You can adjust for seasons: During the summer, you can have the air conditioner stay off during the cooler morning hours and start cooling the house as everyone gets up and starts moving around. During the winter, you can have your heater stay off while you are away at work and turn on about a half hour or so before you get home so that you are coming home to a nice, warm house.
The most recognized standards for HVAC design are based on ASHRAE data. The most general of four volumes of the ASHRAE Handbook is Fundamentals; it includes heating and cooling calculations. Each volume of the ASHRAE Handbook is updated every four years. The design professional must consult ASHRAE data for the standards of design and care as the typical building codes provide little to no information on HVAC design practices; codes such as the UMC and IMC do include much detail on installation requirements, however. Other useful reference materials include items from SMACNA, ACGIH, and technical trade journals.
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