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Liu. Stanley T/Evaluatlon of ventilation TA43S .use V97;1977 C.1 NBS-PUB-C 1977

V) NBS BUILDING SCIENCE SERIES 97

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

Evaluation of

ilation Requirements and

Energy Consumption In Existing

New York City School Buildings
The Building Science Series

The Building Science Series disseminates technical information developed at the National Bureau of Standards on

building materials, components, systems, and whole structures. The Series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems. These publications, similar in style and content to the NBS Building Materials and Structures Reports (1938-59),

are directed toward the manufacturing, design, construction, and research segments of the building industry, standards organizations, and officials responsible for building codes. The material for this Series originates principally in the Center for Building Technology of the NBS Institute for Applied Technology. The publications are divided into three general groups: Building Systems and Processes; Health, Safety and Comfort; and Structures and Materials. For further information regarding these publications

please contact the Program Planning and Liaison Unit, Center for Building Technology, Institute for Applied

Technology, National Bureau of Standards, Washington, D.C. 20234.

[See mailing list announcement on last page]
m 5 1977 Evaluation of Ventilation Requirements

'X^^^ and Energy Consumption in Existing

I. .\ New York City School Buildings

4 ^> ,y

_Q^Vj ... d

\r\'^'^\ Stanley T. Liu, Charles M. Hunt,

^ and Frank J. Powell

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Sponsored by the Division of Advanced Technology Applications

National Science Foundation

Washington, D.C. 20550

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued April 1977
Library of Congress Cataloging in Publication Data

Liu, Stanley T. Evaluation of ventilation requirements and energy consumption

in existing New York City school buildings. (National Bureau of Standards building science series ; 97) Supt. of Docs. No.: C13.29/2:97.

Include bibliographical references.

1. School buildings—Heating and ventilation—New York (City) L Hunt, Charles Maxwell, 1911- joint author. II. Powell, Frank J., 1923- joint author. III. Title: Evaluation of ventilation require- ments and energy consumption ... IV. Series: United States. National Bureau of Standards. Building science series ; 97. TA435.U58 no. 97 [LB3218.N7] 690'.021s [690'.7] 77-608072

National Bureau of Standards Building Science Series 97

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 97, 69 pages (Apr. 1977) CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

For sale by the Superintendent of Documents, U.S. Government Printing OflSce Washington, D.C. 20402- Price $2.10 Stock Number 003-003-01768-0
ABSTRACT

A study was made, under the sponsorship of the National Science Foundation and in collaboration with the New York City Board of Education, of the energy consumption and ventilation requirements of typical existing urban public schools, for the purpose of determining

the pattern of energy usage in such public schools so that effective energy conservation measures can be taken both for existing schools and for future new school design.

Electricity and fuel-oil consumption data from May 1970 through April 1973 on 19 existing schools provided by the New York City Board of Education were analyzed. Analysis showed

that the overall energy consumption of 17 of the 19 schools varied by a factor of less than

2. Average yearly consumptions per 1,000 ft^ (92.9 m^) gross floor area of 5,250 kWh of

electrical energy and 417 gallons of No. 6 fuel oil (2.03 x 10^ J and 0.017 m3 per m^ of

gross floor area), were selected as a norm typical of the existing schools. These figures

correspond to 82,400 Btu/year-(gross) ft2 (29.7 W/m^) at the building line or an estimated

126,000 Btu/year-(gross) ft2 (45.4 W/m2) when calculated in terms of raw fuel at the generating plant. The figures can be used for future comparison purposes with a new energy conser- vation school. A computerized thermal energy simulation, using the program NBSLD, was performed on one of the schools having an energy consumption close to the norm. The results

showed good agreement between the predicted and measured monthly electricity and fuel-oil con- sumption data. Detailed analysis of the pattern of energy consumption showed that 75 percent

of the thermal energy during the heating season was used for the heating of outdoor air for

ventilation purposes, and 80 percent of the electrical energy was used for lighting.

A ventilation test was conducted over a 4-day period in a typical classroom. It was

found that a reduction of the air change rate from the normal 4.6 changes per hour to 1.3

changes per hour did not significantly change the indoor environment as expressed in terms

of temperature, relative humidity, oxygen content level, and CO2 concentration level. However, computation indicates that, when no mechanical ventilation was provided, the CO2 con- centration level would exceed the 0.5 percent safety limit, indicating that natural air infiltration alone will not provide adequate ventilation for the general health and safety of the

students

.

Key Words: CO2 concentration; computerized thermal simulation; energy conservation

in schools; energy consumption; energy utilization in schools; oxygen

content; reduced ventilation rate; school operation schedule; ventilation test

iii
Table of Contents

Page

1. Introduction 1

2. Energy Consumption of Selected Existing Intermediate and High Schools in New

York City 2

2.1 Analysis of Energy Consumption Data

.....

2

2.2 Observations on the Operating Schedules of Existing Schools 10

3. Computerized Analysis of the Energy Consumption Pattern of a Typical Existing

School 13

3.1 Calculation of Indoor Space Conditions by Building Thermal Simulation ... 13

3.2 Construction Data and Operation Schedules of the Selected School 13

3.3 Analysis and Discussion of Results 14

4. Ventilation Test 25

4.1 Objective of the Test 25

4.2 Description of Test Classroom and School Schedules 28

4.3 Test Setup and Instrumentation 36

4.4 Discussion of Test Results 38

4.5 Estimate of CO2 Concentration Under Natural Air Infiltration Condition . . 54

5* Conclusions 55

6. References 58

7. Appendix - Calculation of Air Exchange Rates From Tracer Dilution Measurements . 59

iv
List of Tables

Table 1 Description of the 19 Schools Included in the Energy Consumption Survey

Table 2 Three-Year Averaged Monthly Electricity Consumption in 19 Schools

Table 3 Three-Year Averaged Monthly Fuel-Oil Consumption in 19 Schools

Table 4 Operation Schedules of the 5 Schools Visited

Table 5 Major Data on Buildings in School No. 6 for Computerized Energy Analysis

Table 6 Components of Total Calculated Energy Consumption by Type of Usage for School

No. 6

Table 7 Types of Energy Usage as Fractions of Total Calculated Energy Consumption in

School No. 6

V
List of Figures

Figure 1 Averaged (3-Year) Yearly Electrical Energy Consumption in 19 Schools

Figure 2 Averaged (3-Year) Yearly Fuel-Oil Consumption in 19 Schools

Figure 3 Averaged (3-Year) Yearly Energy Requirement in 19 Schools

Figure 4 Schematic of School No. 6

Figure 5 Lighting Schedules of School No. 6 During a School Day (Heating Season)

Figure 6 Occupancy Schedules of School No. 6 During a School Day (Heating Season)

Figure 7 Ventilation Fan Schedules of School No. 6 During a School Day (Heating Season)

Figure 8 Comparison of the Monthly Average Temperatures for the Selected Weather Year and

the Years 1970-1973

Figure 9 Comparison of Predicted and Actual Measured Monthly Fuel-Oil Consumption in School

No. 6

Figure 10 Comparison of Predicted and Actual Measured Monthly Electrical Energy Consumption

in School No. 6

Figure 11 Comparison of Actual Measured Monthly Fuel-Oil Consumption With Corresponding

Predicted Values

Figure 12 Comparison of Actual Measured Monthly Electrical Energy Consumption With Corresponding Predicted Values

Figure 13 Schematic of the Classroom in School No. 10 Used for the Ventilation Test

Figure 14 Schematic of a Window Section of the Ventilation Test Classroom

Figure 15 Photograph of the Floor Exhaust Grille in the Test Classroom

Figure 16 Photograph of the Ceiling Exhaust Grille in the Test Classroom

Figure 17 Variation of the Outdoor Dry-Bulb Temperature During the 4-Day Ventilation Test Period

Figure 18 Variation of the Outdoor Relative Humidity During the 4-Day Ventilation Test Period

Figure 19 Variation of Outdoor Wind Speed During the 4-Day Ventilation Test Period

Figure 20 Photograph of the Relative Humidity Sensor and Thermocouple Setup in the Test Classroom

Figure 21 Photograph of the Test Setup in the Classroom for Ventilation Tests

Figure 22 Photograph of the Instruments Used in the Ventilation Tests

Figure 23 Indoor Air Temperature Variation During One Class Period (Normal Condition, Both

