Which plate exchanger for a heat pump?

This article will discuss the topic of selecting the appropriate heat exchanger for a heat pump. Choosing the right exchanger is crucial for the efficiency and performance of the entire system. There are many tips and criteria to consider when choosing a plate exchanger. First, technical parameters such as efficiency, operating temperature, and fluid flow should be taken into account. Additionally, attention should be paid to the material from which the exchanger is made, as well as its size and construction. Improper selection can have serious consequences for both the heat pump's performance and the entire system. If the exchanger is too small or made of the wrong material, it can lead to low heat pump efficiency, high operating costs, and failures. Therefore, it is worth consulting with a professional before making a final decision.

What Is a Heat Pump?

A heat pump is a heating device that utilizes thermal energy from the environment and converts it into heat energy for heating the air in a building and for heating domestic hot water. It operates on the principle of heat exchange between two mediums - cooling one and heating the other. In the case of central heating installations, the heat pump extracts thermal energy from the air or ground and then transfers it to the heating circuit in the home. This form of heating is more environmentally friendly and energy efficient than traditional methods such as gas or oil furnaces. A heat pump can also provide hot water, which is particularly important in daily activities such as washing or bathing.

Why Is a Heat Exchanger Essential for the Operation of a Heat Pump?

First, it's worth mentioning that there are 2 heat exchangers that can cooperate with a heat pump. The first is an integral part of the pump and is essential for its operation - this is the internal exchanger, often made of Freon and resistant to high pressures.

The heat exchanger (internal) is an essential element in the operation of a heat pump. The heat pump operates on the principle of heat transfer, i.e., transferring thermal energy from one medium to another. In the case of space heating, the heat pump extracts heat from the external environment, such as air or soil, and transfers it into the building. The internal heat exchanger plays a crucial role here, allowing the transfer of heat between the coolant and the heating fluid without their direct contact. Thanks to this process, the heat pump can efficiently transfer heat to the rooms, ensuring their effective and economical heating. The heat exchanger is therefore an indispensable element that enables the efficient operation of the heat pump.

The second exchanger - the plate exchanger - sometimes called external - can be used to separate the heat pump from the heating system, e.g., when the system is old and we want to protect the heat pump from its potentially unhealthy environment (open circuit installation) - or when the heat pump circuit contains glycol, protecting the pump from freezing. This second exchanger is essentially independent of the first - the Freon exchanger - and is installed for a different purpose. It doesn't always need to be installed.

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Consequences of Choosing the Wrong Heat Exchanger for a Heat Pump

The Freon exchanger, or internal, is a part of the heat pump and is rarely chosen by us, usually supplied by the manufacturer as part of the set. However, the plate exchanger for separating the heat pump from the heating system or domestic hot water - we usually choose ourselves (without the involvement of the heat pump manufacturer) and we should do it well or ask a specialist for help.

Choosing the wrong heat exchanger for a heat pump can have serious consequences. Primarily, it can lead to a decrease in the efficiency of the heat exchange process. If the exchanger is not properly matched to the building's needs, it may not provide enough heat, resulting in increased energy consumption and costs. Improperly selected heat exchanger parameters can also increase noise and shorten the life of the heat pump itself. Therefore, it is important to select the heat exchanger carefully to meet the specific needs of the building and avoid these potential problems.

How to Choose a Plate Heat Exchanger for a Heat Pump?

Choosing the right plate heat exchanger for a heat pump is a crucial step in ensuring the effective operation of the entire system. Plate heat exchangers are often used in heat pumps due to the efficient heat exchange process between the fluids in the entire heating system.

When selecting a heat exchanger for a heat pump, atmospheric conditions in which the heat pump will operate must be taken into account. In cases where there is a risk of low temperatures, it is necessary to protect the system from freezing. For this purpose, glycol is often used, which has a much lower freezing point compared to water (a mixture of glycol with water in proportions of 3:2 freezes only at -37°C). Therefore, a crucial aspect in such cases is the ability to use glycol with a particular heat exchanger.

When choosing a plate exchanger, attention should be paid to its efficiency, construction, and material to ensure the optimal operation of the entire system. Selecting the right plate heat exchanger for a heat pump is a challenge that requires a careful analysis of all factors affecting its performance. Heat exchange is a key process in heat pumps, so ensuring the effective operation of the plate exchanger is extremely important.

Selection of Exchanger Surface Area for Heat Pumps - Calculations

Nordic Tec, a supplier of heat exchangers for heat pumps, uses a selection calculator, which suggests the correct ratio of heat exchange surface area on the exchanger to the power of the heat pump, depending on the supply temperatures the heat pump will provide to our system. The calculator applies specifically to plate exchangers from Nordic Tec:

• For heating/ DHW systems operating at min. around 50°C - for every 10 kW of heat pump power, a heat exchanger with a heat exchange surface area of approximately 1.50 m² should be selected.
• For heating/DHW systems operating at min. around 30-35°C - for every 10 kW of heat pump power, a heat exchanger with a heat exchange surface area of up to 3.00 m² may be necessary.

