Maximum distance between collectors and tank?

[aurumdeus]

Hi,

I'm looking at installing a solar water system for a friend. He runs a B&B so has much higher hot water needs during the summer, and also a very high annual bill for heating and water. So it seems like he's ideally suited for a solar thermal system to at least reduce the costs.

We live in the south of France so we get a huge amount of sun throughout the summer.
The problem is that his house is near a historic building, meaning he isn't allowed to install panels on his roof, and also there is a line of trees on the road at the front os his property that put the house and nearby garden in shade for most of the day.

There is a place in the garden where collectors could be installed that will have sun right through the day, even in winter. However it's about 20 metres from the house, and probably 35 metres from where the tank is by the time it's gone round corners etc. I understand that greater distances lead to a less efficient system.

I've done a lot of searching online but I can't find anything specific about what distances are viable, and what aren't. The pipes will be buried under the garden so it would be easy to heavily insulate them in order to conserve as much heat as possible.

Does anyone have any input on this? Would a pipeline of that length still be worth installing?

Many thanks in advance!

 

[SparkyChick]

I think you may have been better signing up for the plumbing forum, not the electrical one, however if I was to hazard a guess (bearing in mind, I don't work with the wet stuff unless it's to make sure things are safe after a flooding) it all depends on how well insulated the return pipes from the collectors are.

Wrap them in thin cloth and your losses are going to be high, smother them in good insulation and paint them black so they absorb heat from the outside to minimise the temperature gradient and you'll probably be good (the last part about painting them to minimise the temperature gradient... that's an out and out guess based on my limited understanding of thermodynamics)

 

[mattg4321]

Or install PV panels and use them to power immersion heaters.

I don't fit either but it might be worth looking at PV. I was under the impression solar thermal had pretty much died a death.

 

[aurumdeus]

mattg4321, I'd thought about the option of using PV, but the panels are more expensive and far lower efficiency. So it would end up being far more expensive and providing less of the needed hot water, rendering the system un viable.

I will have a look at that plumbing forum, thank you SparkyChic.
There i a bit of an absence of forums for solar thermal, and this subsection of the electrical one popped up when I did a google search so I thought I'd give it a shot.

I can potentially bury the pipelines on something like 100mm waste pipe filled with blown insulation or fibreglass which I think would deal with any problematic heat losses. It's frustrating that there is so few resources available for solar thermal, while it's so easy to calculate voltage drops and wire diameters for PV.
I understand the reasons for each, but that doesn't stop it being annoying!

I'll see what the plumbers can come up with. Thanks for the input.

 

[Worcester]

There are LOTS of control and safety issues to consider when installing a solar thermal system. You can't soft solder for instance. You can't use normal flexible heat main, you'll probably need to use pipework similar to this:
50m will only set you back about £20/m plus VAT plus delivery
Flexipipe 2 in 2 insulated DN25 - https://www.seconsolar.com/flexipipe-2-in-2-insulated-dn25-306-p.asp

Some commercial systems have similar pipe lengths, that is not necessarily the issue.
Insulation is critical and temperatures of up to 170°C ARE the issue.

So, the key things are safety, heat and hydraulic losses.
Small pipe, high speed, possibly lesser thermodynamic losses, higher hydraulic losses, greater pumping costs.
Large pipe, lower flow speeds, higher thermodynamic losses, lower pumping losses.

 

[aurumdeus]

Thank you Worchester, that's good to know. I didn't realise that they get quite that hot! I will continue researching what would be needed for piping etc. It's good to know that the system is potentially viable, if done correctly.

 

[SpecialistEnergy]

20 metre run is not that unusual - Worcester has it right in that you would probably end up using DN25 stainless pipe as your best option. If you can bury it 1 mtr down it is likely to stay above 10 degrees even through winter, and you could even add extra insulation if you are so minded. As soon as the pipe comes above ground you can convert the more expensive DN25 pipe back to copper.

If you are looking for an installer I will throw my hat in the ring! 15 years experience : )

 

[aurumdeus]

Thanks for the info SpecialistEnergy. I would be looking at 30-35 metres run most likely. Possibly less, apparently there is another spot that gets a decent amount of sun as well that's a bit closer. I'm not in the country at the moment so I'll have to investigate and measure when I get back.

So copper can be used as long as it's with compression fittings not solder, otherwise it's the steel pipe. Insulation is cheap, so if it increases efficiency for a minor cost then I'm all for it. Regarding installation, I live in the south of France so that' quite a journey!
I'm also hoping to do it DIY to keep costs down, and learn how the whole thing works. I will of course be careful...

 

[mydigitalhome]

Suggest go to Veidian Solar and they will sort you out. Really good and very helpful. I specify them in Gibraltar with great results.

 

[SpecialistEnergy]

Using solder fittings was pretty common years ago but got outlawed in the MCS regs I believe. I think the concern was excess flux not getting flushed out and reacting with the glycol - can't say I ever saw any damage to systems because of this myself... I certainly wouldn't object to using solder on a fitting or two down near the cylinder where the temperatures are a lot lower