Swimming in a warm, comfortable pool is a great way to relax and enjoy the outdoors but to make sure the water stays warm, you need a heat pump. Heat pumps work by drawing heat from the surrounding air and transferring it to the water, but sometimes frost can build up on the heat pump's evaporator coils, which can affect its performance. This is where your heat pump’s defrost mode comes in. In this mode, the heat pump melts any frost or ice that has accumulated on the evaporator coils, which helps to keep the heat pump working properly and the pool water warm. In this blog, we'll take a closer look at defrost mode in pool heat pumps, and explain how it works, why it's important, and things you need to know about defrost mode when selecting a heat pump for your pool.

1. When does your heat pump go into defrost mode?

Your heat pump goes into defrost mode when the ambient temperature drops and frost accumulate on the heat pump's evaporator coils, which can reduce your pump’s efficiency and potentially cause damage. During defrost mode, the heat pump temporarily switches from heating the pool water to melting the frost, usually by reversing the flow of refrigerant and using heat from the compressor to melt it.

2. What are defrost cycles?

Defrost cycles in heat pumps are periodic interruptions in the normal heating operation, designed to remove any frost or ice build-up on the evaporator coils. Defrost cycles typically last a few minutes to half an hour, depending on the size of the heat pump and the amount of frost build-up.

3. How does your heat pump reverse the refrigerant flow during a defrost cycle?

The heat pump reverses the refrigerant flow during a defrost cycle using a component called a reversing valve. The reversing valve is an electrically-operated device that changes the direction of the refrigerant flow in the heat pump.

During normal operation, the refrigerant flows from the evaporator coil to the compressor, absorbing heat from the atmosphere and using it to heat the pool water. During a defrost cycle, the reversing valve is activated, switching the direction of the refrigerant flow so that it now flows from the compressor to the evaporator coil. This allows heat to be transferred from the hot, compressed refrigerant to the evaporator coil, melting any ice that has formed on the coils.

Once the defrost cycle is complete, the reversing valve switches back to its original position. The refrigerant flow is reversed again, returning the heat pump to its normal operation. This allows the heat pump to continue to provide efficient and effective heating for the pool, even in challenging conditions where frost build-up is likely to occur.

4. At what temperature does a pool heat pump go into defrost mode?

Typically, heat pumps are designed to go into defrost mode when the ambient temperature drops below a certain point and frost start to accumulate on the evaporator coils. The exact temperature at which this occurs varies between heat pump models, but it is usually in the range of 0 to 4°C (32 to 40°F). In addition to the ambient temperature, various other factors also play a role in determining when a heat pump goes into defrost mode.

5. Factors other than ambient temperature that defrost mode of your heat pump depend on

1.      Humidity levels: High humidity levels can cause frost to form more quickly and frequently on the evaporator coils, leading to more frequent defrost cycles.

2.      Airflow: The flow of air over the evaporator coils can affect the rate at which frost builds up and the efficiency of the defrost cycle.

3.      Type of heat pump: Different heat pump models and manufacturers may have different defrost cycle settings, based on factors such as the size of the unit, and the design of the evaporator coils.

4.      Type of refrigerant: Different refrigerants have different properties, such as boiling points, that can affect the rate at which frost forms and the efficiency of the defrost cycle.

5.      Type of pool cover: The use of a pool cover can help reduce the rate at which frost builds up on the evaporator coils by reducing the amount of humid air that comes into contact with the coils.

6. What are some of the reasons that a heat pump does not go into defrost mode?

1.      Thermostat issue: If the thermostat that controls the heat pump is not functioning properly, your heat pump might not go into defrost mode, even if ice builds up on the evaporator coils.

2.      Control board problem: If the control board that manages the defrost cycle is faulty, it may not trigger the heat pump to go into defrost mode, even if the thermostat is working correctly.

3.      Low refrigerant levels: If the heat pump is low on refrigerant, it may not be able to operate efficiently, including entering into defrost mode.

4.      Blocked air flow: If airflow to the evaporator coils is restricted, such as by a dirty filter, the heat pump may not be able to enter into defrost mode.

5.      Reversing valve failure: If the reversing valve that is responsible for reversing the flow of refrigerant during a defrost cycle is faulty, the heat pump may not be able to go into defrost mode.

7. Defrost mode energy consumption

The amount of energy used during defrost mode is relatively small compared to the overall energy consumption of the heat pump, but it can still add up over time and affect the operating costs. It's important to make sure that the heat pump is properly maintained and operated, as this can help to reduce energy consumption during defrost mode.

The most important thing to keep in mind about defrost mode in heat pumps is that it is a necessary process to maintain the efficiency and effectiveness of the heat pump. By ensuring that the defrost mode is functioning properly, you can help to prolong the lifespan of the heat pump and ensure that it continues to provide efficient and effective heating for your pool.