Can I harness the excess heat in my conservatory ?

[joe90]

As some of you will know I am building a conservatory on the south side of my house some 10 meters long by 2.5 meters deep. Everyone tells me it will overheat and I accept this as a consequence of being able to have a warm sunny space in the shoulder months.

 

Like all well insulated houses my main energy usage will be DHW ( especially in summer) so it seems sensible to try to harness some of that excess heat ( overheating) into my DHW in some way. The house roof is going to have a decent overhang to try to limit mid summer overheating into the rooms on the south side and I thought that the top of the roof of the conservatory should be  non transparent ( the bit next to the house wall) again to limit the mid summer overheating of house rooms. So one question is how much roof should be non transparent? .

 

I fancy putting radiators in this space and painting them black to harness the sun and uplift the DHW temp somewhat, or I could put PV panels and not have the problem of dealing with cooked solar panels. I need to decide soonish so I can install pipes or wiring through the build in the near future ready for connecting next year.

 

i am away on site for the week ( with no broadband) so I will be able to respond on Friday.  Discuss and enjoy ?.

[Crofter]

I once stayed for a few days in a self built 'eco house' where thr south facing conservatory had a rammed earth brick wall separating it from the rest of the house. The conservatory had louvred opening windows to help remove excess heat. The idea was that the bricks would heat up through the day and then slowly release that heat into the main body of the house. I only stayed there for a few days and it was snowing so can't really report how well it worked. Especially as the owners made us sleep in a tin shed outside rather than in the house itself. They were a bit weird.

 

Another thought: if you start roofing over your conservatory, it becomes part of the house according to building regs. So even though you are reducing energy loss, you might find that suddenly you have to make big changes to the glazed area and insulation to keep the whole house compliant. Apologies if you are already ahead of me on this one.

 

Third thought: don't put PV *inside* a conservatory! You will lose a percentage of the energy as it passes through the glass. Maybe roof mount them to give extra shading without losing the 'conservatory' status?

[Ferdinand]

21 minutes ago, joe90 said:

As some of you will know I am building a conservatory on the south side of my house some 10 meters long by 2.5 meters deep. Everyone tells me it will overheat and I accept this as a consequence of being able to have a warm sunny space in the shoulder months.

 

Like all well insulated houses my main energy usage will be DHW ( especially in summer) so it seems sensible to try to harness some of that excess heat ( overheating) into my DHW in some way. The house roof is going to have a decent overhang to try to limit mid summer overheating into the rooms on the south side and I thought that the top of the roof of the conservatory should be  non transparent ( the bit next to the house wall) again to limit the mid summer overheating of house rooms. So one question is how much roof should be non transparent? .

 

I fancy putting radiators in this space and painting them black to harness the sun and uplift the DHW temp somewhat, or I could put PV panels and not have the problem of dealing with cooked solar panels. I need to decide soonish so I can install pipes or wiring through the build in the near future ready for connecting next year.

 

i am away on site for the week ( with no broadband) so I will be able to respond on Friday.  Discuss and enjoy ?.

 

Most of that sounds sensible but would it be more efficient to have panels outside and a usable conservatory?

 

You could probably mount PV panels on a separate frame above the conservatory ... or perhaps on the wall above as a Brise-Soleil, which would come out over most of the roof.

 

(Underhill House on GD did this and it is a still one of my favourites.)

 

And could you use one of the anti-solar films to help keep it cool?

 

Ferdinand

 

Edited March 27, 2017 by Ferdinand

[Onoff]

Solar thermal from BEER cans!

 

[Onoff]

 

 

+

 

=

 

QED

[PeterW]

Air source heat pump ..! Use it to draw the heat from the air and will also cool the space too

[joe90]

Peter, I too have an air source heat pump which will heat water and perhaps cool the slab like JSH , are you saying mount it in the conservatory???

[PeterW]

Things like the Earth Save cylinder have a small ASHP in the top and take hot air from the house into the water. Not sure you could put a big ASHP in a conservatory as they shift a lot of air. 

