This project concerns the replacement of an existing gas heating system by a hybrid HP+gas solution in an existing multifamily building. With the goal of having the maximum annual heat production from HP origin, six air/water heat pumps were implemented on the rooftop. One of the previous gas boilers was kept for the peak loads in winter.
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The existing MFH (multi-family building), built in 1992 in Geneva, contains 68 apartments, within 4 floors, plus commercial establishments on the ground floor (restaurant, bakery, …). It suffered no major envelope retrofit before this project and the total gas consumption amounted to 1’000 MWh/yr (for space heating and domestic hot water of 7’563m²). (Photo credit SIG, CSD Ingénieurs SA)
Lessons learned
Ongoing monitoring, but so far:
- Major air HP constraints encountered: noise emissions, vibrations, safety… These implied important costs and planning work.
- Hybrid HP+gas system: optimization of the gas boiler switching point is crutial for a good HP share in the overall heat production (specially with an old boiler without variable power output).
- The constraints of the old heat and DHW distribution system should not be underestimated.
Key facts
| Building | Heat pump and source | |||
| Location | Geneva, Switzerland |
Number of HP | 6 | |
| Construction | 1992 | Installed power | 6 x 30 kW |
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| Heat distribution | radiators | Operation mode | hybrid (HP + gas) |
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| Heated area | 7,563 m² | Heat source | ambient air | |
| Level of insulation | low (1992 standard) | Existing gas boiler | 240 kW | |
| Heating system | Domestic hot water | |||
| Heat demand | 700 MWh/yr | Type of system | central | |
| Heating temperature | 65 °C (@ -7° ext) |
Max. temperature | 60 °C | |
| Circulation system | yes | |||
| Other information | ||||
| Electric and gas energy consumption | 190 MWh/yr electric
230 MWh/yr gas |
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| Investments costs | unknown | |||
| PV installation | no | |||
Description of the technical concept
This project, part of a Geneva pilot program to replace fossil fuel boilers by heat pumps (HP) in MFH, concerns the replacement of a gas heating system by a hybrid HP+gas heating system. With the goal of having a maximum heat production from HP origin, six 30 kW air/water heat pumps were implemented on the rooftop. For the peak loads in winter, a 240 kW gas boiler was maintained.
It should be mentioned that:
- The building rooftop was retrofitted before the HPs were installed. No other retrofit action was undertaken.
- The heat and DHW distribution system was not modified.
The 6 HPs are divided into 2 groups of 3. 1 group exclusively for space heating, the other can either do space heating or domestic hot water. The gas boiler, when functioning, can work simultanioulsy with the HPs.
Case study sheet CH Daru