Document VJ7vLO7kv9Jp91rbravMJ3m1q

American Society of Heating and Ventilating Engineers Guide, 1929 Table 2. Desirable Indoor Temperatures in Summer Corresponding to Outdoor Temperatures Degbsbs Outside Dry Bulb 95 90 85 80 75 70 B Dry Bulb 80.0 78.0 76.5 75.0 73.5 72.0 Degrees Inbids Wet Bulb 65.2 64.5 64.0 63.5 63.0 62.5 Effective Temperature 73.4 72.2 71.1 70.2 69.3 68.2 height. For rooms above this height, add 2 per cent per foot of height to the breathing-line temperature for each foot or fraction of a foot difference between the mean height of the vertical wall,.glass, roof or ceiling surface, and the height of the breathing line. In determining mean air temperatures just above floors which are next to ground or unheated spaces, a temperature 5 deg. lower than breathingline temperature may be used, provided breathing-line temperature is not less than 55 deg. fahr. INSIDE TEMPERATURES FOR SUMMFR Where buildings are being artificially cooled for human comfort during the summer a different scale of inside temperatures is required and this inside temperature must depend to a large extent upon the variation in outside temperatures. It is manifestly undesirable and impracticable to maintain a temperature of 70 deg. inside when it is 95 deg. outside, nor can it be said that the inside temperature should be maintained 15 deg. below the outside temperature. At 95 deg. outside and dry air, a tem perature somewhat lower than 80 deg. might be desirable. On the other hand with 85 deg. outside a 70 deg. temperature inside would be entirely too cold. In other words, the spread between the inside and outside temperature must be varied as the outside temperature varies. Table 2 is based on average moisture conditions outside and upon the assumption of relative humidities inside, between 50 and 60 per cent, which is usual in such installations. OUTSIDE TEMPERATURES IN WINTER The outside air temperature used\in computing the heat loss from a building 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 tem perature 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 must not be more than 15 deg. fahr. above the lowest recorded temperature as reported by the U. S. Weather Bureau (Table 3) during the preceding 10 years for the locality in which the heating system is to be installed. The outside temperature assumed and used in the design should always be stated in the heating specifications. 6 Chapter I--Heat Losses from Buildings . If U. S. Weather Bureau reports are not available for the locality in question, then the U. S. Weather Bureau reports for the station nearest to this locality are to be used, unless some other temperature is specifically stated in the specifications. In computing the average heat transmission losses for the heating season the average outside temperature from October 1 to May 1, shall be used. This is to be that reported by the U. S. Weather Bureau during the preceding 10 years, for the locality in question. GENERAL STATEMENT ON TEMPERATURES AND WIND VELOCITY In order that no misunderstanding may occur, the specifications for all heating systems or plants shall include a clause covering the following points: 1. The lowest recorded outside temperature in the locality, as reported by the U. S. Weather Bureau for the preceding 10 years; 2. The outside-air and inside breathing-line temperatures which were assumed and actually used in making the heat loss computations; 3. The heating load should be calculated on a temperature not more than 15 deg. above the minimum outside temperature recorded for the locality for the preceding 10 years and at a wind velocity which is. the highest recorded in the locality for such temperature (i.e., for a tempera ture 15 deg. above the minimum) for the locality in which the heating plant is located. Both wind velocity and direction are to be taken from the U. S. Weather Bureau records of 10 years. OUTSIDE TEMPERATURES IN SUMMER' The maximum cooling load in summer may be calculated for an outside dry bulb temperature not to exceed 95 deg. and a wet bulb temperature not to exceed 77 deg. While higher outside dry bulb temperatures are frequently observed they are either of short duration or accompanied by low relative humidities. Weather Bureau reports are frequently mis leading in this respect as they report the maximum temperature for the' day with the relative humidity which occurs during a different period and which usually is much higher than the relative humidity occurring at the maximum temperature. Any statement of weather conditions which gives a wet bulb temperature higher than 80 deg. in the United States is questionable. Definition HEAT TRANSMISSION COEFFICIENTS The amount of heat expressed in B.t.u. which is. transmitted in 1 hour per square foot of the material as used in the building, for a difference in temperature of 1 deg. fahr. between the air on the inside and outside of the building, is called the coefficient of heat transmission for the material. The heat transmission coefficient for any given building ma terial depends upon the structure of the material and its density.. Heavy or dense materials, the weight of which per cubic foot is high, usually transmit more heat than light or less dense materials, the weight of which per cubic foot is low. 7 X