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Another quick calorifier query


starman

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How should I plumb the flow and return on the  twin coils of my (vertical) calorifier? One from the engine, the other from the Webasto. 

It always seemed logical to me to feed in hot supply at the upper and the cooled exit at the lower of each coils. But on various diagrams (including Surecal) I’ve seen it the other way - hot at the bottom of each coil. Is there a correct way?

 

And I’m presuming the engine fed coil is the lower coil and the Webasto the upper one. Correct?

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I'm surprised by the Surecal instructions.

I would always plumb the hot from the heat source to the top, and the return at the bottom, whether it is pumped or gravity.

 

Trying to do as they show seems to be working against convection / gravity to me.

You plumb the hot from your engine to the top of a skin tank, not the bottom - why should the calorifier (effectively just extra "skin tank) be treated differently?

That said, I seem to recall someone claiming heating engineer experience recently firmly stating on here that the likes of me are wrong!.......)

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Depends alot on how your pipework is installed.

It may be better sometimes to feed the hot 'in' at the bottom as this will/may prevent airlocks. Its all pumped so will make little difference but like you all my systems are hot 'in' at the top (I use self bleed valves above top fitting).

If you spend more time running your engine than running the webasto, plumb the bottom coil to the engine. Again it may make no difference-it depends on how far down both coils go-if the upper coil is higher you will only be heating higher up the tank.

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4 minutes ago, alan_fincher said:

I'm surprised by the Surecal instructions.

I would always plumb the hot from the heat source to the top, and the return at the bottom, whether it is pumped or gravity.

 

Trying to do as they show seems to be working against convection / gravity to me.

You plumb the hot from your engine to the top of a skin tank, not the bottom - why should the calorifier (effectively just extra "skin tank) be treated differently?

That said, I seem to recall someone claiming heating engineer experience recently firmly stating on here that the likes of me are wrong!.......)

There’s a fundamental difference between a skin tank and a calorifier. The skin tank doesn’t constrain the flow very well, so it’s important to send hot in at the top so it doesn’t take a shortcut to the outlet, without getting intimate with the skin to lose heat. Especially if the baffling is poor.

 

In a calorifier, the hot flow is constrained within a relatively small bore pipe so it doesn’t make a lot of difference which way it flows. It is also pumped, which makes any convective circulation force inconsequential. Putting the hot in at the bottom of a calorifier helps mix the contents (by convective circulation) so the water will heat up more evenly overall. A bit.

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15 minutes ago, Stephen Jeavons said:

All domestic central heating systems I've ever seen have the 3-port valve going in at the top of the hot water cylinder (i.e the supply from the boiler via the pump) with the return at the bottom.

Why should a boat's calorifier (different name, same thing) be any different?

I agree, but not so long ago someone who said he was a qualified plumber came here and said for pumped systems it should be in at the bottom and out at the top. 

Since on a boat you are usually using the coil to heat a tank of water for later use, rather than an instantaneous heating situation, I suspect it doesn't much matter which way you do it.

 

But note that for a gravity (non-pumped) system it is essential that it is plumbed for hot in at the top and cold out at the bottom.

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As @nicknorman  stated above, the system is pumped so during the heating cycle it makes little noticeable difference which way round it's plumbed when heating.

 

However, it can make a significant difference to how long the water in your tank stays hot: if the convection current in the hot calorifier and cooling engine are working together to promote flow when the engine is stopped, the flow in the circuit will cool the tank through the engine.  Since the  warm water in the calorifier will tend to rise to the top connection and the cold water in the engine will tend to fall fall towards the bottom of the engine, you should connect these together to oppose one another.  This is the same as the Surecal version you quote.

 

Another consideration, for similar reasons, is to take the calorifier supply & return pipes down to base level and back up to the respective coil connections.

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  1. This ^^^^^ except I would try hot in the top of the coil first because often the pipe run will stop therm-siphoning. This would especially be true in the calorifier take off was between the engine thermostat and skin tank

 

Edited by Tony Brooks
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10 minutes ago, Tony Brooks said:
  1. This ^^^^^ except I would try hot in the top of the coil first because often the pipe run will stop therm-siphoning. This would especially be true in the calorifier take off was between the engine thermostat and skin tank

 

Yes indeed - prudence would suggest leaving the tails long enough to be swapped if necessary. Unfortunately,  mine weren't, and neither did they go down to the deck, but nothing a couple of new hoses at antifreeze change time couldn't so out! :)

 

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If you put the engine feed in at the top and return at the bottom when the water is hot it is possible there will be some convection driven flow through the engine block, just like a back boiler convection system. This will cause the water in the tank to cool faster than otherwise. Good for warming the engine when the webasto is on but not desirable.

