Hopeful in the SW!

[Brian Paul]

After many years of renovations & extensions we thought our building days were over. But now we are Northerners looking to build our very last house in the SW (after we have negotiated planning). I've followed discussions on Buildhub for around 18 months since our circumstances changed. 

We are looking to build a near passive house of around 120 m2.  

My initial questions are about heating requirements for such a building. Passive house figures suggest around 1800 kWH p/a and allowing for 'near passive' I'm looking at 2500 kWH p/a. Historically about 25% will be in January - ~600 kWH - giving around 20 kWH per day with a possible peak demand of 2kW. 

So: 1. Are these figures realistic?  

2. Our proposed solar PV would provide a net surplus over the year with an import requirement of around 2500 kWH during October to March.  (Which near enough equates to heating demand.) Using an ASHP with COP 2.5 (not seasonally adjusted & I'm not an optimist) this could be reduced to 1000 kWH.  (or 600 kWH if very optimistic) So is it worth specifying an ASHP?  How long do they last? Cost of servicing? 

 

Any advice gratefully received.

 

 

 

[SteamyTea]

Welcome

There is the SW, and then the proper SW.

I am at the proper end.

Wind is one thing to factor in, it saps heat away quite rapidly.

But basically you can just about design anything, thermally.

Be careful with the Passivhaus figures, some times they are primary energy and not usage energy.

I use about 4 MWh/year for everything.

Could use 1MWh less if I swapped my resistance heating for a heat pump, or put in PV to heat my water.

 

So yes, ASHP.

Thick, well insulated walls, MVHR, spend time on making the place super airtight, initial design helps here, and never be tempted to put in a wood burner.

Edited November 3, 2020 by SteamyTea

[joe90]

Welcome from someone else in the SW (Devon, not that rough bit called Cornwall ????). Orientation makes a big difference too, on our plot a turned the house through 90’ to make the back, with most windows and conservatory, face South (despite being told we would overheat). I didn’t do any calculations but went with passive principles and guess work based on other people’s info on this thread. It works very well.

[SteamyTea]

58 minutes ago, joe90 said:

Devon, not that rough bit called Cornwall

The Horror that is Cornwall.

But only the second worse planning office.

Edited November 3, 2020 by SteamyTea