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Post by Deleted on Apr 21, 2017 20:23:07 GMT
Accumulator in the cold supply from pump before NRV, expansion vessel in the hot out - odd diagram gives it as expansion vessel cauliflower cold inlet after the NVR, I haven't told my expansion tank it's in the hot out so it's happy in its ignorance In the hot it fills with (and wastes) about half an accumulator of hot. In the hold it wouldn't. My NRV appears to be part of the calorifier so I'd have to put it in the hot which is annoying. It will be fine, our NVR is immediately before the cauliflower feed.
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Post by lollygagger on Apr 21, 2017 20:28:13 GMT
In the hot it fills with (and wastes) about half an accumulator of hot. In the hold it wouldn't. My NRV appears to be part of the calorifier so I'd have to put it in the hot which is annoying. It will be fine, our NVR is immediately before the cauliflower feed. It will be fine, but it would be better between the nrv and calorifier
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Post by JohnV on Apr 21, 2017 20:40:56 GMT
I remember having a massive argument with a senior partner when I was building a bit of custom designed gear, because it used computer memory without a CPU ......"You mustn't do it that way !" "Why not, it, works fine and saves lots of money" ....... "because it wasn't designed for that" "so bloody what ..... it works !!!" I quit very shortly after. He was a very good development engineer but a lousy designer, totally unable to think outside the box.
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Post by Deleted on Apr 21, 2017 20:47:16 GMT
It will be fine, our NVR is immediately before the cauliflower feed. It will be fine, but it would be better between the nrv and calorifier Go on, I'm intrigued. Thermal expansion affects the whole of the hot system (and some of the cold in the absence of a NRV In the cold supply) why would it be better?
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Post by lollygagger on Apr 21, 2017 20:51:31 GMT
It will be fine, but it would be better between the nrv and calorifier Go on, I'm intrigued. Thermal expansion affects the whole of the hot system (and some of the cold in the absence of a NRV In the cold supply) why would it be better? It'll expand the cold back down the cold feed loosing no heat. In the hot it would expand the hottest water into the new accumulator where it would cool. This would be the first water into the hot pipe when a tap is turned too making it take longer for hot to reach the tap.
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Post by lollygagger on Apr 21, 2017 20:55:03 GMT
Thinking about it the pump would pump both up anyway so not sure how the extra one works as expansion. Set to higher pressure?
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Post by Deleted on Apr 21, 2017 20:57:30 GMT
Go on, I'm intrigued. Thermal expansion affects the whole of the hot system (and some of the cold in the absence of a NRV In the cold supply) why would it be better? It'll expand the cold back down the cold feed loosing no heat. In the hot it would expand the hottest water into the new accumulator where it would cool. This would be the first water into the hot pipe when a tap is turned too making it take longer for hot to reach the tap. Ah right, so you mean your boat is too long! We don't have this problem with a sensibly proportioned boat... But, the loses have to be pretty minimal as to make no real difference. Stick a tmv on the hot outlet to mix the hot hot to 60° and that will help anyway 👍
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Post by Deleted on Apr 21, 2017 20:59:53 GMT
Thinking about it the pump would pump both up anyway so not sure how the extra one works as expansion. Set to higher pressure? Yes. Accumulator 7psi Expansion vessel 36psi I've a table with accumulator pre charge pressures in relation to pump cut in pressure. Remember, the accumulator is to smooth pump running and the expansion vessel is to cope with, well, expansion!
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Post by lollygagger on Apr 21, 2017 21:00:26 GMT
It'll expand the cold back down the cold feed loosing no heat. In the hot it would expand the hottest water into the new accumulator where it would cool. This would be the first water into the hot pipe when a tap is turned too making it take longer for hot to reach the tap. Ah right, so you mean your boat is too long! We don't have this problem with a sensibly proportioned boat... But, the loses have to be pretty minimal as to make no real difference. Stick a tmv on the hot outlet to mix the hot hot to 60° and that will help anyway 👍 1/2 a sink full each time? I don't have a hot expansion yet so it's yours that must be like being the other end of a narrowboat when you run the hot tap.
