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What is the greenest way of heating our new studio?

Posted by Cathy Debenham on 10 September 2013 at 10:46 am

Q: We have planning permission to replace existing garage with a fully insulated garage and studio. What is the greenest / most efficient way of providing hot water and heating to the studio?

We have mains electricity; access to plenty of wood; oil (which we use as sparingly as possible); and our own water supply. We installed a 4kw array just in time for the full FIT in December 2012 and have been so impressed we were wondering if roof-installed pv panels might be a partial answer (though we know we won't qualify for a further FIT).   Someone has suggested pv generated hot water and underfloor heating; someone else has suggested a woodburner with back boiler and a couple of radiators.

A: When you are planning a build is absolutely the right time to be thinking about these things. I'm going to give a few thoughts on possibilities, given your criteria of wanting to be green. However, at the end of the day practicality and costs often determine what we go for, so I suggest you talk to a few installers to see what best fits your budget.

Heating and solar PV panels don't really go hand in hand, as when you need the heat most, there's least sun. So, even though you would actually be eligible for further feed-in tariff (albeit at the new lower tariff) if you extended your array, it wouldn't be a good option for providing heating and hot water.

Given that you have access to plenty of wood a wood burning stove with back boiler seems a sensible solution. You could have radiators or underfloor heating with that. If you wanted to benefit from the renewable heat incentive (RHI), you would have to go for a pellet stove - which would mean an ongoing fuel cost, but less work and hassle cutting logs and feeding the stove. Alternatively, as you say the studio is going to be fully insulated, you could go for an air source heat pump and underfloor heating.

If you want to make the heating system even greener, solar thermal panels work well with either biomass or heat pumps. They would provide most of the hot water in the summer when you don't want to light a wood burning stove, and heat pumps aren't so efficient. Solar thermal installations are also eligible for the RHI and can be integrated into the roof during the build. Because they are complementary you can receive RHI for both a heat pump and a solar thermal system concurrently.

There are people who would argue about the greenness of both biomass and heat pumps: the former because burning wood does emit carbon, and the latter because it uses dirty electricity from the grid. However, both are preferable to oil. 

Photo: Martin Pettitt

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Comments

3 comments - read them below or add one

karen

karenComment left on: 7 October 2013 at 9:59 pm

I am planning a granny flat extention and have been considering the very same green questions. My solar 4kw PV array generates very well but not enough for the 36 square meter extention. I think the insulation is key but I am still deciding  if an air source heat pump with massive insulation is the way to go. Incidentley the Greener group installed my PV array (Good job too) so I might ask them to give me some suggestions based on the plans.

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wookey

wookeyComment left on: 1 October 2013 at 2:41 pm

The best way to heat the studio is to design it so it hardly needs any. That means passivehaus principles (or AECB gold). It does depend on the building orientation whether there is much potential for solar gain, but really high levels of insulation and airtightness is the way to go whatever else you do. A passive building requires so little heat (10% of a typical UK building)  that just having a small electric heater for the few days a year when it's needed is the most cost-effective.

Insulation and good building detailing is very cheap in comparison to energy costs over 30 years, and the right thing to do from an emissions point of view. The passivhaus premium is now less than 10%, and on some sites has involved no extra cost at all, so not doing it is foolish IMHO.

I'd say that any new hot water system should be solar thermal, but the PV incentives distort this and make it a financially, if not ecologically, sensible choice. Winter is trickier, and you have good advice above.

 

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The Greener Group

The Greener GroupComment left on: 10 September 2013 at 12:44 pm

Read this post with interest as it is a question we are asked frequently as renewable energy installers. If the property is to be well insulated I agree that either an airsource heat pump or wood burner would work well and both have their pros and cons as mentioned above.

One thing I would like to add is that Solar PV and heating can go hand in hand it just depends how you use the energy generated fom your PV system. We are installing lots of Solar PV powered immersion heaters for customers who like to switch off their traditional boilers in the summer and just use the excess power generated from their PV system to heat the water in their water cylinder. It would compliment a wood burner very well. The wood burner would heat all the water and space you needed in the winter. You would not need to (or want to) fire up the burner in the summer months and could rely on the solar immersion switch to provide hot water during the months when the sun is out.

Immersion swithces are great, however the effectiveness of the above solution would depend on how much of the energy your PV system generates is used on site and how much is exported. If you know this it would be easy to work out how much hot water could be heated.

 

This is certainly a much cheaper option than a solar thermal system

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