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NRV for calorifier.


nb stumpy
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My calorifier has moulded insulation from manufacture. It has 3 seperate heat sources available, engine, central heating or immersion. Water temperature is good no matter what source however invariably temperature is greatly lowered overnight. I now believe hot water is now syphoning back to the engine and cooling although I don't really understand how much can effectively be cooled without some mechanism to aid circulation. Question: should I fit a NRV to the top or bottom connection of the calorifier Engine Coil?  Supplementary how once the back flow of water to the engine has commenced is a continuous flow possible achieving such a degree of cooling? Any help or suggestions greatly received as clearly I'm totally baffled!

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You could try simply swapping the upper and lower engine connection on the calorifier, that sometimes works at the risk it just might make bleeding the engine circuit more difficult. You could also try a horizontal pipe run away from the top connection or even a down bend to provide a high spot in the coil but then you would be wise to add an air bleed screw.

 

Otherwise, a flap type NRV in the hot pipe to the calorifier (usually the top connection).

 

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Tony appreciate your input, I will definitely fit a valve when I'm allowed back on board. Do you think the back flow is minimal as I don't see a means of continuous flow around the engine unless of course the flow is back through the cooling tank on the swim?

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Ah, thank everyone for input  I thought maybe I could prevent major heat loss and have a tank full of hot water still available in the morning it sounds like I've misread other various feeds on this issue and warm water in the morning with natural cooling is the best I can hope for. My question is a result of too much time to muse whilst in lock down.

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The more valves and gubbings you put in the plumbing the more problems you are storing up for the future.

 

If the pipes from the engine fall away from the engine to as low as possible before going to the calorifier coil there will be no gravity circulation.

 

The hot flow pipe from the engine should go to the bottom tapping on the coil in the calorifier because feeding the hot water into the coolest water in the calorifier improves the heat transfer and it also makes bleeding the air from the coil at the top connection a lot easier.  This will also stop gravity circulation robbing you of the hot water by the morning.

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I've never noticed any leakage into my radiators either. After a day cruising obviously the calorifier is full with hot water and after mooring for the night I normally wash up cup saucers plates etc that have accumulated throughout the day, obviously this permits cold,hot water dilution so prior to showering I run the engine to ensure I have plenty of hot water and generally after the shower I might run the engine for maybe ten minutes. Again any further take off of hot water is topped up with cold so I'm normally not keen on depleting the hot water unnecessarily.  Regardless of what precautions or extremes I go to the water temperature in the morning couldn't be described as anything more than luke warm. This not a major annoyance I just thought that for very little effort of fitting NRV there might be easy benefits but then maybe not enough to make it worth while.

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Insulation to the calorifier is the moulded type which would be part of the manufacturing process I would guess it to be maybe inch and a half two inches maybe. Hot water pipe from calorifier to hot water taps throughout the boat are not insulated at all.

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4 minutes ago, nb stumpy said:

Insulation to the calorifier is the moulded type which would be part of the manufacturing process I would guess it to be maybe inch and a half two inches maybe. Hot water pipe from calorifier to hot water taps throughout the boat are not insulated at all.

 

You can always put a jacket on top - slows down the cooling process and keeps it a fair bit warmer overnight.

 

 

CAM00321.jpg

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1 hour ago, nb stumpy said:

Tony appreciate your input, I will definitely fit a valve when I'm allowed back on board. Do you think the back flow is minimal as I don't see a means of continuous flow around the engine unless of course the flow is back through the cooling tank on the swim?

 

I suspect it thermo-syphoning. The hot water in the calorifier heats the  water in the engine coil that then rises and flows "backwards" through the top pie into the engine where it cools, drops and flows back cool into the calorifier. The way to test this is to end the day with a calorifier full of really hot water and wait for the engine to cool, maybe 3 hours or so. Then feel the calorifier pipes close to the engine. If one is warm then it is thermo-syphoning. I doubt the warm water gets anywhere near the skin tank, It just flows into the engine, cools and back to the calorifier. That is for a typical system. The calorifier take off is typically on the engine side of the cooling thermostat. Even on Shires with a separate  calorifier thermostat.

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Thanks again I think this post describes the process that I had no understanding of. Before fitting a NRV I will certainty check the pipework as the engine cools, if there is a back flow then the valve might provide a benefit. Honestly, it was understanding the process that was probably more important than the loss of hot water. I've read a number of feeds on similar subjects without understanding how it worked. I couldn't really understand how a full calorifier of hot water could be cooled effectively by a relatively small coil. Relatively small when looking at the respective surface areas. If as you describe though once a back flow is established a continuously flowing circuit is established then through heat transfer the calorifier will become progressively cooler until a median temperature is established. Yes?

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1 hour ago, nb stumpy said:

Thanks again I think this post describes the process that I had no understanding of. Before fitting a NRV I will certainty check the pipework as the engine cools, if there is a back flow then the valve might provide a benefit. Honestly, it was understanding the process that was probably more important than the loss of hot water. I've read a number of feeds on similar subjects without understanding how it worked. I couldn't really understand how a full calorifier of hot water could be cooled effectively by a relatively small coil. Relatively small when looking at the respective surface areas. If as you describe though once a back flow is established a continuously flowing circuit is established then through heat transfer the calorifier will become progressively cooler until a median temperature is established. Yes?

 

Yes and it normally has 12 hours or so to do its worst.

 

If you fit one make sure the valve is facing the right way. Nothing horrible will happen if you don't but you won't get any hot water.

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1 hour ago, nb stumpy said:

Hot water pipe from calorifier to hot water taps throughout the boat are not insulated at all.

I would insulate these from the calorifier outlet until they drop below the top level of the tank. The pipe close to the outlet will be at tank temperature and losing heat. As the water in the pipe cools there will be convection in the pipe itself with cooler water descending back into the tank and being replaced by more hot water. Overnight that could amount to a significant heat loss. 

 

Old fashioned airing cupboards relied on the heat from uninsulatedhot pipes, and had slatted shelves to allow this to dry damp clothing. I doubt you need this on the boat.

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2 minutes ago, David Mack said:

I would insulate these from the calorifier outlet until they drop below the top level of the tank. The pipe close to the outlet will be at tank temperature and losing heat. As the water in the pipe cools there will be convection in the pipe itself with cooler water descending back into the tank and being replaced by more hot water. Overnight that could amount to a significant heat loss. 

 

Old fashioned airing cupboards relied on the heat from uninsulatedhot pipes, and had slatted shelves to allow this to dry damp clothing. I doubt you need this on the boat.

 

I did our boat that way (airing cupboard) and it was very useful but probably not so easy with a horizontal calorfier. I agree it may help to insulate the pipes but I not sure how much difference that would make with plastic pipe or rubber hoses. Still a couple of lengths of clip on foam insulation is not that much.

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3 minutes ago, Tony Brooks said:

 

I did our boat that way (airing cupboard) and it was very useful but probably not so easy with a horizontal calorfier. I agree it may help to insulate the pipes but I not sure how much difference that would make with plastic pipe or rubber hoses. Still a couple of lengths of clip on foam insulation is not that much.

Fair point. I was thinking more in terms of copper pipe, which is what I have on Belfast.

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