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Post by Deleted on Apr 21, 2017 21:04:34 GMT
Ah right, so you mean your boat is too long! We don't have this problem with a sensibly proportioned boat... But, the loses have to be pretty minimal as to make no real difference. Stick a tmv on the hot outlet to mix the hot hot to 60° and that will help anyway 👍 1/2 a sink full each time? I don't have a hot expansion yet so it's yours that must be like being the other end of a narrowboat when you run the hot tap. No, nothing like that, it's not hot immediately but doesn't take long to get it there. Size wise we are 8l for hot expansion, 6l for accumulator. Again I have a table for expansion vessel size relevant to pump cut out pressure and cauliflower size. We are bigger than really needed for 70l of hot and a 20psi pump.
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Post by lollygagger on Apr 21, 2017 21:09:53 GMT
If your pump kicks in pretty quickly that would keep whatever cold was left in your hot pipe accumulator at bay too.
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Post by JohnV on Apr 21, 2017 21:13:51 GMT
In mine if you turn on the water as you go to step into the shower enclosure then by the time you have stepped in the water is hot Approx 3 foot of 15mm pipe between tank and shower mixer ...... to hand basin is about 6 foot so takes a tiny bit longer.
(Galley has it's own cauliflower with short runs to kitchen sink .... designed like that because bathroom and galley are nearly 40 foot apart)
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Post by Deleted on Apr 21, 2017 21:23:07 GMT
The only deviation I made was to set the expansion pre charge to the same pressure as the PRV - the same method used in domestic unvented hot water systems - a system I am well familiar with in our house. Most boat or motorhome instructions give 5psi above pump cut out as the pre charge pressure - that would be 25psi in our case, I'm not convinced the PRV hold at such a low pre charge. As John points out, it's all very well on paper but we don't live on paper
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Post by Deleted on Apr 22, 2017 9:19:50 GMT
Go on, I'm intrigued. Thermal expansion affects the whole of the hot system (and some of the cold in the absence of a NRV In the cold supply) why would it be better? It'll expand the cold back down the cold feed loosing no heat. In the hot it would expand the hottest water into the new accumulator where it would cool. This would be the first water into the hot pipe when a tap is turned too making it take longer for hot to reach the tap. Having had a sleep after a long day I've had another think on the expansion position. The thermal expansion occurs through the whole hot system, putting the expansion after the NRV and before the cauliflower doesn't minimise any loss of hot. The NRV does! Before I redid our system we didn't have a NRV, The cockpit shower was the first outlet serviced by the system, right above the cauliflower and pump - hot water would be present at the cold of the shower after a good run. Some omit the NRV if the distance between cauliflower and cold tap is far enough to accommodate the thermal expansion and risk of hot emerging at the tap. Scolding hot water at aa tap was the reasons I fitted a tmv to the cauliflower hot outlet - I couldn't risk hot being present wether due to the lack of a NRV or TMV as our dwarf is perfectly capable of fiddling with the shower and risked scalding herself.
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Post by lollygagger on Apr 22, 2017 9:30:23 GMT
It'll expand the cold back down the cold feed loosing no heat. In the hot it would expand the hottest water into the new accumulator where it would cool. This would be the first water into the hot pipe when a tap is turned too making it take longer for hot to reach the tap. Having had a sleep after a long day I've had another think on the expansion position. The thermal expansion occurs through the whole hot system, putting the expansion after the NVR and before the cauliflower doesn't minimise any loss of hot. The NVR does! Where does the expanded water go? Where it can, into an accumulator. The hottest water is at the top of the tank and coldest at the bottom. If the accumulator is in the cold feed after the NVR it will fill with the coldest water from the bottom of the calorifier. If in the hot it will fill with the hottest water from the top of the accumulator. I am right you know. That's the logic. Whether that really makes much difference in the greater scheme of things, or is the icing on the cake is the reality I suppose.
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