New house design stage

[Greenbeast]

As a bit of a "curved ball" what about a bit of Thermal Mass?    I am all for highly insulated, controlled ventilation etc. but in my experience you get a more stable and just as importantly "comfortable" atmosphere in a house if it has a bit (ok a lot) of thermal mass. Obviously this works better if the house is occupied 24/7. My thinking, (no actual hard facts or figures so please discuss/dismiss as you feel fit), is in the summer the thermal mass limits the day time temp rise whilst giving it up in the evenings, works well in the "shoulder" months. The building is incapable of sudden temperature changes, so after a cold frosty night in the winter the house is still warm in the morning.  The disadvantage of a lot of thermal mass is it can take several days to warm the house if you go a way for a few days, but now we have a GSHP running I just leave it "ticking over" 24/7.

The house we have is an old farmhouse with thick walls and a massive central brick chimney - admittedly you would not do a new build this way, but it is well insulated with an inner skin of 5" (125mm) thermal (celcon) blocks and a foam filled cavity. The external wall is 12 to 18" solid brick. It is a large house (over 200 m sq) yet the heating from the GSHP uses about 1800kWh of electric, per year (approx 7200kWh heat). We do have a woodburner in the north facing lounge which contributes a bit but not very much.

Just a thought.

Roger

Indeed, as i said i would love to have rammed earth, that really speaks to me from many levels, but the OH will not go for it ("you're not building our house from mud")
As we never go away the issue of 'reheating' the mass is not a concern

[marshman]

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

I have a GSHP with UFH. The GSHP was install just under 2 years ago - wish I had done it sooner.  The key is good design, properly sized ground loops, and run it 24/7 to keep floor temps very low - a well designed system should not have "hot floors" so nothing to upset the dogs. The only time we notice that our floor is actually warm is in the kitchen during a really cold spell, even then it is just pleasant. All other times you just notice that it doesn't feel cold if you walk on it with bare feet. All the other rooms have thick carpet so you can't seem to feel it at all.  The average temp of the floor is only just above room temperature. I don't have any room stats, zone valves or any of that complication, just one circulating pump and a buffer tank, it all runs from the outside stat and the controller on the heat pump. It just controls the average temp of the circulating water in the UFH based on the rate of heat loss from it. The flow to each room has been gradually tweaked to give the correct temperature in each room (basically warm in the living areas and cooler in the bedrooms).  

My view is on the heating side is keep it simple, there is nothing to go wrong bar the circulating pump (Grundfos Alpha running at its very lowest auto setting - approx 7W). Trouble is it will be very hard to convince a heating design engineer to throw all the bells and whistles away (room stats, zone valves etc.) I suspect you will also need a degree of thermal in the building to "smooth" the temperature - see my earlier post.

Roger  

[A.L.]

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

[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

[smegal]

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

They can jump on the sofa/bed.

[Greenbeast]

all 8 of them? the biggest weighs 60kg. 

 

[djs63]

The dogs must give a fair bit of heat!
And a tiled floor would conduct ufh best and be easy to clean dig hairs and foot prints.  We have Gshp fir 8 years, excellent.

[Greenbeast]

The dogs must give a fair bit of heat!

i wonder if there's a heat loss calc that takes them into account... 

[Fionn]

Allow about 1W per kg of dog I reckon 

[djh]

Glazing orientation isn't that critical - we're mostly north facing (forced by the house) with no shading on the south orientation, and aren't having to work too hard to hit EnerPHit - and PHPP shows virtually no overheating risk. Don't concentrate on sorting the glazing orientation out at the expense of it working as a house.

In our build it was very critical. Perhaps that's a difference between EnerPHit and PH level, or just some difference between the overall designs. If you have most windows with a northerly aspect, then I'd be very surprised if you did have any overheating risk, but most people try to increase solar gain more.

i wonder if we would like to spend hours laying on a 24C floor

We spend all summer lying on a bed at that temperature or more at times. We find it very pleasant.

The dogs must give a fair bit of heat!

i wonder if there's a heat loss calc that takes them into account...  

The usual rule of thumb is 50 W for a dog, 100 W for a human, 5 W for a cat 0.5 W for a mouse. All a bit less when inactive. PHPP takes account of human occupants; I don't remember about dogs.

[pdf27]

We do have plenty of space for gshp actually. I kinda hadn't considered it because my parents have not had the best time with it. Is it worth while (I really, really hope the house will have a good solar array)?

It is certainly my preferred option if I can make the budget work. As a solution it is more efficient, quieter and more robust than an air-source heat pump, and both are preferable to gas.

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

PH is limited to 10W/m2 in extremely cold weather, the predictions for my EnerPHit build are about 14W/m2. A screeded floor with tiles on top will provide 60W/m2 of heating if the water enters at 40°C and leaves at 30°C (i.e. an average of 15°C warmer than the air - 4W/°C). That means a 24°C floor would only occur in an EnerPHit house at the design low temperature (i.e. when it's properly brass monkeys outside - at which point the dogs would probably rather appreciate a warm floor to lie on), and never at all in a PassivHaus.

In our build it was very critical. Perhaps that's a difference between EnerPHit and PH level, or just some difference between the overall designs. If you have most windows with a northerly aspect, then I'd be very surprised if you did have any overheating risk, but most people try to increase solar gain more.

I suspect so - in the PHPP report the EnerPHit option has a 0.34% risk of overheating, the Passivhaus option has a 3.4% risk of overheating despite lower solar gains - it looks like the whole thing becomes significantly harder to balance as the energy consumption goes down. The thing is, the difference between the two is only 9 kWh/m²/year of heat - or about 300 kWh of electricity supplied to a good GSHP. The OP was talking about self-design rather than getting it modelled up, so I was assuming that he was more at the EnerPHit performance level than the PH level.

[Greenbeast]

Thanks for that. Gives me plenty to think about.

[djh]

The thing is, the difference between the two is only 9 kWh/m²/year of heat - or about 300 kWh of electricity supplied to a good GSHP.

The difference between the PH and EnerPHit limits is actually 10 kWh/m²/a (difference between 25 kWh/m²/a and 15 kWh/m²/a) but that's neither here nor there.

More relevant is that there's no way I could ever justify the capital cost of a GSHP with my heat demand. I couldn't even justify the costs of a gas boiler, so I just have an electric post heater. At some stage I may consider an ASHP, depending on how circumstances change, but it's not on the horizon yet.

[pdf27]

The difference between the PH and EnerPHit limits is actually 10 kWh/m²/a (difference between 25 kWh/m²/a and 15 kWh/m²/a) but that's neither here nor there.

That was taken from the options I was given for our build - which came out as 23 or 14 kWh/m²/year - you're right, I should have quoted from the standard though.

More relevant is that there's no way I could ever justify the capital cost of a GSHP with my heat demand. I couldn't even justify the costs of a gas boiler, so I just have an electric post heater. At some stage I may consider an ASHP, depending on how circumstances change, but it's not on the horizon yet.

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. 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.
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.

[Bodidly]

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