Grilles Open)

Figure 24 Indoor Air Temperature Variation During One Class Period (Ceiling Grille Blocked)

Figure 25 Indoor Air Temperature Variation During One Class Period (Both Grilles Blocked)

Figure 26 Variation of Indoor Air Temperature During One School Day (Both Grilles Blocked)

vi
Figure 27 Variation of Indoor Relative Humidity During One School Day (Both Grilles Blocked)

Figure 28 Variation of Indoor

Both Grilles Open)

CO2 Concentration During One Class Period (Normal Conditions,

Figure 29 Variation of Indoor

Blocked)

CO2 Concentration During One Class Period (Ceiling Grille

Figure 30 Variation of Indoor

Blocked)

CO, Concentration During One Class Period (Both Grilles

Figure 31 Variation of Indoor CO2 Concentration During One School Day (Both Grilles Blocked)

Figure 32 Steady-State Indoor CO2 Concentration Level Vs. No. of Occupants

Figure 33 Decay of Indoor CO2 Concentration in Empty Classroom (Both Grilles Open)

Figure 34 Decay of Indoor CO2 Concentration in Empty Classroom (Both Grilles Blocked)

Figure 35 Estimated Steady-State CO2 Concentration in a Classroom Vs. Air Change Rate

vii

Evaluation of Ventilation Requirements and Energy Consumption

in Existing New York City School Buildings

Stanley T. Liu, Charles M. Hunt, and Frank J. Powell

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

1. Introduction

12 3/'^ Numerous articles and detailed research studies—' '— indicate that the nation con- tinues to face increasing demands for fuel and electrical energy which in turn impose great

pressures on available supplies. This situation, coupled with air and thermal pollution

problems of the nation, caused leaders to declare that conservation of energy resources is

of paramount importance in government and industry.

Energy used in buildings for space heating and cooling, lighting, hot water heating, and

mechanical ventilation constitutes a large portion (32 percent) of energy consumption in the

United States, as was recently documented by a Stanford Research Institute report^,/ . it is

estimated that at least 10 to 20 percent, and maybe as high as 40 to 50 percent^/ of energy

used in buildings could be saved in the design and construction of new buildings by a comprehensive thermal analysis in the design of the building envelope, by a more careful evaluation

of fresh air ventilation requirements and lighting requirements, and by the utilization of

efficient energy conversion equipment.

Public school buildings, as a group, constitute a significant portion of the public buildings in the cities of the United States. The Center for Building Technology of the National

Bureau of Standards, under the sponsorship of the National Science Foundation, and with the

collaboration of the Board of Education of New York City, undertook a study in 1974 on the

pattern of energy consumption, and the effect of ventilation on a classroom environment, in a typical urban public school. The purpose was to obtain detailed information on the energy

usage of school buildings in order to develop guidelines for energy conservation in the design

and construction of future energy-efficient school buildings. This report presents the results

of this study.

Work done at NBS on this project consisted of two parts. The first part involved (1) an analysis leading to the selection of a typical existing school in New York City to be used as

a norm for comparison with a future new energy-conserving school, and (2) a detailed computer

thermal analysis of the selected school using the NBS program called NBSLD^' to determine the

breakdown of its energy usage with respect to lighting, heating, ventilation, and equipment

operation, in order to identify the importance of the major areas of energy consumption in

the new school design. The selection of a typical existing school as a norm was based on a study of the fuel-oil and electrical energy consumption data from May 1970 through April 1973,

of 19 schools of varying size as supplied by the Board of Education of the City of New York.

Field trips to five of the 19 schools were taken jointly with the Board of Education and its

principal investigator, Richard Stein and Associates, to obtain a cypical school schedule and

operating data for various mechanical equipment. These data were then used as input to the

NBS computer program for the thermal analysis.

The second part of this report gives the results of a one-week ventilation test conducted

in a typical urban classroom in New York City to determine the effect of reduced ventilation

on the interior environment, including the concentrations of carbon dioxide and oxygen, the

change in dry-bulb temperature, the variation of relative humidity, and the activity and re- sponse of the students. These results are expected to provide information on the reduction

of the rate of ventilation as a means of reducing the energy consumption.

Details of the above two parts of the project will be discussed in the following sections.

See references at end of text.

1
2. Energy Consumption of Selected Existing Intermediate

and High Schools In New York City

2.1 Analysis of Energy Consumption Data

The electrical energy and fuel-oil consumption data for 19 schools on a monthly basis

for 3 years (May 1970 - April 1973) were furnished by the Board of Education of New York City.

These schools ranged In size from 160,000 to 400,000 square feet (14,860 to 37,160 m^) of gross

floor area and consisted of 6 Intermediate schools and 13 high schools. A brief description

of these schools Is given in Table 1.

The numbering of the schools In Table 1 was chosen to correspond to Increasing electrical energy consumption. From Table 1, It Is seen that most of these schools are of the cavitywall type construction (e.g., 4 Inch (10.2 cm) brick, 2 Inch (5.1 cm) airspace, 6 Inch (15.2 cm)

concrete block), 3 stories high, with a celling height ranging from 9 feet to 11 feet (2.7 to 3.4 m) , and window to exterior wall area ratio of 0.40 to 0.50. Space heating Is provided

mostly by steam via perimeter fin-tube radiators located below the window sills. Most of the

schools have no space cooling. Ventilation is provided by openable windows and roof-top ex- haust fans with an exhaust rate of 560 cfm (0.26 m3/s) per classroom. Classroom lighting is

provided by fluorescent fixtures with an electric power consumption of 2.0 to 2.8 watt/ft2

(21.5 to 30.1 W/m2) floor area.

Data for the 3-year~averaged monthly electricity and fuel-oil consumption for the 19

schools are tabulated in Tables 2 and 3, and the 3-year-averaged yearly energy consumption

data are plotted in Figures 1 to 3.

Figure 1 shows, in order of increasing amount, the yearly electrical energy consumption.

It is seen that the variation in electrical energy consumption of the 19 schools is quite

large, ranging from 3,600 kWh to 15,000 kWh per 1,000 ft^ gross floor area (1.395 x 10^ to 5.81 X 108 j/m2) . Howevei , by eliminating school No. 19, which is a wlndowless school with

a high lighting level of 5.5 watt/ft2 (59.1 W/m2) of classroom area, the range for the remaining 18 schools is 3,600 to 8,700 kWh, with an average of 5,450 kWh per 1,000 ft2 of gross

floor area (1.39 x 108 to 3.37 x 108 J/m2 with an average of 2.11 x 108 j/m2)

.

If, in addition, school No. 18 is also omitted (to be consistent with the average fueloil data discussed in the next paragraph), the average value becomes 5,250 kWh per 1,000 ft2

of gross floor area (2.03 x 10^ J/m2) for the remaining 17 schools.

Figure 2 shows, also in order of increasing amount, the yearly fuel-oil consumption in

gallons/1,000 ft2 (gross floor area). It is seen that the variations for the 19 schools were

also quite high, ranging from 300 to 890 gal/1,000 ft2 (.0122 to .0363 m3 per m2 of gross

floor area). However, when the last two schools (Nos. 18 and 19) are omitted, the remaining

17 schools show a much narrower variation in fuel-oil consumption, ranging from 300 to 520

gal/1,000 ft2 (.0122 to .0212 m) with an average value of 417 gal/1,000 ft2 gross floor area

(.017 m3 per m2 of gross floor area). The reason for the high oil consumption in school No. 19 was probably due to the use of steam for space cooling (absorption chiller), while the

other schools' steam was used only for space heating and domestic hot water heating. The reason for the high oil consumption for school No. 18 is unknown, because no system data were

available for this school.

Figure 3 shows the overall energy consumption pattern both at the building line and at the power generating plant for the 19 schools surveyed, in terms of Btu/ft2 of gross floor

area. The heating value of No. 6 fuel oil was assumed to be 153,000 Btu/gal (4.27 x lOlO j/m^),

and the electrical generating plant efficiency was taken to be 30 percent. It is seen that,

when the last two schools (Nos. 18 and 19) are omitted, the variation of energy consumption

from the lowest consumption school to the highest one for the remaining 17 schools is less

than a factor of 2, with most of them lying in a fairly narrow range (60,000 to 90,000 Btu/ft2

(6.82 X 108 to 10.23 x 108 J/m2) at the building line).

