NATIONAL BUREAU OF STANDARDS REPORT

1+5U5

Engineering Manual for Protective Construction

Part V

Heating and Air Conditioning

of Underground Installations

by

R. S. Dill

B. A. Peavy

Report to

Office of the Chief of Engineers

Department of the Army

<&>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

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specialized research, development, and engineering in the field indicated by its title. A brief

description of the activities, and of the resultant reports and publications, appears on the inside

of the back cover of this report.

Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instru- ments. Magnetic Measurements. Process Technology. Engineering Electronics. Electronic

Instrumentation. Electrochemistry.

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Mineral Products. Porcelain and Pottery. Glass. Refractories. Enameled Metals. Concreting Materials. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

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Data Processing Systems. Components and Techniques. Digital Circuitry. Digital Systems.

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Gas Liquefaction.

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Radio Standards. High Frequency Standards. Microwave Standards. • Office of Basic Instrumentation • Office of Weights and Measures
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

IOO 3 -IO-I483 I February 21, 195& USkS

Engineering Manual for Protective Construction

Part V

Heating and Air Conditioning

of Underground Installations

by

R. S. Dill

B. A. Peavy

Heating and Air Conditioning Section

Building Technology Division

To

Protective Structures Section

Protective Construction Branch

Office of the Chief of Engineers

Department of the Army

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, re|

unless permission Is

25, D, C. Such peri

cal ly prepared If tl

Approved for public release by the

ln part ' is prohlbi,ed

Director of the National Institute of

,ndards ’ Washing,on _ , . „ jort has been specifi- Standards and Technology (NIST)

on October 9, 20 1 5.

PROTECTIVE CONSTRUCTION BRANCH

ENGINEERING MANUAL FOR PROTECTIVE CONSTRUCTION

PART V

HEATING AND AIR CONDITIONING OF UNDERGROUND INSTALLATIONS

Chapter 1

Introduction

1-01 Purpose

1-02 Scope

1-03 Historical Background

I-0I4 Structural Arrangement; Definitions

1-05 Tactical Operating Conditions; Definitions

1-06 Symbols

1-07 Data Forms

1-08 Equations

1-09 Figures

1-

10 Tables

Chapter 2

Principles and Design Objectives

2-

01 Function of Underground Installations

2-02 Design Criteria and Limitations

2-03 Air Conditioning Requirements

2—0I4 Air Conditions for Personnel Efficiency

2-05 Air Conditions for Material Preservation

2-06 Outside Air Requirements

2-0? Disaster Condition Air Supply
*
2-0 8 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 Estimates

3-02 Heating Loads

3 -O 3 Warmup, Bare Chamber

3 -0i| Heating Load, Bare Chamber

3-05 Heating Load, Inner Structure

3 -O6 Cooling Loads

3-07 Dehumidification, Bare Chamber

3-08 Dehumidification, Lined Chamber

3-09 Dehumidification, Inner Structure

3-10 Waste Heat Disposal

3-11 Air Conditioning Effect of Tunnels or Shafts

3-

12 Evaporation from Pools or Damp Surfaces

Chapter 4

Heat Absorption of Rock Around Underground Spaces

4-

01 Principles

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

4-03 Equations for Heat Transfer, Air to Rock

4-04 Heat Absorption of Underground Reservoirs

4-05 Heating or Cooling of Air by Tunnels

4-06 Thermal Properties of Rock
-

.

•

.
4-07 Initial Underground Conditions

4-08 Thermal Properties of Materials and Structures

(U, U», K, etc.

)

4-09 Vapor Permeability of Materials

4-

10 Underground Water

Chapter 5

Air Conditioning Processes and Systems

5-

01 Sizes and Shapes of Underground Chambers

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

5-10 Small Structures in Large Underground Chambers

5-11 Air Conditioning Processes for Larger Installations

5-12 Central Air Conditioning Systems

5-13 Cooling Effect Applied to Annular Space

5-14 Self-Contained Air Conditioners

5-15 Chilled Water Systems

5-16 The Ice Reservoir as a Heat Sink
' •

V
Chapter 6

Equipment and Operation

6-01 Equipment Selection

6-02 Economy of Operation

6-O3 Air Conditioning System Components

6-Olq 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 Chemical or Sorbent-Type Dehumidifier

6 -I 3 Mechanical Dehumidifiers

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 I4 Ave., New York 1, N. Y.

3 . "Deterioration of Materials", Greathouse and

Wessel, Reinhold Publishing Co., I43 O Park Ave.,

New York, N. Y.

I4. Report No. 3OII4A, Engineering Division, Industrial

Test Laboratory, Philadelphia Navy Yard.

5. "Personnel Shelters in Modern Warfare"

6 . U. 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 , 194°*

8 . "A Study of the Principles of Air Conditioning

in Underground Installations"; Bertram Broberg,

Report No. 122 ; 1/1112BF , 1 April 1954, Royal

Fortification Administration, Bureau of Fortification, Sweden

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

Nature Magazine, Vol. 151, page 123, Jan. 30 , 1943

10. "Some Physical Aspects of Storage of Works of

Arts", Rawlings, Journal Institute Heat, and Vent.

Engineers, 1943, 11, 175

11. "Engineering Aspects of Wartime Storage of Art

Treasures", Fletcher, Journal, Inst. Heat, and

Vent. Engineers, 19I4

3

, 11 , 186

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

Inst. Heat, and Vent. Engineers, 19I46 , 12.354

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

Journ. Inst. Heat, and Vent. Engrs., 1948, 14, 194
./

'

.V
References (Cont*d)

II40 "Heating and Ventilating Plants in German Underground Installation", Journ., Inst. Heat, and

Vent. Engrs., I 9I48 , 16, I4

I4I4 .

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

Oxford University Press, London, 19U7

.

16. "Measurements of Heat Losses from Slab Floors'1 , National Bureau of Standards, BMS Report IO3, GPO.

17. " Moisture Condensation in Building Malls", H. W.

Woolley, National Bureau of Standards, BMS Report

63, GPO

.

l 8 o "Evaporation of Water from Saturated Surfaces",

Powell, Trans. Inst. Chem. Engineers, Vole 18,

page 36, 191+0 .

19® "Cooling of Shipboard Electronic Equipment"

National Bureau of Standards Report No. I4 II46 , May 1, 1955-

20.

"The Industrial Environment and its Control" by

Jo M. Dallavalle, Pitman Publishing Corp, New

York.

21.

"Mechanical and Electrical Engineering Handbook"

Construction Division, Public Buildings Service,

General Services Administration, January 1958®

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

23o "Weather Elements",

Inc., N. Y. , I 9I42

by T, A. Blair, Prentice-Hall

y
,V; ;

I
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 information 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.
1 -

.

.
2

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 phenomena 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 conditioning 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 underground structures may include steam, hot water or warm air

heating systems, mechanical or absorpti ve- type air conditioning 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 structure, 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.
' .

.

.
- 3 - 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 critical

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.
'

-

. . . r : -

'
- h - 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.

I-O3 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 recent

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. Pew, 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 a 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
- . ~ t

"

...

-

.

.

,

•

..
- 5 -

and thus an unused tunnel or other underground space is a

means of air conditioning. When this process has been employed in the past, the underground 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. It is contemplated that a more exhaustive

study of this subject shall be made a part of the present

program on underground air conditioning.

Underground spaces were utilized in Norway, Sweden,

Germany, and Japan during World War II, chiefly as manufacturing 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 seven percent had air conditioning and only forty-seven percent had other than

natural ventilation. Heating was reported as provided in

twenty-seven 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 l|7F and 95 bo 100 percent relative humidity. The under

ground 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 forced-circulation system apparently utilizing electric heat. For venti

lation, small amounts of air from the space, at I

4 7F and near- saturation, were introduced into each building as required.

It was found that when the buildings were warmed to 6 I4F the

interior relative humidity was near 57 percent which was con

sidered satisfactory for long term storage of the pictures.

No cooling means or dehumidifying means was required and no

dehumidifications 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.
. :

: ',v

- • • -v . *

' - ,* -

.-V

.. .
- 6 -

I-OI4 Structural Arrangements, Definitions

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:

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 cover

ing of concrete or another material in contact with the rock

walls and ceiling. The wall covering, or liner, may have

sufficient thermal resistance to affect 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 (Section I4-O5) and influences

the dehumidification load (Section 3-O9).

Annular Space: The space around an internal structure,

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

underground chamber.

1-

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 (Section

2-

0

4

) and as required for operation of equipment.

7

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.

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 on revivification of the

air for survival.

1-06 Symbols

Symbols utilized in this work are as follows:

A = Area, ft z

; A]_, A2 , and A3 for floor, walls and

ceiling respectively; A ! for internal structure;

A for exposed rock, A^ for wetted surface

a = Radius, ft; a]_ for equivalent cylinder, &2 ?or

equivalent sphere

B = Mathematical quantity for use in section I4-O5

C = Mathematical quantity for use in section I4-O5

C = Conductance, Btu hr“-*-f t“^F“^

c = Specific heat, Btu lb“^F“^; c* for water

F - Mathematical quantity for use in sections of

Chapter I4.

