Just started a self-build in Dorset. Exciting times!

[JohnMo]

On 01/03/2024 at 20:57, NailBiter said:

Thermal mass is an accepted term? https://en.wikipedia.org/wiki/Thermal_mass Splitting hairs feels like a waste of energy (pardon the pun)

Wikipedia, is a site any tom dick or Harriot can upload too. Nothing scientist about that site. If I wanted to upload and say the world is flat and made of chocolate I could.

 

5 ACH is pretty rubbish, especially if wanting MVHR.

 

ASHP in sun is a daft idea, an ASHP doesn't use radiated heat, it takes air temperature so make no difference if located in sun or shade for efficiency. Being in the sun messes with the temperature probes, so not the best idea.

42 minutes ago, NailBiter said:

Durasol block marketing and then came to understand more about cold bridging and the other issues they have.

Not done the heat loss calculations obviously, as there is almost zero cold bridging with durisol blocks.

[ProDave]

47 minutes ago, NailBiter said:

A 114x 600watt panel solar array (not including fixings but including cable, optimisers and inverters) is only around £12,000 which would be paid for within 2 or 3 years by the bills we don't have to pay let alone anything we can export in summer. The issue with solar is not installing it has an opportunity cost. That said the cost of solar has decreased a lot lately which offsets it.

Am I reading that right?   114 panels each rated at 600W.  If so that is a total peak output of 68 kW

 

That like everything on this build is 10 times what could be considered "normal"

 

First best of luck in getting the DNO to allow a 68kW grid tied solar PV system on a domestic connection.

 

Then just how do you propose to self use anything other than a tiny portion of that in the summer?

[ProDave]

51 minutes ago, NailBiter said:

Agreed, our guys are currently targeting 5 ACH, do you feel that is reasonable? I had a long call with the architect yesterday and they seem to be suitably concerned about the MVHR and how the ventilation will work. We do need a really good engineer though, can you recommend one?

5ACH is poor.  You should be targeting less than 1ACH and MVHR should be considered a must have.

 

If your architect does not understand MVHR you need to find someone that does.

[JohnMo]

On 01/03/2024 at 22:44, NailBiter said:

Divide our square meterage by 3 and you still get a big number (400m2)

That is still massive

[JohnMo]

1 hour ago, NailBiter said:

114x 600watt panel solar array

Hope you get all your ducks aligned before committing, would not be very good if the DNO imposes a limit of 16A on exports, because the local grid cannot handle anything more than that..

[BotusBuild]

I'm glad I was not the only one wondering whether 114 panels was a typo 🙂

[NailBiter]

31 minutes ago, JohnMo said:

ASHP in sun is a daft idea, an ASHP doesn't use radiated heat, it takes air temperature so make no difference if located in sun or shade for efficiency. Being in the sun messes with the temperature probes, so not the best idea.

The idea came from this house: https://architecturetoday.co.uk/introducing-the-uks-first-net-zero-carbon-home/

My understanding is a heat pump steals heat from the environment. This is the opposite effect of a fridge that behaves poorly when it has no ventilation to its coils. I'm no expert though. 

Edited March 5 by NailBiter

[NailBiter]

27 minutes ago, ProDave said:

5ACH is poor.  You should be targeting less than 1ACH and MVHR should be considered a must have.

 

If your architect does not understand MVHR you need to find someone that does.

Noted, although it is likely the mistake is my end, our architect is a Certified Passive House designer so is unlikely to have made such a mistake. I'll double check though thanks for flagging it. 

[Thorfun]

6 minutes ago, NailBiter said:

Noted, although it is likely the mistake is my end, our architect is a Certified Passive House designer so is unlikely to have made such a mistake. I'll double check though thanks for flagging it. 

passivhaus is below 0.6ACH.

 

i would hazard a guess that as a certified passive house designer your architect is concerns that a property of the size you're proposing just won't get passive house accreditation so hasn't gone down that route as has possibly chosen an ACH that's attainable for such a large property.

[NailBiter]

28 minutes ago, JohnMo said:

Hope you get all your ducks aligned before committing, would not be very good if the DNO imposes a limit of 16A on exports, because the local grid cannot handle anything more than that..

National Grid can't confirm anything until the G98/G99 certificate is in but they said this:
 

Quote

At a minimum you will be able to export 11.04kW at three phase through the G98 scheme however I would imagine after relaying mains and the new connection to your property the true figure would exceed this.

 

There would be no cost implication if we were to overlay the existing mains.

 

Three phase is certainly achievable but may take a longer time to complete due to the required overlay.

 

There was also some discussion of some weird named network they had which could increase this significantly but I can't currently find the correct email.

 

It will take a long time to get setup but I've also been speaking with a nearby https://energylocal.org.uk club to try and understand what it would take to sell this power directly to neighbours.