Based on the above analysis, it is seen that for the purpose of the selection of the

typical energy consumption for an existing school, the average yearly value of 5,250 kWh for

electricity and 417 gallons for heating fuel oil, both on a per 1,000 ft2 gross floor area

basis (2.03 x 108 J/m2 for electricity and .017 m^ per m2 of gross floor area for oil), can be used for future comparison purposes.

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2.2 Observations on the Operating Schedules of Existing Schools

The designed lighting level, ventilation rate, type of building shell construction, glass

area, and number of occupants are not the only parameters that affect the energy requirements

of a school building. The v/ay a school is operated (such as the daily and weekly class schedule, the interior temperature setting, and the schedule for turning on and off the various

mechanical equipment components) also has a major impact on its actual energy consumption.

For example, a building with its lights on 24 hours a day will consume twice as much electrical energy as the same building with lights on only half the time. It is estimated that with

every degree increase in thermostat setting above 70 °F (21.4 °C) , 2.5 to 3 percent additional

heating energy is required^./ in a 5,000 degree-day climate. Therefore, for a detailed energy

analysis of a school building, the various operating schedules of the school have to be determined. To this end, field trips to 5 of the 19 schools were taken jointly with the Board

of Education and its principal investigator, the Richard Stein and Associates, to collect

these data. The 5 schools were Nos. 2, 6, 10, 17, and 19. Two of the schools were at the

high and low ends of the energy consumption profile as seen from Figure 3 (No. 2 at the low

end and No. 19 at the high end), while the other 3 schools were closer to the average energy

consumption. The reason for selecting the two extremes was to determine whether there was

any relation between the energy consumption and the operating schedules. The results of this

survey with respect to the daily class schedule, daily lighting schedule, daily heating and

ventilation schedule, weekend schedules, and indoor temperature settings of classrooms, gymnasium, auditorium and cafeteria, are tabulated in Table 4. The information contained in

Table 4 was obtained by observation and talking to the school custodian, engineer, and fireman.

The following summary of the operation of the 19 schools is taken partly from the data

in Table 4, and supplemented by other information recorded during the visits.

1. Daily classes for the intermediate schools start at 8:30 a.m. and end at 2:50 p.m., which is also the period when the classroom lights are on.

2. Daily classes for the high schools start at 7:30 a.m. and end at 4:30 p.m.

3. School space used during nighttime is generally for adult activities and

sports.

4. School space used during weekends is generally limited to Saturday use of the

gymnasium. Schools are generally closed during holidays and during Christmas

and Spring recess.

5. During the heating season, the boilers are fired in the morning approximately

1 1/2 to 2 hours before the students arrive to preheat the school buildings,

and are shut off approximately 1/2 to 1 1/2 hours before the students are dismissed from the school.

6. During the heating season, the classroom exhaust schedule and the gymnasium,

auditorium, and cafeteria ventilation schedules are identical to the boiler

operating schedule.

7. The thermostat settings of the schools are in the 70 to 73 °F (21.4 to 23.1 "C)

range and are locked and controlled by the fireman. However, due to the location and mounting of the thermostats, they are sometimes either blocked accidentally by a cabinet or recessed such that they will not give an accurate control of the room temperature.

8. It is possible to shut off the heat to unoccupied classrooms during nighttimes

and weekends, while maintaining heat to the gymnasium. This is accomplished

by closing the valve leading to the steam supply pipe serving the unoccupied

classrooms. This procedure was carried out by the fireman of school No. 2,

and may partly account for the low fuel-oil consumption shown in Table 1.

9. The auditorium in the schools was usually unoccupied or only sparsely occupied during the school day.

10
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10. School No. 19 was the only school visited that had air-conditioning. The

school was a windowless school with a higher than usual lighting level

(5.5 watt/ft^ (59.2 W/m^) classroom floor area) and a longer than usual

school schedule (open 7 days/week, 52 weeks/year for both teaching and com- munity activities). The boilers supplied steam for space heating during

the winter and for the absorption chillers during cooling season. The windowless design and the operating schedule probably caused the high energy

consumption rate for this school.

The information gathered during the visit to the schools was used as input to the NBSdeveloped building thermal load determination program in order to obtain a detailed energy

consumption pattern of a typical existing school. The computer analysis is described in the

following section.

3. Computerized Analysis of the Energy Consumption

Pattern of a Typical Existing School

3.1 Calculation of Indoor Space Conditions by Building Thermal Simulation

Numerous papers have been published and calculation manuals prepared on the subject of

heating/cooling load determination. Very few of the computerized models, however, have the

capability of handling fluctuations in indoor air temperature as in the case of the schools

studied in this report where the boilers are actually shut down during nonoccupied periods of

time and the indoor temperature is allowed to drift below the set value of the thermostat.

The heat transfer calculations for room temperature prediction are similar to the heating/cooling load calculations. The former, however, are somewhat more complex than the latter

because they require exact heat transfer calculations for heat conduction through exterior

surface and infiltration heat exchange. The National Bureau of Standards, over the last several years, has developed a computer program which computes the room heating/cooling load re- quirement, as well as the temperature fluctuation of a room not heated or air-conditioned,

when the building is subjected to hour-by-hour randomly fluctuating outdoor climatic conditions. The program is called "NBSLD" and consists of various subroutines for calculating heat

gains and losses, which are similar to those recommended by the ASHRAE Task Group on Energy

RequirementsZ^ . One major extension of the program beyond the recommended ASHRAE Task Group

algorithms is a routine called RMTPK, which solves for the hour-by-hour heating/cooling load

requirements or temperature variations, taking into account the transient heat conduction and

thermal storage in the building and internal mass, through the use of a series of simultaneous

heat balance equations. The details of this routine, and the general description of the overall program, are given in references [5] and [8].

3.2 Construction Data and Operation Schedules of the Selected School

In order to aid in the design of new energy conserving schools and to investigate the

application of the NBS computer program NBSLD to school design, one of the schools visited

during the field trip was selected for a detailed analysis of its energy consumption pattern

with respect to its requirements in heating, ventilation, lighting, and mechanical equipment

operation. Once a suitable mode for the energy consumption in an existing typical school is

established, areas of major energy consumption can be identified, and new designs can be

devised and applied to minimize or reduce the energy requirements in these major areas.

The school selected for this detailed study was school No. 6 because its yearly consumption in fuel oil was approximately the average of the 19 schools studied. Since the computer

program "NBSLD" is a thermal energy analysis program and the space heating requirement of a building is intimately associated with the building shell design and ventilation requirement,

emphasis was placed on selecting a school which has an average fuel-oil consumption.

The No. 6 school selected for the analysis is a high school facility having an overall

floor area of 254,000 sq. ft. (23,600 m^) and is located in Queens, New York. The facility

is composed of 3 buildings: a 3-story classroom and administration building, a gymnasium.

13
and a cafeteria and auditorium building with a basement which houses the shops and special purpose classrooms. A schematic of the three buildings is shown in Figure 4. The major features

of the 3 buildings are described in Table 5, and the operating schedules for the lighting, ventilation, and occupancy during weekdays are given in Figures 5 through 7.

During Saturday, only the gymnasium is open (from 10:00 to 17:00 on a 24-hour clock) with

50 percent of the lights turned on, and 100 percent ventilation (from 9:00 to 13:00). The

classroom building is heated from 9:00 to 13:00 due to its fin-tube radiator configuration

where the flow of the steam into the radiator is controlled only by the room thermostat. The

exhaust fans, however, are assumed to be off. The cafeteria and auditorium buildings are not

heated. The whole school is considered closed during Sunday and holidays including the whole

spring and winter recess periods.

During the occupied period, the buildings are assumed to be ventilated with fresh air

according to the rates and schedules shown in Table 5 and Figure 7 . When the ventilation

systems are off, an air infiltration rate of 1/4 air change per hour is assumed for all buildings. The value 1/4 is based on an actual measurement undertaken at school No. 10 which has

a similar type window construction as school No. 6. Details of that test will be discussed

later in this report.

In order to compute the hour-by-hour heating loads or temperature variations, actual

weather data typical of the New York City location were required on an hourly basis for one

year. The school year September 1962 to June 1963 was selected from the ten-year period of

1955-1964. The months included in the selected period contained neither the coldest nor the

warmest month during the major heating season of December to February when compared with the

corresponding months over the ten-year period.

