Switching heating sources using solenoid valves

[abudhabidickie]

Fitting solar water heating panels on a roof appears relatively straightforward - especially with the great posts on this site showing how it is done. 

But .... connecting to the solar panels to the hot water storage tank is much more tricky.  In my case it will mean replacing the cylinder and lifting a large amount of carpet and flooring to lay the connecting pipework.

Has anyone any experience of using solenoid valves to switch between the boiler and solar water heater, as at first glance this would appear to allow the use of the existing heating coil in the hot water tank and avoid the need to do a lot of plumbing.

[wyleu]

One of the first things to consider is how does it fail? if there isn't any mains on the hottest day will it fail gracefully? and if it fails on the coldest day will the pipes survive?. In connecting the boiler and the solar panels in the way you describe you have to be sure that the fluid is suitable for both tasks. Also the systems need to run at the same pressure so this will probably compromise one or other of the components.

[Antman]

Since the reqiuired pipework is presumably already accessible, why is it not possible to replace the cylinder without upping lots of flooring?

Presumably you have a viable route from the loft (or other potential panel location) to install the solar pipework, therefore these can be simply connected to the replacement cylinder. The only contentious point may be the solar cylinder being higher than the existing one which can create 'issues' when you say "I need to remove the next shelf in the airing cupboard...". Even then, the pipework changes are usually above the floor on existing pipework?

Regardless of other reasons, solenoid valves tend to get noisy - clicking audibly every time they operate - which will get annoying in the summer with the solar cutting in regularly. It is surprising how far through system pipework a solenoid 'click' will echo!


You might be able to achieve what you desire by strategically placing one-way (non-return or check) valves in both the solar and DHW boiler return pipes from the cylinder. The DHW boiler coil check valve needs to be 22mm and intended for higher temp use. You may need additional manual bleed vents though to guarantee air removal on filling.

This will permit/retain independent control of boiler and solar ciircuits. You would still need a separate solar pump.

Antman

[O MidKnight]

If both systems were filled to the same pressure and with antifreeze of the same make I might do it on my own system. But a customers - no. I once went along to see why a system was losing pressure. No leaks - no cold water tank overflow running but checking the pipe work found that it had been connected to a towel rail via diverter valve on the main central heating circuit. Normal 10 gallon fill and expansion tank fitted in loft was overflowing.  Had to remove stat and cap pipes to towel rail plus add extra antifreeze and water mixture via killaspray pupm up bottle- all then well and good. This was on a system where the installers would not go back to service it or offer warranty after it was installed