objects due to temperature

lag resulting from heat capacity.

An advantage of underground storage is steadiness of

temperature. For this reason a smaller factor of safety is

deemed adequate in an underground chamber, and it appears

that a condition of 75 F and 50 percent humidity, recommended

for personnel efficiency and feasibility with conventional

compressor equipment is satisfactory for storage and use of

most materials and equipment. Special low humidity may be

required for instrument shops or other space where steel or

other sensitive materials are worked without lubrication or

rust preventives.

Water is essential to most kinds of material deteriora=

tion. Some metals are attacked by oxygen, atmospheric con=

taminants or electrolytic action in the presence of water.

Organic materials support mold or mildew when damp or moist.

Obviously, therefore, condensation must be prevented on or

within materials in storage. Some materials, however, are

sufficiently hygroscopic to absorb damaging amounts of water

at humidities less than 100 percent. Therefore some humidity

safely below the saturation point must be maintained.
1

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“

TABLE 2-1

Humidity Tolerance of Some Materials

for 30-Month Period

Item Humidity Nature of

Damage, Severity A* B* c* Damage

Mild Steel, polished,

unprotected 15 30 65 Rust

Steel (Ball Bearings

Rust Preventive applied

by Manufacturer) 65

90

Rust

Steel (Ball Bearings

heavy Polar Comp.) 65

Alloy Steel 90

Galv. Steel 65 90 Tarnish and Rust

Brass and Bronze 15+ 90+ Tarnish

Aluminum and its Alloys 90+ Tarnish

Rubber, Plastic, Rayon 90+ Mildew

Flax, Wool, Cotton, Hair,

Leather, Sponge, Hemp.,

Sisal, Paper, Wood 65 90 Mildew

Soap, Bars 90 Disintegration

Tinned Cans (Canned Food) 45

Cloth (Life Preserver) 65 90 Rotting of Cover

Paint Brushes 65

Small Arms, Lubricated 65 90 Mildew and Rust

Instruments (Clocks,

Gages, Voltmeters,

Telescopes, etc.) 45

*A - No visible deterioration

*B - Very slight deterioration

*C - Intolerable deterioration
» 0 i
6 -

Pure, distilled, water is an active solvent for some

materials and may be responsible for some deterioration.

Atmospheric contaminants, including sulfur dioxide and

hydrogen sulfide, present in some industrial region atmospheres, are injurious to some materials. The amounts

present during the tests on which Table 2-1 is based are

not known. The tests were conducted at the Philadelphia

Navy Yard (Ref. h)

Excessive dryness is harmful to some materials. Commutator brushes in electric motors suffer by ''dusting^' at

low humidities. Paper, excelsior, straw, leather, hemp

rope and feathers, as in bedding, become brittle and disinte

grate upon handling under these conditions. Typical glue

does not seriously lose strength in dry atmospheres, but

woods in general shrink and the forces generated are often

sufficient to break joints in furniture or other wooden

equipment. Dry-cell batteries also deteriorate more

rapidly at low humidities.

The metal parts of munitions can be stored under the

same condition as machine tools. For propellants, air conditions with relative humidity not exceeding 60 percent and

temperature between 50 and 60 F have been recommended. In

surveillance tests, it has been found that powder that had

lost potency had been exposed to either dampness or relatively high temperature for considerable periods. It is

also regarded as good practice to avoid sub-freezing temperature and extreme dryness. Exact data on the conditions

causing deterioration are lacking, and the best means of pre

venting or retarding deterioration is to maintain optimum

conditions at all times.

Explosives may often be stored in relatively small

chambers remote from each other to minimize the effects of

accidents. The air conditioning equipment for such chambers

should be selected with reference to minimizing pipe and

duct runs. Since occupancy may be infrequent, little or no

ventilation may be required. Equipment capable only of

dehumidifying and moderately heating such chambers may be

adequate in many such applications.

2“06 Outside Air Requirements

The amount of fresh or outside air required actually

depends on activity or rate of doing work. Present practice,

however, is to supply sufficient air to avoid unpleasant

odors from persons, from tobacco smoke, from cooking or

other products due to occupancy. No reason appears for
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departing from this practice in underground installation for

any normal period of operation. Selection of a fresh air

requirement involves the factor of intermittent occupancy,

which, for equal air freshness, allows different air supply

rates for different room volumes, as shown by the data in

Table 2-2, taken from Reference 1.

TABLE 2 -'2 Minimum Outdoor Air Requirements to Remove

Objectionable Body Odors Under Laboratory Conditions

Air Space Outdoor Air

Per Person. Ft^ Per Person. cfm

Heating Season, With or

without air recirculation

Sedentary Adults of Average

Socio=Economic Status 100 25

200 16

300 12

500 7

Laborer 200 23

Heating Season, Total Circulation

30 cfm

Sedentary Adults 200 12

Cooling Season, Total Circulation

30 cfm

Sedentary Adults 200 h

The available data are not conclusive. Those contained

in References 1 and 2 indicate that 10 cfm of fresh air per

person is satisfactory for space occupied by non-smokers,

while 15 cfm or more is necessary to prevent objectionable

odors when heavy smoking prevails. Lower rates of air supply might serve tolerably for underground installations, but

technical data on which to base such recommendations are not

available

Fresh air must be conditioned, sometimes including

cleaning, before introduction to occupied spaces. If complete protection is required against radioactive particulates, gases, and biological agents, it must also be

purified (6-08).
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2“07 Disaster Condition Air Supply

During an extreme emergency or disaster condition, all

outside services may be cut off and the supply of fresh air

may be stopped because of power failure, or deliberately

because the locality has been contaminated with radioactive

material, biological agents, or gases. Under this condition,

the occupants of an underground installation may be forced to

rely on resources available in the installation for their

respiration air supply. The situation will be similar in

many respects to that in a submerged submarine.

People thus isolated from a fresh air supply can subsist for some hours or days on the air in the space, and the

length of time depends on the volume of the air available

and on the number of persons present, as well as their

activity. Each sedentary person can be expected to consume

on the order of 0.85 cubic foot of oxygen and exhale about

0.7 cubic foot of carbon dioxide and liberate 0.17 pounds

of water vapor per hour. When the atmospheric oxygen content is reduced from the normal 21 percent to about 1^ percent, or when the CO 2 content is increased from the normal

fractional percentage to more than three percent, serious

loss of vitality and ability occurs. Somewhat worse conditions result in death by suffocation. The data given on

Figures 2-1 and 2-2 based on sedentary occupancy show that

considerable time must elapse before these danger points are

approached, if the volume of the space is large compared to

the number of occupants; but in a crowded space, the limits

may be reached in a comparatively short time. An outside

air supply of two cubic feet per minute per person assures

a carbon dioxide content less than two percent for an

indefinite period of time.

ft. Some preventive means can be provided, for use before

dangerous limits are approached, based on submarine practice.

Carbon dioxide can be removed from the air by means of

various absorbents. In use for emergencies, the sorbents are

spread on rubber blankets or other suitable surfaces and

exposed to, the air. Increasing the air flow in contact with

the material, as by means of fans, if available, accelerates

the reaction. Oxygen can be provided under pressure in

bottles, or it can be generated by burning special chlorate

candles. Table 2-3 shows the amount of chemicals required

for air revivification under dynamic conditions.
(
9

TABLE 2-3

Properties of Chemicals for Air Revivification

Chemical Sensible

Required, Water Heat

CO2 O2 lbs per Vapor Liberation,

Chemical Absorbed Liberated man-hr Formation Btu

Lithium

Hydroxide X 0.124 yes 190 per cu

ft CO2

Soda-Lime X .34 yes 139 per cu

ft CO2

Baralyme X .474 yes

Sodium

Superoxide X X .288 no 174 per cu

ft COp & Op

Potassium

Tetroxide X X • 364- no 147 per cu

ft CO2 & O2

Chlorate

Candle X .24 no 94 per cu

ft O2

Note: These chemicals, if used, must be handled and stored

with due caution. In particular, sodium superoxide and potassium tetroxide are strong oxidizing agents and can be a fire

hazard. This fact may preclude their use in some cases.

Chlorate candles should come packaged specifically to avoid

fire hazard.

Table 2=3 is based on forced air flow through the chemicals

(except chlorate candle) and an oxygen consumption of one

cubic foot per man-hour and carbon dioxide liberation of 0.83

cubic foot per man-hour.

These processes also liberate heat, so the relative

importance of temperature rise and humidity rise should be

taken into account in the design for the disaster condition.

On any rise in DB above normal, heat will flow into the rock

temporarily, and the dewpoint would be determined largely by

rock surface temperature. Therefore relative humidity would

not approach 100 percent for some time.
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TEMP.

RISE
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MPJ RSE i ll\l OCCUPIED ! UNVENTIllAT

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UNDE D Sf^ACES

! top SQUARE fEE^ |rOCK | SURfAcE AReJx

R 'PE:rson

ION F

AND lAN' ESTIMATED MEAT

LIBEFJAT ERI PERSON OF 1400 BTU

TIME - HOURS
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Personnel in a crowded space, subsisting as above, can

be expected to suffer ultimately from excessive heat and

humidity. The probable period of isolation has been esti^^

mated for some purposes as one week while relief or rescue

is pending. During that time, the temperature is not

expected to become unbearable in the absence of normal supplies of heat and power. It is estimated that personnel

under disaster conditions might be exposed to temperatures

of 85 to 90 F at humidities approaching 100 percent. This

is not beyond human endurance, but it is beyond the range

at which work with paper, instruments, or electronic equipment can be reliably accomplished. If personnel are expected

to undertake some necessary tasks under a disaster condition,

some means of reducing the humidity is essential. An

enforced limitation of activity during disaster conditions

would prolong the period of comfort. In extreme situations,

lying down on the bare rock surface would promote heat

transfer from the body.

The temperature rise in occupied, unventilated underground spaces is estimated from Figure 2-3 ? which is based

on Equation and the following assumptions;

1. The equivalent cylindrical radius (^-03) for the

chamber is 15 feet

2. The thermal properties of the surrounding rock are;

K = 1.^5 Btu/hr=ft-F

K/^c = 0.038 ftVhr

3 . The heat input rate is on a per person basis, i.e.,

^-00 Btu/hr per person for Figure 2-3, and

h. Rock surface area is on a per person basis, i.e.,

100 square feet of rock surface area per person.

For other values of the heat input rate and rock surface area

per person, temperature rises can be computed by the following

relationships

Temperature rise =

(Actual heat input rate per per son) ( temp . rise from Fig. 2-3)

^(Actual rock surface area per person)

The coefficient of heat transfer U* is discussed in Section

4“08. A U' -value of 1.2 is comparable to a bare chamber,

while the U’ -values of 0,3 and 0.4 approximate an uninsulated

internal structure.
0cc
11-

2-08 Combustion Air and Cooling Water Requirements, Engines

and Boilers

Power generating and heating equipment may be installed

underground for the purpose; (1) To obtain more economical

services, (2) to generate electricity in case of commercial

power outage, and (3) to make the underground installation

self-sustaining under emergency conditions (1-05). Fuelburning equipment most readily meets these purposes.

Because of the limited space usually available for power

plants and the high combustion air requirements, steam

boiler plants for power generation are not considered. This

leaves gasoline and Diesel engine and gas-turbine power

generating equipment. Gasoline equipment is a producer of

carbon monoxide gas and should be used with due precaution

to leaks in the exhaust systems. Steam and hot water

boilers may be used to satisfy heating loads and domestic

hot water supply.

Table 2-^ gives the specific fuel consumption, combustion air, and cooling water requirements of engines. While

it is realized this equipment may operate under all types

of load, the values given in Table 2-h are deemed suitable

for design purposes.

TABLE 2-4

Typical Fuel, Air, and Cooling Water Requirements

for Power Generating Equipment

Diesel Gasoline

Specific fuel consumption, Ib/KW-hr 0.6 0.8l

Combustion air , cfm/KW 2.4 2.3

Cooling water. gpm/KW 0.54 0.54

For heating apparatus, oil fuel consumption is approximately 10 gallons, and air for combustion is 15,000 cubic

feet, for every million Btu of heat load.

The air for combustion does not have to be directly

supplied from the outside, but may be taken from air

exhausted from other facilities, such as toilet and kitchen

exhaust or that exhausted due to replenishment by outside

air for personnel.

-12

2=09 Kitchens and Lavatories

Because natural ventilation is not practical for enclosed

structures or facilities of underground installations, such

as kitchens, dining areas, and lavatories, mechanical ventilation is a necessity. Air quantities necessary for proper

ventilation of these facilities have been cited in different

ways by those interested in this subject. Agreement by all

parties is that there should be no recirculation of air supplied to kitchens, lavatories, toilet rooms, bathrooms, and

rest rooms (Ref. 20).

For kitchens handling foods, at least eight outside

air changes per hour should be provided. From another

source, the quantity of air exhausted from a kitchen should

be not less than four cfm for each square foot of floor

area. The quantities exhausted through hoods over ranges,

etc., should be sufficient to maintain a velocity of 60 to

75 fpni through the projected area (Ref. 21).

For lavatories, toilet rooms, bathrooms, and rest rooms,

at least four air changes per hour shall be provided. From

another source, exhaust air quantities for mechanically

ventilated toilets shall be 50 cfm for each water closet or

urinal, or 2 cfm for each square foot of floor area, whichever is greater. The air for this purpose may consist

wholly or in part of air supplied to offices and work rooms

and exhausted via corridors.

2-10 Climate

The underground installation is not exposed to the

severity of sun, wind, and extremes of weather like a building on the surface. The pertinent climatic characteristics for the underground installation are the initial

tmperature of the surrounding rock mass (4=07) and the temperature variations in the outdoor supply air (4-05)

Although the precipitation for a given locale may have some

effect on the amount of seepage water to be encountered

underground, the porosity of the rock and occurrence and

amount of fissures in the rock make the amount of seepage

unpredictable

,

The initial temperature of the surrounding rock mass

is discussed in Section 4-07. Figure 2-4 (Ref. 22) shows

the approximate temperature of water from wells in the

United States at depths from 30 to 60 feet below the surface, At greater depths, the temperature increases approximately 1 F per hundred feet. Figure 2-4 is also useful for
I
- 13 -

the determination of the mean annual temperature of the

outside air supply to an installation. The mean annual

air temperature is closely approximated by subtracting

2 F from the values given in Figure 2~h.

Figure 2-5 (Ref. 23) gives the mean annual range of

temperature, which is defined as the difference between the

mean temperatures of the warmest and coldest months. The

mean temperature variation for a given locale may be determined from Figures 2-4 and 2“5» For example, if a given

locality has a mean annual temperature of 52 F and a mean

annual range of temperature of ^-6 F, the extreme monthly

mean temperatures are then 52 + 46/2 = 75 F, and 52 - 46/2

= 29 F. For section 4-05, the temperature amplitude 0 'q

is determined by dividing the mean annual range of temperature by two. For the above example, 0 'q = 23 F.