A comparison of the average monthly temperatures for the selected weather year with the

three-year period of 1970-1973, where actual fuel-oil data are available, is shown in Figure

8.

3.3 Analysis and Discussion of Results

The results of the computer simulation are shown in Figures 9 through 12 and in Tables

6 and 7. The computations were done for ten months only, since the school had no cooling

equipment and the summer schedules for the school were not available. The calendar for the

school year 1973-74 was used to determine the dates of holidays and major recesses, because

the selected weather year had the same calendar as the 1973-74 period.

Figure 9 shows the result of the computed monthly fuel-oil consumption in gallons per

1,000 ft^ gross floor area and the 3-year averaged measured fuel-oil consumption, and Figure

11 shows the same result as compared with the measured monthly consumption of the 3-year data

year by year. An average heating value of 153,000 Btu/gal (4.27 x lO^-O j/m^) of No. 6 oil,

and a seasonal boiler efficiency of 65 percent were assumed in converting the heating load to gallons of oil. An average of 3 gallons/1,000 ft^ (12.2 x 10"^ per m2 of gross floor area)

for domestic hot water heating was added to the computed space heating consumption. This particular value was chosen by examining the school oil consumption for the months of May, June,

and September where the only requirement for the fuel oil was for domestic hot water heating.

It is seen that the computed results and the school usage data show fairly good agreement for

both the numerical value and the trend of monthly usage. The agreement between computed and

observed fuel requirement in Figure 9 Indicates that the computer model was a good representation of the energy use processes for this school.

Figures 10 and 12 show the same type of comparison for the electrical energy usage for

the 10-month period. It is seen that the months of January, March, May, June, September, and

October compare fairly well with the actual consumption while the remaining 4 months deviate

significantly from the measured data. It should be noted, however, that those months that

show a substantial deviation all had a number of holidays or major recesses. The schedules

for lighting and equipment operation assumed that the entire school was closed during those

periods, while in actual practice the school may have been opened for either school officials

or for some special purpose such as a major sport event or a stage play or for community use. This can be seen by examining the actual usage data (e.g., the months of December and January

14
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Figure 5 Lighting Schedules of School No. 6 During a School Day

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18
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1970- 1971

1971- 1972

1972- 1973 (INCOMPLETE)

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SCHOOL No. 6 (H.S.)

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20
SCHOOL No.6(H.S.)

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21
SCHOOL No.6 (KS.)

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ACTUAL MEASURED 1971-72

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which had the same electricity consumption). With the school officially closed from December 24 to January 1 for the Christmas recess, the December consumption should be much lower than for

January if the school was in fact closed entirely during the recess. Also, the schedule for

lighting used in the computation was, at best, an estimate of the actual usage pattern which

was subjected to much greater variations than space heating or ventilation equipment operations, since those operation schedules were controlled by a single person, the custodian,

while the lighting switches were accessible to a large number of people.

Table 6 gives a breakdown of monthly energy usage for ventilation, heat loss through

glass, heat loss due to air infiltration and conduction through the building shell, lighting,

ventilation fans, and other miscellaneous equipment. Table 7 gives the various types of energy

usage in terms of fraction of total energy consumption. It is seen from the two tables that

during the heating season (November - February), 76 percent of the heating energy was used to heat ventilation fresb air. The fraction of energy for classroom ventilation was the largest

(27 percent), followed by gymnasium (26 percent), auditorium (14 percent), and cafeteria (8.5

percent) . These data showed that a significant reduction of heating energy could be obtained

by reducing the rate of fresh air intake.

Table 7 shows that the fraction of heating energy used to compensate for heat loss due

to fenestration was 2.5 to 2.9 percent, and for heat loss through the solid parts of the building shell and infiltration, was 17 to 19 percent, with a combined total of about 21 percent.

However, this relatively small fraction does not mean that there is no need to improve the

design of the building shell. The large quantity of heating energy used to heat up the outdoor fresh air for ventilation purpose overshadows the building skin loss. If the fresh air

intake is reduced significantly—for example, by a factor of 2 —the percent building skin loss

will become larger. The heat loss through window glass was the difference between the heat

loss by conduction and heat gain due to solar radiation. This loss represents only 2.5 to 2.9 percent of the total building energy usage and 10 to 14 percent of the total heat loss

through building shell and by infiltration. This is because even though the amount of glass

in the classroom building is large (33 percent, see Table 5), the amounts of glass in the

other two buildings are small and the overall ratio of glass to exposed surfaces, including

roof and ground floor, amounts to only 7 percent of the total building shell area.

Tables 6 and 7 also give the monthly electrical energy consumption for lighting and equipment operation. It is seen that lighting constituted about 80 percent of the total electrical

energy usage and ventilation fans most of the remaining usage. Therefore, any significant re- duction in lighting would reduce the overall electricity usage by a large amount. The power

requirement for ventilation fans will be reduced if the ventilation rate for classrooms and

the air supply rate to the other spaces are reduced.

4. Ventilation Test

4.1 Objective of the Test

As described in the previous section, fresh air ventilation comprises the major heating

energy consumption for the existing schools. Any reduction in the ventilation rate will

therefore contribute significantly to the effort in reducing fuel-oil consumption.

The purposes in providing ventilation air for a classroom are (1) to prevent the buildup

of carbon dioxide gas, and to a lesser extent to prevent the reduction in oxygen supply, to levels considered harmful to the general health of the students; (2) to dilute the intensity

of body odors which may be disagreeable and distracting, in a densely occupied space; and

(3) to provide air movement in the classroom for the purposes of minimizing the temperature

gradient and local pockets of high carbon dioxide or odor concentration.

Chapter 4 of the 1974 Applications Volume of the ASHRAE Guide and Data Booki^ states that,

with regard to health consideration, 1 cfm (0.47 x 10-3 m^/s) of outdoor air per student is

required to provide the necessary oxygen content, and 4 cfm (1,89 x 10-3 m3/g) of outdoor air

per student is required to limit the CO2 concentration to 0.6 percent by volume. These values

are applicable to a room with from 110 to 457 ft^ (3.12 to 12.98 m^) of airspace per student.

In the same reference, the requirement for odor-free air (not necessarily outdoor air) varies

from 29 cfm (13.6 x 10"^ m?/s) per student at 100 ft^ (2.84 m^) of airspace per student to

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27
1

12 cfm (5.64 x 10"^ m^/s) per student at 475 ft-^ (13.49 m^) of airspace per student. The

Occupational Safety and Health Administration (OSHA) of the Department of Labor set the limit

in CO2 concentration for an occupied space at 0.5 percent by volume. Volume 3 of the Shelter

Design and Analys published by the Office of Civil Defense, Department of Defense, rec- ommends a minimum limit of 17 percent oxygen concentration by volume and a maximum limit of

0.5 percent CO2 concentration by volume for prolonged shelter occupancy.

In order to determine the effect of reduced ventilation rate in an existing school class- room located in an urban area, a ventilation test was conducted in the classroom of one of

the 19 schools described previously in this report. The major purpose of the test was to investigate the level of CO2 and O2 concentration prevailing in a classroom under normal educational conditions when the ventilation rate was reduced from the designed rate. The effects

on room temperature and relative humidity were also investigated, and the reactions of the

students and teacher were observed to see whether there were any signs of discomfort.

The school used for this test was school No. 10 listed in Table 1. The arrangement for

NBS to conduct this test was made by R. G. Stein and Associates, with the permission and cooperation of the New York City Board of Education. The period of test was 4 days in April of

1974.

4.2 Description of Test Classroom and School Schedules

The classroom selected for the test was a science classroom used as an instruction class- room for 7th and 8th graders and was located on the second floor of school No. 10 in Brooklyn,

New York. The school was a single building intermediate school with about 1,500 students ranging from the 1st to 8th grade. The overall dimensions of the classroom measured approximately

25 feet wide (7.62 m) and 36 feet long (10.97 m) with a ceiling height of 10 feet (3.05 m)

.

