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Post by Telemachus on Oct 24, 2019 21:09:20 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 Well your boiler’s output is low for the size of radiators, which means the rads are never going to get very hot.
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Post by peterboat on Oct 24, 2019 23:48:38 GMT
Well your boiler’s output is low for the size of radiators, which means the rads are never going to get very hot. 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.
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Post by Telemachus on Oct 25, 2019 7:07:24 GMT
Well your boiler’s output is low for the size of radiators, which means the rads are never going to get very hot. 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.
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Post by lollygagger on Oct 25, 2019 7:53:02 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. Soooo.... 15l/min (max) - will it need slowing down?
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Post by Deleted on Oct 25, 2019 7:57:57 GMT
Maybe you could use a vehicle auxiliary pump and run it on step-down voltage converter.
If you used a brushed type you could run it on a small pwm and experiment.
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Post by lollygagger on Oct 25, 2019 10:59:24 GMT
Maybe you could use a vehicle auxiliary pump and run it on step-down voltage converter. If you used a brushed type you could run it on a small pwm and experiment. I've already bought the brushless pump.
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Post by Telemachus on Oct 25, 2019 11:05:56 GMT
Maybe you could use a vehicle auxiliary pump and run it on step-down voltage converter. If you used a brushed type you could run it on a small pwm and experiment. Some brushless types will work with PWM, including the one I linked to earlier.
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Post by Telemachus on Oct 25, 2019 11:11:08 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. Soooo.... 15l/min (max) - will it need slowing down? That’s perhaps a little high but then again, the figure is a bit meaningless. Centrifugal pumps deliver a specified flow rate at a specified pressure (or head). Depending on the gauge of pipe used, complexity and length of pipe runs etc, there will be some differential pressure in the system and so the actual flow rate is likely to be less. You could probably throttle it a bit with a gate valve. However there is no particular problem with overly high flow rate, except for noise. Heed the comment about it not being self priming. Don’t install it at a local high point, or you will never get the air out of it!
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Post by lollygagger on Oct 25, 2019 12:04:44 GMT
Soooo.... 15l/min (max) - will it need slowing down? That’s perhaps a little high but then again, the figure is a bit meaningless. Centrifugal pumps deliver a specified flow rate at a specified pressure (or head). Depending on the gauge of pipe used, complexity and length of pipe runs etc, there will be some differential pressure in the system and so the actual flow rate is likely to be less. You could probably throttle it a bit with a gate valve. However there is no particular problem with overly high flow rate, except for noise. Heed the comment about it not being self priming. Don’t install it at a local high point, or you will never get the air out of it! Thinking about controlling the pump. Apparently it will work with a pwm controller. If I have a thermostat on the boiler or pipe leaving the boiler through the speed controller it'll cycle on and off like crazy until all the circulating stuff is heated up above the stat temp? Could I split the 12v+ to the motor with one feed through a thermostat for full power at say 80 degs and one through a controller so it's always circulating at a slower speed? Or will full speed back feed 12v into the pwm controller and break it? What I really need is a 12V programable heat sensitive pump speed controller.
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Post by Telemachus on Oct 25, 2019 12:52:45 GMT
That’s perhaps a little high but then again, the figure is a bit meaningless. Centrifugal pumps deliver a specified flow rate at a specified pressure (or head). Depending on the gauge of pipe used, complexity and length of pipe runs etc, there will be some differential pressure in the system and so the actual flow rate is likely to be less. You could probably throttle it a bit with a gate valve. However there is no particular problem with overly high flow rate, except for noise. Heed the comment about it not being self priming. Don’t install it at a local high point, or you will never get the air out of it! Thinking about controlling the pump. Apparently it will work with a pwm controller. If I have a thermostat on the boiler or pipe leaving the boiler through the speed controller it'll cycle on and off like crazy until all the circulating stuff is heated up above the stat temp? Could I split the 12v+ to the motor with one feed through a thermostat for full power at say 80 degs and one through a controller so it's always circulating at a slower speed? Or will full speed back feed 12v into the pwm controller and break it? What I really need is a 12V programable heat sensitive pump speed controller. 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.
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Post by lollygagger on Oct 25, 2019 12:58:32 GMT
Thinking about controlling the pump. Apparently it will work with a pwm controller. If I have a thermostat on the boiler or pipe leaving the boiler through the speed controller it'll cycle on and off like crazy until all the circulating stuff is heated up above the stat temp? Could I split the 12v+ to the motor with one feed through a thermostat for full power at say 80 degs and one through a controller so it's always circulating at a slower speed? Or will full speed back feed 12v into the pwm controller and break it? What I really need is a 12V programable heat sensitive pump speed controller. 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.
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Post by Deleted on Oct 25, 2019 13:17:35 GMT
I'd be tempted to have a play with one of these little toys DC 12V Digital LED Thermostat Temperature Control^Switch Module XH-W1209CCOTPI | ebay.us/5Knintless than a fiver. Could try strapping the temperature sensor to the pipe with cable ties. That way you can play around with the switch temperature see what works best. That one (which is UK stock despite the strange eBay link) works up to 110'C.
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Post by lollygagger on Oct 25, 2019 13:17:36 GMT
The Webasto Thermo top C rates it's pump at 9L/minute. Yes I should have bought one of those before anyone points it out! The one I did buy is rated at 15L/min and the stove won't provide 5KW to the back boiler so I think I will have to slow it dowm. l
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Post by lollygagger on Oct 25, 2019 13:24:27 GMT
I'd be tempted to have a play with one of these little toys DC 12V Digital LED Thermostat Temperature Control^Switch Module XH-W1209CCOTPI | ebay.us/5Knintless than a fiver. Could try strapping the temperature sensor to the pipe with cable ties. That way you can play around with the switch temperature see what works best. That one (which is UK stock despite the strange eBay link) works up to 110'C. Good Idea.
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Post by Deleted on Oct 25, 2019 13:27:29 GMT
When I did a Rayburn install years ago on a narrow boat I put an open vent in the flow pipe through the top of the cabin and the header tank went on the return pipe also routed to outside.
That way if any boiling happened it would simply eject outside.
That was a 28 and 22mm system with no pump. Flow 28mm vertically up to highest point immediately and return along the floor.
Worked lovely. The best way to get a thermosyphon working is to go straight up from the boiler. Not a gradual slope but straitht up to the highest point then down from there.
It does result in a rather odd install and a bit unconventional but boy does it work !!
Rads were teed from flow pipe (just below ceiling level) and return pipe (on the floor) using 22mm copper and physics did the rest as physics has no choice.
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