passive house and ufh

[carou]

do I need it as I'm told it's not going to be the instant heat that I need in a PH? I'm told rads with an certain sort of ASHP is better way? 

[JohnMo]

With an ASHP to get best efficiency you need as low a flow temp as practical. UFH you can have flow temps in the 25 to low 30s depending on outside temperature. Radiators will always flow warmer than UFH, just because the surface area of the emitter is smaller.

 

A steady low temperature flow with UFH, very stable house temps.

 

PH don't need much heat, but still likely to need up to 10W/m2. So a 200m2 house is going to need 2kW at -3/4 degs. Or 48kWh per day.

[Mr Blobby]

23 minutes ago, carou said:

do I need it as I'm told it's not going to be the instant heat that I need in a PH? I'm told rads with an certain sort of ASHP is better way? 

 

Who told you that you need instant heat in a passive house, and why?

[ProDave]

Instant heat is the last thing you want in a passive house.  You want a very low level of near constant heat to match the very low level of heat loss.

[carou]

On 02/02/2023 at 20:26, Mr Blobby said:

 

Who told you that you need instant heat in a passive house, and why?

The PHC architect said it was to take into account how the weather can drop off dramatically from day to night in winter in this country. If I ask him to give me the phpp can anyone with the software update it to change it to UFH or make a west facing dorma window smaller? 

Edited February 8, 2023 by carou

[Conor]

We're near passive and we have a low temperature heat pump supplying UFH. It's barely on, max 6 hours a day and house is a constant 20-21c. I don't even think about it day to day. It runs on weather compensation so when we have a mild night, like last night, the flow temp was less than 30c, meaning no overheating.

Edited February 8, 2023 by Conor

[ProDave]

41 minutes ago, carou said:

The PHC architect said it was to take into account how the weather can drop off dramatically from day to night in winter in this country.

But it can drop from +10 in the day to -10 overnight and in a passive house you will hardly notice the temperature inside the house fall overnight.  I suspect your architect has never spent time living in a passive house?

[carou]

I obviously need to have another talk with him with this information. Can anyone update the phpp to take into account changing to UFH or making a window that’s subject to OH smaller? My PHC said it’s a lot of work £+++. How can I tweak it or can’t I? 

[Simon R]

14 minutes ago, carou said:

My PHC said it’s a lot of work £+++.

Our build is  near passive and about 180m2. When we did the sums we needed about 2.5kWh to maintain a 20c difference. Looking at costs we decided to have a small gas combi and run towel rails in our two bath rooms. It was a lot cheaper and less complex than going the uhf route.

In practice we quickly found keeping cool was much more of a problem than keeping warm. The energy modelling had got the solar gain from our east facing windows badly wrong. Fortunately the problem was easily fixed by installing a 3.5kW a2a unit in our open plan living area. Run from PV in summer and cheap overnight electricity in winter it's proved a very economical solution. If the sun shines we need no heating.

[Russdl]

@carou the PHPP is an Excel spreadsheet, a big one but an Excel spreadsheet non the less. If your PHPP has already been done, in other words the spreadsheet has been populated, then minor changes take very little time. Making a window smaller in PHPP would take a matter of seconds. 

Definitely ask your architect for a copy of the PHPP it sounds like s/he may be pulling your leg. 

 

Regarding the heat requirements, as others have said, you don’t need much. The last three nights here have been sub zero but the days have been sunny, consequently the heat has not been on. In this passive house the sun has done its job as advertised. Our heating comes on if the internal temperature in our hallway drops below 20. During the day the sun has warmed the house to around 21 and overnight it’s fallen to the low 20’s. 
 

it’s bloody marvellous actually. 
 

 

[Adrian Walker]

1 hour ago, carou said:

The PHC architect said it was to take into account how the weather can drop off dramatically from day to night in winter in this country. If I ask him to give me the phpp can anyone with the software update it to change it to UFH or make a west facing dorma window smaller? 

The whole idea of a Passive House is that the temperature is constant 24/7. How are radiators going to effectively heat up your insulated concrete slab?

 

 

[Russdl]

52 minutes ago, carou said:

Can anyone update the phpp to take into account changing to UFH

Actually, thinking about it (it’s been a while since I did my PHPP) a heating system isn’t specified. The PHPP just tells you what the heat requirement will be - you choose what to do with that information. 
 

Any other PHPP users confirm my recollection??

 

if you get the PHPP off your architect I’m happy to take a look at it. 

Edited February 8, 2023 by Russdl

[Thorfun]

4 minutes ago, Russdl said:

Actually, thinking about it (it’s been a while since I did my PHPP) a heating system isn’t specified. The PHPP just tells you what the heat requirement will be - you choose what to do with that information. 
 

Any other PHPP users confirm my recollection??

 

if you get the PHPP off your architect I’m happy to take a look at it. 

i didn't have PHPP done but this seems very logical.

 

sounds to me like the OP's architect just can't be bothered or is looking for extra cash.

 

@carou have you sent the heating requirements to a heating engineering company? they'd be able to advise on size of ASHP and emitter requirements?

[Mr Blobby]

23 hours ago, Russdl said:

Actually, thinking about it (it’s been a while since I did my PHPP) a heating system isn’t specified. The PHPP just tells you what the heat requirement will be - you choose what to do with that information. 
 

Any other PHPP users confirm my recollection??

 

 

Correct.  AFAICS there is no heating system specified in my PHPP spreadsheet, only heating demand.

