Hot Water Heat Exchanger

[flicka]

I grabbed this from Clive's post regarding Diesel Heaters.

 

There is no reason why motorhomes cannot have an engine heat exchanger with other forms of water heating. Frankia and Niesmann for example offer this as one of the options, others most likely as well.

C.

 

These were popular in the 70's but I don't see any advertised

Does anyone know of any on the market & if they can be fitted in conjunction with the Truma Water heater.

Seems such a waste of al the engine heat going to waste whilst travelling.

I am also thinking about using it to heat the rear of the M/H when on the road.

[Guest Le Thou]

Hi Flicka

The only way you could extract heat from the engine would be via the use of heat exchangers which are basically like the radiator under you bonnet, this may have some serious long term effects on the longevity of your engine. Based on the amount of coolant swilling around your engine limits the time it takes for your engine to reach working temperature and this level is quite cruicial. If you make too many short trips and your engine rarely reaches the ambient working temperature I feel tis in turn will add to engine wear.

Should you ask the engine to heat up additional pipework and an additional matrix again this will take much longerfor your engine to effectively warm up.

 

[colin]

Last time I looked these where availible, also work in reverse and warm engine up on cold mornings

p.s. crossed over with Le Thou, it should have a thermostat built in so only works when engine up to temp

[Guest peter]

Le Thou - 2008-01-05 9:15 PM

 

Hi Flicka

The only way you could extract heat from the engine would be via the use of heat exchangers which are basically like the radiator under you bonnet, this may have some serious long term effects on the longevity of your engine. Based on the amount of coolant swilling around your engine limits the time it takes for your engine to reach working temperature and this level is quite cruicial. If you make too many short trips and your engine rarely reaches the ambient working temperature I feel tis in turn will add to engine wear.

Should you ask the engine to heat up additional pipework and an additional matrix again this will take much longerfor your engine to effectively warm up.

The coolant does not circulate any pipework outside of the engine block until the thermostat opens and this does not happen until the engine is up to the temperature. so any additional pipework will have no detrimental effect on the engine. As the additional pipework cools down the coolant, the thermostat will close partially until temp is raised again. Boats have used this method of heating up the hot water tank for showers etc for years and these engines last for 30Yrs plus. so if you want a hot water system heater in the rear of your van, why not look out an old car heater. The old Mini springs to mind as it is self contained and easy to remove/install.

[flicka]

Thanks Peter

I can not understand Le Thou's concern regarding the additional pipework increasing water capacity. This method is still used in many Ambulances for rear heaters (admitted they are usually at full operating temperature for most of ther time) but as you say the engine thermostat dictates when the system begins to circulate.

I converted an old ambulance in the 70's that used a heater matrix box and it worked a treat to warm the rear section

Back then it was a Smith Industries product, but I can't find any reference too them today. A Mini Heater Matrix will only supply warmth, not hot water. (but it is a reasonably simple job) supply & delivery hoses, Heater Matrix & electric supply cable for the fan.

 

What I want to do is install a Heat Exchanger to capture Hot Water.

 

Has anyone linked a an Exchanger to a Trauma Water Boiler system. Any info would be appreciated.

[Derek Uzzell]

flicka:

 

Alde market a heat exchanger designed to transfer heat between the cooling system of a leisure-vehicle's motor and Alde's 'wet' central-heating system (or vice versa). CAK offer a range of 'calorifiers' intended to store water warmed by waste-heat from a vehicle's motor - also various auxiliary blown-air matrices of the type you used on your ambulance. Eberspacher and Webasto also produce calorifiers for hot water storage.

 

I'm sure it would be possible to exploit some or other of the above equipment. However, if I were considering doing it, I'd start by sketching on a piece of paper how I might connect together the motor's cooling-system, hot water storage-vessel and the Truma boiler - and then I'd drop the idea! While I can fully appreciate the attraction of free 'domestic' hot water as a spin-off from a motorhome's engine coolant, I believe you need to begin with a heating system designed to produce this bonus rather than try to modify an existing system that lacks the capability.

 

Good luck, but if you can build something that does what you want but doesn't have major drawbacks when it comes to practical usage, then you are a far better man than me.

[Basil]

flicka - 2008-01-05 9:06 PM

 

These were popular in the 70's but I don't see any advertised

Does anyone know of any on the market & if they can be fitted in conjunction with the Trauma Water heater.

 

Kenlow, of aftermarket electric cooling fan fame, are a regular advertiser of these though as it is normally in the Caravan Club magazine non members may not have seen the adverts see

 

http://www.kenlowe.com/history/index.html

 

forth item down the list on the top left of page. Though I believe they are independant and cannot be fitted in conjunction with your existing unit.

 

Bas

[Brian Kirby]

The space heating part should be solvable using any of the above suggestions.  If the rear of the van is cold while travelling, and provided there is room for the water to air heat exchanger, this seems a straight gain. 

However, as an alternative (albeit one that doesn't capture the engine waste heat), if your space heating is via a Truma Combi (possibly others), I wonder if it might be cheaper overall to consider fitting a Secumotion (or DriveSafe) Truma regulator, and the necessary gas cylinder pigtails to go with it.  I believe these units may now be available for after-market fit.  If so, and subject to confirmation from Truma that your heater is also suitable, you would be able to use your normal gas space heating while driving, with complete legality, throughout Europe.  Speak to Truma?

