April 12, 2024
Source: Energy & Management Powernews
The Heidelberg municipal utility has successfully commissioned an innovative CHP system with a unique air-to-water heat pump.
There are actually three systems: Stadtwerke Heidelberg has installed three innovative CHP systems in the Pfaffengrund energy park in the north-west of the city in Baden-Württemberg in recent months. Two are already in normal operation, the third will follow in the middle of the year. A new hall was built for the entire plant. "The three systems can be moved individually," explains Michael Teigeler, Managing Director of Stadtwerke Heidelberg Energie, in an interview with E&M. This reduces starts and stops without having to compromise on flexibility.
The city of Heidelberg is aiming for climate neutrality, with heat supply playing a central role. Stadtwerke has been expanding its range of green district heating since 2011: today, 50 percent of the district heating supplied comes from renewable sources, including a wood-fired combined heat and power plant and biomethane cogeneration plants. An important new component is now also the iKWK plant in the energy park.
A special feature of the iKWK plant is a three-part air-to-water heat pump. In innovative CHP, one or more CHP units are combined with a renewable heat source and an electrical heat generator to form a system. The following components are used in Heidelberg:
- Three CHPs with a total electrical and thermal output of 6 MW and a generation capacity of 21 million kWh of electricity and heat each
- Three air-to-water heat pumps as renewable heat generators with a total output of 4.5 MW and a capacity of 7.8 million kWh of heat
- A power-to-heat system as an electrical heat generator with an output of 2 MW
In particular, the system of air-to-water heat pumps used is unique in Germany to date. It was also not easy to organize a suitable system. In the end, the choice fell on three Sabroe systems from the manufacturer Johnson Controls, which are produced in Denmark. The plant construction was implemented by Engie Germany. "We are the first in Germany to have built a system of this size," says Tobias Enders, project manager at Stadtwerke Heidelberg. "Ammonia is used as the refrigerant as it is more efficient than CO2, for example."
The combined heat and power plants are from Zeppelin Power Systems. They are mainly operated in the winter months from mid-October to mid-March and will run for around 3,500 hours a year in future. This also works well with the heat pumps, says Enders. They generate heat in autumn and spring in particular.
Even without the iKWK, the district heating supply in summer can be covered by a wood-fired CHP plant, a waste recycling plant and several biomethane CHP plants. The iKWK therefore optimally complements the supplier's generation park - in winter, the CHP also covers the heat demand, while the heat pumps do this in the transitional period.
"The heat pumps can no longer be operated at temperatures below five degrees Celsius," explains Enders, "they would freeze." From around 15 degrees Celsius, the heat pumps have a COP of 2.2 and can then be used for Heidelberg's heat supply.
A lot of detailed technical work was required before the entire system was up and running - especially with the air-to-water heat pumps and the associated fans. Each heat pump circulates around 500,000 cubic meters of air per hour. The outside air is drawn in by 180 turbines (60 per unit) and forced into the air cooler. "We extract energy from the outside air, cool it down by five degrees and feed it into a brine system," explains Enders. The brine circuit is connected to the heat pumps. The energy for the district heating network is provided via heat exchangers.
To prevent the cooled air from being sucked in again - and thus severely disrupting the efficiency of the system - Stadtwerke Heidelberg developed the "air house" together with the project developer Enerko, the planning office Simon and the Institute for Industrial Aerodynamics at Aachen University of Applied Sciences. In Heidelberg, there is now a height difference of twelve meters between the air intake and the air outlet at the chimney. The air intake takes place at a height of 4.8 meters, while the air outlet at the chimney is around 17 meters high. The diameter of the chimneys is around four meters.
The third element is a power-to-heat system. It is used whenever there is too much electricity in the grid and produces heat with the surplus electricity, which is stored for later use. "By intelligently interconnecting the various heat generators, iKWK systems can react flexibly to fluctuations in the electricity grid and help stabilize it." The three systems can be started up individually, but are regulated and controlled together. This means that the individual system components can be used more flexibly and more precisely for the balancing energy market.
The iKWK system in the energy park is therefore a key building block on the way to a climate-neutral heat supply. Stadtwerke Heidelberg is investing around 20 million euros in the entire innovative CHP plant.
The plant at a glance
Operator: Stadtwerke Heidelberg
Plant: Three CHP units from the manufacturer Zeppelin Power Systems, each with 2 MW of electrical and 2 MW of thermal output, three Johnson Controls heat pumps, each with a nominal output of 1.5 MW, and a 2 MW power-to-heat plant
Special feature: The system of air-to-water heat pumps used, including the exhaust air ducts
Contact: Tobias Enders, Contact by Mail , Stadtwerke Heidelberg
Author: Heidi Roider
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