Calorifier heating system - am I making sense?

[IdealStandard]

So I've been planning an adaptation to my heating system for a while - it's one of those things where I'm planning to build something as a stopgap with the potential to expand it later, but I'm not sure by how much.

 

Currently I have a Chelsea Villager Duo stove without a backboiler as a main heat source. It's great, but it's old and keeping in a fire overnight is near enough impossible without using loads of smokeless (which feels like a waste). I have a Rinnai instant water heater that does the job for showers and washing up.

 

I've got a water cooled engine and I set up a really simple system of heating some radiators using a heat exchanger and a small 12v pump. It did the job, but there's obviously no heat storage and what I really want is a system that allows me to flip a switch and have heat in the morning. The radiators are still there, with pipes heading out to the engine bay.

 

The plan was always to leave potential for a calorifier and I think it's now time to sort it out properly.I'm not shorepower quite a lot, but I want to be able to cruise in comfort and use the engine for heat.

 

So.......

 

For my current setup to function I require a calorifier with enough capactiy and heat retention to allow me to run the engine before 8pm and have hot rads for around an hour at 7am.

 

I think I need a single coil calorifier (in the future a backboiler would be sensible, but it's a bit of a pipe dream so not sure I need to plan for it) with pretty minimal capacity but good thermal properties.

 

I also don't want to spend much money!

 

Will 22l be enough?

Is single coil much cheaper than double or should I just get a double to futureproof?

Are the immersion heaters pretty standard in term of efficiency?

Can anyone see any flaws in my current system?

Does the PRV on the calorifier negate the need of a header tank?

 

Any links or leads to cheap/secondhand/good calorifiers?

 

Many thanks

Tim

[nicknorman]

So I've been planning an adaptation to my heating system for a while - it's one of those things where I'm planning to build something as a stopgap with the potential to expand it later, but I'm not sure by how much.

 

Currently I have a Chelsea Villager Duo stove without a backboiler as a main heat source. It's great, but it's old and keeping in a fire overnight is near enough impossible without using loads of smokeless (which feels like a waste). I have a Rinnai instant water heater that does the job for showers and washing up.

 

I've got a water cooled engine and I set up a really simple system of heating some radiators using a heat exchanger and a small 12v pump. It did the job, but there's obviously no heat storage and what I really want is a system that allows me to flip a switch and have heat in the morning. The radiators are still there, with pipes heading out to the engine bay.

 

The plan was always to leave potential for a calorifier and I think it's now time to sort it out properly.I'm not shorepower quite a lot, but I want to be able to cruise in comfort and use the engine for heat.

 

So.......

 

For my current setup to function I require a calorifier with enough capactiy and heat retention to allow me to run the engine before 8pm and have hot rads for around an hour at 7am.

 

I think I need a single coil calorifier (in the future a backboiler would be sensible, but it's a bit of a pipe dream so not sure I need to plan for it) with pretty minimal capacity but good thermal properties.

 

I also don't want to spend much money!

 

Will 22l be enough?

Is single coil much cheaper than double or should I just get a double to futureproof?

Are the immersion heaters pretty standard in term of efficiency?

Can anyone see any flaws in my current system?

Does the PRV on the calorifier negate the need of a header tank?

 

Any links or leads to cheap/secondhand/good calorifiers?

 

Many thanks

Tim

Someone else suggested such a scheme recently and it was generally dismissed by the forum. I think you should do some calculations on the amount of heat energy stored in a hot calorifier (well hot-ish, since it is bound to cool overnight somewhat) and the amount of very cold water in the central heating system (pipes + radiators) that will all get mixed up with the hot when you turn the pump on, and remember that the heating effect of the radiators is proportional to how much warmer than the surrounding they are.

 

My gut feeling is that it would get the rads warm, but not enough to make a significant difference to the boat's air temperature. Sorry I am too lazy to do the calculations for you!

Edited October 13, 2014 by nicknorman

[Alan de Enfield]

Your calorifier will lose heat overnight, the water in your radiators will be cold and you will be mixing cold with 'warm'..........

 

 

NickNorman beat me to it !!!!

[bottle]

At a guess I would expect the heat store (calorifier) will be cold within two minutes after you had turned on the pump to the radiators.

 

So you may have warmed the pipes and radiators but the boat, no.

[IdealStandard]

Interesting.

 

That does make a lot of sense.

 

So plumbing the heat exchanger back in to allow direct heating of the rads from the engine is probably a more effective way of heating them up? Not much use when I'm up at 7, but for lazy mornings it's an option.

 

Ideally I'd have a backboiler with rads in the bedroom (at the stern) as the heat really doesn't make it down there and particularly not overnight.

[nicknorman]

Interesting.

 

That does make a lot of sense.

 

So plumbing the heat exchanger back in to allow direct heating of the rads from the engine is probably a more effective way of heating them up? Not much use when I'm up at 7, but for lazy mornings it's an option.

 

Ideally I'd have a backboiler with rads in the bedroom (at the stern) as the heat really doesn't make it down there and particularly not overnight.

Yes to both of those. The first, we have and it's very good (although we do a lot of cruising. The second, I wish we had because whilst the front of the boat is toasty, the back is chilly in the mornings and we have to burn diesel on the central heating.

[jonesthenuke]

I have a similar approach in my house with a large calorifier used to store heat from a wood burning boiler in the evenings with the aim that it is enough to warm the radiators in the morning. This works OK but the heat store is much larger than a boat calorifier.

 

Here is a very rough estimation of what you could achieve with 22 litres of water as a heat store. Its not enough to be very effective so the calcs are basic.Assume you heat the calorifier as hot has you practically can (say 90 C, approaching 100 C would worry me) and it loses no heat overnight (very well lagged).

 

In the morning you then take heat from the calorifier and dump it to the radiators. Assume you cool the calorifier to 50 C, the rads would be at a lower temperature due to the differential across the heat exchanger so perhaps 45 C by the time the calorifier has cooled down and become ineffective. This would make the rads warm rather than hot. You could assume the boat is cold and "claim" more heat transfer, but I do not think you would feel much benefits from lower temperatures as the heat transfer would be slow (not enough area for the small temperature differential between the water and the air). The change in temperature of the calorifier water defines how much energy you can store and then transfer.

 

The energy removed from the calorifier will be Mass X Drop in temp X Specific heat capacity of water

 

Thus 22 X (90-50) X 4.2 kJ (kilo-Joules) = 3696 kJ

 

By comparison a one kilo-Watt heater would give you 3600 kJ, so its about the same as a 1 kW heater for an hour.

 

To me this does not seem a great benefit, but your rads would be warm(ish). To do better you need much more mass (water in calorifier) as you cannot do much with the temperature change and I am assuming that you would not want to use a fluid other than water.

 

Hope this helps.

 

Chris

Edited to correct some typos

Edited October 14, 2014 by jonesthenuke

[smileypete]

How about making a convertible bed in the saloon for colder nights?

 

Or see if a decent secondhand Airtop or Propex heater turns up?

 

For something Heath Robinson like, could hot water from the Rinnai be passed through a fan matrix, cooled to tepid, then safely recirculated somehow?

 

cheers, Pete.

~smpt~

Edited October 14, 2014 by smileypete