Define house heating needs

The below input data is to define the heating needs of the house and to understand how the need affects the results. The selection can be done in two different ways:

• Select average heat consumption per year (for a definition of the heat consumption, see the simple temperature calculation form).
• Select the highest outside temperature at which heating is still needed for the house (heating a house is partly done by being in it and by using household appliances in the house). Thus, normally a house having a temperature of around 20 to 21 degrees does not need any specific heating above around 16 to 18 degrees.
• Then press the button below, which converts the given house data plus the selected temperature location to a house heat need curve.
• If so desired, it is instead possible to enter the heat need curve directly. This can be interesting to do to simulate either changed outside temperatures, or changes to the house isolation, or if the heat need curve is known through some means. If you specify the house curve yourself, by entering the effect needed per degree celcius in the third box below, then do not press the button below.

Geothermal heat pump definition

The geothermal heat pump is straight forward. It is defined by:

• The COP, which is assumed to be constant for all outside temperatures
• By its maximum output power (again assumed constant for all outside temperatures).
• For the COP calculations presented in the detailed tables available further down, the COP reduction caused by the power needed for circulation pumps, if not included in the stated COP figure, can be included by stating how much yearly consumption the pumps are expected to have. (Some vendors include this in their COP, some do not, most do not).

Heat Pump Effect and COP curve for Air-To-Water

Here the Air-To-Water heat pump is defined. Since the calculations are based on daily temperatures and house needs depending on temperatures, the heat pump must be defined using a COP curve as well as the input power curve for the heat pump.

In order to provide the possibility to calculate on more heat pumps than those for which I have provided data, the data is fetched in two steps.

• By selecting the Air-To-Water pump, and pressing the button to convert the heat pump model selected to heat pump data, the fields defining the Air-To-Water heat pump curves are filled with data from the selection.
• These data can then be altered at will, allowing you to define any behaviour of any heat pump model you want to do calculations on. The curve is based on a third degree curve, and the factors can easily be taken from a diagram using Excel or similar tools. Also, by setting the second and third degree factors to zero, a simple linear curve is easily defined.
• Just like with the house curve, if you want to define the curve data manually, do not press the button after having changed them.
• The specified output power is not used in the calculactions (it is derived from the input power and the COP). Ther value is provided for reference only.
• The specified forward temperature is the forward temperature for the water for which the data are taken. To compare different pumps fairly, the same temperature should be used. A rough estimate is that the COP is improved with about 15 percent per 10 degrees lower forward temperature, in the range of 50-35 degrees Celcius.

(or change values manually and do not press the key)

Heating curves for house and heat pumps

One important need is to understand at what temperatures the heat pump can meet the heating need of the house.

• The power need curve of the house is plotted below, and compared to the power outputs of the heat pumps selected. The diagrams are shown over a fixed intervall of temperatures. If you experiment with defining your own curves, the diagrams helps verifying the curves.
• Please note, the lines are unfortunately having a pixel resolution, and thus sometimes drawn a little bit above or below where they should be.

Investment costs

The investment costs are the same as for the simple form for heat cost calculations, and are defined there.

Starts and stops

Heat pumps without adjustments of their speed, will be regulated by starting and stopping the heat pump, thus either producing full output, or not producing any heat at all. If there is too little water in the system compared to the size of the pump, or if the difference between the minimum and maximum forward temperature aimed at by the regulator, then there will be many starts and stops every day. The below values are used to calculate number of starts and stops.

Resulting payback time

Below calculates how long time is needed to get back the investment for the alternatives, assuming that the cost per kwh is 1 SEK.

There is a factor that should be added to the calculations below. If you are situated in a place where the temperature is likely to go below the temperature of the air-to-water heat pump, then the need for additional heating will increase in a jump (from a little extra to using only additional heating). This additional heating might at that time mean you need a larger connection for the house to the power company than with the geothermal heater. The price for that additional connection is not yet included in below calculations, but can easily amount to 750 SEK per year, and even more.

• The electric heater is included as worst case reference, and is thus calculated without an investment in a new electric heater.
• The columns "Air-To-Water heat pump Saving" and "Air-To-Water heat pump years to payback" shows the yearly saving and the number of years it takes to get back the investment for the Air-To-Water alternative, compared to keeping an electric heater. Observe that the less energy is needed for heating, the longer time it takes to get back profit after an investment
• The column "Geothermal saving above Air-To-Water" and "Geothermal heat pump above Air-To-Water years to payback" looks at the additional yearly saving and number of years to achieve a payback for the decision to buy a geothermal pump, compared to buying an Air-To-Water pump. It is thus comparing the time it takes to get back the additional investment for the geothermal pump (the difference in investment) by the improved COP produced by that pump. A more thorough explanation for the reason for doing this kind of comparison is given.
• There are two buttons below, allowing to view more details on both the Air-To-Water pump, and the Geothermal pump. Most essentially, allowing to see needed amount of additional heating, needed due to either the pump being to small for handling all heat, or for the pump not being able to work during all outside temperatures.
• When looking at those details, COP is shown in two columns, one column indicating COP for the output produced by the heat pump, where the only factor reducing the COP is if a value has been defined in the input for circulations pump power not included in stated COP. The other factor shows that COP, further reduced by the additional heating needed by the electrical furnace to achieve the targeted power output.

temperature location: Copenhagen

Resulting pay back times including hot water

Below are similar calculations as those above, but this time assuming that hot water is part of the production from the heat pumps.

• As before, when the heat pumps are not capable of delivering the need, the remaining need is calculated as filled with additional heating from an electric heater.

temperature location: Copenhagen