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1948-49 Theatre Catalog, 7th Edition, Page 454 (441)

1948-49 Theatre Catalog, 7th Edition
1948-49 Theatre Catalog
1948-49 Theatre Catalog, 7th Edition, Page 454
Page 454

1948-49 Theatre Catalog, 7th Edition, Page 454

had the opportunity to project several special cases as to air distribution and return in theatres;

I think that air distribution from ceiling outlets is about the most perfect way this problem can be solved in theae tres. At least, all theatres built in this city in the last years have been designed with ceiling outlets. With ceiling outlets assuring uniform air distribution the location of return air intakes is of secondary importance, although even in these circumstances return grilles located only below the stage do not give quite satisfactory results, as we had the opportunity to prove in one such case.

There are special cases, howevere mostly in small theatres with other floors above the theatre where it is impossible to provide ceiling air outlets. In these cases good air distribution becomes a delicate problem and the location of return air intakes gains more importance in order to help to establish a satisfactory. air distribution.

Some years ago we had to face a problem of a small theatre similar to that described by HT.L/i The auditorium is 97 ft. long, 33 ft., 4 in. wide with 18 ft., 8 in. ceiling height at the screen and 13 ft. ceiling height at the other end. At one side of the conditioned space we found a passage which gave us opportunity to place a supply duct outside the longitudinal wall of the theatre with side wall inlets for air distribution. After careful consideration we reached the conclusion that to assure satisfactory air circulation the main return duct would run parallel with the main supply duct but, of course, at a low level. Placing the return air intakes on the lower part of the same side wall where supply grilles have been placed and with a correct supply air velocity, the air will have to travel across the Whole width of the theatre, returning at about floor level.

The sketches (Fig. 4) show the longitudinal and transverse sections of the theatre. It may be noted that return air intakes have been placed not exactly below supply grilles, but always between two supply grilles.

The job described was completed six years ago and furnishes year Around conditioning to the theatre. In all these .V'eal's not a single complaint has been received as to drafts or faulty air distl'ibution.-
G.S.C. thinks the job can be done satisfactorily.

In the original statement of conditions, the ceiling height at the rear of the theatre was given as 8 ft. This seems too low, and therefore our com ments are based on an 18 ft. ceiling, Which is more normal.

Further, no information is given as to the exposure of the building. WhethRT or not there are adjoining buildings Which are heated or cooled or both makes quite a difference, particularly for those seats near the side walls. We have assumed that there are no adjoin"lg buildings, since that is the more severe condition.


We are of the opinion that a year 7round conditioning system using side wall supply outlets and return air intakes located in the 2 ft., 4 in. rise in front of the stage can be designed to give fairly satisfactory, albeit not perfect, results.

Exhausl' of Ventilation Air

HT.LF is concerned because no provision is made for exhausting an amount of air equal to that supplied for ventilation. It has been our experience that if the main supply fan is designed for 1A3 to 14 in. static pressure above that calculated as required and if the return air duct and the outside air duct are equipped with volume dampers which can be relied upon to control air flow, by adjusting the return air and outdoor air dampers, the proper amount of O.A. will be introduced into the conditioned area which will in turn force out the required amount through entrance doors, window crack, etc. In very tight construction it may be necessary to pros vide ventl openings to the outside to facilitate this exhaust. Such design will also keep infiltration to a minimum.

Further, the ventilation which is required by the projection room, and more than likely by the restrooms, can be designed to act as exhaust from the main theatre area. Also, under conditions where the heat load of the projection or restrooms is small, the amount of heating or cooling required can be supplied by the air drawn through these rooms as it is being exhausted from the theatre. Generally such design is practical if the resultant projection or restroom temperatures are not more than 3 to 5 deg. warmer or cooler than the theatre proper.

So much for the exhaust problem, other worry seems to come from the fact that all of the R.A. is taken from the stage end of the theatre. Assuming 20,000 cfm. supply air, 7500 cfm. outdoor air, and 12,500 cfm. return air, there will be definite air motion both toward the return intakes and also the entrance doors, projection room, and restrooms. If there is the normal aisle between the front row of seats and the stage rise, there should be no discomfort from air flow over the patrons. For if all of the R.A. crosses the aisle within 3 ft. of the floor, using the width of the theatre, there would be an air velocity of 82 to 83 fpm. Actually, assuming an aisle width of 8 ft., the air flow at the first row would be taking place through a cross-section at least 45 by 8 ft., which would result in a velocity of 35 to 36 fpm. The return air grilles should extend more or less completely across the stage rise. By using the space below the stage as a return air plenum and letting the return air intake grilles merely empty into this space, and then having the return air duct draw from this area at the most convenient location, the ductwork can be simplified at no disadvantage to performance.

So, it seems to us that the problem of exhaust and return air can be met with fair satisfaction. To us the real problem is to keep uniform conditions

throughout the area, particularly for the one or two seats nearest the side walls. At this location the circulation due to the supply air diffusion is least edective. On the heating cycle, if there are to be any cold drafts down the wall due to heavy heat losses, they will be most severe at this point; on the cooling cycle this is the location most likely to be in an eddy and therefore slightly warmer. However, since the length of blow of the supply outlets is only 23 to 25 ft., half the theatre width, the outlets will be comparatively small and rather closely spaced. Therefore the use of outlets giving high diffusion effect should induce sufiicient air motion to make even the seats nearest the wall not uncomfortable.

In short, by taking advantage of the projection room and the restroom exhaust system to stimulate air movement I in the rear of the theatre, and by using a fan which can introduce the required amount of outside air against a slight internal pressure, thereby getting the required exhausting through the entrance, etc., we think that the system can be designed to be satisfactory. At the same time we agree that this is not the best layout, and it seems unfortunate that the system cannot be designed for maximum performance.

Disagrees With "S.R.L."

We cannot agree with "S.R.L." that return air intakes near the door will ffbe sure of trouble." It is our experience that low return air intakes are quite satisfactory except when there are appreciable amounts of smoke, etc., to be removed. Since most supply outlets tend to create an eddy area about onethird of the distance from the grille to the floor, under such smoke conditions an exhaust or return air intake drawing from this intermediate level is very effective, particularly with high ceilings. Contrary to, the use of overhead return air intakes can definitely short circuit air away from the room.

The use of 100 percent outside air during those seasons when it is the proper temperature is very eEective if the controls are intelligently and thoroughly used. However, this requires either a very competent operator ifon the jobii or a fairly elaborate control setup. When such 100 percent outside air operation is used, a secondary positive exhaust system is generally requiredeG.S.C.

With this letter, the symposium on air distribution in a theatre came to an end

in the November, 1947, issue of uHeating, Piping and Air Conditioning." To Editor C. M. Burnam, Jr., and to the anonymous participants in the symposium, the editors of THEATRE CATALOG extend very grateful acknowledgments. It is often true that the experts never agree, but it is also true that a wealth of information is generated in the course of the argument. The discussion presented above falls into both categories.
1948-49 Theatre Catalog, 7th Edition, Page 454