[dogman]

I think Earth save have a retrofit unit 

http://www.earthsaveproducts.com/product/ecocent-energy/

 

 

[Ferdinand]

I'll dip out of this one, because I think the basic concept is mistaken, as to my eye it looks like accepting a compromised - perhaps unusable - conservatory and trying to put a sticky plaster on it.  People should not be living in a conservatory repurposed as an inefficient air to water heat exchanger.

 

The better way is to catch it on the roof, and keep the living and heat gain separate. Make it a faux sun lounge which is suitable for summer use with a separate roof or canopy or put the conservatory where it belongs .. on the N side .. and have solar panels.

 

But do you have a calculation of how much water can be heated by air extracted from a conservatory as a sanity check?

 

According to my information x volume of water raised by one degree stores the same amount of extra heat as approx 3000x volume of air raised by the same one degree, and the volume of your conservatory is approx 60 cubic m, of which perhaps 12 cubic m are above head height, but there are many other factors involved, from insolation to efficiency of your heat capture process, at which point I decided I am offered more personal utility by going to bed.

 

Though crudely that implies with 20% system heat collection efficiency you will need to reduce the temperature of all the air in your conservatory above head height say 10 cubic m by approx 15C in order to add 1C to the temperature of a 100l bath of water, ignoring running costs.

 

Does @JSHarris  have a suitable spreadsheet :-)

 

Sorry for the ramble.

 

Ferdinand

 

Edited March 28, 2017 by Ferdinand

[SteamyTea]

You may be able to get a small air to water heat pump that can suck out a few kWhs of energy at the right temperature, and if it can modulate low enough, could be used to control the overall temperature in the conservatory.

It does mean that you will be having a few tonnes of outside air coming into the conservatory every day, which may have an impact on the rest of the house.

 

I don't think there is a simple and cheap DIY method to do it.  You may be better making the overhang out of PV modules or some ST panels and just use the electricity/thermal energy to heat the water in a cylinder and contribute to the ASHP running (make/buy a diverter).

 

You will possibly find that your overall heating costs are pretty low, say less than £250/year.  Water will probably be half that, so with those low levels of spend, the concept of return on investment becomes pointless (I spend more on going for a coffee each week than I do on my energy bills).

Edited March 28, 2017 by SteamyTea

[Gone West]

In the summer most of the heat will enter the conservatory through the roof. If it is fully covered with 25m2 plus possible overhang of PVs that will reduce overheating in the summer. Automatic louvre windows should reduce overheating further if necessary. In the shoulder months the sun will still shine through the windows to keep the conservatory warm.

[joe90]

8 hours ago, Ferdinand said:

I'll dip out of this one, because I think the basic concept is mistaken, as to my eye it looks like accepting a compromised - perhaps unusable - conservatory and trying to put a sticky plaster on it.  People should not be living in a conservatory repurposed as an inefficient air to water heat exchanger.

 

The better way is to catch it on the roof, and keep the living and heat gain separate. Make it a faux sun lounge which is suitable for summer use with a separate roof or canopy or put the conservatory where it belongs .. on the N side .. and have solar panels.

 

But do you have a calculation of how much water can be heated by air extracted from a conservatory as a sanity check?

 

According to my information x volume of water raised by one degree stores the same amount of extra heat as approx 3000x volume of air raised by the same one degree, and the volume of your conservatory is approx 60 cubic m, of which perhaps 12 cubic m are above head height, but there are many other factors involved, from insolation to efficiency of your heat capture process, at which point I decided I am offered more personal utility by going to bed.

 

Though crudely that implies with 20% system heat collection efficiency you will need to reduce the temperature of all the air in your conservatory above head height say 10 cubic m by approx 15C in order to add 1C to the temperature of a 100l bath of water, ignoring running costs.

 

Does @JSHarris  have a suitable spreadsheet :-)

 

Sorry for the ramble.

 

Ferdinand

Interesting as I have a very good friend who has a large conservatory on the south side of his house and he uses it all year with a little shading, I currently have a conservatory on the .North side of our house and whilst a bright  place to sit when it's very warm it's virtually unusable most of the year.

