Motion Picture Herald (Jul-Aug 1936)

maintenance tabs Title and text copyrighted 1936. Reproduction of any part without permission is expressly forbidden AIR-CONDITIONING COSTS: Many operators of theatres talk of air-conditioning, and when told the cost are absolutely astounded. For those who are interested in approximate costs, the following data is given. Though I don't like to pass along any rules of thumb, nevertheless if this will make some theatre operators cost-conscious before they ask three or four companies or engineers to survey jobs, it is worth while in this instance. The following may be used with a fair degree of accuracy for situations north of Richmond, Virginia on the Atlantic coast, and as far west as Cleveland or Detroit: Based upon (I) outside design conditions of 95° dry bulb and 78° wet bulb, and (2) inside conditions of 80° dry bulb and 50% relative humidity, and (3) 5 cubic feet of fresh air per minute per person, and (4) fan capacity to circulate a total of 20 cubic feet of air per minute per person (5 of which is fresh air) — Sensible heat gain: I 10 b.t.u. per seat for light and wall losses: 193 b.t.u. per seat for people heat; 75 b.t.u. per seat for fresh air, equals a total sensible heat gain of 378 b.t.u. per seat. Latent heat gain: 153 b.t.u. per seat for people moisture; I 17 b.t.u. per seat for fresh air moisture; equals a total sensible heat gain of 270 b.t.u. per seat for moisture. Total heat gain per seat equals sensible heat and latent heat, equals 378 plus 270, equals 648 b.t.u. per seat per hour. Therefore, 648 b.t.u. per seat per hour times number of seats in theatre, divided by 12,000 b.t.u. per hour per ton, equals required tons of refrigeration for air-conditioning. Air-conditioning for summer only (not including winter heating coils), completely installed, averages about $15.25 per seat. Smaller theatres may exceed this unit cost, while larger theatres may run lower. Summer air conditioning costs complete averages from $225 to $260 per ton of refrigeration. Hence, required tons of refrigeration (as obtained with above equation) multiplied by $242.50, equals approximate cost of the job. FAN PULSATION: Frequently of late I have had theatre managers tell me that the delivery fan in their theatres seems to pulsate, that is, to blow air strongly for a few minutes, then seem not to be blowing any air at all. I have encountered this situation several times myself, and here is my analysis of it: Every blower, because of its inherent design and the r.p.m. at which it is operating, has a certain definite pressure characteristic. For instance, if you connected the blower to a large balloon it would blow air into that balloon until the pressure in the balloon would equal the blower's pressure characteristic, and after that it would just churn up air and not put any more into the balloon. If some air gradually escaped from the balloon, thereby lowering the pressure in the bag, the blower would again force air into the balloon until the pressure inside equaled the "pressure capacity" of the blower. This is just what happens in some casts in theatres. This condition can be corrected by any one of several methods: (I) Increase the r.p.m. of the blower, thereby increasing its "pressure capacity." (2) Provide gravity vents so that air in greater quantities can escape quickly from the auditorium. (3) Provide a mechanical exhaust from the auditorium. (4) If the existing fan is delivering more than sufficient air into the auditorium, then reduce the speed of the fan to balance the rate at which air escapes from the auditorium. This last case is encountered rarely but is possible. Another possible correction in a case where refrigeration is used is to increase the amount of recirculated air, and decrease the amount of fresh air. The general fault causing this condition is that the designing engineer selected a fan with too low a static pressure (indicated S.P. in fan catalogs) characteristic, or "pressure capacity," as I have used the term here. personally, have never known of them charging anybody for their service. REACTION OF EYES Let's see just what happens to a person's eye when he comes into a dark the atre from a sun-lit sidewalk. When on the street the pupils of the eyes have contracted because of too much light, then upon suddenly entering an almost unlighted auditorium, the pupils try to enlarge quickly to get all the light they can. This physi cal reaction, taking place so quickly, is not only blinding, but extremely uncomfortable. Then, with the pupils of the eyes wide open, the person finally arrives at a seat and turns his eyes on a brilliantly lighted screen. What happens? The pupils must quickly contract again. This contracting and expanding causes a shock that might be campared to jumping back and forth between a very hot shower and an ice cold shower. Some people are so sensitive that they just can't stand it, and consequently, after going through the reverse process upon leaving the theatre, they complain of headaches or a tired feeling in the eyes. The real answer, of course, is to light up your auditorium. It can be done in four out of five theatres. Is your theatre one that suffers from lightatosis? One of the larger lamp manufacturing companies has placed on the market a small compact light meter which costs less than $15. If you can't afford to buy one of these, it might be possible to borrow one in order that you may make a study of the varying light levels you subject your patrons' eyes to as they enter or leave your theatre. EXACT OPERATION OF AIR SYSTEM i could not feel satisfied in completing a discussion of summer operating problems without at least touching upon my pet subject, which is the condition of the air in the theatre. Again, I want to emphasize that there are only a small minority of managers who really know anything about the condition of the air in their theatres. I am not talking only to or of those managers who have some type, good or bad, of air conditioning; I am talking to every man who manages a theatre. If you manage a theatre, the weather ouside and the resulting condition inside should be vitally interesting to you every minute of the day. The outside and inside conditions in general terms, mean nothing; average conditions mean nothing ; exact readings-taken at least four times daily are of the utmost value. DAILY READINGS Every theatre should have some person keep a record of the conditions each day. The average type of thermometer (dry bulb) can certainly be read by any adult person of average intelligence. A good dry bulb thermometer can be purchased for less than $2, so there really is no excuse for not having dry bulb readings at least. In addition to dry bulb readings, wet bulb readings are of vital importance. Relative humidity is a large factor in human comfort. If you don't know how to take wet bulb readings or interpret wet bulb readings, it is certainly high time that you learned, as there are plenty of sources where you can dig up this knowledge, even if you must resort to thumbing over some of your back issues of Better Theatres ! Refer now to the comfort chart (Better Theatres has also presented you with one, and one mav be obtained, along with others, from the publisher) and know definitely 20 Better Theatres