Rogue solar thermal set-up

[Tractor123]

Hi - first post but thought it was the right place to canvas opinion as I always find myself on here when doing various DIY jobs!

I’ve just moved into a house with what I thought was a functioning solar thermal set up. I had no history of the set up when I got the house as the former owner had passed away, and I also had never even seen a set up before so am a complete novice when it comes to solar thermal. The pressure gauge on the system was reading zero and rose slightly when the sun came out and the system started circulating. As such I called a local solar company to come and have a look. He wasn’t willing to do anything to it given the incorrect spec of the set up.

The main problems are:
- Normal central heating pump
- Normal expansion vessel
- No flush/fill valve
- 15mm pipe from the HW cylinder to the pump and part way to the collector, then 10mm for the remainder.
- No pumping station

I think basically my options are
1. Drain it down and turn it off
2. Fit a flush/fill valve, hire a pump and have a go at flushing and refilling it and just let it run until it packs up completely.
3. Buy a solar rated pump/expansion vessel and upgrade the piping to 22mm throughout.

Obviously the costs increase at each level so I’m just wondering what people’s thoughts are and whether anyone has come across anything similar! I’ve added a few pictures but if anyone wants specifics let me know!

Thanks in advance!

 

[StephenStephen]

I'm wondering if he was a solar thermal specialist, or more familiar with PV.

If I were you, I'd be tempted to get a second opinion from a heating engineer.
I would have thought that it may well have been working ok as it is, before the previous owner died.
Have you looked online for a Navitron TDC 3 manual?

 

[Tractor123]

He was an electrical engineer. No idea whether he dabbled with plumbing but there are a few other quirky things in this house! It's a 3 zone system with all the valves, pump and wiring centre conveniently located under floorboards beneath our freshly laid carpets!

Yes it does appear to circulate when the temperature on the roof is sufficient. I have had a look in the manual and it seems to say basically once it's commissioned leave it in auto and that does seem to work.

A second opinion is a good idea. The concerns the initial guy raise were the pump and expansion vessel not being rated to the right temperature that a solar system can run at. Also there is just the one valve that he could find so flushing isn't really possible.

 

[Johntheo5]

There is still a little pressure in the system, you may just have lost air out of the EV, suggest getting a pump, attach it to the schrader valve and pump it up until the pressure reaches ~ 1.5 bar (water end) or stops rising, if it reaches 1.5bar, you are back in business, if not, reduce the pressure back down to its original (now) pressure and just hire a pump and pump in say ~ 3 to 5L of solar fluid, you can buy this, certainly in 10L containers, if not 5L.

Have you a Flat Plate or Evacuated Tube(s) Array?.

 

[Tractor123]

Yes that's a job I'm planning to do today. Will report back if it works.

It's evacuated tube - I've attached an image but it's taken from the road round the corner on my phone so not the most detailed!

 

[Johntheo5]

The problem with solar system fluid is that it degrades and becomes like treacle if the system stagnates very often, ETubes can get up to 250C, if the system protection system has been set up properly then the pump should stop circulating at ~ 110C, the fluid in the array is then blown down into the expansion vessel and will/should return when the system cools back down in the evening.
It would be wise to try and gret a few drops of the existing fluid, if its non viscous and not very dark in colour then probably OK. Anyhow you can just pump in your 5L or so, if the system performs OK then you can allways drain the whole system down and renew the fluid.

 

[ajstoneservices]

Your solar "expert" is one of the recent entrants to renewables who learnt all he knows on a 2 day course. The "book" says it should be installed using expensive components. If it doesn't use them it is **** and will fail very quickly. Well I would be willing to bet any and almost every system installed the way yours has been installed will last longer and give better service than the "book" installed kit.

That Navitron system is a good bit of kit that could be bought back into life very quickly and will continue to give good service for years to come. Starting by raising the pressure. We used to use an adapted garden sprayer for that.