2-11 For references and index to other Chapters of Part

XXV see Chapter 1.
L (1
CHAPTER 3

DESIGN INFORMATION AND DATA

3“01 Heating and Cooling Load Principles

When an underground chamber is being prepared for use,

its temperature is usually initially at or near the natural

underground condition (4--07) . The rock surfaces may or may

not be wet over large areas. For most occupancies, the

desired air conditions are a DB temperature of about 75 F

and relative humidity of about 50 percent (55 F dewpoint),

and an initial period of heating is required. For a short

warmup period, it is usually necessary to supply heat in

addition to that generated by the occupancy. A steady heat

input to the chamber will cause the air temperature to rise

a few degrees above the existing temperature of the rock

face of the chamber, and the air temperature will then rise

further only as the rock is warmed by the heat absorbed

(*+“03, Equation 4-04). When the desired air temperature is

ultimately reached, regulation of the heat input, preferably

by a thermostat, is required to maintain a constant air temperature. Under this condition, the absorption of heat by

the rock (4-03, Equation 4“05) will slowly diminish with

time (over several years), and the rock face temperature

will gradually approach that of the air.

At some stage in this process, it is probable that the

heat generated by the occupancy will become greater than

the rate of absorption by the rock. At this point, cooling

will be necessary to maintain a constant air temperature,

in an amount governed by the excess of the generated heat

over the heat absorption rate of the rock.

If large areas of the rock are moist, or much water

vapor is generated by the occupancy, limitation of the

relative humidity to 50 percent may require removal of

vapor, either by ventilation with outdoor air or by

dehumidification equipment, even during the warm-up period

(3“05). The latent heat of the vapor, depending on its

source and disposal, may materially affect the sensible

heat balance of the chamber.

3“02 Warm-up Period

a. Bare Chamber - Installation of permanent heating

equipment with sufficient capacity to supply all the heat

necessary to achieve a very short warm-up period is not

recommended. The initial heat absorption rate of rock

surrounding a warmed chamber (4-03) is comparatively very
# ^

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"2

higho If a quick warm-up is necessary, temporary heaters

should be considered, because permanent equipment large

enough for the purpose will be much over-size after a few

months of operation. Electric heating is practicable for a warm-up period. However, the cost is comparatively high

and the necessary wiring, transformer, and heaters add to

the cost unless the are provided for and chargeable to some

other purpose . If a few months can be allowed for the warmup, it should be possible to warm the spaces with the permanent heating equipment, avoiding the necessity for temporary heaters. Fuel-burning heaters, if used, may often

be supplied with combustion air and vented, as a temporary

measure, through shafts or tunnels provided for other

purposes

.

Power equipment, such as electric motors or internal

combustion engines used during excavation, contributes

heat to a space and may alleviate the warm-up problem.

The rock heat absorption is likely to be the greatest

heat loss from the bare chamber during the warm-up period.

Determination of rock heat absorption is covered by

Equation

b. Internal Structure - It should be possible in many

instances to warm up an internal structure in a satisfactorily short time by means of the permanently installed

heating equipment. The internal structure insulates the

occupied space from the surrounding rock, thereby reducing

the heat required to attain and maintain the desired temperature, Heating equipment is usually installed with some

excess capacity as a factor of safety, and this can be

utilized during the warm-up period. The relation between

heat input and warm-up time can be computed by means of

Equation

3“03 Operation at Steady Air Temperature

a. Bare Chamber - The necessary heat supply or net

load at any instant is equal to the rock heat absorption

minus the total internal load. The rock heat absorption

decreases with time when the chamber air is held at a steady

temperature. Equation ^--05 is recommended for computing

rock heat absorption.

When the internal load exceeds the rock heat absorption, the difference must be removed by some air conditioning

means

.

I
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-3 -

So far as heating load is concerned, a chamber lined

with concrete can often be treated the same as an unlined

chamber of the same size. The thermal properties of con-’

Crete are similar to those of rock and the thickness is

relatively small. Acoustical or other insulating materials

applied to walls or ceiling affect the heat transfer. In

general, insulating materials applied to the rock will tend

to reduce the warm-up period, and lengthen the time for the

rock to approach the chamber air temperature during the constant air temperature period.

b. Internal Structure - Under the normal or steady

temperature condition, the rock surrounding an internal

structure warms more slowly than the rock around a bare

chamber. The heat loss from the structure to the rock at

any instant can be computed by means of Equation 05.

3“0^ Cooling Loads

The net cooling load of an underground space is the sum

of all Internal loads minus the heat absorption of the surrounding rock (^-03). The internal loads include heat and

moisture from personnel, waste heat from boilers, engines,

electric motors, lights, cooking equipment or other apparatus utilizing electric energy. Most of the power utilized

in underground installations is likely to be supplied electrically and the. heat liberated from electric equipment can

computed by the relations

1 KW = 3^12 Btu per hour

1 Horsepower = 25^5 Btu per hour = 0.7^6 KW

For a motor driving a machine that converts the power

to heat, such as a lathe, a grinding machine, etc., all the

energy utilized appears as heat in the surrounding space.

If a motor drives a pump or blower, a fraction of the input

energy is imparted to the fluid being pumped; the rate of

energy or heat liberation in the space around the motor and

driving gear is equal to the input power times the decimal

equivalent of the over-all efficiency of the motor and

driving mechanisms.

All the energy from electric lights, either incandescent or fluorescent, is converted into heat. Part of this

heat may be removed by special water or air cooling means

in some cases; otherwise it forms part of the cooling load.

Personnel liberate heat and water vapor and the rate

depends on state of activity. Some typical data for design

purposes are given in Table 3"1.

Table 3~1

Sensible, Latent, and Total Metabolic

Heat Loss per Person, Btu/hr

Room Sitting or Moving Slowly Light Working

Temp

.

Sensible Latent Total Sensible Latent Total

84 180 220 400 150 510 660

82 200 200 400 180 480 660

80 220 180 400 210 450 660

78 240 160 400 240 420 660

76 256 144 400 270 390 660

74 272 128 400 300 360 660

70 300 100 400 350 310 660

60 360 70 1+30 460 200 660

50 440 40 480 550 110 660

40 510 110 720

Cooking is responsible for both sensible and latent

loads. For electric cooking, the total load is equivalent

to the energy utilized, but part is latent while the remainder

is sensible load. In most instances, it may be possible to

vent vapor from kitchens and avoid imposing the latent and

some of the sensible load on the air conditioning coils.

If an apparatus is cooled by the evaporation of water

into the surrounding air, the total load is not affected;

part of the load becomes latent and the rest remains

sensible load.

Fresh or outdoor air introduced for ventilation (2->06)

must at times be cooled and dehumidified. The resultant

load may be reduced by passage of the air through siipply

shafts or tunnels (4=05)

3^05 Dehumidification

a. Bare Chamber -= The dehumidification load of a bare

chamber includes water vapor from equipment and processes,

if any, and personnel (3~0^), dehumidification of fresh air

(2“06), and evaporation from surrounding damp rock. Bare

rock condenses water from the surrounding air whenever its

surface is below the air dewpoint, and, conversely, water

evaporates from damp rock, or from pools, whenever the surface temperatube exceeds the dewpoint (^-10) . The rock

therefore tends to govern the humidity in the chamber by
L I

i (
“5

holding the dewpoint at its own surface temperature. The

rock cannot be relied upon indefinitely as a dehumidifying

means, because its surface warms with time when receiving

heat from the air in the chamber (4-03) (See 5”10).

Water in the liquid state, either from leaks due to

fissures in the rock or from condensation, must be drained

away by trenches, gutters, pipes, etc. Water in the vapor

state, from personnel or processes, as well as that due to

evaporation from damp surfaces, must be removed by ventilation or by dehumidification effected by the air conditioning means provided.

b. Lined Chamber - Use of vapor barriers (4-09) or of

thermal insulating materials (4-08) in direct contact with

rock surrounding underground spaces is not generally to be

recommended. The hydrostatic pressures that can be

generated due to the depth of an underground working are

greater than can be restrained by ordinary vapor barrier

materials or even by moderately heavy concrete liners.

Assuming that the water head is at times as deep as the

overburden, the possible pressure is represented by the

equation

= 0.43 d

Py = hydrostatic pressure, psi

d = depth, ft

Insulating material applied directly to rock walls or

to concrete in contact with such walls is likely to be wet,

either by condensation or by ground water or both, with

resulting damage to the insulating material or to its

fastenings. A vapor barrier on the chamber side of the

insulation does not protect it from ground water, and such

a barrier on the rock side of the material does not protect

it from condensation.

From these considerations it appears that, if insulation is to be used, an air space is desirable between the

insulation and the rock and, if the air space is provided,

there are some advantages to making its width sufficient to

permit access for purposes of inspection and repair, particularly for multi-story installation. This done, the

liner becomes substantially an inner structure and can be

treated as such.

A concrete liner, may be installed in an underground

space to improve its appearance or to reduce the chances

of spalling, but it should not be considered effective as
\

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either thermal insulation or a vapor barrier. The dehumidification load in such a space is subject to the same considerations as that for a bare chamber,

c. Internal Structure - If the walls, ceiling, and

floor of an internal structure are vapor-proof, the water

vapor to be removed by the air conditioning apparatus is

equal to that liberated by the equipment and personnel

(3“04) within the structure. Conditions in the annular

space do not directly affect those within the structure.

If the walls, ceiling, and floor of the internal

structure are pervious, the water vapor to be removed by

the air-conditioning apparatus is then the algebraic sum

of the water vapor liberated by personnel and equipment and

that entering the internal structure through the walls,

ceiling, and floor by permeation, or by convection from the

annular space.

Compared to convection, migration or water vapor by

either capillarity or diffusion through a material may have

feeble and often negligible effects in transferring water

vapor. Leaks exist in most ordinary structures and therefore if a difference in air pressure is maintained between

I the inside and outside of an internal structure, the interior

humidity is likely to be affected by the resultant air flow.

In the absence of an air pressure difference, migration of

vapor through a barrier such as a wall or ceiling may be

estimated on the assumption that the flow is proportional

to the vapor pressure difference and to the permeance of

the barrier (4-=09).

The surrounding rock can be relied upon as a dehumidifying (and cooling) means, so long as its surface remains

adequately cool. If the surface becomes warm, due to heat

received from the internal structure or due to the passage

of warmer air through the annular space, the rock will cease

to be a means for maintaining an acceptable humidity.

. 3-06 Waste Heat Disposal

\ During normal operation, waste heat from such equipment as Diesel engines, refrigeration condensers, etc., can

be dissipated in water as from an available stream or pond,

or into the air by means of air-cooled or evaporative condensers or cooling towers. However, during attack or under

some post attack conditions (1-05) it may sometimes be necessary to utilize special heat disposal means (4-04) incorporated within the underground installation.

i
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=7

An underground reservoir is an obvious and practical

heat sink for use when outside water service is cut off.

It must be adequate in size or capacity to absorb the waste

heat from the equipment to be operated for the duration of

the estimated period of need.

There are two ways to utilize an underground reservoir

(4-04). The water can be passed through the equipment to

be cooled and wasted outside the installation, or the water

can be used by recirculating it from and to the reservoir

until it reaches its maximum utilizable temperature, and

then be passed finally through the equipment and wasted

outside. Somewhat more heat can be absorbed by a reservoir

of a given size when the water is recirculated to the

reservoir, because the surrounding rock also absorbs heat.

A possible disadvantage of recirculating to a reservoir is

that the surrounding rock will be left warm at the end of a

period of emergency and may require much time and water for

cooling in preparation for a next attack.

For estimating purposes, it can be assumed that for an

internal combustion engine about 30 percent of the heating

value of the fuel burned appears in the jacket cooling

water. For an air conditioning refrigerating machine, the

condenser and jacket cooling water receive about five times

the heat equivalent of the electric energy that drives the

compressor

.

The heat absorbing capacity of a reservoir with wastage

of water outside after use is given by Equation 4—06. The

heat absorbing capacity of an underground reservoir as a

function of time, if the water is recirculated and retained,

is given by Equation 4-07.

3=07 Air Conditioning Effect of Tunnels or Shafts

The initial or undisturbed temperature in a tunnel or

shaft with an overburden of 70 feet or more is likely to be

at or 'hear the mean annual temperature, which is in the

range of 70 to 75 F in many regions. This is usualiy above

the winter outside design temperature and below the summer

outside design dry-bulb and dewpoint temperatures. A tunnel or shaft is therefore a possible means for tempering

the air in winter and partially conditioning it in summer

(4“07). For a long tunnel and small flow, the air passed

through a tunnel assumes nearly the earth temperature, say

77 F, and therefore the tunnel can dehumidify outdoor air

in summer, and if ground water is present can humidify it

in winter. Such a large wet tunnel with a small air flow
c <
8 ^

can therefore condition air to approximately 55 F saturated

at all seasons. Air at this condition, warmed to 75 F,

assumes a relative humidity of 50 percent.

For a specific tunnel there is a limit to the cooling

and heating capacity, depending on the dimensions, the

nature of the surrounding rock, etc. The mathematical

relations governing heating and cooling of outside air by

tunnels are given by Equations b-11 and 4-12. Remarks

about tunnels in this section apply substantially also to

shafts or other openings of equal dimensions.

3“08 Evaporation from Pools or Damp Surfaces

Ground water can have several effects that influence

•structure and equipment design, including the following.

It can exert pressure on any vapor barrier or liner

installed to prevent its ingress into underground spaces

( 3

“ 05 )* It can affect the conductivity and heat capacity

of pervious rock (4=08) . To evaporate water from damp surfaces or open pools requires heat (4--10) and can add to the

heating load. Water evaporating absorbs the same latent

heat as it gives up when it condenses. Therefore, in some

cases, the effect of evaporation as from damp surfaces in a

space being cooled is not to change the total air conditioning

load, but is to convert part of the load from the sensible to

the latent type. If a machine or apparatus is cooled by the

evaporation of water and if the resulting vapor is vented

outside without reaching the cooling coils, the heat conveyed

is not added to the cooling load.
tc
CHAPTER ^ HEAT ABSORPTION OF ROCK AROUND UNDERGROUND SPACES

4-01 Principles

The geological formation around an underground installation is termed rock in this chapter. Usually, at required

depths, locations will be chosen where the space will be

surrounded by rock, rather than clay, sand, or another

material, in consideration of strength and stability require

ment s

,

The air temperature in an occupied underground space

is usually maintained above the initial temperature of the

surrounding rock. Accordingly, heat flows from the air to

the rock, at a rate dependent on their temperature difference. With time, the nearby rock is warmed, and the

heat input required to maintain a given air temperature

decreases. When or if the internal heat load, such as the

heat liberated from lights, motors or other equipment, and

personnel, exceeds the rate of heat absorption by the rock,

the space air temperature will rise, unless the excess heat

is removed by some cooling means such as ventilating air or

air conditioning.

