With The Building Load Coefficient

In Section 9.1.2 it was shown that building heat loss is proportional to the indoor-outdoor temperature difference. Our review of different building components, including infiltration has demonstrated that each individual component can be assigned a proportionality constant that describes that particular component's behavior with respect to the temperature difference imposed across it. For a wall or window, the proportionality constant is the U-factor times the component area, or "UA." For a slab-on-grade floor, the proportionality constant is the F-factor times the slab perimeter, or "FP." For infiltration, the proportionality constant is 0.019 time the air flow rate in cubic feet per hour. While not attributed to the building envelope, the effect of ventilation must be accounted for in the building's overall temperature-dependent behavior. The proportionality constant for ventilation is the same for infiltration, except that it is commonly expressed as 1.10 times the ventilation air flow in cubic feet per minute.

The instantaneous temperature-dependent performance of the total building envelope is simply the sum of all the individual component terms. This is sometimes referred to as the Building Load Coefficient (BLC). The BLC can be expressed as:

BLC = lUA + IFP + 0.018 Q^ + 1.1 Qvent (9.12) Where:

lUA = the sum of all individual component "UA" products

ÏFP = the sum of all individual component "FP" products

QINF = the building infiltration volume flow rate, in cubic feet per hour

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