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.
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
- 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 | Heat source | ambient air |
| Construction | 1992 | Number of HPs | 6 |
| Heated area | 7563m² | Installed power | 6 x 30 kW HP (A2/W50) |
| Level of insulation | low (1992 standard) | Operation mode | hybrid (HP + gas) |
| Existing gas boiler | 240 kW | ||
| Heat demand | 700 MWh/yr | Other Information | |
| Space heating | 71% of demand | Electricity cons. | 190 MWh/yr |
| Heating temperature | 60 °C (@ -7° ext) | Gas cons | 230 MWh/yr |
| Heat distribution | radiators | Investments costs | unknown |
| Domestic hot water | 39% of demand | PV installation | no |
| Type of system | centralized | ||
| Max. temperature | 60 °C | ||
| Circulation system | yes |
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 delivered by: Team Switzerland (CSD Ingénieurs SA)