913 Temperatures for Instantaneous Calculations

The indoor and outdoor temperatures for equation (9.1) are those conditions for which the heat loss needs to be known. Traditionally interest has been in the design heat loss for a building or component, and is determined by using so-called "design-day" temperature assumptions.

Outdoor temperature selection should be made from the ASHRAE Handbook of Fundamentals, for the geographic location of interest. The values published in this chapter are those that are statistically known not to be exceeded more than a prescribed number of hours (such as 2-1/2 %) of the respective heating or cooling season.

For heating conditions in the winter, indoor temperatures maintained between 68 and 72°F result in comfort to the greatest number of people. Indoor temperatures maintained between 74 and 76°F result in the greatest comfort to the most people during the summer (cooling) period.

We will see in later sections that other forms of temperature data collected on an annual basis are useful for evaluating envelope performance on an annual basis.

The next section will take up the topic of how the U-factors for various envelope components are determined.

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