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On 30/01/2020 at 17:15, Detling said:

If you put the engine feed in at the top and return at the bottom when the water is hot it is possible there will be some convection driven flow through the engine block, just like a back boiler convection system. This will cause the water in the tank to cool faster than otherwise.

I fitted a 12V shut-off valve to stop this from happening. Opens when engine is started and closes when engine is turned off. It also closes if the calorifier gets too hot (have a domestic style cylinder-stat to limit temp to 60C)

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34 minutes ago, Stephen Jeavons said:

I fitted a 12V shut-off valve to stop this from happening. Opens when engine is started and closes when engine is turned off. It also closes if the calorifier gets too hot (have a domestic style cylinder-stat to limit temp to 60C)

I'd be interested in the details of the valve Stephen.

 

I don't know whether you know, but you may be losing some hot water storage capacity/efficiency by limiting your tank temperature to 60 degrees. Whilst about 60 is typical for a household domestic immersion heater thermostat, the typical narrowbost tank has a mixer valve which sets the domestic hot water delivery temperature by mixing cold water with the stored hot as it is drawn. Storing the same quantity of water at the maybe 80 degrees your engine might heat it to (governed by your engine thermostat) delivers a greater volume of hot tap water when mixed to a lower temperature as determined by the mixer valve. In theory, a typical tank of 55 litres mixing at 50:50 would deliver 110 litres of hand hot water. It won't, but it illustrates the principle.

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Hi,

Yes, I know off-grid boaters and continuous cruisers like to have stonking hot calorifier water. My boat spends most of its time at a Res mooring with only the occasional cruise so I haven't had the problem of limited hot water. Unfortunately, retrofitting a thermostatic valve is going to be tricky in my installation due to a lack of space in the airing cupboard so I'm going to have to make do unless the requirement becomes critical in the future. My calorifier cupboard already looks like a steam-punk sculpture as I have a 3-port valve on the other coil along with all its pipework. If I ever go for a long cruise anywhere, I may yet have to do the installation of a thermostatic mixer. Thanks for the hint.

 

Stephen

 

Edited by Stephen Jeavons
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On 03/02/2020 at 08:52, Sea Dog said:

I'd be interested in the details of the valve Stephen.

I'm using one of these with power from the engine key-switch via a cylinder-stat. Temperature can be set as high as I want. You could wire without the cylinder-stat (although you'll probably need a relay to close the valve as it needs to be powered to either open or close).

Stops heat transfer back to the engine from the calorifier

 

https://www.ebay.co.uk/itm/12V-Motorized-Ball-Valve-1-2-3-4-1-Electrical-Valve-3-5Wire-DN15-20-25-145PSI/123299613819?hash=item1cb53acc7b:m:m6Dx1h3PsZm4sbz_DnV-xqA

 

s-l1600.jpg

Edited by Stephen Jeavons
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On 03/02/2020 at 07:55, Stephen Jeavons said:
On 30/01/2020 at 17:15, Detling said:

 

I fitted a 12V shut-off valve to stop this from happening. Opens when engine is started and closes when engine is turned off. It also closes if the calorifier gets too hot (have a domestic style cylinder-stat to limit temp to 60C)

If you do a bit of googling on legionares disease I think you will find that 60 isn’t hot enough to be sure of killing the nasty bugs.

just saying....

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7 hours ago, Sea Dog said:

Exactly. You need to take precautions to interrupt the thermosyphon, as you have.

... and as I have done with my valve above. Different solution, same effect.

11 hours ago, jonathanA said:

If you do a bit of googling on legionares disease I think you will find that 60 isn’t hot enough to be sure of killing the nasty bugs.

just saying....

True, but if you need to kill bugs in the hot water tank, chances are you're already drinking them from the cold tank.  No house I've ever owned has had the hot water cylinder hotter than about 55-60C. The motive for having a scalding hot water tank in this context is mainly so the hot water will last till the next heating cycle. I don't have that problem as I'm on shore power 99% of the time. My flow boiler does it auto-magically.

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