I am in desperate need for advice/help

In April I had a Hot water Solar panel system installed. The contract was for 2 panels and only 1 was installed. The company is using the small print stating that they can change the specifications.

The average temperature readings at the collector have been:
May … 38c
June … 41c
July … 37c

And the highest temperature recorded in the hot water tank is 43c (5th June)

Numerous calls etc to the company and they then sent an “independent” inspector to do a report on the installation.

Inspector stated that the pipe insulation needs to be upgraded to 19mm thickness (at present is Armaflex 15mm)

And that increasing the Pressure from the present 1.5bar to 3bar would raise the temperature in the collector to a satisfactory level.

The company is using this report to refuse to install the 2nd panel

The specifications of the system are:

210 litre dual coil hot water tank, with small immersion top-up
The collector positioned 19.7metres from the Hot water tank,
Type of collector is Sunpower Solar Water Heater Co., Ltd SPA-58-1800-18-C (3.12m²).
Roof position Azimuth: -50°.
Latitude: 50.92 °, Longitude: 1.42 °

Am in Hampshire

Any advice or help would be greatly appreciated

I can't see how raising the system pressure will increase the temperature. The temperature of the collector depends on three things, the amount of heat in from the sun and the heat out, i.e. the water flow conducting the heat away and heat leaking away due to poor insulation.
If you want a higher temperature, reduce the water flow. The problem with the tank temperature is that when you use hot water, its replaced with cold. So without knowing your hot water useage its not possible to make any judgement on this set up. The insulation on your (excessive) pipe length could will make a significant difference to the performance. I do not think that 19mm is at all impressive. it would be interesting to know the diam of these pipes (flow and return). If your pipes are 22mm then their surface area is 2.64 sq. m, if 15mm then about 15/22 X 2.64~1.6 sq.m, I would expect at least 2" of insulation on them as they are comparable to the the collector it self.
Frank

Thank you for replies

Water usage is minimal, 3 showers in the morning and washing up in the evening, pipework is all 22mm.

I have reduced the flow which has helped. The figures above are with reduced flow.

I have now been informed that I have to have my own report done on the system, If anyone can help please get in touch.

Am in the GU32 area

thanks

Heat loss through the 22mm pipe is approx 7c

I removed the heat sensor from the tank and strapped it to pipe which went into the tank. Then compared it to the Collector temperature.

Knowing the heat loss I then reset the perameters so that the pump came on at +16 and off at +10c

Doing this stopped the pump from removing heat from the Hot water tank

Thanks Chuckey

I can now see having 22mm pipe is a serious disadvantage. Unfortunately a lot of work has been done in the loft which would make it difficult to replace the pipe work with 15mm copper. (Load bearing steels and stud work now obscure the solar pipe work)
Maybe to use 15mm pre-insulated,stainless steel on a roll would solve the problem of heat loss.

But would I still need another panel to give enough heat to heat 210 ltr tank?

Yes it is, but so far have been unable to find anyone who is prepared to give a report on the system.

Chuckey has given brilliant advice and knowledge. and I am starting to understand why my system is not working properly.

in the mean time I am still after a written report so that the company will put it right

Hi Onceaknight...

I've probably misunderstood, but when you say the azimuth is -50, what exactly do you mean? as my understanding on that would be that you mean the panels are facing northwest (or northeast if the '-' was just a dash rather than a minus), which essentially means that other than last thing in the evening when the sun is weakest, your panels will only be absorbing heat from diffuse radiation - ie it will only get direct sunlight for an hour or so a day, the rest of the time it's just working off the light reflected from the clouds etc.

If I've got this right, then there's no way anyone should ever be installing panels at this angle in this country - well at least not without pointing out this issue to the customer, and IMO making them sign something specific in the contract to show that they'd been told the location was unsuitable, but wanted to do the installation anyway.

Also a 40 metre pipe run (return) from tank to collector, in 22mm pipe for one panel I'd think would be an utterly stupid set up - guidance is to have the panel as close to the tank as possible to minimise heatloss from the pipes. 22mm pipe = 0.32 litres per metre of pipe, meaning over 12 litres of water in the pipe between collector and tank, and probably around 2 litres in the collector and 1.5 -2 litres in the coil in the tank... ie the water spends 3 times as long in the pipes as it does in the tank and collector combined, or 6 times as long in the pipes as it does in the collector, and obviously all the time it's sat in the pipes it's losing temperature.

