Four bed house with a pumped, open-vented system.
In 2010 I installed a second 160 litre cylinder in the attic heated by the solar panel, directly above and "in tandem" with the existing house cylinder in the airing cupboard. Water flows from the F&E tank, into the bottom of the solar cylinder, out the top and into the bottom of the house cylinder below, then out of the top to the taps and shower pump. The expansion pipe from my solar cylinder simply joins the expansion pipe from the house cylinder below.
Since 2010 we have noticed that the hot water supply to the showers is poor in winter; even when the downstairs cylinder is full of 60c water, showers are unsatisfactory and soon become tepid.
This has puzzled me until a couple of days ago when a shower was in use and the pump running and I happened to put a hand on the expansion pipe coming out of the downstairs cylinder to find it freezing cold. Suddenly I understood what was happening: the pump is sucking cold water round through the expansion pipes from the top of the cold solar cylinder in preference to sucking it out of the downstairs cylinder and cold water is mixing with the hot, giving us the tepid showers. We don't notice it in summer when the solar cylinder is full of hot water.
So my first reaction is to fit an old one-way valve I've got into the downstairs cylinder expansion pipe so as to prevent it sucking cold water out of the upstairs cylinder.
But thinking about it, the valve takes quite a bit of effort to overcome when you blow through it and simple thermal expansion probably won't overcome that resistance, meaning expansion might reverse-flow out of the downstairs cylinder. So I'm inclined to extend the expansion pipe so that both cylinders have their own pipes runnng parallel to the F&E tank. Then I noticed that the expansion pipes are in 22mm, which I guess may be a plumbing convention so as to give more capacity to the pipework and reduce the loss of hot water into the F&E tank on expansion.
Would you go down the one-way valve route or the twin expansion pipes route?
Would you use 22mm?
Sorry about the long post - it's hard to explain clearly.
In 2010 I installed a second 160 litre cylinder in the attic heated by the solar panel, directly above and "in tandem" with the existing house cylinder in the airing cupboard. Water flows from the F&E tank, into the bottom of the solar cylinder, out the top and into the bottom of the house cylinder below, then out of the top to the taps and shower pump. The expansion pipe from my solar cylinder simply joins the expansion pipe from the house cylinder below.
Since 2010 we have noticed that the hot water supply to the showers is poor in winter; even when the downstairs cylinder is full of 60c water, showers are unsatisfactory and soon become tepid.
This has puzzled me until a couple of days ago when a shower was in use and the pump running and I happened to put a hand on the expansion pipe coming out of the downstairs cylinder to find it freezing cold. Suddenly I understood what was happening: the pump is sucking cold water round through the expansion pipes from the top of the cold solar cylinder in preference to sucking it out of the downstairs cylinder and cold water is mixing with the hot, giving us the tepid showers. We don't notice it in summer when the solar cylinder is full of hot water.
So my first reaction is to fit an old one-way valve I've got into the downstairs cylinder expansion pipe so as to prevent it sucking cold water out of the upstairs cylinder.
But thinking about it, the valve takes quite a bit of effort to overcome when you blow through it and simple thermal expansion probably won't overcome that resistance, meaning expansion might reverse-flow out of the downstairs cylinder. So I'm inclined to extend the expansion pipe so that both cylinders have their own pipes runnng parallel to the F&E tank. Then I noticed that the expansion pipes are in 22mm, which I guess may be a plumbing convention so as to give more capacity to the pipework and reduce the loss of hot water into the F&E tank on expansion.
Would you go down the one-way valve route or the twin expansion pipes route?
Would you use 22mm?
Sorry about the long post - it's hard to explain clearly.
