Thermal capacity is the amount of heat energy that a heat pump can produce over a given period of time. This parameter is usually measured in kilowatts (kW) and is an important characteristic of a heat pump's performance, as it determines the extent to which it can meet the heating or cooling needs of a building.
Meaning of thermal power
Heating capacity: The amount of heat energy delivered by the heat pump in heating mode.
Power per unit of time: Thermal power shows how much heat the system can emit over a given time (e.g. 1 hour).
Unit of measurement: Thermal output is given in kW, which varies depending on the efficiency and size of the system.
What affects thermal performance?
Heat pump type:
- Air-to-water heat pump : It extracts heat from outside air, its efficiency and performance depend on the outside temperature.
- Ground-water heat pump: Uses a more stable heat source, providing higher and more constant heat output.
- Water-to-water heat pump: Very efficient because the temperature of the water varies less than that of the air.
Environmental factors: Temperature significantly affects the performance of a heat pump.
- High outdoor temperature: The system is more efficient, higher heat output can be achieved.
- Low outdoor temperature: The efficiency of the system may decrease, especially in the case of an air-to-water heat pump.
Heat transfer system: Low-temperature systems (e.g. underfloor heating) require less energy and therefore operate more efficiently with a heat pump.
Building heat demand: A larger building requires more heat energy to maintain the appropriate temperature, therefore a heat pump with a higher heat capacity is required.
Example of heat output calculation
Conditions:
- Annual heat demand of a family house: 15,000 kWh .
- The COP value of the heat pump is: 4 (i.e. 1 kWh of electrical energy can produce 4 kWh of thermal energy).
Heat output requirement:
Daily heat demand in winter:
Monthly heat demand = 15000 kWh / 5 months = 3000 kWh / month
Daily heat demand = 3000 kWh / 30 days = 100 kWh / day
Daily operation of the heat pump (e.g. 10 hours):
Required heat output = 100 kWh / 10 hours = 10 kW
Based on this, a heat pump with a heat output of 10 kW would be suitable for the given house.
Relationship between thermal output and COP
The efficiency of a heat pump is determined by the COP (Coefficient of Performance) value:
Thermal output (kW) = Electrical energy used (kW) x COP value
Example:
If the heat pump consumes 1 kW of electrical energy and the COP is 4, the heat output will be 4 kW.
Heat output of different heat pump types
| Heat pump type | Thermal performance stability | Typical environmental conditions |
|---|---|---|
| Air-water | Fluctuating | The outside temperature has a significant impact. |
| Ground-water | Stabile | Geothermal energy is predictable due to its stability. |
| Water-water | Very stable | High heat capacity of river or groundwater. |
Thermal performance optimization
Correct sizing: The size of the heat pump must match the building's heat demand.
Improving insulation: Improving the building's insulation can reduce energy demand, so a system with a lower thermal output may be sufficient.
Regular maintenance: The efficiency of a heat pump can only be maintained in the long term with proper maintenance.
Using low temperature systems: Using underfloor heating or wall heating reduces the energy demand of the heat pump.
Summary
Thermal capacity is one of the most important parameters of heat pumps, determining the extent to which a system can meet heating or cooling needs. Environmental factors, the building's heat demand and the type of heat pump have a significant impact on thermal capacity. Correct sizing and installation, as well as regular maintenance, are key to optimal operation.