Nic Posted June 3, 2023 Share Posted June 3, 2023 Hi new to the hub and about to embark on a first self build next year . I understand the principle of air tightness and the need for a mhrv or hrv ( what the benefits of either ) but what I struggle with ( living in the uk) is they say you don’t need any other form of heating, even some manufacturers saying underfloor heating isn’t necessary? Anyone got any thought on that or live in a home with only hrv ? thanks Link to comment Share on other sites More sharing options...
JohnMo Posted June 3, 2023 Share Posted June 3, 2023 Hi and welcome. I would take the manufacturer blurb with a pinch of salt. If you base your ventilation rates on passivhaus then heating via the ventilation system is limited to 10W/m2, otherwise the dust in the air starts to give off a burning smell. So basically a really well designed and built house would be ok, but I wouldn't design a house with all my eggs in one manufacturers basket. If you embed UFH pipes, they cost very little and gives you somewhere to move to if things aren't quite what you expect. 1 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted June 3, 2023 Share Posted June 3, 2023 Welcome. MVHR is ventilation. By definition the mass flow rate of the air in it is quite small. A few kilograms a minute. The specific heat capacity of air is also very low, 1 kJ/kg.K. There are 3,600 kJ in a kWh, or 10p worth of mains gas. So to get a meaningful rise in temperature, you either have to pump a lot of warm air in i.e. larger ducts, or have a high temperature (think a fan heater). So either noisy, or smelly. 1 1 Link to comment Share on other sites More sharing options...
Adsibob Posted June 3, 2023 Share Posted June 3, 2023 (edited) You probably only need ufh in the ground floor and, if you want that warm tile underfoot feeling, in the bathrooms. My house is nowhere near passive, but the bedrooms are well insulated following an extensive refurb and extension, and apart from our kids bedrooms, which SWMBO insists need to be 21C at night, we never have the heating on in the bedrooms. The MVHR is pretty good at averaging out the temperatures to an extent and imo bedrooms are best at about 18.7C anyway. So keep your ground floor slab warm during winter and your ground floor will be 21 and your bedrooms on the upper floors will get close to that. Edited June 3, 2023 by Adsibob 1 Link to comment Share on other sites More sharing options...
Nic Posted June 3, 2023 Author Share Posted June 3, 2023 Ok that sort of confirms what I thought so my next question is if I have a hpv Will that also run the underfloor heating ? What’s the best solution to utilise say Solar from the roof and a heat pump , so that I run hot water underfloor heating and a ventilation system? thanks again Link to comment Share on other sites More sharing options...
Adsibob Posted June 3, 2023 Share Posted June 3, 2023 17 minutes ago, Nic said: Ok that sort of confirms what I thought so my next question is if I have a hpv Will that also run the underfloor heating ? What’s the best solution to utilise say Solar from the roof and a heat pump , so that I run hot water underfloor heating and a ventilation system? thanks again If by HPV you mean Passive Ventilation with Heat Recovery, I’m afraid I can’t help, as I don’t know much about it, or why you would choose it over MVHR. But plenty of people here have Mvhr and warm up their uFH pipes with water generated from green methods, such as a heat pump, supplemented by solar. Link to comment Share on other sites More sharing options...
Nic Posted June 3, 2023 Author Share Posted June 3, 2023 Ok I need to do a bit more reading as I’m getting confused 😂 the self build I’m doing will be approx 160m2 over two floors and will be built highly insulated and airtight ( without going for the passiv certificate) . I guess what I need to know are what I my best options for 1 heating the underfloor heating 2 ventilation of the house 3 hot water 4 there will be a solar system option with battery and also need to know best option for the electric supply to the property. we are only 3 permanent adult in the two bed house normal electrical demands thanks again for your patience Link to comment Share on other sites More sharing options...
JohnMo Posted June 4, 2023 Share Posted June 4, 2023 10 hours ago, Nic said: Ok I need to do a bit more reading as I’m getting confused 😂 the self build I’m doing will be approx 160m2 over two floors and will be built highly insulated and airtight ( without going for the passiv certificate) . I guess what I need to know are what I my best options for 1 heating the underfloor heating 2 ventilation of the house 3 hot water 4 there will be a solar system option with battery and also need to know best option for the electric supply to the property. we are only 3 permanent adult in the two bed house normal electrical demands thanks again for your patience Isn't this a cut and paste of another topic you recently started? So back to your original question. MVHR and HRV are basically the same thing, they take air from the house and at an efficiency of 70-90% heat the incoming air. The other spin on this is MVHR with built in heat pump. The later is good for heat a DHW cylinder but not convinced it will also heat the house. The next option is some form of post heat on the supply to the house after leaving the MVHR unit. As mentioned above is constrained by flow rates of the ventilation system. As a side note not cheap and generally needs high flow temps so not best partner for an ASHP. As I like saying keep things simple, ventilation let it be ventilation and get on with ventilation. Heating and DHW can be done with a single heat source of your choosing. UFH in a well insulated house has low flow temps, so an ASHP ends being the cheapest to run, and you can cool the floor in summer for free if you have solar. Link to comment Share on other sites More sharing options...
Nic Posted June 4, 2023 Author Share Posted June 4, 2023 Thanks again, being to get a picture ASHP for underfloor ( 1 ground floor zone ) and same ASHP for hot water via a cylinder. MVHR to do just it’s thing then solar and battery? To supplement/supply domestic electrics . how does solar cool underfloor? Please once again big thanks Link to comment Share on other sites More sharing options...
SteamyTea Posted June 4, 2023 Share Posted June 4, 2023 28 minutes ago, Nic said: how does solar cool underfloor? Please once again big thanks PV is used to run a heat pump that is set up for cooling. Design and build the place right and there is little need for cooling (and heating). Link to comment Share on other sites More sharing options...
Hastings Posted June 7, 2023 Share Posted June 7, 2023 Somewhere on this forum you will find folk who have very positive experience of simply heating a well insulated house directly with electricity using an inexpensive "Willis heater" heating water in the groundfloor slab briefly, overnight on economy rate electric. You can always add a heat pump to do it instead later. 1 Link to comment Share on other sites More sharing options...
JohnMo Posted June 7, 2023 Share Posted June 7, 2023 On 04/06/2023 at 10:16, SteamyTea said: little need for cooling (and heating). Not sure I could agree. If its 30 outside for day/weeks on end, as soon as you open a window or door or get any solar gain, your house will start getting warmer. You house will get hot. An ASHP that can do cooling is zero cost investment if you are having an ASHP anyway, if you have UFH all you need is a thermostat that can do heating and cooling control. We had -9 for about three days last winter (24/7), then several days where the temperature never got above zero. We needed plenty of heating. I sure most house would. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 7, 2023 Share Posted June 7, 2023 40 minutes ago, JohnMo said: We had -9 for about three days last winter (24/7), then several days where the temperature never got above zero. We needed plenty of heating. I sure most house would Why I said. On 04/06/2023 at 10:16, SteamyTea said: little need for cooling (and heating). Rather than zero. Link to comment Share on other sites More sharing options...
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