- 8 -

F = Degrees Fahrenheit or temperature difference, F.

f = Function of; depends upon

G = Mathematical quantity for use in equation 4-08

h = Surface heat transfer coefficient, Btu hr-lff^F-^

K = Thermal conductivity, Btu hr"^ft"^ (f /f t

)

k = Thermal conductivity, Btu hr“^ft“^ (f /in . ) L = Length, ft; distance from entrance of tunnel

section I4-65

L = Length, ft, of wetted area, figure I4 — 12

M = Mass, lbs; M’ = mass (lbs) of water per foot of

tunnel or reservoir

m = Length, ft, of underground space

N = Mathematical quantity for use with equation [4-06

n = Width, ft, of underground space

Pw

= Water pressure, lb in."^

p

= Pressure, lb in."^. p g - vapor pressure, water on

a surface; p a , vapor pressure, water vapor mixed

with air

Q, = Heat transferred or absorbed, Btu

Q,a= Air flow rate, cfm

R = Ratio, for use with equation 14-05

q = Heat transfer rate, Btu hr~-*-ft”^, from air to

rock; q* for constant rate

q-\ = Heat absorption per foot of length of reservoir,

Btu hr - 1 f

t

-1

q^= Heat absorption of reservoir, Btu hr"*l

s = Height, ft, of underground chamber
'
- 9

-

T = Temperature, F; T 0 for outside air; Tp for initial

rock; T 3 for work surface; Tp for inside air design

temperature, T a for annular space

t = Time, hours

0 = Temperature increase, degrees F; 0 3 for rock surface

0p for inside air; 0^ for air at distance L from

tunnel entrance; ©w

for water in a reservoir

U

1 PI

0 = Heat transmittance, Btu hr J-ft“'r-F“ , for a wall or

other heat barrier

U ,:= Heat transfer coefficient, Btu hr”^f , from

air in occupied space to surrounding rocks; for

no internal structure, U ' = h

V = Velocity, ft hr“l

V = Mathematical quantity for use with figures L|-l

and [j-2

W = Water flow rate, lb hr”^-; W' for evaporation of

water

w = Angular velocity

Z = Mathematical quantity for use in section l\- 05

p = Density, lb ft"3; p' for water

1-07 Data Forms

Some forms for recording data and to serve as work

sheets are suggested as follows

s

Form A - Design Information

B - Heating and Cooling Loads

C - Rock Heat Absorption, warmup

D - Rock Heat Absorption, Normal Operation

E - Heat Absorption Capacity of a Reservoir

F - Cooling or Heating of Air in Tunnels or Shafts

These forms are expected to be improved as indicated by

future use and experience. Extra copies should be obtained

or provided as required for different problems.

FORM A

Underground installation air Conditioning Design

Data and Computations

design information Date:

Location:

Purpose:

dimensions, Rock Chambers

Length, m ft; width, n “ ft; Height, s* ft

Floor area, a'®

z ft ; Internal area, ap ft ; Volume FT

Remarks:

Dimensions, Internal structure ( 1 F USED)

Length - ft; W 1 DTH “ ft; Height

floor area * ft 2

; internal area *

Z ft ; Volume FT

Depth of over burden FT

Geological Formation

Ground water condi tion ______________

Climate winter Summer

min . des .

DB, F

WB, F __________________

RH, jo

Rain Fall, insSnow, ins.

Rock temperature, Initial undisturbed,

Required Inside Air Condition

Personnel

F

Persons

Max.

Prepared by

FORM B UNDERGROUND l N8TALLAT! ON A8 R CONDI TJ CN( NG DESIGN

heating 4 Cooling Loads

Heat Gain Btu hr" 1 personnel, Persons x 270 (Sens.); x 230 (Lat)

Lights; KW x 3415

Electric motors kw x 34 o

5

Cooking Equipment

Other Equipment

Total internal Load

Fresh air Supply, Summer

Total Cooling Load

Fresh air Supply, winter

Cfm x 1,08 (0, - 0L ) -

Sensible Latent

Time from Start, Hours 2000 5000 i0,000 20,000

Rock ht. abs. btu hr" 1

Total Cooling Load

Net Cooling Load

Total heating Load

FORM C

Underground ! nstallati on air Conditioning design

DATA AND COMPUTAT I C NS

HEAT ABSORPTJON BY ROCK SURROUNDING AN UNDERGROUND

Installation; Warm-up Period

Chamber Dimension, Ft.s Length, m= ; Width, n*

Internal Area, Eq. 4—0 e , a * 2 (mn * ms ns)

Equiv. CyL, Radius, Eq. 4-02, 4 , a/2ttm

Equiv Sphere, Radius, Eq. 4-03, \

^v,/v (cylinder) fig. 4~i

^v^/v (sphere)* Fig. 4-2

Rocks Density,^- ; Conductivity K*«= ; Sp.heat, cn - T -T “ F; U' (SEE 4-08)-

y

i 'l 'r

; Height, sFT

FT

; Temp., t r

= F

Find relation between warm-up time (t, hours) and heat input, (Btu. hr _ *ft”2

) BY MEANS OF EQUATION 4-04-

F- Kt/pcdf (USE <3j for CYLINDRICAL CASE, f l for sphere) -

FIND F (F) - , FROM FIG. 4-3 (Cyl),IN 4-4 (SPHERE).

Solve for heat Reqd for Warm-up Period with the equation

<£* =

1(0

1 Btu hr

-1 ft-2 =

<j|f(F) k/u^

Rock Heat absorption, Total per hour, Ac^' - Btu hr ”*

•If V,/V exceeds V

2/V, utilize Cylindrical case •if v

2/v Exceeds v,/v, utilize spherical case

••Btu per hour for one square foot and for a temperature gradient of one deg f PER FOOT OF THICKNESS.

FORM 0

heat absorption by Rock Surrounding an Underground

Installation; Normal Operation

Properties of Rock;

Conductivity, K=* ; Density;^- ; Sp. heat, cProperties of Structures

heat Trans- Coef- air to rock, u'- ; Radius of Equiv-Cyl- or Sphere, ft

maintain air Temp. ,T

( , above initial Temp. T r

; T

( -<T

r N ©

(

Rock Surface temp-, Ts

, use above initial temp., t ; Ts - T r - Os at any instantWith equation 4-05, solve for rock heat absorption,

„ —4 _? Btu hr ft 6

n- $J'/K * ; R (Fig 4-1 or 4 -2 ) •

FORM E

HEAT ABSORPTION OF AN UNDERGROUND RESERVOIR (PIPE OR TUNNEL)

Filled wi th Water

Permissible Temp. Rise of water,

A HEAT ABSORPTION OF

Properties of Rock:

Thermal Conductivity, kProperties of Water:

©

w

- DEG F IN TIME, t- HOURS FOR

Btu hr

; Density ; Sp. heat, cDensi Tfj

p

’ 62.4; $p. HEATjC 8 ” 1,0

Dimensions of Reservoir (for rectangular cross-sections)

width, n - ft-; Height, s - ft.; length, l - f

Radius of Equivalent Cylinder, ft * (s + u)/jr “ FT -

In equation 4-08, 0*/^, * F ( F > G )

F - Kt//>C<K' =

G - 2/OC/ /o'C =

Values of f (f, g) are given by the curves on Figure 4-7

then ©k/^, - f (F, g) =*

<|

( - Btu hr" 1 ft"'

required length, l Vt, ft -

3 Volume, SNL • FT-

FORM F, PAGE t

Cooling or heating of air in Tunnels (or Shafts)

Continuous air Flow, annual Weather Cycle

Dimensions of tunnel

Length L - ft; width n - ft; height, s = FT

Perimeter, P, 2{n s) • et; s. area, ns - hydraulic Radius, 2ns/P - a = ft

Properties of air Entering Tunnel from outside

mean annual Temp. - Initial rock Temp, 'W Tr #

Temp. diff.» Outside air and mean annual Temp., ©

0

*

FT

max. Value of ©

q

, ®o

“

air Velocity in Tunnel jsp.

Properti es of Rock

CONDUCTIVITY, K - ; DENSITY,^ »

Coef. of Heat Trans, air to Rock, |

=

Constants computed from above date for use in equations on page l

w - 0.00071 7 radians per hour

FT HR

; SP. HEAT, C

=

; Diffusivity, ©£ =

z - a / */<

0* fiL/Va

C - F (fc>,Z) FIG. 4-8

B » ( fe' Z ) F|G - 4"9 "

f’ c

C’B t w|/V

FORM F, PAGE 2

Solution of Equation for Tunnel Heat Transfer

Maximum and minimum temp, at Point L in a Tunnel, ( Eq. 4-i i ) —cc # ©^ - * ©*> 6

u =

T

1 - T ©' - , ALSO T b - ©»• ®

L R L

R L

Temp. ©

l

, in tunnel at point L at time t» ( Eq. 4— j. o

)

© - ©' £

_CC ' cos (wt - wl/v - C

0 B

)

= 0 cos (wt - )

Outside air Temp. ©

q

( Eq. 4-09)

0 » o' cos wt

0 0

Rate of Heat Loss or gain by air in Tunnel at point L and Time t, (Eq. 4-12)

<| - 0.0566 V a

2 (o

q - o^)

Temperatures and Heat Flow Rates During annual Weather Cycle

JUL 15 SEP 15 NOV 15 Jan 15 Mar i 5 may 15

Tjme hrs 0 1460 2920 4380 5840 7300

wt Radians

Outside Temp,* ©0 , F

Temp at L,*

Temp Diff (©0-©l ), F

HEAT LOSS OR GA^N,BTU,/HR~ ,

0

©• =

0

1 .047 2.094 3.142

-®o*

4. i 89 5.236

•For actual temperatures, algebraically add the mean annual temp. t r to ©

0 or ©

L

.

i

10

1-08 Equations

Hock heat absorption - instantaneous

q = U» (Tp - T s ) 3-01

Heat transmittances through walls of an inner structure

q

= U (T ±

- T a ) 3-02

Hydrostatic pressure-relation to depth or heat of water

Pw = 3-03

Area of a rectangular chamber (parallel walls, ends,

floor, and ceiling)

A = 2 (ran +ms + ns) Lj,-01

Radius of a cylinder with thermal characteristics

similar to those of a rectangular chamber

ap = A/2 m l4~02

Radius of a sphere with thermal characteristics

similar to those of a rectangular chamber

a2 = A/J4 U-03

Heat loss to rock during warmup period (constant

heat absorption rate)

9 sK/q»a = f (F) I4 -OI4 F = Kt/pca2

Utilize fig. 4 - 3 or I4 - I4 to find values of f (F)

Heat loss to rock with constant temperatures maintained

in an installation

q = U' 0^1 - 0 s /9l)/R L|-05

Determine R from fig, 2-1 (cylinder) or 2-2 (sphere)

For values of 0 s /9p in equation 4-03>

0 s /9i = f(F, N) 4-06

F = Kt/pca2

; N = aU » /K

- 11

Values of f (P, N) are given on figure 2-5 (cylinder)

or 2-6 (sphere)

Heat extracted by water from engine jackets, condensers,

etc

.

