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his paper will discuss methods

used to solve the problems

related to air conditioning

the Harris County Domed Stadium.

Specically, the problems arose as

a result o the size o the building,

which is larger and greatly dierent

rom any other that has ever been air

conditioned, and thus created design

problems not experienced previously.

Te engineers in this case were embark-ing on a project o unknown problems

in unknown areas. As the work began

to develop, the architects rst inquired

as to whether the proposed building

was practical and easible to air condi-

tion. o orm a better conception o

the physical relationships o the space,

the ollowing will be helpul: Te clear

height o the roo at the center is about

212 t above the playing eld and the

diameter o the circular building is

about 640 t at the point rom which

air is distributed. Te overall area

enclosed is some 9 acres. Seating is

provided or 56,000 or ootball.

Tere were a number o actors that

had to be considered in the easibil-ity study, including, rst, the roo

design. Tis was related to the ability

to grow grass inside the stadium, the

acoustics, the cooling load, and the

problems o heating such a space. Te

second major actor to be considered

BY I.A. NAMAN, P.E., FELLOW/LIFE MEMBER ASHRAE REPRINTED FROM ASHRAE JOURNAL, AUGUST 1966

concerned the air to be circulated. Te

questions that occurred to us were as

ollows:

1. Is the quantity o air required or

cooling and heating within reasonable

limits or practical distribution?

2. What about the eeling o com-

ort related to this amount o air

circulation?

3. How can the air be distributed

over so large an area without extend-ing ductwork to areas where obstruc-

tions could not be permitted?

4. Will the noise o distributing the

air be excessive?

Te next major consideration

concerned the problem o the smoke

Domed StadiumAir-Conditioning Design

I.A. NAMAN, P.E., FELLOW/LIFE MEMBER ASHRAE

Mr. Naman is the ounder o I.A. Naman +

Associates, Inc., a consulting engineering rm

located in Houston. Mr. Naman opened the

rm in 1947 and built it into one o the largest

engineering rms in Houston. One o his sig-

nature accomplishments was designing the

air-conditioning system or the Houston Astrodome in the 1960s.

Mr. Naman graduated rom Rice University with a degree in

mechanical engineering and received his masters in mechanical

engineering rom the University o Illinois.

He has served on the board o Houston Industries, as

a guest lecturer at Harvard University and Massachusetts

Institute o Technology, as a teacher at the University

o Houston and Rice University, and in leadership roles

in technical societies. He is an ASHRAE Fellow and Lie

Member and a Lie Member o the National Society o

Proessional Engineers.

Mr. Naman, now 91, enjoys traveling the world, includ-

ing a world cruise taken last year. He resides part-time in

Houston and part-time at his ranch in Milano, Texas.

The following article was published in ASHRAE Journal, June 2009. Copyright 2009 American

Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. It is presented for educationalpurposes only. This article may not be copied and/or distributed electronically or in paper form

without permission of ASHRAE.

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cloud. Tere is a seeing distance o

about 540 t, as a maximum, rom

which the spectators would be able to

see a ootball clearly.Having observed the smoke cloud

that occurs in open air stadiums

when viewed at night over the crowd,

when oodlights make the smoke

particularly visible, it was realized that

tobacco smoke might possibly present

a real problem. I it were to be a prob-

lem, there was a question as to what

F I G . 1 Smoke tests were conducted in the stadium to determine acceptable limit of smoke cloud.

the solution might be, and more than this, how it could be

examined to begin with.

Another matter which was o particular interest in the

easibility question was in regard to possible weather. An

experience had been reported previously regarding large

dirigible hangars, where unusual weather conditions were

reported to have resulted in rainall inside the hangar, even

though it was not raining outside. Tere was speculation

that we might have such a situation in the stadium where

og, haze, sel-generated turbulence in the nature o a tor-

nado, cloud ormations or even rain, might conceivably be

experienced. Was this something which really could hap-

pen or was it only a ear with no real basis?Te next question concerned the method o temperature

control. How could the temperature be controlled in so

large an area, with particular emphasis on location o ther-

mostats, the type o control automation required, and the

type o air systems required to obtain proper temperature

control. Tere was some concern that temperature sensing

would be difcult in the seating areas at locations where

it would be meaningul. Tere might be some question as

to the particular system rom which the air nally reached

some specic point. Tat is, we might nd that, due to

turbulence, the air in a given area was not always com-

ing rom the same air handling system. Further, with the

extreme height involved, stratication could be particularly

serious, especially in the winter, and there was a question

as to whether this could be avoided.