 

It is highly likely we will never fit a system with 114 panels, I was more interested in the cost to do so and whether it would fit to see if it were notionally possible. Whilst brackets to get the panels on the roof or a frame to fit ground mount panels would add expense I was surprised at how cheap it could be.

I set a fictional power budget of 50kwh a day which is approximately what our combined houses use right now. Obviously this is likely high for a build like ours if we do it correctly. 

 

Export can be limited, solar systems can be DC oversized by up to 200% and with the east-west orientation of the array there is only a very short period of total generation but a much wider time period of generation. I am a little stuck on working out how this compares to a south facing system in the winter. 

It may be a different way of doing things but it isn't necessarily wrong (although if you know any specific areas I've messed up or made poor assumptions please let me know, it is super useful).

Edited March 5 by NailBiter

[NailBiter]

3 minutes ago, Thorfun said:

passivhaus is below 0.6ACH.

 

i would hazard a guess that as a certified passive house designer your architect is concerns that a property of the size you're proposing just won't get passive house accreditation so hasn't gone down that route as has possibly chosen an ACH that's attainable for such a large property.

Perhaps I moved the decimal point in my head, I'll email the architect so I can't transpose it.

Edited March 5 by NailBiter

[JohnMo]

18 minutes ago, NailBiter said:

The idea came from this house

The only bit I would take away from that is doing DHW heating when the day is at its warmest.

[NailBiter]

3 minutes ago, JohnMo said:

The only bit I would take away from that is doing DHW heating when the day is at its warmest.

Apologies to be forward. I know the credentials of the person making the claim (that it works) but I don't know the credentials of you making the counter-claim (that it does not). Would you mind me asking you what credentials you posses to back your counter-claim?

Edited March 5 by NailBiter

[JohnMo]

14 minutes ago, NailBiter said:

Would you mind me asking you credentials you posses to back your counter-claim?

On a public forum no. You can take what I say or ignore it.

 

Just look at the theory of how a heat pump works. Basics are - refrigerant is at a much lower temp than the surrounding air. Air is forced through a heat exchanger by a fan. Inside the heat exchanger is refrigerant, it absorbs the airs heat (hot moves to cold).  The warmer the air the more energy it allows to be transferred the refrigerant, so better the CoP. 

 

The sun being out doesn't change the localised air temperature (in open space), heat pumps will move many 100s of m3 of air each hour, so it makes zero difference if the heat pump is located in the sun or not - air will be moved from everywhere.

[NailBiter]

1 hour ago, JohnMo said:

Not done the heat loss calculations obviously, as there is almost zero cold bridging with durisol blocks.

I was really tempted by Durisol (although their administration issues are obviously nerve-racking) or even Isotex but enough people said enough bad things about them that it would have been foolhardy to continue. I don't really have much frame of reference for how true everything said about them is.
 

 

5 minutes ago, JohnMo said:

On a public forum no. You can take what I say or ignore it.

Apologies but with it being so important to get right I will have to listen to the accredited professionals.

 

 

7 minutes ago, JohnMo said:

Just look at the theory of how a heat pump works. Basics are - refrigerant is at a much lower temp than the surrounding air. Air is forced through a heat exchanger by a fan. Inside the heat exchanger is refrigerant, it absorbs the airs heat (hot moves to cold).  The warmer the air the more energy it allows to be transferred the refrigerant, so better the CoP. 

 

The sun being out doesn't change the localised air temperature (in open space), heat pumps will move many 100s of m3 of air each hour, so it makes zero difference if the heat pump is located in the sun or not - air will be moved from everywhere.

I really don't have the knowledge to say if any of this is correct but I'd imagine the case surrounding the heat pump could be heated up by the sun hitting it. It is also likely that on the roof insolated it will be significantly warmer than if it were sat on a North wall for example.

[JohnMo]

4 minutes ago, NailBiter said:

imagine the case surrounding the heat pump could be heated up by the sun hitting it.

It certainly would be heated, the air used to provide the heat passes through a heat exchanger not the casing. Either way take or leave anything said here or anywhere else. You going have so much excess solar not sure if will make a difference what the CoP is anyway. I've only around 7kW in the north of Scotland and my battery was full and cylinder heated by immersion to 70 degs by 3pm on a sunny day in March, you could be doing that most days of the year.

[NailBiter]

3 minutes ago, JohnMo said:

You going have so much excess solar not sure if will make a difference what the CoP is anyway. I've only around 7kW in the north of Scotland and my battery was full and cylinder heated by immersion to 70 degs by 3pm on a sunny day in March, you could be doing that most days of the year.

