Cornish Cottage Renovation and Extension

[Aggierockdoc]

Firstly many thanks to those who have both set up and contribute to this forum.

 

I'm a geophysicist turned builder who is returning to the UK from overseas and about to start a Cornish Cottage Renovation and Extension project.

 

 

I'm very much interested in all things heating related especially GSHP technology, insulation, UFH and heat storage.

 

I look forward to some sound evidence based discussion that cuts through all the cowpoo associated with some of this technology.

 

All the best

 

Stephen

Edited July 20 by Aggierockdoc
pressed something accidentally

[Onoff]

Welcome.

 

(Looking forward to something powered by radon!)

Edited July 21 by Onoff

[SteamyTea]

Welcome.

 

Which part of Kernow, it is quite long.

(Just cottoned onto your username, may place your house)

Surf is better in Costa Rica.

 

You will be talked out of GSHPs pretty quickly, but Kensa are your people to talk to down here.

Edited July 21 by SteamyTea

[Aggierockdoc]

That was quick... my dual location has already been figured out! (cf Steamy Tea - good to see some Cornish representation...).

 

On 21/07/2024 at 04:34, SteamyTea said:

Which part of Kernow, it is quite long.

(Just cottoned onto your username, may place your house)

Surf is better in Costa Rica.

As regards house placement... if you know Goonvrea you might well know the house.

 

But the last comment is the important one ...

On 21/07/2024 at 04:34, SteamyTea said:

You will be talked out of GSHPs pretty quickly

I've always considered GSHPs as a better option because of the physics of heat transfer... ie water is around 20x better at moving heat from a surface than air. Plus, I have the space for a slinky loop that I can install myself. Plus I'm assuming our climate and ground heatflow is better suited than other areas in the UK because of our "southerly" latitude and minor temperatures swings. But, and there's a big but... GSHPs are sooo much more expensive.

 

Also I'm intrigued by an older thread that I found from SteamyTea, TerryE and JSHarris. (I commend JSHarris for his code and suggest he can bore me anytime with such work). His wall temperature profile that shows how stable the interior temperatures are whilst the exterior wangs about betwen 10 and zero.

 

 

Anyhow let me try to set out a cogent message that relates my interest in the consensus on AHSP vs GSHP and also the concept of seasonal heat storage, thermal inertia and thermal penetration.

 

 I'm keen to understand some of the fascinating comments made within this thread. In particular from StormyTea, TerryE and JSHarris.

 

On 05/12/2016 at 23:46, TerryE said:

Been playing over at the other place and as usual the topic came to inter seasonal storage and how the ground under the house can be helpful.  As I know it can't, and felt I had to show this yet again, I quickly knocked up a little model in LISA, then made a video of it.  Here it is, it shows that there is hardly any thermal penetration: Youtube - Thermal Inertia

When I click on the youtube link I get a message describing this as private and I need to sign in on Youtube, which I try to avoid... is there any other way to get this?

 

I'm assuming the lack of thermal penetration is because fourier's law (-k.dT/dx) tells us that heat flow will be much greater up than down? But what if the heat source is under an insulator?

 

I bet every non-technical person now mentions the guy in Grand Designs, with his heat storage system. I suspect his design is a very special case.

 

From my back of a fag-packet calculations I was thinking that the problem with storage is just size. EG. If you had a house with footprint of radius r, the notional heat island under the house would have a volume of half 4/3. pi. r^3. If this hemisphere touches the water table where the water just whisks away your heat and never goes above 12C. You'd chop your volume at the base ... a bit like an upside down egg.

 

Assuming for this exercise that it doesn't ... a half 4/3. pi. r^3 would give a volume of around 1000 m3, for r=8. Multiply that by heat capacity of say 800 J/kg.k and density of 1500 kg/m3 and delta T of say 5 degree on average gives c. 1800 kwh of heat storage. (Is this right?)

If so, this aint much when you consider a stone/cob home will need about 15,000 kwh a year to stay warm. My 1800 kWh estimate for storage doesn't really factor in how much heat buggers off out the bottom of the storage volume and leaks out the sides. The only utility I could see with trying to inject summer heat under your house to create a heat store, would be for relatively short time scales - say between sunny periods and cloudy periods... and even that doesn't account for whether you could realistically get much of the heat back...

 

Hmmmm.... I'm convincing myself of the futility of heat storage: you can't put enough heat in to store on the time-scale that you want, and even if you did, you might only get a small proportion of it back.

 

Comments welcome on whether the issue with storage is just size and also the ASHP vs GSHP angle.

 

Regards

 

Stephen

 

 

 

 

 

 

 

 

[SteamyTea]

TL:DR (about to fill my empty food cupboards).

Are you around on the 3^rd August, it is Carnival, so I will be in Aggy telling everyone they are wankers and starting a fight (actually it was not me  but I know who did start it).

