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 | |
| Heat distribution | radiators | Operation mode | hybrid (HP + gas) | |
| 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 | |||
| 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.
