stubiff Posted April 1, 2021 Share Posted April 1, 2021 All, grateful for some recommendations/options for the following please. Winter heat demand of around 850W. No water based UFH or rads, i.e. only HW distribution to be to taps/showers. No HW storage, e.g. cylinder. Ignore cost and efficiency implications for the moment. TIA. Link to comment Share on other sites More sharing options...
jack Posted April 1, 2021 Share Posted April 1, 2021 That's an extremely low demand. I'd have thought electric towel rails in bathrooms, supplemented with a small electric heater (maybe portable) for really cold spells, would be sufficient. Link to comment Share on other sites More sharing options...
ProDave Posted April 1, 2021 Share Posted April 1, 2021 Will the house likely need any cooling in the summer? If so a small air to air heat pump (air conditioner) will do all the heating you need efficiently and do cooling in the summer if required. Why no hot water tank? That forces you to have an instant water heater which will be limited in power and the showers might be disappointing. Link to comment Share on other sites More sharing options...
pdf27 Posted April 1, 2021 Share Posted April 1, 2021 40 minutes ago, stubiff said: All, grateful for some recommendations/options for the following please. Winter heat demand of around 850W. No water based UFH or rads, i.e. only HW distribution to be to taps/showers. No HW storage, e.g. cylinder. Ignore cost and efficiency implications for the moment. TIA. Even with just a fan heater and towel rails, you're looking at heating bills of ~£200/year which is seriously cheap. For that set of requirements unless you really want cooling I'd just go for whatever heater you like the look of best - definitely towel rails, if you've got MVHR a post heater is a good option and if not some sort of small convector. HW is likely to be more challenging - that spec looks like point of use heating plus an electric shower, but that might be a bit clunky and give low flow rates and high costs. A small cylinder with an immersion is probably cheaper if you can cram it in anywhere and can use off-peak power. 1 minute ago, ProDave said: Why no hot water tank? That forces you to have an instant water heater which will be limited in power and the showers might be disappointing. Might be a very small house with that winter heat demand meaning insufficient space for a cylinder, but if you can fit in a hot water tank run off an immersion heater that's definitely going to be nicer to live with. Link to comment Share on other sites More sharing options...
stubiff Posted April 1, 2021 Author Share Posted April 1, 2021 Will add more later but 850W is based on MVHR 85%, ACH 0.6, 0.11 U-values, 0.7 windows, 1.2 doors, 84 sqm floor area, 16 degree temp diff, 1.5 storey. Link to comment Share on other sites More sharing options...
ProDave Posted April 1, 2021 Share Posted April 1, 2021 You must be in a warm part of the country. I sized my heat loss on 30 degree temp difference (+20 inside -10 outside) Link to comment Share on other sites More sharing options...
pdf27 Posted April 1, 2021 Share Posted April 1, 2021 4 minutes ago, stubiff said: Will add more later but 850W is based on MVHR 85%, ACH 0.6, 0.11 U-values, 0.7 windows, 1.2 doors, 84 sqm floor area, 16 degree temp diff, 1.5 storey. At ~10W/m2 then an MVHR post heater will work and is probably the cheapest option. You probably want supplemental heat in the bathrooms for comfort however - either heated towel rails or underfloor mat. Note that the alternative certification criteria for Passivhaus is 10W/m2 and considered quite hard to achieve in a small house like this, so your heat loss calcs may be optimistic. I'd certainly agree with @ProDave that 16°C temperature difference (i.e. a design low temperature of +4°C) looks very small. Link to comment Share on other sites More sharing options...
PeterW Posted April 1, 2021 Share Posted April 1, 2021 (edited) So 850w is ~10w/m2 is Passiv spec - sure you’ve done the calcs correctly ..? If so, 2 people will give you ~500w in winter and you’re heating requirement is near none existent. Have you done a shade / cooling analysis..? And 85m over 2 floors ..? That’s a 7x6m structure ..?? Edited April 1, 2021 by PeterW Crossed with Pdf27..! Link to comment Share on other sites More sharing options...
stubiff Posted April 1, 2021 Author Share Posted April 1, 2021 (edited) Will look at the calcs again. But, the floor area in the xls is only used to calc the ground floor loss. So 84 would be 6x14 footprint, say. Total volume is 302 m cubed. I mentioned -20 in another thread (as the xls uses this in the first section) but someone said to use the monthly table to work out the costs. Based on -10 its 1491W, on -20 its 1951W, so, yes, max requirement would be higher. Edited April 1, 2021 by stubiff Link to comment Share on other sites More sharing options...
stubiff Posted April 1, 2021 Author Share Posted April 1, 2021 Ok, maths was wrong! 1950W at -10. Link to comment Share on other sites More sharing options...
ProDave Posted April 1, 2021 Share Posted April 1, 2021 7 minutes ago, stubiff said: Ok, maths was wrong! 1950W at -10. So a perfect candidate for a 5kW ASHP with under floor heating and an UVC for hot water. If only those were not on your black list...... Link to comment Share on other sites More sharing options...
stubiff Posted April 1, 2021 Author Share Posted April 1, 2021 Not ruling them out totally, just a preference. What about an air2air heat pump style for heating and cooling. Latter, or not overheating, will be top priority. Maybe we’ll just have all the windows on the north side! Re cylinder - didn’t want stores of heat (summer) but maybe modern ones are well insulated. Link to comment Share on other sites More sharing options...
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