The hourly energy use of storage gas or
oil storage water heaters is given by the following equation.The hourly energy use of storage gas or
oil storage water heaters is given by the following equation.
|
WHEU = HARLj × HPAFj j LDEFj |
Equation 32 |
where
WHEUj = Hourly energy use of the water heater (Btu for fuel or kWh for electric). The above equation provides a value in unit of Btu. For electric water heaters, the calculation result needs to be converted to the unit of kWh by dividing 3413 Btu/kWh.
HARLj = Hourly adjusted recovery load (Btu). HPAFj = 1 for all non-heat pump water heaters.
LDEFj
= The annual load dependent
energy factor (LDEF) is given by Equation 33. This equation adjusts the nominal EF rating
for storage water heaters for different load conditions.
|
é æ æ AAHARLj × 24 ö öù LDEFj = min êLDEFmax , max ç LDEFmin , ln çç ÷÷ (a × EFj + b) + (c × EFj + d )÷ú êë ç è 1000 ø ÷úû è ø |
Equation 33 |
where
a,b,c,d = Coefficients from the table below based on the water heater type.
|
Coefficient |
Storage Gas |
|
a |
-0.098311 |
|
b |
0.240182 |
|
c |
1.356491 |
|
d |
-0.872446 |
|
LDEFmin |
.1 |
|
LDEFmax |
.90 |
 |
AAHARLj = Annual average hourly adjusted load (Btu) = 1 ∑HARL . Note that calculation of
j8760
1
AAHARLj requires a preliminary annual simulation that sums HARLj values for each hour.
EFj = Energy factor of the water heater (unitless). This is based on the DOE test procedure. EF for storage gas water heaters with volume less than 20 gallons must be assumed to be 0.58 unless the manufacturer has voluntarily reported an actual EF to the California Energy Commission.