Qw = M (T w - T

p

) Li-07

Heat absorbing capacity of water-filled reservoir

or pipe

QwK/qi = f (F, G)

F - Kt/pca2

; G = Zpc/p'c'

Values of f (F, G) are given on figure 2-8

Temperature of outside air at time t for assumed

steady periodic annual change

9 0 = 6^ cos w t

Temperature in a tunnel at point L and time t when

outside air follows steady periodic change

0< = ± 0 ' e

~C ' C

L o Rate of heat loss or gain by air in a tunnel at

time t and up to point L

Q, = 0.0566 Va2

(0 Q

- ©L ) For heat transfer coefficient (transmittance)

from an interior structure, air to air

U =

1.65

1

1.65

For heat transfer coefficient from an interior

structure to surrounding rock

1

_i— + I

1.65 c +

.»

1

1«25

14-08

14-09

U-ll

24-12

U —1.3

u» L4-II4

1- - 12

09 Figures

2-

1 Oxygen depletion in unventilated occupied spaces

2-2 Carbon dioxide concentration in unventilated occupied

spaces

2-3 Temperature rise in unventilated occupied spaces

4-1 Values of R, equation I4 - 05 s for the cylinder

4-2 Values of R, equation lj-05, for the sphere

4-3 Equation I4 — 0 I4 ; constant rock heat absorption rate;

condition for cylinder

I4 -I4 Equation I4 — 0I4 ; constant rock heat absorption rate;

condition for sphere

4-5 Equation lq — 06 ; for rock surface temperature; constant

air temperature cylindrical case

I4-6 Equation I4 — 06 ; for rock surface temperature; constant

air temperature spherical case

lq—7 Equation I4 -O 8 ; for reservoir heat absorption at a

constant rate

4-8 Derived values for use with equations 4-10 to 4-13

4-9 Derived values for use with equations 4“10 to 4“13

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

1-

10 Tables

2-

1 Humidity tolerances of some materials

2-2 Fresh air requirements of personnel

2-3 Properties of chemicals for air revifif ication
-

.
- 13

2-4 Capacities of some sorbent materials

2-

5 Air requirements for engines, boilers, etc.

3-

1 Cooling loads due to personnel

4-

1 Heat transfer coefficients for underground structures

4-2 Water vapor permeabilities of some materials

- 14 - CHAPTER 2

Principles: 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. Form A

is suggested for recording the necessary data.

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-OLj.) in

working spaces and for material preservation (2-05) in

storage spaces as well as shops, offices and other spaces

where 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 inner structure

(l-ol)).
.
- 15 - Location determines the climate and the geological

formation (I4-O6) that will surround a proposed underground

structure. Climate ( 1 - 10 ) in turn, governs the conditions

of outside air (2-06) available for ventilation, the prevalence of underground water (4-10), availability of water for

equipment cooling (5-12), and the initial earth or rock temperature (J4-O7),

Floor area and volume of an occupied space depends upon

population, function and internal load (3-01)

o

Environmental conditions, in particular 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 (2-05).

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 (5-18)*

The initial temperature (i|- 07 ), thermal conductivity

and heat capacity of the surrounding rock (4-06) affect the

heating and cooling loads in an underground chamber (5-01),

2-03 Air Conditioning Requirements

For design purposes an interior air condition of 75?

and 50 percent relative humidity can be assumed in many

cases. This condition is within the practicable range

attainable with conventional equipment (6-1) and available

data show it to be suitable for personnel efficiency (2-04)

and for 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

.
--
- 16

Air conditions maintained in a space may differ from

those assumed for design purposes, as indicated by practical

consideration after operations have commenced. Special air

conditioners may be required for special purposes, such as

storage or work with unusual materials.

2 -01] Air Conditions for Personnel Efficiency

Experience has shown that personnel can sustain a considerable range of temperature from about 6£ to 8£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 75F and percent

relative humidity may be assumed for design purposes ( 2 -O 3 ) 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 percent

or more of the subjects were found to be comfortable during

some tests conducted 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 is concerned where

convection heating and cooling will predominate. The findings

are more likely to result in adjustments to existing data.

The condition 7!?F and ^>0 percent relative humidity is

warmer than the 68 or 70F 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 and load

on the cooling equipment. It is common experience that many

peoples are more comfortable at a DB temperature of 75>F

winter and summer than at a DB temperature of 70F. The condition 75F and 50 percent is safely below the conditions of

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 I4O to 65 percent is satisfactory for the preservation

- 17

of most technically useful materials at substantially steady

temperature conditions, either in storage or in use as in

shops, office or communication centers.

An important exception is unprotected mild or 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.

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 3. The data in Table 2-1 were extracted

from that source.

- 18 - 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. i Sisal, Paper, Wood

J

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,

volt meters, telescopes, etc . ) 45

ttA - No visible deterioration

#B - Very slight deterioration

*ttC - Intolerable deterioration

- 19

The data in Table 2-1 indicate the necessity for a low

humidity for the preservation 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 controlled. 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 75F 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 deterioration. Some metals are attacked by oxygen, atmospheric

contaminants 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.

Pure, distilled, water is an active solvent for some

materials and may be responsible for some deterioration.

Atmospheric contaminants including sulfur dioxide and
|gI
20

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. I4 )

.

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 disintegrate

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

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 £0 and 60F 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 preventing 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. This indicates that equipment capable of dehumidifying and moderately heating such

chambers is applicable in many typical cases.

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 departing from

this practice in underground installation for any normal

period of operation. Selection of a fresh air requirement is

complicated by the factor of intermittent occupancy which

21

relates room volume to air change rate for equal air freshness. This situation is reflected in 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

Type of Occupancy Per Person, Ft3 Air Supply CFM

Heating Season, Air not conditioned

Sedentary Adults of Average

Socio-Economic Status 100 25

200 16

300 12

500 7

Laborer 200 2-3

Sedentary Adults, Heating Season 200 12

Sedentary Adults, Cooling Season 200 h

The available data are not conclusive. Those contained in Reference 1 and 2 indicate that 10 cfm 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 satisfactorily for underground installations during

normal operation 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 (5-lQ)»

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 either deliberately or because of power

failure because the locality has been contaminated with

22

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 the

number of persons present. Each sedentary person can be expected to consume on the order of O .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

II4 percent or when the CO2 content is increased from the

normal fraction of a percent 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.

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 surface 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 re vi ficication

under dynamic conditions.

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 dew point would be determined largely

by rock surface temperature. Therefore, relative humidity

would not approach 100 percent for some time.

Personnel in a crowded space, subsisting as above, can

be expected to suffer from excessive heat and humidity. The

probable period of isolation has been estimated for some

purposes as one week while relief or rescue is pending.
I

]

.



Sir S=3


- 23

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 or 90F 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.

Table 2 - 3 . Properties of Chemicals for Air Revivification

Chemical

C 02

Absorbed

0 2

Liberated

Chemical

Required,

lbs. per

man -hr

.

Water

V apor

Formation

Sensible Heat

Liberation, Btu

Lithium Hydroxide X 0 . 12)4 yes 150 per cu.ft,

C 02

Soda-Lime X 0.34 yes 135 per cu.ft.

C 0 2

Baralyme X 0.474 yes

Sodium Superoxide X X 0.288 no l?)l per cu.ft.

CO2 and O2

Potassium

Tetroxide X X 0. 36I4 no II4 7 per cu.ft.

C 0 2 and 0 2

Chlorate Candle X 0.2)4 no 9I4 per cu.ft.O2

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

with due caution. In particular sodium superoxide and potassium tetroxlde 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 1 cubic

foot per man-hour and carbon dioxide liberation of O.83 cubic

foot per man-hour.
-
- 2k - 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 the operating conditions of (1-05).

Fuel-burning equipment most readily meets these purposes.

Because of the limited space usually available for power

plants steam boiler plants for power generation are not considered because of the high combustion air requirements.

This leaves the gasoline and diesel 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 —14 gives the specific fuel consumption, combustion

air and cooling water requirements. While it is realized this

equipment may operate under all types of load, the values

given in Table 2 -l\ are deemed suitable for design purposes.

TABLE 2 -U

Power Generating Equipment

Diesel Gasoline

Specific fuel consumption, lb/KW-hr 0.6 0.81

Combustion air, cfm/KW 2.I4 2.3

Cooling water, gpm/KW 0.514 0.514

For heating apparatus, the fuel consumption is approximately 10 gallons and the air supply is 15 3 000 cubic feet

for every million Btu f s 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.

- 25 - 2-09 Kitchens and Lavatories

Because natural ventilation is not practical for enclosed structures or facilities of the underground installation 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 shall

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

area. The quantities exhausted through hoods over ranges,

etc. shall be sufficient to maintain a velocity of 60 to

75 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 cfrn 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 temperature of the surrounding rock mass (

Jq —07 ) and the temperature variations in the outdoor supply air (

I

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 rock and occurrence and amount of fissures

in the rock would make the amount of seepage quite unpredictable.
.
- 26

The initial temperature of the surrounding rock mass

is discussed in Section L}-07. Figure 2 — 14 (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 IF per hundred feet. Figure 2-4 is also useful for

the determination of the mean annual temperature of the

outside air supply to an installation 9 The mean annual

temperature is closely approximated by subtracting 2F from

the values given in Figure 2—14 . Figure 2-5 (Ref. 23 ) gives the mean annual range of

temperature which is defined as the difference between the

mean temperature of the warmest and coldest month. The

mean temperature variation for a given locale may be determined from Figures 2 —14 and 2-5. For example, a given

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

annual range of temperature of I46F, the extreme mean temperatures are then 52 + 46/2 = 75F* and 52 - 4&/2 =29F.

For section 4~05j the temperature amplitude 0 O , is determined by dividing the mean annual range of temperature

by two. For the above example @ 0 = 23F.
.
- 27 - CHAPTER 3

Design Information and Data

3-01 Heating and Cooling Load Estimates (3-02 through 3-06)

Steps recommended for determining the net loads for

heating and air conditioning equipment are set forth below.

