Central heating systems required for 1 storey new build

[Adam NT]

Hi there

We have a home in the wilds of North Yorkshire, which has a derelict detached barn.  We are hoping to demolish and rebuild the barn to create an annex and workshop.  The annex may be used as a granny-flat (various elderly relatives), or may end up being a home for our son - either way it will be additional accommodation for the house. We are trying to decide what is the best central heating system to go for. A few things you need to know:

·        There is no gas in the Dale where we live

·        We will probably be able to put south facing solar panels on a 13m long roof

·        We live in a National Park so are unlikely to get permission for a wind turbine – a shame as it constantly blows a gale – though we could ask

·        The annex may not be used all year round (certainly for the first few years)

 

The building will be 13.5m by 7m and single storey – possibly split level as it’s on a slope. 

 

We currently have an oil fired central heating system for the main house but are not sure what to use for this new build.  Ideally we would like it to be self-funding energy wise – ie it uses solar/other to heat the building and water.  What would you use for such a build?  A friend recommended an ASHP, possibly with solar to power it?  Would this be more cost effective than electric radiators?  I think we’ll need an immersion for the water whatever we do?  If we had solar, presumably we would need a battery store to have energy on an evening? 

 

Any comments will be greatly received.

Thanks

Adam

[SteamyTea]

You will have a number of problems being energy self sufficient.

Wind and especially solar power, which is several times cheaper than wind, is very difuse energy. So you need lots of area that is unaffected by shading. South facing is best, but systems can be split up electrical, so they can perform better.

An ASHP is now, if bought independently, the cheapest renewable heating/DHW system you can get.

Linking PV and an ASHP is not technically hard, it just gets expensive.

If you have mains power, have a word with your DNO to see what size system you can connect. The usual limit is 4 kW, actually 16 amps per phase.

 

DO NOT tell them you want an ASHP. That will just cause problems.

[billt]

2 hours ago, Adam NT said:

Ideally we would like it to be self-funding energy wise – ie it uses solar/other to heat the building and water.  What would you use for such a build?  A friend recommended an ASHP, possibly with solar to power it?  

 

Forget it, however much you spend on solar collectors you won't get enough energy in the winter.

 

We have a 14kW PV system. In December it generated 115kWhr or 3.7kWhr per day; not enough for the average houses standing consumption, let alone heating. In November it averaged 9kWhr per day and in January 8kWhr per day. (February's better at 13kWhr per day so far.) In this house our typical electricity (non heating) consumption is 10-14kWhr per day. Heating is 120-160kWhr per day in the winter, or about 30-40 times the amount of energy generated in January. Admittedly we use a lot of energy in a poorly insulated house, but the principle remains.

 

In your situation I would try to ensure that the new building has extremely high levels of insulation and air tightness; possibly oriented so that any winter solar can be used directly (south facing windows, but designed to avoid summer overheating). After having done that the heat requirement should be so low you might be able to get away with direct electrical heating, failing that a small ASHP should work.

 

PV is useful for about 8 months of the year, but not for heat in the winter.

[Iceverge]

If you can buy an ASHP at a reasonable price it's the best option. 

 

I looked at a friend's similar project recently, almost exactly the same size for space heating and DHW. 

 

U values 0.12 ceiling, 0.18 walls 0.16 floor. 0.6ACH airtightness, MVHR and good airtightness detailing. Annual heat demand about 3000kWh. 

 

He is able to get an ASHP for €4000 through work so that's what I based my calcs on. I compared direct electric, an exhaust source heat pump, an A2A heat pump and an immersion and various combinations. 

 

The A2A + ESHP was the cheapest overall but could risk some rooms being too cold in a bungalow as it depends on air movement to heat the house. 

 

The ASHP was a close second, combined with UFH in a thick concrete slab would allow cheap overnight heating with the slab as a storage heater as well as excellent comfort. 

 

Forget renewables until you've got a structure that is as efficient as possible. Insulation has a far longer lifespan than any PV panels or wind turbines.