Hot Water from Engine Calorifier vs Diesel Heater?

[Cancunia]

My hot water currently comes from the engine which heats water in the immersion tank, but the boat also has a Mikuni diesel heater with radiators which according the manual can also be used to heat the hot water. So, just wondered if it's better while moored to run the engine to heat the water and also charge the batteries or if I just want hot water to plumb the diesel heater into the immersion?

 

 

[Tony Brooks]

In at typical narrowboat the Mikuni should be baled to do both at the same time, heat the hot water and heat the radiators. There may be valves that allow you to turn the radiators off in the summer and/ or select rads, hot water, both.

 

If you have a shoreline to keep the batteries charged, then not running the engine would be best in most people's eyes because it reduces the wear on an expensive item.  With no shoreline, we are in or approaching the time of year when solar is unlikely to provide enough charge, especially as the Mikuni uses electricity all the time it is running, so the chances are that you will have to run the engine.

[Cancunia]

1 minute ago, Tony Brooks said:

In at typical narrowboat the Mikuni should be baled to do both at the same time, heat the hot water and heat the radiators. There may be valves that allow you to turn the radiators off in the summer and/ or select rads, hot water, both.

 

If you have a shoreline to keep the batteries charged, then not running the engine would be best in most people's eyes because it reduces the wear on an expensive item.  

Thanks, I'll take a look at the plumbing when I get a chance. I'll be on winter moorings from Nov so as you suggest, I can use the hookup for the batteries.

[GUMPY]

If you have an immersion heater that's the cheapest, easiest, quickest way to het the water when on shore power.

[David Mack]

In boats with water cooled engines and a diesel heating boiler the calorifier is fitted with two heating coils, one for the engine coolant and one for the boiler circuit. That way you can heat the domestic hot water with the engine, the diesel boiler or both at the same time.

 

[blackrose]

11 hours ago, GUMPY said:

If you have an immersion heater that's the cheapest, easiest, quickest way to het the water when on shore power.

 

Unless you wake up in the mornings and want to quickly heat up the boat with the diesel heater for an hour or two, in which case hot water can be obtained as a free byproduct.

 

It depends on the time of year, the boat and other forms of heating available, but for the last few weeks I've been letting my stove die down overnight and don't get it going in the morning because it will be too hot in the boat during the day, but I still need to heat the boat up first thing so I use the Webasto and also get what's effectively free hot water.

[Paul C]

I don't think its a "free" byproduct in that case. 

[blackrose]

18 minutes ago, Paul C said:

I don't think its a "free" byproduct in that case. 

 

Why not? If I'm primarily using the Webasto to heat the boat for a couple of hours on a nippy morning then the hot water comes as a free byproduct as far as I'm concerned.

 

It's the same as people saying they get free hot water while cruising. If you're primarily using the diesel for propulsion and you get a tank of hot water then that's also a free byproduct. What's the difference between that and what I'm saying?

Edited October 12 by blackrose

[David Mack]

Webasto will use more fuel if it is heating the calorifier and the radiators, compared to heating the radiators alone. For the engine it will make no difference. Without the calorifier you will just shed more heat through the skin tank.

[blackrose]

13 minutes ago, David Mack said:

Webasto will use more fuel if it is heating the calorifier and the radiators, compared to heating the radiators alone. For the engine it will make no difference. Without the calorifier you will just shed more heat through the skin tank.

 

Really? I really don't think there's much in it and I'm sure any difference is cheaper than using the immersion to heat the calorifier from cold, which is the point I originally responded to. My Webasto Thermotop 5kW uses about 0.35 litres/hour (with the calorifier). I wonder how much less it would use without?

 

What about a stove with a backboiler connected to a calorifier? Would you say that's not free hot water as a byproduct of using the stove for heating, or are we saying it will use more coal so it's not free? I'm sure some people on the forum have been claiming it's free and nobody has ever challenged them.

Edited October 12 by blackrose

[Paul C]

22 minutes ago, blackrose said:

 

 

What about a stove with a backboiler connected to a calorifier? Would you say that's not free hot water as a byproduct of using the stove for heating, or are we saying it will use more coal so it's not free? I'm sure some people on the forum have been claiming it's free and nobody has ever challenged them.

 

1st Law of Thermodynamics - energy cannot be created or destroyed - would suggest not. In the case of the stove, unless the backboiler is up to the same temperature as the rest of the stove (which will never happen), it will act as a heatsink and x units of coal will produce slightly less temperature rise. You could put more coal on to get the boat to comfy temperature (in a similar time to a stove with no backboiler), or you could put the same amount of coal on and it would take longer (and there would be less coal remaining unburnt).

