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Pipe Sizes For Solar Hot Water System


UlsterRugby1999
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Im hoping that you might be able to clear up some confusion for me. My present solar hot water set-up has a pipe run from manifold return to SHWT of approx 5.5m. The collector surface is 3.75m². When I was researching the subject pre installation I was advised to use 22mm copper pipe. Recently, I have seen a few articles where people have used 16mm copper. Would I be wiser to step down to 16mm pipe? Thanks in advance. Paul

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Hi Théière and thanks for posting. The flow rate valve indicates that it is set at No1 (on a scale from 1 - 3.5) If I set it to more than this I get little heat at all. Any lower and it, effectively, produces no flow at all and T1 just gets hotter and hotter. The pump is a simple central heating pump set at position 1 which indicates 1450. Its says its a Class F-TF 100. I did take photos to try and post them but I havent a clue how to do this. Does this help?
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It sounds as if the pump even on position 1 is circulating too fast for the current climate to have warmed the water sufficiently. That said the thermostat should be switching the pump on and off as required. The smaller pipe will restrict flow so slowing it down to allow more heat gain but you could try restricting the flow using the valves either side of the circulator (assuming you have them).  In summer you would probably want 22mm pipe so a variable speed pump (expensive) of flow restrictor (wastes energy) may be needed. Tricky from behind a PC and I am probably not the best person on the forum regarding solar heat although I do understand hydraulic flow.
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Thanks again Théière. By reducing the flow using the valves either side of the pump am I not effectively doing the same as I do with the flow rate valve? If I turn the flow rate down a little the manifold T1 sensor does increase in temperature but we dont seem to get any extra hot water from this. I assumed that the flow rate either was to slow or I had effectively strangled the pumps ability to circulate. If you think that closing down these valves might help Im happy to try it. Thanks again. Paul
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Just thinking that you may get a better range of flow by a little adjustment of the valves on the pump rather than the courser adjustment of the flow rate valve. To set these things up you really need a flow gauge of some kind, I use an ultrasonic flow meter as I would on the swimming pools, without it it's trial by error. Good luck though, I just dug out my solar heating book just in case it was needed.  
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