Calling All Solar Heating Experts

Calling All Solar Heating Experts

Author
Discussion

Supernova190188

Original Poster:

887 posts

138 months

Wednesday 27th August 2014
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I'm not sure if it's either simply the time of year or whether I have actually changed something on the control panel on the solar hot water heating control panel. I was messing about with the control panel a couple of weeks back, flicking through the options etc, however now we don't seem to be getting hot water through the taps, doesn't seem to actually be doing anything. Is this due to the time of year and temperature decreasing - although I'm sure it doesn't matter that much on solar panels as I thought they rely more on light than temperature.
As I look at it at the minute, the settings on the Velux control panel are:
Red Dial - 30c
Blue Dial - 25c
Pressure - around 2 bar
Col - 22.7c
tst - 35.1c
53 - 36c
n % - 0
h P set - 8022

On this panel are 4 pipes - 2 out the right hand side and 2 going from the top , all these pipes are cold to touch , and 1 of the ones going out the top , the left most one is copper and has a red box on which says solar on it - this is warm to touch but the pipes are cold.

If this means anything to anybody as it may as well be in Chinese to me? Any help would be appreciated to stop the missus moaning about the water being lukewarm or cold!

Rickyy

6,618 posts

218 months

Wednesday 27th August 2014
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If the collector temp is lower than the cylinder temperature, the pump won't operate.

On the Worcester system I think the panels have to be 8 degrees warmer than the cylinder before the pump operates. Although you can adjust this in the settings menu.

Not sure what system you have, but you should be able to manually switch on the pump to check that it's working.

They do work more on light than temperature, but they do need direct sunlight.

Paul Drawmer

4,865 posts

266 months

Wednesday 27th August 2014
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Our solar thermal system will be supplying 95% of our domestic hot water for several more weeks yet.

The heat from the solar panel is transferred to your hot water storage by the circulation pump.

The controller monitors the temp at the collector (panel) and at solar coil in the tank.
When the temp at the panel is sufficiently higher than the coil, the pump switches on to move the fluid round between the panel and tank, transferring the heat and heating the tank whilst cooling the coil. When the temperatures fall below the preset activation difference. the pump stops. If you draw off no water during a sunny day, the temperatures in the both the tank and panel will steadily rise as heat is transferred.

The switch on and off temperature deltas need to be adjusted to get the greatest heat transfer. Each system is different, but for example, my pump will switch on at 13 degrees difference, and off at 8. If your 'off' is too near or greater than the 'on' no heat will get transferred.

There will probably be a limit temp to prevent the pump getting too hot in the event of malfunction. If this gets set too low, then the system won't work. For example if the limit has been set to 30C - you wont get hot water.

Not knowing your system (red dial blue dial mean nothing to me) I can't be more specific.

Supernova190188

Original Poster:

887 posts

138 months

Friday 29th August 2014
quotequote all
The system is a velux TFF 200 if you know it ? I haven't seen the collector temp higher than either internal tank temp recently anyway , not sure if it is during the warmest part of the day. I did notice on the side of the tank, a white plastic box , seems to be a thermostat of some sort, set at 60c, range from 30-90. This was hanging down a bit , as if it's been knocked, so could this affect it at all?
Cheers

Paul Drawmer

4,865 posts

266 months

Friday 29th August 2014
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I googled your system and the pdf instruction sheet is the first find. There's a lot to it, but the solar control instructions are all there in section 3.

Murph7355

37,651 posts

255 months

Saturday 30th August 2014
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From the figures you've given, if it's anything like my (Rayotec) system then it won't be operating as the collector temp is lower than the tank temps.

I've half considered removing mine as I'm far from convinced that it's worth having the ugly things on the roof (system was installed by the previous owners).

Most of our hot water use is first thing in the morning (0600ish) with a small bath amount in the evening (kid's bath). Even in summer I'm not convinced the system is able to give a tank full of hot water during the time it's most needed, so the boiler often fires.

On top of that we've been in our place for 3.5yrs and had to have a call out twice - first time due to a leaking joint (apparently not uncommon as the fluid used can cause issues) and the second time due to a suspected leak or the system fluid boiling so it needed topping up. (If the tank water remains hotter than the maximum set for too long there's a safety bleed off to prevent damage to the panels - in the middle of summer when the sun's at its hottest you rarely want a boiling hot shower so logically the amount of times this is likely to happen increases!).

It's cost us more in servicing than I think it's saved in oil.

These systems are a nice idea , but particularly in this country I think they're a very flawed one, and for anyone paying top whack for an install I simply can't see the payback being remotely sensible.

Paul Drawmer

4,865 posts

266 months

Saturday 30th August 2014
quotequote all
Solar thermal systems do work. Ours supplies nearly all our domestic hot water between May and end September. In terms of cost/payback I agree that if you have to pay someone else to put it in, and you have a modern gas boiler, then the payback time may be longer than makes financial sense.

If you already have one, or can install it yourself, then it's well worth it. It does need understanding how to get the best out of it.