 

As it's a new build there is going to be no sticking plasters anywhere but with a little forethought if placing some pipes or cables in appropriate places I can later on harvest some solar gain then all will be good.

 

I will not have solar panels on my cottage roof as I think they look will spoil it's athetics, if I do have solar it will be on my workshop roof. And maybe a few on the conservatory if they can be made to blend in as shading ( dual purpose).

 

i am more interested in how much shading I need to reduce summer overheat in the rooms adjacent to the conservatory but leave enough glass to give winter low light into the back of the house.

 

right, I am now off to site for a few days.

 

 

 

 

 

 

 

 

[Ferdinand]

55 minutes ago, joe90 said:

Interesting as I have a very good friend who has a large conservatory on the south side of his house and he uses it all year with a little shading, I currently have a conservatory on the .North side of our house and whilst a bright  place to sit when it's very warm it's virtually unusable most of the year.

 

As it's a new build there is going to be no sticking plasters anywhere but with a little forethought if placing some pipes or cables in appropriate places I can later on harvest some solar gain then all will be good.

 

I will not have solar panels on my cottage roof as I think they look will spoil it's athetics, if I do have solar it will be on my workshop roof. And maybe a few on the conservatory if they can be made to blend in as shading ( dual purpose).

 

i am more interested in how much shading I need to reduce summer overheat in the rooms adjacent to the conservatory but leave enough glass to give winter low light into the back of the house.

 

right, I am now off to site for a few days.

 

Cheers for the reply.

 

Leaving aside my own slightly tangential opinions, I think that protective films applied to the roof dg units may have potential, or perhaps an oversailing awning - but that is less aesthetically appealing.

 

Jeremy specifically mentioned the "too transparemt to notice" brand he uses on the bedroom window here:

 

Quote

We have two different films, as we also wanted to add some privacy at the front.  Both are equally effective at reducing solar gain, but the almost clear film on the bedroom windows is clear enough that you'd not notice it's there from inside looking out.  The films are both made by Solargard : http://www.solargard.com/uk/

Ferdinand.

 

Edited March 28, 2017 by Ferdinand

[Nickfromwales]

Anyone have any input on this ? Looks good, but may need to sell a kidney ? Discuss please ( @JSHarris I'm sure you've mentioned transparent / semi-transparent Pv panels for the side of your house ? ). 

 

@joe90, You'll remove the excess heat in your conservatory pretty damn quickly, so I think you'll soon see any attempt to capture that will be non cost effective IMHO. Anything you do capture would probably still not even cover depreciation and ongoing maintenance / future replacment of the heat recovery equipment, and would be damn obtrusive / ugly too. 

Id recommend some openers with electromechanical actuators linked to a room stat to just dump excess heat to atmosphere. That would stop the early morning / midday overheat from massively affecting the rest of the house, but it would just be a guess as to what it would do to the mvhr. Will this room have doors to isolate it from the adjoining room?

[Jeremy Harris]

I tried to get prices for Polysolar glazing about a year ago, as I want to build a covered walkway at the East end of our house, so we can walk down to the wheelie bin area from the back door without getting wet.  I know that we get more sun on that wall than we do anywhere else, as the cladding has weathered far more there than elsewhere, so having translucent solar panels as the roofing seemed a good idea.  Sadly, getting a price for a one-off project seemed impossible, as no one seems to sell just the panels.  My plan was to use the panels with a standard alloy bar glazing system, similar to the sort of stuff used to make conservatories.

[SteamyTea]

I think the easiest and cheapest option to fit PV would be to make up your own frame to take regular modules.

[joe90]

Thanks guys for all your input, all good info and I take the point, apart from film to protect, that harvesting is not worth the effort apart from maybe P.V.Panels on the shading part.  On that subject, how far do people think I should extend the shading out from back wall of the house. Or to put it another way ( as my dimensions are not known yet) at what sun angle should the shading start protecting the house?.