The power consumption of the electrical heater also had an
important effect on the system effectiveness. The electrical heater
in Exp. 2 approximately started at 9.0 min, which was later than
that in Exp. 1 (at 6.0 min). And the running duration of the electrical
heater in Exp. 2 (5.0 min) was shorter than that in Exp. 1
(7.0 min). The power consumption of the electrical heater in these
two experimental schemes were 1495 kJ and 1017 kJ, respectively.
The temperature of the incoming tap water supplied to the HWT
was improved by the water pre-heated loops in the WHED, which
delayed the start-up of the electrical heater and observably
reduced the operating time and the power consumption of the
electrical heater.
The COP of the system in the whole experiment could be calculated
by Eqs. (4)–(6), and the system COPs in Exp. 1 and Exp. 2 were
2.19 and 3.21, respectively. The system COP significantly increased
by 46.6% with the water pre-heated loops. Therefore, the novel
heat pump water heater assisted with SDW could make full use
of the waste heat in SDW and had high energy efficiency