In arriving at solutions, each o the problems was given

careul consideration and answers were obtained either by

theoretical analysis, experimentation or both. In the roo

design, grass-growing problems had to be examined and

experiments perormed to provide data on such items as:

l. Te amount o light required or growth in the summer.

2. Te amount o light required or keeping the grass

alive in the winter.

3. Te eect o temperature variations on the grass and

the eect o changes in humidity.

4. Te kind o grass best suited or the application.

Te latter, in turn, involved the ability to grow the grass

outdoors in the Houston area as well as its ability to propa-

gate properly under the limited light and controlled condi-

tions inside.

Te acoustical problem was studied, and it was deter-

mined that approximately 50% o the roo area must be

devoted to sound-absorbing materials. Tis limited thelight-admitting areas to those not acoustically treated. In

studying the roo problem it was realized that the amount

o light required or the grass had to be held at a mini-

mum, since this also adds to the cooling load. Te design

o the light admitting panels would also determine the

heating load as well as aect the stratication problem. Te

solutions to the various matters involved in the roo design

took place in several steps. In the rst, there was an ini-

tial consultation with a physicist regarding the amount o

light, in oot-candle hours, that might be anticipated rom

the area o the roo available or admitting light.

Second, a preliminary calculation o the cooling load was

required to prepare early cost estimates and indicate air han-

dling requirements.

Tird, a search o literature was made, relating to the

smoke problem and the planning o proper tests.

Fourth, research was initiated into air distribution in a

large space.

Fith, an analysis was made o the thermodynamics and

psychrometrics o the possible weather problem.

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Sixth, an analysis o the possible air motion patterns and

the manner in which these could aect thermostat operation

was studied. Tis led to a control design which permitted

manual instead o automatic setting o discharge tempera-ture, i it became necessary, as well as the ability to control

any area by any selected thermostat, regardless o location,

depending on air motion pattern. Parenthetically, the very

early determinations o cooling load, air handling volume

requirements, smoke cloud control and air distribution

methods were surprisingly close to the nal calculations and

arrangements and to the actual loads experienced.

All preliminary evaluations showed the project to be easible,

and the architects were so advised, but many areas o doubt

remained, requiring urther analysis and perhaps experimenta-

tion. Ater the architects were given approval to proceed with

preparation o working drawings, each o the problems was sepa-

rately researched, solutions were developed and rened and each

interrelated actor was likewise developed and rened. Te devel-

opment o detailed solutions is o interest and will be discussed.

Te roo design, with light-admitting panels, progressed

slowly and the cooling load, together with associated air dis-

tribution requirements, could not be established nally until

this was settled. It took two years. Te particular matter

which took the greatest amount o time was the determina-

tion o light requirements or the grass. Tis alone requiredone and a hal years o research, even to learn the amount o

light required or the various grasses and to choose a grass

which could satisactorily be used.

Te economics o the roo structure design and light

panels were another major research problem. Many methods

were examined to limit the light and heat in summer and

to increase to a maximum the amount o light in the win-

ter. Te consideration here was o course the act that the

position o the sun varies greatly rom summer to winter.

Houston is located at 30 deg north latitude and in June the

sun is almost directly overhead at noon. In December it does

not rise past 37 deg above the horizon and, as can be readily

seen, the amount o light admitted into the space in June

would tend to be ar greater than that in December. Hence,

i the light available in December were made adequate or

the survival o the grass, that in June would be ar in excess

o the minimum requirements and would greatly increase

the cooling load. Tus, a means o limiting the excess light

and heat in the summer was o particular interest, but was

never achieved within economic limits.

Another interesting matter regarding the roo was brought

out during wind tunnel tests o scale models o the proposed

roo. It was ound that during periods o high wind, the shape

o the roo was such that the wind would be deected in a

manner to cause a negative pressure at the center o the dome.

Tis would cause a decrease o pressure inside the stadium,

with respect to the outdoors, because o the large exhaust open-

ings that were proposed to be located at the very top center

o the dome. Tis lowered pressure within would prevent the

doors rom being opened (since they must open out, by Code)

and people could not get out o the building during such a

high wind. Our solution was to provide emergency switches at

all main exit doors, so that they could be operated to close thedampers in the exhaust openings in the event o an emergency.

Te tobacco smoke problem was o major concern.

Fortunately research conrmed, the only published data that

we were able to discover, that on Madison Square Garden.

Calculations based on the previous work indicated a neces-

sity or accepting a level o smoke that would be termed

commercially acceptable.

