The system specified as the primary water heater should be that intended to heat the bulk of the hot water during the course of the year. For example, supplementary electric water heating should be disregarded if provided only for backup where the principal water heating system is from a central heating boiler, as should other devices intended for or capable of heating only limited amounts of hot water.
Supplementary electric water heating should be assumed during the summer months where operation of the main water heating system results in provision of space heating. The secondary water heating fuel type is electricity. DEAP assumes that a fraction of 0.33 of the annual water heating is provided by the supplementary electric water heating.
Where a dwelling has no water heating system present, direct electric water heating is assumed to meet the hot water demand. In this case supplementary electric water heating during summer is not specified as the main water heating is an electrical heat source. If there is no cylinder present, then hot water storage losses are not specified.
Systems where the main water heater can supply domestic hot water (DHW) independent of space heating should not have ’supplementary electric water heating during summer‘ specified. These systems include the following (note that any switches or valves must be accessible by the homeowner and may or may not be located on the boiler control panel):
The following systems should have supplementary electric water heating during summer specified, as the water heating and space heating functions are not independent:
Where there is a heat pump with an immersion, then ’supplementary electric water heating in summer‘ is deselected. The efficiency of the main water heater is determined based on heat pump system data entered in accordance with DHW Heat Pumps section.