Alternatives To An ASHP

[joe90]

17 hours ago, Matt60 said:

The insulation is Dritherm 32, I suppose that is mineral wool. I could just about change it, I originally asked for a 200mm cavity but the architect, bricklayer and builders merchant all said it would cause issues with Catnics that could span a 200mm cavity. When I suggested separate steels or concrete lintels I was told it would be costly to have the steels as they would all have to be individually calculated and the steel supply could delay things. The builders merchant said there is no off the peg Catnic type steels that would suit.

I have a 200mm cavity with dritherm insulation, brick arches in the outside skin, normal concrete lintels in inside skin. Catnics are a thermal bridge (IMO). I also have 200mm insulation under the slab, 2g windows and an 5KW ASHP, no PV , my house is a constant 21’. It can be done.

[AliG]

This seems very overthought.

 

Most of the cost of heating a house is due to heat loss.

 

The heat loss is driven by the temperature differential between inside and outside and the amount of insulation.

 

Keeping a house at a constant 23C does not use much more energy than 21C, around 15%. Thus an ASHP will be more than capable of doing this. You could set the thermostat at 22C and kick it up to 23C if you wanted to warm it up.

 

Also a house with UFH generally feels warmer at a lower air temperature than a house without it as the heat is closer to the floor than the ceiling.

 

The only time you might worry about it being slow to warm up is if you have been away on holiday and the whole house has cooled down. Then you need to warm up the fabric of the house as well as the air inside it.

 

We have a gas boiler, but only run the UFH flow at 38-42C and I can actually watch a room heating up on the Heatmiser charts when the heating kicks in. Actually the thing that has most impact on the speed of a room heating up is the floor covering. Tiled rooms heat up in a fraction of the time fo the rooms with wooden floors where I need to run the flow at a higher temp.

 

Using PV for heating is a non starter as stated and an ASHP is going to be a lot cheaper to run than direct electrical heating. You will also get RHI payments if it is a new build, although time is running out for these.

 

 

 

[TerryE]

You need to do the thermal calcs.  On a new build, you can get the wall / roof / slab U-values 0.15 or better quite easily IMO, and for minimal cost.  The downside is wall depth needed, but if you plan this in, then there isn't a material cost -- except that it make makes it a little more inconvenient for your building crew -- hence you need to focus on quality assurance and avoid construction flaws (like sloppy or omitted insulation installation) which cause thermal bridges and will compromise the build.  Next up if you have a thermal shell of this spec, are the air-related losses which will dominate your heat budgets, so you also need a level of air-tightness and MVHR.

 

My personal experience of building a house of this class is that the internal heat flows are 10× greater than interior to exterior losses.  The bottom line if you achieve this is that you will need to top up heat -- e.g. through a in-slab UFH installation -- but that you don't need any other CH installation or rads as room to room temperatures will only vary by a degree or so.  (In the coldest 3 months, we also boost the heat for the top 2 floors by using a small oil-filled electric heater on a timer switch in my office on the 1st floor for a few hours overnight.)   Overall, the whole house maintains a 22½-23°C temperature 24×7.

 

We use a Willis for my slab heating, and I can't make the cost-benefit case to install an ASHP as I won't recover the installation costs over a 10-year payback.  However, that is because we have a high-spec passive-class house.  IMO, an initial install of an ASHP is a safe option for most reasonably energy-efficient new builds.

[Matt60]

Thanks for all the replies, I appreciate it and as I've said before, the heating is the biggest worry I have for the whole build to be honest.

 

My architect has come back with my U values today which are a bit better than some of those estimated, I'll post the spec below.

 

So to turn this thread on it's head, with the following values, if it were your house and you don't like the cold - what system would you fit? For clarity, don't denigrate someone else's system - what would YOU do? I will read and research any suggestions. Again, thankyou for your responses and thankyou in advance for the systems you can suggest.

 

My specs;

 

New Ground Floor Construction – U-Value 0.12 W/m2K:-

• 75mm sand / cement screed.
• Selected underfloor heating to be installed within screed.
• 500 gauge separating layer.
• 150mm Celotex XR4000 insulation.
• 1200 gauge polythene DPM.
• Selected 150mm deep PCC beam and block floor.
• 150mm min. ventilated void below.