 

Similarly, the fact that the calorifier is in the circuit will act as a heatsink and the diesel boiler would either work harder, or go for longer. 

 

Contrast with the example of turning the engine on only to charge batteries vs charging batteries AND heating water. An engine is effectively a miniature CHP plant (combined heat and power) and because the heat which would be otherwise wasted (to the environment, via the skin tank warming some canal water) is also being used in a useful way, the overall efficiency will go up significantly if both tasks are accounted for.

[Tony Brooks]

25 minutes ago, blackrose said:

 

Really? I really don't think there's much in it and I'm sure any difference is cheaper than using the immersion to heat the calorifier from cold, which is the point I originally responded to. My Webasto Thermotop 5kW uses about 0.35 litres/hour (with the calorifier). I wonder how much less it would use without?

 

What about a stove with a backboiler connected to a calorifier? Would you say that's not free hot water as a byproduct of using the stove for heating, or are we saying it will use more coal so it's not free? I'm sure some people on the forum have been claiming it's free and nobody has ever challenged them.

 One only has to think about the energy the stove or Webasto is passing into the system and the amount of energy that therefore needs to come from the fuel. Stove or Webasto will have to provide the energy to heat the water in the calorifier so if they do not provide more energy the time needed to get the boat and calorifier up to temperature will be longer so although, under those circumstances, the appliance will burn the same amount of fuel per minute, but it will do it for longer so more fuel is burned. That is all nice in theory and confirms Paul's assertion, but as the time taken to heat the calorifier is fairly short as long as no hot water is drawn off then The amount of extra fuel used may not be that great, and as in the majority of cases the calorifier is always heated that extra fuel burn would be considered normal, so in that respect it looks like a by product of heating the boat, but it is still not free heat.

[blackrose]

Ok so I stand corrected. It's not free but it is a byproduct and given the difference between diesel consumption of 0.35 litres/hour with the calorifier and whatever marginal difference in diesel consumption heating 4 rads without the calorifier, it's also a cheap byproduct.

[Gybe Ho]

1 hour ago, David Mack said:

Webasto will use more fuel if it is heating the calorifier and the radiators, compared to heating the radiators alone.

 

 

I was looking at a Webasto plumbing diagram recently and it showed the calorifier heating coil from the diesel heater connected like an extra radiator on the main radiator circuit. If that is normal then I assume people install a valve to exclude the calorifier at times?

 

Does anyone know the emitter wattage of a calorifier coil? It would be interesting to know what proportion of the diesel heater output goes to heating water.

[Tacet]

1 minute ago, Gybe Ho said:

 

Does anyone know the emitter wattage of a calorifier coil? It would be interesting to know what proportion of the diesel heater output goes to heating water.

It depends on the difference in temperature of the heating and the heated water.  But 500w or 1000w has been mentioned here in the past for typical circumstances.

 

Back to Blackrose point, as has been said, engine heat is a waste product that would otherwise be dumped in the canal whereas calling for hot water from the Webasto is increasing its demand.  However, it is quite possible (depending on size of boiler and number of rad and other things) the Webasto will run more efficiently when made to work harder - so, at a guess, the increase in diesel burned could well be quite small.

[Gybe Ho]

6 minutes ago, blackrose said:

Ok so I stand corrected. It's not free but it is a byproduct and given the difference between diesel consumption of 0.35 litres/hour with the calorifier and whatever marginal difference in diesel consumption heating 4 rads without the calorifier, it's also a cheap byproduct.

 

Not really. There are 10kWh of raw energy in a litre of diesel but it is difficult to extract more than 3kWh in anything fitted on your narrowboat. With regard to cost this likely works out near to the kWh price a marina will charge for shore power.

 

Those 4 rads on your boat are unlikely to consume more than 2Kw even when the cabin temp is freezing. It takes 3 kWh to raise 55 litres of water from cold to 60 (c). If a calorifier coil is designed to heat the tank is a useful time period we can conclude more than 30% of your diesel heater output is taken by the calorifier.

[ditchcrawler]

24 minutes ago, Gybe Ho said:

 

I was looking at a Webasto plumbing diagram recently and it showed the calorifier heating coil from the diesel heater connected like an extra radiator on the main radiator circuit. If that is normal then I assume people install a valve to exclude the calorifier at times?

 

Why would you want to , unless you only want cold water on the boat and then you can just use the cold tap.

[Tony Brooks]

25 minutes ago, Gybe Ho said:

was looking at a Webasto plumbing diagram recently and it showed the calorifier heating coil from the diesel heater connected like an extra radiator on the main radiator circuit. If that is normal then I assume people install a valve to exclude the calorifier at times?

