Principle and example of heat pump for preparation of domestic hot water

Keywords: heat pump, heat exchange, domestic hot water, air conditioner

1 Introduction

In order to protect the natural environment and improve people's living standards, the development and utilization of green energy (non-polluting natural energy sources such as solar energy, geothermal energy, etc.) should be a new technology actively promoted by the building hot water discipline. This article discusses the use of heat from air or air-conditioning water as a source of hot water for domestic hot water through a heat pump.

2, the working principle of the heat pump

The heat pump works by using the principle of "air conditioning" to transfer the heat energy from the air or water. However, unlike the air conditioner, it is not to discharge heat to the outside but to transfer it to the water to achieve the purpose of heating water, and at the same time to produce cold air (or cold water). ), remove excess water from the air. The heat supplied during operation of the heat pump is greater than the heat it receives from air or water. This is because the air pressure surface of the heat pump also converts electrical energy into heat energy output, without the pollution of fuel or gas heating equipment. The development and application of heat pumps has been in the United States for more than 20 years and is used in more than 50,000 systems. Applications in Hong Kong have also been used for more than a decade and are used in multiple systems. It has also been applied in Shenzhen for several years. According to the different sources of energy, heat pumps can be divided into water and water series, gas water series and other types. Figure 1 shows the structure and working process of a heat pump with air as its energy source. In the figure, after the refrigerant is vaporized, it is pressurized by the compressor and sent to the pool water heat exchanger through a three-way valve (this type of heat pump is generally used for heating of the swimming pool and dehumidification of the air), and the high temperature gaseous refrigerant is liquefied by the pool cooling. Then flow to the collector. The liquid refrigerant evaporates in the low-pressure evaporation coil through the expansion valve. When the refrigerant evaporates, it absorbs a large amount of heat energy and cools the air flowing through the outside. After the refrigerant is vaporized, it is pressurized by the compressor and then flows through the three-way valve to the pool water heat exchange. Device. The air-conditioned chilled water enters the evaporative heat exchanger, and the liquid refrigerant evaporates in the low-pressure evaporating coil to absorb the chilled water heat energy to lower the chilled water temperature. The vaporized refrigerant is pressurized by the compressor and returned to the condensing heat exchanger. The liquefied in the condensing coil releases heat and heats the domestic water.

3. Engineering application examples

On the side of the evaporating heat exchanger, the chilled water is returned to the heat pump through the circulation pump, and the water temperature is lowered by 4 degrees per cycle. On the side of the evaporating heat exchanger, the hot water is also fed into the heat pump after circulating the water pump, and the water temperature can be increased by 5 degrees per cycle. When the water temperature of the hot water tank reaches 65 degrees, the compressor stops working. In order to improve the efficiency of the heat pump, the * hot water tank is used as the preheating water tank, and the heat pump only provides the basic heat load. The second hot water tank with heating elements acts as a post-heating means for the water. The volume of the second hot water tank is calculated based on the heat required for the entire building to be serviced by a heat pump or air conditioning system. The Hong Kong Gold Coast Hotel is a five-star hotel. It was originally designed to use a fuel hot water boiler. It was then combined with a heat pump and a volumetric electric heater in accordance with the requirements of the Hong Kong Environmental Protection Department and the power department. There are four heat pumps in the hotel's domestic hot water, two of which are installed in series, and the original heat exchanger (3 for rooms and 2 for kitchen) is used as the second-stage hot water storage tank. According to the total heat demand of the hotel, a total of 5 volumetric electric water heaters are selected. Due to the limitation of space between underground equipment, the total heat capacity of the four heat pumps cannot meet the total demand. During the peak water supply period, 2-3 electric water heaters need to be put into operation. The hotel has embarked on the renovation of the second phase of the work, and then installed four gas-water series heat pumps for the dewatering of the pool water and the air, and supplemented the shortcomings of the domestic hot water heat pump.

4 Conclusion

As a new non-polluting environmental protection equipment, heat pump has been widely used in developed countries and regions. China has joined the WTO and successfully bid for the 2008 Olympic Games. The Green Olympics and the Science and Technology Olympics have been adopted by the International Olympic Committee as our basic policy. Recognition. In the next seven years of construction, heat pumps will be widely used in hot water systems and air conditioning systems.