Upstairs heating options for passivehaus - electric or wet systems; looking for advice

[JohnMo]

19 minutes ago, zzPaulzz said:

Yep, I heard that. Where do you think I need to watch for dew forming? Pipes above the slab, or on the floor tiles? 

Pipes at 16 degs you should be ok. If you are getting any condensation on the floor you have big issues.

 

19 minutes ago, zzPaulzz said:

Hoping the MVHR will help.

Nope. Will do very little.

 

 

 

[zzPaulzz]

21 hours ago, Nickfromwales said:

From experience, with MBC ph offerings, MVHR ’may’ just get you by if you leave it at max wallop for purge. That’s if it’s used to prevent vs cure btw. 

 

At anything less, it’s no dice I’m sorry. One in Dorset was just stuck at 24/25°C and even with a Chinese heat pump MVHR with active cooling, the ‘occupant’ moaned to me that the cheap option she selected, against my advice, was useless.

I’d recommend that you power up the roof lights and use the controls to trigger these to crack themselves open at say 22°, with rain sensors to close them etc etc. 

 

The automated purge from those, in your absence, may be the difference between a stinking hot house to an ok one; manual opening roof lights needs you to be there to manipulate them. Don’t think for one minute that this is in any way a) practical or b) possible in real life.

My planning for clients is aimed at the residence being at an acceptable ambient by the time they retire of an evening, vs solutions which compromise life after the heads hit the pillow.
 

One of the absolute joys of having a cellulose blown 300mm wall and 400mm roof, with MBC twin wall, is the sheer graveyard silence it brings. Having roof lights open in bedrooms at night would do my head in tbh, same annoyance I get when staying in hot hotel rooms with roof lights, and the result is a poor nights sleep.

That's my plan for the days where the PHPP predicts overheating: crack open the electric velux windows to create some passive stack cooling.  

[zzPaulzz]

21 hours ago, JohnMo said:

Pipes at 16 degs you should be ok. If you are getting any condensation on the floor you have big issues.

 

Nope. Will do very little.

 

 

 

Yep, not counting on it. 

[Nickfromwales]

9 minutes ago, zzPaulzz said:

That's my plan for the days where the PHPP predicts overheating: crack open the electric velux windows to create some passive stack cooling.  

Good stuff. 
 

Velux can be controlled by a wall remote, and iirc these can provoke the opening at a particular set point, eg you then don’t have to run around upstairs checking room temps to decide to open them or not. That would be a hellish existence, and imho wholly impractical, but as above also then reliant on human interventions.

 

Automating that, very simply, seems a perfect solution, and offers zero reliance on any occupant. 

 

You may want to explore the MVHR going into boost at the same time, say if the FF temp gets higher than 22.5/23°c

[Mike]

3 hours ago, zzPaulzz said:

crack open the electric velux windows to create some passive stack cooling.

Unfortunately the chances are that this won't work well when you most need it.

 

Passive stack ventilation is driven by the difference between indoor and outdoor temperatures; on a hot summer day that difference can be small, resulting in very little stack effect - so very little cooling. In fact the outside temperature may exceed the internal temperature, causing the stack to operate in reverse and drawing in warmer air. For it to have a chance of working you'd also need to crack open some vents or windows, so that the air you hope will go out the Velux has somewhere to come from.

 

I'd strongly suggest a chilled slab or aircon instead. If choosing the former then, as @JohnMo says, don't over chill the slab; in France the regs say that floor surface should go no lower than 18°C to avoid condensation.

 

 

Edited 16 hours ago by Mike

[zzPaulzz]

3 hours ago, Mike said:

Unfortunately the chances are that this won't work well when you most need it.

 

Passive stack ventilation is driven by the difference between indoor and outdoor temperatures; on a hot summer day that difference can be small, resulting in very little stack effect - so very little cooling. In fact the outside temperature may exceed the internal temperature, causing the stack to operate in reverse and drawing in warmer air. For it to have a chance of working you'd also need to crack open some vents or windows, so that the air you hope will go out the Velux has somewhere to come from.

 

I'd strongly suggest a chilled slab or aircon instead. If choosing the former then, as @JohnMo says, don't over chill the slab; in France the regs say that floor surface should go no lower than 18°C to avoid condensation.

 

 

My Zehnder Q350 can be configured to turn on the supply or extract, or both (normal balanced mode).  I wonder if I'll get a good cooling result if I use Home Assistant at dusk to switch the MVHR to supply only, chill the slab and also open all the Velux. Then, before dawn close the windows and switch the MVHR to balanced mode with summer bypass.  Thoughts?  

[JohnMo]

1 hour ago, zzPaulzz said:

My Zehnder Q350 can be configured to turn on the supply or extract, or both (normal balanced mode).  I wonder if I'll get a good cooling result if I use Home Assistant at dusk to switch the MVHR to supply only, chill the slab and also open all the Velux. Then, before dawn close the windows and switch the MVHR to balanced mode with summer bypass.  Thoughts?  

My view and experience with MVHR is don't expect any cooling from it.

 

Chilling slab is an all day affair - low and slow wins the day.

 

Maybe better, once house is warmer than outside open all the windows, when outside is warmer than inside do the opposite. Keep floor temp cooler than 20 all the time, boost floor cooling if room get over 23.

 

Leave the MVHR to do it thing, no place for home assistant, just set it up at commissioning and leave to run.

[Nickfromwales]

3 minutes ago, JohnMo said:

Chilling slab is an all day affair - low and slow wins the day.

