What is air source heat pump trigeneration?
Air source heat pump trigeneration refers to a system based on air source heat pump technology. It is also called an air source air conditioning water heater or an air source heat pump three-in-one machine.
Structure and working principle of air source heat pump trigeneration system
The air source heat pump trigeneration system includes several components. These include the main unit (water pump, expansion tank, etc.), the indoor terminal (wire controller, etc.), the floor heating section (water distributor, thermostat, etc.), and the central hot water section (water tank, return water control, etc.).
The system can operate in various modes to meet different needs. Common modes include:
- Hot water production: The hot water heat exchanger’s circulating water pump works. The air conditioning heat exchanger’s circulating water pump does not work. The fan of the fin heat exchanger runs. After the compressor starts, the working fluid releases heat in the hot water heat exchanger and absorbs heat in the fin heat exchanger.
- Hot water production and cooling: Both the hot water and air conditioning heat exchangers run. The compressor releases heat to the hot water heat exchanger and absorbs heat in the air conditioning heat exchanger for cooling and heating hot water.
- Cooling only: Only the air conditioning heat exchanger runs. The compressor absorbs heat through the fin heat exchanger and releases it to the air conditioning heat exchanger to cool.
- Heating only: The air conditioning heat exchanger runs alone. The compressor absorbs heat in the fin heat exchanger and releases it to the air conditioning heat exchanger to heat.
Advantages and Disadvantages of Air Source Heat Pump Trigeneration System
Advantages
Ordinary air-cooled heat pump units must release a large amount of condensation heat into the environment while cooling, and this part of heat exacerbates the urban heat island effect. Take a unit with a heating capacity of 12kW as an example, it releases about 10318 kcal of heat into the air every hour, and this heat can raise the temperature of 1200kg of water by 10℃ within 1 hour. For many such enterprises and institutions, domestic hot water is needed all year round. If the trigeneration waste heat recovery technology is adopted, a large amount of domestic hot water heating costs will be saved every year.
At present, heat pump manufacturers and well-known air-conditioning manufacturers have successfully developed air-cooled trigeneration products. This product heats domestic hot water while cooling and heating, and each function can also operate independently. The trigeneration unit realizes full heat recovery in the cooling state, reducing the initial investment cost.
Disadvantages
Trigeneration technology primarily serves indoor air conditioning, with domestic hot water as a secondary function. Heat pump units are typically sized based on room loads. Domestic hot water loads, however, are smaller, causing the system to operate in cooling mode most of the summer.
Due to varying regional water quality, bathing water exchangers must frequently flow in new water. This requires high corrosion resistance in heat exchangers. Some trigeneration units face corrosion penetration in the heat exchanger, allowing water to enter the fluorine system. This often leads to the scrapping of the air conditioning unit. To prevent corrosion, a secondary heat exchange system is used. However, this raises the condensing temperature, reduces the COP, and decreases efficiency.
The domestic hot water temperature is usually set at 45°C, increasing the heat pump’s condensing temperature. In cooling mode, traditional air conditioners operate normally with a 35°C condensing temperature. However, when the trigeneration system provides both cooling and hot water, the condensing temperature rises to 45°C. As a result, the condensing pressure increases from 1.7MPa to 2.7MPa. This raises the compression ratio, reduces the COP, and increases energy consumption.
Control complexity and solutions to heat distribution problems
System control complexity
The control complexity faced by the air source heat pump trigeneration system mainly comes from its simultaneous handling of multiple tasks – cooling, heating and hot water supply. To ensure efficient operation, the system needs to be able to flexibly switch between different working modes and accurately control energy output. At present, there are two main forms of trigeneration systems: switching water circuits and switching fluorine circuits.
Switching fluorine circuits: By controlling different valves to switch functions, the system is complex, with too many components, a high failure rate, and inconvenient installation and maintenance.
Switching water circuits: By controlling the three-way valve of the water circuit to achieve function switching, it is relatively simple and reliable, but the requirements for the water tank are high, and the life and design of the water tank are crucial.
To overcome these challenges, it is crucial to adopt advanced control algorithms. For example, a control system based on fuzzy logic can cope with uncertainty and achieve more efficient energy conversion. In addition, integrated intelligent monitoring and predictive maintenance systems can help improve control efficiency and reduce operational risks.
Uneven heat distribution problem
The problem of uneven heat distribution usually stems from thermodynamic limitations in system design and operation. To solve this problem, the thermal design of the system can be optimized, such as using more efficient heat exchangers and improved fluid dynamics design.
This not only improves the heat exchange efficiency of the system, but also helps to distribute heat more evenly among the various parts. In addition, by implementing a zoning control strategy, the heat output can be dynamically adjusted according to the actual needs of different areas to ensure uniform distribution of heating and cooling.