The purpose is to determine first, the required rate of

steady heating to bring the chamber from its initial tempera

ture to a desired air temperature (warmup period), and

second, the net rate of heating or cooling required to maintain the chamber at the desired constant air temperature sub

sequently

.

A. For the warmup period (use Form C (1-07)

(1)

For each chamber, compute the constant rock

heat absorption rate, q', for the desired warmup period, to,

and final chamber temperature, Tp. Determine Aq 1 for each

chamber.

(2)

For the whole installation, add the values

of Aq 1 for the several chambers,,

B. For the constant air temperature or thermostated

periods (use Forms B and D (1-07) dealing with each room

or chamber separately).

(1) Determine the maximum internal sensible and

latent heat loads. This represents the condition of normal

operation at maximum capacity.

(2) Determine the internal sensible and latent

loads under the standby condition.

(3) Determine the rate of rock heat absorption

for a bare chamber, or the wall, floor and ceiling heat

loss for an internal structure, at selected times.

( 14 ) Subtract item 3 from the sensible heat load

in item 1 to yield the cooling load for the room during

normal operation. If item 3 exceeds the sensible heat

load in item 1, heating rather than cooling is required

for the room.

- 28 -

( 5 ) Subtract the sensible heat load in item 2 from

item 3 to obtain the heating load during the standby condition. If this sensible heat load exceeds item 3, cooling

is indicated during the standby condition.

(6) Add the separate net sensible and latent loads

for the several rooms for use in determining size and type of

heating, cooling and dehumidifying equipment.

3-02 Heating Loads

The heating load of an underground chamber is the sum

of the heat absorption of the surrounding rock (3-02), the

heat used to evaporate water from damp exposed surfaces

(3-10), and the heat necessary to warm ventilating air

(2-06) o Any heat liberated by machines, personnel or processes (3-06) in the space can be deducted from the heating

load in any room or chamber provided such heat is well distributed . The warming of an underground space typically falls into

two periods, the warmup and the thermostated period (I-OI4).

The heat required for warming the rock surrounding a chamber

can be computed ( lq — 02 ) by means of Equation — 0J4 . The heat

absorbed by the surrounding rock when a constant temperature

is maintained in the chamber can be computed (14-02) by means

of Equation I4-O5.

3-O3 Warmup, Bare Chamber

Installation of permanent heating equipment with sufficient capacity to supply all the heat necessary to achieve

a very short warmup period is not recommended. The initial

heat absorption rate of rock surrounding a warmed chamber

(Ij-02) is comparatively very high. If a quick warmup is

necessary, temporary oil-burning 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 (5“05) is practicable for a warmup period. However,

the cost is comparatively high and the necessary wiring,

transformer and heaters add to the cost unless they 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.

- 29

Power equipment such as electric motors or internal

combustion engines, used during excavation, contribute heat

to a space and may alleviate the warmup problem.

The rock heat absorption is likely to be the greatest

heat loss from the bare chamber during the warmup period.

This is governed at any instant by the equation

qi = u» (Ti - T s ) 3-01

q' = heat flow, Btu per hour per square foot of

rock surface exposed to the chamber

U 1 = heat transfer coefficient, Btu per hour, for

one square foot of rock surface and for each

degree difference in temperature between the

air in the chamber and the rock surface

Tj_ = temperature of the air in the chamber, F,

average

T s = temperature of the rock surface, F, average

Equation (3-01) is often inadequate because the rock

surface temperature, Ts, is unknown. The rock around a warmed spaced receives heat and Ts changes accordingly. This

more complicated case is covered by Equation J4 —OI4

• (4-03)

3-04 Heating Load, Bare Chamber - Normal Operation

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. It Is governed

at any instant by Equation 3-01 but since, this equation does

not take account of changes in Ts, Equation 4“05 is recommended for computing rock heat absorption.

When the internal load (3-06) exceeds the rock heat absorption the difference must be removed by some air conditioning means.

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 concrete

are similar to those of rock and the thickness is relatively

small. Acoustical or other insulating materials applied to

- 30 -

walls or ceiling affect the heat transfer. Equation 3-01 is

applicable to lined chambers, but the value of U' must be

appropriately chosen for any wall surfacing material used

( 4

-08 )

.

3-05 Heating Load, Inner Structure

It should be possible in many instances to warm up an

inner structure in a satisfactorily short time by means of

the permanently installed heating equipment. The inner

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 warmup period. The relation between heat input and warmup time can be computed by means of

equation I4 -OI4 (I4 -O3 ).

Under the normal or steady temperature condition, the

rock surrounding an inner 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 I4 -O5 , ( 4 —0 3 ) . Equation 3-01 is valid for an inner

structure at any instant with a proper value of U* (I4-O8).

The heat loss from an inner structure at any instant

can also be computed by the equation

q = U (Tp - T a ) (3-02)

q = heat flow, Btu per hour for one square foot

U = heat transmittance, Btu per hour for one

square foot of wall, ceiling or floor and

for each degree F in air temperature difference inside and outside the structure

Tq= air temperature, inside the structure, F

T a

= air temperature outside the structure in

the annular space between the structure

and the rock

Values of U ( 4 —0 8 ) are not the same for underground

structures as they are for exposed walls of surface buildings.

For surface buildings, the value of U is ordinarily based on

an assumption of a wind with a velocity of l£ miles per hour

on the outside. Underground, the outside surface film coefficient and the transmittance, U, must be selected with
.
- 31 -

proper reference to air velocity. In many cases the same inside and outside film coefficient, 1.65, probably is adequate.

Equation 3-02, like equation 3-01* I s often insufficient

because one temperature, T a , is variable with time. The heat

loss of the structure at any instant can be computed by means

of equation (I4 -O3 ).

3-06 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 (I4 -O 3 ). 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 be computed

by the relation

1 KW = 3l|12 Btu per hour

Also

1 Horsepower = 25 I46 Btu per hour = .7I46 KW

However, because the efficiency is less than 100 percent,

it is often assumed for estimating purposes that a consumption

of one kilowatt of electric energy is necessary to produce one

horsepower, at least for small motors.

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 equal to

one minus the overall efficiency of the motor and driving

mechani sms

.

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.

- 32 -

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~l

Room Sitting or Moving Slowly Light Working

Temp. Sensible Latent Total Sensible Latent Total

8I4 180 220 400 150 510 660

82 200 200 400 180 480 660

80 220 180 400 210 450 660

78 240 160 00 240 420 660

76 2^6 144 400 270 390 660

74 272 128 400 300 36O 660

70 300 100 400 350 310 660

60 360 70 430 460 200 660

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 supply

shafts or tunnels (4-05).

- 33

3-07 Dehumidification , Bare Chamber

The dehumidification load of a bare chamber includes

water vapor from equipment and processes, if any, and personnel ( 3

- 06 ), 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

dew point, and, conversely, water evaporates from damp rock,

or from pools, whenever the surface temperature exceeds the

dew point (J4 -IO). The rock therefore tends to govern the

humidity in the chamber by holding the dew point at its own

surface temperature, except for small structures in large

chambers (5-10). 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 ( 14 - 03 ).

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

.

3-08 Dehumidification, Lined Chamber

Use of vapor barriers (

I

4 —09 ) or of thermal insulating

materials (

I

4 — 0

8

) 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 (3-03)

= 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 materials or to its

fastenings. A vapor barrier inside the insulation does

not protect it from ground water and such a barrier outside

the material does not protect it from condensation.
R

^ ast;.
- 34 - 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 changes

of spalling, but it should not be considered effective as

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

3-09 Dehumidification, Inner Structure

If the walls, ceiling, and floor of an Inner structure

are vaporproof, the water vapor to be removed by the air

conditioning apparatus is equal to that liberated by the

equipment and personnel (

3

—0 6 ) within the structure. Conditions in the annular space do not directly affect those

within the structure.

If the walls, ceiling, and floor of the inner 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 inner structure through the walls, ceiling, and floor by

permeation, or by convection from the annular space.

Compared to convection, migration of 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

the inside and outside of an inner structure, the interior

humidity is likely to be governed 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 (^-09).

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

If the surface becomes xvarm, due to heat received from the

inner structure or due to the passage of warmer air through
.

.

I
- 35 -

the annular space, the rock will cease to be a means for

maintaining a satisfactorily low humidity.

3-10 Waste Heat Disposal

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

can be dissipated in water as from a brook, river, or

creek, if available, 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 heat disposal

means built into or in conjunction with the underground

installation.

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 isolation.

There are two ways to utilize an underground reservoir

(I4-OI4). The water can be passed through the equipment to

be cooled and wasted outside the installation, or the water

can be used to absorb heat while remaining in the reservoir

Somewhat more heat can be absorbed by a reservoir of a

given size when the heat is added to the water while it

remains in the reservoir because the surrounding rock also

absorbs heat. A possible disadvantage of the method for a

reservoir of limited size, is that the surrounding rock

will be left warm at the end of a period of isolation and

may require too much time and water for cooling in preparation for the next attack. If a reservoir is large

compared to the load imposed upon it ? the arrangement can

serve for a long period of time.

For estimating purposes it can be assumed that, for an

internal combustion engine, about 30 percent of the heat

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 I4-O7. The

heat absorbing capacity of an underground reservoir as a function of time, if the water is recirculated and retained

is given by equation I4-O8.

3-11 Air Conditioning Effect of Tunnels or Shafts

The initial or undisturbed temperature in a tunnel

or shaft with an overburden of 50 feet or more is likely

to be at or near the mean annual temperature which is in

the range $0 to 55 F in many regions. This is usually

above the winter outside design temperature and below the

summer outside design temperature and dew point for such

regions. A tunnel or shaft is therefore a possible means

for tempering the air in winter or of partially conditioning it in summer. For a long tunnel and a small flow, the

air passed through a tunnel assumes nearly the earth temperature, say 55 F. Also, such a tunnel can dehumidify

outdoor air in summer, and humidify it in winter if ground

water is present. A large wet tunnel with a small air flow

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 5 0 percent.