 

But yes, thermal storage is really down to size.

Edited July 22 by SteamyTea

[Aggierockdoc]

Unfortunately I won't be back until September at the earliest. 🤔... so my pump-action super-soaker will have to stay under wraps for another year. Are water pistols still banned? I'm wondering if we know each other... ever met anyone who used to work at the old "hot-rocks" project, then disappeared to warmer climes?

 

Anyhow thanks for confirming my suspicion regarding thermal storage and size. and I guess I'm going to be digging some trenches.

 

 

[SteamyTea]

45 minutes ago, Aggierockdoc said:

ever met anyone who used to work at the old "hot-rocks" project

Had a talk when I was at university by someone that was involved, think that was about 2006.

Are you an old CSM fellow?

2 hours ago, Aggierockdoc said:

if you know you might well know the house

Yes I know it.

May be worth getting a moderator to delete some of this conversation.

Just click on Report Post and take down the location stuff, they are a bad bunch on the North Coast.

 

45 minutes ago, Aggierockdoc said:

Are water pistols still banned

Only when it is raining, and in Newquay at all times.

Edited July 22 by SteamyTea

[MikeSharp01]

1 hour ago, Aggierockdoc said:

I've always considered GSHPs as a better option because of the physics of heat transfer... ie water is around 20x better at moving heat from a surface than air.

Very true the problems though seem to come from the Engineering rather that the physics so the machine is more complex, has more things that can go wrong and so costs more and therefore has a longer payback in pure £. Not sure on the embodied carbon side of the equation, or the availability of; support - ASHP's don't have much good support and reliable installers. We chose not to have one because of space. 

[ProDave]

I looked into GSHP's for here.  I soon concluded even if I did all the digging work to lay the slinky myself, the cost of the pipe, fittings, and the brine to fill it was way more than the cost of the GSHP.  Then when you see the advice is replace the brine every 10 years, the ongoing costs outweigh the additional efficiency compared to an ASHP.

[MikeSharp01]

1 hour ago, SteamyTea said:

But yes, thermal storage is really down to size.

So in this context size, or perhaps volume / form factor, is everything.

[jack]

Welcome!

 

2 hours ago, Aggierockdoc said:

 the physics of heat transfer... ie water is around 20x better at moving heat from a surface than air.

 

True enough, but heat capacity is not the only factor.

 

The environmental heat source (assuming heating mode) for a GSHP is not the water in the ground loops, but the ground the loops are in. While the water in the ground loops is great at transferring heat from the internal heat exchanger, the transfer between the loops and the ground they're in is by far the limiting factor.

 

I was all for a GSHP until learned it would have been ~5 times the cost for a moderate improvement in COP and a lot more hassle onsite during the build.

 

The energy bill for our all-electric house was £1000 the first year we moved in (8 years ago). Even if a GSHP had halved our energy usage, the payback period on the difference between ASHP and GSHP would have been something like 30 years. Admittedly that would have been significantly reduced with the increases in energy costs over the last couple of years!

[Roger440]

I looked (briefly) at storage. Using old milk tankers. Buried.

 

Rough calcs suggested id need 2 to keep house warm through winter. They are £5k a pop. Plus need burying.

 

Additional complication was very high water table, so heat would be constantly sucked away unless significant work was done on drainage etc.

 

Simply makes no sense in the real world.

 

 

[TerryE]

On 22/07/2024 at 18:34, Aggierockdoc said:

His wall temperature profile that shows how stable the interior temperatures are whilst the exterior wangs about between 10 and zero.

 

Actually the code and graph were mine; the context was a passive house twinwall (high insulation with decent thermal capacity) with an outer stone skin.  This is a world away from the thermal characteristics of you stone cottage (which is of similar construction to my previous house).  The U-values you get from a solid stone wall are terrible as stone is an awful insulator compared to a passive profile (the U-values are typically 10-20× greater).  Yes there is little temperature variation inside as the walls are just always cold in the winter. You can really only mitigate this by adding something like an inner aerogel backed plasterboard liner to the exterior walls.

 

As heat just wicks away through every external surface, you just need to input a lot of heat to get a comfortable room temperature.  

[SteamyTea]

4 hours ago, TerryE said:

The U-values you get from a solid stone wall are terrible as stone is an awful insulator compared to a passive profile

Yes, but it is a lot more complicated than that (to quote Ben Goldacre).

While a homogeneous stone may have a greater thermal conductivity than a non homogeneous wall buildup i.e. OSB, insulation, air barrier, plasterboard etc, a 'stone walled building' generally has a complicated (messy) wall. They were often have stone face, then lots of rubble, which traps air (and moisture), then a breathable (crumbling lime plaster) coating, then an inappropriate decorative coating (1970s wallpaper and vinyl paints). Then a hole or two knocked through them for ventilation.