Consideration of these effects is obviously essential

in the computation of heating or air conditioning loads,

but, unfortunately, heat flow of this transient type is not

subject to simple analysis. The pertinent mathematical

solutions are too complex for everyday use, and for this

reason a simpler approximate method of calculation has been

evolved and checked against experimental results obtained

in several underground spaces.

The recommended method for estimating heat absorption

by surrounding rock is based on consideration of an assumed

underground space, either spherical or cylindrical in shape,

with thermal characteristics similar to those of a chamber

to be utilized. The heat flow equations pertaining to

spheres or cylinders are simpler than those for other shapes

The data presented for use with the equations in this manual

(4=03) are based on analytical numerical solutions of the

equations for cylinders and spheres in terms of functions

numercially evaluated by means of the digital computer

facilities of the National Bureau of Standards,

Usually, a new underground space must be warmed to some

acceptable air temperature in preparation for occupancy.

Heat may be supplied to the space for this purpose at a
c

C i
relatively large, constant rate, until the desired air temperature is attained. If the permissible warm-up time is

specified, the required heat supply rate can be computed as

indicated in Item 5 of Section 4-02.

After the warm-up, presumably a constant air temperature

will be desired in the space, at or near 75 F. The heating

or air conditioning system is then expected to operate on

thermostat. The surrounding rock absorbs heat at a rate that

decreases with time, and the absorption rate at any instant

can be computed as indicated in Item 6 of Section ^-02.

4-02 Procedure for Estimating Heat Transfer, Air to Rock

Data forms found in Appendix A to this Chapter are

recommended for use in the following steps for estimating

the heat transfer from an underground space to surrounding

rock.

1. Compute the internal surface area of the space.

Projected areas can be used; irregularities left in walls,

ceilings, and floors after blasting can be ignored. Equation 4-Cl is applicable. (Form A.)

2. Cbtain values for R, for the cylinder from Figure

4-1, and for the sphere from Figure 4=2. If Rq for the

cylinder exceeds R2 for the sphere, the cylinder is the best

approximation to the space considered. Utilize the sphere

if its R=value exceeds that for the cylinder. (Form B.)

3. Compute the radius of a cylinder of the same

internal area as that of the space, using Equation 4-C2,

or compute the radius of a sphere of the same internal area

by means of Equation ^-C3, whichever is applicable. (Form B,

)

4. Ascertain the initial temperature of the rock, thermal conductivity, density, specific heat, and coefficients

of heat transfer. These may be found from geological data,

testing of samples, or estimated from information given in

Sections 4=C6, 4-C7, k=C8, and 2=1C. (Form B.

)

5 . For a given warm-up time (4-C3), determine the

required heat input by means of Equation h-Oh. In conjunction with this equation, utilize Figure 4=3 for the cylindrical case, or Figure 4-k for the spherical case. (Form B.)

6. Compute the rock heat absorption rate for the constant air temperature, or thermostatt ed condition (^-C3)

by means of Equation 4-C5. Equation ^-C5 will yield the
€C
"

3 ”

heat absorption rate for the cylinder (Figure or for

the sphere (Figure 4-6), whichever was selected for an

approximation to the space being considered. (Form C.)

4“03 Equations for Heat Transfer, Air to Rock

Equations applicable to the procedure for computing

heat transfer into or from rock are as follows:

Area of an Underground Chamber, either square or rectangular .

If the space is not a parallelpiped, that is, if the

ceiling is arched or if other major irregularities in shape

exist, or if there are doors or partitions of significant

size, the area. A, should be adjusted accordingly by some

appropriate method.

Equivalent Cylinder or Sphere

Radius of a cylinder with thermal characteristics

approximately similar to those of the space considered:

Radius of a sphere with thermal characteristics

approximately similar to those of the space considered:

Steady heat input required to raise the air temperature in a space in a specified time from the initial rock

temperature to a desired air temperature.

A = 2(mn + ms + ns) (^- 01 ) A = wall, ceiling, and floor area, ft^

m = length, ft

n = width, ft

s = ceiling height, ft

^3 27rm

(^- 02 )

(^- 03 )

q ( 4- 04 )
IiL
q' = Steady heat input to air in the space,

Btu/hr-ft^

X = Thermal conductivity of surrounding rock,

Btu/hr-ft-F

Q± = Temperature difference, air temperature to be

maintained in the space minus initial rock

temperature, F

a = Equivalent radius of space, ft; an for the

cylinder, a2 for the sphere; selected from

Equation h-02 or 4-03, whichever corresponds

to the highest R-value (Figures h~l and k-2)

F = Kt/^ca^; F]_, cylinder, Fp? sphere; f(F]_) is

found in Figure ^-3 and f(F2) in Figure h-kt = Time for warm-=up period, hr

p

- Density of rock surrounding the space, Ib/ft^

c = Specific heat of rock, Btu/lb“F

U' = Coefficient of heat transfer between conditioned

space and rock face, Btu/hr-ft^-F; see Section

k~08

Thermostatted Period ~ Constant Air Temperature

Heat input (decreasing with time) necessary to maintain

a desired steady air temperature in a space:

q = f(F,N) 0j_U'/R (4-05)

All symbols for Equation (4— 04) are applicable.

q

= Rock heat absorption rate (decreasing with

time), Btu/hr-ft^

N = aU'/K; values for f(F,N) are found in

Figures 4-5 and 4-6

t = Time measured from the start of the warm-up

period of the space, hr

R = Factor involving the ratio of the volume of

heated rock around the cylinder or sphere to

that around the actual configuration. Values

of R as a function of the dimensions of a

space are taken from Figures 4-1 and 4-2.
ctc

t

c

/

I

i

I

\

I

'
0.04

EpmrtOTr 4^57'SPHEF^ICAL CAjSEi

SURFACE, IWITH CONSTANT ! AIR TEMP.

F_= Kt/Dca
J

r>

ii

u

t

<

j

5

;

i

(I

I

\

J

if"'

I
For sample problems involving the use of the equations

found in Section 4-03 and for further discussion refer to

Appendix B.

4-04 Heat Absorption of Underground Reservoirs

An underground reservoir of water, or water and ice,

may be provided as a sink for the waste heat from engines,

air conditioning equipment, or other apparatus, for use

during emergencies ( 1 - 05 ) when outside services are cut off

(3"06). Spaces prepared for this purpose are likely to be

long and tunnel-like for reasons of economy in excavation,

and to provide necessary rock surface area. Therefore, in

the capacity calculations, the tunnel shape is assumed and

the cylindrical approximation is employed.

Reservoir Use with Water Wastage

If the water in the reservoir is pumped through engine

jackets or refrigeration condensers, etc., to absorb heat

and is then wasted outside the installation, the time t in

which the reservoir will be emptied can be computed by the

equation;

t = M(Tw“Tp)/Qw, hr (4-06)

M = Mass of water in reservoir, lb

T-^ = Temperature of water discharged from engine

jacket or condenser, etc., F

Tp = Temperature of water available from reservoir; F

Q-w = Heat to be absorbed by the water, Btu/hr

Reservoir Use with Water Recirculated and Not Wasted

If the water is recirculated from the reservoir to the

engine jackets or condenser and back to the reservoir, the

heat-absorbing capacity of the water is increased by the

heat-absorbing capacity of the surrounding rock and the

total rate of heat absorption can be computed by means of

the equation:
I»

ii

f

• ;

Xz

>i-

u

s

V v

•

I -i^j.-:

i X »-

I

c

I

. - r

<
-6

where 9-^ = Temperature rise of water above the initial

water temperature, F

= Constant rate of heat input to the water from

external sources such as engine jackets or

condensers, Btu/hr per foot length of reservoir

F = Kt/yoca^

t = Time from initial application of q^, hr

a = (s+n)/TT, radius of equivalent cylinder, ft

sn

G

M*

P

c

Height of reservoir, ft

Width of reservoir, ft

2Tra^^c

M*c'

Mass of water in

reservoir

Density of rock.

Specific heat of

reservoir, Ib/ft^

Ib/ft^

rock, Btu/lb“F

Specific heat of water, Btu/lb-F =

length of

1.0

m = Length of reservoir, ft

The function f(F,G) of Equation 07 is plotted in

Figures 4-7 and *+-7A, and Form D (Appendix A) is suggested

as a work sheet for its use. This equation yields the heat

absorption rate per foot of length, for a reservoir of

equivalent radius, a, for a specified water temperature rise

0w in a specified time, t.

In order to obtain the best effect from a reservoir

used as a short-time heat sink, water should be taken from

the lowest point in the reservoir and heated water discharged to the highest point, because the warmest water

will stratify in the upper levels, while the water taken

from the bottom will be the coldest available for cooling

purposes

.

When the water temperature oreaches its maximum allowable temperature, the water of the reservoir is wasted outside the installation, and the time to waste the water can

be determined using Equation 4-06.
rcc

1

f

}

I

I

f
EQUATION 4-07

(RESERVOIR HEAT ABSORPTION Ij

I AT CONSTANT HEAT RATE

0.02 0.03 0.04 0.05

F = Kt/pca^

0.06 0.07

0.020

0.018

0.016

0.014

0.012

0.010

0.008

0.006

0.004

0

0,01

0.002

\
J

A.

'••

ifaiMHMiHaMMayi
()')

0

-- I'-'

. - .L .

... - : 1

: .

N

CD

in

fO

CVJ

o

o CO CJ

CVJO

O

CL\

II

lj_

GO (J) I

o
I

ij
- 7 “

Condensers of refrigeration equipment allow an entering

water temperature as high as 100°F. Temperatures above this

reduce efficiency and may be damaging to the refrigeration

equipment due to high pressures. Heat exchangers of prime

movers such as diesel engines may allow entering water temperatures up to 160 F or higher. Because of the differences

in the allowable water temperature rises, separate reservoir

systems should be designed to accept heat from the two

separate heat sources.

Cooled Reservoirs

In some cases, it may be felt necessary to maintain a

given reservoir at a temperature below the initial rock temperature, in order to provide additional heat absorbing

capacity for an emergency period.

Cooling the Reservoir; The rate of heat removal from

the water necessary to lower its temperature by Qq degrees F

in a given period of time may be computed from Equation 07.

When the desired water temperature has been reached, further

heat must be continually abstracted from the water to remove

the heat being transferred from the surrounding rock. The

required rate of heat abstraction by refrigeraion equipment

under this condition is given by the following equation:

q. = KOqKF) (4=08)

where qj_ = Rate of heat abstraction from water at time

tf Btu/hr per foot length of reservoir

0jL = Temperature difference between initial rock

temperature and the constant water temperature

to be maintained in the reservoir, F

F = Kt//?ca2

t = Time from start of cooling of reservoir, hr

and 1(F) is found on Figure 4=8. Other symbols are found

following Equation 4=07.

Heat Sink Capacity of Cooled Reservoir: The capacity of

the cooled reservoir to absorb heat at a constant rate qq for

a time t, until the water temperature rises 9-^^ degrees F

above its temperature at the start, can be determined using

Equation 4=07.
€

it
8 -

Iced Reservoirs

If the reservoir is filled or partially filled with a

mixture of water and ice, the water temperature will remain

at or near 32 F during the addition of heat imtil all the

ice is melted. During this period of time, no heat will be

transferred to the surrounding rock, and the time in hours

required to melt the ice can be computed by the equation:

l44w

Q

(4=09)

where Q

= Constant rate of input of heat to the

reservoir, Btu/hr

W = Weight of ice in the reservoir,- lb

l44 = The latent heat of fusion of ice, Btu/lb, After

the ice has mblted, heat will be transferred to the rock, due

to the temperature rise of the water. The further heat sink

capacity of the reservoir after the ice has melted can be

determined as for the cooled reservoir, using Equation 4=07.

The design of an -underground reservoir using an ice and

water mixture demands careful consideration of the method of

distributing ice along the length of the reservoir. Further

discussion of this subject is given in Section A

reservoir filled with ice only at the front end maintains an

average water temperature of about 34 F in the remaining

length of reservoir and serves to provide an additional heat

sink capacity due to sensible cooling of the water and sur=

rounding rock below the initial temperature of the rock.

For sample problems involving the use of equations

found in Section 4=04, refer to Appendix C.

4“05 Heating and Cooling of Air by Tunnels or Shafts

Fresh or outside air needed for ventilation is often

introduced to installations through shafts or tunnels with

bare walls, so that the air flows in contact with the surrounding rock. For a tunnel in continuous use, heat is

transferred alternately from the air to the rock in summer

and from the rock to air in winter. Savings are possible

under both conditions, since the delivered air is warmed in

winter and cooled and possibly somewhat dehumidified in sum=

mer, thus reducing the heating and cooling loads, respectively (3“07). The temperature of the air at exit, like
»

(-
9

“

that at entrance, oscillates above and below the mean annual

temperature, but the amplitude of the temperature change is

smaller at exit.

This problem is subject to analytical treatment if it

is assumed that the average outside air temperature departure varies seasonally according to the equation:

00 = Oo ' cos wt (4“10)

where the time, t, is equal to zero on July 15, giving a

maximum temperature on July 15 and a minimum temperature on

January 15. ©o' is the amplitude or maximum temperature

departure of outside air from the mean annual air temperature. Because the variation of outdoor temperature is based

on seasonal changes and not on diurnal changes, ©o' may be

calculated as shown in Section 2-10.

Based on the above assumptions, equations are given for

calculating the following temperatures:

1. The temperature departure, 9^, at a distance L from

the outside entrance to the tunnel and at time, t:

n 0L ©o' e"AA' cos(wt-A'B) (4--11)

2. The amplitude, or maximum air temperature departure

at point L:

9 L

= ©o e“AA' ( 4-12 ) where A = g(z,N), Figure 9

A' = KL/c'W

a =2 S/P, equivalent radius, ft

B = f(z,N) Figure ^-9

c* = Specific heat of air = 0.24- Btu/lb-F

e = Base of natural logarithms = 2.718-

h = Coefficient of heat transfer between air and

surface of rock, Btu/hr-ft^-F (Suggested values

are given in Figure 4-10)

K = Thermal conductivity of rock, Btu/hr-ft-F

I)
(-
10

L = Distance from outside entrance of airway, ft

N = ah/K

P = Average transverse perimeter of airway, ft

S = Average transverse area of airway, ft^

t = Time, hr

W' = Weight rate of air flow, Ib/hr

w = Angular velocity = 2tt/8760 = 0.000717 radian/hr

z = a >1 w/cp<

= Thermal diffusivity of rock = X/^c, ft^/hr

0 = Departure of temperature from the mean annual

temperature, F: 0', maximum departure or amp=-

litude; 0o , outside air; 0^, at distance L in

airway. Refer to Section 2=10,

Form E is suggested as a’' work sheet *for problems of this

type. If a tunnel or shaft* is used only intermittently as an

airway, the equations in this section do not apply. However,

it is believed that these equations will give conservative

values for heat exchange in that full utilization of the heat

capacity of the surrounding rock is not realized for the

intermittent operation.

