HOW DOES A HEAT PUMP WORK?

The main elements that make up and enable the operation of a heat pump are:

• Compressor: Enables the refrigerant to be pressurized, thereby raising the temperature to a high level.
• Evaporator: A heat exchanger that allows the transfer of energy from the heat source (air, ground, or water) to the refrigerant. In the evaporator, the refrigerant heats up and changes to a gaseous state.
• Condenser: A heat exchanger that ensures that the hot refrigerant releases heat into the heating system. In the condenser, the refrigerant cools down and condenses, returning to a liquid state.
• Expansion valve: Reduces the pressure and, consequently, the temperature of the refrigerant, absorbing heat at the evaporator. It also regulates the volumetric flow so that the evaporator receives only as much cooling fluid as it can vaporize.
• Buffer tank: Reduces the number of compressor starts, maintains a uniform temperature of the heating water (and thus greater temperature comfort in the premises). In air/water heat pumps, it also serves as a heat source for efficient defrosting of the evaporator.
• Refrigerant: The working fluid, a medium responsible for heat transfer, stability, and durability, as it undergoes constant temperature changes and transitions from a liquid to a gaseous state. Refrigerants can be toxic and flammable, and there are also four natural and less environmentally harmful ones. In the Adapt heat pump, we use a special refrigerant, R452b, which does not harm the ozone layer and reduces greenhouse gas emissions by 68% (compared to conventional heat pumps).
• Flow-through electric heater: Potential assistance in heating and for performing thermal disinfection of sanitary water (anti-legionella protection).
• Temperature sensors: Included at the inlet and outlet of the heat source, where they work against freezing and damage to the plate heat exchanger or as an indicator of consumption or temperature difference between the inlet and outlet of the source. Sensors in the supply and return lines enable the limitation of the maximum temperature and the shutdown of the heat pump when a certain return water temperature is reached.

Heat pumps operate on the principle of interdependence between temperature, pressure, and the volume of gas or refrigerant. If we reduce the pressure of the gas, the temperature decreases; if we increase it, the temperature rises. The operation takes place with the help of three circuits: the first is the heat source (air, ground, or water), the second is the so-called refrigeration circuit, which includes only the heat pump, and the third is the heating system (underfloor heating, radiator heating, or hot water heater).

Heat pumps transfer (pump) thermal energy from the heat source (ground, water, or air) to the heating system using electrical energy. This happens in a closed circuit, where the liquid working medium (refrigerant) evaporates, compresses, and liquefies again. This is the only way to raise the thermal energy from a lower temperature level to a higher level. The refrigerant remains in the circuit and is not consumed or released into the environment.

Air/Water Heat Pumps

How does an air/water heat pump work? Air is an endless source of energy and is available everywhere. The latest air/water heat pump designs allow heating even at an outside temperature of up to -25 °C. Even at such a low air temperature, you can still save 50% of energy. This is the most cost-effective type of heat pump, and both installation and maintenance are simple and inexpensive. Air/water heat pumps are usually designed to independently cover all heat losses of the building up to an outside temperature of -5 °C. Below this threshold, the heat pump can operate with another heating source. This way, we can cover more than 98% of the heat requirements of the building with the operation of the heat pump. For new buildings, an electric heater is usually used as the second heating source, while in existing buildings with a good conventional heating source, it can also be used. Electronic control allows easy setting of the switching point to the second heating source.

Water/Water Heat Pumps

How does a water/water heat pump work? Groundwater heat is a very favorable energy source for a heat pump. Its advantage lies in a relatively constant temperature level, approximately between +7 and +12 °C. To utilize groundwater, two boreholes are drilled near the building, one for extraction and the other for the return of groundwater. A submerged pump is inserted into the extraction borehole. During operation, the pump pushes water through the heat pump, where it extracts thermal energy and returns it, cooled by a few degrees Celsius (from 2 to 4 °C), through the other borehole, located a few meters away (15–20 m), back into the groundwater. The amount of water in the suction well must be sufficient for continuous operation during peak heating demands. A water permit is required for groundwater pumping, and the water must be chemically analyzed before starting the work. Groundwater is an ideal heat source due to its relatively high temperature, resulting in high coefficient of performance (COP) values for the heat pump. The COP is the ratio of useful thermal energy to the supplied electrical energy for operating the compressor and other electrical devices in the heat pump. High-quality air-to-water heat pumps have a COP above 3, meaning that for 1 unit of invested electrical energy, we obtain 3 units of thermal energy.

Water-to-water heat pumps provide a significant thermal output with very small external dimensions. The robust and innovative design is further enhanced by a special plate heat exchanger made of stainless steel, which transfers heat from one fluid to another.

