UNEP REPORT Alternatives to HCFCs in refrigeration and air conditioning sector 61 S ection 02 economic reasons why this development and rapid market introduction took place in Japan: The normally large hot water consumption in Japanese ■■families due to the habit of taking hot baths. A dense population in many areas living in relatively small ■■apartments with a high square meter price. High electricity prices and competition on the energy ■■market from natural gas. Pressure and subsidises from government to reduce ■■fossil fuel. Utility companies wanting to compete with natural gas ■■supporting the development and subsidising installation. CO2 offers an attractive solution as it can generate very high water temperatures reducing the required storage volume significantly versus HCFC/HFC options. The unit is physically similar to the external unit of a split air conditioner. The performance of supercritical operation with CO2 compared to the HCFC/HFCs will be relatively better if high water temperature is required. In the case of water being heated from 10°C to 90°C hot water, CO2 will work well whereas it would not easily be achieved with conventional technologies. It would be possible to achieve maximum around 70°C with R-134a in standard systems. The COP of lower temperature lift will increase significantly more for HFC than for CO2 and the higher direct global warming would need to be evaluated versus the lower direct energy consumption i.e. indirect effect on global warming. The compressors used in these heat pumps are two-stage compressors with a direct current (DC) motor designed for variable speed. The heat pumps marketed in northern Europe are modified specially to adjust to the hot water tank and be more suitable for the application in buildings where the larger part of the energy is used for heating rather than for hot water. The hot water tank used for the heat pump in the tested system had a volume of 223 liters. These heat pumps have been evaluated in detail in a project at the Department of Energy at The Royal Institute of Technology in Stockholm [Yang et al. , 2009].Some of the conclusions are highlighted below. The test aimed at evaluating the CO2 heat pump with a heating capacity of 4.7 kW versus a traditional heat pump used for space heating and hot water production under Northern European conditions. The experiences of that test give indications under which conditions CO2 with the technology available today could be competitive and how standards (e.g. EN 14511) developed to test traditional systems might not give a good or “fair” indication on the possible benefits of a new technology. CO2 has different characteristics from traditional systems so the performance will be less dependent on the exiting temperature of air or water in the condenser but more dependent on the inlet temperature. Current standards are developed for the existing systems and are not adapted for products that would benefit from a changed strategy to operate the system. These different characteristics change the optimum design of the whole system where the CO2 heat pump is applied. Without changing the test conditions and/or system, design tests will not give a good indication on how the heat pump would work in neither new nor existing systems. It is important not to evaluate new technologies based only on old standards. At the same time many published comparative tests use references that might not describe the best available alternative technology. It is easy to find a poor system to compare with and generalise based on a specific case (authors comment). HeatpumpRadiator Fig. 2.18 Heat pump system with CO2 and tank for hot water production.