Our water tank is a tall thin 210L (That's 2X the size of a std tank) We regularly get 210l of water at over 60C during the year.

Solar thermal systems do need to be managed in respect of their use, and the user needs to know how to set the system up. Our system has been in for 5 years and has not needed any attention.

Perik Omo

1,883 posts

147 months

Saturday 30th August 2014
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Same here. We also have a 200l tank and two panels on the roof and has worked very well and saved us a fortune as we have no gas here and all hot water would have had to be by immersion heater. The system has worked very well in summer and winter and has had to be "topped up" twice since it was installed in 2007. Our system was set up by the installers and we have never had to touch it apart from checking the temps of the panel and the tank, normally do this if we have had a few overcast days and looks like the system needs a boost from the built in immersion.

ARH

1,222 posts

238 months

Saturday 30th August 2014
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My solar thermal works well, this time of year I barely use any lpg to heat water. Just checked my 210 litre tank this morning and it is at 32 degrees and that is after a dull and rainy day yesterday It was installed by the previous owner about ten years ago. I have had no problems with it.

Supernova190188

Original Poster:

887 posts

138 months

Saturday 30th August 2014
quotequote all
Now I thought I'd whack the boiler on to heat the water up , however that won't bloody come on now, was working last night fine. No lights on it at all , fuse box is fine! Bloody things!!

Supernova190188

Original Poster:

887 posts

138 months

Saturday 30th August 2014
quotequote all
Boiler is now working , I'm wondering after having a poke around whether it could be anything to do with a blocked pipe perhaps ? Now the boiler is on there is a water pipe going into the water tank , it goes past a tap marked 'coil insulator in', then round a 90 degree left bend and 3-4 inches later round a right hand bend, however this water pipe is very hot to touch all the way up to the first bend, but then the pipe is only lukewarm on the next bend , literally 3-4 inches later , this piping then hits a junction with a big red box simply marked 'hot water'. There is a pipe below too that does the same, which has a 'coil insulator out' tap on it. Is a blocked pipe a possibility ? seems unlikely that both pipes would be blocked.

dickymint

24,101 posts

257 months

Saturday 30th August 2014
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You have offended the Sun Gods and need to sacrifice a few OAP's

Paul Drawmer

4,865 posts

266 months

Sunday 31st August 2014
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dickymint said:
You have offended the Sun Gods and need to sacrifice a few OAP's
I am an OAP. What's the point of your post?

dickymint

24,101 posts

257 months

Sunday 31st August 2014
quotequote all
Paul Drawmer said:
dickymint said:
You have offended the Sun Gods and need to sacrifice a few OAP's
I am an OAP. What's the point of your post?
Just my usual dig at anything remotely pro "green" subsidised crap that stinks of FIT paid for by those that can ill afford it on their energy bills..... especially OAP's less fortunate than yourself? But I'm guessing that you've been around these forums long enough to realise my point anyway?

Murph7355

37,651 posts

255 months

Sunday 31st August 2014
quotequote all
Paul Drawmer said:
Solar thermal systems do work. Ours supplies nearly all our domestic hot water between May and end September. ...

Our water tank is a tall thin 210L (That's 2X the size of a std tank) We regularly get 210l of water at over 60C during the year....
Out of interest, how many of you are in the house/how much water do you use and typically when?

Also, what's the max temp you have set on the water tank?

(Same Qs to Perik and ARH).

We've got a 250l tank...it was originally set for a max water temp of 95degC (!) but we tried it a couple of times last summer with the boiler off and there wasn't sufficient hot water the next morning for a shower. The tank is lagged, but only with what looks like (to me) a relatively thin blanket.

Paul Drawmer

4,865 posts

266 months

Sunday 31st August 2014
quotequote all
dickymint said:
Just my usual dig at anything remotely pro "green" subsidised crap that stinks of FIT paid for by those that can ill afford it on their energy bills..... especially OAP's less fortunate than yourself? But I'm guessing that you've been around these forums long enough to realise my point anyway?
Solar thermal systems do not attract a FIT payment. Some later systems may have a small RHI, but these early systems are subsidy free you'll no doubt be pleased to hear.

Paul Drawmer

4,865 posts

266 months

Sunday 31st August 2014
quotequote all
Murph7355 said:
Out of interest, how many of you are in the house/how much water do you use and typically when?

Also, what's the max temp you have set on the water tank?

(Same Qs to Perik and ARH).

We've got a 250l tank...it was originally set for a max water temp of 95degC (!) but we tried it a couple of times last summer with the boiler off and there wasn't sufficient hot water the next morning for a shower. The tank is lagged, but only with what looks like (to me) a relatively thin blanket.
As the solar can only heat your water during the day, you may need to work around it in order to get the best benefit from it.

At the end of the heating day, our hot water is as hot as it's going to get from the sun. We do a bit of washing up, but that's all for the evening. There's no point in heating the tank now, just for it to lose heat during the night.
In the morning, the boiler is set to come on, it will heat the top half of the tank to 50C (Most people shower at less than 50C). WE use most of out hot water first thing in the morning - showers etc.
During the day we try not to use hot water as it will give the tank a chance to get up to heat again using the solar heat.