Ground/Water Heat pumps

Geothermal heat pumps (ground/water heat pumps) harness the thermal energy stored in rocks or the earth. A substantial amount of solar energy is stored there, which can be utilized for heating homes and/or domestic water. The amount of energy that can be extracted from the earth depends on the soil composition, heat pump capacity, and the utilization method. Heat is extracted using a liquid circulating in a closed pipe system, either laid at a depth of 120–130 cm (horizontal collector) or inserted into wells ranging from 60–140 m deep (vertical probe). The circulating water transfers heat to the heat pump, which, with the aid of added electrical energy, elevates it to a higher temperature level (up to 63 °C), returning it cooled by approximately 4°C.

Cooling with the Help of a Heat Pump

Although heating and cooling are opposing temperature processes, a heat pump combines them. Heat pumps provide cooling actively on the primary level (reversible heat pumps, where the compressor operates during cooling) and passively (in geothermal heat pumps and water/water heat pumps, where only primary pumps operate). On the secondary level, the transfer of cold air to spaces must also be ensured, achievable through dynamic cooling (convectors) or quiet cooling (floor or wall cooling).

The most efficient and cost-effective heating-cooling systems are reversible air/water heat pumps. These enable economical heating of spaces and domestic water in winter and heating of domestic water and cooling in summer. Some special designs allow utilizing waste heat from cooling for heating domestic water or even a pool during the cooling mode. Reversible air/water heat pumps, providing effective heating in winter and cooling in summer, offer the simultaneous heating of domestic water in both modes. KRONOTERMOVE air/water heat pumps come with a built-in feature for both heating and cooling spaces.

In commercial buildings, convectors are often installed for both cooling and heating. The advantage of convectors in cooling is the ability to remove moisture from the air, reducing the need to lower the desired cooling temperature significantly. However, convectors (especially for heating) must be sized more generously to heat at lower hot water flow temperatures. Every Celsius degree reduction in the flow temperature represents a 2.5% improvement in the efficiency of the heating system with a heat pump.

Many mistakenly believe that it is not worth having heat pumps, arguing that they are only in use for part of the year, during the heating season. A heat pump can be used all year round, and it is not turned off even in the summer months when there is no need for heating. Just from the perspective of heating domestic hot water, heating heat pumps are used in all months, as we need hot water throughout the year, not just in winter. Even if we have another existing source for heating water, there is no need to turn off the heat pump.

It is strongly advised not to turn off the heat pump, especially in the case of radiator heating. If the heat pump is turned off, the heated water in the radiators will quickly drop below 20°C, triggering the electric heaters when the heat pump is in operation. Heat pumps are designed so that, for the protection of the compressor, the water in the heat pump should not be colder than 20°C. At a lower temperature, the heat pump switches to electric heaters, and due to their constant operation, the electricity consumption can be up to three times higher.

Our ADAPT heat pump, for example, adjusts its heating capacity to the building’s needs. It automatically turns on or off as needed. There is also no concern about heat pumps consuming too much electricity during idle periods, as they only require electricity for operation.

Now that you know how a heat pump works, it is crucial to carefully consider which one would be suitable for your household. The dissatisfaction of users with the performance of heat pumps sometimes does not depend on the heat pump itself but rather on the incorrect selection of the appropriate type or thermal power of the pump. This is largely dependent on the heating surface, encompassing the entire area where we reside, even if, for example, we do not heat a hallway or heat a space only occasionally. The proper selection of a heat pump based on thermal power also depends on the insulation of the building (roof, facade) and the insulating properties of installed windows.

It is essential to emphasize that when choosing a heat pump, the provider must be presented with the actual needs. If you prefer a warmer temperature in winter (e.g., 24-26°C or otherwise), you must take that into account and communicate it. Information about your lifestyle is also crucial – for example, if additional family members with four members visit the upper floor on weekends, which is otherwise not heated, or if you need larger quantities of hot water, etc. These are basic data for determining the required power, considering the design temperature for each location. The fact that certain heat pumps on the market are not designed to operate in our climate should not be neglected. We have specifically designed heat pumps for operation in our climatic conditions, and they function even at -25 degrees Celsius.

In summary, it is important to present all needs and desires, as this is the only way to choose the most suitable heat pump that will serve you well and for a long time, even in the coldest winters.

What if there is a power outage is a question and fear we often hear. Completely unjustified because when there is a power outage, even gas or oil heating systems do not operate. The only thing that can heat the home during electrical outages is a fireplace. In today’s time, electrical outages are rare and exceptionally quickly resolved, and buildings (especially well-insulated ones) do not cool down so rapidly.

Heat pumps are designed in a way that always allows the option of an additional source. In case of an electrical outage or any reported error, the operation switches to the additional source during the interim. The additional source is easily configured in the menu settings on the control panel of the indoor unit of the heat pump for the duration of error resolution. At KRONOTERM, we address errors exceptionally quickly, as we have our own service with rapid responsiveness anywhere in Slovenia and always have spare parts available. Furthermore, almost 50% of issues are resolved remotely without a home visit, thanks to our smart application Cloud.KRONOTERM.

If you wish to have a worry-free heating system for your home, need additional information, or would like personal advice, contact us at info@kronoterm.com .