As thermal energy moves from hotter to colder inside the wall, all those elements increase (and depending where you measure, decrease) in temperature. This causes the moisture to partially evaporate and physically move, often condensing somewhere else.

This is often seen as a simple 'cold spot' problem, but is often a bigger overall problem.

While excess internal heating may seem to reduce the symptoms, the problem is still there, just waiting to rear its ugly head (and often throw some fungal spores around for a laugh).

There is not really a technical solution to old, non homogeneous, wall buildups that allows the thermal conductivity to be reduced, even building an insulated timber frame structure inside, only masks the problem, you just end up with cold, damp outer walls.

 

So old buildings really need to be knocked down and rebuilt, no reason they cannot look similar (except modern building codes specify how high some windows can be).

[Roger440]

19 minutes ago, SteamyTea said:

Yes, but it is a lot more complicated than that (to quote Ben Goldacre).

While a homogeneous stone may have a greater thermal conductivity than a non homogeneous wall buildup i.e. OSB, insulation, air barrier, plasterboard etc, a 'stone walled building' generally has a complicated (messy) wall. They were often have stone face, then lots of rubble, which traps air (and moisture), then a breathable (crumbling lime plaster) coating, then an inappropriate decorative coating (1970s wallpaper and vinyl paints). Then a hole or two knocked through them for ventilation.

As thermal energy moves from hotter to colder inside the wall, all those elements increase (and depending where you measure, decrease) in temperature. This causes the moisture to partially evaporate and physically move, often condensing somewhere else.

This is often seen as a simple 'cold spot' problem, but is often a bigger overall problem.

While excess internal heating may seem to reduce the symptoms, the problem is still there, just waiting to rear its ugly head (and often throw some fungal spores around for a laugh).

There is not really a technical solution to old, non homogeneous, wall buildups that allows the thermal conductivity to be reduced, even building an insulated timber frame structure inside, only masks the problem, you just end up with cold, damp outer walls.

 

So old buildings really need to be knocked down and rebuilt, no reason they cannot look similar (except modern building codes specify how high some windows can be).

 

Does a cold damp outer wall matter if it is, to all intents a rainscreen?

 

Granted, not many can sacrifice that much interior space, (ie, the air gap plus internal wall bild up) but its viable on bigger building like barn conversions.

[saveasteading]

On 22/07/2024 at 18:34, Aggierockdoc said:

GSHPs as a better option because of the physics of heat transfer

 

5 hours ago, TerryE said:

The U-values you get from a solid stone wall are terrible

 

You'll get plenty of differing opinions on here, but very few favouring ground source. Quite right too.

That's unless you have hot rock underground, or the ground effectively has a stream passing through it to bring in new energy.

Ground source sucks the heat out of the ground and it is not replaced. Slinkys are actually getting their energy from the air and the sun, so will work nicely in the summer, so forget them too.

Air is replaced constantly so.....

ASHP for my next project too, without a doubt.

 

Stone buildings. Is yours like ours, granite with 600mm thickness in 3 layers?

There is good info in Scottish 'heritage' sites.

We have kept the structure as it keeps the weather out, and built a timber tent inside, for insulation and tidiness. 

 

The stone gives you more insulation than is normally imagined and dampness is also a minor to zero issue if you repair and look after the wall properly (understanding lime too).

 

Results of our stone building: Only partially occupied. Very happy with temperatures and ASHP heating efficiency.  No damp. Steading saved.

 

Yours looks splendid and will be just great if you take best advice and study study study.    ohhh and don't assume that the local builders know much (or anything) about science, or good building practice. .

Good luck and keep asking.

 

[SteamyTea]

1 hour ago, Roger440 said:

Does a cold damp outer wall matter if it is, to all intents a rainscreen

Probably not if there is enough of a moisture break between inner and out leaves.

 

As @saveasteading says, probably not an issue if you keep it all warm enough and look after it.

 

If you can see St. Agnes Head, it is about to rain, if you can't see it, it is raining. So any shallow GSHP tends to work down here, because, as you say, they are really ASHPs with solar heated water being an intermediate energy transfer medium.

 

I very much suspect that the OP knows the geology down here better than most.

Heating peak loads are generally lower in Cornwall, even if the yearly energy usage is high in older houses.

Edited July 24 by SteamyTea

[TerryE]

42 minutes ago, saveasteading said:

The stone gives you more insulation than is normally imagined

 

In our previous ~2-300 year old Cotswold stone farmhouse we put it a silicon DPC back in the mid 80s and completely repointed over the next 10-20 years the infill showly turned from damp loam to bone dry dust and grain husk.  The effective U-value slowly improved down to around 1½  W/m²K.  The main problem was that the house leaked air terribly and the floor slab was uninsulated.   Our current house has a U-value for exterior walls, roof, floor in the range 0.12-0.15  W/m²K and an an ACH of around 0.4, plus MVHR.  Just no comparison in terms of winter comfort.