A tunnel in continuous use for transporting outdoor

air extracts heat from the air in summer and imparts an

approximately equal amount of heat to the air in winter.

The outdoor temperature, plotted against time throughout

a year describes an approximate cosine curve and the air

leaving the tunnel describes a similar curve but with a

smaller amplitude. The amplitude of the air temperature

variation at the exit end of the tunnel indicates the heating and cooling effects of the tunnel. For a long tunnel

and small air flow this amplitude will be small, as discussed above. For any 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 equation I4 -IO, (I4 -O5 ). Remarks about

tunnels in this section apply substantially also to shafts

or other openings of equal dimensions.

3-12 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 as shown by equation 3"03o It can affect the conductivity

and heat capacity of porous or hygroscopic rock (ij-08).

To evaporate water from damp surfaces or open pools requires heat (I| -10) and can add to the heating load. Water

evaporating absorbs the same latent heat as it gives up
.
- 37 -

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.

- 38 - CHAPTER 4

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 requirements.

The temperature in an occupied underground space is

usually maintained above that of the surrounding rock and

consequently heat flows from the space to the rock. In the

absence of internal load, the heat supplied to the space must

equal that absorbed by the rock. When the internal load,

such as the heat from lights, motors or other equipment and

personnel, exceeds the heat absorbed by the rock, the difference must be removed by some cooling means such as an air

conditioning apparatus.

The rock surrounding a continuously warmed space itself

becomes warm with time, its surface temperature increases

and its heat absorption rate decreases. 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 differential equations are too complex

for everyday use and for this reason an approximate method

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 numerical solutions of the equations for

cylinders and spheres obtained by means of a large electronic

computer, available at the National Bureau of Standards.

Usually, a new underground space must be warmed to

some acceptable temperature in preparation for occupancy.

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

- 39 -

relatively large, constant rate. If the desired temperature

and permissible warmup time are specified, the required heat

supply rate can be computed by means of Item 6 under Procedure (I|-02).

After the warmup, presumably a constant temperature will

be desired in the space, at or near 75>°. 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 by means of Items 7 and 8 under procedure (lj-02).

I4 —02 Procedure for Estimating Heat Transfer, Air to Rock

The procedure recommended for estimating heat transfer

from an underground space to surrounding rock is as follows;

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 I4-OI is applicable.

2. Obtain the value of V]_/V for the cylinder by

means of Figure I4 —1 and of V2/V for the sphere by means of

Figure lq —2 .

3. If V]_/V exceeds V2/V, utilize the cylinder as the

best approximation to the space considered; if V^/V exceeds

V]_/V, utilize the sphere.

I4 o Compute the radius of a cylinder of the same internal area using Equation I4 — 02 and compute the radius of

a sphere of the same internal area by means of Equation

I4-O3.

5. Determine the initial temperature of the rock,

thermal conductivity, density, specific heat, and overall

coefficient of heat transfer. These may be found from

geologic data, testing of samples, or estimated from information given in section I4-O6, I4 —07 , and lq —0 8

.

6. For a given warmup time ( 2q— 03 ) , determine the required heat input by means of Equation I4-OI4. Utilize

Figure I4-3 for the cylindrical case or 1| — J4 for the spherical

case in conjunction with this equation. Data Form C is

suggested as a work sheet (1-07).
»•
- 4o -

7. Compute the rock heat absorption for the constant

air temperature, or thermostated condition (I4 -O3 ), by means

of Equation 14-05° Equation l|-05 will yield the heat

absorption for the cylinder or for the sphere, whichever

was selected for an approximation to the space being considered.

8. Adjust the results obtained under Item 7; divide

the heat absorption obtained for the cylinder by the ratio

ViA or divide the results obtained for the sphere by the

ratio Vn/V. This will yield an approximation to the heat

absorption for the space under consideration that can be

used in heating and air conditioning load estimates. Data

Form D is suggested as a work sheet (1-07).

4-03 Equations for Heat Transfer, Air to Rock

Equations applicable to the procedure for computing

heat absorption by rock are as follows:

Area of an Underground Chamber, either square or

rec t angular.

A = 2 (mn + ms + ns) (4-01)

A = wall, ceiling and floor area, ft 2

m = length, ft

n = width, ft

s = ceiling height, ft

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

ceiling is arched or If either major irregularities in

shape exist, the area. A, should be adjusted accordingly

by some appropriate method.

Radius of a cylinder with thermal characteristics approximately similar to those of the space considered:

ax = -A. dl-02)

2 rr m

Radius of a sphere with thermal characteristics approximately similar to those of the space considered:

( 4

-03 )

- Ill -

Hock heat absorption; steady heat input required to warm

the rock surrounding a space in a specified time:

£sK = f (F) ( l|-Ol|

)

q ’a

©s = Temperature rise of rock surface, above

initial temperature, deg. F.

K = Thermal conductivity of rock, Btu hr-^-ff-1-

q' = Rock heat absorption rate, Etu hr"-*-ft”^

a = Radius, ft; S]_, for the cylinder; ap for

the sphere; selected for the approximation

from Equation I4 -O 2 or I4 -O 3

F = Kt/pca2

; F]_, cylinder; Fp, sphere

t = Time permitted for warmup period, firs

p = Density of rock surrounding the space,

lb ft-3

c = Specific heat of the rock, Btu lb“^-F"^

To utilize Equation I

4 -OI4 first compute the value of

F, then determine the value of 9 aK/q’a from Figure I4 -O 3

for the cylinder or Figure I|-L| for the sphere « From the

value of 9 aK/q * a thus established, determine the heat

absorption of the rock q», in Btu per hour and per square

foot. It will be noted that the heat absorption rate,

determined with Equation Iq — Olq depends on rock surface

temperature rise, 9s.

Rock Heat Absorption; Constant Air Temperature (Thermostated Condition)

q = (l-9 s /©i) U ’ 9 i /R (4-05)

q = Rock heat absorption rate, Btu hr“lft“^«

The value of 0s/©i in equation I4 -O5 is

given by Equation I4 -O 6 , and is a function

of F which involves the time, t, for which

the thermostated condition has been continued.

It will be seen that the rock heat absorption

rate q decreases as time t increases. See

Form D ( 1-07 )

.

- i|2 -

U’ = Overall average coefficient of heat transfer,

Btu hr“lft"2 j for each degree temperature

difference between the rock surface temperature and the temperature of the air within

the heated or air conditioned space,, For

an internal structure, the relevant air

temperature is that inside the structure.

(4-08).

@i = Temperature difference, air temperature to

be maintained in the air conditioned space

minus initial rock temperature, deg. F.

9s = Temperature rise of rock surface, above

initial rock temperature, deg. F.

R = Vp/V for the cylinder or V2 /V for the sphere.

Values are taken from the charts, Figures

4-1 and 4 —2 • These values are used also for

choosing between the cylindrical and spherical

approximate solutions as stated in item 3

under procedure

0s = f (F, N) (4-06)

0i

Values of 63/61 are taken from the charts. Figure 4-5

for the cylinder or Figure 4“& for the sphere. On this

figure

N = aU'/fc

The quantity N must be computed for use with the charts

For an internal structure under the thermcstated condition, the heat loss per square foot from any particular

room at any time equals U0 (Ti - Ta) , which can be shown to

equal

quG _R

-U» + where q is given by Equation 4-05, U0 is taken from Table

4»1 (4—08) for the internal structure, and R and U * are

as defined for Equation 4-05» The total heat loss from the

room is the sum of the losses from the walls, ceiling, and

floor.

RATIO,

LENGTH

TO

WIDTH

=

m/n

° = d

°

o

o

oIt:

o

CVJ

o

o

IT)

o

cvi

q

RATIO,

LENGTH

TO

WIDTH

=

m/n

CONSTANT ROCK HEAT ABSORPTION

EQUATION 4-04, CYLINDRICAL CASE

0.30

0.04

0.4

0.06

0.6

0

0

0.02

0.2

F = Kt/Jeca2

0.08

0.8

0.10

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

F

2

=

Kt/pCdf
1iiBBBBBB
0.4

0.8

1.2

1.6

2.0

0

10

20

F,

=

Kt/yocaf

F,

=

Kt/yoca
{ > ( • ^ • •>Vi
X

"cvoo

<no'

ooo'

r-6<£> oino' o'

tod

! e/ se = (n

0.2

0.4

0.6

0.8

1.0

0

5

10

F

2

=

Kt/p

ca 2 2

F2

=K

t

/p

- 43 -

ll-Olj Heat Absorption of Underground Reservoirs

An underground reservoir of water may be provided as

a sink for the waste heat from engines, air conditioning

equipment or other apparatus for use during emergencies

(1-5) when outside services are cut off (3-10) • Spaces

prepared for this purpose are likely to be long and tunnellike 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.

If the water is used to absorb heat from engine

jackets or refrigeration condensers, etc., and is then

wasted outside the installation, its heat absorbing capacity can be computed by the equation:

Qw = M (Tw-T

p

) (i|-07) = Heat absorbing capacity of the water, Btu

M = Hass of water in the reservoir, lbs

Tw = Temperature; water discharged for engine

jacket or condenser, etc; F

Tp = Temperature; water available from reservoir;

F

If the water is recirculated from the reservoir ,to the

engine jackets or condenser and back to the reservoir, the

heat-absorbing capacity is increased by the heat-absorbing

capacity of the surrounding rock and the total capacity can

be computed by means of the equation:

©wK = f (F, G) (14-08)

qi

where @w = Temperature rise of water above the initial

water temperature, deg. F.

qp = Constant heat transfer rate to the water

from an external source such as engine

jackets or condensers, Btu hr"l per foot

length of reservoir

F = Kt/pca2

f(F,G)

=0

w

K/q,

0.2 0.3 0.4 0.5 0.6 0.7

EQUATION 4-08

RESERVOIR HEAT ABSORPTION

AT CONSTANT HEAT RATE

F = Kt/oca2
c-^'y yc/'
- hk -

t = Time from initial application of qp, hours

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

s = Height of reservoir, ft

n = Width of reservoir, ft

G = ZiT a

2

pc

M 5 c

= 2pc/p , c’ (for a cylinder completely filled

with water)

M ,:= Mass of water in reservoir, lbs per foot

length of reservoir

p*= Density of water, lbs ft“3

c = Specific heat of rock, Btu lb"-L F"^

c*= Specific heat of water, Btu lb“-*-F”-*-

m = Length of reservoir, ft

Equation Jq— 0 8 is plotted in Figure l\-7 and Form E is

suggested as a work sheet for its use. This equation yields

the heat absorption per foot of length, q^ , for a tunnel of

radius, a, for a specified water temperature rise 6W in a specified time, t.

