Does an ASHP stack up financially?

[SteamyTea]

12 minutes ago, J1mbo said:

Octopus Energy have said that they are planning to offer ASHP at £5.5k fitted within 18 mo

I will do that next month.

It won't be what you want, or need, and probably won't perform very well.

But I will make £3k out of it.

 

Or

 

They are doing it to comply with ECO rules/targets and will only install them in places that are suitable, and may be very low quality installations.

[J1mbo]

It's a obviously a headline, but the principle is pretty straight-forward - make more of something and the unit cost is reduced. They appear to be partnering with Vaillant based on the videos they have published of their research and training centre.

Edited December 24, 2021 by J1mbo

[SteamyTea]

41 minutes ago, J1mbo said:

make more of something and the unit cost is reduced

Called the learning curve.

[joth]

1 hour ago, jack said:

21 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.

 

Agree not too much risk of condensation if only cooling UFH to ~16C. However, note that @Mr Blobby said he was planning to install FCU upstairs. These work better the colder you can make them. Ours is a delight down at 5ºC, but that's when we got floods of condensation in the plant room until I ripped out the MCS lagging and did it all properly.  Also, if running UFH and FCU cooling simultaneously, there will be colder water in the system right the way up to the UFH mixing valve, which (depend on the schematic and layout) may cause more issues even in UFH-specific pipework than if cooling UFH alone.

 

(Also if running both together note you need some way to set separate heating vs cooling set points on the UFH mixing valve. I can vouch for the ecodan FTC6 with electronic mixing valve being very good for this)

 

 

[TerryE]

On 21/12/2021 at 11:14, Iceverge said:

TLDR:

1. Pathologically minimise your heating demand in design and construction stage.  

2. Install UFH + willis heater  and a heat pump compatible UVC. 

3. Run your house for a year on E7. 

4. Use the data to make the best decision. 

 

Having an in-slab UFH implementation helped us a lot and made everything pretty simple.  We've got a 3 storey detached house with four largish bedrooms and one storage / drying room with the heating requirement peaking at around 30 kWh in the winter months (and little solar gain because of our house orientation and planning constraints).  If we heat only in the E7 window, that's just under 4kW net heating, and the thermal mass of the interior is such that this gives us ~1°C ripple on room temperatures.  If we don't heat the house (an accidental experiment) then it cools overall by around ~1°C per day.

 

This all depends on the "devil in the detail" during construction: all insulation installed to spec; decent air tightness, MVHR; no oops thermal bridges.

 

A constant heating strategy would peak at ~1½ kW so IMO a typical small 8 kW ASHP would be total overkill.  I don't know what the true replacement life of an ASHP is, but it would need to be 10 years or so for us to justify its procurement and installation cost. 

 

Over 4 years in and I have made a few tweaks to our system:

• The CH + DHW is controlled by a dedicated RPi using Node-RED for sequencing etc.
• We have added a Home Automation System (HAS) running on another RPi and using Home Assistant with lots of ZigBee  devices doing the usual home automation stuff.  This system also controls an Oil-filled electric radiator we have on our 1st floor landing which we run 0-7 E7 hours  in the winter; this uses a smart plug which also reports actual power used. This rad plus E7 Willis Heating keeps the whole house nice and toasty. 
• The HAS and CH systems use MQTT to swap set-points and logged data, but it's all set up so that the CH system will still run happily if the HAS isn't available.

This automation approach might seem complex, but the H/W and install costs were in the few £100s.   It all works pretty much automatically with minimal maintenance.

 

The biggest wobbles to our system are caused by visitors staying, such as one of our kids + family, as this adds an extra 4 bio-radiators that move from room to room and can cause local over-heating if we all sit in one room for too long.  The simple answer here is passive-house heresy: open a window or two for a bit to dump the extra heat.?

 

 

 

 

[Mr Blobby]

On 29/12/2021 at 09:53, TerryE said:

...

• The CH + DHW is controlled by a dedicated RPi using Node-RED for sequencing etc.
• We have added a Home Automation System (HAS) running on another RPi and using Home Assistant

 

 

Node red.  Very interesting, and not heard of it before so thank you for mentioning it.  I have installed the HA add-in and will take a look.

 

On 29/12/2021 at 09:53, TerryE said:

 

 The simple answer here is passive-house heresy: open a window or two for a bit to dump the extra heat.?

 

You're right of course but we're on a noisy stinky main road hence trying to cool with windows closed if possible.  Will be interesting to see how well it works.

 

 

[DragsterDriver]

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

I think most people discount an ASHP because of the high cost, and then compare the high cost of an ASHP with a £2K boiler.

 

I think most are looking at prices installed by an "ASHP specialist" at £10K or more.?  But before you dismiss that as too expensive look up the actual cost to buy an ASHP and pay a plumber and an electrician each a couple of days labour to install it.  You might find it is a lot cheaper.

 

Several of us on here have bought them cheap and DIY installed them.

 

Can't comment on likely running cost without knowing what you are building?  Something that just scrapes through building regs? or a passive house? or somethiing in between.  There is no doubt ASHP's work best with UFH throughout upstairs as well, and are better suited to low energy houses.

 

Don't forget the cylinder maintenance or standing order costs when working out the cost of LPG.

this is what I came to find.

 

MCS installers are having a laugh price wise, charging massive amounts for install and then the £5k rhi amount into their pocket as a bonus amount on top. 