The main problems are:
- Normal central heating pump
- Normal expansion vessel
- No flush/fill valve
- 15mm pipe from the HW cylinder to the pump and part way to the collector, then 10mm for the remainder.
- No pumping station

Nothing wrong with using a central heating pump.
Nothing wrong with using that expansion vessel.
You could fit a fill/flushing valve but you don't need to.
I did a solar thermal course at Worcester Bosch back in 2005 where I was told we had to use 22mm pipe. They were wrong then and it is wrong now. I only ever used it on large systems once I realised it was a very poor choice in a system such as yours. 10mm pipe is perfect for your system.
Pumping stations have been a major failure in many of the system I have serviced/repaired.

A recent example


Edit: I wouldn't add propylene glycol to the system at this stage. You need to know why it has lost pressure first so just top it up with water. The TDC has a frost protection setting.

 

[Tractor123]

Thanks for that - reassuring at least that the whole system isn’t just condemned then like the engineer who visited said.

I inflated the expansion vessel to 1.5 bar but no move from the pressure gauge, so I released it back.

I also drained some fluid out of the filling port and very little came out. I’ve attached a picture - it looks like urine but smells like antifreeze which I’m hoping is a good sign! Would it have been the pink fluid that I’ve seen online discoloured or is there a yellow version too?

I also operated the pressure relief valve and nothing came through the tundish. I ran the pump and tried to operate it again and a small amount flowed slowly - I was expecting more to be honest but I guess with not enough fluid in the system and a low pressure vessel that could be expected?

Thanks for all the help by the way - very grateful!

 

[ajstoneservices]

There is a good chance your system was filled with fernox alphi 11. That is clear hen new.

What pressure did you leave in the ev. I would have left it at 1bar.
Have you found a high level manual air vent on the system. It might in the roof where the pipework from the collector enters or on the roof. You will need to vent and fill the system.

 

[Johntheo5]

When I self installed my system 14 years ago, I precharged the 18L EV to 1.5 bar and kept filling to 2.0bar, this gave a nice little reserve of 3.L in the EV when cold, it also means the fluids saturation temperature (boiling point) is 133C, a 18L EV with precharge/filling pressures of 1.0/1.5bar will have a reserve of 3.6L and a saturation temperature of 127C, whatever pressures are choosen I would ensure a difference of 0.5bar to give that reserve.

 

[Tractor123]

I managed to rig up a filling loop from the garden hose into the isolation valve and charged both the system and the pressure vessel to 1.5 bar. Managed to do it out adding any air too which is a plus. I forced the pump to circulate for a while and bled from the high level vent a few times before refilling. Seems to have held pressure for the last few hours - will keep an eye on it over the coming days. Luckily the weather is looking quite mild plus I didn’t have to add too much so I don’t think freezing is a huge danger.

Assuming the water pressure and expansion vessel hold what would be a good way of flushing it? Or would it be easier to just drain and refill?

Thanks for all the help so far

 

[Tractor123]

Seems to be holding pressure although it has dropped a little. I need to recheck and see if it’s just the pressure in the expansion vessel or whether I’ve lost some fluid.

Does anyone have any thoughts on how to refill this type of set up (given there is only one port) without adding a fill and flush valve? All the central heating refill pumps you can rent need 2 ports I believe.

 

[Johntheo5]

I re charged a relations system years ago with a 6M circ (old) pump, I cut a hole in the bottom a 10L plastic container and rigged up a connection to the pump, I then reduced the EV (air end) pressure to 0.1bar and maintained it at this 0.1 bar until I had the full charge of 9L in this system pumped in, (obviously venting the system as well where I could) I then kept pumping in more until I got ~ 0.35bar which I think gave me a reserve of ~ 3L in the 18L EV, I then pumped up the air end to 1.5bar, its still working fine ~ 6 years later. Job was made easier using this low head pump because the EV was in the attic and the HW cylinder in the u/stairs airing cupboard.

 

[Tractor123]

I can’t say I’ve got an old pump lying around but I was wondering if one of those drill pumps (pretty cheap on amazon) and a laborious bleed process would work?

 

[Johntheo5]

Yes, give that a go, you should certainly get enough head.