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I have posted before about my heating system which is simply not performing. The installer does not fully understand the issues, so I am left to try to improve things. I am trying to base the modifications on an understanding of hydronic systems which I am trying to get my head around. I have two questions I would like to ask.
Firstly, I suspect that the boiler circulator is undersized. The boiler protection circuit is not correct as there is no hydraulic separation. I proposed to fix this by adding the pipe shown dotted. It will be 25mm copper and about 300mm long.
Now the boiler is 30kW. I have calculated (see attached sketch) that the flow required to remove this heat from the boiler is about 29l/min. I further believe that the TacoNova thermostatic mixing valve (TMV) will have a pressure drop across it of about 9m with this flow (see attached spec sheet). The current Wilo Star RS 26/6 circulator cannot produce this head. From this I conclude that the circulator will not do the job. Have I got this right?
Secondly, I have read in John Siegenthaler's book and elsewhere that the pressure vessel should be as close as possible to the inlet side of the circulator. In Fig5-78 (see attachment) the pressure vessel is separated from the inlet port by the TMV. There can be a significant pressure drop across this TMV. Also because of the low pressure drop across the boiler, the pressure vessel is close to the outlet port of the circulator, not the inlet port. This seems to go against the practice of placing the pressure vessel near the inlet port. What am I missing?
I hope someone out there can help me understand these issues. Thanks in advance.