Heat pump is a device that transfers heat from a lower temperature substance or space to a higher temperature space, and it is a device that allows the original heat to be transferred in the opposite direction. Heat can be spontaneously transferred from high-temperature objects to low-temperature objects, but not in the opposite direction, while heat pumps can first obtain low-grade heat energy from natural air, water, or soil, and work through one part of electricity, and then provide people with high-grade heat that can be utilized. The types of heat pumps can be divided into air-to-water heat pumps, water-source heat pumps, and ground-source heat pumps according to the source of heat.
Air source heat pump is the most widely used and popular heat pump. This article focuses on air source heat pumps.
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Water source heat pump
Generally, the superficial groundwater buried below 20metres of the surface can be maintained at about the annual average temperature of the region all year round, and it is an ideal natural source of cold and heat. The water source heat pump system is a one of energy-saving HVAC system that uses the characteristics of groundwater(groundwater, rivers, lakes, ocean, etc.), and it can be divided into “open-loop system” and “closed-loop system”.
A closed-loop system pipes a mixture of water and antifreeze to a water source, such as a lake, where it flows through coils or heat exchange plates in the water, exchanging heat with the water. The heated mixture is then piped to a heat pump and exchanged heat with the refrigerant.
In an open loop system, water is extracted from the source and piped directly to the heat pump, and then exchanges the heat with the refrigerant and returns the water to the source. As this involves extraction and discharge from water sources, an extraction permit and a discharge permit from the local environment agency may be required. Therefore, before installing ground source geothermal heat, it is necessary to know whether the conditions of local water source and the geological structure of the site are suitable for drilling wells to extract water and use.
Ground source heat pump
Geothermal heat pump, also known as ground source heat pump. Beneath the surface of the earth, the temperature is a constant 50 to 60 F (10 to 15.56℃), a natural and everlasting source of heat, and the ground source heat pump takes advantage of this constant heat source by transferring and concentrating the heat to provide users with space heating, cooling, and domestic hot water. In short, if you want to get the heat from the surface’s earth, you need to dig a well with a depth of 10 to 20m³(Depth depends on local geology and geothermal conditions).
Ground source heat pump principle
The figure shows that the air from the living space is flowing into the system and has heat added to, or taken from it. This heat is then either deposited (if the air is warmer than desired) in the ground. If the air is cooler than desired, heat is taken from the ground.
The principle of the air source heat pump is opposite to the working principle of an air conditioner, it uses one part of electricity power to drive the compress, and then absorbs up to 4 parts of free heat from the outside air, the final output can be up to 4parts of heat to heat the swimming pools, radiators, underfloor heating systems, or warm air convectors and hot water in your home. It can get heat from the air even when the temperature is as low as -30℃. The heat they extract from the ground, air, or water is constantly being renewed naturally, saving you on fuel costs and reducing harmful CO2 emissions.
How do air source heat pumps work?
The following is the specific process of the working principle of the air source heat pump：
The compressor absorbs the low-temperature and low-pressure refrigerant gas from the evaporator, and by consuming part of the electricity to drive the compressor work, compresses the low-temperature and low-pressure gas into a high-temperature and high-pressure superheated gas, and then discharges it to the condenser for heat exchange with water. The superheated gas is liquefied and turned into a liquid. After being throttled and depressurized by an electronic expansion valve, it becomes a low-temperature and low-pressure liquid and then enters the evaporator to absorb the heat in the air and vaporize into a superheated gas, which is finally compressed by the compressor, and so on. Then it works continuously to produce hot water.
Among the three types of heat pumps, the air source heat pump is the most advanced, has the highest energy efficiency ratio, the most convenient installation, and has the lowest cost in the world. It is also the most popular and best-selling energy-saving heating and cooling equipment in the market. Its main components are a compressor, evaporator, condenser, and throttle valve (Expansion valve).
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Compressor
A compressor (also called a “vapor pump”) is a driven fluid-mechanical device that elevates low-pressure gas to high-pressure gas, and is the heart of a heating system. It inhales low-temperature and low-pressure refrigerant gas from the suction pipe, drives the piston to compress it through the operation of the motor, and discharges the high-temperature and high-pressure refrigerant gas to the exhaust pipe to provide power for the heating cycle, thereby realizing the heating cycle of compression→condensation (discharge heat)→expansion→evaporation (endothermic)
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Condenser
The condenser is a part of the heating system and belongs to a type of heat exchanger. It can convert gas or vapor into liquid and heat the water in a very fast way with the heat in the tube. The gas is passed through a long tube (usually coiled into a solenoid) to dissipate heat into the surrounding water, such as metals copper conducts heat well and is often used to transport steam. In order to improve the efficiency of the condenser, heat sinks with excellent thermal conductivity are often attached to the pipes to increase the heat dissipation area to accelerate heat dissipation. The working process of the condenser is an exothermic process, so the temperature of the condenser is relatively high.
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Evaporator
The evaporator is a very important part of the four major heating elements. After compression and liquefaction, the low-temperature refrigerant passes through the evaporator and exchanges heat with the outside air to achieve the purpose of absorbing energy from the air.
