Does an ASHP stack up financially?

[Iceverge]

3 hours ago, SBMS said:

Would the engineer, data-geek in me love to try this to arrive at a data-driven decision? Yes. Would my 'nesh' wife who stabs the boost on our current wall stat so much its fallen off, let me? Not in a million years.

 

Very low risk really. You'd still be installing a heating system. No difference in performance between a 6kw willis and a 6kw heat pump. Have you read this? 

 

 

Otherwise just but a big ASHP, a big UVC and forget all about it. Physiologically it's much easier to pay £50 extra on the mortgage every month rather than £50 on electricity.    

 

[jack]

The thing that would swing it towards an ASHP for me is the opportunity for cooling. We have concrete floors downstairs, and the ability to run the ASHP in cooling mode makes our downstairs a very pleasant place to be in a run of hot weather.

 

In fact, if I were building again, I'd consider tile throughout, including the bedrooms. I'd buy a load of fitted rugs to lay down in the bedrooms in winter (with no or minimal heating), and cool the bare tiles in summer.

[Iceverge]

3 hours ago, SBMS said:

Out of interest, we're doing traditional construction (brick and block with 100mm full fill cavity and 150mm floor insulation with UFH)

 

Double those numbers! Have a look at @tonyshouse blog. http://tonyshouse.readinguk.org/ and the Denby Dale House. 

 

 

 

 

 

1 hour ago, SteamyTea said:

Brick and block is another term for leaky.

 

0.31ACH50. However you're right, it took at least 100 man hours DIY to get this. Probably more. Timber frame, blown cellulose, tapes and membranes for me if this shack ever gets blown away. Also factory built can be rubbish too. Depends on quality control and onsite installers. 

[SteamyTea]

2 minutes ago, jack said:

I'd consider tile throughout, including the bedrooms.

Having been up at my Mother's house that has a very expensive tiled kitchen floor, I would avoid it.  What looked nice years ago now looks dated, and chipped/cracked.

I have parquet flooring, which I like as I grew up with it, but most people dislike it now.

[joe90]

3 minutes ago, SteamyTea said:

very expensive tiled kitchen floor, I would avoid it.  What looked nice years ago now looks dated, and chipped/cracked.

It could not have been good quality tiles, my neighbour (a tiler by trade) tiled his garage with porcelain tiles and he jacks his cars up, does his own mechaniking etc etc and apart from oil stains in the grout it still looks good years afterwards.

[jack]

39 minutes ago, joe90 said:

It could not have been good quality tiles, my neighbour (a tiler by trade) tiled his garage with porcelain tiles and he jacks his cars up, does his own mechaniking etc etc and apart from oil stains in the grout it still looks good years afterwards.

 

Yup, porcelain all the way. Decent porcelain tiles will last forever. Worst case you can always dig out a broken one and replace it.

 

46 minutes ago, SteamyTea said:

I have parquet flooring, which I like as I grew up with it, but most people dislike it now.

 

I really like parquet flooring. We were very close to having our downstairs floors being parquet throughout. I'm still not sure whether we made the right choice going for concrete. 

[joe90]

13 minutes ago, jack said:

I really like parquet flooring. We were very close to having our downstairs floors being parquet throughout. I'm still not sure whether we made the right choice going for concrete.

I nearly bought a shed load of old wooden blocks from a school to lay herringbone style but they are thick and would have insulated our UFH and not matched other floors in height,  I thought of sawing them all down in thickness but the work was too much on top of all the build work so settled for engineered oak flooring (much easier).

[jack]

11 minutes ago, joe90 said:

I nearly bought a shed load of old wooden blocks from a school to lay herringbone style but they are thick and would have insulated our UFH and not matched other floors in height,  I thought of sawing them all down in thickness but the work was too much on top of all the build work so settled for engineered oak flooring (much easier).

 

We were looking at reclaimed parquet blocks on eBay on and off for a year leading up to the build kicking off, but it always seemed like a lot of work and a fair bit of risk. They were generally stuck down with a bitumen based adhesive, which is an absolute pig to deal with. You could buy stuff that had been cleaned etc, but that was always crazy expensive for what it was.