 

When the kids were young, they ran around naked in doors in the winter but then again gas was dirt cheap in the 90s so the boiler was going flat out when we were in the house.

Edited July 24 by TerryE

[saveasteading]

19 minutes ago, TerryE said:

the house leaked air terribly and the floor slab was uninsulated. 

I have read that air moves readily through cross walls, horizontally. Thus any walls retained as stone features could be a heat sink.

We have sealed the innards through boring modern methods, so any draughts are between the vapour control layer and the outsides. Repairs to the lime pointing will be the work of years.

The floors are all modern now. Most of the farm quality floors had to be broken out anyway so are now insulated and heated.  Beware existing door lintel heights if thinking of building up the floors.

[TerryE]

6 hours ago, saveasteading said:

Beware existing door lintel heights if thinking of building up the floors.

 

I am 182 cm tall, and a couple of our internal doors were about 181 !!  I'd just duck slightly automatically, but about twice a year (especially is some spoke to me from behind) I'd forget and clip my bonce.  Ouch.  🤣

[saveasteading]

6 hours ago, TerryE said:

especially is some spoke to me from behind) I'd forget and clip my bonce

They do that on purpose, just as you stand straight on the other side.

 

It's not something I immediately thought of in doing a conversion, that there is a conflict between improving the floors, undermining existing walls, and door heights. An experienced builder told me that lots of people get it wrong. 

[Aggierockdoc]

Many thanks to everyone for their cogent responses. I'm now wondering what my best options are...

 

At the moment my thoughts are that I should:

• clad the North side of the house if the planners will let me, in order to up-rate the U-value for that side of the house
• insulate the hell out of the floor so that I can limit heat loss through the floor... (maybe 150mm?)
• accept that on the South side of the house I have a high U-value and maybe mitigate heat loss slightly by way of a 25mm interior perlite/lime render and shutters on the windows
• insulate the hell out of the roof to limit heat-loss out the top (?250mm)
• install a MVHR system and find/close up all the little draught holes that I can find - invite a local shaman/smudging expert with a blower door to help
• install a wood burner to provide another heat source that mitigates the cost of the all the electricity I'm going to need for my ASHP

Any other suggestions gratefully received.

 

In terms of answers and comments...

 

Firstly for saveasteading:

 

I believe our walls are 600mm thick and in 3 layers, but the layers are: c.40mm lime plaster; c.400mm cob; 150mm stone (killas not granite).

Message understood re: builders... and studying hard.

 

On 24/07/2024 at 17:58, saveasteading said:

Stone buildings. Is yours like ours, granite with 600mm thickness in 3 layers?

Yours looks splendid and will be just great if you take best advice and study study study.    ohhh and don't assume that the local builders know much (or anything) about science, or good building practice. .

 

 

For TerryE:

 

Apologies for not referencing your code and diagram correctly...

 

On 24/07/2024 at 11:52, TerryE said:

 

Actually the code and graph were mine; the context was a passive house twinwall (high insulation with decent thermal capacity) with an outer stone skin.  This is a world away from the thermal characteristics of you stone cottage (which is of similar construction to my previous house).  The U-values you get from a solid stone wall are terrible as stone is an awful insulator compared to a passive profile (the U-values are typically 10-20× greater). 

Also, I got a U-value of c. 1.0 from ubakus for a close approximation to my wall. I up-rated (ie raised) the default U-value for clay blocks to 1 W/m2.k to approximate to cob, which makes it around 4x worse than building regs. Better than solid stone, but still not great.

 

SAWWall_South-1.pdf

 

For ProDave:

 

Duly noted.

 

On 22/07/2024 at 20:02, ProDave said:

I looked into GSHP's for here.  I soon concluded even if I did all the digging work to lay the slinky myself, the cost of the pipe, fittings, and the brine to fill it was way more than the cost of the GSHP.  Then when you see the advice is replace the brine every 10 years, the ongoing costs outweigh the additional efficiency compared to an ASHP.

 

 

And finally for SteamyTea...

 

Re knock it down and start again... funny you should say that... I'm trying to convince my wife we need to knock down the bit on the East side and rebuild that at least. But that's going to take a lot of persuading and a metric shit-tonne of money (notice that's a metric shit-tonne not an imperial shit-ton)... I like to get my units right.

 

[Dave Jones]

personally i would clad the whole place in external wall insulation and render. Couple benefits, wont lose room space, help fixing air tightness and covers up that miserable depressing grey stone.

 

some nice new windows, fitted and taped well and you will have no problem keeping it warm cheap with an ASHP.