CHP plant with fivefold benefit

22.04.2025

Source: E & M powernews

The refurbishment of the North Canteen of the Göttingen Student Union also involved renewing the energy supply. The new CHP plant not only generates energy efficiently for the canteen kitchen.

Studierendenwerk Göttingen has replaced the North Canteen with a highly functional new building with a CHP plant and an expanded catering concept. After the trial run in April, the new "Campus Gastronomy in the North" (CGiN) is expected to serve several thousand meals a day to students on two floors from May. This will replace the North Canteen, which has become too small after four decades.

For the energy supply, those responsible have opted for a CHP energy center that combines five forms of energy - electricity, steam, heating, hot water and cooling - to supply the students and the canteen kitchen. Waste heat sources that are not normally used were also "tapped" in order to achieve optimum energy efficiency.

The energy center was installed on the top floor of the CGiN. In future, it will not only supply CGiN, but also other buildings on the campus via local heating networks - one for high-temperature heat and one for cold local heating. These include a daycare center, a guest house and two halls of residence with around 700 student places.

When planning the generation plant and building technology, it was important to Studierendenwerk Göttingen to optimize operating costs "in a way that makes sense in terms of energy efficiency and sustainability and leads to a significant reduction in CO2 emissions," said Jörg Magull, Managing Director of Studierendenwerk Göttingen, when the plans were presented to the public at the beginning of 2024.

"Gas will be used as the primary energy source; steam-powered cooking appliances and dishwashers make this necessary. By continuing to use an efficient energy supply, combined with heat recovery, the primary energy used will be put to the best possible use," explains Carmen Heine, Head of Facility Management at the Studierendenwerk. Both food preparation and dishwashing (around 38,000 pieces of crockery a day) with hot water supply require a high temperature level in order to meet the tightly timed requirements of canteen operations. This is another reason why the Studierendenwerk opted for a highly efficient CHP system.

The barrier-free new building complies with the KfW 40 standard. Compared to the old building, the floor space has been increased. This increases the number of canteen seats from 770 to 1,050. The new canteen also offers a pavilion concept for serving food and self-scanner checkouts. Up to ten different dishes will be on offer in future, of which a total of over 3,000 will be served at lunchtime.

The old canteen had an annual energy requirement of around 950 MWh of heat and 869 MWh of electricity. Cooking was purely electric, while heating was provided by the University of Göttingen's district heating network. The switch to steam cooking appliances and absorption cooling as well as the co-supply of halls of residence will increase the heat requirement, including steam, to around 1,850 MWh per year in future, while the amount of electricity still to be purchased from the supplier will fall to around 150 MWh per year. As a result, operating costs and CO2 emissions will be significantly reduced as a highly efficient combined heat and power plant will be used to generate its own electricity.

The new generation system consists of two compact CHP modules from the manufacturer Sokratherm (type GG 140 and GG 202) including a steam generator, external exhaust gas heat exchangers and downstream condensing heat exchangers. An absorption refrigeration system and exhaust air heat exchangers were also integrated. The system and the cold local heating network with the heat pumps installed decentrally in the buildings were planned by engineering firm Geese.

The five forms of energy generated by the new system are as follows:

1. around 348 kW of electricity

2. around 179 kW of steam at 1 bar for cooking appliances and dishwashers. At times when steam is not required, the steam generator is bypassed and more high-temperature (HT) heat is generated accordingly. A conventional steam boiler is integrated in parallel as redundancy and to quickly cover peak loads from the cooking demand.

3. 333 kW HT heat (VL/RL: 83/70 degrees Celsius) for the CGiN and feed into the HT local heating network

4. around 290 kW low-temperature heat (VL/RL 40/25 degrees Celsius) from the various waste heat sources for the cold local heating network. The guest house with 100 and two student residences with around 700 places were connected to this network, each of which is heated by decentralized water-to-water heat pumps. The heat pumps work particularly efficiently thanks to preheating with CHP waste heat. Low-temperature sources are the CHP condensing heat exchangers with 76 kW and the cooling air heat exchanger of the CHP units with 42 kW. 80 kW are added from the condensation waste heat from CO2 refrigeration and the exhaust gas heat from conventional steam generation provides a further 40 kW.

5. cold water for room cooling via two "Hummel" absorption cooling units from the manufacturer W. Baelz & Sohn, which use the HT heat from the CHP units to generate cold water. The dining rooms and kitchen are cooled both via the air conditioning systems and via radiant ceiling panels in the dining rooms to cover the base load.

In addition, a CO2 compound refrigeration system is used to generate process cooling for food storage and serving as normal cooling (NK) and cooling down to minus 20 degrees Celsius for the deep-freeze and shock-freeze areas. Refrigeration is distributed to around 60 refrigeration points throughout the canteen via a CO2-carrying refrigeration pipe network. The waste heat from refrigeration is used separately at HT (hot gas cooling) and low temperature (NT) level (condensation) and fed into the corresponding heating networks.

Ultimately, almost all waste heat sources from the energy center are used consistently to heat the connected buildings and air-condition the canteen. This means that the energy supply for the new CGiN canteen achieves a particularly high level of overall efficiency.

Author: Heidi Roider