View All Issues » December 2011

The typical approach to calculating a degree day would be to take the high and low temperature for the day, add them together, divide by two and subtract that number from 65. This historical method of calculation works very well when the only source of heat is either oil or propane. When a heat pump is used as an additional heat source, this calculation can result in poor delivery drop sizes. Typical heat pumps can generate heat when the outside temperature falls as low as 35-40 degrees, and can eliminate the need to produce heat from the primary oil or propane furnace until temperatures drop below those points.

Some of our customers have found a creative method in ADD Energy E3® to forecast heat pump accounts. These users created a new “heat pump” climate table (aka, degree day table) and assigned these delivery locations to it. They run SETD every day for these degree day tables, but don’t accumulate degree days until the average temperature falls below the temperature where heat pumps lose their effectiveness. For example, assume that point is 40 degrees. As long as the average temperature is 40 or above, you would accumulate zero degree days per day in the heat pump climate table. However, once the average temperature falls below 40, you would accumulate degree days using the standard formula, subtracting the average temperature from 65. For example, if the average temperature on a given day is 35, you would accumulate 30 degree days for that day. This method has improved delivery drop sizes for a number of ADD customers.