 

Edited to add: we did consider the best of both worlds with porcelain wood-effect parquet, but I don't remember why we chose not to go with it in the end.

[saveasteading]

1 hour ago, jack said:

The thing that would swing it towards an ASHP for me is the opportunity for cooling. We have concrete floors downstairs, and the ability to run the ASHP in cooling mode makes our downstairs a very pleasant place to be in a run of hot weather.

 

You must live in a very hot place. I can't think I have ever thought a floor indoors, anywhere in the world,  was too hot. Or that a British house was too hot indoors.

In a very poorly insulated house of lightweight material it might be possible, but control of sunlight and ventilation should sort that.

Hottest summer temperature perhaps 30C dropping to only 20C at night, but how often does that happen, and a well built house keeps most of the heat outside.? 

 

Thinking of southern Europe, (40C only down to 25 regularly) new houses do have cooling, but the traditional houses don't need it, using the design-as -a cave principle.*

 

I have experience of office temperatures being too high, but that is for a metal building with 100mm insulation and with multiple occupancy. Then the ASHP was used in reverse.

 

Good to have the option but would barely be used I suggest.

How often do you use it and do you know it is helping significantly?

 

* In Spain they brought in a law that public buildings could not be cooled to below 22C (???) or heated above 25 (???) as it is a waste of energy.

 

 

[SteamyTea]

4 minutes ago, saveasteading said:

can't think I have ever thought a floor indoors, anywhere in the world,  was too hot. Or that a British house was too hot indoors.

Often caused by solar gain through very large, badly orientated windows.

When the Aircon broke in our house in the West Indies, sleeping on the floor did not help.

We ended up going to the beach and slept there. Where we lived was windy, dry and not exceptionally hot, I miss it.

[Andehh]

6 hours ago, SBMS said:

This is really interesting - is this a recent quote? A 3k price differential in capital outlay is certainly compelling. We are not at the quoting stage yet so perhaps my assumption that ASHP install costs would be 5-10k higher than gas are simply wrong. Are you currently building?

 

 Several weeks ago, it's a large new build & what our builder would knock off if we stepped down from an ASHP. He has been reliable with other cost adjustments so I have no reason not to trust this figure within reason! ?

[joe90]

19 minutes ago, saveasteading said:

a well built house keeps most of the heat outside.? 

Yup, insulation works both ways

 

20 minutes ago, saveasteading said:

Hottest summer temperature perhaps 30C dropping to only 20C at night,

Saves going abroad fir a holiday, certainly cheaper (if it’s ever allowed again thanks to Covid!)

 

22 minutes ago, saveasteading said:

using the design-as -a cave principle.

Thermal mass??. (I,ll get me coat).

[saveasteading]

5 minutes ago, joe90 said:

Thermal mass??. (I,ll get me coat).

I carefully avoided those words so as to keep the thread on point.

[SBMS]

11 hours ago, joe90 said:

 For example my house is well insulated but not quite passive levels 

@joe90 firstly - thanks for the welcome, forgot earlier. Secondly - what was your insulation strategy, construction method and level of insulation for a 5kw ASHP?

[SBMS]

11 hours ago, nod said:

We are building a similar size house over two floor

@nodWhere abouts you building? We are just outside preston so have the dreary, wet lancashire climate so interesting you've gone ASHP as some state northern, wet climates are not ideal for ASHP.

[joe90]

46 minutes ago, SBMS said:

@joe90 firstly - thanks for the welcome, forgot earlier. Secondly - what was your insulation strategy, construction method and level of insulation for a 5kw ASHP?

250mm insulation under screed with UFH pipes, block inner wall wet plastered and parged between floors, warm roof with 400mm rockwall between i joists. 200mm cavity with batts, brick outer skin, double glazing (with special coatings to make nearly as good as triple) hardwood frames. As I said before I did no calculations but went on gut instinct (and copied others here with similar ?)

[jack]

20 hours ago, saveasteading said:

You must live in a very hot place. I can't think I have ever thought a floor indoors, anywhere in the world,  was too hot. Or that a British house was too hot indoors.

 

You've never been in a house in the UK that you thought was too hot? I find that surprising. I've been in several.

