Document yyamyo9D3zOGKjqLqbN50ron

American Society of Heating and Ventilating Engineers Guide, 1934 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 or less dense air to rise, as where a direct radiation system is installed, the temperature 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 per foot of height apparently decreases as the height of the ceiling increases, ac cording to present available information. It is the common practice of engineers to allow a change in temperature of 2 per cent per foot of height above the breathing line in determining the probable air temperature at any given level for a direct radiation system, and this value is, no doubt, sufficiently accurate in most cases, although it is not probable that this rule applies to heights above 20 ft. 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 unit heaters, fan-furnace 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 heaters, air temperature, and direction and velocity of air discharge. In some cases it has been possible to reduce the temperature between the floor and ceiling to a few degrees, whereas, in other cases, the temperature at the ceiling has actually been increased because of improper design, instal lation 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 tem perature at any given level for any of these types of heating and ventilating systems, unless the manufacturers are willing to guarantee that the par ticular type of equipment under consideration will maintain a smaller temperature differential for the specific conditions involved. Temperature at Floor Level: In determining mean air temperatures just above floors which are next to ground or unheated spaces, a tempera ture 5 deg lower than the breathing-line temperature may be used, pro vided the breathing-line temperature is not less than 55 F. OUTSIDE TEMPERATURES The outside temperature used in computing the heat loss from a build 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 temperatureo 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 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, it is possible that more than 15 deg above the minimum may be allowed, due primarily to' the fly-wheel effect of the heat capacity of the structure. The outisde 106 Chapter 7--The Heating Load temperature assumed and used in the design should always be stated in the heating specifications. Table 2 lists the coldest dry-bulb tempera tures ever recorded by the Weather Bureau. theInf WtheeatrheeproBrtusrefoaru trheeposrttastaiorne nnoetaarevsatilatoblethfiosrltohcealloitcyaalirtey itnoqbueesutsioend,! unless some other temperature is specifically stated in the specifications! In computing the average heat transmission losses for the heating season in the United States the average outside temperature from October 1 to May 1 should be used. WIND MOVEMENT The effect of wind on the heating requirements of any building should be given consideration under two heads: 1 Wind movement increases the heat transmission of walls, glass, and roof, affecting poor walls to a much greater extent than good walls. 2. Wind movement materially increases the infiltration (inleakage) of cold air through the cracks around doors and windows, and even through the building materials them selves, if such materials are at all porous. It is entirely possible that a building may require more heat on a windy day with a moderately low outside temperature than on a quiet day with a much lower outside temperature. It will, therefore, be evident that the wind movement in any locality must be given careful consideration in computing the probable heating requirements of a building, and for the purposes of calculation, not less than the average wind movement in any locality during December, January and February should always be pro vided for in computing (1) the heat transmission of a building, and (2) the heat required to take care of the infiltration of outside air. The first condition is readily taken care of, as explained in Chapter 5, by using a surface coefficientf0 for the outside wall surface, which is based on the proper wind velocity. In case specific data are lacking for any given locality, it is sufficiently accurate to use an average wind velocity of approximately 15 mph which is the velocity upon which the heat transmission coefficient tables in Chapter 5 are based. In a similar manner, the heat allowance for infiltration through cracks and walls (Tables 1 and 2, Chapter 6) must be based on the proper wind velocity for a given locality, as.explained in Chapter 6. In the case of tall buildings, special attention must be given to infiltration factors, as also explained in Chapter 6. HEAT FROM SOURCES OTHER THAN HEATING PLANT The heat supplied by persons, lights, motors and machinery should always be ascertained in the case of theaters, assembly halls, and in dustrial plants, but allowances for such heat sources must be made only after careful consideration of all local conditions. In many cases, Jffiese heat sources should not be allowed to affect the size of the installation at all, although they may have a marked effect on the operation and con trol of the system. In general, it is safe to say that where audiences are involved, the heating installation must have sufficient capacity to bring the building up to the stipulated inside temperature-before the audience 107