Your solar system is very impressive particularly how you mounted those vertical panels. There was some recently published researched suggesting vertical panels are more efficient than first realised.

https://www.pv-magazine.com/2023/11/10/researchers-shed-light-on-mysterious-higher-energy-yields-in-vertical-pv-systems/

[NailBiter]

10 minutes ago, JohnMo said:

It certainly would be heated, the air used to provide the heat passes through a heat exchanger not the casing.

Would the air not be heated up as it passed through the casing to get to the heat exchanger (or if the heat exchanger itself is directly insolated perhaps even via that). I'll do some more digging to get to the bottom of it but any increase in CoP (particularly by something as simple as where you site the system) is a good thing.

Edited March 5 by NailBiter

[Thorfun]

25 minutes ago, NailBiter said:

Apologies but with it being so important to get right I will have to listen to the accredited professionals.

i understand this but one thing i've learnt (and there have been many!) during my journey is that not all 'accredited' professionals are created equal. nothing beats getting the opinions of others (even if they are complete strangers on the internet) as they generally do not have any sort of vested interest in the questions you're asking or solutions you're trying to find. and then you can compare the answers and make an informed decision.

 

Also there are many ways to skin a cat. and just because someone says one way is best doesn't mean there isn't another way that is equally as good.

 

just my 2 cents.

Edited March 5 by Thorfun

[NailBiter]

12 minutes ago, Thorfun said:

i understand this but one thing i've learnt (and there have been many!) during my journey is that not all 'accredited' professionals are created equal. nothing beats getting the opinions of others (even if they are complete strangers on the internet) as they generally do not have any sort of vested interest in the questions you're asking or solutions you're trying to find.

 

Also there are many ways to skin a cat. and just because someone says one way is best doesn't mean there isn't another way that is equally as good.

I certainly welcome all opinions but hopefully those opinions welcome being challenged. It's my job to work out which opinions seem reasonable (in my opinion and with expert help) to implement this build accordingly. Hopefully leaving a paper trail behind for the next person that finds themselves in my position.

 

There seems to - hopefully the above wasn't an instance of it - be a real habit among humans (particularly as they age) to claim things aren't possible or don't work without taking the the time to properly look at and consider new ideas.

"When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong."

I wholeheartedly agree there is almost always more than one way to skin the cat however.
 

Edited March 5 by NailBiter

[Thorfun]

11 minutes ago, NailBiter said:

There seems to - hopefully the above wasn't an instance of it - be a real habit among humans

and there is also a habit of humans not admitting they're wrong especially when there's been a large financial outlay or it might lose them face. so just because someone says "it's brilliant and works exactly as i hoped" or "i'm really happy with my purchase and wouldn't have done anything else" doesn't necessarily mean they're telling the truth as they don't want to look bad or admit they made a mistake.

 

it takes a brave person to admit they were wrong

[JohnMo]

26 minutes ago, NailBiter said:

Would the air not be heated up as it passed through the casing to get to the heat exchanger

A bit a write up here

https://www.linkedin.com/pulse/does-heat-pump-work-better-its-sunshine-graham-hendra

 

 

[SteamyTea]

This seems like it is going to become interesting, and expensive.

Should be able to chip in with comments every now and again.

[saveasteading]

 

 

 

1 hour ago, Thorfun said:

not all 'accredited' professionals are created equal. nothing beats getting the opinions of others 

Us lot on BH have the advantages of

1. having many and various skills and experience. 

2. can take an overview, unclouded by insular expertise.

3. can dare to be wrong.

4. Can think and state ...'but surely'...and wait to be corrected.

5. are very often collectively right.

 

When my (and other) advice is not heeded I usually drop out of conversations. Maybe I'm wrong or maybe there's no point in further discussion.

I've said nothing on this though so will read along.

 

But I agree that being in the sun won't make much difference to an ashp, but being next to a big masonry wall in the sun might be a fair bit better than in a permanently dark and damp alley.

 

[NailBiter]

18 minutes ago, saveasteading said:

When my (and other) advice is not heeded I usually drop out of conversations. Maybe I'm wrong or maybe there's no point in further discussion. I've said nothing on this though so will read along.

 

That's fair enough, I don't mean to be dismissive of advice provided just trying to sort through what to take account of.

There is some more info here: https://sustainability.stackexchange.com/questions/9621/air-source-heat-pumps-does-prevailing-wind-matter

It seems that it is complicated but broadly:

 

Definitely need: Airflow, don't create a cool micro climate near ASHP (but consider creating warm one)
Definitely helps: Run ASHP during hot part of day when heat differential between inside and outside low.
Might help: Sunlight (for defrosting the coil if run in low temperatures)
Definitely avoid: High winds (causes frosting of the coil), Placement where servicing is hard. Restricted Airflow
Don't forget: Noise and pipework likely more important than most of the above.

Edited March 5 by NailBiter