Heat pumps are three to five times as efficient as a fossil fuel boiler. But they cost more to buy and install. This means that in order to determine the payback time of a heat pump, we need to know its running costs.
Luckily help is at hand! The My Heat Pump tool, developed by SoftHVAC, can calculate the cost of electrical power consumed by a heat pump during a year and compare it with the cost of using an electric, gas, solid fuel or liquid fuel boiler.
In addition, it also shows the CO2e greenhouse gas emissions from the small amount of electricity consumed by a heat pump – depending on the geographical area you are in – and compares them with the emissions from combustion of gas, solid or liquid fuel.
Below, we walk you through the different sections of the tool.
Tariffs
To calculate the cost of the consumed energy carrier, the user enters the prices for these energy carriers in the given region.
For electrical power you can select a single or double (day and night) tariff for electrical power and observe the savings due to the usage of the double tariff, as electrical power is cheaper at night.
Climatology
In order to perform the most accurate calculation, the application uses the database of outside air temperatures of each day for the last 10-15 years for a particular city.
The user selects the city out of the 187 currently available – this can also be done via the map. That city’s recent average temperature data will be used.
If the desired city is not in the list, the nearest city within the radius of 200 km can be selected, to have similar weather data.
Today the application contains 187 cities. In addition, you can send a request to the developer to add a new city.
Heating purpose
In this section you can select one or more heating purposes:
- Heating.
- Hot water supply.
- Ventilation.
The capacities the operating time of the heaters within twenty-four hours should be entered.
For the hot water supply you can select the priority of its operation in relation to the heating.
If the priority is on (as a rule it is on), during water consumption of the hot water supply, heating of the heating system is stopped. This allows to heat pump capacity and its cost to be reduced.
If the priority is off, both heating of the heating system and hot water supply is performed simultaneously
Heat pump
You can select the type of heat pump: air-source or geothermal.
The heat source of an air-source heat pump is the outside air, while for a geothermal heat pump it is the ground or groundwater.
Also, the coefficient of conversion of electrical power into thermal (‘COP’) is entered in this section, at the respective temperature of outside air and heat carrier. This data can be found in the technical documentation of the heat pump.
Operating mode
Two modes of a heat pump operation are available: bivalent or monovalent.
Monovalent mode – the heat pump has a capacity equal to or higher than the maximum capacity of the system. For example, if the heating system capacity is 15 kW, the heat pump should be selected for 15 kW as well.
Bivalent mode – the heat pump has a capacity lower than the maximum capacity of the system and the lacking capacity is compensated by a separate electric heater.
The temperature at which the electric heater is turned on is called the bivalent temperature.
You may ask why do you need an electric heater, since it is less efficient than a heat pump? It’s all about climate.
Let’s consider the case for the city of Prague:
- Minimum temperature of the heating period is -12 °C.
- Maximum temperature of the heating period is +12 °C.
- Number of days of the heating period is 215 days.
- Heating system capacity is 15 kW.
Looking at climatological data, the temperature was between -12 and -3 °C for only 9.3 % of the heating period duration (20 days out of 215).
So, we can select a heat pump capacity sufficient up to the temperature of -3 °C (bivalent temperature), and at lower and more unusual temperatures an electric heater would be switched on in addition to the heat pump (see Figure below).
Then the capacity of the heat pump at -12 °C will be 7.5 kW and the capacity of the electric heater will also be 7.5 kW. The amount of heat produced by the electric heater will be only 4.67 %/year.
Thus, we managed to reduce the heat pump capacity by 50% (from 15 kW to 7.5 kW) and consequently its cost, with a minor increase of electrical power consumption.
The blue colour on the “Bivalent temperature” diagram shows the area of operation of the heat pump and the red color shows the area of operation of the electric heater.
By means of the “Level” slider you can change the ratio of the heat pump and electric heater capacity, which will also change the bivalent temperature. It is recommended to adjust the bivalent temperature so as the heat produced by the electric heater is qte ≤ 5 %/year.
Result
The “Result” section presents the main data:
- – Cost of usage for a heat pump, electric, gas, solid and liquid fuel boiler per year.
- – Heat pump capacity.
- – Electric heater capacity.
- – Thermal performance of an electric heater.
- – Bivalent temperature.
- – Useful heat provided.
- – Electrical energy consumption.
A more complete calculation result can be obtained by downloading the report as an Excel file.
In addition, many diagrams have been created:
The calculation of CO2e emissions for the heat pump and electric boiler is performed based on CO2e emissions from the produced and imported electrical power in the selected country. These data are constantly changing in different countries, so they are also regularly updated in the application.
Saving and opening the calculation
The calculation can be downloaded and then uploaded from the project file so that it can be reopened for viewing or editing in the future.
Conclusion
With this tool you can:
- Select the most appropriate heat pump.
- Determine the payback period of a heat pump.
- Provide a potential customer with a visual calculation to convince them to purchase.
- Compare the cost-effectiveness of the heat pumps from different manufacturers.
- Identify cities where a heat pump is most economically feasible.
- See how much the greenhouse gas emissions are less from a heat pump compared to combustible fuel boilers.
Developer: SoftHVAC
