5.8 B7.3. Small consumer Electric Instantaneous Water Heater

The hourly energy use for instantaneous electric water heaters is given by the following equation.

where

WHEUj,elec =                         Hourly electric energy use of the water heater (kWh). HARLj =                         Hourly adjusted recovery load (Btu).

EFj            =           Energy factor from DOE test procedure (unitless).

0.92       =          Adjustment factor to adjust for overall performance. 3413      =          Unit conversion factor (Btu/kWh).

B7.4.  Mini-Tank Electric Water Heater

Mini-tank electric heaters are occasionally used with gas tankless water heaters to mitigate hot water delivery problems related to temperature fluctuations that may occur between draws. If mini-tank electric heaters are installed, the installed units must be listed in the CEC Appliance Database and their reported standby loss (in Watts) will be modeled to occur each hour of the year. (If the unit is not listed in the CEC Appliance Database, a standby power consumption of 100 W should be assumed.)

where

WHEUj,elec               =           Hourly standby electrical energy use of mini-tank electric water heaters (kWh)

MTSBLj                     =           Mini-tank standby power (W) for tank j (if not listed in CEC Appliance directory, assume 100 W)

B7.5.  Large commercial Gas or Oil Storage Water Heater

Energy use for large storage gas is determined by the following equations. Note: large storage gas water heaters are defined as any gas storage water heater with a minimum input rate of 75,000 Btu/h.

where

WHEUj                  =      Hourly fuel energy use of the water heater (Btu). HARLj                  =      Hourly adjusted recovery load (Btu)

SBLj                =      Total Standby Loss (Btu/hr). Obtain from CEC Appliance Database or from AHRI

certification database. This value includes tank losses and pilot energy. If standby rating is not available from either of the two databases, it shall be calculated as per Table F-2 of the 2015 Appliance Efficiency Regulations, as follows:

SBL = Q/800 + 110 (V)1/2, where Q is the input rating in Btu/hour, and V is the tank volume in gallons.

EFFj           =      Efficiency (fraction, not %). Obtained from CEC Appliance Database or from manufacturer’s literature. These products may be rated as a recovery efficiency, thermal efficiency or AFUE.