Collective air-to-water heat pump for co-ownership

As part of the energy renovation of a collective residential building with 11 flats of 88 m² each (approximately 968 m² heated), the old plant room with a 234 kW oil boiler was replaced by an installation of 5 Panasonic Aquarea High Power heat pumps at 16 kW each, in cascade — 80 kW total. The new system provides heating only.

The project aimed to significantly reduce energy consumption, eliminate fossil fuel dependency, cut operating costs, improve overall efficiency, modernise the plant room and benefit from intelligent controls adapted to the building's real needs.

The five Panasonic heat pumps operate in cascade via Panasonic manufacturer controls. At low demand, a single unit runs; as needs increase, a second, third, fourth or fifth unit starts progressively. This modulation avoids over-consumption, limits unnecessary starts, improves seasonal efficiency and distributes running hours evenly across all units.

Main pipework was installed in 54 mm steel, carrying the flows required for total installed output with low pressure drop, good flow distribution and optimal pump operation.

An 800-litre mixing vessel was installed between the heat pump primary circuit and the heating distribution network. It provides hydraulic decoupling between the heat pump circuit and the distribution circuit, increases water volume (limiting short cycles, improving thermal inertia, stabilising temperatures, protecting compressors) and acts as a thermal buffer to absorb rapid load variations.

To ensure identical operation of all five heat pumps, each return was fitted with a TA balancing valve. These valves deliver nominal flow on each unit, prevent one heat pump from working harder than another and ensure even load distribution — essential on multi-generator installations.

The installation is managed by Panasonic cascade controls handling unit start/stop, sequencing, automatic rotation, flow temperature via the heating curve, optimisation of the number of running units and safety monitoring (temperatures, flows, pressures, alarms).

Before/after comparison: old installation — 234 kW oil boiler, approximately €25,000/year in oil, significant maintenance, high CO₂ emissions. New installation — 5 Panasonic 16 kW heat pumps (80 kW), approximately €12,000/year in electricity, renewable energy valorised, intelligent controls, reduced maintenance.

Annual saving: €25,000 − €12,000 = €13,000 per year, a 52% reduction in energy spending while maintaining the same comfort level for residents. Beyond the financial aspect, replacing oil with heat pumps significantly reduces greenhouse gas emissions thanks to the coefficient of performance (COP).

Replacing the 234 kW oil boiler with a cascade of 5 Panasonic 16 kW heat pumps, together with an 800-litre mixing vessel, 54 mm main pipework, TA balancing valves on each return and full Panasonic cascade controls, has fully modernised the plant room. This project is a concrete example of successful energy transition in collective housing.

Work carried out: replacement of a 134 kW oil boiler supplying building heating and instantaneous domestic hot water via a plate heat exchanger, with a cascade installation of 2 Panasonic Big Aquarea T-CAP Series M heat pumps at 30 kW each — 60 kW total.

The Big Aquarea T-CAP Series M range is designed for apartment buildings, renovation projects and centralised heating/DHW installations, with cascade capability up to 300 kW and flow temperatures up to 75 °C depending on configuration.

The building comprises 19 studio flats. The new installation now provides collective heating, domestic hot water production, supply to two 380-litre DHW tanks (760 litres total storage) and full management through bespoke controls.

The two Panasonic heat pumps operate in cascade: they do not necessarily start together. The controls manage the units according to the building's real demand. At low load, a single unit may run; as demand rises, the second unit provides backup. This limits unnecessary starts, improves overall efficiency and spreads wear between both machines.

The installed 60 kW output replaces a 134 kW oil boiler, but this is not a direct undersizing: the old boiler was sized for instantaneous DHW production, requiring very high peak output. With the new storage tanks, energy is produced progressively, allowing a significant reduction in required output.

Main pipework was installed in 42 mm diameter tubing to ensure adequate flow between the heat pumps, decoupling vessel, heating branches and DHW production. A 400-litre Thermador decoupling vessel was installed: it increases system water volume, limits short cycling, protects the heat pumps and provides hydraulic decoupling between primary and secondary circuits.

The old oil boiler produced hot water instantaneously via a plate heat exchanger. The new principle relies on two 380-litre tanks (760 litres total). The heat pumps reheat the tanks to a setpoint defined by the controls. Storage covers the draw-off of 19 studios without the high instantaneous output previously required. Scheduling can favour DHW production during milder outdoor temperatures, off-peak hours, anticipated peak demand and automatic restart after heavy use.

The controls were fully designed in-house to manage the two-unit cascade, DHW priority, heating flow temperature, the decoupling vessel, primary and secondary pumps, temperature sensors, heating/DHW demands, unit rotation and temperature/flow safety devices. The goal: a stable, economical and durable installation without excessive cycling.

The installation took 3 weeks with a team of 3 — approximately 315 hours (35 h/week) or 360 hours (40 h/week). This includes removal of the old plant room, heat pump installation, 42 mm pipework, 400-litre decoupling vessel, DHW tanks, pumps, valves, sensors, wiring and full control system programming.

Savings come from eliminating oil, the higher efficiency of heat pumps (COP) and DHW storage instead of energy-intensive instantaneous production. As an indication, if the old boiler consumed 10,000 litres of oil per year (~100,000 kWh PCI), useful energy would be around 85,000 kWh at 85% efficiency. With a seasonal COP between 2.5 and 3.2, electricity consumption would be approximately 26,500 to 34,000 kWh/year — actual savings depend on oil and electricity prices and system settings.

This installation fully modernises the plant room: it replaces an old, energy-intensive oil system with a 60 kW cascade heat pump solution that is more progressive, better controlled and suited to the real operation of a 19-studio building. The 400-litre decoupling vessel, 42 mm pipework, two 380-litre DHW tanks and bespoke controls deliver a reliable, stable and optimised installation.