Thermal System

Page: Thermal System

On the page Thermal system the thermal system can be selected and dimensioned.

The following systems are available:

Heat generators Consumers
Heating element Hot water
Heating element Heating
Heating element Hot water and heating
Heat pump Hot water
Heat pump Heating
Heat pump Hot water and heating

System components

Different system components can be parameterised depending on the system selected.

Storage tank

The storage tank is the central element of the thermal system. The heat generators heating element, heat pump or boiler supply the storage tank with thermal energy. Energy is extracted from the storage tank through hot water consumption and heating. Furthermore, thermal losses occur.

The following parameters are available:

Parameter Description
Volume The volume of the storage tank is given in litres. It is understood as gross volume. The net volume used in the simulation is set at 90% of the gross volume.
Height By specifying the height, the radius of the storage tank is obtained. This also results in the shell surfaces, which are important for the calculation of thermal losses.
Thickness of insulation The thickness of the insulation is an important parameter for calculating thermal losses. PV*SOL® is based on rock wool insulation with a specific thermal conductivity of 0.037 W/(m K) at 20 °C.
Temperature of the storage environment The temperature of the room in which the storage is located is specified here. This value is also important for the calculation of thermal losses.
Max. storage tank temperature by boiler The maximum temperature to which the water in the tank is heated by the boiler.
Max. storage tank temperature by heating rod The maximum temperature to which the water in the tank is heated by the heating element. This can be a few degrees Celsius higher than the max. storage tank temperature through the boiler to increase the solar fraction.
Legionella circuit With the help of the legionella circuit, the water in the storage tank is brought to a higher temperature at regular intervals to kill off legionella.

Heating element

Prerequisite: System selection with heating element

The heating element uses excess PV energy to heat the water in the storage tank.

The following parameters are available:

Parameter Description
Stepless The heating element can operate either in fixed steps or with a continuously adjusted output.
Maximum power The maximum electrical power the heater can handle
If the heater works in predefined steps, the number of steps can be entered here. The resulting power levels are displayed below.

Heat pump

Prerequisite: System selection with heat pump

The heat pump uses electrical energy to provide the system with thermal energy at the desired temperature level. The heat pumps stored in PV*SOL® are air heat pumps, i.e. the source medium is the ambient air. The temperature of the ambient air is taken from the climate data.

The following parameters are available:

Parameter Description
Nominal heating capacity The nominal heating capacity in kW represents the maximum value that the heat pump can deliver to the cylinder.
Type Here you can choose between three heat pumps, which differ in their efficiency.
Operating mode Standard: The heat pump operates on the basis of heat demand. PV-optimised: The heat pump only works when excess PV electricity is available.
Blocking times Blocking times can be defined here, which are often requested in connection with heat pump tariffs.

In PV*SOL® we assume a controllable heat pump that can modulate its output.

Hot water

Prerequisite: System selection with hot water

The annual energy requirement for hot water and the corresponding tapping profile (in 1h resolution) can be set here. The tapping profiles were taken from our solar thermal programme T*SOL. Typically, the share of hot water demand in single-family households is about 20% of the total annual heating demand.


Prerequisite: System selection with heating

The parameters on this page can be used to determine the heat consumption. Here too, the basis is the currently selected climate data.

The following parameters are available:

Parameter Description
Room temperature The desired temperature in the living rooms is specified here.
Heating limit If the temperature falls below the heating limit, the heating starts to work. Above it, it is switched off.Heated area
Standard ambient temperature Determines at which outside temperature the full heating load is required. According to the standard, this is the “lowest two-day average air temperature reached or undershot 10 times in 20 years”.
Input of the heating load or heating requirement If the heating load in kW is known, e.g. through technical building calculations, it can be entered directly here. Otherwise, the total heating requirement for the year can be given in kWh.
Night lowering Night lowering can also be parameterised. Enter the temperature by which the temperature is lowered and the start and end time of the night lowering.
Inactive At medium latitudes, the heating is often switched off completely in summer. This can be set here.


The boiler is present in all selectable thermal systems. It ensures that missing energy in the storage is recharged. In the simulation we assume that the boiler can provide the required output. The choice of fuel influences the amount of $\text{CO}_2$ saved.

Type of boiler specific $\text{CO}_2$-emissions in kg/year
Oil condensing 0.28
Gas condensing 0.23
Wood (Pellet, wood chips, logs etc.) 0.04

See also