Are evacuated tubes / solar pipes worth it for heating an outbuilding? (UK)

[bikerchris]

Hello all,

I hope you can help, I don't know any plumbers and just wondered about an idea of mine, it might not be do able for good reason!

I built a 6 x 3m outbuilding a few months ago for myself in the garden, me and wife wanted an office to work in when needed, mainly her (labourer). This is what it's up to so far:

Raft foundation with duct work for lecky / internet later on
100mm single skin blockwork
100mm floor insulation
100mm roof insulation (warm deck)

What I'm intending:
100mm external wall insulation + clad
get some heating!

I built it this way as I wanted to have a constant temperature and of course keep the heating bill down, I thought having insulation on the outside would reduce the sun heating up the structure and when it is heated inside, the blockwork would hold onto the heat like storage heater rads. It works well in summer so far (when I lean the insulation up against the wall...have to save up to get fixings!), but we're getting into the cold bit of the year now.

I was always thinking of electric heating as it's around 20m from house so no hot water rads, but the latest price hike for lecky is a bit scary. I helped a mate recently with re-roofing his house and at the same time we put heat pipes on there for heating water. I was well impressed with the pipes, on a sunny day he showed me them working, by just holding one and pouring water in it. the water came out the other end as steam or bloomin hot water, too hot to touch.

Anyway, I was wondering if they could be used for heating my little outbuilding? My questions are:

1. Are they not popular because they're a bit rubbish? (not much info or availability on internet)
2. Could a few of them be on the roof, then pipework to a radiator inside, with a pump somewhere to push the heating fluid around?
3. Could it be turned off easily or on a thermostat when not needed in summer?
4. On a grim weather day, would they still work well enough?

Anyway, if you have got this far, thank you very much.

All the best
Chris

 

[bikerchris]

Oh and just another thing, I haven't finished the floor yet, so may be it would be better connected with underfloor heating - if the idea isn't stupid in the first place!

 

[ShaunCorbs]

Tbh I wouldn’t but I would go down the route of solar panels on the roof eg elec and a battery inside so it tops it up when your not requiring heat

 

[Ric2013]

Not stupid but may not be cost effective vs electric for the limited heat demand such a well-insulated building may have. Solar thermal not very easy to turn off as the heat in the collector (ie the panels) needs to be dissipated. Also, without storage for the hot water, you'll only have heat available when it's already warm due to solar gain through windows so it may only be worth it if you are going to be making significant and prolonged use of this building.
If you only want heat in the day, it may be worth also looking into photovoltaic to run electric heaters without even bothering connecting the system to the national grid and you then can literally switch it off when not needed. And then use grid electric instead when the weather isn't sunny.
Have you calculated the prospective heat loss for the completed building in terms of W per degree day and checked the local climate. Otherwise cost comparisons are impossible.
Have a chat with the free advice line at the Centre for Alternative Technology charity?

 

[bikerchris]

I really appreciate all of the comments, thank you so much, especially so quickly!

Tbh I wouldn’t but I would go down the route of solar panels on the roof eg elec and a battery inside so it tops it up when your not requiring heat

Thank you Shaun, I did wonder about that way back at the beginning of the build. Cheers!

Not stupid but may not be cost effective vs electric for the limited heat demand such a well-insulated building may have. Solar thermal not very easy to turn off as the heat in the collector (ie the panels) needs to be dissipated. Also, without storage for the hot water, you'll only have heat available when it's already warm due to solar gain through windows so it may only be worth it if you are going to be making significant and prolonged use of this building.
If you only want heat in the day, it may be worth also looking into photovoltaic to run electric heaters without even bothering connecting the system to the national grid and you then can literally switch it off when not needed. And then use grid electric instead when the weather isn't sunny.
Have you calculated the prospective heat loss for the completed building in terms of W per degree day and checked the local climate. Otherwise cost comparisons are impossible.
Have a chat with the free advice line at the Centre for Alternative Technology charity?

Cheers Ric, I did wonder about the on and off'able nature of solar thermal and where that heat energy would go in summer.

