New Build Passive House (Donegal - Ireland)

[Donegalsd]

Hi all,

We have just started  to build a two-story timber frame in Donegal in the North west of Ireland. We are building to passivhaus standards and have an experienced passivhaus builder. I have gained loads of information from this forum and hope to get some more as the build progresses.

We have a lot of south facing glazing (by design - to capture views of Donegal bay) and have added some shading to the ground floor southern windows.

PHPP calculations demonstrated that overheating can be mitigated by adding some cooling from the underfloor slabs. We intend to use a Mitsubishi 8.5kW ecodan and have a Brink passive certified MHRV specified.

Phpp and plans attached.

 

 

Two storey-Floor Plans, Sections, Elevations 280620.pdf

[Dan F]

Welcome!

 

Have you done PHPP calcs yourself or do you have a passive house consultant or architect onboard?

 

I'm suprised at your cooing demand as this is much higher than you'd expect for this part of the world! What is your "frequency of overheating" without cooling? It must be very high..

 

Ideally, you would design the house to avoid so much overheating without needing to rely on so much cooling.   You don't have to sacrifice the view in order to do this, but can use a combination of i) overhangs, ii) temporary shading and iii) solar glass.  The good thing about having PHPP model is that you can try different combinations until you get a good balance.  You may still want some slab cooling, but in my opinion it's not ideal for a design to bake in this  amount of cooling given you are in the north of ireland and not the south of france.

 

Is it too late to at a minumum build in some overhangs at first floor level?

 

On a seperate note, looks like something is wrong in your PHPP as PE/PER demand are far too low.

Edited November 1, 2020 by Dan F

[Donegalsd]

Hi DanF,

 

Thanks.

 

I have a PH consultant (and architect) on board - The PE/PER is missing some data - I didn't quiz the guy on it.

 

At the moment the PHPP is really just a model to ensure that thermal bridge/insulation/window specifications will meet standards, I have another installment to pay before he uploads it to the PHI (and completes it)

 

Without the slab cooling the overheating is between 15% - 25% but that is without any allowance for opening windows or summer bypass or any internal blinds/curtains. Its hard to remember exactly as we have run so many models. Ill have to be paying my consultant again to get him to re-run them all. 

 

We had looked at solar glass but then we were running in to problems with increasing heating demand (plus a 7% increase in window cost).

 

In reality we are pretty rural so keeping windows shouldn't be a problem and we are on the coast so don't have many still days. Our evening and nights are cool too so a night time purge should get the house cool fairly quickly. We have plenty of windows that can open to allow for both through and stack ventilation. So long as the slab can be cooled then it wont be throwing a load of retained heat up during the night. 

 

We have a house plan as single room deep and a simple rectangle to reduce build costs - but have included a brise soliel (1m overhang) over all the south facing ground floor windows. We are likely to change the 1st floor design a little to remove a void and this should help reduce the risk of overheating in the entrance hall and reduce the risk overall.

 

I agree with you though - It is far from ideal to have to rely on active cooling - but its hard to tell the architect to reduce your window size when you are already imagining yourself living in a house with huge windows.

 

 

[Dan F]

If you have PV you could argue that the cooling may be free I guess, but I struggle to understand how a good PH architect/consultant would design something, in Ireland, that has up to 25% overheating to start with!

 

The night purge should ideally be modelled in the PHPP already, that way you'd know if the risk still existed considering this rather than making any assumptions.

 

Has the brise soliel shading been included in the model?  That should help a lot, although you'd probably want something for first floor windows too.  Solar glass will impact winter solar gain which is why IMO the best approach is correctly designed overhangs (that will block light in summer, but allow it in in winter) and/or temporary shading (external venetian/fabric blinds).

 

See if your PHPP consultant will give you the spreadsheet so that you can play around with the variables yourself and work out the best balance yourself.   As long you don't use it for any other projects I don't see why this would be an issue.

 

 

Edited November 1, 2020 by Dan F

[Donegalsd]

Hi,

 

There are loads of new build houses here with overheating problems - Most people don't model or consider it - but mostly we don't have long spells of good bright days and lots of houses leak heat fairly quickly so it is less of a problem for them.

 

I can't really blame the architect, the client (me) specified (and encouraged) the large windows fully knowing that we would have to mitigate for overheating. This house has gone through several iterations (we had already paused the build prior to 1st lockdown) and there came a time that decisions need to be made to keep the process moving - we had agreed the price with the builder (and he has started work) before we got the most recent phpp.

 

I have some of the older models of the PHPP spreadsheets and I was able to get the overheating down to around 8%-ish with G value changes. I'll take your feedback on board though and take a proper look at some of the ventilation modelling. Perhaps low g on 1st floor windows could help.

 

All I have to do is learn how to fiddle about with PHPP. Fun.

 

I have only myself to blame again re. the lack of the detail of the PHPP model - I negotiated a keen price - and I suppose I paid for just enough to get assurances that we would meet spec.

 

I agree with you about overhangs and it is risky not having any shading on the 1st floor windows but we were fortunate to get planning on the site - and probably wouldn't have if we had deviated from the council rural design guide (hence no overhangs).

 

Part of our problem is that where we are in Ireland it is difficult to get experienced people on board in the design process and when you do they are very busy so there are plenty of delays in receiving information and the other part of the problem is me being a cheapskate and looking to save cash at every opportunity but still wanting a quality product.

 

 

[Moggaman]

I’m in the west of Ireland too and aim to build towards passive too.. I think the expertise in terms of PHPP  is probably greater and most prevalent in the UK.

can I ask though, what stops me from hiring a Uk Consultant to look at my drawings and running it through PHPP. ?. I won’t be looking to get it certified , I just want to know where my design stands ?

[Dan F]

1 hour ago, Moggaman said:

I’m in the west of Ireland too and aim to build towards passive too.. I think the expertise in terms of PHPP  is probably greater and most prevalent in the UK.

can I ask though, what stops me from hiring a Uk Consultant to look at my drawings and running it through PHPP. ?. I won’t be looking to get it certified , I just want to know where my design stands ?

 

Nothing stops you.  Our PHPP model was done remotely.

[Thorfun]

we are going for external blinds which we believe are a good solution. although not as cheap as building in an overhang they'll also reduce solar gain in the non-summer months when the sun is lower. plus, for us, it reduces the need to have internal curtains/blinds in those rooms!

[Dan F]

6 hours ago, Thorfun said:

we are going for external blinds which we believe are a good solution. although not as cheap as building in an overhang they'll also reduce solar gain in the non-summer months when the sun is lower. plus, for us, it reduces the need to have internal curtains/blinds in those rooms!

 

Going to automate them?  It's interesting when you can raise/lower them based on room temperature even if you're not at home ?

[Thorfun]

36 minutes ago, Dan F said:

 

Going to automate them?  It's interesting when you can raise/lower them based on room temperature even if you're not at home ?

Yep. Plan is for a loxone system. 

[Dan F]

1 hour ago, Thorfun said:

Yep. Plan is for a loxone system. 

Same here.  Have to share notes on central relay vs. nano relays vs. wireless actuator.   We are starting first fix in 2wks approx.

[Thorfun]

58 minutes ago, Dan F said:

Same here.  Have to share notes on central relay vs. nano relays vs. wireless actuator.   We are starting first fix in 2wks approx.

you're quite a way ahead of me! we probably won't break ground until Jan 2021 so I think I'll be following your install with great interest. ?