Integrating Solar- & Butane-heated Water Systems

My blog here shows how I combined my solar panels and gas CH/HW system...

The plumbing is UK style, so it may not be appropriate for you...

Del

Most impressed with your blog. I have been spending the past 2 hours sketching out what I think would work in my system. If I post it are you interested in tearing it to pieces for me?

Yeh, I love 'armchair' engineering

There is a huge differnce between a carefully designed system for maximum performance, which would go in a new build... and a practical system based on minimum cost/labour fitted to and existing system.

Del

Del the Cat

Before I try any drawings, just a few bits of info.

1. I live on the side of a mountain.

2. The house has mountain below and above it.

3. Water is pumped via petrol generator (unfortunate but solar submersible solar pump was not a financially viable option at the time) from 190 metres down the mountain up to two 3,000 litre storage tanks above the house (the bases of which are approximately 10 metres above the highest part of the ground floor-based domestic water system (which would be the shower head).

4. I have water pipes coming from the base of the water storage tanks into the house.

5. The supply then separates to cold taps/washing machine/cold feed for shower and to input for wall-mounted butane gas heater. From there the output goes to taps and hot feed of shower.

6. There is space above, level with and below the house on which I could lay coiled black pipe to heat in the sun.

7. I have no cylinder or hot water storage container but could purchase one if necessary.

8. I have some old 12v PV solar panels lying around (two or three which are a bit old but should produce something like 100-150 watts between them), a controller and an inverter.

9. I also have a spare water pump - non-submersible along with a large metal ball device that I removed from the top of it and which I believe is some form of pressure switch - it was used on the house before I purchased it when the incumbents had not thought of putting the water storage tank above the house and, (it actually being LOWER than the house!), relied on this switched pump to respond when there was a pressure drop at the taps - I think.

10. I have no spare 12v battery but I could get one if necessary.

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Idea A.

Simply connect a pipe from one of the water storage tanks to some black pipe coiled out on the hillside above the house; connect it to the input of the gas heater and turn off the gas when I think there is enough hot water in the black pipe.

Lots of problems with this, of course.

Idea B.

Connect the pipe coming from the black coiled pipe to some form of temperature sensing valve that will by-pass the gas heater if the water is at a given temperature or go through the gas heater if it is below that temperature.

I don't know anything about temperature-controlled valves.

Idea C.

Use the black coiled pipe to heat the water but have the water stored somehow via gravity feed in a cylinder that would, again supply the house via gravity feed.

Idea D.

Same as Idea C. except with a pump of some sort so I could position the coiled black pipe level with or below the house. NB The ideal situation would be on the top of a flat roof about 5 metres below the shower head in the bathroom. It would be more aesthetic here and there is already a clear and level surface for it to be located. In this scenario I would have to use a pump to get the water to the house - either without a hot water storage cylinder if I am just going to rely on it working when the sun is shining, or with a hot water storage cylinder if I want to use the hot water at night and when the sun is not shining. Naturally I can see that the using the coiled black pipe as a hot water storage medium is impossible because all the heat would be lost as soon as the sun disappears.

I am now aware that I have started to waffle and will hand it across to your armchair.

Let me know what you need. I can take photos and/or video of site and/or give drawings. Whatever makes it easier for you to suffer my ignorance.

My breath is bated.

Joe

I'd have thought...something like D.

Hot/warm water storage tank (doesn't need to be too big, say about a metre cubed) this would have water pumped from it through the plastic pipes, controlled by a pump driven by your PV cells with a temperature sensor near the output end of the blak pipes so that the pupm only runs if this is hotter than the water in the tank.

The output from the tank should feed the butane heater (it the water is hot enought the butane heater won't kick in, if the water is only warm the butane heater will top up the heat). The inlet to the tank is via a level switch/ballcock from your cold supply.

I'd say that's about as simple as you could get.

Del

Thanks.

Okay Del, let's make sure I have this right.

1. Hot/warm water storage tank positioned above the shower head. I do have space on the first floor directly above the butane heater.

2. Hot tank has one output to the input of butane heater. I didn't know butane heaters had a temp sensor for input water - but it you say so, then I am sure you are right.

3. Hot tank has a ballcock that connects to one input.

4. The single input to the hot tank splits via a three-way valve (?) to two pipes - one from the cold water tanks which is gravity fed, and the other from the solar-heated coil, which is pumped.

5. When the water level of the hot tank drops, the ballcock opens and either:

a. if the water in the solar-heated coils is hotter than that in the hot tank, the valve closes to the input from the cold water tanks and opens to input from the solar-heated coils, at which point there is a pressure drop that is sensed by the sensor on the pump which then operates and pumps the solar-heated water to the tank - stopping when the ballcock closes.

or

b. if the water in the solar-heated coils is not hotter than that in the tank, the valve allows water to enter from the cold water tanks - stopping when the ballcock closes.