Values of h, the surface film coefficient of heat transfer for various values of V, the air velocity in the tunnel

or shaft, are given on Figure 4—10.

Appendix D contains an illustration of the use of

Equations 4-“ll and ^=12.

4-06 Thermal Properties of Rock

Rock heat absorption computations depend on the thermal

properties of the rock and it is unfortunate that the availa=

ble data are incomplete and, in some degree, discordant. For

estimating purposes, it is recommended that a specific heat

of 0.2 Btu/lb-F be assumed for any rock and for use in the

equations in this chapter, although rock specific heats as

low as 0.16 Btu/lb-’F have been reported.
ii
GURE-4

ALUES OF A AND B

JNCTIONS OF JZ' I AND

£<aJATtdN

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 l.l

Z - 0 yco/oL
€ , ;
11 -

For greenstone, present in the mountains of Virginia,

experimental measurements show a thermal conductivity of

about 1.5 Btu/hr“ft=F, with a density of I86 Ib/ft^. These

figures have been used in demonstration problems in connection with this work and are regarded as good assumptions, at

least for preliminary estimates in many cases. When precision is required, however, more precise values can be

obtained, either by tests on selected specimens, or by the

use of Figure 4-11 in conjunction with petrographic analyses

of specimens. Facilities for making these tests or analyses

are maintained in several laboratories in this country.

The density of igneous and metamorphic rocks generally

falls in the range from 150 to 19 O Ib/ft^, and that of the

sedimentary rocks in the range from 100 to 175 Ib/ft^. For

igneous and metamorphic rocks, the thermal conductivity

falls in a range from 1.2 to 2.0 Btu/hr-ft-F. Grajiites are

found to be in the range 20-40 percen't quartz, 50-73 percent

feldspar, and 5"12 percent mafic. The->factors which determine the thermal conductivity of sedimentary rocks, and which

have to be considered, are numerous; composition, porosity,

temperature, grain size and shape, and fluid content.

4-07 Initial Underground Conditions

At depths of 50 to 70 feet, the undisturbed temperature

of earth or rock can be expected to be within a few degrees

of the mean annual air temperature for the region (2-10) , in

the absence of disturbing factors such as underground fires

or large subterranean streams. At greater depths, the temperature is found to be higher, increasing at the rate of

about 1 F per hundred feet. Earth temperatures thus determined are regarded as adequate for air conditioning estimates

for underground spaces, although a check of the figures is

desirable during the survey of a proposed site.

The earth’s surface is warmed chiefly by solar radiation

and it is cooled by wind, rain, or snow, and by radiation to

the sky, particularly at night. There is therefore an approximately regular diurnal cycle in the surface temperature, but

its effect disappears, practically speaking, at a depth of a

foot or so in the earth. The annual surface temperature

variation is greater and its effects may be significant to

depths of 15 or more feet for some purposes. Some measurements were made at various depths down to I3 feet near

Washington, D, C. , and the results are shown on Figure 4-12

(Ref. 16 ). The curves indicate an annual amplitude of about

4 F, and a mean temperature of about 53 B, at a depth of 13

feet
i

i
„ 12 ~

4“08 Thermal Properties of Materials and Structures

Thermal conductances and other properties of materials or

structures listed in texts or handbooks, including the "Guide"

(Ref. 1), are applicable in connection with underground struc=>

tures. Values of U as commonly listed for walls or other

exposed members are based on an assumed wind of 15 mph velocity

on the outside. An internal structure in an underground chamber

is not exposed to such a wind, although there may be motion or

turbulence due to fans, etc. For estimating, it is recommended

that the outside surface coefficients of exposed ceilings, walls

and floors of internal structures be considered to have the same

values as those ordinarily used for inside surface coefficients.

The coefficient U’ , appearing in Equations and ^-05,

etc. , represents the heat flow in Btu per hour for each square

foot of rock surface for each degree of difference between the

air temperature in the conditioned space and the temperature of

the surrounding rock. For an internal structure, one signifi'-

cant temperature is that within the space, and the other is

that of the surrounding rock surface.

Values of U’ for some materials and structures are given

in Table ^-1 for illustration and possible use in heat transfer

estimates. The fact that particular materials and constructions

are mentioned in the table is not a recommendation that these

materials or constructions should be used. The designing

engineer may select other materials, in which case suitable

values for the coefficients should be otherwise determined.

During experiments in an empty underground chamber with

rock surfaces such as those left after blasting, the air-torock heat transmer coefficient, U’ , with only slight air motion,

ranged from 1.^ to 1.0 Btu/hr-ft^-F, depending on the temperature difference between the air and the rock, with an average

value of 1.2, based on projected wall area, ignoring irregularities left after blasting. For a bare chamber typically filled

with air=warmed objects such as furniture and equipment, radia--

tion between the objects and the rock would tend to yield values

of U* approaching 1.65 Btu/hr-ft^-F. For the surface conductances of internal structures, a value of fo = fi = 1.65 is

recommended for present purposes. With these values, heat trans

fer coefficients of walls, ceilings, and floors of internal

structures can be computed by means of the following equations:

1.65 C ^ 1.25

U (^-13)
r

c

I

t
C = Conductance of wall, ceiling, or floor

of internal structure

TABLE ^=1

Heat Transfer Coefficients for Underground Structures

Btu/hr=ft^=F

Material or Structure

Bare rock surface 1.2 to 1,65

Studs with 3/8” gypsum hoard on one side 0.59

Studs with 3/8” gypsum board on both sides 0.35

Studs with 1/2" insulating board on one side 0.3^

Studs with 1/2" insulating board on both sides 0.l8

Brick, one course = *+" thick 3/8" gypsum board 0.47

Brick, one course “ 4" thick no finish 0.54

Brick, one course = 4" thick 1/2" insulating board 0.30

Brick, two course = 8 " thick no finish O .38

Concrete, 8 " thick no finish 0.49

Concrete construction floors, (3") no ceiling,

no flooring - 0.60

Concrete construction floors, (3") no ceiling,

1 /8 " asphalt tile 0.59

Metal roof deck, bare 0.77

Metal roof deck, roofing and 1/2" insulating board O .31

Wood roof 1" roofing and 1/2" insulating board 0.24

U’ - heat transfer coefficient, based on temperature difference

between chamber air and rock surface.
c(
4—09 Vapor Permeability of Materials

A vapor barrier material may sometimes be Included in

the walls, ceiling, or floor of an internal structure to

reduce the latent air conditioning load or to preclude

harmful condensation inside the wall, ceiling, or floor cori'-

struction. There is no danger of condensation in parts of

an underground structure, except on chilled pipes or sur^

faces, provided the temperature of the surrounding rock is

between the dewpoint and dry^-bulb temperatures maintained

in the conditioned space. In such an application, a vapor

barrier may nevertheless be warranted to reduce vapor ingress

and the latent air conditioning load, if the dewpoint in the

surrounding space is higher than that in the Internal structure. If the surrounding rock should be at a temperature

lower than the dewpoint maintained in the Internal structure,

which is unlikely for more than a relatively short time,

vapor permeation through the walls, which would reduce the

air conditioning latent load, would be impeded by a vapor

barrier. Methods for predicting vapor transfer and condensation in walls are available (Ref. 17 Ref. 1 (Chapter 10 )).

4-10 Underground Water

In damp regions or seasons, water may enter an underground chamber in either of two ways. It may soak through

pervious rock and appear as dampness or a film on the surface, or it may leak in through faults or fissures. Because

the possible hydrostatic pressures are high ( 3

~ 05 ), it is

probably more practical to drain off excess water rather than

to attempt to stop leaks or to treat the rock surfaces and

make them imperviqus.

Evaporation from wet or damp rock surfaces may have

significant effects on the humidity in bare chambers. When

such a chamber is first warmed, the rock can act as a

dehumidifier and tend to hold the dewpoint at the rock surface temperature. In the course of time, the rock surface

temperature increases and water may evaporate from the surface and become part of the latent load. Figure 4-13 Isa

means of estimating the evaporation from wet or damp surfaces, based on data in Reference 18 . The curve gives the

average rate of evaporation, M', in Ib/hr-ft^ for a wet surface L ft long in the direction of air flow parallel to the

surface for a velocity of V ft/min and for a vapor pressure

difference of (Ps-P^) psi, where Ps is the vapor pressure of

water at the temperature of the wet surface, and Pq is the

vapor pressure of the moving air.
A-*! W- "3!' « t * .3 , a4 c
Estimates of evaporation from rock are difficult because

the area of the wet surface cannot be predicted with certainty for a proposed underground chamber » In the installations so far examined in the eastern United States, the wet

area did not exceed 10 percent of the total. In the arid

regions of the west, dampness on the walls would be rare.

For an internal structure, evaporation from the rock

may not be important since the ingress of vapor to the conditioned space can be limited by vapor barriers if necessary;

also, If the annular space is used as an exhaust plenum, most

of the vapor due to evaporation is carried out by the leaving

air* However, materials or equipment such as pipes, ducts,

wiring, or timber enclosed in the annular space or in contact

with the rock should be capable of withstanding humidities

approaching 100 percent, since parts of this space may contain saturated air at times.

For the particular case of a small internal structure

in a large chamber, see f-lO.
P'J* F'ft

r

(

c
Appendix hA

DATA FORMS

The data forms in this appendix are suggested to provld

a systematic procedure for computing ternperati^res and heat

flow rates from the equations in Chapter h® The forms may h

altered or broadened in order to suit indiv/idual preferences
cc
Appendix *+A “ Data Form A

Underground Installation Air Conditioning Design

Data and Computations

Design Information Date;

Location and purpose;

Dimensions, rock chamber

Length, m, ft^ = ; Floor area. A*, ft^ =

Width, n, ft = ; Internal area, A, ft^ =

Height, s , f t = ; Volume, ft^ =

Remarks;

Dimensions, internal structure (if used)

Length, ft = ; Floor area, ft^

Width, ft = ; Internal area, ft^ =

Height, ft = ; Volume, ft^ --

Depth of overburden, geological formation, and moisture

conditions;

Climate, outside air Winter Summer

Minimum Design Maximum

DB, F

BH, %

Rock temperature, initial undisturbed, F =

Required inside air condition, F - % ^RH
r(
Appendix 4a “ Data Form B

Heat Absorption by Rock Surrounding an Underground

Installation; Warm“Up Period

(Refer to Section H—03 and Appendix 4B)

Chamber dimensions: Length, m, ft =

Width, n, ft =

Height, s, ft =

Internal area, Eq 4-01, A, ft^ = 2(mn + ms ns) =

Equiv. cyl, radius, Eq ^^02, aq , ft = A/2rrm =

Equiv. spher. radius, Eq 4-03 , a2 , ft = /aAtt =

Rq* (cylinder) Figure 4—1 =

R 2 ** (sphere) Figure 4“2 =

Rock properties: Density,^, Ib/ft-^ -

Thermal conductivity, K, Btu/h.r-ft-F =

Specific heat, c, Btu/lb-^F -

Initial undisturbed temp, (4-^07), Tj-,

, F -

Design air temperature, Tq, F =

©q- = (Tq - Tr), F

U', (4-08), Btu/hr-ft^-F

Desired warm-up time, t, hours =

F = Kt^ca^

^

~ af(F) + K/U*’

Total rock heat absorption rate, Aq

, Btu/hr -

*If Rq exceeds R2 , utilize cylindrical case (a - aq and Fig. 4-3)

**If Rp exceeds Rq, utilize spherical case (a -- a2 and Fig. 4-4)
f

(
Appendix hA - Data Form C

Heat Absorption by Rock Surrounding an Underground Installation

Steady Temperature or Thermosta tt ed Case

(Refer to Section A-03 and Appendix Ab)

Equivalent radius, rock properties and necessary

are found on Data Form B. Using Equation , s rock heat absorption rate as a function of time

temperatures

olve for the

Equation ^-0^: q = U‘0i f(F,N)/R

N = aU'/K = Time from start of

jjarm-up period, t , hr ?000 £000

F = Kt/^ca^

. .i. w ^L/ vj

f (F,N)*

q (Eq 4-05), Btu/hr-ft^

Rock heat absorption

rate. Aa , Btu/hr

*f(F,N) is

from Fig.

found from Fig. for the cylindrical R-6 for the spherical case.

case and
fo
Appendix - Data Form D

Heat Absorption of an Underground Reservoir Filled with

Water ( Refer to Section h-Ok- and Appendix ^C)

Determination of necessary reservoir length, given other

variables

Permissible temp, rise of water, 9-w, F =

Necessary time duration, t, hours -

Heat absorption rate by the reservoir, Q, Btu/hr =

Rock properties: Density,^, Ib/ft^ =

Thermal conductivity, K, Btu/hr”ft-“F =

Specific heat, c, Btu/lb^F =

Properties of water: Density (average, , Ib/ft^ = 62,

Specific heat, c', Btu/lb-F = 1,0

Dimensions of reservoir for rectangular cross-section:

Width, n, ft =

Height, s, ft =

Radius of equiv. cylinder, a = (s+n)/7r, ft = From Equation ^-07, ©wK/qq = f(F,G)

F = Kt^ca^ =

M' = 2x62,4 (s+n), Ib/ft length =

G = 2Tra^c/M*c' =

f(F,G), from Fig. 4-7 or 4-7A =

qi = ©wK/f(F,G), Btu/hr-ft

Required length of reservoir, L = Q/qi , ft = Total volume of reservoir. Volume = snL, ft^ =
I«
Appendix *+A - Data Form E

W Cooling or, Heating of Air in Tunnels or Shafts

Continuous Air Flow, Annual Weather Cycle

' (Refer to Section 4-05)

Dimensions of tunnel:

Length, L, ft = ; Perimeter, P = 2(n+s), ft = Width, n, ft = ; Area, S = ns, ft^ = Height, s, ft = ; Equiv. radius, a = 2S/P, ft =

Outside air conditions (2-10):

Mean annual temp, T^, F = Mean annual range of temp, Tm, F = Maximum departure, ©o' = Tni/2 , F =

Air capacity:

Air flow rate, V, ft^/min = Air density, o', Ib/ft^ = Air flow rate, W* = 60^*V, Ib/hr = Velocity, v = V/S, ft/min =

Properties of rock

II Density, Ib/ft^ = Thermal conductivity, K, Btu/hr-ft-F = Specific heat, c, Btu/lb F = Thermal diffusivity, o<'= K/^c, ft^/hr =

Coefficient of heat transfer, h (Fig. 4-9), Btu/hr-ft^-F =

-V* w = 0. 000717 radian/hr

z = a /w7o< = *, A (Fig, 4-9) = N = ah/K = ; B (Fig. 4-9) =

A' = KL/0.24 W* = ; Extreme temperature at distance L from air entrance, Eq. 4-12

Maximum temp; Tg_ + ©q ' e'”-^-^* = Minimum temp; T^ “ ©o' =

4
Ifc
APPENDIX NB

Heat Absorption by Rock Surrounding Underground Spaces;

Some Practical Aspects

4B“1 Introduction

_Rock heat absorption is an important factor in the heating and air conditioning of underground spaces, and the

purpose of this appendix is to indicate the range of rock absorption rates that may occur in practice and to show the effects of differences in such factors as size of space thermal properties of rock, and heat transfer coefficient,

' equations of Section h“03 are utilized and rock heat absorption is discussed in terms of q ' , the steady heat flux irom air to rock assumed for a warm-up period, and q, the decreasing heat flux from air to rock that occurs when the air in an underground chamber is maintained at an approxi- mately constant temperature*

li-B-2 Applicable Problems and Equations

^ In order to show the differences that occur due to

of space, thermal properties of rock, and coefficient of heat transfer U' , computed solutions of the rock heat absorption equations are shown graphically in Figures hB-1 to Ab-4 for certain values of these variables

as given in the table below*

vaiiaoies

Chamber Sizes

Length, m, ft

Height, s, ft

Width, n, ft

Surface area. A, ft^(Eq h-01 ) Equiv. radius, , ft(Eq ^- 02 ) R (from Figure V-1)

Thermal Properties of Rodk

Thermal conductivity, K, Btu/h]

Density,, Ib/ft^

Specific heat, c, Btu/lb-F

Thermal diffusivity, K/^c, ft^^

Haat Transfer Coefficients

Transmittance from air in conditioned

space to rock face, U', Btu/hr-ft^^F

1 2 3

200 200 200

10 10 30 17A 35.3 39 . 5- 11310 18830 30120

9 15 24

0.875 0,875 0.875

1 .2

•ft-F 1.2 1.7

179 165

0.21 0,18

.r 0.032 0,057

1.2 O.h
ff
Figures 4b- 1 and 4-B“2 show solutions of Equation 4-04

for the warm-up period with steady heat input, and Figures

4B“3 and hB-h give solutions of Equation 05 for the constant air temperature period with decreasing heat absorption

by the rock.

