Estimating Fuel Requirements and Heating Costs
Estimating fuel requirements and heating costs is not an exact science. It involves too many variables to be anything other than an estimation. Moreover, there are four different formulas used for making these calculations. Depending on which formula is used, it is possible to arrive at four different estimations of fuel requirements and heating costs for a specific situation. It is no wonder, then, that two competent engineers can submit estimates that will differ as widely as 30 percent or more. These facts are not offered to discourage anyone but to present the true picture. Any attempt to calculate fuel requirements and heating costs will not produce precise figures—only an estimate. The problem is to make this estimate as close an approximation to the real situation as possible.
The four formulas used in calculating fuel requirements and heating costs are:
1. Heat loss formula
2. Corrected heat loss formula
3. NEMA formula
4. Degree-day formula
If one formula is used to calculate the fuel requirements and heating costs with one type of fuel (e. g., oil) and another formula is used for a second type (e. g., natural gas), the results are practically worthless for comparison purposes. For example, the NEMA formula (created by the National Electric Manufacturers Association) will present the use of electric energy much more favorably if the results are compared with calculations for oil or natural gas based on the heat loss formula. A true comparison is possible only when two fuels are both calculated with the same formula. Each of these formulas is described in the following sections.
Posted in Audel HVAC Fundamentals Volume 1 Heating Systems, Furnaces, and Boilers