Experimental solar hot water heater , comments please ladies and gentlemen......

[boat fan]

Hi everyone .

 

I have been working on an experimental solar hot water heater.

 

The idea is that all the australian sunshine could be put to work ( pre ) - heating water before it enters an electric hot water heater , saving a lot of power consumption.

 

A simple schematic of the principle is shown here :

 

 

This is the proposed solar collector .

 

This is the first attempt fashioned from PVC pipe :

 

 

Four inch PVC pipe painted black and connected in series.

 

 

The water inside the black pipes was too hot to put your hand into after 4 hours at 25 degrees C ambient temperature.

 

The idea is to circulate the water inside the tubes with a solar powered high temperature tolerant pump until it is hot enough for use.

 

This is the pump and solar panel :

 

 

 

 

■ Overview


● DC brushless motor with energy efficiency technology by micro processor
● Soft start at very low in-rush current, good convenient working directly with PV panel
● Durable permanent magnetic rotor/impeller and fine ceramic shaft
● Advanced magnetic drive technology for static-impeller, without any leakage for ever
● Long life brushless pump, ideal life for 30000 hours
● Heavy duty work, can sustain continual 24 hours’ work
● Automatic overload protection
● Automatic dry-running protection
● Automatic polarity protection
● Low or no maintenance
● Low power consumption

Application
The TS5 solar DC pump can be used for most circulation pump applications without connection to the power grid. Highly efficient, the TS5 can be connected directly to a photovoltaic panel and is characterized by its small size, high efficiency, and extreme low power consumption. The long life brushless motor technology provides maintenance free and quiet service life. This pump is perfect for single family home thermal solar systems or any circulation pump application where conventional power is not available.

Soft start-up
The TS5 Solar DC pump has a soft start-up feature which reduces high in-rush current. When the photovoltaic panel provides sufficient power, the pump goes through the alignment phase by turning the rotor into the position required for start-up. The processor then waits until the capacitor is sufficiently charged. This enables a start-up with minimal power (less than two watt). Cycling due to unsuccessful attempts is minimized. Even after prolonged shutdown, the pump will start reliably.



PV operated
For solar system loops, the TS5 pump can be powered directly from a PV panel. The sun comes up, heat builds in the solar hot water panel and at the same time electricity is made in the PV panel. The pump slowly starts with the smallest amount of current and pushes the heated water to the storage tank. It's all too simple and eliminates all controllers, thermostats and sensors.


● Portable power supplies
● Solar water heater
● Hot pump air conditioner
● Air energy water heater
● Hot Water Circulation
● Radiant Floor Heating
● Solar Applications
● Liquid Transfer
● Beer Brewing
● General Purpose Pumping

 

The problem is to prevent over - heating and melting the pipe work

.

Maybe an insulated cover could be hinged over the collector panel when the water is hot enough ?.

 

The other problem is frost . again a cover at night could be used I guess , and finally , what about pressure build up ( suitable relief valve ? )

 

The hot water could be pumped into this little hot water heater .

 

 

Comments would be most welcome , I think this could work , maybe.?

[johnmck]

I had a commercial system fitted to our previous house, manufactured by Viessman? Even with the British weather, worked a treat. All my hot water April/October was sourced from it. Just had to manage your demand a little. Even winter sun generated heat.

 

Mine was the evacuated tube type, plugging into a manifold with no "wet" connection and therefore frost resistant.

 

Our latest house has no immersion tank, so have not repeated this.

 

Yours should be brill in Aus.

[peterboat]

Made for my last boat worked ok water gets very hot! unless the pvc tube is designed for boiling water you might hit problems. I used copper in mine

[I Spartacus]

I have build a few of these but they were parabolic s,I would agree I would use copper or aluminium, they also look

to have a large diameter this will take longer to heat up, you would normally fill the system with anti-freeze to prevent freezing

Using solar for pumping is a good idea. The suns comes out and the pump starts the brighter the sun the faster it pumps.

 

If you can put some aluminium foil or mirror film behind the tubes to reflect the wasted light back onto the tubes. for

controlling it might be better to get a second tank, when first tank is hot pump to the second tank. Apart from that it is looking good

 

Mark

[MtB]

Is this for installation on a boat? If so I imagine it must be a pretty big boat by UK narrowboat standards.

 

Sadly I have some challenging points to put to you.