All computations for heat flow q or q ‘ are based on a

temperature difference, 0j, , of 25 F. This temperature difference represents an air temperature of 75 F and an initial

rock temperature of 50 F. If a value of heat flow for a different 0j_ is desired, it may be found from the following

relationships

q = Qo ®l/25

q' = q'o ©1/25

where the subscript o denotes the values of heat flow shown

in the figures computed for the temperature difference of 25 F.

The numerical computation of the results presented

graphically is illustrated below, for the case defined by

the variables listed under 1 in the table.

Surface area:

Equation 4~01: A = 2(mn + ms + sn)

= 2(200x17*4 + 200x10 + 10x17*4)

= 11,310 ft^

Equivalent radius •

« Equation 4-02:

2Trm 2ttx200

= 9 ft

From Figure 4=1: R = 0 . 875 ? for m/n = 11.5

p

_ ..Kt 0.032 t

7>ca‘^ pc^ (9)“^ (9

= 0.000395 t

Constant heat input necessary to raise air temperature 25 F

in 20 days:

Since F = 0.000395x20x2^ =0.19

From Figure 4-3; f(F) = f(0.19) = 0.4l4
<r

.In.-': n

/ :

4»

'ft

I

if'

*,,‘"

K.

1
-3

»

I

i

Equation 4-04: ^ af(F) + K/U' 9x0. 4l4- + 1.2/1.

2

= 6.3^ Btu/hr“ft^ or

= 6.3^x11,310 = 71,700 Btu/hr for

20 days.

The average heat input needed for operation with constant

air temperature, one year (8760 hours) after the start of

the initial warm-up:

F = 0.000395x8670 = 3.^6

N = a U*/K = 9x1. 2/1. 2 = 9

From Figure 5: f(F,N) = 0,073

Equation 4-05: q = f(F,N) U'0i/R = 0.073x1.2x25/0.875

= 2.5 Btu/hr-ft^ or

= 38,280 Btu/hr

4B“3 General Discussion

The problems of Section 4b-2 deal with the cylinder as

an approximation for the computation for heat flow because

a cylindrical configuration is likely to be the best approximation for most underground installations. The spherical

configuration is also possible; it exhibits much the same

properties as the cylindrical.

To obtain a warm-up, heat may be supplied to a chamber

at a fast rate during phase 1. Permanent heating installed

to maintain temperature during phase 2 may be inadequate to

provide an adequately fast warm-up. In such a case, utilization of temporary heating equipment to supplement the

heating capacity may be desirable.

a. Effect of size of chamber - The equivalent radius

defined in Equation 4-02 is a measure of all three of the

dimensions of length, width, and height. Figures 4b- 1

through 4B“4 show that the rate of heat absorption per

square foot of rock surface at any given time decreases as

the equivalent radius increases. For example, from Figure

4B“1, for U' =1.2 and time = 80 days, the steady heat input

for the three equivalent radii is as follows:

a= 9 ft, q' =4.0 Btu/hr-ft^ , or 45,240 Btu/hr for the chamber

a = 15 ft, q' = 3.62 Btu/hr-ft^, or 68,160 Btu/hr for the chamber

a = 24 ft, q’ = 3.42 Btu/hr-ft^ , or 103,010 Btu/hr for the chamber
tt \

Vd
The total heat input rate necessary, of course, increases

with increase in radius as expected.

b. Effect of thermal properties of rock =- An increase

in the thermal diffusivity (K/^c) of the rock increases the

amount of heat necessary to warm a space in a given time.

This can be shown from Figures *+B-l and hB-2 for a case

where a = 9 ft, U* =1«2, and time = 80 hours.

from Figure ^-B-1, K/pc = 0.032, q* =4.0 Btu/hr-ft^

from Figure 4B“2, YL/pc = 0.057? q* = 4.71 Btu/hr^ft^

The thermal properties used in the problems of Section hB-2

represent approximate extremes for common rocks, so that

heat flow for most installations probably lie between the

values shown in Figures 4B“1 to 4B“4.

c. Effect of the coefficient of heat transfer, U* “ The factor U' represents the heat transfer coefficient from

the air in a conditioned space to the surrounding rock in

Btu/hr“ft^“F. The temperature difference, in deg F, is

measured between the air in the conditioned space and the

rock surface. Observations in a bare chamber indicated that

the value U' = 1.2 adopted for the present computations is

approximately appropriate. For an internal structure, the

relevant temperature difference is that between the air

within the structure and the rock surface, and the average

U' value depends on the construction of the walls, floors,

and ceilings (Equation 4«13),

The rate of heat transfer to the rock is at all timss

given by U’AT, where AT is the existing temperature dif“

ference between the air and the rock surface. However, U*

for a bare chamber decreases approximately as the one-third

power of AT, and in addition, its effect on the rate of rock

heat absorption also decreases with time, as is shown by the

tendency of the curves for U' = 1.2 and U' = 0.4 in Figures

4B"1 to 4B“4 to converge with time.

"cr* 5

FIGURE B-l

CONSTANT RATE OF ROCK HEAT ABSORPTION REQUIRED

TO RAISE AIR TEMP. 25 F FOR A GIVEN TIME PERIOD

, - : ROCK PROPERTIES

K = 1.2 BTU/HR-FT-F

p

- 179 LBS/FT3

C - .21 BTU/LB-F

U‘= 1.2 —U = 0.4

80 120

TIME - DAYS

160 200
c
CONSTANT

TO RAISE

FIGURE B-2

RATE OF ROCK HEAT ABSORPTION REQUIRED

AIR TEMP. 25 F FOR A GIVEN TIME PERIOD

ROCK PROPERTIES “ f

K = 1.7 BTU/HR-FT-F

p

- 165 LBS/FT^

C = .18 BTU/LB-F

U'= 1-2 —U = 0.4

u.

01X\

Z5

I-CD y

5

#i

f—

Q.

010

CO

CO 4

5

UJ1

2 M

Q

TIME - DAYS
i

' ?;!
C\i / h-

' LL

£rX

OD

O"

O

hCuX

O

(f) CD<

<

LUX

o

o

q:

U-o

UJ

K-<

I)
c

c<

'fl*

a

•I

G
APPENDIX

Problems Illustrating Use of Equations

for

Underground Reservoirs

INTRODUCTION

The underground reservoir as a sink for waste heat dis--

posal during an emergency condition has been discussed in

Sections 3"06, A-OA, and The purpose of this appendix

is to illustrate by problems the use of the equations of

Section A“OA, and to discuss the relative merits of the heat

absorbing capacity of the surrounding rock as a function of

time and the equivalent radius*

AC“1 Sample Problems “ Variation of Equivalent Radius*

Assume the heat generation rate for an underground instal

lation during an emergency period is two million Btu/hr, and

that the installation must be self-'sustaining for a period of

ten days. The reservoir temperature is initially 5^2 F and

the highest water temperature permissible is 100 F. Deter^

mine the necessary lengths of reservoirs for the cross-= sections given in Table Ac-»1. Thermal properties of the sur^

rounding rock are:

K = 1.A5 Btu/hr-ft-F

P = 185 Ib/ft^

c = 0.2 Btu/lb-F

and for equation A—07

F = Kt/^ca^ .1?-A5_..._x , 10 , X 2A _ 185 X 0.2 X a^

G = 2tt X 185 X 0 . 2 a^

1.0 X M

*

9»A/a2

232.5 a

2 M'

QwK _ (100-52)1. A5 69.6

Ql “ Qi
G
TABLE 4C-1

Computation of reservoir lengths for 10-day operation

Width of reservoir, n, ft

Height of reservoir, s, ft

Equivalent radius, a = (s+n)/7r

M', 62 . 4 sn, Ib/ft length

F = 9 . 4/a 2

G = 232.5 a^/M'

f(F,G), from Fig. 4 - 7A

= 69 . 6 /f(F,G), Btu/hr ft

Length, m = 2xl0^/q^, ft

Volume of water, mns , ft^

Total heat added, 240x2x10^,

( 10® Btu)

Heat in water, 48x62 . 4xVol.

,

(106 Btu)

Heat in rock, ( 10^ Btu)

Percentage of heat in rock, %

Water contact surface, ft^

No. 1 No. 2 No. 3

15 20 20

15 20 30

9 . 5

>+ 12.73 15.91

14 , 040 24,960 37,5^0

0.1033 0.0580 0.0371

1.51 1,51 l »57

0.0171 0.0105 0.0073

4,070 6,629 9,539

491 302 210

110,475 120,800 126,000

480 480 480

330.9 361.8 377.9

149 ol 118.2 102.6

31»1 24.6 21.4

29,460 24,160 21,000

Table 4c-l shows that for a reservoir of smaller crosssection and longer length, a greater proportion of the heat

is absorbed in the surrounding rock, and that this proportion

is approximately proportional to the surface area in contact

with the water. Also, the volume of water or amount of excava

tion is less for the reservoir with the smallest cross-section

If a reservoir is to be used ultimately as a heat sink

for the waste heat from a prime mover such as a Diesel

engine, the maximum water temperature can probably be higher
0
than 100 F. For case Number 2 with other conditions the

same but with the maximum allowable water temperature equal

to 160 F instead of 100 F, the length of the reservoir is

m ^

2 X 10^ X 0.0105 ^

( 16015^

74 ?

13^ ft;

the volume of reservoir required is 5356OO ft^; and the per--

centage of the total heat input absorbed by the rock is

2^-.6 percent.

It will be noted that the percentage of the heat

absorbed by the rock did not change. The reason is that

this percentage is governed by the time available for heat

absorption by the rock, for a reservoir of a given equiva-"

lent radius.

hC-2 Sample Problems *- Variation of Time

Case Number 2 of Section ^C-l will be used as an

example, in which lengths of reservoir will be determined

for a heat input rate of 2 x 10^ Btu/hr for time durations

6, 8, 10, 12, and l4 days, and for a water temperature rise

from 52 F to 100 F.

G = 1.51

F = Kt/^ca^ = I.h5t/l85 X 0.2 x (12.73)^ = 0.0002»+2t

It will be noted that the percentages of total heat

absorbed by rock in Table ^-C“2 increase as the duration of

heat input increases. This shows the influence of time when

the reservoir size is adjusted to yield the same temperature

rise 9-^^, for different durations of heat input.

To illustrate further, consider the reservoir 192 ft

long in Table ^C“2, which was raised in temperature from 52

to 100 F in six days with a heat input rate of 2 x 10° Btu/hr.

If the heat input rate had been 1 x 10^ Btu/hr, the same

temperature rise would have occurred in 13*8 days, and 30^5

percent (versus 20.1 percent) of the input heat would have

been absorbed by the rock. The total heat added to the

reservoir would have been 331 x I06 Btu (versus 288 x 106

Btu) . This shows the increases of heat sink duration and

capacity that result when the rate of waste heat input to

a given reservoir is restricted as much as possible.
c

Ci
TABLE hO-2

Step"by“Step Computation of Reservoir Lengths

(Width = Height 20 ft)

Time, Days

6 8 10 12 14

F = 0. 00024-2

1

0.034-8 0.0465 0.0580 0.0697 0.0813

f(F,G) 0.0067 0.0086 0.0105 0.0123 0.0141

qj = 69.6/f(F,G) 10,388 8,093 6,629 5,659 ‘+,936

Length,

m = 2xl0^/q 2 192 247 302 353 4o5

Vol. of water,

mns, ft^ 76,800 98,800 120,800 141,200 162,000

Total heat added,

(106 Btu) 288 384 480 576 672

Heat in water,

(106 Btu) 230 296 361.8 422.9 485«2

Heat in rock,

(106 Btu) 58 88 118.2 153.1 186,8

Percent of heat

in rock, % 20.1 22.9 24.1 26 .6 27»8

I

L-C”3 Sample Problems “• Cooling of Reservoir

In some cases it may be necessary to maintain the ternperature of the water in the reservoir at a temperature lower

than the initial earth temperature „ As a sample problem,

take the reservoir of case Number 2 of Section ^C=-l, for

which the dimensions are 20 by 20 by 302 ft» Determine the

refrigeration necessary to cool it from an initial temperature of 52 F to 40 F in 25 days, and determine the refrigeration necessary to maintain the water at 40 F subsequently.

For equation 4—07

G

F

= 1.51

1.4-5 X 25 X 2^

IB5xo72lTT12 . 73 ) ^ 0.145
c

Ct
From Fig. 4==7, f(F,G) = 0.0233

^ yl^y Btu/hr ft

Q

= '^^2" "0Q^'" ~ l8.8 tons of refrigeration

With l8,8 tons of refrigeration, the water is cooled from

52 F to ^-0 F in 25 days.

The refrigeration necessary to maintain the reservoir

at ^0 F (Table ^-C“3 can

Fig. 4-9.

