Air Source Heat Pump Compatibility with Existing Underfloor Heating Pipes.

Hadders_123
Hadders_123 Posts: 5
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edited 23 January at 2:51PM in Heat pumps
Hi.  I'm interested in a new build house that has underfloor heating; but this is powered by gas - not what I'm wanting.  So I would like to replace the gas boiler for an ASHP.  The layout of the building looks suitable.  My question is what do I need to look for in terms of the specification of the under floor water pipes and the hot water cylinder.  My feeling is that the pipework will be compatible; but it would good to have this confirmed.  Thanks in advance.

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  • ProDave
    ProDave Posts: 3,614
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    The UFH pipes ought to be okay.  But the hot water cylinder may not be suitable.  ASHP's work best at a lower temperature, so for best performance you normally fit a larger HW cylinder so you can store the hot water a bit less hot, and the tank needs a high capacity heat input coil so the water from the ASHP heating it does not need to be so hot.

    Is the house completed yet?  Or is there a completed show house you can go and look at and take a photo or several of the hot water tank?
  • propertyrental
    propertyrental Posts: 2,179
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    post on the alternative energy board. Lots of people in the know there.

    https://forums.moneysavingexpert.com/categories/lpg-heating-oil-solid-other-fuels
  • ComicGeek
    ComicGeek Posts: 1,538
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    Given that gas is going to be around for some time still, and going to be cheaper to run than ASHPs at the moment, why would you want to spend money ripping out a perfectly good heating system?

    Unless the new build has underfloor heating throughout (upstairs as well?), there's going to be more changes needed than just the cylinder.

    Some cheap/poorly designed underfloor heating systems are sized based on 55 degrees Celsius flow temps (especially in screed systems for ceramic floors), which wouldn't make them suitable for ASHPs either.
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    Hadders, why don't you want  heating via gas?

    In essence tho', wet UFH is generally ideal for use with heat pumps. The weak point, as pointed out above, is the DHW. However, if you can get a cheaper overnight rate (and sometimes also available in afternoons), then your hot tank can be topped up using this. 

    In theory, the heating costs could be not far from the current gas rate. This would need confirming, tho'. And there's the not insignificant cost of the ASHP itself.

    Any thoughts of adding, say, a PV and battery system later?



  • Hi.  Following up on the replies.  I'll be putting an 8kW solar system on the roof + a 5kW battery.  It's a bungalow, so UFH throughout.  Not completed but I'll be having a look around a show home in a few weeks.

    I'm expecting to have to replace the HW cylinder.

    I do understand those suggesting sticking with gas, and actually this won't be an immediate project like the panels; but I do want to have the option in a few years time, so want to assess the compatibility before I but.

  • ComicGeek
    ComicGeek Posts: 1,538
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    Solar and battery won't be sufficient to run the ASHP in winter, you will still be drawing from the grid on gloomy winter days.

    Great on those sunny spring days like today - I can fill our 20 kWh batteries from our 4kWp PV system today. You're only going to get 4 kWh of usable storage in your battery - after you fill it up in half an hour on a sunny day, what are you going to do with the other 50 kWh of generated electricity that peak summer's day??

    Would be cheaper to just make sure you have a diverter system linked to the existing hot water cylinder immersion, and then install a couple of cheap split AC units to run when you have sufficient free elec - at least you can choose which system to run and get free air con in the summer when you're baking in the new bungalow.
  • Good points.  In my current house I do have a HW diverter (Eddi) and a 4kW PV system.  We also have an EV that sucks in any surplus on bright days.  On Octopus E7 I get a similar night import rate to the SEG export rate.  
    On a well insulated modern home in the winter I'm hoping it'll stay a good temperature from running ASHP on night rate, maybe even charge the battery on cheap electricity and then use the battery and the trickle from the panels to power the ASHP intermittently during the day.  I would definitely be using some day rate electricity but hopefully not too much.  Dropping gas I would get about £120 pa head start from the daily standing charge. 
    Hadn't thought about AC units for the summer - interesting idea.
  • ComicGeek
    ComicGeek Posts: 1,538
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    In my view, any battery which is smaller in kWh than the kWp of the PV system is not going to be of much use for overnight charging. It's really only to take out the peaks and troughs in PV generation over the course of an hour or so - that annoying situation when you switch on the washing machine just as it turns cloudy.

    I put anywhere between 4-16 kWh into my 20 kWh batteries overnight while also charging our EVs on Octopus Go, guessing on the weather the next day. If the weather the next day is going to be really sunny then I don't charge the batteries at night at all. I haven't used any peak rate elec since it was installed, but have got very close to the 20% discharge limit on a number of occasions. There's still days in March when the 20 kWh battery is full and I'm exporting PV generation with my smaller system (house is warm, cylinder is heated, 2 EVs are all charged!) - for at least half the year you're paying to generate more than you can use. 

    If it's a cold day, then I run our air con units in the main bedrooms, living and dining rooms for 1 hr in the morning to get quick heating at about 2p/kWh. That drains about 15% of the batteries. If it's really cold, then I also run the gas boiler and rads in the other rooms for a bit longer, but try and keep that to a minimum.

    Personally I wouldn't install anything over a 4 kWp PV system but spend a bit more on a battery to get to 10 kWh at least. Any issues with power cuts in that area? The emergency power system part of the battery system is what pushed me in that direction to begin, we're always having 6-12 hr power cuts here.
  • ProDave
    ProDave Posts: 3,614
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    On a well insulated modern home in the winter I'm hoping it'll stay a good temperature from running ASHP on night rate, maybe even charge the battery on cheap electricity and then use the battery and the trickle from the panels to power the ASHP intermittently during the day.  I would definitely be using some day rate electricity but hopefully not too much.  
    That first quoted sentence is a big IF assuming you are talking about a standard developer built house.
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