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New build heating / energy choices

RedRhino

By RedRhino
in New House & Self Build Design

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RedRhino Member

RedRhino

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We were fortunate to be given a tour of this Passiv Haus build during its construction: https://www.passivhaustrust.org.uk/news/detail/?nId=1117

Lots of points of interest; for example no heating except an ornamental wood burning stove (in 550 m2) and towel radiators. 

We have friends about to buy a plot for self-build home. They are near retirement so the house will have high occupancy. What do folks think is best practise for heating and energy mgmt? 

Here is my view:
Prioritise insulation of the total envelope and air tightness. 
MVHR is essential for air quality
Orientation to the sun to get solar gain but with shading from high summer sun to reduce over heating
Wood burning stove with external air feed for energy security / aesthetics
Solar panels with provision for more if initial funds are limited - charging an electric car will be a continuous demand. Our 3.8 pKW panels heat our DHW for 2/3 of the year with Solar iBoost. 

Batteries? They will be cheaper in a few years.

Heating? if demand is small I think I might forego gas and the associated standing charge, also the installation cost of boiler + wet ufh. Instead maybe just electric ufh on the ground floor. It's more expensive to run but cheap to install. Solar will offset some cost. In the depths of winter burn wood?
I haven't said an ASHP. I just feel its a lot of cost and the efficiency is poor when you need it most. 

I can see the weakness in the above is winter DHW. If you need to run baths in winter that is a lot of electricity cost. 

 

I'd be grateful for opinions. 

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JohnMo Advanced Member

JohnMo

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Hello and welcome.

 

Always a bit suspicious when they we don't need heating and the house is huge.  So from the link the heat load is 11 W/m2, the floor area is 550m2, so on a cold design day that's 6kW.  Where is that heat coming from, a couple of hours of sun in mid winter may heat a couple of rooms, but a few overcast days it's going to get cool, so I doubt the fire will be cosmetic for long.

 

Small house 100m2, that heat demand is 1.1kW, small panel heater would do it on the coldest days.

 

A2A heat pump, for heating and cooling?  Cheapish to install, cheap to run.  

 

UFH, or fan coil units, small heat pump and UVC for hot water.  Needn't be that expensive.

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Conor Advanced Member

Conor

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No right or wrong for a low energy house. Key thing is the energy use is minimal so the costs and impacts have a low baseline. Gas, oil, direct electric, stove, ASHP all justifiable options.

 

So, if you want opinions...

 

For us, in a 350m² passive ish house, UFH throughout and a ASHP. It's on once a week at the minute for about 8hours.ngets the house from 17c to 20c in that time, house then drops to 18c in a few days. Briefly considered a stove but it's probably the least environmentally friendly way of heating a house. And the least useful as it's not evenly distributed through the house.

 

And ASHP with UFH is the most expensive option (ours came in at about £9k for everything) but it's the cleanest and most versatile option. Especially if you have a decent solar PV array and you can effectively cool your house for free during the summer. Can't do that with a stove. 

 

The cooling worked so well for us that I'm highly unlikely to bother with all the external shading the architect specced (based on PHPP saying overheating was a risk). At a guess it'll cost north of £4k... That is the same as the capital cost of the ASHP, and it's saved its own outlay instantly. 

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ProDave Advanced Member

ProDave

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1 hour ago, RedRhino said:

I haven't said an ASHP. I just feel its a lot of cost and the efficiency is poor when you need it most. 

I dispute that.  Sub zero temperatures here today and my ASHP is working fine to heat my low energy house.  If you just buy and ASHP and get a normal * plumber and electrician to install it (or do some yourself if capable) they need not be expensive.  

 

* by normal I mean someone capable of reading and installation manual.  I have been shocked on occasions at wrongly fitted ASHP's because they apparently cannot read and connect it as though it were a gas boiler.

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RedRhino Member

RedRhino

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"ASHP with UFH is the most expensive option (ours came in at about £9k for everything) but it's the cleanest and most versatile option. Especially if you have a decent solar PV array and you can effectively cool your house for free during the summer. Can't do that with a stove. "
 

This is a good point. In summer PV generates an excess of energy and using it to cool the house is well, cool.

 

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JohnMo Advanced Member

JohnMo

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Some heat pumps (with the correct cylinder) will cool the house while heating DHW at the same time. DHW is heated free from the waste heat extracted from the house.  If you have PV, cooling and DHW could be provided free in the summer.

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joth Advanced Member

joth

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40 minutes ago, ProDave said:

If you just buy and ASHP and get a normal * plumber and electrician to install it (or do some yourself if capable) they need not be expensive.  

 

I think this is fair advice for a self builder, but here we're passing advice to a friend of a (not?) self builder, who are near retirement and don't have the wherewithal to come do their own research on this, so I'd be very doubtful of their odds vetting plumbers and electricians ability to perform a job they've never done before.

Unless you're an enthusiast, the average consumer would be better purchasing from an experienced installer, ideally one that's registered with the manufacturer they install from.

 

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joth Advanced Member

joth

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23 minutes ago, JohnMo said:

Some heat pumps (with the correct cylinder) will cool the house while heating DHW at the same time. DHW is heated free from the waste heat extracted from the house.  If you have PV, cooling and DHW could be provided free in the summer.

Literally at the same time? So like a 4 pipe air to water heat pump?

Sounds a good idea, I didn't know such a thing existed.

 

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ProDave Advanced Member

ProDave

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17 minutes ago, joth said:

Literally at the same time? So like a 4 pipe air to water heat pump?

Sounds a good idea, I didn't know such a thing existed.

 

Surely only a water to water heat pump can do that?

 

(wait to be proved wrong with a clever diagram)

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JohnMo Advanced Member

JohnMo

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Air to water heat pump ASHP.

 

Not water to water, uses refrigerant to refrigerant. Instead of routing the hot refrigerant gas to an air cooler, when in cooling mode, they route it to a cylinder with a refrigerant coil. Disposing the heat to water.  Once heating cycle complete it goes the normal route to the outside air.

 

Argo clima is the make I have seen.

Edited by JohnMo
Clarity
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