From Equation 4-08

^ _ KOimKF)

Q

- _

= 0.4381(F),

be computed from Equation 4-08 and

12,000

tons of refrigeration.

TABLE 40^3

Refrigeration necessary to maintain 40 F water in

a 20x20x302 ft reservoir

Time after start

of cooling

60 days (l440 hr)

4 months (2880 hr)

1 year (876O hr)

3 years (26,280 hr)

= Kt/^ca2 l( F), Fig. 4-9 0, tons

0.35 8.7 3.81

0.70 7.0 3. 06

2.12 5»o 2.18

6 . 38 3*7 1.62

4c~3 Sample Problem - Reservoir Filled with an Ice and

Water Mixture

The reservoir (20 ft by 20 ft by 302 ft length) of

case Number 2 of Section 4c--l is employed to illustrate the

case of a reservoir containing 40 percent ice by volume.

The time duration of the usefulness of the reservoir is

determined by using the reservoir water as chilled v/ater

until the water has been heated to a temperature of 50 F,
c

C:
and thereafter using the reservoir water as condenser water

for refrigeration compressors for water temperature in the

range from 50 to 100 F. Because refrigeration equipment is

not operating during the time when the temperature is below

50 F, the heat input rate to this reservoir is' reduced by

the rate of energy input required to drive this equipment

(3“06). If the heat input rate to the reservoir is two

million Btu/hr with operation of this equipment, and its

coefficient of performance is assumed to be , then the heat

input rate without its operation is approximately 1.6

million Btu/hr.

From Table hc^l, the total reservoir volume is 120,800

cubic feet and the ice volume is h8,320 cubic feet and, for

an ice density of 57»5 Ib/ft^, the weight of ice, W is 2.7/8

X 106 lb. From Equation 4-09 5 the time tq to melt the ice is

tn = I44W 144x2.778x108

^ Q l3xl08 250 hours.

The weight of water in the reservoir after ice meltage

is 62.4 X 72,480 + 2.778 X 108 pounds, or M’ = 24,1/0 pounds

per foot length of reservoir. To determine the time t2 for

a temperature rise from 32 to 50 F at a heat input rate of

1.6 X 108 Btu/hr, Equation 4-0/ yields

. 0 . 004,

From Figure 4->7A F = Kt/^ca^ = 0.024

^ , 0. 024x185x0. 2x(12 . 73)2 __ and t2 = — hours.

To determine the time t^ for a temperature rise from

50 to 100 F at a heat input rate of 2 x I08 Btu/hr, and with

the assumption that the rock temperature is substantially

uniform at 50 F at the end of time t2. Equation 4-07 yields

f (F,1.58) (100-50)xl. 45x302

2x108 “ 0.0109

From Figure 4~7A F = 0.059

and t^ = 244 hours
(ic I
=7

The time duration of the reservoir without wastage of

the water is the sum of the times ti + t 2 + t 3

= 593 hours.

In comparison to the same reservoir with an initial water

temperature of 52 F, the time duration for the reservoir is

extended 3^3 hours by the use of a 40 percent ice and water

mixture in the reservoir. Similarly, the time duration is

increased only 103 hours with the initial temperature of the

water at 32 F. With wastage of the water through the con-- denser, the extension tu of the time duration can be cal^-

culated by Equation 4-Od, if it is assumed that the maximum

discharge temperature of the refrigeration condensers is 110 F,

ti+

7 » 301x106(110-^100

)

2x10^

= 36 hours.

This yields a total time duration of 629 hours or 26.2 days.

Design considerations and further discussion regarding

the ice reservoir is found in Section 5“16.

I
<L

<i

i
CHAPTER 5

AIR CONDITIONING PROCESSES AND SYSTEMS

^-’Ol Sizes and Shapes of Underground Chambers

Underground chambers intended for protective purposes

may be from one hundred to several hundred feet below the

surface. Sizes vary in accord with requirements but, in

usual cases, such chambers are typically in the form of

tunnels. The width is not likely to be less than 8 to 10

feet nor the ceiling height less than 10 or 12 feet, because

smaller openings do not permit use of conventional exca-^

vating machinery. Cost of excavation in dollars per cubic

yard is less when the opening permits use of power shovels

and trucks for handling the spoil. Widths are not likely

to exceed 30 to 40 feet, depending on the strength of the

rock. In height, the space may be single or mult i'^story

,

Chambers at lesser depths, not designed to resist

atomic bomb attack, may be round or irregular in shape with

pillars left during excavation to support the roof.

Large chambers may be subdivided into rooms to improve

acoustical conditions, for privacy as in offices, or to

isolate areas for other purposes.

^^02 Access Tunnels and Shafts

The simplest kind of underground installation may con=

sist of a single chamber and have a single shaft or tunnel

for both access and ventilation. A tunnel is usually pre~

ferred, because with a slight slope it can serve also for

natural drainage and because it is more convenient for

access, particularly for equipment or material. Larger

installations, or those designed for human occupancy,

usually have at least a tunnel plus a shaft and may have a

multiplicity of either to provide adequate services, access,

and ventilation. Forced ventilation is essential for most

occupied installations.

Either a tunnel or shaft used as an air intake has an

appreciable air conditioning effect, serving to warm and

sometimes to humidify air in winter, and to cool and

dehumidify it in summer (4=05). This effect can be deducted

from the total required heating or cooling capacity for the

occupied spaces.
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5“03 Simple Installation, Single Shaft

An installation consisting of a chamber below ground

with a single shaft to the surface, may seldom be recommended on account of the inconvenience of access and the

difficulty of ventilation and drainage. The behavior of

natural ventilation in such installations is considered

here for completeness. Under this condition, natural venti=

lation will be slight, as it is in a deep well. In the

absence of gas from the earth, it may be possible for a few

men to work in such a chamber for short periods, but pre«

cautions are essential and forced ventilation should be

provided for any lengthy occupancy. If undisturbed, the

chamber will remain near the rock temperature and the humidity

near saturation. In winter, the enclosed air may be warmer

than that above ground and thus have a tendency to rise.

Ventilation by chimney action, however, is practically

inhibited by the interference of the air rising through the

shaft with that which must enter through the same opening

to replace it. In summer, the enclosed air will usually be

cooler than that above ground. There will therefore be no

ventilation by chimney action and the air in the chamber

will stagnate.

5“04 Simple Installation; Two or More Shafts

An installation of this kind is self-vent ilating in

winter but is not ventilated by chimney effect in summer.

In winter or when the air in the chamber is warmer than the

atmosphere outside, chimney action, once started by wind or

a difference in height of two shafts, will cause a continuous air change, with air flowing down one shaft and up

another. Under this condition, the chamber is self-drying.

Outside air, if warmed by passing through a shaft and cham^

her, can absorb water as vapor and conduct it to the outside.

In summer, or when the chamber is cooler than the atmosphere outside, the air stratifies or stagnates in the chamber

and the humidity approaches saturation if water is present.

Ventilation is limited to that due to wind effects or to the

minor amount caused by changes in barometric pressure.

5“05 Simple Installation, Single Tunnel

An installation consisting of a chamber with a single

tunnel for access and drainage may be useful in some cases

for the storage of munitions or other material requiring

infrequent attention. In a bare chamber, the air approaches

the temperature of the surrounding rock and the humidity
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approaches 100 percent if water is present. However, if an

enclosure or inner structure is provided and is warmed,

either electrically or otherwise, its interior assumes a

relative humidity less than 100 percent. (5-10)

Temperature differences between the chamber and the

outside will exist during summer and winter, but no considerable natural ventilation can be relied upon through a

single tunnel. For any occupancy other than occasional

entrance, such as to place or remove stored goods, forced

ventilation should be provided. This can be accomplished

by means of a fan and duct in the tunnel, arranged either

to conduct outside air into the chamber, or to exhaust air

from the chamber.

5"06 Simple Installation, Tunnel and Shaft

A simple installation consisting of an underground

chamber with a tunnel and shaft tends to be self-ventilating

during all seasons. In winter, or when the interior is

warmer than the atmosphere outside, air flows by chimney

action in through the tunnel and out through the shaft, and

in summer or when the temperature relation is reversed, the

air flow reverses, and the air passes down through the shaft

and out through the tunnel. In winter, the chamber tends to

be self-drying, because water evaporates from the rock, which

is warmer than the dewpoint of the air, and is conveyed to

the outside by the air current. In summer, in humid regions,

the rock may condense water from the air and become wet.

Drainage of the condensate may be necessary by means of

trenches or /also pipes in the tunnel. To a lesser degree,

daily weather changes and winds cause ventilation of such

installations for the same reasons.

Small insulated structures in such a chamber can be air

conditioned by warming (5“^10), in that the relative humidity

can thus be reduced. In other weather, outside air can be

used to cool the chamber and surrounding rock, removing the

heat and moisture escaping from the inner structure, thus

facilitating this air conditioning process.

For heavy or continuous occupancy, or if noxious gases

are involved, forced ventilation may be essential.

5"07 Installations with Multiple Access Openings

A large installation intended for the protection of

personnel or processes is likely to have two or more access

tunnels, first, so that an alternate is available if one
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tunnel should become blocked and, second, for convenience in

handling traffic. Access tunnels can be used for the discharge of vitiated air from an installation but their use as

air intakes is not generally recommended. Vehicular exhaust

gases may contaminate the intake air. Also, if used as

intakes, access tunnels are found to be too wet in summer

and too cold in winter, with walls, floor, and ceiling often

coated with ice. Usually, the exhaust from Diesel engines,

flue gases from boilers, and other fumes, are vented through

special shafts, while exhaust from kitchens and toilet

facilities is vented with the air from the other occupied

spaces. Separate air intakes are desirable, and shafts are

often preferred to tunnels for this purpose, because the distance downward to the installation is less than the horizontal distance from outside. The shaft is often less expensive, because it is shorter, although the cost of excavation

in dollars per cubic yard may be less for a horizontal than

for a vertical opening. In some cases, a sheet-metal fresh

air duct, run through an access tunnel may be preferable to

a separate ventilation tunnel or shaft.

Types of Internal Structures

It is possible to install practically any kind of structure in an underground chamber that is used on the surface,

but an inner structure in an underground chamber is not exposed

to the sun and wind like a building on the surface. The

humidity in many underground spaces is initially high, but the

temperature is usually mild so that the use of heavy insulation is not justified, except in special cases. The vapor

transfer problem may require different treatment. The roof

of an internal structure may be designed to catch both dripping water from the ceiling of the chamber, and spalling rock

fragments

.

The air in the annular space around an internal structure is likely to be at relative humidities in excess of 70

percent if even moderate areas of the rock are damp or wet.

The outer parts of internal structures, their supports, and

service pipes and lines in the annular space, must be of

materials resistant to, or protected from, corrosion due to

high humidities.

Internal structures differ in size and in the ratio of

their size to that of the enclosing chambers. Often, internal structures are designed to fit enclosing chambers, with

relatively small clearances. Simple partitions, even if

they do not reach to the ceiling, afford some privacy in

offices and may be used to improve acoustical conditions

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Addition of thermal insulation to the walls, ceiling,

and floor of an internal structure may he useful if the

interior of the structure is to he heated to some temperature above that of the surrounding annular space for relatively short periods of time* If the two spaces are kept

at the same temperature, or when, after long periods of time,

the rock surrounding the chamber approaches the chamber or

internal structure air temperature, insulation between them

cannot have any effect. If the annular space and surrounding

rock are cooler than the structure when it is being cooled by

air conditioning, the rock will reduce the cooling load by

absorbing heat. In this case, the use of insulation may be

detrimental. In some circumstances, a small internal structure in a large chamber may advantageously be thermally

insulated (5”10).

Application of vapor barrier materials in the walls,

ceilings, or floors of internal structures is not benefit

cial under all circumstances (*+-09)*

Thus, from an air conditioning standpoint, the walls

and ceilings of an internal structure can consist of any

material presenting an acceptable finish to the interior,

suitably supported on a frame. As previously mentioned, a

roof is often desirable to exclude drip.

If either an interior structure or its contents are

subject to deterioration from dampness, the structure should

be continuously air conditioned, not only during normal

operation, but during standby or unoccupied periods, however

long. If the internal load is small so that the surrounding

rock remains cool and at a temperature lower than the desired

interior dewpoint, the air conditioning process may consist

in simply warming the structure to reduce the relative

humidity (5”10).

5“09 Acoustical Treatments

Sound waves reverberate in a bare rock chamber and some

treatment may be necessary in occupied spaces where a low

sound level is essential. It is usually impractical to

apply acoustical material directly to the surfaces of the

rock on account of water pressure ( 3 “ 05 ) or wetting by con=

densation. Internal structures are a solution to the problem, and the treatments of walls or ceilings for sound

absorption can be the same as those for surface buildings.

In chambers where a ceiling is not needed for protection

against dripping water or spalling rock, partitions not

reaching to the top of the chamber (5“08) are a possible

solution to the problem.
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Air conditioning devices 5 including fans, blowers,

pumps, and compressors, are often sources of noise. Treatment of such equipment, and of ducts or pipes, to minimize

propagation of noise is covered in texts on air conditioning.

5-10 Small Structures in Large Underground Chambers

Under favorable circumstances, the relative humidity

inside an internal structure can be satisfactorily controlled for material preservation by simply warming the air

within the structure. The surrounding rock is relied upon

to control the humidity, since condensation occurs on its

surface when the dewpoint exceeds the rock surface temperature. Insulation of the walls of the internal structure is

desirable to retard the warming of the rock by heat from the

structure, but these walls must be permeable to permit

migration of water vapor from the structure to the rock.

This arrangement may be useful when a large cool underground space is available and the required space and the

internal load are small. Excavation of a suitable chamber

probably would be uneconomical, but sometimes an abandoned

mine or other underground opening may be so utilized.

A leakproof roof is essential to protect the interior

or contents of the structure from drip, should any occur.

The walls must be pervious and vapor barriers are not

desirable, because the surrounding rock is relied upon to

control the humidity (3-05, ^-09) « Heavier insulation reduces

the heat requirement of the structure and slows the heating

of the surrounding rock by heat from the structure. This

either lengthens the period of possible use of such an

installation or permits the use of a larger internal structure in a given chamber. This type of air conditioning

can be facilitated if the chamber is selectively ventilated with cold air, as in winter and at night, since heat

absorbed from the inner structure can thus be removed. The

surrounding rock serves as a large heat sink and makes this

process possible.

5”11 Annular Space Used as Cold Air Plenum

It is possible to cool an internal struqture in an

underground installation by utilizing the annular space

between the structure and surrounding rock as a cold air

plenum held at or near the initial rock temperature. An

outstanding advantage of such an arrangement is that the

surrounding rock, remaining cool, would in a time of emergency offer a large contiguous heat absorptive capacity.
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This would be available to reduce considerably the cooling

load required of the air conditioning system, and without

any supplied air conditioning, would greatly extend the

period of tolerable temperatures and humidities in the

installation.

