Twin coil calorifier

[Maudesmaster]

I have an Eberspacher hydronic 5 if instead of water circulating through 1 coil and returning to heater I pipe from 1st coil through second coil will it heat the water in the tank faster? 
I ask because heater set to cycle 1 hour rads a lovely hot if I set timer for more heater cuts out due to over heat 

[Tracy D'arth]

Yes.

[David Mack]

2 hours ago, Maudesmaster said:

I have an Eberspacher hydronic 5 if instead of water circulating through 1 coil and returning to heater I pipe from 1st coil through second coil will it heat the water in the tank faster? 
I ask because heater set to cycle 1 hour rads a lovely hot if I set timer for more heater cuts out due to over heat 

Not initially, as the first coil will extract all the heat from the circulating water anyway, but as the calorifier warms up the second coil will start contributing, so overall heat up time will be quicker.

[Guest]

2 hours ago, David Mack said:

Not initially, as the first coil will extract all the heat from the circulating water anyway, but as the calorifier warms up the second coil will start contributing, so overall heat up time will be quicker.

I don't think the first coil will extract "all" the heat. This rather depends on the size of the coil. It may also depend upon the location of the coils and whether the cylinder is vertical or horizontal. For what it's worth I  asked much the same question some years ago. You got more encouraging answers than I got. 😁

I did exactly what you are suggesting on a horizontal cylinder and the heat up time was slightly better than half. (Better than I was expecting!) I suspect that heating both ends of the cylinder reduced the amount of circulation required to get it all up to temperature.

[Tracy D'arth]

2 hours ago, David Mack said:

Not initially, as the first coil will extract all the heat from the circulating water anyway, but as the calorifier warms up the second coil will start contributing, so overall heat up time will be quicker.

The first coil will have insufficient surface area to transfer all the heat to the stored water so the second coil will transfer more. So it will warm up faster with both coils connected.

[PD1964]

I see you say over heating and your thinking of using both your coils on one heat source and not doing it the normal way of Heater coil and engine coil, can you use your engine for hot water? 
 Why would you want your heater on, on a lovely hot day?

Edited September 5, 2022 by PD1964

[Tony Brooks]

27 minutes ago, PD1964 said:

I see you say over heating and your thinking of using both your coils on one heat source and not doing it the normal way of Heater coil and engine coil, can you use your engine for hot water? 
 Why would you want your heater on, on a lovely hot day?

 

Probably because there may be valves that need adjusting to put more hot water through the coil and less through the rads.

[jonathanA]

I'm wondering whether connecting both coils in parallel (both connected across the boiler) rather than series (one after another), would be the best way of transferring the maximum heat into the cauliflower ?

[Thames Bhaji]

You will get greater heat transfer with the liquid on either side of the heat exchanger moving faster across the surface. With the coils in series (as opposed to parallel) the water inside will be travelling twice as fast, so I think this would transfer more of the heat. 

[jonathanA]

Half as fast as twice the distance surely ? 

[Tracy D'arth]

Assuming the flow rate doubles when in parallel it will be faster but it is unlikely to double the flow rate with the same pump head, the resistance of the coils is quite low.

Foe ease of plumbing and venting I would go for series, lowest coil bottom connection to the flow and return from the top of the upper coil.

[Thames Bhaji]

26 minutes ago, jonathanA said:

Half as fast as twice the distance surely ? 

You have the same volume of water being pushed down either one or two pipes at a time - if it’s going down one it will be going twice as fast. 

[Maudesmaster]

3 hours ago, PD1964 said:

I see you say over heating and your thinking of using both your coils on one heat source and not doing it the normal way of Heater coil and engine coil, can you use your engine for hot water? 
 Why would you want your heater on, on a lovely hot day?

It’s a 3LW Gardner cooling via skin tanks and doesn’t get warm at all 

[Tony Brooks]

7 hours ago, Maudesmaster said:

It’s a 3LW Gardner cooling via skin tanks and doesn’t get warm at all 

 

Not sure if you are talking about the engine or calorifier. If it is the engine then something is wrong, have you checked the thermostat. If the engine gets hot but not the calorifier then where are the calorifier connections on the engine and are you sure there is no air lock in the calorifier coil. If you mean that the calorifier does not heat up when from the boiler then how is it piped relative to the boiler and rads, and are you sure there is no air lock in the coil. Finally, are there any NRVs in the coil circuit. If so are they correctly orientated and of the flap type. The spring type MIGHT be stiff enough to prevent circulation.

 

An hour with the boiler running at temperature should get you adequate hot water.

[Maudesmaster]

Thank you

The engine cooling never get very hot so didn’t pipe to califorier there is no thermostat at present the housing for it is not recessed round the rim for the thermostat to fit into Not bothered too much as engine will never be cold it is a mid engined narrow boat 

I have bled all pipe work no air in system 

And tried turning rads off and adjusting rad inlet valves 

I think with the heater over heating cycling has choked the workings a bit  so probably in need of a service, it takes a couple of attempts to fire up now fair bit of smoking on first attempt 

 

Thank you all for input 

[Tony Brooks]

If the coil circuit is properly bled then I get the impression there is a pipe work or valving problem preventing the coil getting enough hot water. If this were mine I would be drawing a diagram.

 

Edited to add: how old is the calorifier, I am wondering it the outside of the coil is badly furred up. That would reduce heat transfer.

Edited September 6, 2022 by Tony Brooks

[IanD]

2 hours ago, Tony Brooks said:

 

Not sure if you are talking about the engine or calorifier. If it is the engine then something is wrong, have you checked the thermostat. If the engine gets hot but not the calorifier then where are the calorifier connections on the engine and are you sure there is no air lock in the calorifier coil. If you mean that the calorifier does not heat up when from the boiler then how is it piped relative to the boiler and rads, and are you sure there is no air lock in the coil. Finally, are there any NRVs in the coil circuit. If so are they correctly orientated and of the flap type. The spring type MIGHT be stiff enough to prevent circulation.

 

An hour with the boiler running at temperature should get you adequate hot water.

 

Measurements show that a typical size calorifier with a standard size heating coil (e.g. Surecal 55l) only heats the water up by about 16C per hour, regardless of whether the coil is heated by the engine or a boiler (or a generator).

 

https://www.perseverancenb.com/post/how-to-measure-the-calorifier

 

So an hour might get it up to 40C which is hot enough for a shower. The coil only has just over 1kW capacity which is not enough to absorb the heat generated by a standard Eberspacher or Webasto, so these will shut off due to overheating unless other loads like radiators are also connected.

 

The newer Eberspachers can throttle down to much lower power levels (1.3kW?), in this case using both coils instead of one would absorb 2kW which is enough to stop it overheating and short-cycling -- and would heat up the water twice as fast, around 30C per hour.

 

Alternatively some calorifier suppliers (e.g. coppercylinder.co.uk) can supply calorifiers with higher yield coils which will heat the water faster (boiler and engine) and prevent short-cycling, but this obviously means paying for a new calorifier...

 

https://www.coppercylinder.co.uk/customise-your-hot-water-cylinder.html