Description
How does a CO2 heat pump work?
An air-to-water heat pump is a very efficient device that uses energy in ambient air to generate heat. It uses a refrigerant cycle with a compressor and heat exchanger to extract heat from the ambient air and transfer the heat to the water. According to the International Energy Agency (IEA), heat pumps are three to five times more efficient than gas boilers, while using (renewable) electricity as an energy source rather than fossil fuels.
Many heat pumps use hydrofluorocarbon (HFC) refrigerants, such as R32, which have a high global warming potential (GWP). These refrigerants will soon be phased out by the EU F-gas regulations. Leomon's heat pumps use the natural refrigerant CO2, which has a Global Warming Potential (GWP) of only 1, meaning the technology is green and future-proof!
CO2 air-water heat pumps are ideal for:
1. High temperature domestic hot water production
2. High temperature radiator heating for existing moderately insulated houses.
Coefficient of performance (COP) of CO2 heat pumps
Since the tank is well insulated, heat loss is low. It is recommended to achieve maximum conductive heat transfer between hot water system water and cold water during water discharge and charging. In contrast to conventional heat pump systems for combined space heating and DHW heating, the CO2 heat pump system achieves the highest COP in combined heating mode and DHW heating mode. The COP is the lowest in heating mode. Therefore, the greater the annual DHW heating demand, the higher the SPF of a combined CO2 heat pump system.
The lower the return water temperature of the space heating system and the lower the domestic hot water storage temperature, the higher the COP of the CO2 heat pump. The heating system return water temperature is low and the proportion of domestic hot water heating capacity is moderate, which means that a larger part of the annual heating demand can be met by operating in combined heating mode, and the COP of this mode is considerably higher than in space heating mode alone.
During the operation of combined heating mode and domestic hot water heating mode, the COP of the CO2 heat pump is greatly affected by the water temperature of the outlet water system after the city water preheating heat exchanger. The lower the gas cooler inlet temperature, the higher the COP.
CO2 heat pump compressor
The COP of a CO2 heat pump is generally more sensitive to changes in compressor efficiency than that of traditional A/W and W/W heat pump systems. Therefore, it is particularly important to use high-efficiency compressors. After independent in-house research, engineers developed a highly efficient compressor.
CO2 heat pump pressure control
CO2 heat pump systems will be more complex than state-of-the-art residential heat pump systems due to the need for high-efficiency gas coolers, additional valves and piping for fluid bypass, inverter-controlled pumps in the system, water loops, and specially designed water storage tanks. The application of optimal high-side pressure control will further increase the efficiency of the CO2 heat pump system.
CO2 heat pump gas cooler design
Since the critical temperature of CO2 is low, the CO2 heat pump unit will release heat by cooling the CO2 at supercritical pressure in the gas cooler. In order to achieve high COP, useful heat must be released over a large temperature range, resulting in a relatively low CO2 outlet temperature from the gas cooler. It is important to produce system water within the required temperature range of 60 to 85°C. In order to provide the highest possible COP for CO2 heat pump units, various gas cooler configurations were evaluated. The final design of the gas cooler increased heat transfer by 30%.
Special storage tank for CO2 heat pump
During water discharge and replenishment, conductive heat transfer between the system water and the cold city water in the storage tank may cause the gas cooler inlet water temperature to drop significantly. The large temperature difference between the system water and the city water combined with the smaller controlled charge flow increases the heating capacity of the gas cooler. This in turn increases the COP of the CO2 heat pump.
One possible way to improve internal conductive heat transfer is to separate the system water and city water via a heat exchanger. This concept has proven to provide satisfactory improvements in thermal performance and better functionality of the entire heating system. Further functional and thermal performance can be optimized with special storage tanks. In this tank system, water and domestic hot water are separated. A heat exchanger between the input city water and system water reduces the return temperature of the gas cooler.
Contact us
If you are planning to purchase a CO2 heat pump, please contact us. Our heat pump experts will give you the best heating solution.