I think the building will be used for around 10 hours a day, 5 days a week.

Looks like that's 2 votes for PV, I'll look into this route more now, cheers!

I haven't checked the heat loss yet, well I sort of have, but it was using generic websites. They mentioned around 13k BTU's.

I didn't know that alternative tech charity existed, I'll have a google around.

Thanks again, really appreciated. I will follow up and how it's done.

 

[exedon2]

We did do a fair it of solar thermal at one point (was a very easy way to get sap rating of a new build up).
Certainly wouldn't recommend it for what your doing the only time you will probably get enough heat out of it is when you least need it!
When a company the size of Kingspan gets out of solar thermal think that says it all.
P V panels all the way.

 

[bikerchris]

We did do a fair it of solar thermal at one point (was a very easy way to get sap rating of a new build up).
Certainly wouldn't recommend it for what your doing the only time you will probably get enough heat out of it is when you least need it!
When a company the size of Kingspan gets out of solar thermal think that says it all.
P V panels all the way.

Thanks exe for commenting, a great in site.

Very good point about the big boys getting out the game, I have seen that they are good only in certain climates and mainly for making hot water (in america).

 

[oz-plumber]

Why don't you have a look at Reverse Cycle Split Systems.
Most have a COP of 3 and over.
Meaning 1 kW of electric input delivers 3 kW of heating or cooling. ( in basic terms )
But you will get heating in winter and cooling in summer.

 

[bikerchris]

Why don't you have a look at Reverse Cycle Split Systems.
Most have a COP of 3 and over.
Meaning 1 kW of electric input delivers 3 kW of heating or cooling. ( in basic terms )
But you will get heating in winter and cooling in summer.

Thank you for this, funnily enough this was originally recommended by a builder mate, I can pay direct and have it fitted and supplied for around £1200. I just had a misguided idea that I could lower the typical cost of heating some how. My only worry about the split system is the noise outside, I'm around 10m away from neighbours (on the other side of a fence and I put a small conc slab in outside the building where I was hoping it would go (floor mount externally).

I was quite happy with the cooling side of things, when we had that hot weather a few months ago, I leaned the insulation boards up against the outside, partly covering the door (patio doors around 2.4m wide). I got temp differences of up to 10C (30'ish outside), which I was really pleased about.

 

[Ric2013]

PV to run ASHP might be a winner?

I'm not against solar thermal, by the way, and I think it's worth looking into provided you realise you'll need a buffer tank (fancy version of a large hot water cylinder). You'll actually get more far more heat per sq m than PV will give you if you're using PV it to run electric heating.

Actually I'm quite sceptical of both in UK climate, but depends how much output you need. For space heating, they both give you more energy in the summer when you don't need it sadly. The C.A.T. tried an experiment to see if they could store summer heat created by thermal panels into the winter and couldn't keep it warm enough ('it' being around 30,000 litres of water IIRC) and I'm told the Building Research Establishment tried something similar and also failed. Storing electricity for a few months is technically possible if you can afford the batteries, but it's just not cost-effective.

 

[bikerchris]

PV to run ASHP might be a winner?...

Thanks for the follow up Ric, very much appreciated.

PV and ASHP might be a great combination for sure.

I guess what I really need to do is know how much heating I actually need, as a starting point? I've befriended a local plumber and he says he can run the calcs for me, which is nice!

That is incredibly interesting info, thank you very much. I would hope that the sun would shine at least once or twice a week, so if I went the battery route I would hope there's enough juice to heat/cool. As a backup I guess I could have a simple fan heater, but it's noise I could do without!

P.S. Sorry for the delay in responding, not quite sure what happened there, I had drafted most of it but didn't press the send button!

 

[Ric2013]

As a backup I guess I could have a simple fan heater, but it's noise I could do without!

All resistive electric heaters are equally efficient (near 100%) at converting electricity to heat, so doesn't need to be a fan heater if you are thinking of the electrical heating route. The best electric heating is whatever makes you feel comfortable for the least electricity consumption.