In such an arrangement, air is discharged into the

annular space at a temperature approximately equal to the

natural initial temperature of the rock (^-“07). The cool

air in the annular space plenum is drawn into and distributed in the internal structure as required to maintain

the desired interior conditions. The air discharged from

the internal structure, except for that exhausted as

vitiated air, may be discharged directly into the annular

space through a cooling coil which lowers its temperature

to that of the surrounding rock. Alternatively, it could

be returned to a central cooling system and, after being

cooled, ducted back to the annular space.

In this arrangement, the cooling load is equal to the

internal heat generation, since the rock is not being

changed in temperature. The dewpoint in the interior

structure would be approximately the same as that in the

annular space, which in turn would be limited to not more

than the temperature of the rock surface. For this reason,

very steady control of the internal structure dewpoint is

possible, at a value governed by the rock temperature. In

many areas in this country, natural rock temperatures are

in the range 50 to 55 F, which would conduce to internal

structure conditions of 75 F dry^bulb and k2 to 50 percent

relative humidity (2-04, 2--05)® In areas where the natural

rock temperature is colder or v/armer , heating or cooling of

the rock to maintain a desired dewpoint is possible.

Thermal insulation of the structure is not useful when

the structure must be cooled, but insulation would be bene--

ficial if the internal structure must be warmed during a

prolonged unoccupied period, to maintain a desired relative

humidity.

The heat-absorbing capacity of the rock surrounding the

annular space in such an arrangement, which would be availa“

ble for use during a period of emergency operation, can be

calculated by means of Equation (4--03), using for the

steady heat input to the rock the generated structure heat

load minus the cooling being supplied by the air condi“

tioning system as regulated during the emergency period.

In Equation for this case, the U'-value should be

that for a bare chamber (4-08).

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To obtain optimal limitation of the temperature and

relative humidity in the internal structure during such

operation in an emergency period, with restricted cooling

by the air conditioning system, the annular space air

should be drawn into the structure through the cooling

coil, and the structure air discharged to the upper levels

of the annular space, which are reversals of the air flow

directions during normal operation.

If the annular space is to be used as a cold air

plenum, leakage of air between the plenum and access

passageways should be prevented to avoid discharge of

cold air into warm passageways,

5=“12 Air Conditioning Processes for Larger Installations

Several air conditioning processes or arrangements

merit consideration for the larger underground installations. Recirculation of part of the air for economy in

operation is essential, while fresh or outdoor air in proportion to population (2-06) must be supplied with any system in an appropriate manner. Hallways in internal structures or the surrounding annular spaces can be used for

return air passages.

Either central air conditioning systems (5“13) or zon,e

or room air conditioners (5-1^) are feasible. The problem

of locating large ducts is avoided if zone or room conditioners are used and the control problem is in some degree

simplified. Either self-contained air conditioners with

built-in condensing units, or remote-type air conditioners

with chilled water coils can be used. Heating may

be accomplished by a separate system or by heating coils

included in the air conditioners.

A special arrangement consists in cooling the annularspace around an internal structure with conditioned air and

ducting the return air instead of the supply air

5-“13 Central Air Conditioning Systems

The use of large central air conditioning systems in

buildings has declined in recent years and the apparent

reasons are the necessity for large, long ducts, inflexibility under moderate loads, as in mild weather, and the

relative low cost of unit equipment due to quantity production. The same reasons favor individual room or zone conditioners in underground installations.
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In typical systems so far -utilized underground, con^-

ditioned air is ducted to the working spaces, while the

annular space around the inner structure may be used as a return plenum. Fresh or outside air is introduced into the

supply system at one or more convenient points, with care

to assure good distribution. The total air flow must be

sufficient to remove heat and water vapor originating in

the various rooms or spaces and fresh air must be supplied

in proportion to population { 2 ^ 06 ).

5“1^ Self-Contained Air Conditioners

Use of a multiplicity of self-'Contained air conditioners, one for each room or zone, simplifies the zoning

and control problems, possibly improves over-all reliability

in some degree and is a means of avoiding the use of large

long ducts, with the attendant necessity for insulating them.

Noise (5“’09) may be important if such equipment is used,

since occupants may be situated close to the source. Selfcontained air conditioners include condensing units in preassembled cases or packages and, for use underground, these

condensers presumably will be water-cooled and water from

outside must be piped to and away from each machine. Fresh

air must be ducted to the spaces served in proportion to

population and, preferably, this air should be either

tempered in the supply system or pass through a conditioning

coil before entering the occupied space. Self-contained airconditioners may contain hot water or steam coils for use

when heating is required. Condensate due to the dehumidifying process must be drained away, and this probably can

be accomplished conveniently in most cases by piping to

conduct the condensate to a drain in the annular space or

under the floor.

Self-contained air conditioners can be arranged to

serve as heat pumps and thus warm spaces when required, as

well as to cool and dehumidify them. Most of the heat for

warming a space with this arrangement is taken from the

water used at other times to cool the condenser. Precautions against freezing the heat exchanger may be

essential

.

5“15 Chilled Water Systems

Use of chilled water in unit air conditioners for

individual rooms or zones has the advantage of simplicity

and flexibility of control. Chilled water lines should be

insulated if they pass through spaces with high dewpoints

to prevent condensation on their surfaces, with resultant
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corrosion and to conserve the cooling effect of the water.

In air conditioned spaces, such pipes may require insula“

tion to prevent troublesome condensation and dripping.

Control may be effected by starting and stopping the

fans in the units, by means of dampers to control the air

flow through the cooling coils, by regulating the flow or

temperature of chilled water to the coils, or by a com-- bination of these methods,.

Cold water from wells, streams, ponds, or cooling

towers can be used in cold weather, instead of the water

chiller, thus reducing the refrigeration load and expense

of operation.

Heating coils can be installed in the air conditioning

units along with the cooling coils, if desired. Fresh or

outside air for ventilation must be separately ducted into

each occupied space or zone.

5“l6 The Ice Reservoir as a Heat Sink

An important design feature of some protective install

lations is the ability to function for a period of time while

isolated from outside sources of power, water, etc. This

usually means that the use of outside cooling towers, ponds,

and wells is also precluded, so that some self'-contained

heat sink is required, and the properties of ice strongly

recommend it for the purpose. The use of reservoirs as heat

sinks during emergency periods is discussed in Section

which also presents the equations necessary for computations.

As mentioned in ^“04, the difference in acceptable cooling

water temperatures for refrigeration compressors and Diesel

engines practically demands two reservoir systems, either or

both of which may be iced.

At the start of emergency use as heat sinks, either or

both of the iced reservoirs can be used to fui'nish chilled

water directly to unit air conditioner cooling coils until

the reservoir temperature rises to about 50 F. At this

time, operation of the refrigeration compressors will become

necessary, and the heat rejected to their condensers must

be absorbed by the reservoir reserved for air conditioning

equipment use. The computation of the time for the reservoir to rise in temperature is accomplished by means of

Equation ^-07 (See Appendix ^-C).

The maximum temperature limit for the water in the air

conditioning reservoir is probably in the range of 100 to

110 F, since higher water temperatures may result in
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excessive head pressures in the refrigerating compressors.

When this temperature is reached, the discharged condenser

water is furnished to the Diesel engine cooling system and

wasted outside.

The Diesel engine reservoir can be raised to higher

temperatures before its water reaches maximum recommended

entering temperature, after which its water must be wasted

outside. The two reservoirs should be proportioned, with

respect to their respective loads, so that when the Diesel

reservoir is emptied, the engine can be cooled by water

wasted from the air conditioning condensers, until this

supply also has been exhausted,

A reservoir filled with an ice and water mixture

requires a method of distributing ice along the length of

the reservoir. Ice introduced at the open end of a reser^

voir does not distribute itself along the length of the

reservoir to a sufficient depth and some mechanical means

must be made available for this purpose. The most satis^

factory ice distribution method appears to be to use ice in

small cubes, cylinders, or chunks and a helical^scr ew con“

veyor. The screw conveyor should reach from the open to the

far end of the reservoir and be mounted a distance above the

water level somewhat more than one^tenth of the depth of the

water, so that ice would not reach the screw conveyor for

movement until the underlying ice rested upon the floor of

the reservoir. Ice would be dumped into the reservoir at

the open end from ice making machines. When the ice at the

dumping point piled up to the level of the screw conveyor,

it would be moved in the direction of the far end, filling

the reservoir to the bottom as the ice front progressed.

A simple pendant-lever control at the far end of the reservoir moved by the ice front, would automatically stop opera-’

tion of the conveyor and ice-making equipment when the

reservoir became completely filled. Meltage of the ice

front by heat transfer from the surrounding rock would

allow the pendant-lever control to fall to an operating

position, causing more ice to be added to the reservoir.

For inspection and maintenance of the screw conveyor, a

walk-way should be placed near the conveyor.

Laboratory experiments have indicated that the best

shape of ice for movement in a reservoir is cubical,

spherical, or cylindrical, in pieces on the order of one

inch in size. Ice in the crushed or flake form tends to

agglomerate in compacted slushy masses which resist movement . Experiments have shown that the average ice volume
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in a water and ice mixture is from 40 to 50 percent for

hollow cylinder ice, and it is probable that for non-hollow

small shapes, the ice volume percentage would be materially

greater

.

The ice reservoir may be used as a source of chilled

water for the air conditioning system during normal operating (non-emergency) conditions. But this is not recommended, because the ice-making equipment producing ice for a

reservoir operates at lower efficiencies than conventional

equipment for air conditioning.

5-17 For references and index to other Chapters of Part

XXV see Chapter 1.
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CHAPTER 6

EQUIPMENT AND OPERATION

6“01 Equipment Selection

Use of equipment requiring a minimum of floor area and

volume is essential for saving on first cost, because every

cubic foot of necessary space must be excavated in rock.

This recommends against the use of large ducts and inordi^

nately large apparatus. A general advantage lies with small

ducts and high velocities, and small, high-capacity equip-*

ment, including fans, coils, boilers, if used, etc. The

limiting factor on machine speed and air velocity is often

noise, which must be kept within tolerable limits for each

space, depending on its intended use.

Tolerances should be stated for specified design conditions (2“0'3)® A requirement of 75 R and 50 percent

relative humidity, without a stated tolerance, can result

in the installation of unnecessarily large equipment. An

economical and usually practical requirement is a temperature of 75 F and a relative humidity not exceeding 50

percent. Humidities significantly below 50 percent, if they

occasionally occur, are not likely to cause serious discomfort or to affect furniture or equipment.

6-02 Economy of Operation

Use of natural means as far as possible for effecting

air conditioning processes is an obvious way to promote

economy of operation. An underground installation may be

cooled with outside air in winter, if such air in sufficient

quantity can be delivered to the space at some temperature

below about 65 F. Water, if available from outside, may be

used for cooling in a chilled water system, if its temperature is about 50 F or below. A shaft or tunnel large

enough to cool a space at considerable depth below the

ground surface during normal operation may be inordinately

expensive, but cooling with winter air may be feasible for

shallow Installations or for deeper installations during

a standby condition when the load is small. For the deeper

installation, the shaft or tunnel provided to furnish fresh

air during full occupancy may be ample to cool the space

with winter air during standby or partial occupancy. These

generalizations must be used as guides in the design or

selection of equipment for particular installations. They

cannot be made more specific because circumstances are

different for each case.
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When, as in summer, cold outside air or water is not

available for cooling, mechanical refrigeration must be

relied upon. Examination of some typical cases indicates

that the important loads under the most severe condition,

such as fully occupied installation under full operation

in summer, are as follows:

1. Equipment, including electronic gear

2. Personnel

3. Lights

h. Conditioning of fresh air

For this condition, the refrigerating machines must carry

the full load, except for the heat absorbed by surrounding

rock, which may not be important if item 1 is high. Significant economies cannot then be achieved by special

manipulations. However, experience shows that protective

structures may be on standby with partial or zero occupancy

for long periods, and it is during such times that economies

are possible, as follows:

Minimize the fresh air supply to cool rooms or spaces.

It is unnecessarily expensive to supply mechanically conditioned air in sufficient quantity for full occupancy when

a space either is not occupied or contains only a skeleton

force. Controls, either manual or automatic, are desirable

that will regulate the fresh air supply in accord with

occupancy as closely as possible.

Utilize waste heat in spaces requiring heat. Unoccupied spaces are cooled by the surrounding rock, and under

this circumstance may require heat to maintain a suitable

relative humidity for material preservation. Heat rejected

by refrigerating machines may be used for this purpose in

an adaptation of the heat pump principle. Heat from engine

jacket water can be utilized if a storage means such as a

warm water reservoir is provided.

6-03 Air Conditioning System Components

Conventional, commercially available, heating and air

conditioning equipment is in general adaptable to underground

use. In a typical system, the fresh air coming from a tunnel

or shaft may first pass through a tempering coil (6-04) to

warm the air in winter, and assist in preventing condensation

and drip from ducts. If close control of humidity is

required, the air may next pass through an air washer (6-05)

or spray coil (6-06). Such devices are not considered necessary in most cases, because a cooling coil (6-07) can be
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relied upon to cool and dehumidify the air with sufficient

precision in summer, and the precision expected of an air

washer is not required in winter « An air cleaner (6“-08)

ahead of the coils is a precaution against a deposit of

dust or lint on the tubes or fins that might impede the air

flow or heat transfer. An air filter also tends to eliminate

variations in velocity and make the flow uniform across the

face of a coil or air washer, and this is beneficial to the

performance of coils or air washers. An air purifier (6-08)

is required in many protective structures to exclude biological agents and radioactive particles. Such a device is

frequently installed so that outside air passes through it

before entering other components of the system, at least

during emergency periods. The conditioned fresh air is

taken by a fan or blower (6-09) and distributed to the

various rooms or zones through a duct system (6-10).

For conditioning each room or zone, air may be recir--

culated through an air conditioner, which may include both

heating and cooling coils, as well as an air filter (6-08)

and a fan or blowers (6-09) . Unit air conditioners may not

require ducts if set in the rooms they serve. Conditioners

serving zones may supply air through ducts (6-10) connected

to grilles or louvers in the various rooms. Return air may

pass directly to a unit air conditioner or, for a zone, a

passageway or hall may serve as a return. Grilles in doors

are often used to permit egress of air from rooms to halls.

If low humidities are required for special purposes,

and if moderate warming and no cooling are required in some

space, either a chemical dehumidifier (6-12) or a mechanical dehumidifier (6-13) may be used advantageously, and if

extraordinarily low humidities are required, a chemical

dehumidifier may be preferable.

6“0U Tempering Coils

Tempering coils in surface buildings are usually heated

with steam instead of water to reduce the probability of

damage due to freezing in winter. Steam can also be used in

a coil serving an underground installation, and without

seriously affecting cost, if steam must also be supplied for

other purposes, such as cooking. However, if steam is not

otherwise required, and if the installation is heated with

hot water, it is in many cases possible to use hot water in

the tempering coil without danger of freezing for the

following reasons.

