Heat in the home

[pwa]

Condensation occurs when warm moist air touches a cold surface whose temperature is below the air's dew point. Poor ventilation or still moist air trapped in a corner can cause it and...mould can grow. If you have rockwool inside a plasterboard skin you probably wont have a problem. This type of wall insulation is almost standard in new builds.

Al

It is a brick-rockwool-brick sandwich. With render on the outer surface. No dampness at all. It dates from about 1970, so must be an early example of cavity insulation.

[simonineaston]

Friends of mine emigrated to New Zealand in the '80s and built their house out of straw bales, slotted into a wooden frame and then hard-rendered - at least that's my understanding of the design. It's apparently cool in summer and snugly-bugly in winter.

[pwa]

Friends of mine emigrated to New Zealand in the '80s and built their house out of straw bales, slotted into a wooden frame and then hard-rendered - at least that's my understanding of the design. It's apparently cool in summer and snugly-bugly in winter.

That sort of construction would be a nightmare if you had a rat infestation. I'm sure the thermal properties are great, though.

[Biospace]

Friends of mine emigrated to New Zealand in the '80s and built their house out of straw bales, slotted into a wooden frame and then hard-rendered - at least that's my understanding of the design. It's apparently cool in summer and snugly-bugly in winter.

That sort of construction would be a nightmare if you had a rat infestation. I'm sure the thermal properties are great, though.

That and the fire hazards are two natural responses, however neither is an issue any more with straw builds than conventional I'm told. It's a fantastic building material provided it remains dry hence the typically large eaves, it's quick and easy to assemble and with enormous levels of insulation - both sound and heat.

I must admit that I haven't got my head around why cavity insualtion sometimes results in dampness. Our house has cavity walls filled with Rockwool (mineral wool) that must have been put in as the walls were built. And we have never had any dampness. Is the problem confined to expanding foam introduced after construction?

This webpage descibes things well, http://www.askjeff.co.uk/cavity-wall-fill/

Internal insulation for solid walls can affect the dew point and create condensation problems, below are a couple of discussions considering this.

http://www.greenbuildingforum.co.uk/new ... e=1#Item_0
https://www.heritage-house.org/damp-and ... ation.html

My younger son who is a carpenter has recently been working on old timber framed house in a coservation area - he was installing a breathable insulation to deal with this problem.

Breathable membranes are important when insulating old houses but there's plenty more which needs to be taken into consideration - not least, the building as a whole rather than a particular wall or room. I seem to remember reading an article which suggested that any gap is an invitation for condensation and introducing new ones was a recipe for problems in an old building.

A building with solid walls and as built, without what we might term 'insulation' is a ventilated, thermal mass with the structure itself acting as insulation and with a temperature gradient from inside to out. Creating an insulated space within the building reduces the temperature of the structural walls, two considerations being careful management of airflow, both in the uninsulated gaps and the insulated spaces and an awareness of how floor, roof and other spaces may become more prone to interstitial condensation, with mould and wood rot the result. The last time I looked, there wasn't much formal research, but this https://www.heritage-house.org/document ... _final.pdf is a good guide.

[axel_knutt]

This webpage descibes things well, http://www.askjeff.co.uk/cavity-wall-fill/

I'm pretty sure that's the same website I read 20 odd years ago, a few days after I'd had a quote for CWI, and just in time to avoid signing on the dotted line. I considered it a narrow escape then, and I still do now.

[al_yrpal]

Both articles very interesting...

In my South Oxfordshire house we had the wool insulation injected, there was a tiny area in a downstairs cloakroom that suffered from a small area of damp. I always wondered why. The insulation didnt seem to make any difference to comfort or lower bills noticeably.

Now living in a 1799 brick built Georgian House with single skin outer walls there is no noticeable rain penetration whatsoever. The walls are very thick though. Two tiny areas of rising damp have been easily fixed by drilling and inserting dry rods.
Our annexe and adjacent garage which were once stables and a coach house has rising damp in an adjoining cavity wall which I have drilled and inserted dryrods. It is drying out nicely.

Al

[Jon in Sweden]

Our house in Sweden is a 1957 built, three story (well, two plus basement, though because we sit on a hill, it's closer to four stories on the back) house with about 240 square metres.

Heating is primarily geothermal (170m deep borehole) with secondary heating from a 10kw woodburning stove in the kitchen (35 square metres) and an air/air heat pump in the living room (40 square metres).

The house seems to be incredibly well insulated. We've had down to minus 22c so far this winter and honestly, from inside, you couldn't tell.

We have been using firewood when the electricity price is high (it's priced on a daily, rolling basis) but the geothermal is always set to 17c.

Firewood usage has been around 1 to 1.5 cubic metres a month and electricity for heating was 700kwh in December.

Despite being more than twice the size of our last three UK houses, it's much cheaper to run and uses far less energy per square metre, despite the winters here being so much colder.

We need to replace the windows at some point in the coming years and that should improve things further.

We will be installing a 10kw solar panel array on the roof in spring, and despite us going for the leasing option (which is a bit more expensive, but no upfront costs), that should reduce our overall electricity bill by about a third.

Houses are much, much better built here than in the UK.

[Biospace]

Heating is primarily geothermal (170m deep borehole) with secondary heating from a 10kw woodburning stove in the kitchen (35 square metres) and an air/air heat pump in the living room (40 square metres)

.... electricity for heating was 700kwh in December.