 

 

That is perfectly normal, but any single port fitted is usually to allow balancing, like the lock shield valves on radiators. Some use a three port valve to allow the heat to be directed to rads only, calorifier only, or both. This would usually be used to allow the calorifier can be heated in the summer without having the radiators emitting heat and without messing with all the radiator valves. Arguably more important now a lot of solar is in use, so engines do not have to be run frequently for battery charging..

[Gybe Ho]

5 minutes ago, Tacet said:

It depends on the difference in temperature of the heating and the heated water.  But 500w or 1000w has been mentioned here in the past for typical circumstances.

 

 

Thanks. I inferred a similar figure by working backwards from a reasonable expectation of heat up duration.

 

Is HW a nearly free incidental by product of diesel central heating? Scientifically definitely not.

 

In the case of a narrowboat operating in holiday mode where the cabin and calorifier is never cold and then the HW "byproduct" cost is less than the end of meal gratuity at a waterside pub.

 

In the case of a CCer narrowboat offgrid for the winter and where the calorifier is bought up to 60(c) twice a week then yes the cost is noticeable, say £10 to £20 a month however the hardcore offgridder will have a back boiler and the stove will run on scavenged wood.

[Tacet]

You're well adrift  with your additional monthly  cost of heating a calorifier when the CH is operating anyway.

 

£20 will buy 20 litres of diesel at the domestic split.  Blackrose says his Webasto uses about 1/3 litre per hour - and that is for both space heating and domestic hot water; let's say (again generously) that the hot water consumes one third.  

 

So, he can have the Webasto heating the calorifier for about 180 hours per month for £20 of diesel.   Which is more than enough to heat a cylinder twice a week!

[Gybe Ho]

11 minutes ago, ditchcrawler said:

Why would you want to , unless you only want cold water on the boat and then you can just use the cold tap.

 

See my budget CCer usage profile just above.

 

A calorifier maintained at 60(c) will loose* 1+ kWh of heat a day. Assuming solar dump provides free hot water 7 months of the year, a regime of occasional hotwater could save £50 a year plus the immeasurable value of feeling like the noblest of eco warriors.

 

 

* On some boats the "lost" calorifier energy will heat the cabin but not on my design.

[matty40s]

1 hour ago, Gybe Ho said:

 

I was looking at a Webasto plumbing diagram recently and it showed the calorifier heating coil from the diesel heater connected like an extra radiator on the main radiator circuit. If that is normal then I assume people install a valve to exclude the calorifier at times?

 

Why would you assume that ??...again you are doing something that 99% of installations do not do, and Webasto dont show on their plumbing diagrams.

I have never installed a shutoff valve to a Eberspacher ,mikuni, or Webasto system, and never had that request.

[StephenA]

1 hour ago, Gybe Ho said:

 

I was looking at a Webasto plumbing diagram recently and it showed the calorifier heating coil from the diesel heater connected like an extra radiator on the main radiator circuit. If that is normal then I assume people install a valve to exclude the calorifier at times?

 

Does anyone know the emitter wattage of a calorifier coil? It would be interesting to know what proportion of the diesel heater output goes to heating water.

 

You might want to put a divert so that you can run the Webasto and the calorifier withput running the radiators.

[blackrose]

1 hour ago, Gybe Ho said:

 

Not really. There are 10kWh of raw energy in a litre of diesel but it is difficult to extract more than 3kWh in anything fitted on your narrowboat. With regard to cost this likely works out near to the kWh price a marina will charge for shore power.

 

Those 4 rads on your boat are unlikely to consume more than 2Kw even when the cabin temp is freezing. It takes 3 kWh to raise 55 litres of water from cold to 60 (c). If a calorifier coil is designed to heat the tank is a useful time period we can conclude more than 30% of your diesel heater output is taken by the calorifier.

 

Well there seems to be some difference between your view and Tacet's who like me thinks the difference could be marginal. 

 

I was talking diesel consumption rather than heater output, but assuming they correlate then you're saying that if I isolate the calorifier coil my Webasto would only be burning 0.25 litres/hour (30% less than my current consumption). Sorry but that just doesn't stack up with the consumption figures I've got because once the calorifier is heated (30mins) it's no longer drawing heater output and I'm running the heater for often much longer than that.

Edited October 12 by blackrose

[matty40s]

1 minute ago, StephenA said:

 

You might want to put a divert so that you can run the Webasto and the calorifier withput running the radiators.

It is always recommended that at least one rad on the circuit is left partially open ( usually the bathroom one, as the heater units dont like just a calorifier for output, run too low, and coke up.