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Throttle valve (Expansion valve)
The expansion valve is a device that controls the flow of refrigerant by changing the throttling section or throttling length in the heating system. It is generally installed between the evaporator and the liquid storage cylinder. The expansion valve makes the liquid refrigerant of medium-temperature and high-pressure pass through its throttling to become wet vapor of low temperature and low pressure, and then the refrigerant absorbs the heat in the outside air in the evaporator. The expansion valve controls the valve flow through the change of superheat at the end of the evaporator to prevent insufficient utilization of the evaporator area and the occurrence of cylinder knocking.
Air source heat pump life expectancy
The service life of an electric heat pump/gas water heater is about 5 years, the service life of an air source heat pump is 2~4 times that of it, and the general service life is 10-20 years. What are the factors that affect the service life of an air source heat pump?
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Product quality
The service life of the heat pump unit is affected by the quality of the units. The better material and manufacturing technology, the longer the service life, this is a prerequisite.
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Equipment Operating Time
Under normal circumstances, the daily operation time of the unit does not exceed 12 hours (continuously working). After this time, the probability of failure of the unit will increase, and the service life of the unit will also be affected. Therefore, it is necessary to reasonably select the unit equipment, or compared with the on/off heat pump, you can choose the inverter type because the inverter heat pump can automatically adjust the operating frequency and operating time of the unit according to the ambient temperature and the set target temperature, avoiding the compressor restarting and stopping process continuously and reduce the service life of the unit.
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Outside Ambient Temperature
For the unit, the ambient temperature is also a major factor that directly affects its service life. When the ambient temperature is lower or higher, a special type of heat pump unit should be selected to ensure that the unit can still start and operate normally at low/high temperatures. What ambient temperature is not suitable for heat pump unit operation? It depends on the working conditions of the heat pump you purchased. Different brands of heat pumps have different ambient temperatures. Such as a heat pump’s ambient temps range is 5℃~40℃, which means this heat pump can not operate at the ambient temps lower than 5℃ or higher than 40℃, otherwise, it will cause the unit to fail and shut down and reduce the service life, and if it runs in this condition for a long time, it will reduce the life of the unit. In addition, it is very important whether the unit has a defrosting function in a low-temperature environment.
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Number of Compressor Starts and Stops
The compressor plays a decisive role in the longest life of the unit because if the unit is started and stopped frequently, the compressor will be impacted by excessive current, which will reduce the life of the unit.
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External Factors
External factors mainly refer to human factors, which are reflected in whether the unit is installed and debugged by professional and technical personnel. During the use process, attention should be paid to avoid working under high water temperature and high-pressure conditions, and attention should be paid to the installation location of the unit away from oily smoke and smoke. The place where there are fallen leaves, so as not to affect the wind blades and endanger the life of the unit.
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Maintenance
Poor and lack of maintenance can lead to accelerated component wear and significantly reduced service life. Heat pumps in coastal areas can also have significantly shorter lifespans as salt corrodes condenser units. If with a preventive maintenance program, the service life of your HVAC /heat pump system will last longer because small problems are fixed before they require expensive repair. Some of the most important maintenance tasks a heat pump needs to do include:
- Inspect and clean pipes, filters, blowers, and coils
- Verify adequate airflow
- Check for refrigerant leaks and verify refrigerant charge
- Lubricate the motor
- Reduce plant growth around outdoor components
Air source heat pump efficiency
A measure of heat pump efficiency is the Coefficient of Performance (COP) or Energy Efficiency Ratio (EER)–these terms actually mean the same thing, COP for heating standard, EER for cooling standard. COP refers to the ratio between how much energy a heat pump produces and how much electricity it consumes. The Seasonal Coefficient of Performance (SCOP) is often used as a year-round and realistic measure – it is based on the COP and normalized climate under different conditions. Under the same working conditions, the higher the COP, the better the performance of the machine and the more energy saving.
The heat pump units is mainly reflected in high efficiency, energy saving, environmental protection, and safety. No flammable or explosive gas, no electrical propelling components, absolutely safe; no waste gas, waste water, and waste residue discharge, absolutely environmental protection; the annual average operating cost of the air source heat pump unit is only 1/4 of the electric heat pump, and 1/3~1/2 of the fuel and gas heating equipment, 1/1.5 of general solar equipment.
Compared with coal-fired boilers, oil boilers, gas boilers, and electric water heaters, air source heat pump water heaters have the highest thermal efficiency. The efficiency of oil boilers is 65%-75%, that of electric water heaters is 70%-80%, and that of air source heat pumps is as high as 300%-500%(In theory, the efficiency of air source residential heat pumps can deliver heat up to 600%(Data refer to the Energy Efficiency Council). Because the heat pump water heater has a thermal efficiency of 300%-500%, the cost of producing hot water is extremely low, and it can help users save a lot of energy power in long-term operation.
For example, using a 750W~910W air source heat pump of 220V~240V power supply, each time (Compressor works once) can produce 160L~180L of hot water, which can be used by 2~4 people, and the daily power consumption is 2~3KW/h(when the ambient temperature is low in winter, the power consumption will be slightly higher, but still the most energy-efficient). If using a 2000W 200L electric water heater, it needs to consume 15 kW/h of electricity every day for heat preservation and heating (the power consumption will be higher in winter). So compared with electric water heaters, air source (heat pump) water heaters can help users save up to 70~80% of electricity bills per month, and at the same time, it can reduce a lot of greenhouse gas emissions.
