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 1 hour ago by Mike