Freezing of the heat pump - causes, effects

Winter months can surprise us with negative temperatures that can drop to even -25 degrees Celsius. Such low temperatures can lead to problems with the freezing of heat pumps. Heat pumps are devices that utilize energy from the external environment - air, water, or soil, to generate heat for heating buildings. However, in extreme conditions, when the temperature drops below a certain level, the water in the pump can freeze, causing damage to the device. The consequences of heat pump freezing can be serious, including system breakdown, the need for repair or replacement of the pump. Therefore, it is important to properly protect the pump from freezing, for example, by properly insulating it and using special preventive measures. Can every heat pump freeze? Why do some heat pumps freeze? What are the consequences of heat pump freezing? How to protect the pump in winter? You will find the answers to these questions in the article below.

Can Every Heat Pump Freeze?

Answering the question posed in the heading - no, not every heat pump is equally exposed to freezing. Split heat pumps are not as prone to freezing as monoblock construction because the water circulation is located inside the building. In the case of split heat pumps, the outdoor unit extracts heat energy from the environment and transfers it to the indoor unit. The indoor unit is responsible for heating the building. The water circulation is closed, which means that there is no direct contact with external weather conditions. Therefore, split heat pumps are not exposed to freezing, even in very low temperatures. In winter, when the temperature outside is very low, a split heat pump can still operate relatively efficiently, providing heat to the interior of the building. 

The situation is different with monoblock heat pumps, which are much more prone to freezing in winter months compared to split pumps. An outdoor monoblock air source heat pump is much more exposed to adverse weather conditions. Therefore, there is a certain risk of pipe freezing, especially during power outages, preventing the activation of heat pump freeze protection mechanisms. If the temperature outside drops below zero, the water or refrigerant, which fills the pump unit, may freeze, which in turn can cause component rupture. If this happens, the pump may in extreme cases be essentially scrapped. 

In What Conditions Do Heat Pumps Freeze?

Heat pumps can freeze in adverse conditions, such as power outages or low ambient temperatures (below 0 degrees Celsius for water). When the power supply to the system is interrupted, the heat pump stops working, causing the refrigerant circulation to stop. If at this time the outside temperature is lower than the freezing point of the refrigerant, the phenomenon commonly known as "heat pump freezing" may occur.

It is also worth noting that power outages do not necessarily have to occur for this phenomenon to happen. Very low ambient temperatures combined with poor pump protection (lack of insulation, improperly selected refrigerant) can also contribute to heat pump freezing. If the refrigerant is inadequately matched to the prevailing weather conditions (incorrect concentration, wrong type) and is not adequately protected from freezing, it may freeze in pump components, leading to damage.

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Effects of Heat Pump Freezing

When a heat pump freezes, it can lead to various consequences that affect its performance, efficiency, and even components. Here are the consequences of heat pump freezing. It is worth noting that each of the consequences mentioned below may ultimately lead to the total damage of the device, resulting in significant costs of replacing the pump with a new one.

Reduced Efficiency, Leading to Higher Costs

When elements of the heat pump, especially the evaporator coil, freeze (e.g., due to lack of proper insulation), the heat exchange process is hindered or even impossible. This reduces the efficiency of the heat pump because it struggles to absorb heat from the surrounding air. As a result, the heat pump may be forced to work harder and longer to achieve the desired room temperature, leading to significantly increased energy consumption and higher utility bills.

Shortened Operating Cycle and Increased Consumption

A heat pump that is not prepared for prevailing weather conditions may freeze, resulting in intermittent operation. This not only strains the components but also leads to increased consumption, potentially shortening the overall system lifespan.

Risk of Refrigerant Issues

Freezing can affect not only the components themselves but also the refrigerant. Such a situation affects its improper circulation within the heat pump components. When the refrigerant does not flow properly, the heat exchange process may be disrupted. This, in turn, can cause other problems, including potential compressor damage due to the return of liquid refrigerant to the compressor during defrost cycles.

Component Damage

The expansion of freezing water in the system components can cause physical damage to the internal components of the heat pump. For example, ice formation in the coils can lead to bending, distortion, or even cracking of the coil fins or tubes. Such damage can result in costly repairs and reduced heat pump lifespan or even total failure.

How to Protect the Heat Pump from Freezing?

To protect the heat pump from freezing, follow the manufacturer's guidelines. First and foremost, install a protective system to prevent pump damage during low temperatures. This can be achieved by using special thermal insulation to cover the pump. Additionally, in case of extremely low temperatures, check if the pump is equipped with a defrost system that removes any ice buildup (this is usually the standard today). Regularly check for any damage or leaks that could result from freezing. If in doubt, consult with a professional who can help protect the pump from the adverse effects of low temperatures. It is also worth performing the following actions to prevent the installation from freezing.

1. During power outages, drain the water from the unit through the drain valve and blow it out (in case the pump does not have an additional emergency power source).
2. If you want to avoid point #1, add a battery or generator to the installation.
3. Additionally, protect the installation by insulating the pipes.
4. If you live in areas where frequent and prolonged power outages occur, such as in some mountainous regions with outdated infrastructure - fill the system with an antifreeze solution. Point 4 is particularly noteworthy, and some heat pump manufacturers even require filling the heat pump circuit with a non-freezing liquid (usually glycol mixed with water).

The above actions, especially the use of glycol, should protect your heat pump from freezing even during the coldest temperatures. It is worth remembering that, to ensure the proper operation of a monoblock heat pump system working on glycol, an appropriate heat exchanger for the pump must also be selected - to connect the glycol circuit of the heat pump to the heating or hot water system in our home or apartment (it is recommended that the central heating system in our home works on water, so the heat exchanger in this case serves to separate the glycol circuit). In our offer, you will find, among others, the following plate heat exchangers dedicated to pumps:

• heat exchanger for heat pump Ba-32-30 1" 175 kW
• heat exchanger for heat pump Ba-32-50 1" 285 kW
• heat exchanger for heat pump Ba-32-70 1" 385 kW

It is important to note that selecting heat exchangers for monoblock heat pumps working in glycol/water systems is not intuitive or straightforward. To ensure our pump's ability to work at the lowest possible temperatures (thus ensuring the lowest electricity bills in a given application), the heat exchanger must have a sufficiently large heat exchange area. Such selection should definitely be made by individuals with knowledge of selecting heat exchangers for heat pumps, bearing in mind that not every plumber has the appropriate training or experience in this matter. In the case of selecting a too small heat exchanger, our heat pump may require operating at higher temperatures (to achieve thermal comfort in rooms), which in turn will result in higher electricity consumption. In cases of extreme undersizing of the heat exchanger, the entire system may essentially not function - to the extent that it will mean a cold building without thermal comfort.