The room was located on the north side of the building with the north wall facing a city street. The two window sections of the north wall measured approximately 10 feet (3.05 m) by 5 feet

(1.524 m) each, and were of the pull-open type with hinges located at the bottom. The windows

were kept closed throughout the 4-day test period. The door in the south side of the room

led into the double-loaded corridor, and the door at the west side of the room near the north

windows led into a small teacher's preparation room which was used as the instrument and working area during the test. Both doors were kept closed when the class was in session. The

east side wall was a solid interior partition wall with classroom on the opposite side. A

schematic of the room is shown in Figure 13, and a window section in Figure 14. Eight fluorescent lighting fixtures of four 40 W tubes each were hung 2 feet (0.61 m) from the ceiling.

Excluding the ceiling beams, columns and the laboratory benches, the room had a net volume of

7,860 ft3 (223 m3) . Two 9.25 inch (23.5 cm) by 13.25 inch (33.7 cm) ventilation exhaust

grilles, each connected to a roof-top exhaust fan with a total design flow rate of 560 cfm

(.264 m3/s), were located just above the floor level near the south door and in the ceiling

near the south column, respectively (Figure 13). Photographs of the grilles are shown in Figures 15 and 16. Fin-tube type radiators were located below the whole length of the window

sill. The steam flow was controlled by a thermostat located at the mid-height of the south

column

.

The school class schedule was from 8:30 a.m. to 2:50 p.m., with two 15-minute home-room

periods at the beginning and end of the school day and eight 40-minute regular class periods

with 4 minutes between each period for the changing of classrooms. Students came into the

classroom one minute before the beginning of a period and left the room at the end of a period.

The exhaust fan system was turned on at 6:45 a.m., run throughout the day, and turned off at 4:30 p.m. Because of the mild spring weather, the boilers were run only 2 hours in the morning before the classes started.

The weather conditions during the 4-day test period were generally mild with a daily tem- perature range from 40 °F to 70 °F (4.8 to 21.4 °C) . The dry-bulb temperature, relative humidity, and wind speed of the 4-day test period are shown in Figures 17 through 19. These data were obtained from the Weather Bureau of New York City.

28
1 ft = 3. OAS X 10

-1

(CORRIDOR)

ROOM SIZE = 25.33'Wx35.75'Lxl0'H (INSIDE WALL TO WALL)

Figure 13 Schematic of the Classroom in School No. 10 Used for the

Ventilation Test

29
1 in. = 2.54 cm

1 ft = 3.048 X

10"-'- m

9'-n"

2'-3"

*TYPICAL

I I I

1 S

THE HINGES ARE LOCATED AT BOTTOM

WITH PULL HANDLE AT TOP. WINDOW

FRAMES ARE STEEL, AND THE GLAZING

IS SINGLE PANE.

Figure 14 Schematic of a Window Section of. the Ventilation Test Classroom

30
Figure 15 Photograph of the Floor Exhaust Grille In the Test Classroom

31
32
33
34
35
4.3 Test Setup and Instrumentation*

Temperature, relative humidity, CO2 concentration, O2 concentration, and air infiltration rate were the quantities measured during the test. The locations of the sensors, measuring instruments, and recording device are described below.

a. Temperature : Three copper-constantan 24-gauge thermocouples were used to measure the indoor temperature variations during the test. They were located

along the center ceiling beam with one at the center of the room and the

others 5 feet (1.52 m) from the north column and south columns, respectively.

These 3 thermocouples were suspended from the ceiling beam 5.75 feet (1.75 m)

above the floor. The locations of the 3 thermocouples are indicated by the

dark circle and the symbol (t^ in Figure 13. One Dewar bottle with a mixture

of water and crushed ice was used as the ice-point reference for the thermocouples. The millivolt output of the thermocouples was recorded on a Strip

Chart Recorder. The output of the thermocouple located at the center of the room was recorded continuously while the output of the other two were checked

once every class period.

b. Relative Humidity : An American Instrument Relative Humidity Transducer (No.

15-7012) was used to measure the indoor relative humidity. The sensor was suspended from the ceiling and located at the same location as the center thermocouple and is represented by the symbol in Figure 13. A photograph of the RH sensor and the center thermocouple as installed is shown in

Figure 20. The millivolt output from the sensor was recorded continuously on

a Strip Chart Recorder. The accuracy of the humidity sensor was checked at selected levels in the range of 10 to 90 humidity using standard salt solutions and was found to have an accuracy of +2 percent.

c. Carbon Dioxide Concentration : At the stations indicated in Figure 13, four

lengths of 1/4 inch (0.64 cm) plastic tubes were suspended over the middle

four lighting fixtures to collect air samples from the classroom. The two

in the front of the room were located 6 feet (1.83 m) away from the chalk

board (west wall), and 13 feet (3.96 m) from the north and south walls, re- spectively. The two in the back of the room were located 7 feet (2.13 m)

from the back wall (east wall) and 13 feet (3.96 m) from the north and south

walls, respectively. The ends of the sampling tubes were 6 feet (1.83 m)

above the floor. The 4 tubes converged into a junction which was in turn connected to a diaphragm type vacuum pump. The output of the vacuum pump was connected to a MSA LIRA 300 Infrared CO2 Analyzer. The millivolt output of

the analyzer was recorded on the second channel of the Strip Chart Recorder.

The analyzer was calibrated before the test, and was checked twice a day with

384 parts per million CO2 concentration standard reference gas, and the zero setting was checked at the same time with pure nitrogen gas.

d. Oxygen Concentration ; Sample gas from the room collected through the plastic sampling tubes through the vacuum pump was also connected to a Bacharach

Instrument Company Model 514-010-00 continuous Electrolytic Oxygen Detector

Cell. The millivolt output from the cell was recorded on the second channel

of the other Strip Chart Recorder. The cell was calibrated before the test and was checked twice a day with a 20.92 percent oxygen concentration standard reference gas, and the zero setting was checked at the same time with

a pure nitrogen gas.

e. Flow Rate Through the Exhaust Grilles : Flow rate through the exhaust grilles

was measured with a vane anemometer at the center and at 4 points located

two inches (5.08 cm) from the sides along the center lines of the grilles.

After the test, one grille was brought back to NBS and the flow rate through

Commercial instruments are identified in this report in order to adequately specify the

experimental procedure. In no case does such identification imply recommendations or en- dorsement by the National Bureau of Standards, nor does it imply that the equipment identified is necessarily the best available for the purpose.

36

the grille was measured by the vane anemometer which was calibrated in the

NBS air filter flow-test chamber.

f. Room Air Change Per Hour : The ventilation rate of the classroom under four

different exhaust conditions was measured by the SF5 tracer dilution method.

A brief description of the principle of the method is given in the Appendix.

These measurements were conducted at the end of each school day after the

students had left the school.

The test was conducted under three different exhaust flow rate conditions.

They were: (1) normal operation condition with both grilles open, (2) one

exhaust grille (ceiling grille) blocked by taping a plastic sheet over the

opening, and (3) both exhaust grilles blocked. In addition, an SF5 tracer

gas measurement for room air change rates was conducted when the ventilation

system in the entire school building was shut off. This measurement was to determine the rate of air infiltration under natural conditions. It should

be pointed out that the room air changes per hour with both grilles blocked

and ventilation system operating was not the same as the natural rate of air

infiltration with the ventilation system off, since the fans in the adjacent

rooms draw air from the test room through the opening under and around the

door via the corridor. The operation of the ventilation system creates a negative pressure difference between the test room and outside and increases

the air change rate over the value caused by natural infiltration alone.