 

New External Brickwork Cavity Walls (350mm overall thickness) – U-Value 0.18 W/m2K:-

• Selected 103mm brickwork outer leaf.
• 150mm cavity to be fully filled with Dritherm 32 or similar approved insulation.
• 100mm Durox Supabloc (3.6mm2) or similar approved blockwork inner leaf.
• 12.5mm Gyproc Wallboard on dabs with skim coat finish.

 

New External Rendered Cavity Walls (350mm overall thickness) – U-Value 0.17 W/m2K:-

• K-Rend render or similar approved render.
• 100mm Hemelite Standard (3.6mm2) or similar approved blockwork outer leaf.
• 150mm cavity to be fully filled with Dritherm 32 or similar approved insulation.
• 100mm Durox Supabloc (3.6mm2) or similar approved blockwork inner leaf.
• 12.5mm Gyproc Wallboard on dabs with skim coat finish.

 

New External Boarded Cavity Walls (350mm overall thickness) – U-Value 0.16 W/m2K:-

• Selected composite boarding to be fixed into 25mm or 38mm x 50mm tanalised timber vertical battens.
• 100mm Hemelite Standard (3.6mm2) or similar approved blockwork outer leaf.
• 150mm cavity to be fully filled with Dritherm 32 or similar approved insulation.
• 100mm Durox Supabloc (3.6mm2) or similar approved blockwork inner leaf.
• 12.5mm Gyproc Wallboard on dabs with skim coat finish.

 

New Pitched Roof (Vaulted Ceiling) – U-Value 0.18 W/m2K:-

• New zinc roof to be fixed in accordance with the manufacturer’s instructions on a selected underlay.
• 18mm WBP ply or OSB/3 to be fixed into timber rafters / raised tie roof trusses.
• 50mm min. ventilated air gap between the Celotex insulation and breather membrane.
• Insulate between rafters with 100mm Celotex XR4000 insulation or similar approved.
• Insulate under the rafters with 40mm Celotex TB4000 insulation or similar approved.
• 15mm Gyproc Duplex Wallboard (foil backed) with skim coat finish.

 

New flat roof (Warm Roof) – U-Value 0.16 W/m2K:-

• Selected single ply flat roof membrane.
• 18mm WBP ply or OSB/3.
• 120mm Celotex XR4000 insulation or similar approved.
• Vapour Control Layer (VCL).
• 18mm WBP ply or OSB/3.
• Flat roof joists (sizes to be determined by Structural Engineer)
• 15mm Gyproc Wallboard with skim coat finish.

 

New Pitched Roof (Flat Ceiling) – U-Value 0.11 W/m2K:-

• New zinc roof to be fixed in accordance with the manufacturer’s instructions on a selected underlay.
• 18mm WBP ply or OSB/3 to be fixed into timber rafters / raised tie roof trusses.
• Raised tie trusses.
• Insulate between the ceiling joists with 200mm fibreglass insulation and 200mm fibreglass insulation to be cross laid over.
• 15mm Gyproc Duplex Wallboard (foil backed) with skim coat finish.

 

New Pitched Roof (Above Garage / Vaulted Ceiling) – U-Value 0.19 W/m2K:-

• Selected slate tiles to be laid in accordance with the manufacturer’s instructions on 25 x 50mm tanalised timber battens.
• Selected Tyvek or similar approved breather membrane on attic roof trusses.
• 25mm min. ventilated air gap between the Celotex insulation and breather membrane.
• Insulate between rafters with 150mm Celotex XR4000 insulation or similar approved.
• 15mm Gyproc Duplex Wallboard (foil backed) with skim coat finish.

Edited February 26, 2021 by Matt60

[TerryE]

8 minutes ago, Matt60 said:

New External Brickwork Cavity Walls (350mm overall thickness) – U-Value 0.18 W/m2K:

 

Turning this on it's head, why has your architect spec'ed such a crappy profile?  Another layer of  Dritherm would drop the U-value to nearer 0.11 W/m²K for minimal extra build cost albeit with a 470mm wall profile.  It seems that architect's are just so f***ing conservative to be unbelievable.  See @tonyshouse blog.

 

Even so,  you can't make any as-built thermal performance predictions until you have an air-tightness and MVHR design.

[Matt60]

5 minutes ago, TerryE said:

 

Turning this on it's head, why has your architect spec'ed such a crappy profile?  Another layer of  Dritherm would drop the U-value to nearer 0.11 W/m²K for minimal extra build cost albeit with a 470mm wall profile.  It seems that architect's are just so f***ing conservative to be unbelievable.  See @tonyshouse blog.

