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Post by lollygagger on Oct 25, 2019 13:33:17 GMT
Ah, well I have a floor level plastic pipe webasto system so thermosyphon is not an option.
I was planning a header tank on the output side of the boiler and crossing my fingers.
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Post by Deleted on Oct 25, 2019 13:35:04 GMT
I think it might boil off. The good thing about an open vent on the flow and a header on the return is the gas can escape two ways (both open vented) but the header tank won't boil off.
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Post by lollygagger on Oct 25, 2019 13:41:16 GMT
I'm glad I started this thread.
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Post by brummieboy on Oct 25, 2019 14:01:11 GMT
55C even on a return, is pretty cool for a central heating system. Especially with a hard-to-regulate heat source like a stove. It’s bound to go over that once the boat warms up, unless the boiler output is mismatched to the radiator load. Mine doesnt Neither does mine. With a thermostat set at 65oC, the operating time is intermittent, as I said earlier. With a 5kw boiler, you don't need to many radiators to eat that. I actually only have one radiator, and once the pump has primed the circuit, I rely on thermosyphoning to continue.
As I plug the pump into the socket I plug the T.V. into, that is not a bad scenario.
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Post by Telemachus on Oct 25, 2019 15:08:41 GMT
I think it is likely that feeding 12v into the output of a 12v PWM controller would be fine but without seeing the circuit I couldn’t be certain. But anyway, maybe you should try it with the thermostat first, and see how it goes. No point in adding complexity if it transpires it’s not actually needed. Yes I think the thermostat might cut in and out a bit - it probably doesn’t have enough hysteresis. But does that actually matter? The other thing to consider is that the motor probably presents something of an inductive load and this might cause arcing of the thermostat contacts. You might consider adding a freewheel diode to the thermostat contacts to eliminate this. Unfortunately I wouldn't know a freewheel diode from a resistor. I read Tony Brookes advising someone to use a car type relay to switch the pump, that's more my level. A freewheel diode is just a diode connected backwards (ie reverse biased) across the pump. The property of inductance is to try to preserve current. So when the thermostat switch opens and the current through it suddenly stops, the inductance “sucks” current really hard trying to preserve the current, resulting in a voltage spike and arcing. With a freewheel diode, at the moment the contact opens and the inductance “sucks” current, the diode will go into conduction and satiate the inductance’s desire for current. Such a diode could be had for a few pence but saves the switch contact from arc damage.
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Post by peterboat on Oct 25, 2019 17:18:45 GMT
No it isnt my rads can get that hot you cant touch them...............at the top but by the bottom they are cooling down so the water hits the pump cool, the pump isnt on a fast speed and is thermostatically controlled, I installed the system Nick and checked it with a laser temp gun. Even the whispergen doesnt get that hot water leaves it at 70c and returns much cooler having done its work.
Ok well in that case, the circulation rate is rather slow. This means that for a given radiator area, you are getting less heat than you could. Ie the radiators are only hot at the top, cooler lower down, and thus could have been smaller to get the same heat output, with a faster pump. Not that it matters for you, obviously your system works for you. My point was that to recommend a pump with max temperature of 55C for a stranger’s heating system, is not a good idea, especially when there are plenty of pumps out there with max temperature 100c or hotter. Again you are wrong I have to have 5 KW of radiators as a cooling system for the whispergen which runs infrequently because I have a huge solar array. My Rayburn can easily heat my large well insulated boat on a low setting which means I have warm rads rather than hot and a cool pump on the return from the rads, I designed it that way
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Post by Deleted on Oct 25, 2019 17:20:38 GMT
Impossible. It can't be done. How could you doubt Telemachus when he is so obviously right in everything? Well that is other than boat builder choice but what the hell you can't have it all can you.
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Post by Telemachus on Oct 25, 2019 17:39:56 GMT
Ok well in that case, the circulation rate is rather slow. This means that for a given radiator area, you are getting less heat than you could. Ie the radiators are only hot at the top, cooler lower down, and thus could have been smaller to get the same heat output, with a faster pump. Not that it matters for you, obviously your system works for you. My point was that to recommend a pump with max temperature of 55C for a stranger’s heating system, is not a good idea, especially when there are plenty of pumps out there with max temperature 100c or hotter. Again you are wrong I have to have 5 KW of radiators as a cooling system for the whispergen which runs infrequently because I have a huge solar array. My Rayburn can easily heat my large well insulated boat on a low setting which means I have warm rads rather than hot and a cool pump on the return from the rads, I designed it that way As I said, it works for you, mr defensive. The point is a general one, which is that a pump only rated at 55C isn’t suitable for a circulating a normally designed radiator /back boiler system and therefor shouldn’t be recommended as a general purpose CH pump. As you have pointed out, with the specifics of your unusually designed system, it works for you. You are getting sulky because you think I am criticising you but I am not. Do calm down!
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