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The professional tool for planning, design and calculation of heat pump systems


Looking for a user-friendly specialized tool for the planning and design of heat pump systems? Then our program GeoT*SOL® is the perfect partner for your planning.

You can choose between different heat sources and system configurations for your location. A key feature is the integration of solar thermal systems for domestic hot water or space heating. Requirements, losses and consumption are determined as a result of the dynamic minute-step simulation. These form the basis on which electricity consumption, annual coefficient of performance and costs are calculated, taking into account off-periods and tariffs. With these parameters GeoT*SOL® evaluates the efficiency of the system. Heat price and yield are given for the heat pump and a comparison system.

System Requirements

GeoT*SOL english

  • Internet Access
  • Processor: Intel i3 oder äquivalent
  • Memory: 512 MB
  • Hard Disk Drive: 350 MB
  • Monitor Resolution: at least 1.024 x 768 Pixel
  • Operating System: Windows 7 (mit aktuellem Service Pack), Windows 8.1, Windows 10
  • Graphics: 64MB
  • Other: Microsoft .Net Framework 4.7.2 Redistributable Package

Program Details

NEW! New bivalent systems with boiler and heat pump

New bivalent hydraulic systems with a boiler have been added, in addition to the monovalent and monoenergetic systems with heat pumps and solar thermal systems. It is thus possible to simulate existing systems with a boiler, where a heat pump has been added. New plants with a boiler as a backup can also now be displayed and optimized.

The mode of operation can be selected and parameterized for the simulation from a large number of possible combinations of monovalent, monoenergetic and bivalent systems with parallel, partially parallel or alternative operation.

As well as heat pumps, boilers can now be selected from a comprehensive and up-to-date database of nearly 1,600 products.

NEW! Completely Reworked VDI 4650 (2016)

The new VDI 4650 from 2016 is mainly based on field monitoring projects from Fraunhofer ISE and thus depicts heat pump systems more realistically. New are performance-controlled heat pumps as well as solar support.

From March 16, 2019, the new VDI 4650 (2016) will apply to all new applications for funding from the German Federal Office of Economics and Export Control (BAFA). This means that there is still a transition period until March 15, 2019 for applications under the old VDI Directive.

Heat Sources

The principle behind a heat pump is quite simple: A heat pump extracts heat from a lower-temperature external heat source (ground, groundwater or air) and then uses drive energy to emit that heat at a higher temperature in the form of useful heat. GeoT*SOL® supports the following heat sources:


The heat stored in deeper soil layers is extracted by brine/water heat pumps with geothermal probes. This requires one or more holes drilled vertically into the ground.

Near-surface heat is gained through heat transfer pipes – the geothermal collectors – which are laid horizontally at depths of about 1.5 m. They make use of the heat flow, which is taken from the layers of soil above and below the collectors.

Ambient Air

Air/water heat pumps suck outside air through air channels and extract the heat contained therein. This is released to the water-powered heating.


Water is extracted from the groundwater by a suction well, and after flowing through the heat pump is redirected into the ground via an injection well.

System Types

With GeoT*SOL® you can simulate five different heat pump system types, from simple to very complex, each for configuration with geothermal heat probes, air, geothermal collectors or groundwater.

Climate Data Generator MeteoSyn

The climate database from MeteoSyn contains global data records. You can select the relevant location on an interactive map or you can select the locations from a list. New climate data can also be created by interpolation of existing climate data. In addition, it is possible to load other climate data in wbv format.


The dynamic minute-step simulation over the course of the year gives you the following parameters for the selected heat pump system:

  • The annual coefficient of performance for the heat pump, the heat pump system and the generator system (heat pump system with solar thermal system) for comparison purposes ACOP according to VDI directive 4650.
  • Where appropriate the solar fraction, i.e. the amount of collector energy relative to the sum of generated energy.
  • If applicable, the solar fraction, i.e. the share of solar energy towards the total generated energy requirement.
  • The amount of energy generated by the heat pump and (when appropriate) the solar collector circuit, on an annual basis.
  • The annual electrical energy required for the heatpump, source-side pumps and auxiliary heating.
  • The annual generated energy for the heatpump and solar cycle.
  • Annual losses of the storage tanks and pipes.
Financial Analysis

The financial analysis provides important arguments for property owners. It is determined by way of the heat price by allocating investment costs (minus subsidy) and operating and maintenance costs (including anticipated increases in electricity costs) to the generated heat energy over appropriate periods (service life, interest on capital). You can then use the heat price to compare the heat pump to other heating systems, such as gas or oil-fired boilers.

Additional results provided are the net present value and the modified internal rate of return with reinvestment premise.