It was impractical to try to eliminate the smoke cloud

entirely. Further, economics dictated the use o air reclama-

tion by means o electrostatic lters and activated carbon.

In choosing the acceptable limit o smoke cloud, a simple

experiment was arranged to give simulated visual condi-

tions by the use o a glass box, permitting us to view a

color movie o a baseball game through smoke introduced

into the box. Te smoke density was careully controlled

and properly instrumented to give an accurate visual rep-

resentation o the eect o various smoke densities. Te

greatest density that was considered acceptable was chosen.

A total o about 2 million cm o air is circulated in

the stadium, as determined by the smoke elimination prob-

Houston Astrodome.F I G . 2

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lem and not by the cooling-heating

load alone, although they happened to

agree very closely. en percent outside

air, approximately 250,000 cm, was

required to limit the carbon dioxide

build-up and all o the air had to be

ltered electrostatically in order to

achieve the limit o smoke density

desired. Eye irritation due to tobacco

smoke was limited by treating 627,000

cm with activated carbon.

Te possible weather problem

inside was virtually eliminated by

the realization that the space must

be kept under constant temperature

control at all times, summer and win-

ter. However, condensation on cold

suraces in winter was the only serious

matter that was anticipated ater care-

ul analysis. Other possibilities that

were imagined that could develop were

not ound to be consistent with mete-

orological actors involved.

emperature controls were o par-

ticular interest. More was involved

than just the problem o thermostat

location already mentioned. When

the playing eld itsel is to be used or

seating perhaps 10,000 people, how

could this be handled by perimeter

thermostats? Te large eld area obvi-

ously could not be adequately con-

trolled rom the perimeter and a radio

thermostat was developed that would

control any o the main air handling

units which may readily be switched

to it. Te thermostat can be carried

onto the playing eld and located at

the speakers stand or at any other

convenient spot.

Control problems must be quickly

recognized during an event and any

equipment ailure corrected. Only an

automated, logging arrangement with

alarms or o-temperature indication

could quickly locate the point o trou-

ble and help to determine its source.

Electrostatic air lter ailures must be

alarmed, as well as temperatures, and

o course pilot lights should indicate

equipment operation. A new develop-

ment was an ultra violet smoke density

meter which continually indicates the

smoke cloud.

Reading the article written by I.A. Naman, P.E., Fellow/Lie Member

ASHRAE, on the actors considered in the easibility study and subse-

quent design o the Houston Astrodome, ormerly the Harris County

Domed Stadium, brings back memories o countless baseball and

ootball games I was ortunate to attend there over some orty years.

It is a tribute to Mr. Naman and all involved in the design and

construction o this historic acility that not once during my many

hours spent inside the Astrodome did I eel anything but comort-

able. Temperature, humidity, smoke control (when smoking was

allowed) and the acoustics o the acility were all controlled so well

that, ater getting past the awe o seeing the acility or the rsttime, the environment could be taken or granted.

Most are probably aware o a problem that did surace that was

outside the scope o a mechanical, electrical and plumbing engineer.

Since the roo was designed to allow in the light necessary to grow

grass, there was a glare on sunny days that prevented the elders

in baseball games rom seeing baseballs hit high in the air. To over-

come this problem, the individual roo panels were painted with a

coating. While this solved the elding problem, growing grass inside

became impossible.

Much to the chagrin o athletic purists, the Monsanto Companyhad invented a grass substitute sold under the name Chemgrass.

A RETROSPECTIVE FROM 2009 ON I.A. NAMANS FIRST OF ITS KIND D OMED STADIUM

It was renamed Astrotur ater its use in the dome in 1966.

Astrotur is now used regularly in proessional and high school

stadiums across the country. From an engineering standpoint,

refecting light rather than having it pass through the roo over

9.5 acres probably had a substantial reduction in the cooling

load, but added to the heating load.

In 2002, Reliant Stadium, a new retractable-rooed stadium,

was built adjacent to the aging Astrodome within Reliant Park.

The historic acility is now rarely used and only hosts occasional

concerts and high school ootball games and currently has no

major tenants. In its ailed bid to host the 2012 Olympic Games,Houston included renovating the Astrodome or use as a main

stadium. The dome also garnered widespread attention in the

atermath o Hurricane Katrina in 2005 when thousands o

evacuees rom New Orleans were housed there.

The Astrodome was a rst o its kind. Thanks to Mr. Naman

and the design team or the Astrodome, the design o the many

indoor stadia that ollowed was made simpler by the success o

this pioneer.

Hugh McMillan III, P.E., Member ASHRAE

Senior Mechanical Engineerccrd partners, Houston