Document 0gjDoDe742L7v1ma8OJndJxkM

HEATINC VENTILATING AIR CONDITIONING GUIDE 1943 effective temperature for sedentary persons, as determined at the A.S.H. V.E. Research Laboratory, is 66 deg. According to Fig. 6, Chapter 2; for so-called still air conditions, a relative humidity of approximately 50 per cent is required to produce an effective temperature of 66 deg when the dry-bulb temperature is 70 F. However, even where provision is made for artificial humidification, the relative humidity is seldom maintained higher than 40 per cent during the extremely cold weather, and where no provision is made for'humidifica tion, the relative humidity may be 20 per cent or less. Consequently, in using the figures listed in Table .1, consideration should be given to whether provision is to be made for humidification, and if so, the actual relative humidity to be maintained. Table 1. Winter Inside Dry-Bulb Temperatures Usually Specified3 Type of Building . Dec Fahr Type of Building Dec Fahr Schools-- Class rooms.____ 70-72 Assembly rooms.. :: 68-72 Gymnasiums.. 55-65 Toilets and baths.. . 70 Wardrobe and locker rooms.. 65-68 Kitchens--.;___ ____________ 66 Dining and lunch rooms....... 65-70 Playrooms.........................,----- 60-65 Natatoriums.......----------------- 75 Hospitals-- Private rooms____ Private rooms (surgical).. Operating rooms.________ Wards.______:..............,___ Kitchens and laundries.-- Toilets................. ............... Bathrooms.--....... 70-72 70-80 70-95 68 66 68 70-80 Theaters-- Seating space,......... Lounge rooms Toilets. ....... ' 68-72 68-72 68 Hotels-- Bedrooms and baths Dining rooms. ...... Kitchens and laundries Ballrooms:.............. Toilets and service rooms..1..... 70 70 66 65-68 . 68 Homes. _____ Stores.-.. . ... Public buildings. Warm air baths Steam baths Factories and machine shops Foundries and boiler" shops Paint shops, ____ .- 70-72 65-68. 68-72 120 no 60-65 50-60 80' -------. ............... u. y-uuin temperature to be maintained depends on the relative humidity and air motion. These three factors considered' together constitute what is termed the effective-temperature. (See Chapter 2.) ' ' -~ ' :' \ " Temperature at Proper Level: In making the actual heat loss compu tations, however, for the various rooms in a. building it is often necessary to modify the temperatures given in Table 1 so that the air temperature, at the proper level will be used. By air temperature at the proper level is meant, in the case of walls, the air temperature at the mean height, be tween floor and'ceiling; in the case of glass, the air temperature at the mean height of the glass; in the case of roof, or, ceiling, the air temperature at the mean height of the roof or ceiling above the floor of the heated room; and in the case of floors, the air temperature at the floor level. High Ceilings:. Research data concerning stratification of air in build ings are lacking, but in general it may be said that where-the.increase in' temperature is due to the natural tendency of the warmer on less dense air to rise, as where'a direct radiation system is: installed, the.temperature 130 CHARTER 6. HEATING LOAD of the air at the ceiling increases with the ceiling height. The relation, however, is not a straight line function, as the amount of increase pier foot' of height apparently decreases as the height of the ceiling increases, ac cording to present available information1. Where ceiling heights are under 20 ft, it is common engineering practice to consider that the Fahrenheit temperature increases 2 per cent for each foot of height above the breathing line. This rule, sufficiently accurate for most cases, will give the probable air temperature at any given level for a room heated by direct radiation. Thus, the probable temperature in a room at a point 3 ft above the breathing line, if the breathing line temperature is 70 F, will be [1.00 .+ (3 X 0.02)] 70 = 74.2 F. With certain types of heating and ventilating systems, which tend to oppose the natural tendency of warm air to rise, the temperature differ-' ential between floor and ceiling can be greatly reduced. . These include fan-furnace heaters, unit heaters, and the various types of mechanical ventilating systems. The amount of reduction is problematical in certain instances, as it depends upon many factors such as location of air outlets, the incoming air temperature, and direction and velocity of the air discharge. In some cases it has been possible to reduce the temperature between the floor and ceiling by a few degrees, whereas, in other cases, the temperature at the ceiling has actually been increased because of improper design, installation or operation of equipment. So much depends upon the factors enumerated that it is not advisable to allow less than 1 per cent per foot (and usually more) above the breathing line in arriving at the' air temperature at any given level for any of these types of heating and ventilating systems,, unless the manufacturers are willing to guarantee that the particular type of equipment under consideration will maintain a smaller temperature differential for the specific conditions involved.1 OUTSIDE TEMPERATURES The outside temperature used in computing the heat loss from a builds ing is seldom taken as the lowest temperature ever recorded in a given locality. Such temperatures are usually of short duration and are rarely repeated in successive years. It is therefore evident that a temperature somewhat higher than the lowest on record may be properly assumed in making the heat loss computations.' The outside temperature to be assumed in the design of any heating system is ordinarily not more than 15 F above the lowest recorded tem perature as reported by the Weather Bureau during the preceding 10 years for the locality in which the heating system is to be installed. In the case of massive and well insulated buildings in localities where the minimum does not prevail for more than a few hours, or where the lowest recorded temperature is extremely unusual, more than 15 F above the minimum maybe allowed, due primarily to the fly-wheel.efiect of the heat capacity of the structure. Table 2 lists the coldest dry-bulb temperatures ever recorded by the Weather Bureau at the places listed. Recommended design temperatures are, given in Fig. 1. 1A.S.H.V.E. Research Report No. 958--Temperature Gradient Observations in a Large Heated Space, by G. L. Larson, D. W. Nelson and O. C. Cromer (A.S.H.V.E. Transactions, Vol. 39, 1933. p. 243), A.S.H.V.E, Research Report No. 1011--Tests of Three Heating Systems in an Industrial Type of Build ing, by G. L. Larson, D. W. Nelson and John James (A.S.H.V.E. Transactions, Vol. 41, 1935, p. 185). 131