Figure 21 is a photograph of the setup in the test classroom showing the location of the

thermocouples, relative humidity sensor, and the sample air intake tubes. Figure 22 shows

the instruments used for the test which were located in the teacher's preparation room adjacent to the test classroom. The equipment in the front of the photograph is the reference

calibration gas container and the SFg tracer gas equipment. The instruments on the counter

are (from left to right) the vacuum pump, CO2 Analyzer, Oxygen Detector Cell, Dewar Flask,

Strip Chart Recorder, Thermocouple Switch Box, Strip Chart Recorder, Digital Voltmeter, and

D. C. Power Supply.

4.4 Discussion of Test Results

The results of the test under the different ventilation conditions .nre shown in Figures

23 to 34.

a. Temperature and Relative Humidity : Figures 23 through 25 show the variation

of the room temperature during a class period (40 minutes) under the three

test conditions: (1) both grilles open, normal operation, (2) ceiling grille

blocked, and (3) both grilles blocked. The time scales were from the beginning of the class period to the end of the period. It is seen that the tem- perature rose at the beginning of the period when the lights were switched on

and students entered the room. However, the temperature remained within the

range of 70 °F to 80 °F (21.4 to 27.0 °C) throughout the class period. Figures 26 and 27 show the variation of the indoor temperature and relative humidity during a school day under the most severe conditions tested; namely, when

both exhaust grilles were blocked off. (The outdoor temperature and relative

humidity are also plotted on the graphs.) It is seen that the presence of

students and lighting caused the temperature to increase 5 °F (2.8 °C) and the

relative humidity to increase 5 percent. However, both the temperature and

relative humidity stayed within the comfort region of 70 to 80 °F (21.4 to 27.0 °C) and 20 to 30 percent. The variations of temperature and relative

humidity under the other two less severe conditions were similar to Figures

26 and 27 and are not shown. However, it should be pointed out that the outdoor conditions over the 4-day period were very mild. Under a more severe outdoor condition—for example, hot and humid conditions—the blocking of the

grilles and the corresponding reduction in air movement might cause the room

air to become stuffy.

38
39
40
BOTH GRILLES OPEN (4.6 AIR CHANGE/HR.)

CLASSROOM NET V0LUME=7860FT' ( 223 m^)

No. OF OCCUPANTS = 23 (AGE = 12-13 YR.)

OUTDOOR TEMPERATURE = 44° F (7*'C)

*'C = 5/9 (*»F-32)

0 10 20 30

ELAPSED TIME-MIN.

Figure 23 Indoor Air Temperature Variation During. One Class Period

(Normal Condition, Both Grilles Open)

41
<

o

o

o

65-

60

CEILING GRILLE BLOCKED (3.0 AIR CHAN6E/HR.)

CLASSROOM NET VOLUME = 7860 FT^ (223m^)

No. OF OCCUPANTS »25 (AGE» I2~I3 YR.)

OUTDOOR TEMPERATURE = 45.5 •F (7.8 *C)

X = 5/9(*'F-32)

T"

10 20 30 40

ELAPSED TIME-MIN.

Figure 24 Indoor Air Temperature Variation During One Class Period

(Ceiling Grille Blocked)

42
BOTH GRILLES CLOSED (1.25 AIR CHANGE/HR.)

No. OF OCCUPANTS = 30 (I2~I3 YR. OLD)

1st PERIOD OF THE DAY

OUTDOOR TEMP = 57** F (I4.2*»C)

°C = 5/9 (°F - 32)

60

6 10 20 30 40

ELAPSED TIME-MIN.

Figure 25 Indoor Air Temperature Variation During One Class Period

(Both Grilles Blocked)

43

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45
C02 Concentration: Figures 28 through 30 show the buildup of CO2 concentration under the three test conditions. The periods chosen for these graphs are

those which had no students in the classroom during the preceding one or two periods so as to show the rate of CO2 buildup from near normal concentration

conditions (0.05 to 0.07 percent). The air change rate under the three test conditions as measured by the SF5 tracer gas technique was 4.6 air changes per

hour (both grilles open, normal operation), 3.0 air changes per hour (ceiling

grille blocked), and 1.3 air changes per hour (both grilles blocked), respectively. It is seen from Figures 28 to 30 that the levels of CO2 concentration

under all three conditions were far below the 0.5 percent safety limit cited

at the beginning of this section. This is expected, since in terms of cfm per

student the most severe conditions of 1.3 air changes per hour with the 30 occupants in the test room (net volume of 7,860 ft^ or 223 m^) still gave a value

of 5.5 cfm/student (2.60 x lO"^ m^/s per student) which was higher than the

4 cfm/student (1.89 x 10~3 m3/s per student) specified in reference 9. However, Figures 28 to 30 do show that when the air changes per hour were decreased,

it took a longer time for the CO2 concentration to reach a near steady-state

level. The steady-state level increased as the ventilation rate was decreased.

Since the rate of CO2 production for an adult is higher than for a child, it

is expected that the steady-state CO2 concentration level would be higher for

students of high school age, even though the safety limit of 0.5 percent still

would not be exceeded because the ratio of CO2 production for a 12-year-old

child to that of an adult is about 0.7.

Figure 31 shows the variation of the CO2 concentration for a school day when

both grilles were blocked. It is seen that the maximum concentration level

reached was 0.16 percent by volume, and the level decreased rapidly whenever

there was an unoccupied period. The patterns for the other two test conditions were similar and are not shown.

Figure 32 shows the level of CO2 concentration at the end of a class period as

a function of the number of occupants. As would be expected, the level increased

as the number of occupants increased. The scattering in the data points might

be due to differences in age and activity level for the students during different class periods.

It is also possible to estimate ventilation rates from the rate of decay of

CO2 concentration. However, the air entering the space has a finite concentration, and this must be taken into consideration, as indicated in the Appendix.

If the outside air entering the room is assumed to have a concentration of 0.05

percent CO2, the rate of decay shown in Figure 33 corresponds to 4.1 air changes

per hour compared with 4.6 air changes per hour obtained by using SF5 dilution.

There is still residual curvature in the concentration vs. time plot when the

concentration is corrected for CO2 in the incoming air. This suggests that the rate of mixing of tracer with air does not keep up with the rate of ventilation

(11). This is true especially at the higher ventilation rate. A similar analysis of the data in Figure 34 indicates an air exchange rate of 1.3 air changes

per hour, compared with the same value obtained with SFg.

O2 Concentration: Under the three test conditions, no noticeable change in the

the level of oxygen content in the test room was detected. This result was ex- pected, since with the respiratory quotient (or rate ratio of CO2 production

to oxygen consumption) for a normal person being equal to approximately 0. an increase of 0.1 percent in CO2 concentration results in a decrease of less

than 0.2 percent in O2 content in the room. This amount was an order of magnitude below the safety limit of 3 percent decrease from normal level, and was outside the range of accuracy of the detector cell used.

Exhaust Flow Rate Through Grilles and Air Change Measurement : The total ex- haust flow rates through the two grilles were measured by a vane anemometer,

and the air change rates of the room were determined by the NBS SF5 Tracer Gas Technique, for 4 different test conditions, as listed below:

46
1 1 1 1 1 \ 1 10 i5 20 25 30 35 40

TIME -MINUTES

Figure 28 Variation of Indoor CO2 Concentration During One Class Period

(Normal Conditions, Both Grilles Open)

47
IxJ

-JO

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OQ

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o

a:hz

bJO

Z

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CEILING GRILLE BLOCKED (3.0 AIR CHANGE/HR.)

No. OF OCCUPANTS = 25 (I2~I3 YR. OLD)

CLASSROOM NET VOLUME = 7860 FT^(223 m^)

T

5

T"

10 15 20 25

TIME -MINUTES

30 35 40

Figure 29 Variation of Indoor CO2 Concentration During One Class Period

(Ceiling Grille Blocked')

48
.20

18-

.16-

BOTH GRILLES BLOCKED (1.25 AIR CHAN6E/HR.)

No. OF OCCUPANTS =30 (IZ'-IS YR.OLD)

1ST PERIOD OF THE DAY

CLASSROOM NET VOLUME =7860 FT^ (223m^)

1

10 20

TIME- MINUTES

Figure 30 Variation of Indoor CC)2 Concentration During One Class Period

(Both Grilles Blocked)

49
% *(3WmOA A9) NOIlVyiN30NO0^O0%

50
0.5 H

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q:

0.4-

0.3-

UJz 0.2 O

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CO^ CONCENTRATION AT END OF A CLASS PERIOD

(DATA FOR ONE CLASSROOM)

CLASSROOM NET VOLUME = 7860 FT* (223 m^)

(BOTH GRILLES BLOCKED)

1.25 AIR CHAN6E/HR.

- ROOM COi CONCENTRATION AT END OF DAY WHEN

BUILDING IS EMPTY

T

10 20 30

No. OF OCCUPANTS

"T"

40

Figure 32 Steady-State Indoor CO2 Concentration Level Vs. No. of Occupants

51
z> .20-

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TR .09-

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NO .07-

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BOTH GRILLES OPEN (4.63 AIR CHANGE /HR.)