 

Even so,  you can't make any as-built thermal performance predictions until you have an air-tightness and MVHR design.

 

Such passion - love it!!

 

As I have alluded to before, I tried to go 200mm cavity, but you cannot get an off the peg Catnic to span that distance and paying a structural engineer to calculate every aperture for steels looks very expensive. @joe90 has kindly offered that he has used brick arches and concrete lintels, but I will have a couple of sets of bi-folds which would be too wide to use this as a solution. I think?

 

I'm not about to become that pain in the arse client, and so I will stick with the values above for better or worse. With that in mind, I would still be interested to know what systems people would use. ?

[joe90]

27 minutes ago, Matt60 said:

but you cannot get an off the peg Catnic to span that distance

Why are you hung up on catnic lintels, they are cold bridges, why have lintels at all in the outer brick skin (you spec brick outer leaf), why not build arches like they did hundreds of years ago (and I did a couple of years ago). For the bifolds where arches were not possible I used concrete lintels (set back slightly) and cut bricks into slips which when glued on matched the bricks ? I will post pics in the morning when it’s light if you want? The best solutions are the easiest ones!
 

Edited February 26, 2021 by joe90

[Matt60]

4 minutes ago, joe90 said:

Why are you hung up on catnic lintels, they are cold bridges, why have lintels at all in the outer brick skin (you spec brick outer leaf), why not build arches like they did hundreds of years ago (and I did a couple of years ago). For the bifolds where arches were not possible I used concrete lintels (set back slightly) and cut bricks into slips which when glued on matched the bricks ? I will post pics in the morning when it’s light if you want? The best solutions are the easiest ones!
 

 

It's not me that is hung up on anything, I know sod all about this. I have an architect, bricklayer and builders merchant who have all independently said the same thing, and I do not have the knowledge to challenge it or suggest an alternative, though I have suspect there are some from the outset. I get what you are saying re brick arches, I think but cut bricks into slips when glued.... not the foggiest. Yes please, do post - simpler the better, nothing to prove, I know lots about stuff I like and need to know to earn a living, but very little about this. ?

[Iceverge]

Watch the videos about the denby dale passive house from green building store. Here's the first one in the series. It's an hour spent that will make your house comfortable fro generations. 

 

 

Also whoever is doing your insulation calculations is telling you porkies. At a quick take your floor comes closer to 0.14 W/m2K nad your wall 0.2W/m2K. 

 

Ditch the dot and dab. It's terrible for airtightness. 

 

 

[pdf27]

7 hours ago, Matt60 said:

 

Such passion - love it!!

 

As I have alluded to before, I tried to go 200mm cavity, but you cannot get an off the peg Catnic to span that distance and paying a structural engineer to calculate every aperture for steels looks very expensive. @joe90 has kindly offered that he has used brick arches and concrete lintels, but I will have a couple of sets of bi-folds which would be too wide to use this as a solution. I think?

 

I'm not about to become that pain in the arse client, and so I will stick with the values above for better or worse. With that in mind, I would still be interested to know what systems people would use. ?

Looks like you can get off-the-peg concrete lintels up to 4800mm as a special order, and 3600mm is a stock item. How wide are your bi-folds?

 

Catnics look to be easy for the builders because they only have to put in a single lintel. If you put in two, one on each leaf, then the width of the cavity doesn't come into it. It's also worth noting that there is no requirement for a structural engineer to calculate every aperture even if your bi-folds are too big for anything but a steel - you use off-the-peg concrete lintels for all the other windows, and get the calculation done for the bi-folds. For very big bi-folds you probably need to get a structural engineer's calculation anyway. Something that simple should only be £50-100 at most.

 

So far as "pain in the arse client" goes, the critical word there is "client". If you wanted a 200mm cavity, the people you are paying for a service should be figuring out how to get it for you within your budget, and if they can't do so explaining what the impact of doing it would be and suggesting alternative ways of achieving the same insulation value. There **may** be good reasons for using a 150mm cavity, but "a particular type of lintel which is easy to draw the details for isn't available in this width" isn't one of them.