 

Given you're in Oz I'm surprised you need to design this yourself. I suspect you may be attempting to re-invent the wheel. If it was possible and practical to do it the way you are attempting, it would already have been done many times over and there would be commercially available systems on the market for you to buy and install.

 

So this prompts the question, why not just buy a commercially available solar water heating systems that is known to work? I suspect the answer is they are indirect systems which use some pretty sophisticated electronic control systems and they are quite pricey, but still the question stands. Why not buy and use a household system?

 

You have already identified the reasons for the complexity in a commercially available system.

 

1) They use indirect, evacuated tube collectors in order to cope with the 'overheating' problem that crops up when there is no demand for the heat when the sun is out. With your direct system the domestic water in your plastic tubes will boil if you're not there to use up the hot water. If you let the steam out you then need to replace the lost water to make it work again. With evacutated tube systems the fluid heated is designed to boil and change into vapour when there is excess heat input and stay in the tubes, then condense back into liquid when it all cools down or there is hot water demand. (So I understand. I'm not particularly knowledgeable about solar water heating.)

 

2) Frost resistance. The fluid in the tubes needs to contain antifreeze, so you can't have it supplying your taps or hot water store directly. You'll need a heat exchanger or a calorifier (tank with a coil of pipe inside).

 

Hope this helps without appearing too negative.

[boat fan]

Thank you gentlemen , this is encouraging.

 

I fear that I would indeed melt the PVC , as we get low to mid 40 degree C here at times in high summer ( December to Feb / sometimes early March.)

 

My thought was that if I used 4 inch (100 mm ) pipes they may not boil.

 

Mark , I get the foil idea , I actually stretched some inside this plywood box , but the picture does not show it so well.

 

Maybe even no foil as the water inside that 4 inch pipe got so hot that I could not put my hand inside after 4 hours at 25 degrees.

 

I think the collector may be a little too large , it holds 110 litres , I made it that size in the hope I would not boil it so easily..

 

I think your double tank idea is pretty smart.

 

If you look at the side of the box you can just see the polystyrene foam insulation , 50 mm thick.

 

It`s below the plywood on the bottom too.

 

 

Do you think I could blow this up because the pressure will expand the water too much ?

 

Maybe the glazing would not be needed either ?

 

Failing all that , I was considering just getting a copper coil laid inside a shallow plywood box.

[MtB]

Given you've already built the collector as a direct system, one way to prevent it boiling in the sun would be to have a pipe thermostat which operates a sun shade which moves across to shield the pipes from the sun when the tubes get up to about 60 or 70 degrees C. This would be operated by a solar powered motor, naturally!

 

 

You'd still need to consider what happens if the shading device fails though...

[boat fan]

Thanks Mike , I was typing as you posted , what you say , it all makes sense .

 

I wasn`t sure if I wanted a large batch type heater on the roof , ( all that weight ? )

 

On a narrowboat you have ballast and weight is not really a big hassle , but this is a pontoon hulled vessel , they are relatively poor weight carriers .

 

I cannot really go much over 7 ton all up .

 

I have the space on the roof as the boat is 12 feet wide and the roof is 32 ft long.

 

Then when you said steam ........

 

It`s harder to find small solar set ups here but may be able to find something.

 

thanks for taking the time to reply , much appreciated.

Given you've already built the collector as a direct system, one way to prevent it boiling in the sun would be to have a pipe thermostat which operates a sun shade which moves across to shield the pipes from the sun when the tubes get up to about 60 or 70 degrees C. This would be operated by a solar powered motor, naturally!

 

 

You'd still need to consider what happens if the shading device fails though...

 

What about a copper coil ?

[MtB]

 

 

What about a copper coil ?

 

 

A copper coil is better as it can cope with a few bar of steam pressure. I suspect your plastic pipes are only rated to contain zero pressure at 100 degrees C.

But first, can you address the freezing problem? Do you ever get frost where you are?

[boat fan]

I thought I would produce the hot water during the day and either drain back or pump the hot into the water heater or other small insulated tank atnight ?

 

BTW , Mike , don`t worry about sounding negative , I actually really appreciate your no bs straight talk approach.

 

And , yes mike frost on some nights , not very often but still , sometimes.

Edited May 18, 2016 by boat fan

[LEO]

Good idea, I have a system which works off conventional solar panels, generates electricity, inverter converts to 240 volts, which is used for for household power and any surplus (of which there is a fair amount) diverts to an immersion heater any surplus after that diverts to the National grid.

 

Works really well.

