drcarrera

Hi We've just had a Vaillant ASHP system installed together with a uniSTOR HP cylinder. However, there's a problem with the primary circuit thermostat in that the hysteresis seems to be in the order of 20 oC . As the ASHPs output at 50 oC this means that if we set the stat to 50, it doesn't trigger until it drops to near 30 oC which is too cold for showers etc. If we increase the stat to, say 60, so it triggers at 40, it's then permanently on as obviously the water won't ever reach that temperature. The stat for the immersion which sits next to it seems fine, with a hysteresis of around 5 oC Does anyone have any experience of this type of cylinder/stat and know if the hysteresis is adjustable in any way, or is it just faulty? It's the right hand stat in the diagram below. TIA. Chris

Thanks for the replies. Yes, it's impossible to eliminate shading from a practical point of view with multiple rows. Unfortunately we don't have the space for a single row of 12 panel width so we're looking at two or three rows. I do wonder whether we should simply reduce the total number of panels so we can have a 2-high single row. Also, my gut feeling is that even though we'll be having battery storage, as we'll also have an ASHP we shouldn't just be looking at total annual production and shouldn't maximise that at the cost of lower winter production. So many variables!

Hi We're looking to install a ground mount system probably comprising 24 375W panels. As we'll need to install in two or three rows, is there a recommended distance between each to minimise shading? I appreciate there's bound to be some when the sun's very low (unless we lay them all flat!) but for 1.7m high panels at, say 40o , would a 1m gap between front of row and back of one in front be enough to avoid too much loss? We're in the south of England, by the way. Also, would it make sense for each row to be on a separate inverter? Any pointers gratefully received!

I have, but quite a lot of variation between various quotes - from 14 to 20! House is around 20 years old so reasonable insulation wise and has a floor area of around 320 sq/m with high ceilings. I've estimated we use about 35000 KWh pa for heating and HW although we also have an oil Aga which complicates things. CH/HW and Aga use 54000 KWh but how much of the Aga is cooking and how much space heating is anyone's guess.

I assume it's this one, which is 20kW as far as I can see : https://ecoforest.com/en/products/heat-pumps/air-source-heat-pumps/ecoair-evi-4-20/

Has anyone any experience of Ecoforest ASHPs? I've had a quote which recommends two 10kW Arotherms but with a single Ecoforest unit as a cheaper alternative. Aside from the company website I can't find anything about them, good or bad! The Vailants have a 7 year warrantee which is a plus and I guess there may be an advantage of redundancy if one breaks down but if I could be confident the Ecoforest is a decent unit it's two year warranty wouldn't be much of an issue if it saves me money over the two Vaillants!

Has anyone experience of installing or using a fire rated oil storage tank? Our conventional tank needs replacing but current regs mean it will be impossible to site the new one where the current one is (next to wooden cladded garage with a path and wall on other side). I came across the 30 minutes fire protected tank by Tuffa which they say allows it to be installed adjacent to a building whilst being compliant to current regs. It's a bit smaller than I'd like but that would be a price worth paying if it meant it could be a straight swap for the old one. None of the installers I've spoken to over the last year or so have mentioned it as an option so I wonder if it's just a new development or if there are other issues I'm not aware of. cheers, Chris

We do have a log fire in the lounge for the few very cold evenings when the UFH takes a while longer to get things comfortable so that would be feasible - even more so if we keep the Aga. Also, we currently don't tend to heat the whole house at once as the office and "day" room are on a separate circuit and this goes off before the UFH comes on, although of course this would probably change if going to a lower temperature system. But to go back to the original question... So lets now say worst case scenario with heat loss on the few nights a year when the temp drops to -5 is around 6kW. Add 4 kW for ventilation losses. 2kW for DHW (unlikely - there are only two of us) Let's add 25% if the house was built by cowboys with disregard for buildings regs. Hey presto! We now have 15kW! Is that really how the ASHP suppliers would have calculated it? If so it rather makes all the measuring and calculations rather pointless! I still think there's something fundamentally wrong with my heat loss calculations, though. I'm also beginning to wonder whether the Aga uses a much larger proportion of the oil than I think. So in light of all this, perhaps the oil/ASHP hybrid system as recommended by one supplier would be the best way to go. I would have rather just had an ASHP, though.

I guess it should be but just went with what the spreadsheet had as default. I suppose I could assume a slab temp of 35 (assuming that's the UFH temp). But then one could also argue the heat loss behind a standard rad will be far greater as well as it will be way higher than room temp - then the calculations start getting too complicated! Anyway, I've just increased the floor temp delta to 27 degrees and the difference it makes isn't so significant as to make the end result for the whole seem any more correct.

As the house was designed and built with UFH I'm hoping there's a reasonable amount of insulation. It certainly seems to work well enough. The UFH covers around 95 m2 of the total (i.e. the entire footprint of the main, 3-storey house) although 30m2 of that is usually off as its the kitchen. For the calculations I've assumed constant 8 degrees under-house temp with floor u of .25.

Many thanks for the replies. Sorry, the kWh was a typo – should of course be MWh (as a physicist I should as least have got that right!). I’ve revised that figure a bit but work it out as follows: We use around 5250l of oil per year but have an Aga, which uses around 2500l per year. So 2750l on heating and DHW which is around 28.5 MWh. The boiler runs at around 93% efficiency which gives an output figure of around 26.5 MWh per year (in practice it's probably less than this as the boiler's quite old). Obviously there's a degree of space heating from the Aga as well which based on estimated latent output could be as much as 9 MWh but this is very localised . Incidentally, heating is UFH to most of the ground floor and radiators elsewhere. My back of a fag packet heat loss calculations for a temperature delta of 20 degrees are as follows : Area u value Loss Walls 212.3 0.35 1486.1 Windows 47.0 2.00 1880 Doors 9.1 3.00 546 Roof 149.9 0.16 479.68 Rooflights 3.0 1.20 72 Floor 140.2 0.25 420.6 Total 4884.38 I haven't included ventilation losses but it still seems way too low. U values are largely based on buildings regs when the main house was built in 2004. I've attached the spreadsheet as well. I'm obviously inputting something incorrectly. Heat loss calculation.xlsx

Hi I'm trying the decide whether to replace our oil fired boiler with an ASHP, the main drivers being that the current boiler and tank will need replacing soon, the oil tank takes up a lot of room, and I'd like to have a modern more ecologically friendly system. However, I can't tally the sizing requirements I've been quoted with my own figures. It's a five bedroom house, built in 2004, with a total floor area/volume of around 300m2/700m3 and a footprint of 150m2 (some of it is single storey, some 3 storey). My own usage figures, using the very helpful spreadsheet on here, based on average temps etc come out to around 25KWh per year which tallies quite well with the known oil usage of 3000-3500 l per year. However, the worst daily heat loss figures I'm calculating are 5000W average and 7000W peak. The two quotes I've been given so far calculate 14KW and 17KW! Even adding what's needed to heat a large DHW tank on top of space heating I don't quite see how they're so high. The 17KW one has recommended a hybrid set up with 16KW ASHP and oil boiler which seem a bit excessive. Am I mis-interpreting the daily heat loss figures from the spreadsheet?