 

As for cooling the floor, to save me repeating myself, have you read any of the several threads on floor cooling? Having worked in air-conditioned offices for many years in Australia, I find floor cooling to be a much more comfortable way of cooling a space than air cooling.

 

One hot day is fine. A couple is okay. It's when you get a run of several hot days that the heat gradually creeps up. Having cellulose insulation in the walls and roof is a blessing and curse - it buffers heat really well, but when it eventually warms up, it has a lot of energy to re-radiate into the house. It takes days to heat up, and days to cool down.

 

We don't have insect screens (something I'll definitely be addressing eventually), so we can't ventilate at night. We do have an ASHP and concrete floors with UFH, so it makes sense to cool them. We also have a lot of PV, so on sunny days, cooling is effectively free - I only tend to run the cooling during the day when the sun is up.

 

20 hours ago, saveasteading said:

Good to have the option but would barely be used I suggest.

How often do you use it 

 

These are more interesting questions imo.

 

This year, much of summer was mild and very overcast. We only used it for maybe a week.

 

Maybe two or three years ago we had a couple of multi-week hot, sunny periods with high overnight temperatures. I believe we ran the underfloor cooling for at least a month or maybe even six weeks over the course of three or four months that year.

 

At a guess, I'd say we've averaged three or four weeks of cooling across the summer over the last six summers since we moved in.

[Mr Blobby]

On 22/12/2021 at 10:39, jack said:

 

As for cooling the floor, to save me repeating myself, have you read any of the several threads on floor cooling? Having worked in air-conditioned offices for many years in Australia, I find floor cooling to be a much more comfortable way of cooling a space than air cooling.

 

 

 

A few people (who suspisciously dont use ashp for cooling) warned me to avoid cold floors hence we were plannig to install some fan coils upstairs instead of using the UFH for cooling.  Which introduces extra cost and complexity.

Am I making a bad deceision here?  Should I keep it simple and cool the floor?

 

 

 

[ProDave]

13 minutes ago, Mr Blobby said:

 

A few people (who suspisciously dont use ashp for cooling) warned me to avoid cold floors hence we were plannig to install some fan coils upstairs instead of using the UFH for cooling.  Which introduces extra cost and complexity.

Am I making a bad deceision here?  Should I keep it simple and cool the floor?

 

 

 

Several of us only have heating downstairs. The one and only time so far the house got too hot one summer, I coerced the ASHP into cooling mode and it chilled the floor downstairs, but that did nothing to cool the bedrooms upstairs that were the rooms that were really too hot.  That is where I am considering adding an FCU in the 2 main bedrooms that will do cooling when needed and could also do heating if we found we needed it.

 

So far the cost and work involved has not yet been justified by the very few times we would actually use them.

[IanR]

18 minutes ago, Mr Blobby said:

 

A few people (who suspisciously dont use ashp for cooling) warned me to avoid cold floors hence we were plannig to install some fan coils upstairs instead of using the UFH for cooling.  Which introduces extra cost and complexity.

Am I making a bad deceision here?  Should I keep it simple and cool the floor?

 

I'd do both.

 

Cooling via UFH is very effective, but slow to respond. It is more-or-less free, just select an ASHP that allows cooling out-the-box and doesn't require a hack. I did have to pay for an accessory on my Nibe, but most brands don't require that and I'm not sure if Nibe still does. You may pay a little more for the UFH controller, to understand the cooling requirement. The one thing you have to avoid is lowering the surface of the slab below the dew point. The hotter the internal air and the higher the relative humidity, the higher the dew point, but as a surface temp of 18°C on the slab provides very effective cooling, it's unlikely you'd need to be getting close to the dew point, but some logic in setting the flow temp may be useful. Loxone can do all this for you is you plan some Home Automation.

 

The slow response of UFH in a slab, means it's best not to let temps get to high before cooling is employed. Fan-coil units, perhaps working off the same cooled buffer as the UFH, will give a more instant cooling effect, as it is cooling the air directly. But, as they are only cooling the air, when you switch them off the air temp will rise again, heated by the fabric off the building.

 

Having both seems to me the best of both worlds. I wish I had included fan-coil units within my build, and am now considering them as a retrofit.

 

 

[joth]

16 minutes ago, IanR said:

 

I'd do both.