[TerryE]

On 03/01/2022 at 21:22, Mr Blobby said:

Node red.  Very interesting, and not heard of it before so thank you for mentioning it.  I have installed the HA add-in and will take a look.

 

NodeRED uses connect-the-block pre defined modules to implement control. Lots of YouTube videos on it. You can do complex stuff in JavaScript which is pretty straightforward if you've ever done any programming.

[J1mbo]

On 05/01/2022 at 08:43, DragsterDriver said:

this is what I came to find.

 

MCS installers are having a laugh price wise, charging massive amounts for install and then the £5k rhi amount into their pocket as a bonus amount on top. 

RHI is paid to the homeowner directly, the installer doesn’t see any of it (directly)

[saveasteading]

1 minute ago, J1mbo said:

RHI is paid to the homeowner directly, the installer doesn’t see any of it (directly)

 

If the RHI scheme is like the previous grants for solar panels/ turbines/ green stuff generally then the approval process costs a fortune and the approved installers charge accordingly and take the money.

I'm sure there are installers who give best value, but they will be very busy.

 

It was the same with lottery funding to schools and trusts....they had to use an approved architect to propose the scheme, which then generally ended up costing more than it would without the funding.

[DragsterDriver]

3 hours ago, J1mbo said:

RHI is paid to the homeowner directly, the installer doesn’t see any of it (directly)

 
 

to clarify what I mean is:

parts £5k

labour £10k

 

knowing you’ll pay through the nose because you’ll get £5k of it back. 

[jack]

On 03/01/2022 at 21:22, Mr Blobby said:

Node red.  Very interesting, and not heard of it before so thank you for mentioning it.  I have installed the HA add-in and will take a look.

 

Worth a search of BuildHub for "node red" (in quotes). It's been discussed before a few times.

[SBMS]

On 21/12/2021 at 21:02, joe90 said:

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 ?)

@joe90 Can you share your Air permeability test/changes per hour?

[joe90]

5 minutes ago, SBMS said:

@joe90 Can you share your Air permeability test/changes per hour?

Ooh er, can’t remember and my house docs have disappeared, was fairly good, @SteamyTea can you remember? I made a note of where any leaks were and have rectified them but never got to have another test.

Edited January 17, 2022 by joe90

[SteamyTea]

44 minutes ago, joe90 said:

50 minutes ago, SBMS said:

@joe90 Can you share your Air permeability test/changes per hour?

Ooh er, can’t remember and my house docs have disappeared, was fairly good,

I seem to remember that it was around 1.5, which pissed you off as you wanted under 1.

But there were the few leaks around a couple of windows, and where the air intake came in for your wood burner (a very good reason to not have one, just another large hole to fill up).  You filled the holes where the cables and pipes came in at the time, but don't think they were that bad.  Can't remember if you adjusted the kitchen to conservatory door, think you did.

[joe90]

Thanks @SteamyTea, yes sounds about right, yes I wanted under 1, I remember now, it probably is now I have fettled the windows etc

[ProDave]

Mine was 1.4 which I was disappointed with, I wanted under 1, but they guy doing the testing nearly wet himself with excitement proclaiming how good it was.

[dpmiller]

^same here. I've subsequently tightened up some questionable door seals

[SBMS]

In a traditional brick and block construction what’s the consensus on the main areas where airtightness can be lost? Our SAP guys have gone for an air change of 4 which is clearly higher than I would like. With well fitted doors and windows, warm roof and plasterboard on dot and dab, what sort of a difference might we expect with a well built shell? I know recommendation is wet plaster and parging between floors but I wondered if there are any real world examples from members where dot and dab and no parging were used?

[joe90]

I too recomend parge and wet plaster fir airtightness. I believe one of the major “leak” areas is timbers in blockwork, timber shrinks and moves so difficult to mitigate this potential leak area. Attention to detail here is a priority.

[JohnMo]

Dot and dab, will not stop leakage, so unless you seal the block work, 4 ach may be as good as you will get.  It could be worse.

 

We have Durisol ICF, which is made of woodcrete, which leaks like a sieve.  I did a parge coat, with sand cement and lime.  On an airtest prior covering with plasterboard, we had leaks in window corners and at dpc.  The walls themselves had no leaks.

[SteamyTea]

Ideal you want the airtightness to include the insulation. Would rather defeat the object of it if air can pass through it.

[ProDave]

56 minutes ago, SBMS said:

Our SAP guys have gone for an air change of 4 which is clearly higher than I would like

That is standard for the design SAP.  When you get the house built and an air test done, they will update it to an as built SAP with the actual figures.

[joth]

34 minutes ago, SteamyTea said:

Ideal you want the airtightness to include the insulation. Would rather defeat the object of it if air can pass through it.

 

It's common that these are split to different layers of the wall build up, e.g. for a wind-tight layer outside the insulation, and airtight layer on the inside.

e.g. https://www.pavatex.com/uploads/tx_sbdownloader/120913_Pavatight_eng_12.pdf

and https://www.isocell.com/en/airtightness-systems can both work that way

[TerryE]

On 17/01/2022 at 20:49, SBMS said:

Our SAP guys have gone for an air change of 4 which is clearly higher than I would like.

 

TBH, this is because of crap quality control during typical builds. Our actuals are closer to 0.5, because we designed in airtightness into our build and made sure we chose subs who knew how to build to this standard.

 

You posted elsewhere that you are still in the planning phase so what targets you design your house to and how you implement this is still very much under your control.

Edited January 20, 2022 by TerryE