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    • CommentAuthorBowman
    • CommentTimeNov 4th 2017
     
    I've searched but can't find anything that specifically answers this question.

    Were looking at a 12kW ASHP to provide UFH and DHW for an eco refurb in Devon. 9kW would probably do except when we have guest. So a couple of questions really:

    1. We are comparing Panasonic, LG, Samsung, Daiken - is there any significant difference in terms of reliability or value?

    2. ASHP would be sited on garage roof against house gable with TS below in garage. Generally looking at 300L TS but would we better off looking at monoblock or split systems?

    also:

    Is there anything we should specifically avoid?

    Thanks in advance,

    Bowman
    • CommentAuthortony
    • CommentTimeNov 4th 2017
     
    Split, beware of vibration noise

    I can’t see a good reason for a thermal store, increases capital cost and heat losses.

    Most are very reliable now
  1.  
    A colleague has had very good experiences with, and good technical and monitoring support from, Mitsubishi (not on your list, I realise). Avoid resonance! A friend has a neighbour with an ASHP and the friend's house 'buzzes'!
  2.  
    Split the DHW and UHF.

    You will need a TS for the DHW as I doubt that an ASHP would keep up with a shower and a kitchen tap simultaneously.

    As for a TS for the UFH, that could depend upon the type of electricity charging. If you have some sort of off peak rate then you will have to do the sums regarding the pay back of a TS and only using off peak or just using electricity as needed and no TS complication and heat losses. If there is no off peak then with a TS you are just storing heat with losses for the time when you need it instead of producing heat when you need it.

    BTW a 300lt TS could be about right for the DHW. heat it to about 45 -50deg. which should be enough with an occasional boost to 60deg to keep those worried about legionnaire bugs at bay. Running a low DHW temp requires a bigger store because there is less dilution at the point of use.
  3.  
    Why would a TS need boosting to 60 re Legionella? The risk, as I understand it, relates to stored DHW. With a TS the DHW is not stored. If TS is in a closed loop there will, again as I understand it, never be a risk of inhalation of an aerosol.
  4.  
    I have an ecodan 12.5kw which I installed myself.

    I've had no issues with it whatsoever and the technical help I got from Mitsubishi was excellent even though I bought it secondhand and needed help setting it up and added my own UFH controls.

    You say 9kw will do except when you have a guest? What difference does a guest make to the size of the unit? It may make a difference to the size of the store but not your heatloss calcs.
  5.  
    Posted By: Nick ParsonsWhy would a TS need boosting to 60 re Legionella? The risk, as I understand it, relates to stored DHW. With a TS the DHW is not stored. If TS is in a closed loop there will, again as I understand it, never be a risk of inhalation of an aerosol.

    Depends how the TS is used for DHW. If the TS has a heat ex. coil or plate heat ex. (not a good idea IMO) to provide the DHW then there is no stored DHW but if the TS is used like a conventional indirect DHW tank then there is stored DHW and apparently some legionella risk.
    There is an advantage, IMO, of using the TS like a conventional indirect DHW tank as it is easier to get better flow rates for the DHW.
    FWIW the backup immersion coil in my DHW tank (300lts) which has a built in thermostat will only heat the tank to just about 60deg. It is adjustable from about 45 - 60deg.
    •  
      CommentAuthordjh
    • CommentTimeNov 5th 2017
     
    Posted By: Peter_in_Hungaryif the TS is used like a conventional indirect DHW tank

    If the TS is used like a conventional indirect cylinder, then it IS an indirect cylinder and not a TS! And if it was an open-vented thermal store then it CAN'T be used as a pressurised indirect cylinder.

    There is an advantage, IMO, of using the TS like a conventional indirect DHW tank as it is easier to get better flow rates for the DHW.

    Err, in which case buy an indirect cylinder to start with, not a TS! But the flow rates with PHEs are pretty good, and obviously something to check before buying a TS.

    FWIW, the immersions in my TS will heat it as hot as I care to set them.
    • CommentAuthorBowman
    • CommentTimeNov 5th 2017
     
    Thanks All,

    @Victorianeco - as a family of four there is normally a fight over our existing shower in the morning, we'll soon have two showers; when we have guests it would normally be another family so we could easily use two showers and a sink simultaneously.

    Okay - so a split system it is (less to lug onto garage roof).

    My preferred supplier specialises in LG, Samsung and Hitachi.