U-05 Heating or 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

alternately transferred from the air to the rock in summer and from the rock to the air in winter. Savings are

possible under both conditions since the air is warmed

in winter, thus reducing the heating load, and cooled in

summer, thus reducing the cooling load (3=11). The temperature of the air at the exit, like that at the entrance,

oscillates above and below th(e mean annual temperature but

the amplitude of the temperature change is smaller at the

exit.

- 45 -

This problem is subject to analytical treatment if it

is assumed that the outside air temperature varies seasonally

according to the equation

0O = ©j, cos wt (I4-O9)

©o = Outside air temperature minus mean annual

temperature, deg F, at time, t.

©^ = Outside air temperature minus mean annual

temperature s deg F, maximum or minimum.

w = Angular velocity, 21T radians per year

= 0o000717 radian hr“l

t = Time, hours (t = o when 0 O = 9<j)

Based on this assumption, equations yielding results

relevant to air conditioning are as follows;

For the temperature at distance L in the tunnel and

at time, t.

©L = ©^ e~c

' c cos (wt - WL/V - C »B) (J4 -IO)

Maximum and minimum air temperatures at point L;

summer and winter design temperatures

©jJ = + ©^ e

"c ’ c (4-11)

Rate of heat loss or gain by the air in length L at

time, t;

q

= 0.0566 Va2

(0 O

- @L ) (lq-12

)

Total heat gain of air in winter (equals total heat

loss of air in summer)

Q = 157.7 Va2

©^ Jl+e"0 ,C - 2 e"C ' C cos (wL/V + C »B)

(4-13)

A = Average cross section area of airway, ft 2

a = 2Aj P, hydraulic radius of airway, ft.

B = f2

(a, b) (4-9)

where

- 46 -

b = h/K ]a. /w

C = f^_ (z, b) (Figure I4 — 8 )

C '= hL

Va

e = Base of natural logarithms

h = Coefficient of heat transfer between the moving

air and the surface of airway, Btu hr“lft^p-l

K = Thermal conductivity of rock, Btu hr”lf t "2 (p/f t

) "1

L = Distance from outside entrance of airway, ft.

P = Average perimeter of airway, ft.

T = Period, 8760 hr (1 year)

V = Velocity of air stream, ft hr“l

w = Angular velocity, 2 Tr /T - 0.00071? radians hr"~

z = a yw/a

a = Thermal diffusivity ft 2hr“l

© = Departure of temperature from the mean annual

temperature, Fj 0’, maximum departure or

amplitude; 0 O , outside air; ©^, at distance L

in airway

B, C, and Equations iq *=-12 and I4 *=13 are based on the assumption

that the density and specific heat of air are 0.075 lb ft "3

and 0.018 Btu ft~3F“l, respectively.

Form F is suggested as a work sheet for problems of this

type. If a tunnel or shaft is used intermittently as an airway, the equations in this section do not apply without modification and the effects of such an airway cannot be estimated unless the method of using it is stated.

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 „

z

0.3 0.5 0.7 0.9 z

AIR

STREAM

VELOCITY

—

IOOO

FT.

HR’

- 47 -

4-06 Thermal Properties of Rock

Rock heat absorption computations depend on the ther

mal properties of the rock and it is unfortunate that the

available data are incomplete and, in some degree, discordant. For estimating purposes it is recommended that a

specific heat of 0„2 Btu lb-lp-l 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.

For greenstone, present in the mountains of Virginia,

tests and experience show a thermal conductivity of about

1.5 Btu hr “If t“2(F/ft

) “1 , with a density of 186 lbs ft"3.

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 testing some specimens

for conductivity or by the use of figure I4 -II in conjunction with a petrographic analysis of some specimens.

Facilities for making these tests or analyses are maintained in several laboratories in this country.

For igneous and metamorphic rocks the density generally falls in the range from 150 to 190 lbs ft“3, and that

of the sedimentary rocks in the range from 100 to 175 IBs

ft“3. For igneous and metamorphic rocks, the thermal conductivity falls in a range from 1.2 to 2.0 Btu hr“lft~2

(F/ft)"l. Granites are found to be in the range 20-40 per

cent quartz, 50-73 percent feldspar and 5 “12 percent mafic

The factors which determine the thermal conductivity of

sedimentary rocks are numerous; composition, porosity,

temperature, grain size and shape, and fluid content all

have to be considered.

4-07 Initial Underground Conditions

At depths of 50 to 70 feet, the temperature of earth

or r ock can be expected to approximate the mean annual

temperature for a region 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 IF 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 any proposed site.
'

.
FIG.

+-II

-Is



- U8 -

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 13 feet near

Washington, D. C. and the results are shown on Figure I4 —12

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

I4 F and a mean temperature of about 53F at a depth of 13 feet.

Li —0 8 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 structures, with one notable exception. 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 interior 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 in interior structures be considered to

have the same values as those ordinarily used for inside

surface coefficients.

The coefficient U 1 , appearing in equations 3-01, 14-05

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

square foot of rock surface for each degree of difference

between the temperature of the surrounding rock and the

temperature in the conditioned space. For an interior

structure, one significant temperature is that within the

space and the other, that of the surrounding rock surface.

Values of U and of U ! for some materials and structures

are given in table I4 -I 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.

For a rock surface such as that left after blasting,

the surface air film heat transfer coefficient averaged
'
- 49 -

h = I.I4 Btu hr"-*-f in some tests in an underground

chamber with only natural air motion. This figure is based

on projected wall area, ignoring irregularities left after

blasting. For the surface conductances of interior structures, a value of f0 = f± = 1.65> is recommendeded for present

purposes. With these values, heat transfer coefficients of

walls, ceilings and floors of interior structures can be

computed by means of the following equations:

u0 = 1 (4-11)) + i_ +

1

1.65 c 1.65

U» = —— (4-15)

-JL + I- + 1.65 G 1.25

C = Conductance of wall, ceiling or floor

of interior structure

- 50 -

TABLE 4-1

Heat Transfer Coefficients for Underground Structures

Material or Structure

Bare rock surface

Studs with 3 /8

U gypsum board on one side

Studs with 3/8” gypsum board on both sides

Studs with l/2” insulating board on one side

Studs with l/2H insulating board on both sides

Brick, one course - 4" thick no finish

Brick, one course - l\ u thick 3/0" gypsum bd.

Brick, one course - 4” thick l/2" insulating

board

Brick, two course 8

n thick, no finish

Concrete, 8

n thick, no finish

Concrete construction floors, (3”) no ceiling,

no flooring

Concrete construction floors, ( 3 ”) no ceiling,

1 /8 " asphalt tile

Metal roof deck, bare

Metal roof deck, roofing and l/2 n insulating

board

Wood roof 1" roofing and l/2u insulating board

TJ0 u»

1.40

0.6? 0 .S 9

0.37 0 . 3b

0.36 o. 3 l) 0.19 0.18

0.60 o. 5 i) 0.51 0.147

0.32 0o30

0.41 0.38

o . 5k 0.49

0.68 0.60

0.66 0.59

0 o 90 0.77

0.33 0.31

0 0 2.5 0.24

UQ = heat transfer coefficient, based on temperature difference between air in conditioned space and air outside,

in the annular space, with zero wind.

U* = heat transfer coefficient, Btu per hour for each square

foot of rock surface area and for each degree F difference in temperature between rock surface and air in

conditioned spaces.

- 51 -

1| — 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 construction. The danger of condensation in parts of an underground structure is not considered great, particularly if

the space is continuously air conditioned, because the temperature differences or gradients are not severe compared

to those that occur in surface buildings. Data are lacking

but it appears that condensation might occur in a construction such as a double-faced wall containing insulation.

A vapor barrier might therefore be installed in or near the

outer surface as a precautionary measure.

A method for predicting vapor transfer and condensation

in walls is presented in "Moisture Condensation in Building

Walls'* (Ref. 17) with some data on the permeabilities of

some materials used in buildings. The method is based on

the theory that water vapor transfer through a meterial is

proportional to vapor pressure difference between the two

sides and that resistances are additive as they are for heat

flow. It is known that this is only an approximation but

it may be close enough for practical estimating purposes.

Another uncertainty in this field concerns the vapor permeance of materials which differs considerably between specimens of the same material. However, the data in Table I4 —

2

were selected to show the range of the permeances of some

materials used in buildings as observed by Babbitt (a)

and Teesdale (b), reported in Reference 17.

TABLE 2

Permeance of Some Materials to Water Vapor

Material

Thickness

Inches

Permeance

P

Resistanc

(i/p)

Wood - spruce ( a) O .563 3.148 0.287

Wood - pine (a) 0 . 6)45 2.52 .397

Paper, kraft, 1 sheet

Asphalt felt, Ip-lb.

,

(a) O.OOij 168.00 0 c 0

dull surface

Asphalt-coated paper.

(a) 0.032 13«50 —

j

r-

• 0

50 lb

Plasterboard, between

( b)

heavy

1.04 .962

sheets of paper (a) 0.37 70.20 .014

Unit of permeance, P : ance in perms = 0*49

= 1

P)

grain1 ft”2hr‘ (lb/in^

)

( Perme-
.

>>* •
600

800

1000

1200

1400

- 52 -

I4 -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 on the surface, perhaps

with streams running or dripping downward, or it may leak

in through faults or fissures. At the greater depths,

entrance of water through fissures, rather than through

pervious rock, is usual because a- site in hard rock Is

likely to be chosen, if possible, for structural strength.

