Calorifier Overnight Heat Loss, is This a Solution?

[BargeeSpud]

Hiya,

 

We're getting used to the new boat's systems & have found that we've built in a problem, namely the calorifier totally loses hot water overnight.

 

The set up is this:

 

Vertical 75litre twin coil calorifier supplied by gravity feed - 22mm coil - from back boiler or Webasto (isolated during winter), immersion heater, & engine or generator (via "Y" valves). There is an isolation valve located on the cold inlet to the calorifier from the back boiler.

 

First, after discovering the problem of going cold overnight, I realised that with the stove unlit, the immersion was in effect gravity heating the boat & I set the above mentioned isolation valve to the off position hoping it would make a difference which it didn't, well maybe slightly but not much. The gravity cicuit top pipe gets noticeably warm up to 6 to 8 feet either side of the calorifier, so heat from the hot water in the calorifier is being dissipated into the heating circuit.

 

I'm wondering whether fitting a 2nd isolation valve in the hot outlet side of the gravity circuit from the calorifier would stop the heat being dissipated like this.

 

Yes? Or is there something else I need to consider?

 

Cheers.

[Iain_S]

Another possible source of heat loss is via the engine circuit, which can thermosyphon backwards when the engine is cold. Possible cures are hoses between engine and calorifier which dip below the level of the engine, or I have seen it recommended that the connections are made top of engine to bottom of calorifier coil and top of coil to engine return, as the water pump will overcome the thermosyphon effect when the engine is running.

 

Iain

[Machpoint005]

We simply have a stop cock on the pipe from the engine -- shutting this preserves the hot (well. quite warm) water overnight as it prevents the calorifier from warming the engine.

[DHutch]

Said stopcock could be electrically operated from the ignition feed I guess?

 

 

Daniel

[Machpoint005]

Said stopcock could be electrically operated from the ignition feed I guess?

 

 

Daniel

 

Now there's a project to think about!

I'll probably be sticking with the Mark 1 human left hand for a while yet, though.

[BargeeSpud]

No, the engine/generator circuit is not the source, they have yet to be filled & are isolated at the moment. The reason I ask about the 2nd isolation valve on the gravity circuit is that I have to drain the system down to add antifreeze to it for the Webasto & that would be a good time to break in to fit the extra valve.

Edited May 18, 2015 by BargeeSpud

[Detling]

The danger with any isolation valve is that you will forget to open it. The webasto needs a heat dump or if will object and shut down, do that too often and they can go into a sulk and need an expensive man to fix them. The back boiler also needs to be able to release heat or at least vent it's steam before it explodes.

[MtB]

Another possible source of heat loss is via the engine circuit, which can thermosyphon backwards when the engine is cold. Possible cures are hoses between engine and calorifier which dip below the level of the engine, or I have seen it recommended that the connections are made top of engine to bottom of calorifier coil and top of coil to engine return, as the water pump will overcome the thermosyphon effect when the engine is running.

 

Iain

 

 

The simplest answer is to raise the height of the calorifier. Put it well above the engine and the stove to prevent any reverse thermo-syphoning.

 

Mucking about with isolation valves, electric valves, non return valves etc is tinkering with the symptoms rather than the cause of the problem, and often comes with unpredictable side effects.

 

 

MtB

[Flyboy]

Hiya,

 

We're getting used to the new boat's systems & have found that we've built in a problem, namely the calorifier totally loses hot water overnight.

 

The set up is this:

 

Vertical 75litre twin coil calorifier supplied by gravity feed - 22mm coil - from back boiler or Webasto (isolated during winter), immersion heater, & engine or generator (via "Y" valves). There is an isolation valve located on the cold inlet to the calorifier from the back boiler.

 

First, after discovering the problem of going cold overnight, I realised that with the stove unlit, the immersion was in effect gravity heating the boat & I set the above mentioned isolation valve to the off position hoping it would make a difference which it didn't, well maybe slightly but not much. The gravity cicuit top pipe gets noticeably warm up to 6 to 8 feet either side of the calorifier, so heat from the hot water in the calorifier is being dissipated into the heating circuit.

 

I'm wondering whether fitting a 2nd isolation valve in the hot outlet side of the gravity circuit from the calorifier would stop the heat being dissipated like this.

 

Yes? Or is there something else I need to consider?

 

Cheers.

Fitting a non return valve in the engine to calorifier hot feed pipe should fix the problem. You could also try a loop or dip in the engine hot feed pie, it doesn't take much to stop a thermo syphon.

[MtB]

Fitting a non return valve in the engine to calorifier hot feed pipe should fix the problem. You could also try a loop or dip in the engine hot feed pie, it doesn't take much to stop a thermo syphon.

 

 

All this focus on stopping reverse circulation through the engine is ignoring the problem described in the OP.

 

That of reverse circulation in the radiators.

[BargeeSpud]

 

 

All this focus on stopping reverse circulation through the engine is ignoring the problem described in the OP.

 

That of reverse circulation in the radiators.

 

Thank you Mike, I'm glad someone was paying attention!

 

Some clarification is in order I think &, Mike, please correct any errors I might make in my description of how I believe a gravity heating system works.

 

When the the water in the back boiler of a solid fuel stove heats up, convection will occur in that the heated water will rise to the top outlet, drawing cooler water into the bottom inlet of the boiler. This heated water progresses through the top of each radiator as the cool water at the bottom of the radiator is drawn out towards the boiler & so you get a circulation without the need for a pump. Any calorifier installed in a gravity system is, in effect, just another radiator that heats water rather than air space, provided it has a suitable coil.

 

Now, my situation is that because I can't totally isolate the calorifier from the gravity system like I can with individual radiators, any heat contained within it is being transferred to the cooler water within the calorifier's gravity coil & despite the fact it can't circulate because the bottom gravity valve is closed, that heat is being dissipated some 6 or 8 feet along the top "hot" pipe of the gravity system to either side of where the calorifier is tee'd into it. Thus, I'm losing all my hot water overnight.

 

My thinking is that because the calorifier is installed in exactly the same way as a radiator in my gravity system, fitting an isolation valve in the top "hot" outlet of the gravity coil, should prevent the heat being dissipated to the rest of the gravity system, or at least slow it right down to the bare minimum. All I was asking is whether my thinking is correct or whether I should consider an alternative solution. The problem is totally unrelated to the Webasto or the engine/generator as these are not capable of heating the calorifier at the moment, they were merely mentioned to give a complete picture of my installation & maybe I shouldn't have mentioned them at all.

Edited May 19, 2015 by BargeeSpud