 

Cooling via UFH is very effective, but slow to respond. It is more-or-less free, just select an ASHP that allows cooling out-the-box and doesn't require a hack. I did have to pay for an accessory on my Nibe, but most brands don't require that and I'm not sure if Nibe still does. You may pay a little more for the UFH controller, to understand the cooling requirement. The one thing you have to avoid is lowering the surface of the slab below the dew point. The hotter the internal air and the higher the relative humidity, the higher the dew point, but as a surface temp of 18°C on the slab provides very effective cooling, it's unlikely you'd need to be getting close to the dew point, but some logic in setting the flow temp may be useful. Loxone can do all this for you is you plan some Home Automation.

 

The slow response of UFH in a slab, means it's best not to let temps get to high before cooling is employed. Fan-coil units, perhaps working off the same cooled buffer as the UFH, will give a more instant cooling effect, as it is cooling the air directly. But, as they are only cooling the air, when you switch them off the air temp will rise again, heated by the fabric off the building.

 

Having both seems to me the best of both worlds. I wish I had included fan-coil units within my build, and am now considering them as a retrofit.

 

 

+1 to all that.

 

Whichever way you do cooling, you'll need to ensure all the pipework, clips, pumps, valves etc are all 100% insulated with no gaps, otherwise you'll get condensation dripping, which would not be good for a pipe buried behind plasterboard. Installers will do basic pipework insulation, but rarely to the detail level needed for cooling. (e.g. the primary pipework should first be insulated *then* clamped into place, rather installed then insulated which is standard practice in UK)

 

If using FCU remember to size the buffer tank accordingly.  This was my main mistake. Planning to fix this once the heating season finishes.

 

 

 

[jack]

19 hours ago, Mr Blobby said:

A few people (who suspisciously dont use ashp for cooling) warned me to avoid cold floors hence we were plannig to install some fan coils upstairs instead of using the UFH for cooling.  Which introduces extra cost and complexity.

Am I making a bad deceision here? 

 

Did they give you a specific reason for recommending you not use ASHP cooling?

 

Condensation would be the main potential issue. We only heat/cool our downstairs floor. The ASHP pipework comes into the plant room and is connected to the manifold only a couple of feet away, so there's very little exposed pipework. I run the cooling at a temp of 15 or 16 degrees, from memory.

 

In this situation, we get a slight breath of condensation on the metal parts of the manifold, but nowhere else and there certainly isn't enough to drip. I'm certainly not worried about condensation on the floor surface itself, as I doubt it ever drops below about 19 degrees.

 

It might be more worrying of you're running long sections of pipework inside walls and within floor cavities. But if you keep the temps reasonable, I doubt it'll be an issue.

[J1mbo]

16°C is probably warmer than the incoming cold water supply. Then again that doesn't run 24 hours I suppose.

[J1mbo]

On 21/12/2021 at 11:24, SBMS said:

Hi Temp - yes, as mentioned my parents have just signed up (here in Lancashire) for 38ppl fixed for 2 years with extragas. I think the LPG prices on nottenergy as based on variable non fix. But wholesale LPG commodities are now increasing in line with natural gas so its likely that price is going to shift over next few months.

 

Picking up on this. I presume the 38p is exc.VAT @ 5% and the boiler efficiency will be about 90% in the end. With 7.08kWh per litre in the fuel, this works out at 6.26p per kWh at point of use. With electric currently at 20p on the cap then SCOP of 3.2 breaks even. If it's under-floor heating throughout then SCOP of 4+ is achievable.

 

It seems likely that both of those prices will rise dramatically in the next six months. CCL will also likely be moved away from purely electric.

 

You know that the property will end up with ASHP at some point; it would make sense to just do it now in my opinion to avoid system design changes (and costs) later. I'm not sure if an underground tank was envisaged but the quotes I had suggested that the installation costs of such can be more than the cost of an ASHP itself.

[J1mbo]

On 21/12/2021 at 08:48, ProDave said:

I think most are looking at prices installed by an "ASHP specialist" at £10K or more?

 

Octopus Energy have said that they are planning to offer ASHP at £5.5k fitted within 18 mo. As the sector is currently so small, the prices will fall dramatically as it grows.