In Japan, recently heat pump water heaters using CO2 have been introduced in the market. Moreover, in Japan, inverter drives are quite wide spread. Therefore, the focus of Japan has been the development of adequate test procedures and calculation methods for these systems.

Fig. 1: System layout of the systems with combined DHW –floor heating tested in the Japanese project

Japan has performed test rig measurements of a CO2-system with combined floor heating and possible additional heat use for radiator heating or drying, which are quite new in the Japanese market. Fig. 1 shows the layout of this system. The single hot water operation is to be tested ac¬cording to the Japanese Standard 4050:2004. Testing is performed for three seasons (winter, summer, intermediate) and three typical days (cold, average, warm) with fixed space heating load profile and tapping profiles for the respective conditions. Testing is performed for the operation modes single DHW and combined SH/DHW. In single DHW, there are the three days cold, average and hot, in combined operation winter mode, the cold and average day are tested, in intermediate season the warm day. By defining tapping patterns, transient effects due to the respective load profile are included in the testing results.
In accordance with this testing approach of JRA 4050:2004 Japan has worked out a calculation method based on a "typical day approach" for the respective seasons. The results of the testing for the respective seasons are weighted with a number of days in the season for all operation modes to receive the seasonal performance of the heat pump operation.
Fig. 2 depicts the tested heat pump system and its specifications.

Fig. 2: System layout of the systems with combined DHW –floor heating tested in the Japanese project