DIY Solar water heating, evacuated tube, direct type (no heat exchanger)

[rleverett]

Hi I live in south Devon (UK) and am in the process of connecting a DIY evacuated tube water heater to my hot water tank by tapping into the hot and cold water pipes, which with a pump, will circulated the heated water into the tank, and heat it.
I asked my local plumber to put a tee into the hot and cold pipes so that I could continue piping the system in myself.
He refused to do this as he was unsure as to the flow pattern of the finished system, and thought that it could pump hot water into the cold water tank in the roof?
Does anyone have details to re-assure the plumber that this will not happen?
Regards Bob.

[inetdog]

Hi I live in south Devon (UK) and am in the process of connecting a DIY evacuated tube water heater to my hot water tank by tapping into the hot and cold water pipes, which with a pump, will circulated the heated water into the tank, and heat it.
I asked my local plumber to put a tee into the hot and cold pipes so that I could continue piping the system in myself.
He refused to do this as he was unsure as to the flow pattern of the finished system, and thought that it could pump hot water into the cold water tank in the roof?
Does anyone have details to re-assure the plumber that this will not happen?
Regards Bob.

Naptown has posted in this forum the best way to add a solar PV circulating system to a standard water tank, and the plumber is correct: you do NOT want to just put a tee in the hot and in the cold line at the top of the tank.
You want to add a tee to the bottom drain outlet and cut off the dip tube from the cold water inlet shorter than the original length. For the full details and diagrams, search for Naptown's post. I will try to find it and add a link to my reply.

Found it. No pictures, but a very good description. It applies just as well to a combined gas or electric and solar thermal single tank as it does to a pure storage tank.

http://www.solarpaneltalk.com/showthread.php?8142-Replacing-solar-hot-water-tank&p=54721&viewfull=1#post54721

Your plumber should be able to understand the description and will realize that it will work to heat the cold water first.
Make sure that your heating panels and piping are safe for domestic water of course. And you will need to use a manual or automatic drain system or a heating loop if you have to worry about freezing. That can be much more difficult with a direct water heating system than with a separate coolant loop and heat exchanger, since that allows you to use antifreeze in the panel loop.

[rleverett]

Thanks for the reply, unfortunately, there is only one tank to confuse the issue, and the only heat exchange is used by the gas water heater.
I am not sure what is meant by a nipple for the drain valve, but english tanks rarely have a separate drain, mine is at the end of the cold water inlet to the base of the tank and access is very restricted?
Nor do I believe english tanks have a dip tube, sorry.
regards Bob.

[inetdog]

Thanks for the reply, unfortunately, there is only one tank to confuse the issue, and the only heat exchange is used by the gas water heater.
I am not sure what is meant by a nipple for the drain valve, but english tanks rarely have a separate drain, mine is at the end of the cold water inlet to the base of the tank and access is very restricted?
Nor do I believe english tanks have a dip tube, sorry.
regards Bob.

If English tanks do not have a dip tube, then the cold water inlet must be at the bottom already (as you just said). US tanks tend to have both inlet and outlet lines going through the top of the tank.
Given that, taking the water from anywhere along the inlet pipe (but the closer to the tank the better) with a tee and returning it to the hot water outlet line (with another tee) will be the best you can do. There are commercial systems that put a heat exchanger into the inside of the tank using a special mechanism inserted through the pressure relief valve hole. Do English tanks have a separate temperature/pressure relief valve fitting at the top or does that also just connect to the single hot water outlet? (Or is it missing entirely and tanks blow up regularly?)

[rleverett]

Hi yes the inlet is at the base of the tank and I wanted my plumber to do as you say, tee into the hot and cold pipe, but he will not do that as any reverse flow will leave him liable for damages?
we can get mini/compact heat exchanger made up from ebay which fit in the electric immersion heater port, but I am reluctant to lose the electric heater as I have solar panels and that is an efficient way of heating.
We do not have safety valves as most systems have the hot water piping open to the atmosphere in the form of a swan neck pipe which discharges above the water level to the cold water tank in the loft space, this causes no problems and means the tank cannot explode.
It's a pity we don't have the separate drain plug as I could fit what we call a "surrey flange" and run the solar panel water in and out of the tank independant of any surrounding pipework?
Regards Bob.