 

M

[I Spartacus]

110ltr is far to large, how big is your hot water storage tank ?, you should be looking at designing the collector for the size of your tank

lets say you get 1000W M2 solar radiation where you live, you should easily get 50 % of that with no problem. at 8 hrs a day that is 4kw over 8 hrs

that is a lot of heating you going to have, so something 1M2 square might meet your requirements.

 

It gets expensive trying to control solar !!!

[boat fan]

I thought I would just mention that I have a lot of water available because I can draw it straight from the river.

 

This barrel holds 200 litres ,the water contains very fine colloidal silt but it settles within 24 hours to be able to be used for showering and washing.

 

 

 

 

 

 

Silt settled after 24 hours.

 

I can make 200 Litres of water for showers or washing every 24 hours if needed.

 

So , In that sense ,I could afford to " steam off " or lose almost any amount of water every day .

 

 

This hand pump can draw water straight from the river.

110ltr is far to large, how big is your hot water storage tank ?, you should be looking at designing the collector for the size of your tank
lets say you get 1000W M2 solar radiation where you live, you should easily get 50 % of that with no problem. at 8 hrs a day that is 4kw over 8 hrs
that is a lot of heating you going to have, so something 1M2 square might meet your requirements.

It gets expensive trying to control solar !!!

 

Well , that is helpful thank you !

 

I have only the little 25 liter hot water storage tank at the moment , but I can add a storage tank of any size i guess.

[boat fan]

110ltr is far to large, how big is your hot water storage tank ?, you should be looking at designing the collector for the size of your tank

lets say you get 1000W M2 solar radiation where you live, you should easily get 50 % of that with no problem. at 8 hrs a day that is 4kw over 8 hrs

that is a lot of heating you going to have, so something 1M2 square might meet your requirements.

 

It gets expensive trying to control solar !!!

 

 

Hmm...i`m out of my depth already Spartacus .

 

The data I have found for south Australia and the region of this river is

 

19 - 22 Megajoules per day ( averaged ) / square metre , I have no idea what that would be in terms of Watts .

 

It`s a lot of sun though

Edited May 18, 2016 by boat fan

[Alan de Enfield]

20Mj = 5555 watt hours

Edited May 18, 2016 by Alan de Enfield

[cuthound]

Given you've already built the collector as a direct system, one way to prevent it boiling in the sun would be to have a pipe thermostat which operates a sun shade which moves across to shield the pipes from the sun when the tubes get up to about 60 or 70 degrees C. This would be operated by a solar powered motor, naturally!

 

 

You'd still need to consider what happens if the shading device fails though...

Could you use a thermostat to divert the overtempaerature hot water into a radiator to lose excessive heat?

 

Edited to put my post outside of the quoted comment.

Edited May 18, 2016 by cuthound

[I Spartacus]

Taking into cloud cover that sounds about correct, as Alan has said 5555 watt hrs, that's a lot of power available to heat water

[WotEver]

With you having that huge cold water tank, perhaps the hot water PRV could vent into it. That would make that side of it simple.

 

Tony

[MtB]

Yes using the sun to heat water is the easy bit.

 

The hard bit is stopping it overheating the water when there is too much sun. I see no strategy for addressing this point at all yet...

(Either stopping the overheating fro happening, or allowing it to happen and dealing with the consequences in a safe way.)

[boat fan]

20Mj = 5555 watt hours

 

Thank you for converting that for me Alan.

that is a lot of power isn`t it !

 

Could you use a thermostat to divert the overtempaerature hot water into a radiator to lose excessive heat?

 

Edited to put my post outside of the quoted comment.

 

Sounds like a workable solution cuthound.

 

Taking into cloud cover that sounds about correct, as Alan has said 5555 watt hrs, that's a lot of power available to heat water

 

Indeed it is .

 

With you having that huge cold water tank, perhaps the hot water PRV could vent into it. That would make that side of it simple.

 

Tony

 

The good constructive comments keep on coming thank you all so much , I think I have a whole new perspective on this now .

 

Yes using the sun to heat water is the easy bit.

 

The hard bit is stopping it overheating the water when there is too much sun. I see no strategy for addressing this point at all yet...

(Either stopping the overheating fro happening, or allowing it to happen and dealing with the consequences in a safe way.)

 

Mike you have experience with boilers so , in your opinion , is there a relief valve I can fit to a copper coil that could just vent steam off , and somehow draw ( pump ) more cold water back into the coil without turning this thing into a bomb ?