For most of the summer with just two of us here, the boiler doesn't cut in at all, the heat in the tank in the morning is higher than the thermostat is set at. The tank has double thickness foam lagging.

I have set the max temp at 90C. This is to protect the circulation pump from over heating. The max temp setting will only have an effect on the sunniest of days, it won't change your actual hot water temperature.

If you keep drawing off hot water during the day you will get a lot of lukewarm water, but it won't get really hot. To test if it is working, just don't use water during a sunny day and see how much the bottom of your cylinder heats up.

The action of the panel/pump is cyclic. It will turn on as the panel temp rises, then off when that heat is transferred to the tank, then on when the panel next gets heated by the sun. On my system, during the hottest days of the year, the pump is on more than it's off. During a dull day it will turn on for a couple of minutes, and then off for ten.

The secret to getting the most heat out of it, is the set the switch on and switch off differences correctly.

dickymint

24,101 posts

257 months

Sunday 31st August 2014
quotequote all
Paul Drawmer said:
dickymint said:
Just my usual dig at anything remotely pro "green" subsidised crap that stinks of FIT paid for by those that can ill afford it on their energy bills..... especially OAP's less fortunate than yourself? But I'm guessing that you've been around these forums long enough to realise my point anyway?
Solar thermal systems do not attract a FIT payment. Some later systems may have a small RHI, but these early systems are subsidy free you'll no doubt be pleased to hear.
Very pleased to hear you are not getting a subsidy wink

A few posts ago you said "they do work" However a few months ago you said this.........


"However...if you have a modern gas boiler, I doubt if you would be able to prove any actual cost saving, since modern water heating systems are so efficient. I reckon I have made a saving as I did the work myself."

So does it really work and what is your payback time?



Murph7355

37,651 posts

255 months

Monday 1st September 2014
quotequote all
Paul Drawmer said:
...
I have set the max temp at 90C. This is to protect the circulation pump from over heating. The max temp setting will only have an effect on the sunniest of days, it won't change your actual hot water temperature....
Ours does (if I'm reading you correctly).

The max temp on the solar thermal seems to be the thermostat for that "circuit". There's also one for the boiler "circuit" I believe.

So if I set the max temp on the solar system to, say, 90degC, if sunny enough for long enough, the water in the tank will get much hotter than the 'stat the boiler is set for (say 50degC). Which matches experience of running a hot tap in very sunny weather.

On our system there's actually no other way for this to work. The system either keeps circulating to bleed off the heat in the panels to the hot water tank, but hence getting the water hotter and hotter. Or it keeps the tank sensible but then the panels get too hot (and potentially boil the fluid).

The challenge I have in understanding the logic of the system is that it only works to any useful degree when it's really sunny. Which is also when most people don't need anywhere near as much hot water anyway smile

It is no doubt doing "something", but how much difference it's making fiscally is very difficult to ascertain - for me anyway, as the system has always been here and it is not possible to isolate it without causing issues with the system itself.

This year's decent weather is all but gone. For next year I may try better insulation on the tank and isolate the boiler when it starts to get sunny. See if it can cope. I guess another alternative would be to shower etc in the evening...but that's not ideal.

Edited to add - the system pump starts when panel to tank diff is 10degC, and goes off again when it drops to 5degC.

Paul Drawmer

4,865 posts

266 months

Monday 1st September 2014
quotequote all
dickymint said:
Very pleased to hear you are not getting a subsidy wink

A few posts ago you said "they do work" However a few months ago you said this.........


"However...if you have a modern gas boiler, I doubt if you would be able to prove any actual cost saving, since modern water heating systems are so efficient. I reckon I have made a saving as I did the work myself."

So does it really work and what is your payback time?
Yes it really does work - the sun heats most of our hot water for 5 months of the year.

This was what I wrote on another forum on the shortest day of the year in 2009:-
<< Winter update.
It is very cold today. -5 last night and only up to +1 during the day today, with no sun, overcast all day.
Our cold water tank is in the loft, insulated from the cold and sitting on top of the airing cupboard where the hot water tank is.
The water in the cold tank is at about 17C most of the time.

Whenever we heat water by the boiler for use, it has to be raised from 17C to 60C when the cylinder thermostat switches the boiler off.

Today the water at the bottom of tank had been raised by just 6 degrees from 17 to 23C. That's just by the solar panel absorbing infrared and turning it into heat.

Yesterday it was similarly cold, but we had bright sunshine all day (about 8 hours) and in the winter sun on nearly the shortest day, the cold water was raised to 35C.

Even though we now heat our water with gas every day, part of the work is done by the solar panel.

The improved insulation on the tank helps as well. Most days, the boiler heats water for half an hour in the morning only.>>

I've lost my payback calcs, but I think it's as long as ten years at 2009 gas prices. It would be longer if buying a commercially installed system.