NO STUDENT IN SCHOOL BUILDING

CLASSROOM NET VOLUME =7860 FT^ (223 nrt')

-T—

10

r I r— 20 30 40

TIME -MINUTES

—I

50

Figure 33 Decay of Indoor Concentration in Empty Classroom (Both Grilles Open)

52
DECAY OF COi CONCENTRATION FOR AN EMPTY CLASSROOM

BOTH GRILLES BLOCKED (BUILDING EXHAUST FANS ON)

NO STUDENT IN SCHOOL BUILDING

CLASSROOM NET VOLUME = 7860 FT^ (223 n?)

1.25 AIR CHANGE/HR

TERMINAL VALUE (AMBIENT CONDITION)

10 —120 —I

1

30 40

TIME -MINUTES

—I—

50 —T" 60 —

r

70

Figure 34 Decay of Indoor CO2 Concentration in Empty Classroom

(Both Grilles Blocked)

53
Test

Conditions

Both

Grilles

Open

Ceiling

Grille

Blocked

Both

Grilles

Blocked

Building

Ventilation

System Off

Air Change/Hour 4.6 3.0 1.3 0.23

(SFg Tracer)

Grilles Exhaust 440 cfm 240 cfm 0 cfm 0 cfm

Rate

(Vane Anemometer) (0.208 (0.113 (0 ra/s) (0 m^/s)

m^/s) rn^/s)

It is seen from the above that when both the grilles were blocked but with the

building ventilation system in operation, the test room still had an air change

rate 5 times greater than the rate when the entire building ventilation system

was shut off. It is therefore emphasized here that the results of CO2 concentration and oxygen content discussed in the previous subsections are not applicable to a classroom or a building where no mechanical ventilation system is

provided for the building and the only means of air change is by natural air

infiltration. The natural air change rate would be higher in winter time due

to larger temperature differences between the indoor and outdoor air and due

to higher wind speeds; hov7ever, it is doubtful that the increase would be as large as a factor of 5.

e. Observation of Students' Reaction During the Test Period : During the 4-day

test period, the reactions of the students were observed by a research psychologist of the Sensory Environment Section of NBS. The psychologist sat in on classes and personally assessed the changing classroom environment. Student

comments were noted, and changes in dress, posture, and conduct were observed.

In addition, informal discussions were conducted with the teacher at the con- clusion of each class period.

Throughout the test period, no differences in temperature, humidity, odor, or eye irritation were noted by the observer. No changes in student behavior were

observed. The students showed some curiosity about the test setup and inquired

as to the purpose of the experiment. However, no comments were made indicating

a change in air temperature, or air quality. The teacher was informed of the

changes in test condition at the beginning of each day, and was unable to detect

any difference in the classroom environment.

4.5 Estimate of CO2 Concentration Under Natural Air Infiltration Condition

To avoid the possibility of exceeding the safety limit of 0.5 percent CO2 concentration

in other classrooms not under observation and instrumentation, the most severe condition, in

which the entire ventilation system of the building would be shut off, was not tested.

The CO2 concentration in a room or a building can be estimated by the following equation:

Cr (t) = Cr + j(C - Cr ) + ^\ {1 - exp (-At)}

o j o o VA^ I c

where

Cr (t) = room concentration of CO2 at time t

Cr = room concentration of CO, at time t = o

54
c constant outdoor ambient CO, oN = number of occupants In a room

G = average volume rate of production/occupant

V = volume of room

= air change rate

t = time

The assumptions for the above equation are:

1. constant outdoor ambient concentration level

2. uniform CO^ concentration throughout the room at any time

3. air change with ambient air at constant CO^ concentration level only

Equation (1) can be rearranged to solve for G, giving

To obtain an average CO2 production rate for the students in the test classroom, the test results of Figure 30 were used. From Figure 30, with A<,=1.3,N=30, Co= .0005, Cro = .00068, Cr = .00143 at t = .667 hr,^and V = 7,860 ft^ (223 m3) , the value of G is computed by

using equation (2). The result is G = 0.44 ft^/hr (3.46 x 10-6 m3/s) per student. This is equivalent to about 540 grams per day which can be compared with 642 grams per day reported by

Wang [12] for college students in an auditorium. In reference 9, the production rate of CO2

for a standard seated adult vas given as 0.75 ft^/hr (5.9 x 10-^ m^/s) . Assuming the production rate of CO2 for an eighth grader to be 70 percent of that for an adult, the value for G will be .525 ft^/hr (4.13 x 10-6 m3/s) which is in reasonably good agreement with the computed

value based on test results.

Assuming G = .50 ft^/hr (3.93 x 10"^ rn^/s) for an average eighth grader, the steady-state

concentration of CO2 in the test classroom with 24 students and an outdoor ambient CO2 con- centration level of .05 percent was computed by equation (1) for various air change rates, and

compared with the results obtained from the tests under the three test conditions. The re- sults are shown in Figure 35.

From Figure 35, it is seen that the estimated and the measured results showed excellent

agreement. Figure 35 also shows that for an air change rate of 0.25/hr, the CO2 concentration

in the test room with 24 students would reach a steady-state level of 0.65 percent which would

be higher than the maximum safety limit of 0.50 percent. (It is therefore concluded that for a building without any mechanical ventilation and with the windows closed, natural air infiltration alone could not be relied upon to prevent the CO2 concentration level from rising

above the maximum safety limit.

Under the sponsorship of the National Science Foundation, an analysis on energy consumption and ventilation requirement for an urban school building in New York City was completed.

The tasks involved in this project included (1) the selection of a norm in energy consumption

for comparison with a future energy-efficient school, based on the actual electrical energy

and fuel-oil consumptions of 19 existing schools, (2) a computerized energy analysis of one

of the 19 schools that had an energy consumption close to the norm, in order to determine the

pattern of energy consumption in the school, and (3) a ventilation test in a classroom to determine the effects of reduced ventilation rate on the general environment of the classroom.

(2)

5. Conclusions

55
I.4H

=3§ 1.2.

.8-

.6-

.4-

2-

24 OCCUPANTS {I2'-I3 YEAR OLD)

CLASSROOM NET VOLUME =7860 FT* (223 m^)

AVERAGE PRODUCTION RATE OF C0j,= 0.50 FTVHR/STUDENT

(3.93xl0^m^/sec)

ESTIMATED

O MEASURED

-O.

T

2

T"

3

AIR CHANGE RATE.K'

Figure 35 Estimated Steady-State Concentration in a Classroom Vs. Air Change

56
The electrical energy and fuel-oil consumption data of the 19 schools were provided by

the Board of Education of New York City. It was found that when two somewhat atypical schools were omitted, the overall energy consumption of the other 17 schools varied by a factor of

less than 2. The two atypical schools had a very high consumption rate. Omitting these two schools, the arithmetic values of 5,250 kWh and 417 gallons, both per 1,000 ft^ gross area

(2.03 X 108 J and .017 m^ per of gross floor area) were chosen to be the average yearly

electrical energy and fuel-oil consumptions of a typical school.

Based on the architectural drawings of the schools provided by the Board of Education,

it was found that most of the schools in New York City were of the cavity-wall type construction, 3 stories high, single-pane glass with a window to exterior wall area ratio ranging

from 0.3 to 0.6 for a typical classroom. Ventilation was provided for the classrooms by top

exhaust fans on the roof, and space heating was provided by fin-tube radiators under window

sills using low pressure steam. Except for a few schools, most schools had no space cooling

equipment

.

The computerized energy analysis was performed on one of the 19 schools. The school had

a configuration typical of those described above and had an energy consumption of 4,624 kWh

and 428 gallons of fuel oil on a per 1,000 ft^ gross floor area basis (1.79 x 10^ J for electricity and fuel oil of .0174 m^ per m^ of gross floor area). Using the operating schedules

provided by the school custodian personnel, architectural and mechanical data from the blueprints and the weather data for the year 1962-63 for New York City, a thermal energy simulation was performed using the NBS-developed computer program NBSLD. The monthly electrical

energy and fuel-oil consumption agreed well with the actual measured energy consumption data.