All results are documented in a project report that you can save and forward to your customer as a PDF or RTF file or print and deliver together with proposal documents. The report contains:

  • Cover sheet with desired project data, such as logo and your firm's contact data.
  • System schematic and results of the annual simulation (relevant energies and ACOP).
  • Specifications and system components.
  • VDI 4650 calculation parameters and results.
  • Summary financial analysis with all parameters and results, as well as useful graphics.
Feature Matrix
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Frequently Asked Questions: Heat Pumps

Heat Pumps

Heat Pumps

Open the heat pump database via the menu item "Database" > "Heat pumps". Now select from the available records a heat pump of the same type with a comparable coefficient of performance (COP) and click with the right mouse button on it. Select from the context menu "Create copy". In the definition window you can enter the model type of the heat pump under product. Enter the required characteristics according to the data sheet. If you do not find all the test points on your data sheet you only have to change the test points which are available and leave the other according to the template. Save everything with "OK".

Heat Pumps

Hot water tanks can help to bridge the off-periods. Furthermore, low temperature heating systems are very inert and can therefore also compensate off-periods. You can thus prove that no supply gaps occur even when using off-periods.


Heat Pumps

This can have various causes.

Hot water priority circuit block the heating:

Even if the performance of the heat pump and the heating element can satisfy the heating load together, it may be that due to the domestic hot water (DHW) priority circuit not enough energy is delivered to the heating circuits . Domestic hot water circulation losses can increase the energy consumption in addition.

=> Check the domestic hot water heating: DHW temperature, size of the heat pump and the heating element and the limits of operation of the heat pump, size of the DHW standby tank.

Monovalent operation mode:

In the monovalent operation mode, the heat pump must deliver all of the energy. If the source temperatures are outside the operating limits, the heat pump is turned off and supplies the heating circuits thus insufficient ( e.g. due to frozen ground when using geothermal collectors or extremely cold ambient air when using air heat pumps). This effect may also occur on a daily basis in the fall, if a low heating demand is present at times with high source temperatures.

= > Operate the heat pump monoenergetic with a heating element.

=> Define a custom heat pump (a copy of an existing heat pump in the database) and adjust the operating limits.

Heat Pumps

The yield of the collector circuit is delivered to the tank. Above a certain size, an increase of the collector area causes that the energy input in the tank is greater than the demand and the tank is heated above the required temperature. At 90°C the collector circuit is turned off. A portion of the yield of the solar system is not used to meet the requirements, but there are increased tank losses generated. These “solar tank losses” are presented on the results page. For optimum sizing of the solar system you have to vary the size of the collector area, the tilt angle and the tank size. Design criteria are efficiency, solar fraction and the solar tank losses.

Heat Pumps

In the program three different seasonal performance factors are shown on the "Simulation Results" page. In addition the SPF according to the VDI 4650 is presented.

Generally the SPF is calculated as follows:

SPF = benefit / expenditure

Depending on the system boundaries which are considered, the energies taken into account differ. It should thus be compared only SPF of the same type.

SPF Heat pump

This SPF limits the energy balance to the heat pump. It is the largest of all SPF and can usually help in assessing the operation of the heat pump. In the monoenergetic operation mode it is usually somewhat higher, since at very low source temperatures (= bad seasonal performance factor of the heat pump), the heating element takes over the supply.

Benefit: The heat supplied by the heat pump heat.

Expenditure: The electricity consumption of the heat pump without external pumps and without heating element.


SPF of heat pump system

This SPF is a good benchmark for the entire system. The efficiency of the heating element is set at 100 %. Furthermore, existing heating circuit pumps on the sink side are not considered.

Benefit: The heat supplied by the heat pump + the energy from the heating element.

Expenditure: The electricity consumption of the heat pump + heating element energy consumption + electricity consumption of external pumps on the heat source side of the heat pump.


SPF Generator system (Heat pump + Solar)

This SPF is usually much higher than the previous SPF, because for the low expenditure of the solar circuit pump a large amount of energy is delivered as a benefit.

Benefit: The total heat supplied by the HP + the energy from the heating element + the energy from the solar collector.

Expenditure: The electricity consumption of the heat pump + heating element energy consumption + electricity consumption of external pumps on the heat source side of the HP + electricity consumption of the solar loop pump.

SPF according to VDI 4650

It is especially relevant for the approval of funding in Germany. This SPF is calculatedby using simple equations decribed in the VDI 4650 (2009). So they may differ from the simulated SPF.

  • Geo T*SOL - Find the right heat pump

    Summary of main features - Planning of heat pump systems with air/water, brine/water or water/water heat pump, consideration of HT/LT rates and off periods

Program Screenshots