They've probably also put the pump at too high a speed due to the volume of water involved, meaning that it will be wizzing through the collector too fast to heat up properly. If the original spec was for 2 panels, chances are they've used the same pump at the same setting for one panel as they were going to for 2, so the waters going through the panel too fast to heat up enough.

and then they've only supplied 2 panels when they specc'd 2 panels. The only way this is possibly acceptable is if the total collector area is the same between the 2 panels - ie. the panel installed is twice as big as the 2 panels originally specced.

there's also no way that increasing the pressure from 1.5 bar to 3 bar will do anything to increase the temperature - pressure obviously can make a difference to the temperature water can take before reaching boiling point, but makes sod all difference at the 40-60 degree temperature range. You should have a look at your manual to see what pressure it recommends for the collectors, but I think I'd be right in saying that most systems actually have a pressure relief valve set at 3 bar, meaning that if you set the pressure at 3 bar when the system is cold, the pressure relief valve will be going off constantly when the system is hot until the pressure falls back to a more acceptable pressure. this is a particularly stupid thing to be telling someone to do in a system that's got in the region of 14 litres of water in it, meaning that if you wacked the pressure upto 3bar, and then ever did actually get some heat in the system you'd end up with a good cup full of water coming out of your pressure release valve.


basically, this looks like a trading standards / small claims court job to me, unless you specifically demanded they installed you the system in this way, and ignored their warnings... does depend on exactly what was specified in the contract I suppose though in terms of the 2 panels thing... meantime, just see if you can find the pump and give it a try with the pump on a slower speed, just in case this sorts it to some extent.

Actually changing the pipe size _is_ a good idea for improved efficiency. 22mm pipe for a small system like this (18X58mm tubes) is a major source of losses, as explained above. It will work, but not particularly well. New installs from people in the know are mostly done with 10mm pipe, which is fine unless you have long pipe runs or a large area of panels, or a very low-power pump. As you have 40m of pipe it's worth doing the sums to check - you might need some 15mm, depending on which pump you have. See http://www.navitron.org.uk/pmwiki/pmwiki.php?n=Main.PipeSizingCalculations for the details

The significant thing is the reduction in volume of 'dead' water in the pipes from 13.3 litres (40m or 22mm pipe) to 0.7 litres.(40m of 10mm pipe).
As the manifold only contains about 1.5l you can see that this is significant, especially in the UK climate where intermittent pump operation is common. The corresponding higher flow-rate also matters, as there is much less residency time between panel and heat-exchanger during which heat is being lost.

I absolutely agree that decent insulation on the pipes is very important too. The more the better, but with low-volume pipework, the insulation becomes a less significant a factor in overall efficiency. A 40m 22mm pipe single panel system will be pretty poor on anything other than a good hot cloudless day.

I'm with Wookey and the raft of professional/experienced installers 10mm for this panel size would be much better. Insulate like a mad insulating fetishist but main problem is that his panel size is too small for the volume of water you are trying to heat. I have 30 x 47 mm tubes (roughly equivalent to 20 x 58) connected to a 210l DPS heat store. In order to have been off grid for hot water this summer I would have needed up to 60 X 47 tubes. OK so heat store need to be kept a bit hotter & mine is a combi store (does heating too) so lots of pumps, pipework & bosses to lose heat (about 3 degrees in 10 hours) but the basics are much the same.

Get more tubes, if the company were going to fit 36 x 58 then that sounds pretty much on the money (although you will need a heat dump for when El ninia stops sodding about with global warming).

S.

Sounds good but there is more to go wrong at the end of the day.

Wookeys side arm stratification dooohicky is the way to go (or a commercial version) if you ask me, but you need big enough cahoolies (collector area) in your system to match you needs in the first place.

S.

Ed davies, if the pipes do not loose heat, then the next time the sun shines, the (old) hot water in the pipe heats the tank, followed (13l later) by the latest batch of hot water from the collector?. Also the return to the collector is at a higher temperature.
(just thought of this!)
Frank

Posted By: chuckeyEd davies, if the pipes do not loose heat, ...

If.

1 tube to 4.3l a (clearly) good ratio for the sort of weather we have been having (and way higher than the Navitron standard recommendation) - I would have thought it would have done better than that but good enough in any case I suppose.

Hope he has a heat dump circuit for when we get back to mad summers!

S.

The sytem does have a heat dump rad...which only lets the Cyl get to 77Degrees...looking through the logs the highest temp was 84 degrees at the collector..so I guess the dump to the Rad works