Special heat pumps lower return temperatures in the system

October 30, 2026

Source: E & M powernews

Thanks to special heat pumps, heat consumption at the Freiham Education Campus in western Munich has been nearly halved. This increases the number of connections to the geothermal network.

The Freiham Education Campus in western Munich requires less heat than originally planned. “Compared to the planned figures, we’ve roughly halved heat consumption,” said Markus Falke, an employee in the Building Construction/Energy Management Department of the City of Munich’s Building Authority. The city attributes the savings to continuous monitoring and optimization of the heating systems. The buildings are heated with district heating from the Freiham geothermal heating plant.

According to the city’s Department of Construction, the specific heat consumption of the school buildings and the adjacent sports park now stands at around 25 to 30 kWh per square meter—significantly below the planned value of 55 kWh per square meter. An additional retrofit with special heat pumps is now intended to keep the return temperatures in the district heating network permanently low. To this end, special heat pumps—“eXergie machines”—developed by Varmeco and its Swiss partner BMS-Energietechnik have been installed. The companies announced this on October 29. This not only reduces heating costs but also takes some of the strain off the geothermal district heating network.

The Freiham Education Campus began operations in the fall of 2019. The school complex includes an elementary school, a special education school, a high school, and a middle school, and can accommodate up to 3,000 students. The neighboring sports park with a swimming pool followed in 2020. Both facilities draw their heat from the Freiham geothermal heating plant operated by Stadtwerke München (SWM). The plant extracts thermal water at a temperature of around 90 degrees Celsius from a depth of approximately 2,500 meters.

The district heating network in Freiham operates with a variable flow temperature of up to 70 degrees Celsius. In the summer, it often drops to 60 degrees Celsius. To make the most of the available heat, the operators aim for return temperatures of less than 35 degrees Celsius. The greater the temperature difference between the supply and return lines, the more heat the network can transport at the same flow rate. Low return temperatures thus create capacity for additional connections. This is where the “eXergie machines”—special heat pumps—come into play.

Heat Pump Creates the Ideal Temperature Stratification

“The exergie machine is a special electric heat pump that allows us to optimize temperature stratification in the heating system,” explains Robert Müller. He is a planner and construction manager from Schwindegg whom the city brought on board for the project. The machines have already been installed on the school campus and at the sports park, each paired with a low-temperature storage tank and a high-temperature storage tank.

The exergy machine serves a dual purpose: On the one hand, it acts as a temperature booster, charging the high-temperature storage tank or the supply line to the consumers. As a result, recharging with district heating is needed less frequently, and when district heating temperatures are low, the exergy machine serves as a reheater. In doing so, it primarily uses self-generated PV electricity. On the other hand, it cools the return flow to the district heating transfer station, which is connected to the bottom of the low-temperature storage tank. Thanks to separately controllable pumps, the heating and cooling effects of these special heat pumps can be precisely adjusted to the degree. “In this geothermal application, ensuring the return flow does not fall below 35 degrees is a key criterion,” says planner Müller. “If the return flow is too warm, the exergy machine kicks in.”

To ensure the best possible energy flows, the planners have installed three-way valves both before and after the heating storage tanks. On the return flow from the consumers, three-way valves ensure optimal, temperature-dependent feed into the storage system. On the supply line to the hot water network, the three-way valve acts as a mixer to maintain a constant supply temperature. For example, when the local PV system is operating at high output, the exergy machine can charge the hot water storage tank to over 70 degrees Celsius and make effective use of the excess electricity; the three-way valve then mixes the temperature down to a level suitable for the domestic hot water network.

A total of eight such exergy machines, each with a thermal output of 20 kW, will be operational in Freiham’s schools and sports complex once the retrofit is complete: one at the education campus, two more at other schools, and five at the sports campus.

The city is pursuing several goals with this retrofit. The systems are designed to limit return flow temperatures under varying consumption conditions, reduce reliance on district heating, and ensure the temperatures required for domestic hot water production. At the same time, the use of locally generated photovoltaic electricity is intended to reduce the heat pumps’ electricity consumption.

Author: Heidi Roider