Edited February 27, 2021 by pdf27

[tonyshouse]

In the old days brick arches were used , catnic lintels available for use in single skin span and load tables for concrete lintels wide openings with imposed loads need calcs anyway 

[gc100]

I have 3 large windows (5.2m, 6.5, and 5m) all in the same room. For the 6.5m I had a box section of steels due to wind shear and the fact there is another (4th) triangle window above . The other 2 just had flitch beams (plate of steel sandwiched between to lengths of wood. None of was very expensive - maybe 1.5k for all of them. 
 

Personally we just went with a vey airtight house and ASHP. We don’t have crazy level of insulation (150mm in the floor) and the heating hardly ever comes on. Just set your house to 23 and be done with it unless you actually like it cooler most of the time. I think ASHP/UFH is terrible at heating a room up quickly- if you need to have that, then perhaps a wood/gas stove would be the most practical and pleasant for the odd days you want it. Or just get an oil heater and hide it behind the sofa!

Edited February 27, 2021 by gc100

[SteamyTea]

9 hours ago, Matt60 said:

My specs;

Not gone though the whole list, but I don't think the specs are hitting the current standards.

 

If that is the case, then sack your architect.

[Jilly]

Not sure if it's helpful, but on my conversion, the architect's technician did the drawings with min regs to pass (conversions have lots of compromises) and he was hung up on that. Every time I asked for more insulation or some green ideas, his research was on the clock! In the end I gave up just to get the BC plans passed and am now trying to increase the insulation as we go. 

[joe90]

Pics as requested,,  as above, don’t forget your the client, they are building/working fir you!!, ask as many questions here as you want, lots of knowledge here ?

 

 

Edited February 27, 2021 by joe90

[joe90]

brick slips are thin sections of genuine bricks that provide the same look as conventional brick work which are commonly used to replicate the appearance of a conventional brick wall in both internal and external applications.

[dpmiller]

I'm gonna say you'll want more floor insulation as a beam&block subfloor will be chilly...

[Gone West]

12 hours ago, AliG said:

Keeping a house at a constant 23C does not use much more energy than 21C, around 15%.

Where did the 15% come from? When designing my house I ran the PHPP for a range of internal temperatures and found at 21C it would use 15kWh/m2a and at 23C 20kWh/m2a so around twice the difference that you indicated. My design may have some peculiarities or the site position may cause some differences but it seems a lot.

20C  12kWh/m2/a

21C  15kWh/m2/a

22C  17kWh/m2/a

23C  20kWh/m2/a

24C  23kWh/m2/a

 

[SteamyTea]

28 minutes ago, PeterStarck said:

Where did the 15% come from

May have come from comparing heating degree days distributions.

If I look at a 2°C difference in my HDDs, I get a 20% difference.  Not surprising as the weather is very variable on the coast.

[PeterW]

10 hours ago, Matt60 said:

As I have alluded to before, I tried to go 200mm cavity, but you cannot get an off the peg Catnic to span that distance and paying a structural engineer to calculate every aperture for steels looks very expensive.

Why..??

 

Use single skin Catnics straight off the shelf - they are all available and you can use either concretes or steel box lintels on the inside blockwork (or both for high load areas) so you don’t need an SEng to do it but you’re talking about £3-400 tops for all the calcs anyway as it’s all standard. 

[AliG]

3 hours ago, PeterStarck said:

Where did the 15% come from

I looked at the JS Harris heatless spreadsheet with similar U-Values to quoted and changed the internal temp from 21-23C.

 

If you think about it, the average outside temp in the UK might be around 10C, so you have changed the temperature differential from 11C to 13C, which is an 18% increase in the differential. 

 

However, you don't have your heating on all year round. I assume that there are 7 heating months with an average outside temperature of between 5 and 6C(using Edinburgh where I am). Thus you are increasing the differential from 15C to 17C which is a 13% increase and pretty much where the calculation came out. I certainly find that I only have the heating on around 7 months of the year. Solar gain provides enough heat the rest of the year.

 

Indeed one issue with heating to 23C is that it might increase how many days of the year you need to run the heating and I did not take that into consideration. That could add another 5-10% to the heating bill, although as discussed on other threads ASHP would be much more efficient on those days with higher outside temps.

 

If you look at JS Harris spreadsheet, and this is somewhat design dependent, heat losses tend to largest to smallest - windows, ventilation, walls, roof floor. The sample house I have in the spreadsheet is my parents' which has a lot of glass, otherwise ventilation would probably be first. Changing the wall U-Value from 0.18 to 0.12 reduces heating requirements by less than 5% and I wouldn't get hung up about it. I would be much more concerned re air tightness in a block built house with dot  and dab plasterboard.

