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Working With It - Sizing

Energy Calculations

Energy calculations can be made using one of three basic methods:

  • Degree-day procedure, which is the simplest but give the poorest results.
  • Bin method, which is relatively simple and accounts for the changing outdoor temperature and partial load conditions. This method is often used on single-family homes. Bin weather data is available from ASHRAE.
  • Hour-by-hour method using one of the many software programs available for these calculations. This method is often used for large commercial and institutional system where considerable detail is required to make a good analysis.

The Energy Estimating Methods section of the ASHRAE Handbook of Fundamentals describes in detail these methods and includes examples. Another good reference is chapter three of the IGSHPA Installation Guide.

The bin method requires a load profile for the building. For most residential and light commercial buildings, a simple method of developing the load profile is often used:

  1. Calculate the heating load at the specified winter design outdoor temperature.
  2. Calculate the cooling load at the specified summer design outdoor temperature.
  3. Assume that neither heating nor cooling is required for a certain range of outdoor temperatures, typically from 62 to 67 degrees.
 
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