• Heat Pump
• CO2 Heat Pump
• Project Presentation

• Thermodynamic cycle
• Heat Pump Design
• Sanyo Eco Cute
• Swedish Report (KTH)

• EES Model
• COP Regression
• Defrost Cycle Model
• Future Dynamic Model ?

• Finnish Case Study
• Our Own Monitoring
• 3 Scottish Case-Studies
• Data Analysis
• Discussion
• Download

• Economical Aspects
• Environmental Aspects

• Potential of CO2 HP
• Recommendations
• Further Work

Recommendation

With our modelling and monitoring work, a list of recommendations has been made in order to optimize the operation of the CO2 Sanyo Eco Cute system.

Recommendation in the Design of the Sanyo Eco Cute System

The design of the Sanyo CO2 Eco Cute system is not totally optimized to maximize the performances. The heat pump (outside unit) in itself seems to perform quite well. However the tank design is not perfect, and in particular, it does not enable to minimize the water return temperature to the heat pump.

• The position of the water flow from the heat pump is located in the middle of the tank which disturbs the stratification of the tank temperatures when the heat pump is running. In addition it tends to heat quite quickly the bottom of the tank where is located the return water flow to the heat pump. It seems more interesting to put the connection of the water inlet from the heat pump at the top of the tank as it was also advised in the report from KTH.
• If the water flow from the heat pump was connected in the middle of the tank in order to assure a sufficient heat storage in the upper part of the tank to meet the domestic hot water demand, a bigger tank could be used to provide a sufficient heat storage while keeping the bottom of the tank at a quite low temperature.
• The way the heat pump is controlled with the position of sensors in the tank spark a lot of starts and stops of the Sanyo system. As the hot water from the heat pump arrives in the middle of the tank, at the same level that the heat for space heating is mainly taken, if the heat flow from the heat pump is not similar than the heat flow to the radiators, the system will tend to start and stop in permanence since there is almost no buffer storage.
• The return water temperature to the heat pump is mainly determined by the return temperature from the radiators and the occurrences of the sterilisation cycles. The cooling capacity from the water coming from the city is definitely not used in the Sanyo tank in order to decrease the temperatures at the bottom of the tank.
• The high number of sterilisation cycles decrease significantly the performances of the installations since the return temperature to the heat pump reaches 50 degree Celsius during the sterilisation cycles. As their efficiency is also controversial, we would suggest to reduce their number but increase their length to be sure that the effect on the legionella is positive.

Recommendation in the Installers of Sanyo Eco Cute System

The Sanyo CO2 system is also quite sensible to its environment of operation and the controls settings. These recommendations should help the installer to optimize the performances of the installations:

• The return temperature from the heating system should be minimized as much as possible since it is the critical parameter which determines the return water temperature to the heat pump. As a result heating systems with low temperatures like under floor heating system should be favoured against higher temperature heating system like radiators for an utilisation with a Sanyo Eco Cute system. The temperature drop of the heating system should also be maximized as much as possible. Too high water mass flow in the radiators should be avoided. In addition, certain rooms of dwellings require in general less heating than the main ones. The water circuit could therefore be organised in such a way that the main rooms are heated with the hot water from the outlet of the tank and the others can be supplied afterwards with milder water.
• In order to cope with the high number of starts and stops of the system, the controls can be adapted. In the setting code menu, it is first possible to set up the temperature difference between the starts and stops of the heat pump. If the difference is increased, it will tend to reduce the problem. However the heating capacity can become insufficient (too low temperature in the middle of the tank), that is why there is another option to increase the temperatures in the middle of the tank. This option should be nevertheless used parsimoniously, because it could increase the temperature at the bottom of the tank.
• The "sterilisation" cycles realized every 4 starts of the compressor are a bit controversial in term of efficiency against the legionella. In the manual, they mainly suggest to use this option in order to increase the temperature of the domestic hot water at the top of the tank. We would simply recommend to suppress it because it reduces the performances of the heat pump.