    TS (or cylinder) I was thinking with separate shower coil and solar coil?
    • CommentAuthorjfb
    • CommentTimeNov 5th 2017
     
    Peter you said - ' If the TS has a heat ex. coil or plate heat ex. (not a good idea IMO) '
    Are you not a fan of just the plate heat exchanger or both - and why?

    thanks
  6.  
    We have one shower but there's plenty of water for four showers in the morning our tank is 210 litres.

    If you want more water you either buy a bigger cylinder or store at a hotter temperature or have the timer to heat up the hot water more frequently.

    An ASHP can't run heating and heat up the hot water at the same so the is no need to oversize the unit.
  7.  
    We have one shower but there's plenty of water for four showers in the morning our tank is 210 litres.

    If you want more water you either buy a bigger cylinder or store at a hotter temperature or have the timer to heat up the hot water more frequently.

    An ASHP can't run heating and heat up the hot water at the same so the is no need to oversize the unit.
    • CommentAuthorBowman
    • CommentTimeNov 5th 2017
     
    We're currently running E7 so my hopes were to run the ASHP overnight to heat the UFH and provide enough DHW through to evening. Extra heat during the evening from the Woodburner.
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 5th 2017 edited
     
    Posted By: BowmanWe're currently running E7 so my hopes were to run the ASHP overnight to heat the UFH and provide enough DHW through to evening.
    Then it is only a matter of doing some simple calculations to establish optimum sizes.
    As you are running on E7, you can get extra DHW for the times you have guests by using the immersion heater after the ASHP has heated up the water. I found that running my 210 lt cylinder up to 50°C was plenty for a bath or two or 3 or 4 showers.
    So you may find that you can store 300 lt at 45°C to get the benefit of the higher CoP, then boost for the last hour with a 3 kW immersion.
    A 12 kW ASHP is pretty big really. 300 lt of mains water raised from 4°C to 45°C will take 14.5 kWh, so the ASHP is only running for just over an hour. A 9 kW ASHP would do the same in just over 1.6 hours.
    To heat up to 65°C from 45°C with E7 will take another 7 kWh, or just over 2 hours.
    So there is plenty of time in the 7 hour window to do other things with the ASHP.

    Being caution and saying that you have 5 hours use of a 9 kW ASHP, then you can get 45 kWh, though this will be reduced depending on your flow and return temperatures.

    You may find that with a little playing about with temperature setting, you can get a reasonable CoP and heat to a higher temperature.

    DHW and Space heating should really be treated separately, they do different things, at different temperatures, at different times.

    You say you want to run the ASHP on E7 and store enough energy to heat the house. Do you know how much energy you need to heat the place and what temperature you will be running the heating system at?
    This is quite important.
  8.  
    I don't think using the UFH at night using E7 and going it lasts till the next evening works. I think you'll be better off running lower temps all day.

    I've oversized my rads and my UFH and rads operate at 35c, it is set to go to 45c when temps drop to - 3 but that is rare. I'd imagine the COP will be excellent but never bothered to calculate it in all honesty.

    I also run my tank at 50c and it drops to about 30c by the evening after showering, dishwasher etc etc. I think it takes about 20 minutes to top back up to the 50c. This is set for 5pm
    •  
      CommentAuthordjh
    • CommentTimeNov 5th 2017
     
    Posted By: VictorianecoI don't think using the UFH at night using E7 and going it lasts till the next evening works.

    It depends on the house it is installed in - how well insulated and airtight it is. If the time constant of the house is long enough, all that matters is how much energy you dump into the fabric, not when you do it. You do need over three times the power though to do it on E7 instead of the entire 24 hour period.
    • CommentAuthorBowman
    • CommentTimeNov 5th 2017
     
    As a refurb we don't have as much control over the existing structure as we would like but the new first floor, roof and all windows will approx 0.1 U value.

    I've calculated peak ASHP loads as 80kWh per day - I guess the question is whether the occasional requirement to run at 12kW would be better served by 9kW plus immersion as needed.

    Whole house heat loss should be around 4.5kW at 25 delta T, so maybe 4.5kW to DHW would be okay?
  9.  
    Posted By: jfbPeter you said - ' If the TS has a heat ex. coil or plate heat ex. (not a good idea IMO) '
    Are you not a fan of just the plate heat exchanger or both - and why?

    thanks

    I am not a fan of plate heat ex. operating on a TS as they need a high flow rate which is pump driven on the primary side. This high flow rate has a v. good chance of disturbing/destroying the stratification in the TS which will drastically reduce the amount of useful heat that can be got out of the TS.