If the fresh air supply is cut off, the coil will not

freeze, because its temperature will be governed by the sur^-

rounding rock, which remains above the freezing point. If

the water supply to the coil is shut off due to equipment

failure or other causes while the air flow continues, the

air may have been warmed considerably by its passage through

the supply shaft or tunnel, so that the temperature may not

go below freezing. The air temperature at the coil at any

time can be computed by means of equations given in section

4-05 = The purpose of tempering coils is to so warm the fresh

air in winter that condensation on ducts is avoided. Heating

to a temperature above the design dewpoint of the occupied

rooms is sufficient, since the heating system should be

designed to carry the loads in the various rooms or zones.

One set of coils is therefore sufficient for the incoming

air. Modulation of water or steam flow or use of a bypass

with automatic dampers are means of avoiding overheating of

the air in mild weather. The coil is shut off in summer.

If the fresh air ducts are insulated to minimize heat

exchange and to prevent condensation on their external surfaces, cooling loads can be reduced by permitting air at

winter temperature to pass directly to conditioned spaces

without preheating. Tempering coils therefore may not be

required in some installations. However, this depends also

on the ability of some air purifiers (6-08) to function when

receiving cold air.

6 -O 5 Air Washers

Air washers (Ref, 1) are a means for comparatively preelse control of humidity, because air, passing through a copious water spray, emerges in a condition approaching

saturation. The temperature of the spray water and of the

entering air can be manipulated to attain a required dew

point such that a specified relative humidity results when

the effluent air is heated to a required temperature. Air

washers, however, are bulky devices; they require attendant

equipment, including pumps and piping; and their operation

can be regarded as uneconomical if the air must be reheated

by burning fuel after dehumidification. To avoid these complications, coils appear to be preferred for most air conditioning purposes and their smaller size recommends them for

underground installations, except where extraordinarily

close humidity control is required for special purposes.

Coils are a practical means for maintaining the air conditions

ordinarily essential for occupied spaces or material storage

(2-04), (2-05).
(
6“06 Air Heating and Cooling Coils

In the heating and, to a wider extent, in the refrigerating and air conditioning field, the word ’"coil" denotes a heat exchanger made of pipe or tubing, either with or without

fins. Pipe in true coil form was once much used for heat

exchangers and the same "coil," by custom, has come to signify

a broad class of heat exchangers, in which single or multiple

parallel tubes permit heat transfer from one body of fluid to

another. For a heating coil, steam or hot water may be passed

through the tubes and, in a refrigerating coil, either a

refrigerant or chilled water may be used in the tubes. The

internal film resistance is usually less than the external,

so the use of "extended surface" coils, with fins affixed to

the outside of the tubes, is common. Such extended surface

reduces the total heat flow resistance so that smaller,

lighter apparatus is required for a given duty» Plain coils

without fins are recommended for heat exchange between

liquids, but extended surfaces are beneficial for exchange

between liquid or boiling refrigerants and air or other gas.

Also, plain coils may be indicated for heating or cooling

air where dirt or frost are likely to be serious problems.

The most convenient and practical procedure for coil

selection is to utilize data on coil characteristics found

in manufacturers' catalogues. Heat transfer in coils is comTM

plex, and practical solutions of problems concerning it are

based on test data extrapolated by means of empirical methods.

This subject is treated in the "Guide" (Ref. 1) and other

handbooks and texts.

6“07 Air Conditioning Units

An air conditioning unit consists of a cooling coil,

sometimes accompanied by a heating coil, with a fan and

usually one or more air cleaners, enclosed in a case or

cabinet conventionally made of sheet metal. A selfcontained unit includes a refrigerating machine, which may

be either air or water cooled. In a remote unit, chilled

water or brine, or a liquid refrigerant is utilized in the

cooling coil. Openings or duct connections are provided in

the case for the supply and return air.

Selection of air conditioning units can usually be

based on catalogue data, as in the case of coils (6“06).

Requirements for self-contained units are set forth in ARI

Standards 1-10-55? "Room Air-Conditioners" and 2~10 "SelfContained Air Conditioners (other than Room Air-Conditioners)"

published by the Air Conditioning and Refrigeration Institute.
i I
Tests for capacity are required by these standards under

ASRE Standard 16-52, "Standard Methods of Rating and Testing

Air Conditioners," published by the American Society of

Refrigerating Engineers.

6“08 Air Cleaners and Purifiers

Air cleaners are desirable to protect coils, motors,

and fans from dust and lint. Since lint probably is the

material most responsible for coil stoppages, and since it

is easily captured, relative simple filters with low resistances to air flow are usually satisfactory for this purpose.

The fresh or outdoor air for an underground installation may be drawn from a location that is clean most of the

time, and it will be cleaned to a degree by passing through

the supply shaft or tunnel. However, extraordinary winds

may stir up dust, or dust may be created by blasting or

mining operations after an installation is occupied. For

these reasons, an air cleaning means for the fresh air ahead

of any other conditioning equipment is recommended.

Recirculated air often contains considerable lint, due

to the wear of clothing, draperies, paper, etc., so that air

cleaners are essential in recirculated air ducts ahead of

fans or coils.

Automatic self-cleaning air filters are found in some

Government agencies where the air flow is large, because they

require attention only at long intervals. Efficiencies

expected are not higher than those for less expensive apparatus. Of the panel-types, the throwaway filter is preferred

by some operators, because it is cheap enough to discard and

hence does not require cleaning. On the other hand, cleanable or automatic self-cleaning filters may be chosen if

storage space is scarce, because it is not necessary to stock

replacements

.

Electrostatic filters are recommended if very fine dust

is a problem. Such equipment is effective in arresting

particles in the submicron range, such as carbon, tobacco

smoke, and tarry matter resulting from the combustion of oil

or coal.

Air filters are at present tested in different ways by

different manufacturers. A dust-spot test has been developed

at the National Bureau of Standards and serves as a basis for

purchase specifications for electrostatic air cleaners, as

well as panel types air filters.
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Air purifiers are designed and constructed by the

Chemical Corps. Information on this type of purifier may be

found in ‘'Collective Protection against Chemical, Biological

and Radiological Warfare Agents,"' Part VI of the Engineering

Manual for Protective Construction.

6'=09 Fans

Fans have been defined (Ref. 1) as low-pressure air or

gas-moving devices that do not cause density changes greater

than seven percent in the fluid passing through them. A

change of seven percent in density corresponds to about one

pound per square inch for air at one atmosphere pressure.

One psi is much greater than the pressure generally required

for air conditioning systems, so fans, rather than blowers,

compressors, or pumps, are used for moving air through them.

Fans are of two genpral types: the axial flow and the

centrifugal. Axial flow fans may be propeller, tubeaxial, or vaneaxial types; and centrifugal fans may have a forward or

backward, curved or straight blades on their rotors. Selection must be based on air flow and pressure requirements and

on space, weight, and noise limitations, if any. The dimensions and performance data on commercially available fans are

generally contained in manufacturers' catalogues. The performance data are usually based on tests conducted according

to one of the existing codes (Ref. 1).

6-10 Duct Systems

The term "duct system" usually signifies an arrangement of sheet metal conduits designed to contain and direct

the flow of air from a source such as an air conditioner to

a space being served and either back again to the source or

to the outside. Air returned to the source is usually

called recirculated air. That rejected outside is classed

exhaust air or vitiated air; it must be replaced in the system by fresh air from out of doors. Especially in underground installations, tunnels or shafts may be used as air

conduits and can properly be regarded as part of the duct

system.

For the design of a duct system, the air supply required

for each space served and for the whole system must be determined. This is usually based on the heating and cooling load

estimates (3=01) and the outside air requirements (2-06).

For heating any space by means of air, the heat delivered by

the air must equal or exceed the heat loss; while for cooling,

including dehumidifying a space, the air flow must be sufficient to carry away both the heat and the water vapor

liberated in the space.
I
The design of conventional warm air heating systems has

been standardized and simplified (Ref. 1) but, especially

for large underground installations, greater air flows are

likely to be required for cooling and dehumidifying than for

heating. Hence, the duct design procedure usually employed

for cooling air conditioning systems (Ref. 1) is likely to

be more properly applicable in most cases. This procedure

is based on the properties of standard air, but the data

given in tables and charts in the handbooks are considered

sufficiently exact for practical use with air near normal

atmospheric pressure, between ^0 F and 90 F and at any

relative humidity.

In a large installation, the use of small, short ducts

is made possible by the employment of a zoned system with a

multiplicity of air conditioners, but the fresh air supply

and return ducts must extend from the outdoors to the far“

thest occupied space. The fresh air duct may therefore

require extraordinary care in its design.

Sheet iron for ducts in underground spaces should be

galvanized or otherwise treated for corrosion resistance.

Aluminum is considered satisfactory for most purposes, as

ordinarily furnished, but this metal is subject to attack

by caustic substances. It should not be used in contact

with masonry or concrete, nor exposed to, drip or seepage of

water containing lime or other caustics. Its resistance to

acid is satisfactory. Tables of recommended thicknesses and

structural details for iron and for aluminum ducts are con=

tained in handbooks (Ref. 1).

High velocities are to be favored in underground installations, since their use permits the ducts to be smaller.

Space underground must be excavated from rock, so use of

smaller ducts, requiring less space, often results in lower

first cost.

6“11 Steam and Hot Water Heating Systems

In an underground installation, the heating load is

likely to be small compared to that for a surface building

of equal dimensions, because an underground structure is not

exposed to the weather. Also, the heating load is likely to

be smaller compared to the cooling load than in typical surface structures. These factors often make it desirable that

the heating system shall be an adjunct to the cooling system

and not a separate system.
)
Either hot water or steam can be used to warm air by

means of coils included in unit air conditioners. Use of

water facilitates utilization of waste heat, since hot water

systems operate at much lower temperatures than conventional

steam systems.

6-12 Chemical or Sorbent-Type Dehumidifiers

Sorbent-type or chemical dehumidifiers can be advantageously utilized for spaces in which extraordinarily low

humidity is required, or in which temperature control is

less important than humidity control (Ref. 1), Substances

on the market for use in such equipment include both

"adsorbents” and "absorbents." By definition, an adsorbent

does not change either chemically or physically when it

becomes wet. Commonly used adsorbents include silica gel

and activated alumina. Typical absorbents are calcium

chloride and lithium chloride.

As an expedient, either an adsorbent or an absorbent

material may be utilized to dry a space by simple contact

with the air. For instance, calcium chloride exposed in

trays will absorb water from the air and the resulting solutions can be thrown away. For any but temporary installations, however, equipment is to be recommended capable of

alternately utilizing the sorbent for dehumidifying air and

then reactivating it by means of heat and ventilation.

Such an apparatus may consist of a cabinet or case containing

fans and a filter, with duct connections for "wet" air and

dehumidified air, as well as ventilating air. Heat for

reactivating the sorbent may be supplied electrically, by

steam and sometimes by the combustion of a fuel. Adsorbents

are utilized in sizes ranging from 300 mesh to 8-l4 mesh

screen. Absorbents are usually employed as aqueous solutions which may be sprayed into the air being dehumidified,

as in an air washer, or exposed to it on the surfaces of

metal plates or of mats of fibrous material, such as glass

wool. Reactivation may be accomplished in a second air

washer through which heated (up to 300 F) outdoor air is

passed. The heat evaporates some of the water from the

solution and this water is carried outside as vapor.

The necessity for ducts from outside may cause inconvenience in some installations. The required length may be

considerable for a deep installation and, if part of the

system is below the dewpoint temperature, condensation with

possible drip through joints occurs.

Selection of a dehumidifier may be based on information

given in Ref. 1 and in manufacturers' catalogs.
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6-13 Mechanical Dehimiidifier

s

A mechanical dehumidifier consists of a refrigerating

machine so arranged that air passes through a cooling coil

and then through the condenser. The air is cooled and

dehumidified by the cooling coil and is then used to cool

the condenser. Such a machine can carry a relatively large

latent load, but does not cool the space it serves; in fact,

heat is delivered to the space served, if the machine is

within it, equivalent to the power it utilizes.

Machines of this type are very useful in spaces with

considerable latent loads and in which moderate heating is

either desirable or of no consequence. They have been

utilized in large numbers as basement dehumidifiers in

residences, and either the same kind or larger models are

applicable to some underground installations. They have the

advantage over chemical dehumidiers that the condensate is

removed as liquid which can be drained away through pipes,

rather than as vapor in air that must be expelled through

ducts. They may be incapable of attaining humidities as low

as are sometimes required, because the cooling coil may frost

before the required dewpoint is reached.

6 = 1^ For references and index to other Chapters of Part XXV,

see Chapter 1.

/

U. S. DEPARTMENT OF COMMERCE

Lewis L. Strauss, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BLHEAU OF STANOAHHS

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

D. C., and its major laboratories in Boulder, Colo., is suggested in the following listing of the

divisions and sections engaged in technical work. In general, each section carries out specialized

research, development, and engineering in the field indicated by its title. A brief description of the activities, and of the resultant publications, appears on the inside front cover. WASHINGTON, ®. C.

Electricity anal Eiectrciaics. Resistance and Reactance. Electron Devices. Electrical In- struments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instru- mentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Engine Fuels. Free Radicals Research.

Atomic and Hadiation S®iaysies. Spectroscopy. Radiometry. Mass Spectrometry. Solid

State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory.

Radioactivity. X-rays. High Energy Radiation. Nucleonic Instrumentation. Radiological

Equipment. ' Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical

Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass

and Scale. Capacity, Density, and Fluid Meters. Combustion Controls. Hrganic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and

Specifications. Polymer Structure. Plastics. Dental Research.

Metalijirgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Metal Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Concreting

Materials. Constitution and Microstructure.

Huilding TechnoSogy. Structural Engineering. Fire Protection. Air Conditioning, Heating,

and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat Transfer. Applied Mathematies. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Hafa Proccssiug Systems. SEAC Engineering Group. Components and Techniques. Digital

Circuitry. Digital Systems. Anolog Systems. Application Engineering.

« Office of Basic Instrumentation. • Office of Weights and Measures. BOULDER, COLORADO

I’ryogenic Enginceriug. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction.

Railio Propagation Physics. Upjier Atmosphere Research. Ionospheric Research. Regular Propagation Services. Sun-Earth Relationships. VHF Research. Ionospheric Communication

Systems.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems.

Navigation Systems. Radio Noise. Troposjiheric Measurements. Trofiospheric Analysis. Radio

Systems Application Engineering. Radio-Meteorology.

Radio Standardii. High Frequency Electrical Standards. Radio Broadcast Service. High

Frequency Impedance Standards. Electronic Calibration Center. Microwave Physics, Microwave

Circuit Standards.