Book - School of Science and Technology

52 The building in winterInside temperatureIn recent years, following the work by Loudon at the Building Research Establishmentto which previous reference has been made, the Guide Section A5 adopted the conceptof environmental temperature to represent the heat exchange between the surfacessurrounding a space and the space itself. Evaluation of this criterion is dependent uponthe configuration of the surfaces and upon the convective and radiant heat transfercoefficients. For the conditions prevailing in the British Isles, environmental temperaturemay be taken as:t ei ˆ 0:67 t ri ‡ 0:33 t aiwheret ei ˆ inside environmental temperature ( C)t ri ˆ mean inside radiant temperature ( C)*t ai ˆ inside air temperature ( C)It is now a well-established convention that inside environmental temperature is usedfor the calculation of conduction loss and that inside air temperature is used for thecalculation of infiltration loss. However, as was noted in Chapter 1, dry resultant temperatureis that which best represents human comfort and a means to facilitate evaluationof the relationship between the various criteria is thus required. This matter will bediscussed later in the present chapter.Outside temperatureTo represent conditions external to a building, outside environmental temperature is theappropriate standard. This is more usually known as the sol-air temperature which is anotional scale derived from the combined effect of air temperature and solar radiation, toproduce the same rate of heat flow as that which would arise if these influences wereconsidered separately. For winter conditions where overcast skies may be assumed toprevail, the outside environmental temperature will be equal to the outside air temperature.With regard to the outside temperature adopted in the British Isles as a design datum,this will vary depending upon the precise location, the thermal mass of the building andthe overload capacity of the heating plant. It may be of interest to follow the developmentof selection for suitable outside air temperatures for design purposes.In 1950, a committee was set up by various institutions having an interest in this subjectand the report Basic Design Temperatures for Space Heating y examined the frequency ofcold spells and the days per annum when a specified inside temperature might not be metby designs based upon an external temperature of 1 C. One argument brought out in thereport was that a heavily constructed building has sufficient thermal inertia to tide over aperiod of a few days of exceptionally cold weather, whereas a lightly constructed buildinghas no such inherent ability. Conclusions drawn from the report were refined byJamieson z and further emphasis given to the importance of thermal time-lag related tothe overload capacity of the heating system.* In this context, the various room surface areas times their surface temperatures and the product dividedby the sum of the areas.yPost-War Building Study No. 33. Choice of Basic Design Temperatures.zJamieson, H. C., `Meteorological data and design temperatures', JIHVE, 1954, 22, 465.