    A heat ex. coil is better but a (very) large coil will be needed to get a good flow of reasonable hot water out of the TS if the TS is only heated to 45 - 50deg.
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 6th 2017
     
    Posted By: BowmanI've calculated peak ASHP loads as 80kWh per day
    That seems high, how large is your house?

    Posted By: Bowman4.5kW at 25 delta T
    Not often you meet that sort of temperature differences. You may be better off for those rare occasions just having some fan heater (cost about 10 quid each).

    You may find that you are better off ditching the E7 and just going for a normal electricity supply.
    Would bring your heating in line with gas, near enough.

    One thing to be vary careful of is the heat loss from any stored water (I am careful to to use the terms thermal store, buffer or cylinder here). The testing procedure assumes a round trip from hot, to cold over a short period of time, not over 24 hours.
    The losses from my old E7, unvented 210 lt cylinder were often higher than my usage. Why I store at 50°C and fitted extra insulation. I also delayed the heating time until later into the E7 period and used the water as early as I could. Saved at least 2 kWh/day.
    • CommentAuthorGarethC
    • CommentTimeNov 6th 2017
     
    Can you get ones that use R32 refrigerant yet? They should be about 7% better performing, and R32 is kinder to the environment. In principle, should cost no more than an R410A. The only complication might be that installers may not yet have had the extra training yet. Daikin were rolling r32 out fastest, but iirc, Panasonic might have been adopting too. Looked into this a while ago, but my own ASHP hopes are currently mired in planning problems 🙁
    • CommentAuthorGarethC
    • CommentTimeNov 6th 2017 edited
     
    Posted By: SteamyTea

    One thing to be vary careful of is the heat loss from any stored water (I am careful to to use the terms thermal store, buffer or cylinder here). The testing procedure assumes a round trip from hot, to cold over a short period of time, not over 24 hours.
    The losses from my old E7, unvented 210 lt cylinder were often higher than my usage. Why I store at 50°C and fitted extra insulation. I also delayed the heating time until later into the E7 period and used the water as early as I could. Saved at least 2 kWh/day.


    Don't have one, but my research also seemed to indicate that losses from cylinders and thermal stores are -awful- and I just couldn't find any with insulation half as much as I'd want even on new ones.

    I think it's this, as much as the higher temp required, that kill ashp performance for DHW. But at least that impact is no worse than on other boiler types.

    In my system, I wanted one which provided DHW directly (so cylinder not thermal store, as wanted to avoided extra heat exchange losses), was massively insulated (at least 10cm of PUR all round) and was only 150l even though we're quite a large household (so heating for anti legionellla would be minimal, and losses reduced). Ideally if the tank fell below 50l of hot, the ASHP would kick in in a "combi" fashion, supplemented by the immersion.

    I thought that would give me a super efficient system, but I couldn't find one which would work that way.
  10.  
    We have a Daikin ASHP for CH, 5 years old and faultless so far. We over sized it as it was only a few £100 for the next size up and its never short of heat.

    I looked at extending it to DHW, but the capital cost of buying and installing a cylinder, plus the value of lost floor space, plus standing losses, plus low CoP at DHW temp, would pay for many many years of hot water.

    At the time it looked like an instantaneous multipoint gas water heater ( Rinnai or similar) was much cheaper overall and lower CO2, even using bottled propane as we are off mains gas.
    • CommentAuthorcjard
    • CommentTimeNov 7th 2017
     
    “Ideally if the tank fell below 50l of hot, the ASHP would kick in in a "combi" fashion, supplemented by the immersion.“

    Asking an ASAP to maintain a store of hot water at minimum 50’C is rather murderous to its efficiency!
    • CommentAuthorGarethC
    • CommentTimeNov 7th 2017
     
    50 litres, not degrees C! I. E. Once we'd got through 100 litres, it would start to reheat the tank. We don't often do baths, so that would go quite far. Mind you, I was targeting 45 degrees for the tank, as I think an ashp can manage that reasonably well?

    Will, take your point about capital cost. Even more so now that electricity is relatively more expensive. But, as I've been discussing on navitron recently, now that marginal electricity generation will fairly soon be supplied using gas at worst, an ashp will only have to manage an spf of about 2 to be greener than gas boilers. So they're great for space heating now, but actually pretty green even for DHW if well specified.
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