 

Back to the OP's original question, UFH is a no brainer I think because of cooling potential and low temps for heating.

 

Also changing a window size should be no big deal.  My architect shares the PHPP sheet with me so the OP's architect should be doing similar. 

 

[joth]

I agree the heat emitters are not mentioned in PHPP. There is some info for the ASHP spec (only relevant if going for PH plus) and about pipework and pumps, but I had all this info supplied by the M&E designer not the PH architect.

 

Another thing to mention is if you are going for a certified passivehaus, it's not just a case of fiddling with the spreadsheet, you also need to have the passivehaus designer submit it to the certifier and get design sign off. If you make edits yourself you are taking over the role of PH designer, and if it ultimately fails certification for any reason the PH designer can wash their hands and say it wasn't their design in the end. So proceed carefully depending how you want the certification to play out.

Tbh if you're serious about getting certification it maybe worth shopping around to find a new PHC as this one seems misinformed and uninterested.

 

 

Edited February 8, 2023 by joth

[Russdl]

21 minutes ago, joth said:

Tbh if you're serious about getting certification it maybe worth shopping around to find a new PHC as this one seems misinformed and uninterested.

Or incompetent/dishonest.

[Kelvin]

What is the advantage of getting certified anyway? I assume it costs money to do so. I’d have though that near passiv gets you 99% of the benefit without the apparent hassle and complication. 

[Russdl]

17 minutes ago, Kelvin said:

What is the advantage of getting certified anyway? I assume it costs money to do so. I’d have though that near passiv gets you 99% of the benefit without the apparent hassle and complication. 

Couldn’t agree more. 
 

We had one meeting with a PHPP Consultant who turned out to be utterly inept - by incorrectly inputting data he effectively rotated the house through 90 degrees resulting in huge overheating numbers coming out of the PHPP. He shared that PHPP with me and I spotted the error, bought my own copy of PHPP and did it myself. There are huge benefits to doing that in my opinion, all the little tweaks that inevitably happen to the design can be checked for impact on the PHPP without paying someone hundreds of pounds. 
 

The end result for us is a non certified passive house that performs as predicted by the PHPP for £thousands less. 

[joth]

1 hour ago, Kelvin said:

What is the advantage of getting certified anyway? I assume it costs money to do so. I’d have though that near passiv gets you 99% of the benefit without the apparent hassle and complication. 

 

I found two potential benefits of certification:

1 it's a good stick to beat any contractor or supplier with that that tries to cut corners on their service after agreeing a price.

2 it's potentially helpful to negotiate a better selling price.

 

#1 happened to us with windows: they supplied double rather than the triple we paid for and the supplier tried to fob us off with "you won't even notice the difference". They backed down  when we reminded them they were supplying to a PH build that would now fail.   

Without certification I'd still have demanded they put it right, but it would have been an even harder 4 way blame game to get them to edit fault.

SonI'd recommend telling every supplier you are planning to certify even if you don't end up doing it.

 

#2 was the view of an estate agent that revalued our house, depends a lot on chance and  is questionable, as passivehaus is not a trademarked name people can use it (or "near" to it) anyway.

 

 

 

 

[Adrian Walker]

3 hours ago, Kelvin said:

What is the advantage of getting certified anyway? I assume it costs money to do so. I’d have though that near passiv gets you 99% of the benefit without the apparent hassle and complication. 

Ecology Building Society will give you a discount.  The difference between near PH and actual PH is the attention to detail both in the design and building.

[Adrian Walker]

1 hour ago, joth said:

 

2 it's potentially helpful to negotiate a better selling price.

 

#2 was the view of an estate agent that revalued our house, depends a lot on chance and  is questionable, as passivehaus is not a trademarked name people can use it (or "near" to it) anyway.

Most, if not all PHs are forever homes.  I have never seen a PH for sale.

 

[PeterW]

14 minutes ago, Adrian Walker said:

Most, if not all PHs are forever homes.  I have never seen a PH for sale.

 

I would hazard a guess in that they are very “bespoke” to their owners plus may struggle to recoup any sort of profit on the cost of build and certification..! 

[Adrian Walker]

3 minutes ago, PeterW said:

I would hazard a guess in that they are very “bespoke” to their owners plus may struggle to recoup any sort of profit on the cost of build and certification..! 

 

Yes, they have been designed to the owner's needs

[joth]

33 minutes ago, PeterW said:

I would hazard a guess in that they are very “bespoke” to their owners plus may struggle to recoup any sort of profit on the cost of build and certification..! 

Sure, but this is happenstance and orthogonal to whether a certified house commands a higher resale value than an otherwise apparently identical uncertified house. In theory it should as you have independent assurance all the invisible things the seller claims (insulation thicknesses, airtightness detail, thermal bridge free) really did get done during the build.

 

Fwiw I personally know a couple people that specifically sought out and viewed or bought already built passivehauses. (At least one built by a developer)

[Adrian Walker]

1 minute ago, joth said:

Sure, but this is happenstance and orthogonal to whether a certified house commands a higher resale value than an otherwise apparently identical uncertified house. In theory it should as you have independent assurance all the invisible things the seller claims (insulation thicknesses, airtightness detail, thermal bridge free) really did get done during the build.

 

Fwiw I personally know a couple people that specifically sought out and viewed or bought already built passivehauses. (At least one built by a developer)

I totally agree, a PH will have lots of proof that it was built well and correctly.

 

The problem is educating people,  especially estate agents