It's easy to notice that the first case typically applies to buildings based on radiator heating, while the second one mostly relates to underfloor heating. Systems supplied with intermediate temperatures or mixed systems - radiators/underfloor heating - should be treated proportionally, and plate exchangers should be selected accordingly.

Heat Exchanger Calculations for Using Glycol or Water

Nordic Tec's heat exchanger selection calculator for heat pumps takes into account the use of glycol, which adversely affects heat transfer. If water without glycol is to be used on both sides of the exchanger (the heat pump circuit is filled with water), the calculations can be reduced by approximately 10%.

How to Choose an Exchanger for a Heat Pump Depending on the Supply Temperature?

During the selection of a heat exchanger for a heat pump, there is also a common mistake made by laypersons regarding the expected supply temperature. In many cases, heat pump investors specify the highest temperature at which the heat pump can operate, e.g., 65°C or 70°C, repeating it from the heat pump salon brochure. This temperature has nothing to do with reality; operating at such temperatures would entail enormous costs and energy consumption, rapid wear and tear of the heat pump, not to mention that in practice, it makes no sense to heat a house at such temperatures. It is necessary to consult with a specialist and inquire about the temperatures at which the system is supposed to operate optimally.

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Characteristics of a Good Heat Exchanger for a Heat Pump

A good heat exchanger for a heat pump is characterized by several important features. Firstly, the material from which it is made should be durable and corrosion-resistant. Stainless steel 316L is often used in this case, as it has high resistance to environmental influences and is also easy to clean.

Another important feature is the appropriate power, i.e., the ability to transfer a sufficient amount of thermal energy from the source to the target medium. The heat exchanger should also have a suitable heat exchange surface area (models start from 0.8-1.0 m² of plate area), to ensure effective heat transfer. The larger the plate area of the exchanger, the closer we get to the possibility of the heat pump operating at lower temperatures - which guarantees lower energy consumption, i.e., savings - and statistically lower pump failure rates due to less wear and tear. Therefore, investing in a larger exchanger may pay off in the long run, although it represents a greater expense compared to plate exchangers for boilers or fireplaces.

The exchanger should also be well-designed structurally to enable smooth flow of the medium and minimize flow resistance. Additionally, it is important for the heat exchanger to be easy to operate and maintain, allowing for quick and efficient cleaning and any necessary repairs. All of these characteristics are crucial for the efficient operation of the heat pump and ensuring thermal comfort in buildings.

In order to ensure access and efficient removal of the heat exchanger from the heat pump installation (for servicing, cleaning, etc.), it is worth considering placing it on a mounting bracket, such as the one shown in the image below, which will guarantee this.

How to Connect a Plate Heat Exchanger to a Heat Pump?

To properly connect a plate heat exchanger to a heat pump in a central heating system, several important steps must be followed. First, clean the surface where the exchanger will be placed, providing adequate space for mounting. Then, check if the heat pump is properly prepared, and all components are functional and correctly connected. If necessary, provide appropriate protections against overloads and ensure that all installation elements meet safety standards.

After ensuring that the heat pump is fully prepared, you can proceed with connecting the plate heat exchanger. Determine the appropriate location for the exchanger and check if it is securely mounted with no loose parts. Then, connect the supply and return pipes of the heat pump to the appropriate fittings on the exchanger. It is important to ensure proper sealing of the connections to avoid leaks.

Remember that most plate exchangers are counter-current devices, and we cannot always freely choose the flow direction. In this case, follow the manufacturer's instructions.

After connecting all necessary pipes and wires, check if the installation is functioning correctly. Ensure that the exchanger properly absorbs heat from the pump and transfers it to the central heating system, keeping in mind that the so-called startup heat loss is higher and should stabilize after the initial system heating. If everything is working correctly, proceed with final adjustments and settings, such as temperature or water flow, to ensure the optimal operation of the entire installation.

How to Maintain a Plate Heat Exchanger Connected to a Heat Pump?

To ensure the proper functioning of the heat pump, it is necessary to regularly check the condition of the heat exchangers connected to it. The cleanliness of the plate heat exchanger is a key element in maintaining its efficiency.

Over time, usually over the years, deposits and contaminants such as scale, rust, or dirt can accumulate on the surfaces of the exchanger plates. These deposits lead to a reduction in heat transfer, resulting in decreased efficiency of the heat exchanger, and consequently, the heat pump will have to compensate for this with higher energy consumption.

Regular cleaning allows for the removal of these deposits and restores the optimal performance of the heat exchanger. It is also important to monitor and maintain the proper operating parameters of the heat pump, such as temperature, pressure, or flow rate. If one side of the heat pump has glycol and the other side has water from the closed-loop system, we can be decidedly optimistic - because the problem of scaling of devices in a closed-loop system is not as pressing. A worse situation occurs when operating in an open-loop system; in that case, it is worth monitoring the operation of the exchanger more frequently and reacting if necessary.

Caring for the plate heat exchanger connected to the heat pump is essential to maintain optimal efficiency and long-term operation of the entire system.