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Question1: If there is insufficient sun to power the pump, but the water in the solar-heated coils is hotter than that in the hot tank, then what happens? Won't this mean that the feed from the cold water tanks is closed off but no water can get to the hot tank from the solar-heated coils because the pump will not work? Or does the three-way valve (?) default to the cold feed?

Question2: The distance from the hot tank to the roof on which the coil will sit is approximately 20 metres. Will this be a problem for the temperature sensor that will need to reach from the hot tank to somewhere on the roof where on which the coil is sitting? Or will it not matter since the water at the end of the solar-heated coil input pipe will be the same temperature as that on the roof?

Question3: Will there be any problems with the direct feed (i.e. no valve of header tank) going to the solar-heated coil. The feed will connect directly to the bottom of the cold water tanks at the top of the hill.

I await your wisdom...

Nah..you are complicating it...3 way valve !

I'll draw a picture when I get home.

I didn't know butane heaters had a temp sensor for input water - but it you say so, then I am sure you are right.

Ha no ..I don't say so...! The butane heater will have a temp sensor on the output...so if it is fed with warm water it will still heat it..but it will take less heat and butane than if it was fed with cold water.

e.g Say cold water in at 10degC. Butane heater will run flat out to get it up to 50degC. If the water going in has been warmed by your black pipe to say 30degC the butane heater will only need to run for a short time or at low power or short bursts (demending on how it actually works) but it will take a lot less butane to get the warmed water up to 50degC.

A hot water cylinder in UK is a closed clinder (not an open topped tank) it has the hot water coming out the top ('cos hot water rises to the top naturally) It is replenished by a cold feed at the bottom. This is the simplest way to do it....if the cold feed is from a gravity feed above the hot water cylinder you don't even need a level switch.... water will come out the top when you open a tap, and will flow in the bottom to replace it. (Obviously you would fit service valves so you can shut off the various pipes).

The black pipe would connect to the cylinder somewhere near the bottom through the pump and pipe and then back into the cylinder somewhere near the top...no valves If the pump stops the flow stops (due to the resistance of all that black pipe...but you could add a non return valve if you wanted... [it's just a spring loaded ball valve] to make sure the water flows the right way and to stop any hot water flowing through the cold black pipe at night).

It's 9:30 AM here..and I s'pose I should do some work

Del

Thanks again Del. I will await your drawing, but I think I am getting a clearer idea now.

Joe

A divert-er and a temperature gage. When temp is low divert to heater and vice verse

Here is the sketch...

You don't really need the vent/breather as the water can expand back to your open feed tank, it can be handy to avoid airlocks though.

This would be a simple 'direct' system so the actual water you use will go through the coil...so you may need to close and drain it if there is a chance of freezing. But you will want to add plenty of stop valves and drain points for service anyway.

The positioning of the inlets and outlets in the hot water cylinder need some thought to ensure optimum mixing and heating. Just remember the hot water will always rise to the top, this is helped by having the hot drawn off at the top and the cold fill at the bottom.

PS There is tons of stuff on the net about diy solar hot water/batch heaters etc.

Del

Del you really are a great guy! Thanks so much.

I will do some more research on this and do a few experiments with the cylinder.

Naturally I will let you know how I get on.

Best wishes

Joe

Have fun... I look forward to hearing how it progresses, particularly with the pipe as it obviously will get hot but not conduct the heat so well ... so there should be some scope for experimentation.

I've just re-roofed an extension with EPDM (sort of rubber) it gets almost too hot to handle, but I don't know how easy it would be to extract that heat.

Cheers

Del

Your roof is interesting. Some form of thermocouple? Suppose it would not be possible now the surface is on. I'm sure you of all people will come up with some brilliant idea. Let me know when you do.

Back to my little hot water project: Tomorrow, I am going to have a play around with the sun and the black pipe I have. Can't quite decide whether to use 25mm or 40mm pipe - I have both. Also, still attracted to the idea of draping it at the top of the mountainside to start with to see what sort of heating I will get. This way I could have a direct gravity feed from the cold water storage above it and simply connect direct to the gas water heater. I can then monitor temperature achieved and what actually happens with the amount of gas being used when the input water is at a higher temperature.

Best wishes

Joe

That sounds like a great and simple idea...

Good Q 25mm or 40...?

40 has more surface area but will hold more water... that would make a good challenge question...except they expect you to know the answer first!

Maybe another post with the specific question...drat you've got me thinking now...

Del

No sooner said than done...

Further to Del the Cat's excellent (and patient!) advice, I found this on the web:

From: http://www.byexample.com/library/illustrations/hotwater/illus_hotwater_3.jpg/image_view

I will be looking for more systems to compare and these will be posted as well.