It was also found that 80 percent of electrical energy was used for the lighting of the school

building, and 75 percent of useful thermal energy produced by the fuel oil was used for heating ventilation air. It is therefore concluded that the most effective ways of reducing energy

consumption for any new school, and also for the existing schools, are to reduce the lighting

levels of the classrooms and the ventilation rates (fresh outdoor air). However, these recom- mendations need to be tempered with study of illumination needs and change in ventilation re- quired by local building codes. The electrical energy consumed by the ventilation fans which

comprised 20 percent of the overall electrical energy consumption would be reduced as a con- sequence of the reduction in the ventilation rate. Since the conduction through the windows

and exterior surfaces and infiltration loss comprised 21 percent of the heating energy, improvements in the construction of the building shell will further reduce the overall energy

consumption of a new school.

Ventilation tests were conducted for four days in a classroom used primarily by seventh

and eighth graders. The purpose of the test was to determine the effects of reduced ventilation on the environment of the classroom, with special emphasis on the CO2 concentration and

O2 content. It was found that under three different ventilation rates, ranging from 4.6 to 1.3 air changes per hour, the temperature and relative humidity all stayed within the comfort

range of 70 to 76 °F (21.4 to 24.8 °C) and 20 to 30 percent. No change in O2 content was detected, and the CO2 concentration at the end of a class period in all cases reached a near steady-state level and did not exceed .16 percent by volume, which was far below the safety

limit of 0.5 percent established by the Occupational Safety and Health Administration (OSHA)

.

However, when the school building was not ventilated by any mechanical means, the air change

rate in the classroom was reduced to only 0.23 per hour. It was estimated that under this

condition, the CO2 concentration level would reach a steady-state level of 0.7 percent by volume, indicating that mechanical ventilation was required to reduce this value to the acceptable level of 0.5 percent or less. The estimate of 0.7 percent CO2 concentration was based

on students in the 12- to 13-year-old age group. It would be higher if the students were of

high school age. However, the ventilation test indicates that reduction of the ventilation

level from the present 5 air changes per hour to 1 air change per hour would permit the CO2

concentration or the O2 content to stay within the established safety limits. The ventilation

test of the present study suggests that significant energy savings in new and existing buildings may be achieved by simply reducing the ventilation rates while still maintaining safe

and comfortable indoor conditions. A strong need exists to conduct additional ventilation

tests of the type reported in the present study for the purpose of supplying needed information to building code officials so that suitable ventilation rates for an energy conserving

building can be established.

57
6. References

1. Dupree, Walter G., United States Energy Through the Year 2000, U.S. Department of Interior,

Washington, D.C. 20242 (1972).

2. Rocks, Lawrence, The Energy Crisis: An Analysis, Crown Publishers, Inc., 419 Park Avenue,

S., New York, New York 10016 (1972).

3. Patterns of Energy Consumption in the United States, Stanford Research Institute, Menlo

Park, California 94025, for Office of Science and Technology, Executive Office of the

President, Washington, D.C. 20506 (1972).

2 4. e = mc , NBS/GSA May 23-24 Roundtable on Energy Conservation in Public Buildings, General

Services Administration Report, July, 1972.

5. Kusuda, Tamami, NBSLD - National Bureau of Standards Heating and Cooling Load Determination Program, APEC Journal, Vol. VIII, No. 6, Winter 1973-74.

6. Technical Options for Energy Conservation in Buildings, NBS Technical Note 789, July,

1973.

7. Procedures for Determining Heating and Cooling Loads for Computerized Energy Calculations,

Task Group on Energy Requirements for Heating and Cooling, American Society of Heating,

Refrigerating and Air-Conditioning Engineers, Inc., 345 East 47th Street, New York, New

York 10017.

8. Kusuda, Tamami, NBSLD - National Bureau of Standards Heating and Cooling Load Determination Program, NBS Building Science Series BSS 69, 1976 (in press).

9. ASHRAE Guide and Data Book - Applications, American Society of Heating, Refrigerating

and Air-Conditioning Engineers, Inc., 345 East 47th Street, New York, New York 10017,

1974.

10. Environmental Engineering for Shelters, TR-20, Vol. 3, Department of Defense, Office of

Civil Defense, May, 1969.

11. Hunt, Charles M. , and Burch, Douglas M. , Measurement of Air Infiltration in a Four-Bedroom

Town House Using Sulfur Hexafluoride as a Tracer Gas, ASHRAE Transactions, Vol. 81, Part

I, 1975.

12. Wang, T. C, A Study of Bioeffluents in a College Classroom, ASHRAE Transactions, Vol.

81, Part I, 1975.

58
Appendix - Calculation of Air Exchange Rates From Tracer Dilution Measurements

Tracer gas is distributed uniformly throughout the ventilated space, and the concentration is measured as a function of time. The rate of decrease of tracer concentration may be

represented by the relationship — = (c^ - c) ^ (lA)

where

c = tracer concentration in the space at time t

c = tracer concentration in the outside air entering the ventilated space

oV = volume rate at which outside air enters the space

V = volume of the ventilated space

In the case of SFg tracer gas Cq is usually o, and equation lA reduces to

dc ^ V (2A)

dt " ^ V

In ^ = - ^ t (3A)

c^ V

where c^ = initial concentration of tracer. If v, V, and t are in consistent units v/V is

the infiltration rate in air changes per unit time. Thus, if In (c/c^) is plotted against

time, the infiltration rate is obtained from the slope.

59
HBS--1t4A tREV. 7^73)

U.S. DEPT. OF COMM. \, PUBLICATION OR RF.PORT NO. 2. Gov't Accession BIBLIOGRAPHIC DATA No. SHEET NBS BSS 97

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Evaluation of Ventilation Requirements and Energy Consumption

In Existing New York City School Buildings

5. Publication Date April 1977

6. Performing Organization Code

7. AUTHOR(S)

Stanley T. Liu, Charles M. Hunt, and Frank J. Powell

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4624414

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Division of Advanced Technology Applications

National Science Foundation

Washington, D.C. 20550

13. Type of Report & Period Covered Final Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 77-608072

16. ABSTRACT (A 200-woTd or less (actual summary of most si^ilicant information. If document includes a significant

bibliography or literature survey, mention it here.) A study was made, under the sponsorship of the National Science Foundation and In

collaboration with the New York City Board of Education, of the energy consumption and

ventilation requirements of typical existing urban public schools, for the purpose of

determining the pattern of energy usage In such public schools so that effective energy

conservation measures can be taken both for existing schools and for future new school

design.

Electricity and fuel-oil consumption data from May 1970 through April 1973 on 19

existing schools provided by the New York City Board of Education were analyzed. Analysis showed that the overall energy consumption of 17 of the 19 schools varied by a factor of less than 2. Average yearly consumptions per 1,000 ft^ (92.9 m^) gross floor area of 5,250 kWh of electrical energy and 417 gallons of No. 6 fuel oil (2.03 x lO^ j

and 0.017 m3 per m^ of gross floor area), were selected as a norm typical of the existing schools. These figures correspond to 82,400 Btu/year- (gross) ft2 (29.7 W/m^) at the

building line or an estimated 126,000 Btu/year- (gross) ft^ (45.4 W/m^) when calculated

in terms of raw fuel at the generating plant. The figures can be used for future com- parison purposes with a new energy conservation school. A computerized thermal energy

simulation, using the program NBSLD, was performed on one of the schools having an energy

consumption close to the norm. The results showed good agreement between the predicted

17. KEY WORDS Csix to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name: separated by semicolons) Concentration; Computerized thermal simulation; energy con- servation in schools; energy consumption; energy utilization in schools; oxygen content;

reduced ventilation rate; school operation schedule, ventilation test

18. AVAILABILITY Ix^ Unlimited

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16. ABSTRACT {A 200-word or less [actual summary ot most sigpidcant information. If document includee a significant

bibliography or literature survey, mention it here.)

Continuation

and measured monthly electricity and fuel-oil consumption data. Detailed analysis of

the pattern of energy consumption showed that 75 percent of the thermal energy during

the heating season was used for the heating of outdoor air for ventilation purposes,

and 80 percent of the electrical energy was used for lighting.

A ventilation test was conducted over a 4-day period in a typical classroom. It was found that a reduction of the air change rate from the normal 4.6 changes per hour

to 1.3 changes per hour did not significantly change the indoor environment as expressed

in terms of temperature, relative humidity, oxygen content level, and CO2 concentration

level. However, computation indicates that, when no mechanical ventilation was provided, the CO2 concentration level would exceed the 0.5 percent safety limit, indicating that natural air infiltration alone will not provide adequate ventilation for the

general health and safety of the students.

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