Defo.

[Thorfun]

2 hours ago, zzPaulzz said:

My Zehnder Q350 can be configured to turn on the supply or extract, or both (normal balanced mode).  I wonder if I'll get a good cooling result if I use Home Assistant at dusk to switch the MVHR to supply only, chill the slab and also open all the Velux. Then, before dawn close the windows and switch the MVHR to balanced mode with summer bypass.  Thoughts?  

What a faff! Just install AC and enjoy the cool house. 😉

[Nickfromwales]

54 minutes ago, Thorfun said:

What a faff! Just install AC and enjoy the cool house. 😉

Exactly what I’m doing for 2 current new build clients.

 

The more I look into it, after a bit over 10 years focussing my interests in the “PH” arena, the more and more this makes absolutely perfect sense. 

[Great_scot_selfbuild]

5 minutes ago, Nickfromwales said:

Exactly what I’m doing for 2 current new build clients.

 

The more I look into it, after a bit over 10 years focussing my interests in the “PH” arena, the more and more this makes absolutely perfect sense. 

@Nickfromwales what's your preferred AC solution?

[Nickfromwales]

Just now, Great_scot_selfbuild said:

@Nickfromwales what's your preferred AC solution?

The correct one for the particular instance, of course!
 

I don’t copy / cut / paste, so each job starts on a clean bit of A4. Not lost a patient yet. 

[Great_scot_selfbuild]

1 minute ago, Nickfromwales said:

The correct one for the particular instance, of course!
 

I don’t copy / cut / paste, so each job starts on a clean bit of A4. Not lost a patient yet. 

Ok, I'll try again; do you have a preferred manufacturer? (or ones you automatically avoid)

[Nickfromwales]

1 minute ago, Great_scot_selfbuild said:

Ok, I'll try again; do you have a preferred manufacturer? (or ones you automatically avoid)

Apologies, it’s late. 
 

I don’t buy cheap, so would go towards recommendations from colleagues who install this stuff on a day to day basis. 
 

If it’s one summer room or garden office, I’d recommend a cheap and cheerful, best-of-the-worst Chinese offering. 
 

For one current client (>£1.5m) I would only recommend going with one of the big hitters, LG / Samsung / Daikin / Fujitsu / Panasonic etc. 

 

This is because of after sales support, parts procurement, more robust installer network / longevity and quality of the kit and so on.

 

To be less evasive, I look at kit to suit a remit, and as I don’t directly install domestic AC I don’t have a go-to manufacturer, specifically, as a blanket solution.

 

I do, however, have some excellent strategic partners who I reach out to in my hour(s) of need.

 

Ive lost count of how many times I’ve recommended a particular piece of equipment or a manufacturer, and then during the construction phase I’ve said that “we’re not going with that any more, and here’s why!”.

 

I maintain, the shoe must fit, so each client gets a few offerings laid out in front of them (“bronze, silver, gold”), and the pros cons and caveats explained comprehensively for each option, and then they are in a position to be left alone to make their own, informed decision based on the information that I’ve gathered and shared. 

[zzPaulzz]

1 hour ago, Thorfun said:

What a faff! Just install AC and enjoy the cool house. 😉

Haha. Maybe, but not expecting to need AC. If the PHPP calcs are correct then the house will only exceed 25°C for a few days a year. 

[Mike]

2 hours ago, JohnMo said:

My view and experience with MVHR is don't expect any cooling from it.

 

Chilling slab is an all day affair - low and slow wins the day.

+1

[Nickfromwales]

2 minutes ago, zzPaulzz said:

Haha. Maybe, but not expecting to need AC. If the PHPP calcs are correct then the house will only exceed 25°C for a few days a year. 

Take that with a big pinch of salt.

 

Consider what that document is actually telling you, which is that if you stay inside for “a few” days a year, you’ll be clinging to life (not just a little uncomfortable).

 

I had the same argument (robust discussion) with a PH certified architectural practice, and beat the lead architect by 1%. PHPP just focuses on the building, and nigh-on ignores the poor buggers locked inside.

 

This particular client then abandoned the £1k they’d invested in the architects recommended M&E designer and went with me, with said architects blessing. When I finished picking apart their proposal, the chap simply said “if all else fails, then you can just fit 2x AC units and that’ll fix any issues” ffs. The list of faux pas was long.

 

They’re no longer the clients architect…as they politely disengaged soon after, with a boatload of the clients money gone forever. 

 

Unfortunately, most folk simply don’t know what lays ahead, but it is very difficult to convey this to someone such as myself, who’s coming from fossil fuel heating in a poor performing current residence, as to the new and different way in which they will find themselves then living. 

 

Oh, what a difference there is! Like night and day different.

 

Consider how horrible a summer is in your (and my) current home, and then multiply it x3.

[Mike]

46 minutes ago, zzPaulzz said:

If the PHPP calcs are correct then the house will only exceed 25°C for a few days a year. 

My PHPP version is ancient, so I can't take that as a guide, but I wonder what data their current climate files are based on. Is it still a historic analysis, or a forward projection? The projected climate of the 205s will look shockingly different to historic data from the 1990s.

 

I think that PHPP uses EnergyPlus weather files (.epw); if so then I'd suggest using the University of Bath forecast data; see my post here:

 

 

 

Edited 7 hours ago by Mike

[Nickfromwales]

6 hours ago, Mike said:

The projected climate of the 205s

What was the value you wanted to type here Mike? I’ll edit it back in.