Hi Jon, do you have any numbers for the (real world) efficiencies of the two different types of heat pump you're using? For those who do heat with heatpumps, I wonder if most are ground source, given the lower winter temperatures in Sweden?

[Jon in Sweden]

Heating is primarily geothermal (170m deep borehole) with secondary heating from a 10kw woodburning stove in the kitchen (35 square metres) and an air/air heat pump in the living room (40 square metres)

.... electricity for heating was 700kwh in December.

Hi Jon, do you have any numbers for the (real world) efficiencies of the two different types of heat pump you're using? For those who do heat with heatpumps, I wonder if most are ground source, given the lower winter temperatures in Sweden?

The air to air heat pump has a coefficient of performance (COP) of 3. So 1kw of electricity in provides 3kw of heat. I think it's a bit more efficient at cooling in summer. Closer to 3.5.

The ground source has a COP of 4.4. It's slow to react though and whilst it's always on, we like the air/air as you can almost instantly heat a room up.

I'd say that more than 50% of houses here have ground source heat pumps now. Air source is sometimes used for central heating but ground source is more common. Air source is usually for supplementary heating.

In terms of overall heating demand for our house - I suspect the total electricity usage from the two heat pumps will be about 7000kwh (providing about 28000kwh to the house). The 9 cubic metres of firewood we burn provides another 7500kwh after efficiency losses.

So 60 kwh per square metre per year. That's about half of the minimum standard for new building in the UK now, but we have much colder winters and our house is 65 years old.

[Biospace]

The air to air heat pump has a coefficient of performance (COP) of 3. So 1kw of electricity in provides 3kw of heat. I think it's a bit more efficient at cooling in summer. Closer to 3.5.

So 60 kwh per square metre per year. That's about half of the minimum standard for new building in the UK now, but we have much colder winters and our house is 65 years old.

Very interesting and impressive, thanks. It highlights the low standards and expectations of housing in Britain. In part, because winters are generally mild and damp with the odd week or two of sub-zero when (usually) there is little wind. We need to improve things very quickly, as well as coming up with a plan for existing buildings.

Are those COP figures the ones quoted by the manufacturer or are they what has been measured in situ? I wonder what the standards for new builds are in Sweden...

[Jon in Sweden]

The air to air heat pump has a coefficient of performance (COP) of 3. So 1kw of electricity in provides 3kw of heat. I think it's a bit more efficient at cooling in summer. Closer to 3.5.

So 60 kwh per square metre per year. That's about half of the minimum standard for new building in the UK now, but we have much colder winters and our house is 65 years old.

Very interesting and impressive, thanks. It highlights the low standards and expectations of housing in Britain. In part, because winters are generally mild and damp with the odd week or two of sub-zero when (usually) there is little wind. We need to improve things very quickly, as well as coming up with a plan for existing buildings.

Are those COP figures the ones quoted by the manufacturer or are they what has been measured in situ? I wonder what the standards for new builds are in Sweden...

I don't have any means of measuring the performance directly, but I have no reason to doubt it as the house is warm and doesn't use many kwh to stay that way.

The existing housing stock in the UK is one thing, but the fact that they are still building such appallingly constructed homes is shameful. Built for profit by people that'll never live in them.

Not sure what the modern standards are like here, but I imagine a fair bit better than our house. I've seen houses advertised for sale with lower energy consumption figures.

[Jdsk]

https://www.tado.com/gb-en/press/uk-hom ... neighbours
https://www.euronews.com/green/2022/12/ ... ated-homes

Jonathan

[Biospace]

Interesting that graphic would suggest Italians appear to be very diligent whereas the Dutch are not much better than us. Perhaps it's a result of the sort of extremes likely to be experienced for a protracted time?

[Mick F]

Why doesn't the map show that UK has Northern Ireland in it, let alone Shetland?

[axel_knutt]

https://www.tado.com/gb-en/press/uk-hom ... neighbours

Spot the howler on their website:

The temperature only goes down by 1c (or whatever) over 5 hours, and yet they say:

"smart thermostats can make significant additional energy savings by ensuring that homes and rooms are only heated when they are occupied"

Er, not if the temperature isn't going down you're not. The energy savings are proportional to the drop in temperature, so the house doesn't stop haemorrhaging money until it's stone cold, because even if the heating is currently off, the stored heat you're losing was still paid for out of your pocket! After 5hours the house is still losing most of the heat it was losing when the CH was on.

It's easier to see the wood for the trees if you look at the way the temperature varies on a section through the thickness of a cavity wall over a heating cycle. Take this plot of my all-but uninsulated house, it shows, over a 72 hour period, the temperature of the inside air, inside surface of the cavity wall, inside of the cavity, outside of the cavity, outside of the wall, and outside ambient, in that order, from top to bottom, and it compares those with the heating both timed and continuous.
.

Scale of the plot is 1sec to 1 hour, and 1V to 1C.

You can see that whilst the inside air temperature drops by 5.3 degrees over 7 hours (& 4.7 over 5 hours), the outside surface of the wall varies by only 0.1C over the daily cycle, and its mean difference above ambient is only about 10% lower with the heating timed than on continuous. This smoothing of the daily temperature variation is caused by the thermal resistance and heat capacity of the wall, and it's the reason why switching my heating off for 29% of the day saves only about 10% off the heating bill, because it's ultimately the outside surface of the wall that's losing heat to the outside air.