Full Description

Heat pump water heaters using CO₂ as a refrigerant have been available in Japan and elsewhere in the world since the early 1990s, withmany devices already installed. However, they have yet to emerge in the United States. One major reason is cost: heat pump systems will costmore than an equivalent electric resistance water heater, and CO₂ systems tend to be have premium features and costs. Another reason for thelack of CO₂ water heaters in the US is that existing models have differed strongly from the conventional water heating equipment seen in the USmarketplace. Models developed under the EcoCute label often have an indoor tank with an outdoor heat pump, and features such as remotecontrols, bath water recirculation loops and others. This study examines a new, integrated CO₂ heat pump water heater developed by a Japanesemanufacturer and marketed in Europe, which removes many of the features common to CO₂ systems and is meant for indoor, single-locationinstallation. The integrated CO₂ system was tested in the laboratory at a variety of conditions to map performance. It was tested in climatecontrolledenvironmental chambers for a variety of ambient air conditions and also in an approximated Energy Factor test. The system tested hastwo modes: a comfort mode in which compressor power is high, and the system always charges to full capacity; and an economy mode in which thecompressor power is low, and the system charges to full capacity during pre-set (generally overnight) hours and reheats only partially during anotherpre-set time period. It was tested in both modes. The system was also installed in a test home in Tennessee which features simulated occupancyand detailed data monitoring. The system was installed in the garage and allowed to run in each of the operating modes at different times. Thewater draw was controlled in the home to a typical load profile. This paper will outline the testing and monitoring approach. Results for both thecompleted laboratory testing and ongoing field testing will be shown.

Citation: ASHRAE Conference Papers, Denver, CO