Such rock is likely to be impervious or nearly so. Because the possible hydrostatic pressures are high ( 3 - 08 ) it is customary to drain off excess water rather than

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

make it impervious.

Evaporation from 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 dehumidifler

and tend to hold the dew point at the surface temperature.

In the course of time, the rock surface temperature Increases and water evaporating from the surface becomes part

of the latent load. Figure I4 -I 3 is a 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 lb hr"^ft - 2 for a wet surface L ft long in

the direction of air flow parallel to the surface for a

velocity of V ft min-1 and for a vapor pressure difference

(Ps-Pa) psi, where Ps is the vapor pressure of water at

the temperature of the wet surface, and Pa is the vapor pressure of the moving air.

Estimates of evaporation from rock are difficult because the area of the wet surface cannot be predicted with

certainty for any 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
.

.

'

'
- 53 - space or in contact with the rock should be capable of

withstanding humidities of 100 percent since parts of this

space may contain saturated air at times.

If a structure is so arranged that the rock remains

cool, at say 55^5 while the interior structure is held at

some higher temperature, say 75F stnd 50 percent humidity,

the rock can serve as a condenser and assist in dehumidify

ing the structure. In this case the vapor barrier is not

needed. This effect can be useful during emergency period

with arrangements suitably designed to employ it. In this

case either dampness or free water in the annular space,

being drained away, has no objectionable effects since

evaporation does not occur from the surface.

Metals and metal foils are practically perfect vapor

barriers except for possible leaks at joints. If leaks

exist in any vapor barriers the resulting vapor transfer

by convection can readily exceed the effect of permeabilit

of materials or diffusion, and convection cannot be predicted since it depends on quality of workmanship.

- 54 - CHAPTER 5

Air Conditioning Processes and Systems

5-01 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

long, narrow 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 excavating 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 or I4 0 feet, depending

on the strength of the rock. In height, the space may be

sin gle or multistory. Lengths are limited only by such

factors as pipe or duct runs, accessibility, etc. Lengths

of 200 feet or more, are sometimes used.

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.

5-02 Access Tunnels and Shafts

The simplest kind of -underground installation may

consist of a single chamber and have a single shaft or

tunnel for both access and ventilation. A tunnel is usually

preferred 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
i'
- 55 - deducted from the total required heating or cooling capacity

from the occupied spaces.

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. This action of

natural ventilation in such installations is considered here

for completeness. Under this condition, natural ventilation

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 precautions 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-Olj. Simple Installation; Two or More Shafts

An installation of this kind is self-ventilating 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 chamber, 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.
-
- 56 -

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

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, arranged in the tunnel, to blow outside air into 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 dew point 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 cause ventilation of such installation

for the same reasons.

Small insulated structures in such a chamber can be airconditioned by warming (5-10) in that the relative humidity

can be thus 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.

- 57 - For heavy or continuous occupancy or if noxious gases

are involved, forced ventilation may be essential.

5-0? 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

tunnel is blocked by battle damage or otherwise 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.

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. Either condition is bad for

personnel, vehicles and cargo. 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.

5-08 Types of Inner 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.

Internal structures differ in size and in the ratio

of their size to that of the enclosing chambers. For some

purposes, small structures may be erected In large chambers

(5-10) . Often, internal structures are designed to fit enclosing chambers with relatively small clearances to
.*
- 58 - utilize all available space. Simple partitions, even if

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

offices and may be used to improve acoustical conditions

(5-09).

Addition of thermal insulation to the walls, ceiling

and floor of an internal structure is not essential unless

the interior of the structure is heated to some temperature

above that of the surrounding annular space for considerable

periods of time. If the two spaces are kept at the same

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.

Application of vapor barrier materials in the walls,

ceilings or floors of internal structures is not beneficial

under most ordinary circumstances. In fact, layers of

material that are impervious or nearly so may increase the

chances of difficulty due to condensation under some conditions. If the surrounding rock is at a temperature below

the deitf point in the conditioned space, the rock assists In

the dehumidif ying process and the vapor barrier retards it.

If the annular space is used as a return plenum, the vapor

pressure difference through the walls tends toward zero.

These considerations indicate that, from the air conditioning standpoint, the walls and ceiling 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 and the surrounding

rock remains cool, the air conditioning process may consist

in simply warming the structure to reduce the relative

humidity (5-10). Use of thermal insulation facilitates control of relative humidity by this means.

5-09 Acoustical Treatments

Sound waves reverberate in a bare rock chamber and

render some treatment necessary in occupied spaces where a
.
- 59 -

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

- 08 ) or wetting

by condensation. Interior structures are a solution to

the problem, and the treatments of walls and 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 and should be comparatively economical,,

Air conditioning devices, 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

condi tioning.

5-10 Small Structures in Large Underground Chambers

Under favorable circumstances the relative humidity

inside an interior 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 dew point 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 pervious to permit migration of water vapor from the struetur

to the rock.

This arrangement may be useful i^hen a large cool

underground space is available and the required air conditioned space and the internal load are small. Excavati

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 (3-07). 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 before the relative humidity becomes excessive or permits the use of a larger Internal structure
-
- 60

In a chamber of limited size. 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 escaping

from the inner structure can thus be removed. The surrounding rock serves as a large heat sink and makes this process

possible.

5-11 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 (2-0[i) must be supplied with any system and may

be either added to the recirculating air at some convenient

point or ducted to the Individual zones or rooms as required

by the design. Halls can be used for return air but the

annular space around the internal structure has been favored

by designers for this purpose.

Either central air conditioning equipment (5-12) or

zone or room air conditioners (5-15) 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 ( 5

- 15 ) 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 annular

space around an internal structure with conditioned air

and ducting the return air instead of the supply air

(5-13).

5-12 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.

In typical systems so far utilized underground, conditioned air is ducted to the working spaces while the

annular space around the inner structure may be used as an
-

'

.
61

exhaust plenum. Fresh or outside air is introduced into

the supply system at one or more convenient points with care

to assure good distribution.

The 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 ). Control of air flow is usually accomplished by automatic dampers, actuated either by a pneumatic or an electric

system, governed by thermostats.

5-13 Cooling Effect Applied to Annular Space

It is possible to cool an internal structure in an

underground installation by utilizing the annular space

between the structure and surrounding rock as a cold air

plenum. The advantage is that the surrounding rock, remaining cold, can serve as a heat sink in time of emergency

when the outside power supply is cut off and the air conditioning system is out of operation.

In a suggested arrangement, air is drawn by a fan from

the structure and forced through a cooling coil from which

it is discharged into the annular space. Adjustable louvers

or other openings are provided in the walls or ceiling of

the structure through which air from the annular space

enters due to the differential pressure created by the fan.

These louvers or other adjustable openings are installed in

the various rooms in accord with their individual requirements for air conditioning. The annular space and hence

the surrounding rock are kept at or near the initial rock

temperature by the cooling coil which absorbs the heat

liberated in the structure. Thermal insulation of the

structure is not beneficial when the structure must be

cooled, but insulation can save heat if the structure must

be warmed during any considerable length of time such as

an unoccupied period.

Such an installation can be ventilated with fresh or

outdoor air drawn through a shaft or tunnel by a fan and

forced through air cleaners or purifiers, if required, into

the annular space. Vitiated air can be exhausted from a

structure through louvers and a duct system, if required,

and out through an entrance tunnel or other opening.

Kitchens, baths or sources of objectionable or noxious gases,

dusts or vapors should be vented with the exhausted air,
/

•

.
62

without recirculation. Heating, if required, must be accomplished with a separate system.

Heat losses or gains through the walls, ceiling and

floor of the inner structure can be computed by the steadystate equation (3-02) and heating and cooling loads can be

computed in the ordinary manner. The rate of warming of

the surrounding rock during an emergency period when power

is not available for air conditioning can be computed by

means of equation ([{-Of)*

If the cooling load is small, installations of this

type approach the conditions of a small structure in a large chamber (5-10) . The cooling equipment obviously becomes smaller with the load.

Chilled water lines in cool annular spaces do not require insulation since the cooling and dehutridification

accomplished by such piping- is effective in air conditioning

the space. Drip from pipes, if any, can usually be conveniently drained away.

The annular space, to be used as a cold air plenum,

must obviously not be connected to an access tunnel.

5-14 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 overall 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.

Self-contained 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 awaj/ 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 air

conditioners 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.
'

«-
- 63 - 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.

5-1^ 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 dew points

to prevent condensation on their surfaces with resultant

corrosion and to conserve the cooling effect of the water

( 5

-13 ). In air conditioned spaces, such pipes may require

insulation to prevent excessive cooling of some rooms or

spaces and deficient cooling of others more remote from

the water chiller.

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 of

chilled water to the coils or by a combination 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 installations 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.
'
- 6k - A suggested heating and air conditioning system for

an underground installation includes the following equipment:

An ice reservoir with sufficient capacity to absorb

heat from the installation through a chilled water air conditioning system during an emergency period.

A water reservoir to receive all waste heat from engine

water jackets, refrigeration condensers, etc. Such waste

heat is used in a hot water system for space heating when

and where required. Excess waste heat is ordinarily dissipated by means of cooling towers, ponds or other means

external to the installation.

(Both reservoirs can consist of unlined excavations

near the installation but separated from each other by

a sufficient thickness of rock to prevent excessive heat

exchange between them-

)

A chilled water air cooling system with a unit air

conditioner in each room or zone in the installation, receiving cold water as required from the cold reservoir.

A hot water heating system includes either separate

heating devices, like radiators or convectors, or heating

coils in the air conditioning units for warming the various

spaces

.

One or more refrigerating machines to extract heat

from the ice reservoir; rejected heat is supplied to the

heating system and excess waste heat is dissipated outside

under normal operation or delivered to the water reservoir

during emergency.

A boiler or boilers to supply heat if waste heat

from the equipment is insufficient at any time, to supply

steam for cooling if required, and to temper the fresh air

if required.