 

I was thinking of something like this , or similar :

 

 

 

 

Control Devices CR Series Brass Pressure Relief Valve, 0-100 psi Adjustable Pressure Range, 1/4" Male NPT by Control Devices

Product Description

This Control Devices CR25-100 pressure relief valve has a brass body, an adjustable relief pressure, a 1/4" male NPT threaded inlet connection, and a fluorocarbon O-ring. The valve's brass body, brass valve seat, and the stainless steel poppet resist corrosion and can be used in operating temperatures up to 250 degrees F. The valve can be adjusted to open between 0 and 100 psi using the micrometer-style nylon knob. This safety valve has an 6 standard cubic feet per minute (SCFM) flow rate and is suitable for low flow pressure relief applications such as in tankless air compressors.

Relief valves remove excess pressure or vacuum from a system. The valve openings allow fluids or gases to escape to decrease pressure, and then close once the valve reaches the reseating pressure limit. They also relieve excess vacuum by opening to release a gas into the system and then closing after it reaches its low-pressure limit. Some relief valves have an adjustment mechanism to set the pressure where the valve opens, making it suitable for various applications. Relief valves are rated according to the volume of liquid or gas that can flow through them and the material that the valve is constructed from must be suitable for the fluid or gas, which may be corrosive or at an extreme temperature, in which it operates. Relief valves are used in a variety of applications, such as air compressors, petrochemical and chemical manufacturing, natural gas processing, and power generation.

 

The small circulating pump I have apparently could handle steam temperatures

[boat fan]

How about diverting the copper coil circulating the hot water through the hot storage tank like a heat exchanger , or even circulating solar heated glycol or similar .

 

That way it could still be kept simple without over heating the fluid in the coil ?

[I Spartacus]

Where I worked they used a valve called a thermostatic divert valve, this was used with huge calorifiers on the HTHW feed it

would divert or close off at a set temperature and divert the flow to a new location. something like the valve on this link

I think they 3 or 4 port valve's you could then just divert it into another tank as required.

 

http://www.thermomegatech.com/product/%C2%BD-thermostatic-mixingdiverting-valve-12-md-316ss/

[boat fan]

Where I worked they used a valve called a thermostatic divert valve, this was used with huge calorifiers on the HTHW feed it

would divert or close off at a set temperature and divert the flow to a new location. something like the valve on this link

I think they 3 or 4 port valve's you could then just divert it into another tank as required.

 

http://www.thermomegatech.com/product/%C2%BD-thermostatic-mixingdiverting-valve-12-md-316ss/

 

That looks like a high quality valve Spartacus .

 

 

I think that could be made to work , thank you for that link.

 

 

Thank you all for your contributions , I think you have set me on the correct path.

 

I will do more research and see if I can come up with something far more compact and made with copper.

 

I love this forum.

Edited May 18, 2016 by boat fan

[I Spartacus]

I can see you like experimenting, and if you still want to use plastic with all those expensive fittings, you should try twin wall

polycarbonate roof sheet painted matt black,you need to make up the manifolds which is fun. but it works very very well.

 

And if it gets to hot there is not a big bang

Edited May 18, 2016 by I Spartacus

[Jon12345]

Hi,

Not sure of there availability in Australia but if you could pick up a second hand Stainless steel unvented ( mains Pressure ) indirect cylinder cheap and use that.

They go for relatively peanuts used and very rarely leak so are a good buy second hand ie:

http://www.ebay.co.uk/itm/megaflo-cylinder-70lts-/252386633955?hash=item3ac36a68e3:g:bKMAAOSw3mpXKxOq

They also come normally with temperature and pressure relief valves included so that's the safety side taken care off and you could fit a small expansion vessel if you decide you need it ( the megaflo has a built in one internally )

Use this indirect cylinder with the solar panel as shown in attached pic, use a simple differential controller so when the solar panel is hotter than the cylinder the pump runs.

http://www.solarproject.co.uk/page2.html#240vcontroller

If you 3/4 fill the cylinder this stops any water being left in the solar panel if the system or electric fails so no worry about overheating. Also in the cold weather ie winter there will be no water in the panel so freezing is not a worry.

Then pipe your cold water from your water tank in to the coil of this cylinder and the outlet of coil in to the cold feed of your electric heater/cylinder you have. It will pre heat the water through the coil and then the electric will top up the rest.