New house design stage

[Greenbeast]

hello again,

re:GSHP, works better with UFH no?
Concerned about UFH because of the dogs, have always assumed i'd put it in a house i'd build until i met my g/f with her pack

-what's your worry regarding dogs? can't think of one - floor of a heavily insulated house is not likely to exceed 24°C

They'll have no respite from the heat if it's too much, i wonder if we would like to spend hours laying on a 24C floor, i suspect not

We have GSHP,UFH and a dog and yes initially when we first got her she would avoid the UFH by sleeping in the doorway alcove as I did not lay any pipes there due a thermal bridging issue. She soon changed her habits and now seeks out warm spots like a cat  > Usual spot is right in front of the wood burner. Doubt the floor ever gets much hotter than 25C as the circulating water never goes over 30C

Thanks for your experience in the matter!

[Fionn]

Another tip is to run your UFH pipes as tightly spaced as is practical - 150mm maximum centres ideally.
Yes you will use more pipe, but pipe is cheap and the increased rate of heat transfer to the slab will allow you run a lower flow temperature for improved COP.

[djh]

This is the one area I don't really agree with PHI - the root of the 15 kWh/m²/year is actually in the alternative standard of 10 W/m² at the design low temperature, itself set by the amount of heat which could be delivered by ventilation air. So if you set a design target which means that the heat can be delivered by ventilation air only, it should be hardly surprising that a system to heat this ventilation air is the cheapest.

Well, yes, but you can heat the ventilation air with a gas boiler or heat pump. But they both have a greater cost and greater maintenance bills than a simple electric heater.

For me however the correct target should be a primary energy one - which means the standard ought to be agnostic about whether a house uses 5kW of heat delivered by a heat pump consuming 1kW, or 1kW of heat delivered by a post heater consuming 1kW. The optimum balance between insulation and heat pump would then be varied depending on the site and personal preferences - on our site, for instance, hitting the 15 kWh/m²/year target is virtually impossible but were we to use a heat pump to generate the 25 kWh/m²/year heat then we would probably end up consuming less primary energy than you do.

I think a heat pump with an SPF of 5 is still fairly unusual, but perhaps I'm out of date. There are problems with basing a standard on primary energy given that it gets used for DHW production and many other things besides space heating and that there are many different ways of measuring primary energy depending on what fuel it is, how that fuel is used, whether it's supplied externally or from the site (e.g. solar, wind or hydro). In fact I was lucky that PHI have updated their PE calculation to a PER calculation, since previously it had been almost impossible to certify a passivhaus with an entirely resistive electric heating scheme. So I would have been forced to buy a heat pump, perhaps a 'combined unit'.

Ultimately the real attraction of PH for me is in the rigorous building physics underlying the model, not necessarily in the somewhat arbitrary standard used.

Yes, it's the basis of the model, which appears to be more scientifically based and less politically influenced than national standards, that attracted me to it in the first place. But the additional quality control and quality assurance that comes from the certification process is also part of it for me. I'm fairly sure that a certified house has actually been built to match the design documents that were used to perpare the certification spreadsheet. It's unlikely that insulation has been left out or just left still bagged up in the loft, for example; the construction photos would make that very difficult. The component certificates for my windows and so forth and the installation certificate for the blown-in warmcel all reassure me that it was built properly. Ultimately, being on site every day is the best way to know, but certificates and tracability provide an objective measure.

[pdf27]

Well, yes, but you can heat the ventilation air with a gas boiler or heat pump. But they both have a greater cost and greater maintenance bills than a simple electric heater.

Indeed - if you're heating with ventilation air then an electric heater is the logical way of doing it. Where I disagree with them is the assumption that heating with ventilation air is particularly desirable - it works for a particular occupant density, climate and insulation level, but I'm not convinced that designing a standard around it is particularly desirable. All it really saves is a few radiators in some (not all) rooms - which seems to be a fairly modest benefit to me.

I think a heat pump with an SPF of 5 is still fairly unusual, but perhaps I'm out of date.