 

4 hours ago, gc100 said:

I think ASHP/UFH is terrible at heating a room up quickly

 

It is or certainly can be. I deliberately run the flow temps hotter than they need to be to make the system more responsive. Using a gas boiler this does not have the issues of reducing the COP that would happen with an ASHP

 

All kinds of things go into the responsiveness of UFH - Slab thickness, flow temp, floor covering and so on. Rooms in my house with wooden floors take hours longer to warm up than tiled rooms. We have 75m screed with warms up faster than having UFH in 150mm of concrete slab.

 

However, now that I have been in the house for a long time and experimented a lot with the heating, what I find is that the heat loss of the house is the main determinant of my gas bills. Thus I just run the heating at 21-22C all the time. It costs maybe 5% more than sometimes letting it cool down and then warm it back up again (you would sometimes benefit from a smaller temperature differential as discussed above, but the house doesn't cool down enough really to benefit from that which is what happens in an older less well insulated house), but with an offsetting gain in comfort with never having to wait for it to warm up. Thus in @Matt60's case I would probably run it at 22C all the time and it wouldn't take long to get to 23C if required. I also suspect that in real life a new better insulated house might feel warmer at 22C than an older house at 23C.

 

 

 

Edited February 27, 2021 by AliG

[SteamyTea]

1 hour ago, AliG said:

Changing the wall U-Value from 0.18 to 0.12 reduces heating requirements by less than 5% and I wouldn't get hung up about it

That is because of the relatively small external wall area as a ratio to to the whole area.

Changing the floor U-Value, when using UFH can have a much larger impact, the delta T is so much greater.

 

[TerryE]

+1 on the main issue with dot & dab being air-tightness.  Builders tend to botch this by using the plasterboard as the main air-tightness membrane, and if you've got any cracking in or voids in the blockwork mortar lines (which you nearly always do) then you get convection cycling behind the plasterboard which just pumps heat out of the house.  There are some good FIR camera walk-arounds of which show this.  Far better to directly plaster or alternatively seal the block work and then batten out to carry the board. 

 

We keep our house at ~ 23 °C and I accept that we may be paying a 15-20% premium for this but that's 15% of a small bill anyway.

 

The problem of 0.18 vs 0.12 is a more subtle one of tipping points.  We loose minimal heat through our walls so we don't have or need any installed form of CH on the upper floors: no radiators, boilers or CH plumbing and this saved a lot of installation complexity and cost.  You should use a Jeremy-style heating spreadsheet and have a play with the parameters and sensitivities and see what the correct mix / trade-offs is for you.  Having a truly energy efficient house (if done properly) doesn't add materially the overall costs because of the consequential savings that you can make.

 

Architects will design crappy performance houses, builders will build sloppily because that is what they are used to, and building to an energy efficient standard is just an inconvenience for them: this is the culture of the UK construction industry.  But you will need to live with the consequences every day after you move in.

[joe90]

On the subject of dot and dab I would not have it in our house, I much prefer solid render/plaster but as Terry says above you could “parge” the walls (seal them with a cement slurry mix) then batten or dot and dab if that’s what you really want.

[Matt60]

Thanks for all the replies, I really appreciate it and there's some interesting points there and It highlights that I have been a bit lazy really. Using the supplied link on one of the above posts I can find single skin Catnics which appear to solve the problem very easily. That said, if I go for the 200mm cavity I'll need a wider footing which adds a further complication and cost. 

 

What I'm gleaning over all from the above is that the difference in U value between 150mm and 200mm is not actually that great, but that in either case, the dot and dab is a real risk to air tightness. What I can say is that every time I have spoken to the bricklayer I have told him that I've seen blocks laid with gaps etc and that I won't accept that at all. I have made it clear that I am looking for air-tightness and I expect every brick and block fully sealed with mortar. Aside from anything else, it looks awful and I have never subscribed to the "you don't see it" school of thought on anything. It's like trades who leave ceiling voids full of crap - there's not reason to do this imo.

 

What would you suggest instead of dot and dab? 

 

My last house was a 1985 place built as a pair by a local builder, it was heated by an oil boiler. I can't help but wonder with the efficiencies of the new place if an oil boiler might make sense? I'm not all that keen on putting such an old fashioned solution in but it would be cheap to install and produce enough heat. Thoughts?