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Designing heating system with air to water heat pump in France, near Lyon

bobflux · 2026-02-25T19:08:55Z

Greetings! I am renovating the family house, and now is the time to finally tackle the 50 years old mess of a heating system... - Location: South East of France, near Lyon. Altitude 214m. Design temperature -7°C. - Two floors (Ground floor and 1st floor), no basement, 192m² per level, total 384m². - Build date 1732. - The house is rectangular, with the longest side facing south. It used to be a huge farm building, that was then divided, so the North and West walls are common with the neighbors (no heat loss). There are many large windows facing South, giving a ton of solar gain. - Thermal mass is enormous: all walls (interior, exterior) are 50cm thick stone, the ground floor has 10cm thick concrete slabs over insulation. When I got the house, it was in a state of disrepair, with roof leaks etc. This has all been fixed. It also leaked heat like a sieve: absolutely not airtight, lots of drafts, single glaze windows, no insulation anywhere, etc. It was heated by an old 20kW groundwater source heat pump, and even with that, electrical consumption was pretty damn high at 20 MWh/year. Thus I did the following: - Loft: airtight vapor barrier on the floor to stop air leaks through the innumerable cracks + lots of careful sealing + 40cm blown in fiberglass (R=7): this took care of the drafts. - Exterior walls: 20cm thick Rockwool exterior insulation (R=5.7), all windows and doors replaced with modern double glazing installed in the thickness of the insulation layer to avoid thermal bridges around the openings. - 12kW PV on the roof with 20kWh battery storage. - All first floor windows: louvred shutters. Ground floor windows: solid wood shutters. Two enormous vaulted patio doors (3.50m x 3.50m): perforated white steel roller shutters. - Installed automatic ventilation So far, very happy with the results. Massive upgrade to the comfort level. There are no drafts. Thermal mass is so high that when the old heat pump broke down (which was rather frequent) nobody noticed for at least 24 hours. No one has any idea what the outside temperature is unless they actually open a door and feel it. Total energy bill from the grid is 2000 kWh/year, electric car included (-90% reduction). In winter, the enormous south facing windows let in a considerable amount of heat when the sun shines, but... due to the thermal mass, it only raises the indoors temperature by 1°C at the end of the day, all the heat is stored. In summer, the shutters are extremely effective against solar gain. Indoor and outdoor temperatures during the last summer heat wave, while the house was empty: Summer comfort without AC requires active measures. The reason for the louvred/perforated shutters is ventilation. When coming back from vacation August 19, I opened the windows, put a large fan in the corridor, and let it run all night. This brought the thermal mass temperature from max 25°C down to 20°C. Now back to the heating system design...

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Air Source Heat Pumps (ASHPs)

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Batpred

(@batpred)

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Joined: 1 year ago

Posts: 746

02/03/2026 7:30 pm

Posted by: @bobflux

↑

There should be a Darwin award for hybrid photovoltaic inverters with backup output that can only be configured via cloud app.

Just love the way you put it! 🤣

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

ReplyQuote

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