Unusual but not unknown - and more importantly it's easier to do the sums with 5:1 than 4.6:1 

There are problems with basing a standard on primary energy given that it gets used for DHW production and many other things besides space heating and that there are many different ways of measuring primary energy depending on what fuel it is, how that fuel is used, whether it's supplied externally or from the site (e.g. solar, wind or hydro). In fact I was lucky that PHI have updated their PE calculation to a PER calculation, since previously it had been almost impossible to certify a passivhaus with an entirely resistive electric heating scheme. So I would have been forced to buy a heat pump, perhaps a 'combined unit'.

Thing is, they've had a primary energy standard of some sort all along - the use of PER has made it rather more rigorous, but it isn't a new idea. When you look at the impact of a house on the environment, it's primary energy that has an impact. I wouldn't get rid of a heat demand calculation at all - doing it and setting a standard is going to be required for comfort reasons - but the 15 kWh/m²/year or 10W/m² standard don't make sense as the correct place to put a stake in the ground for me: I'd sooner see a slightly higher W/m² standard, set by evidence of comfort levels, and keep the PER limits and maybe emphasise them a bit more.
DHW production is a pretty important point though - PH is at the stage where DHW is a bigger energy user than space heating, but the emphasis is still on the space heating target: since DHW use is limited to a few appliances and there are established ways to economise on it's use, this makes little sense to me. It comes out in the wash of the PER calculation at the moment, but I'd sooner see it emphasised a bit more since it and plug loads are the main consumers.

[djh]

"Thing is, they've had a primary energy standard of some sort all along - the use of PER has made it rather more rigorous, but it isn't a new idea."

Indeed but the problems with defining and measuring it and linking it to a building rather than an occupant's lifestyle explain to some extent why it's never been a primary criterion. It moves away from a simple 'fabric first' mentality and towards the monstrosity that was CSH.

[acresswell]

We have GSHP,UFH and a dog and yes initially when we first got her she would avoid the UFH by sleeping in the doorway alcove as I did not lay any pipes there due a thermal bridging issue. She soon changed her habits and now seeks out warm spots like a cat  > Usual spot is right in front of the wood burner. Doubt the floor ever gets much hotter than 25C as the circulating water never goes over 30C

Realise this is an old thread, but I'd second Bodidly...  our dog loves the UFH.  We have a mud room to store coats and wellies.  I tend to leave the UFH switched off in there (so we don't lose too much heat when the door is opened). We tried putting a dog bed in there but she never used it, preferring to sleep on the hard floor right next to the UFH manifold.  We also have our UFH pipes closely spaced and run the UFH at a low temperature, so the floor is probably never more than 25-30 degrees. I don't know what doggy body temperature is, but if we assume it's something like humans at 37 degrees, lying on a floor at 30 degrees would still be cooler than lying under a pile of pack-mates.

My other little tip (nothing to do with UFH) is that if you have any corner of a wall protruding into a room, try rounding it off, or measuring back about 2-2.5" from each corner and then cutting it off at 45 degrees. As long as you know in advance and include a bit of steel bracket inside the wall, it's still perfectly strong, but it's surprising how much difference it makes to how big the space feels, and how much more natural light can get around the room.  I reckon the only down side is that it's a tiny bit harder to fit the skirting board!

[camillitech]

My other little tip (nothing to do with UFH) is that if you have any corner of a wall protruding into a room, try rounding it off, or measuring back about 2-2.5" from each corner and then cutting it off at 45 degrees. As long as you know in advance and include a bit of steel bracket inside the wall, it's still perfectly strong, but it's surprising how much difference it makes to how big the space feels, and how much more natural light can get around the room.  I reckon the only down side is that it's a tiny bit harder to fit the skirting board!

Now, we have quite a few 'corners' like this in our house, though more like 6" and I didn't like them on the plans (neither did my builder) but we kept them and I'm glad we did. As for UFH heating and dogs, in a well insulated house with 8 of them you'll only ever need it in the bathroom. The dogs will be just fine. We've only 1 dog so heat the living area as well but when the family turn up for a couple of weeks with more dogs and bodies the heating rarely comes on and folk start opening windows.

[Greenbeast]

Thanks guys!

[gb484]

post and beam with hempcrete: