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Solar Thermal Hot Water System


Jen-in-Wellies

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7 hours ago, Jen-in-Wellies said:

Always seems like magic to me. How can this thing possibly get so hot! Who makes the controller you've got?

 

Jen

As you can see.....I soldered copper 'tags' to the copper pipe..and these were then bolted firmly to the aluminium plate...so maximum heat was passed into the pipe.

I sprayed it with matt black thermal paint (Halfords) ....then enclosed it in a box with glass on one side ( the non pipe side )..and roof insulation on the other with a layer of tin foil between the roof insulation and the pipe side..so sun heated the aluminium plate on the matt black painted side...and any that passed through the plate was reflected back.

It worked a treat.

 

I've since sold this boat and removed the 12 volt controller. Its in my garage..languishing..

It has two thermal sensors...one on the tank and one on the roof collector...the unit has a differential controller to stop it pumping your hot water up to the roof should the plate outside be colder.

Edited by Bobbybass
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The house we recently bought has a thermodynamic water heating system.

It's something I'd not heard of before but I gather it basically works like a fridge in reverse.

The panel is tucked away under the eaves on the permanently shady side of the house, never seees the sun, and it heats up a 180L cylinder to 55 degrees.

Now I've got it I'll use it (if I can persuade the scaffolders to replace the panel they knackered). Would I buy the system from scratch? Possibly not. 

Anyhow it may be food for thought...

https://www.greenmatch.co.uk/solar-energy/solar-thermal/thermodynamic-panels

Edited by Boaty Jo
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6 hours ago, Bobbybass said:

I've since sold this boat and removed the 12 volt controller. Its in my garage..languishing..

It has two thermal sensors...one on the tank and one on the roof collector...the unit has a differential controller to stop it pumping your hot water up to the roof should the plate outside be colder.

Who makes it please?

1 hour ago, Boaty Jo said:

The house we recently bought has a thermodynamic water heating system.

It's something I'd not heard of before but I gather it basically works like a fridge in reverse.

The panel is tucked away under the eaves on the permanently shady side of the house, never seees the sun, and it heats up a 180L cylinder to 55 degrees.

Now I've got it I'll use it (if I can persuade the scaffolders to replace the panel they knackered). Would I buy the system from scratch? Possibly not. 

Anyhow it may be food for thought...

https://www.greenmatch.co.uk/solar-energy/solar-thermal/thermodynamic-panels

Could work well on a conventional house, like ground source and water source heat pumps, but a problem off grid, like a boat. It needs an electricity supply to run a compressor. Since fridges and freezers are the largest power consumers on many boats, adding another compressor isn't such a good idea.

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14 hours ago, Jen-in-Wellies said:

Always seems like magic to me. How can this thing possibly get so hot! Who makes the controller you've got?

 

Jen

I'll dig it out of the garage and look... I'm going to whack it on eBay at some point anyway..

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2 minutes ago, Bobbybass said:

I'll dig it out of the garage and look... I'm going to whack it on eBay at some point anyway..

Thanks. Just out of interest you understand. Don't bother if it is a hassle, but if it is going on Ebay anyway...

 

The solder the pipe to a copper plate, then attach to the aluminium is a good idea to get excellent heat transfer. Not something I'd seen before. Copper sheet is expensive and aluminium is cheap, so minimising the copper is sensible.

Edited by Jen-in-Wellies
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1 hour ago, Jen-in-Wellies said:

Who makes it please?

Could work well on a conventional house, like ground source and water source heat pumps, but a problem off grid, like a boat. It needs an electricity supply to run a compressor. 

 

Not necessarily! 

 

The website link is completely devoid of technical details, but they *might* work by the vapour-absorption method of refrigeration (which needs no compressor) rather than vapour-compression. The same was as an absorption fridge.

 

 

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1 hour ago, Mike the Boilerman said:

 

Not necessarily! 

 

The website link is completely devoid of technical details, but they *might* work by the vapour-absorption method of refrigeration (which needs no compressor) rather than vapour-compression. The same was as an absorption fridge.

 

 

 

Or indeed even the adsorbtion principle.

 

https://www.britannica.com/topic/adsorption-chiller

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2 hours ago, Jen-in-Wellies said:

Thanks. Just out of interest you understand. Don't bother if it is a hassle, but if it is going on Ebay anyway...

 

The solder the pipe to a copper plate, then attach to the aluminium is a good idea to get excellent heat transfer. Not something I'd seen before. Copper sheet is expensive and aluminium is cheap, so minimising the copper is sensible.

The copper sheet was not expensive.. it was thin..so thin I could cut it with scissors. 

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On 24/08/2019 at 09:55, Mike the Boilerman said:

 

Not necessarily! 

 

The website link is completely devoid of technical details, but they *might* work by the vapour-absorption method of refrigeration (which needs no compressor) rather than vapour-compression. The same was as an absorption fridge.

 

 

They use a compressor. There's a fair amount of info on t'interwibbly: look at solar assisted heat pumps. Probably of limited use on a boat although one can combine the heat exhanger with a photovoltaic. They might be just the thing for our house though, where ur neighbour's trees make normal solar of limited attraction. (Has anyone got a source of agent orange?)

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  • 1 year later...

An update.

Some time over the next few weeks I'll hopefully start to be able to get a bit of thermal hot water on good days, so it was time to check the system out. The level of liquid in the header tank was topped up and the pump tested. The only problem found is that the Mark 3 sunshine sensor has suffered badly from corrosion after a couple of winters exposed to the outside. I knew this was a risk when I made it. I didn't know what sort of alloy the phototransistor body was made of under the gold plating and it turns out to be iron based and it has experienced a lot of resulting corrosion. There is a now low resistance path across between the collector and emitter, tricking the Arduino in to thinking it is bright and warm all the time.

light-sensor-mk-3.jpg.1a8ccaa1ad204431a46ccca082790fbf.jpg

 

For the next version, the phototransistor needs protecting from the elements. I used a piece of 12mm diameter acrylic rod. This had a hole drilled most of the way through and the top was polished with Brasso. I had a bad attack of brain fade and decided to clean the Brasso off with acetone (nail polish remover). Forgot that acetone does not play nice with acrylic and this was the result:

light-sensor-mk-3-5.jpg.c74322ec92d6a5df6c6710bdc2f7838a.jpg

 

Fortunately I had another piece of acrylic rod left and that was kept well away from any acetone. The new phototransistor was wired up, inserted in to the hole in the rod and sealed in with hot melt glue. The rod was then held in a 20mm cable gland to further protect it and mounted outside. I'll probably have to adjust the triggering light levels in the Arduino to suit the change in sensor, but that will need to wait for a warmer day. The mark 4 sensor below:

light-sensor-mk4.jpg.a0f8407cb92972bcce9a219e3f2700de.jpg

 

Jen

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The new light sensor is doing its thing. It turned on the pump for three or four hours over the middle of the day. It bought the water in the cauliflower from below 30 degrees to over 35 degrees, which for February is amazing. The stove was allowed to go out overnight, so that temperature rise is entirely solar thermal. Hot enough to take a bath, even though it isn't Spring yet and my bath is not due ?. The light sensor is turning off the pump when the sun is hidden by cloud, so it seems to be behaving in a similar fashion to the Mark 3 version. May well be able to get away without adjusting the threshold values on the Arduino.

Jen

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5 minutes ago, Jen-in-Wellies said:

May well be able to get away without adjusting the threshold values on the Arduino.

 

I think I'd be tempted to recalibrate anyway, just to get the maximum free hot water.  The sensor is likely starting the pump later and stopping it earlier with the new cover over it.

 

How did you set the original threshold values?  Trial and error or did you measure light levels or temperature at the collector?

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1 minute ago, TheBiscuits said:

 

I think I'd be tempted to recalibrate anyway, just to get the maximum free hot water.  The sensor is likely starting the pump later and stopping it earlier with the new cover over it.

 

How did you set the original threshold values?  Trial and error or did you measure light levels or temperature at the collector?

Just trial and error. It probably wasn't optimal before and definitely isn't now!

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  • 4 months later...

OK, I said I wasn't going to do anything more to this thing and excepting repairs, that was it, but I couldn't resist. 😀

 

The usual failure mode of the Sureflow and Jabsco water pumps commonly fitted is to start leaking from the pump body. When this happens upstream of the pressure sensor it can continue to leak for a long time as you are not clued in by the pump cycling every so often as the water system depressurises. I've ended up having to pump a lot of water out of the cabin bilge as a result in the past.

 

Someone gave me a couple of very simple water sensors, suitable for Arduino and other PLC's. They are interlaced combs of exposed circuit board tracks, across which a voltage is placed. Any water on the circuit board and the resistance across the combs decreases. The more water, the lower the resistance. They are available for a few pounds. Example. Since it was free and there were still a few unused I/O pins on the Arduino that controls my combined solar controller, calorifier temperature gauge and water tank level gauge, I thought, why not!

 

The sensor was mounted on to an old baking tray, which will sit under the pump, with a bit of Kingspan/Celotex type extruded insulation to damp any vibration. There are three pins on the sensor, 5V power, ground and signal. You don't want to power this thing up continuously as this risks electrochemical corrosion of the circuit board tracks, like a boat on a shore line without a galvanic isolator, or similar. To do this, the 5V in line is powered by a digital output pin, that is energised only when taking a measurement. After testing it with a shorter time of one minute between measurements, I've programmed it to energise for 10ms once an hour. Experiments with measuring the sensor pin values while dipping the sensor in an egg cup of water suggested that 200 out of 1023 as a suitable threshold for the analogue read.

 

I'm not going to put the whole sketch here. If anyone wants to see it, PM me. The LED's on the display show cauliflower temperature for 6 seconds and water gauge level for 3 seconds with a half second gap between each every ten seconds. If a leak from the pump is detected, then during the water gauge 3s display, all four level LED's will light up. This will carry on happening for an hour until the next 10ms measurement. If it is still wet, then it will carry on doing this until hopefully someone notices! All the LED's lighting is a warning. There is a similar thing for the cauliflower being over temperature during the 6s part of the display sequence.

 

There is no real need to have made this. I could just as easily look in the water tank cupboard and see if it is wet!

 

Jen

 

The sensor mounted to the baking tray. Ready for the water pump to sit inside. I should probably drill an overflow hole in the tray near the top to prevent the components at the top of the sensor getting wet.

leak-detector.jpg.fbc7e669cd0b3ef0c6d45c3d18649369.jpg

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If there is a big-enough footprint on your tank, and no obstruction inside, there is an ingenious plumbing fitting called an "Essex Flange" that allows you to make solderless pipe connections to a copper tank without needing access to the inside. I used two myself to fit additional 1" BSP connections to the copper hot water tank in my previous house. They are available in 2 1/2" BSP for fitting immersion heaters,  with models suitable for attachment to the curved tank sides or the ends.

 

I was surprised at the effectiveness of solar-heated hot water when visiting the Centre for Alternative Technology in North Wales  back in 1976. It was on a day in that August's drought: no water for the turbine, no wind for the wind generator, the biogas generator had sprung a leak, but the demonstration solar water heater (an array of old pressed steel radiators) produced remarkably hot water, despite it having been overcast all day. 

 

Edited by Ronaldo47
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  • 9 months later...
On 18/10/2018 at 13:54, Tom and Bex said:

Very interesting to see that Bimble kit (although not cheap). I wonder what panel they use? Can't see it listed separately on their site. Flat plate panels (particularly robust ones) are not common but definitely better suited for boats. 

 

We've installed a thermal panel earlier this year, using a second hand flat panel from eBay just resting on wooden bearers on the roof, this controller, and this pump. All connected using 10mm plastic push fit pipe and fittings from toolstation.

 

Unfortunately we have no spare coil in calorifier, and no immersion heater boss to fit one, so had to plumb it direct. This means we can't use antifreeze, so have to drain down for winter (although the controller has an anti freeze setting that circulates water in freezing conditions - ideal for cold nights in spring/autumn but you lose any remaining hot water).

 

Using push fit plumbing, lever valves, and a waterproof plug for panel sensor, it's quick and easy to, turn pump off, disconnect panel, and remove it (5 mins max). We often remove it when cruising as it's very fragile, and already had one panel broken in Birmingham, that's why I'm interested in alternative panels that may be more durable. All that's left on roof when removed, is a small black box with a plug, and couple 10mm pipe stubs showing. 

 

All in all a very worthwhile investment, particularly this summer! We had tank full of piping hot water most days, even after doing couple loads of laundry. Combined with solar PV we could go for week or more without running heating or engine (except to fill up with water!)

 

Tom

 

Hi Tom,

 

If you're still active on here, I have a few questions!:  How did you plumb yours direct? Does it feed into the calorifier or bypass it? Do you have problems with boiling in summer? Is it less effective outside of the summer months than one that uses a coil would be?

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5 hours ago, Woodfern said:

 

Hi Tom,

 

If you're still active on here, I have a few questions!:  How did you plumb yours direct? Does it feed into the calorifier or bypass it? Do you have problems with boiling in summer? Is it less effective outside of the summer months than one that uses a coil would be?

Calling @Tom and Bex.

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On 11/05/2022 at 10:39, Woodfern said:

 

Hi Tom,

 

If you're still active on here, I have a few questions!:  How did you plumb yours direct? Does it feed into the calorifier or bypass it? Do you have problems with boiling in summer? Is it less effective outside of the summer months than one that uses a coil would be?

Still here occasionally😆

 

I Tee'd into hot feed from top of calorifier with 10mm pipe, and from there into solar pump. Output of solar pump feeds 10mm pipe up to solar panel - feed in one corner, output opposite corner. 10mm pipe then runs from panel back to Tee in cold feed at bottom of calorifier. Pump controlled by solarproject.co.uk controller which is really useful all year anyway as a temperature display to check how much hot water you've got!

 

This set up would only work if there's no non-return valves in the calorifier, as pump wouldn't overcome them. My preference would have been to use a separate coil in the calorifier, but ours didn't have a spare coil, or an immersion boss to fit one.

 

There is some points to be aware of for direct solar hot water. You have to be aware of risk of freezing. We remove ours early to mid autumn, and put it back mid spring when risk of frost has diminished. There's frost protection option on the controller, but this will take any heat in the calorifier and heat the outside air! The other point to be aware of is that the panel, pump, and all piping will be at full water pump pressure. Our panel is fine with this, but worth checking panel can cope with full system pressure. 

 

Overall it works very well, but can waste remaining hot water in tank under certain very limited conditions. 10mm pipe works well, and is well insulated throughout which is quite important to prevent heat loss. Most difficult bit is routing pipes out to roof. Our pipes run along the edge of the roof inside, then through drilled holes in roof and terminate in standard 10mm speedfit connector to enable quick and easy removal and draining of panel for winter. No problem of boiling in summer, we only have 1 panel, but have seen tank temp up to 80°c on very hot sunny days. 

 

Happy to answer any other questions you might have. 

 

Tom

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34 minutes ago, Tom and Bex said:

Still here occasionally😆

 

I Tee'd into hot feed from top of calorifier with 10mm pipe, and from there into solar pump. Output of solar pump feeds 10mm pipe up to solar panel - feed in one corner, output opposite corner. 10mm pipe then runs from panel back to Tee in cold feed at bottom of calorifier. Pump controlled by solarproject.co.uk controller which is really useful all year anyway as a temperature display to check how much hot water you've got!

 

This set up would only work if there's no non-return valves in the calorifier, as pump wouldn't overcome them. My preference would have been to use a separate coil in the calorifier, but ours didn't have a spare coil, or an immersion boss to fit one.

 

There is some points to be aware of for direct solar hot water. You have to be aware of risk of freezing. We remove ours early to mid autumn, and put it back mid spring when risk of frost has diminished. There's frost protection option on the controller, but this will take any heat in the calorifier and heat the outside air! The other point to be aware of is that the panel, pump, and all piping will be at full water pump pressure. Our panel is fine with this, but worth checking panel can cope with full system pressure. 

 

Overall it works very well, but can waste remaining hot water in tank under certain very limited conditions. 10mm pipe works well, and is well insulated throughout which is quite important to prevent heat loss. Most difficult bit is routing pipes out to roof. Our pipes run along the edge of the roof inside, then through drilled holes in roof and terminate in standard 10mm speedfit connector to enable quick and easy removal and draining of panel for winter. No problem of boiling in summer, we only have 1 panel, but have seen tank temp up to 80°c on very hot sunny days. 

 

Happy to answer any other questions you might have. 

 

Tom

 

Thanks so much for this Tom.

 

When there's no sun and the pump is off, what's to stop you drawing cold water from the calorifier's cold feed through the solar when you turn on the hot tap? Also, is there a risk of losing hot water as a result of it siphoning up into the panel and dissipating?

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1 hour ago, Woodfern said:

When there's no sun and the pump is off, what's to stop you drawing cold water from the calorifier's cold feed through the solar when you turn on the hot tap?

Technically nothing i suppose, but water will take path of least resistance, and long runs of 10mm pipe, pump, and panel are much more than the straight 15mm Tee piece! Certainly never noticed any change in heat from the water compared to before. 

 

1 hour ago, Woodfern said:

Also, is there a risk of losing hot water as a result of it siphoning up into the panel and dissipating?

I've never noticed that, but that could be because the pipes run down to the pump that is mounted half way down the tank, before heading up to the roof again. Also, as above, the restrictive pipework probably help. We do lose hot water thermosyhoning to the eberspacher though which I keep meaning to sort at some point😥 

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  • 9 months later...

The sensor that tells the pump to start in my solar hot water system is attached to the 20W solar PV panel that drives the circulation pump. As the sun gets higher in the sky, I'm starting to get a contribution on sunny days again to my hot water. The stove back boiler is still doing most of the work though. Today, I found a novel problem. The PV panel and sunlight sensor were saying it was bright enough outside to be worth starting the pump, yet I was getting no warm water from the thermal panel. I wonder why? 😀

solar-fail.jpg.ca318eced4da82ab8954c8351acd6cca.jpg

Fortunately, there is plenty of propylene glycol antifreeze in the system.

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