Pompe a chaleur

[Evianers]

We are thinking of tentatively installed a pompe a chaleur.

However, question is, is there any kind which would also heat our hot water [at present heated by a large gas boiler which also heats the underfloor piping in winter] only in the summer months? If anyone has had one such installed recently, could they please share their experiences. Also the cost, which seems to vary between 6,000 and 18,000 euros, although we have been quoted 20,000 which is out of the question. TIA

[rt29781]

We have a 12kW heat pump that heats our underfloor piping and hot water.  It is sold in the Uk by Trianco and costs £2000ish with a further £200 for transport to SW France.  I fitted the system which is just a plumbing/wiring job.  The heat pump is a grey box about the size of a washing machine.  So far it seems to work well.  Just be aware that heat pumps give out a variable output in proportion to the air temperature.  So a 12kW HP actually only gives 6kW at 0C and 12kW at 20C.  Realistically expect betwenn 6 and 9kW in winter.  Don't contemplate a heat pump without good insulation.

[Evianers]

many thanks for quick response.

[rt29781]

Thinking some more if you already have a gas boiler then I would say keep that and install a heat pump as well.  The reason being in very cold weather the heat pump is very inefficient so use the gas boiler then.  When the air temperature is above 7C air to water heat pumps become much more efficient so use the heat pump then.  Also heat pumps are not good at heating water to more than 55C.  For very hot water a  gas boiler is more efficient.  If you only need water for a shower (38C) then a heat pump is fine.

[Gluestick]

Personally, I would opt for a Bi-Fuel Ballon, using Heures Creuse to provide stored Domestic Hot Water, topped up as necessary by the Heat Pump.

Most successful Heat Pump installations use wet underfloor: however in colder weather additional heating is stillr equired: normally a decent modern and effecient wood burner in the Salon.

Quite some time back I posted considerable performance data culled from a chum's barn conversion in cold windy rural Wales, where the main heating is provided by Heat Pump and Bore Holes. The place being effectively a new build, uses very well insulated wet underfloor and is super-insulated.

If you use the search facility you would find this: makes interesting reading.

 

[rt29781]

Hi Gluestick, we have a woodburner fitted (almost) for next winter....I agree on the woodburner but it seems a shame to pull out a gas boiler that is already working.  Just use it to heat hot water rather than put in a new tank (expensive).  Unless of course the original tank has an immersion with night time heating already installed.  In SW France were we live I believe that air to water heat pumps are the way to go rather than water to water heat pumps as they require a bore hole or a large coil in the garden to extract heat from the ground and that is expensive.  I did consider it but couldn't justify the expense and extra work ( i have a digger and a large plot so I could have done it)  We did pull up all the floors in the house and fit underfloor heating and that was well worth the effort,  prior to that we used an air to air heat pump which works well but leaves the feet cold and that is very uncomfortable.

[broy]

I think its possible to set up a heat pump to preheat water for the gas boiler. But I cant quite work out in my head how its done. But if it works that could be worth thinking about?

[Gluestick]

[quote user="rt29781"]it seems a shame to pull out a gas boiler that is already working.  Just use it to heat hot water rather than put in a new tank (expensive).  Unless of course the original tank has an immersion with night time heating already installed. [/quote]

It is generally accepted, rt, that both Air Source and Ground Source Heat Pumps are not very effective for DHW: they are unable to raise the stored water to a sufficiently high temperature: unless the external ambient air temp (In the case of Air Source) is significantly high: in which case Solar DHW is the most cost-effective. Even using a small Thermal Store, this can only increase the stored water to the effective operating peak temp of the pump.

Most current Thermal Stores used for (e.g.) Bio-Mass and Wood Gasification Boilers etc, store water at circa 90Deg C: which an air source HP will never reach, since their peak operating temp is circa 50 Deg C.

Most stored DHW systems operate on the basis that the top strata of stored water is much hotter than the lowest: and in use, one mixes hot and cold water to achieve the desired temperature for baths, showers, washing and etc.

Wet UF heating is effective at lower carried water temperatures since it uses natural convection: whereas wet CH using radiators, has to operate at much higher core temps to combine natural air convection and radiation; heat rising at mainly waist level means they are doing a fine job of heating the room space just beneath the ceiling!

Most heat Pump systems need some form of secondary heating in times of higher demand, such as Winter evenings, since the COP reduces as the ambient external air temp drops, seasonally, and additionally, the air temp drops even more in the evening: which is the very time most wish to relax and sit.

Using a Ballon, running on Heures Creuse is unit-per-unit the cheapest when compared to either Oil or Gas as a primary fuel: and should stay so, since in excess of 70% of France's electricity is generated by nuclear power. Whereas LNG and LPG are both finite resources and heavily in demand, globally.

A 200L Ballon powered by electricity, is only circa € 225-250.

A Bi-Fuel Ballon is obviously more expensive, since it must have a seondary heat exchanger/calorifier, in addition to the immersed electric element: however this would raise the temp of the stored water to the level of the peak operating temp of the heat pump: remembering, however, that this peak temp is rarely reached in very cold weather and as the extrnal ambient temperature drops, the COP also falls fairly dramatically, this any energy leverage experienced in warmer weather, gradually reduces to zero.

Which is why all such heat pumps enjoy a back up source.