18 May 2017

P.1.3.3 Household Dishwasher with a Monovalent Heat Pump System

Appliances like dryers, washing machines or dishwashers add to a household’s electricity demand considerably. To reduce their consumption of electricity, these appliances can be equipped with heat pumps for providing the necessary heat. In this paper the integration of a monovalent heat pump system into a dishwasher is theoretically analyzed and the simulation results are compared with those from experimental investigations from a prototype and from dishwashers in which technical measures have been taken to reduce energy demand. To calculate the transient heating process, energy balances as well as the heat transfer kinetics were set up in a mathematical-physical model together with the operating characteristics of a specific heat pump. The simulation program allows forecasting of the non-stationary operational behavior of the washing process and heat pump with a high degree of accuracy. The resulting concept places the evaporator in a latent heat storage filled with water. A coaxial heat exchanger serves as the condenser, a rotary compressor provides compression and a capillary tube is used for expansion. The simulated electricity need for the standardized process is 489 Wh with a washing process time of 128 minutes. Experiments with the dishwasher prototype have shown similar results, where the electrical energy need is 503 Wh and the washing process lasts 126 minutes. Dishwashers with electric resistance heating consume around 1000 Wh and dishwashers with a bivalent heat pump system 910 Wh for a comparable process. Through the use of a monovalent heat pump system, the electrical energy need of dishwashers can be reduced by up to 50%