Controls, except safety devices, tempering valves,

and room or zone thermostats, are manual. The large heat

capacity of the ice reservoir results in slow temperature

changes under any condition of operation so that refrigerating machines or boilers need be started or stopped only

at comparatively long intervals.

Under normal operation, the refrigerating machines

operate sufficiently to keep a substantial part of the
' > * >
- 65 - water frozen in the ice reservoir. Water from this reservoir is mixed in tempering valves with water recirculated

through the cooling coils in the air conditioners to cool

and dehumidify zones or rooms where required. A water temperature at or near 50F i s suggested for the water supply to

the cooling coils. Warm water from engines or refrigerating

equipment is circulated to supply heat to rooms or zones

when required.

During an emergency or "buttoned up" condition, the

refrigerating machines are stopped to relieve the Diesel or

other power source of the refrigeration load. The ice reservoir continues to act as a heat sink for the air conditioning load and can continue to serve this function until

it approaches some temperature near The water reservoir

acts as a heat sink for the Diesel engines until its temperature approaches the boiling point.

When either the ice reservoir approaches 50F or the

warm reservoir approaches the boiling point, the refrigerating machines must be started and the ice reservoirs must

serve as a heat sink for both the power plant and the refrigerating machines as long as possible. The limit probably is an ice reservoir temperature near HOP since higher

condenser water temperatures may result in intolerable

pressures in the compressors.

The limit of endurance of the installation is reached

when the temperature in the warm reservoir approaches the

boiling point and that in the ice reservoir reaches the

highest permissible without destructive head pressures in

the compressors.

Designs of reservoirs for emergency periods of specified length can be based on equations included in Chapter I4 . The water would, of course, be much more effective as

a coolant, in Btu per pound, if its latent heat of vaporization could be utilized, but Diesel engines probably are

not constructed to withstand boiling water in their jackets.
>
- 66

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 cf large ducts and inordinately large apparatus. A general advantage lies with small

ducts and high velocities, and small, high capacity equipment 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 (2-03 )• A requirement of 75^ a^d 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 - 2F 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 65F. Water, if available from outside, may be

used for cooling in a chilled water system if its temperature is about 50F 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.

- 67 -

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

ij. 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 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—Olq ) 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

- 68 - washer ( 6 -0£) or spray coil ( 6- 06 ). Such devices are not

considered necessary in most cases because a cooling coil

(6-07) can be 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 uhat

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 recirculated 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 (6-11) 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-OI4 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
.

?

’
- 69 - 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 surrounding 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

instant can be computed by means of equations given in

section I4 -O5 . The purpose of tempering coils is to so warm the fresh

air in winter that condensation on ducts is avoided. Heating to some temperature near that 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 is a means of avoiding overheating of the air

in mild weather. The coil is shut off in summer.

If the fresh air ducts are insulated both 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 (6-8)

to function when receiving cold air.

6-05 Air Washers

Air washers (Ref. 1) are a means for comparatively

precise 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 operationcan 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

- 70 -

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

(2-0lj), (2-05).

Air washers are not covered by any generally accepted

standard testing or rating procedure. Selection is usually

based on knowledge of the performance of conventional designs. Cabinets or cases of air washers are usually sheet

metal, rectangular in shape and long enough to accommodate

from one to several banks of spray heads between diffuser

plates near the entrance, to promote uniform air flow, and

eliminator plates near the exit, to capture airborne water

droplets and provide additional wetted surface. Glass wool

mats are sometimes used as eliminators; the material presents

large areas of wetted surface per unit volume to the air

flow.

In air washers, air velocities in the range from 250 to

600 fpm have been used; [|50 fpm is typical. Spray banks are

about 2 l/2 feet apart. With this arrangement humidifying

effectiveness in the range from 60 to 75 percent can be

attained with a single bank of spray heads and from 85 to

95 percent with two banks of spray heads (Ref. 1). Higher

effectiveness is obtained when the spray heads face upstream.

Humidifying effectiveness is defined by the formula

eh

“ 1

" ^ 2 x 100

Tl - T»

in which

e^ = humidifying effectiveness, percent

= dry-bulb temperature, entering air, F

T 2

= dry-bulb temperature, leaving air, F

T’ = Thermodynamic wet bulb temperature, entering

air, F.
»* '
- 71

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 exchange, 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.

To select a heating coil to serve a given space the

following factors must be known or estimated.

Heating load, Btu per hr. (3~02)

Temperature, air entering coil, F.

Temperature air leaving coil, F.

Face velocity, fpm

Air flow, cfm

Allowable pressure drop, ins., W.G.

Dimensions of coil

Dimension of the allowable space

With these data it is usually possible to select a coil for a given heating load from tables in manufacturers

'

catalogues for the use of either hot water or steam as a

heating medium.
.

.

'
- 72

To select a cooling and dehumidifying coil, the following data are necessary.

Sensible cooling load, Btu per hr. (3-06)

Latent cooling load, Btu per hr (3-06)

Wet and dry bulb temperatures of the air entering

and leaving the coil, F.

Face velocity, fpra

Air flow, cfm

Allowable pressure drop

Dimensions of the coil

Dimensions of the allowable space

The most convenient and practical procedure for coil

selection is to utilize the above data in conjunction with

data on coil characteristics found in manufacturers' catalogues.

Heat transfer in coils is complex, 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’1 (Ref. 1) and other handbooks

and texts.

A Test Code for coils entitled "Standard Method of

Testing and Rating Forced - Circulation Air-Cooling and

Air-Heating Coils" has been accepted by the Air Conditioning and Refrigeration Institute and the Heating and Cooling

Coil Manufacturers Association. Many manufacturers make

the necessary tests or gather the pertinent data by methods

of their own. Sometimes tests of coils are desirable after

installation to determine compliance with guarantees.

The total output of a steam coil can be determined by

measuring the steam condensation rate, in pounds per hour.

This multiplied by the change in enthalpy or total heat

of the steam in condensing yields the output in Btu per

hour. Coils heated or cooled by water or cooled by a refrigerant are more difficult to check because fluid

flow rates and temperature or enthaply changes are difficult to measure in normal operation. The necessary
.

.
- 73 -

measurements are possible in most cases with sufficient

care and skill. A result within ten percent of the true

output would be regarded as a good determination.

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 metah A selfcontained unit includes a refrigerating machine, which

may be either air or water cooled. In a remote unit,

chilled water, liquid refrigerant, or a solution, 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-Conditioner s'* and 2-10

"Self-Contained Air Conditioners (other than Room AirConditioners)", published by the Air Conditioning and

Refrigeration Institute. 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.

6-0 6 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, relatively 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 operation 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.
'

5>
- lb - Automatic self-cleaning oil-bath 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 type air filters. Electrostatic devices

are tested with airborne dust without any artificial contaminant. Field tests of such equipment are feasible. Throwaway and cleanable filters are tested with Cottrell precipitate, which is fly-ash from boilers burning pulverized coal

captured in a Cottrell precipitator at a local power plant.

An efficiency of 90 percent or more is usually specified

for electrostatic air cleaners when tested after installation

with dust naturally prevalent at the site. No dust is added

to the air for the test. Panel type filters typically exhibit efficiencies in the range from 65 to 90 percent when

tested with Cottrell precipitate by the dust-spot method.

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

For the selection of a fan, data are required as

follows

;

Capacity, cfm

System resistance external to fan. Inches, W.G.

Air temperature, P. , or density, lbs. ft. “3

Space or weight limitation

Duct sizes and connections

Noise limitations

Voltage and currents

The dimensions and performance data on commercially

available fans are generally contained in manufacturers'

catalogues. The performance data are usually based oh

tests conducted according to one of the existing codes

such as "Standard Test Code for Testing Centrifugal and

Axial Fans", (1950 Bulletin No. 110 of the National

Association of Fan Manufacturers); "Standards for Fans",

( 19I4

7

, Publication 147-128 of the National Electrical

Manufacturers Association); "Test Code for Fans", (I9I46

publication PTC 11-19146, of the American Society of

Mechanical Engineers); and "Testing and Rating Ventilating

Fans (Axial and Propeller Types)", (1951s Commercial

Standard CS 178-51* published by the Government Printing

Office)

.

Fan performance is usually expressed in terms of static

pressure instead of velocity pressure or total pressure because the static is the pressure available for forcing air

through a duct system regardless of its shape* Utilization

of velocity pressure depends on the shape of the duct system

which is often unknown to the fan designer or manufacturer.

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 general types ; the axial flow and the

centrifugal. Axial flow fans may be propeller, tubeaxial

or vaneaxial types and centrifugal fans may have forward,

or backward curved or straight blades on their rotors.

Selection must be based on air flow and pressure requirement

and on space, weight, and noise limitations, if any.
.
- 76 -

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.

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 50F and 90F 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

farthest occupied space. The fresh air duct, therefore,

may 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

- 77 - 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

contained 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, of ten 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
-

.
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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 3^0 mesh to

8-II4 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

like glass wool. Reactivation may be accomplished in a second air washer through which heated (up to 300F) 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 dew point temperature, condensation

with possible drip through joints, occurs.

Selection of a dehumidifier is based on the following

data;

The moisture load, in grains or pounds per hour,

from all sources

Temperature of the air entering the dehumidifier, F

Required relative humidity, percent

Space or weight limitation

Energy available for reactivation

With this information suitable apparatus probably can be

found listed in manufacturers » catalogues.

Since dehumidifiers may be rated in pounds of water

per hour or per 2 l\ hours while psychrometric. charts show

humidities in grains of water per pound of air, the following relation is useful:

7000 grains = 1 pound, avoirdupois

For estimating purposes it is often assumed that the

temperature of air being dehumidified increases about 10

degrees F for each grain of water per cubic foot removed

from it. For reactivation, the energy required is somewhat
: V >
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greater than the latent heat of the water removed. The

difference Is the "heat of wetting" which is different

for the different sorbent materials.

6-I3 Mechanical Dehumidifiers

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 dehumidifiers, 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 dew point

is reached.
.
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

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research, development,' engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

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Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

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or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

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Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.25) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of

Standards, Washington 25, D. C.