The water heating part would seem to me to need a water to water heat exchanger, in the form of a storage heater, inserted into the cold water feed to the Truma.  This would then feed pre-heated water into the Truma, which it could then heat further if/as required or, when the engine heated stored hot water is exhausted, just feed cold water to the Truma as normal.  However, it would cost time and money to fit, it would take up space, it would complicate winter drain down, and it would only be of benefit for as long as the stored hot water lasted.  Whether the gain of "free" hot water for, say, 6 hours after stopping the engine, would adequately compensate for the inherent losses, I doubt: but it may work for some.

[Derek Uzzell]

I view flicka's inquiry as a close relative of the following:

 

http://www.outandaboutlive.co.uk/forums/forums/thread-view.asp?tid=9644&posts=10

 

Installing a secondary water-storage vessel presents a dilemma - where do you put it in relation to flicka's existing Truma Ultrastore boiler? The boiler and (presumably) the new storage-vessel (NSV) will both have a single input point for water entry and a single output point for water exit. Let's assume the NSV and Truma boiler can each contain 10 litres of water and that the NSV is installed 'in series' with the boiler, with the NSV going between the motorhome's water-pump and the boiler. If the water in the NSV has been warmed by engine heat produced while the motorhome has been driven but the Truma boiler has not been in operation, then, for hot water in the NSV to reach the taps, the 10 litres of cold water in the Truma boiler must first be drawn off.

 

If we swap the boiler and NSV positions so that the NSV is between the Truma boiler and the motorhome's water taps, then hot water from the NSV will be delivered immediately to the taps. However, if there is cold water in the NSV - probably the normal situation for a motorhome - and the Truma boiler is operated, then 10 litres of cold water in the NSV will first need to be drawn off before hot water from the boiler can arrive at the taps.

 

Both of these scenarios (besides being infuriating) will impact adversely on the motorhome's water reserves/waste-water storage capacity and there's bound to be heat dilution as warm water in the NSV enters cold water in the boiler, or vice versa. You really need to have hot water simultaneously in the NSV and Truma boiler to gain true benefit and I can't see that happening too often.

 

An alternative might be to put the NSV 'in parallel' with the Truma boiler. I envisage this involving a 'Y'-connector being inserted in the existing cold-water feed to the boiler so that cold water is also delivered to the NSV, plus a 2nd 'Y'-connector in the existing hot-water feed from the boiler and leading back to the NSV's water output point. The NSV and boiler are now linked 'circularly' and, if an in-line electric pump is put in the pipe-run that forms that circle, it could be used to transfer hot water from the NSV to the Truma boiler while the motorhome is being driven, or hot water from the boiler to the NSV when the boiler is operated. In principle you'd get 20 litres of 'free' hot water in the first instance and twice your original 10 litres hot water storage capacity in the second. It's possible that (with the addition of valves and thermostats in critical positions) this arrangement could be made to work satisfactorily, but I suspect the resultant system would be as complex as a submarine's toilet (and perhaps as potentially lethal!).

 

Of course what one really should be doing (and I expect this is what flicka had in mind) is to transfer waste heat from the motor's cooling system directly to the Truma boiler, thus avoiding the NSV requirement altogether. All you'd need to do is remove the boiler's top cover, fabricate a heat-exchanger that would sit in contact with a large area of the boiler's water-tank and then swathe the top of the heat-exchanger and boiler heavily with insulation. Engine coolant passing through the exchanger should then transfer heat by conduction to the water in the boiler. Piece of cake... ;-)

[Geoff Cole]

A couple of years ago, I hired a camper in New Zealand for 3 weeks it was fitted with a calorifier, run of the engine cooling system with an electric element fitted which automatically maintained the hot water when hooked up. We never run short of hot water even when free camping. The water was always piping hot. Over the 3 weeks we used hardly any gas.No boiler to maintain and virtually nothing to go wrong. I do not know why this is not used here on campers, this system has been used successfully on boats for years.

[Derek Uzzell]

Geoff:

 

The downside of the engine-coolant/230V calorifier system for many (most?) motorcaravanners would be when camping where no hook-up is available for water heating. Alde's 'wet' central heating system has the option of exchanging heat between motor and gas/230v boiler, as do the 'wet' versions of Webasto and Eberspacher diesel-fuelled systems.

 

I don't think the call is there in Europe for the type of system you used in New Zealand: certainly it would be unacceptable to me as I rarely use campsites.

[Brian Kirby]

Derek Uzzell - 2008-01-07 9:23 AM ..........Let's assume the NSV and Truma boiler can each contain 10 litres of water and that the NSV is installed 'in series' with the boiler, with the NSV going between the motorhome's water-pump and the boiler. If the water in the NSV has been warmed by engine heat produced while the motorhome has been driven but the Truma boiler has not been in operation, then, for hot water in the NSV to reach the taps, the 10 litres of cold water in the Truma boiler must first be drawn off........

That's about what I had in mind, Derek, except that I would not expect to get hot water from the system unless the Truma was also on.  Not instantaneous, therefore!  The only advantage of a pre-heated NSV feed to the Truma, would be that for so long as the NSV water remained hot, the gas consumed by the Truma in maintaining its hot water supply would be reduced.  However, I still think the disadvantage of having two water heaters to fill and drain, plus the cost of the extra heater, plus the complexity of installing the engine coolant loop, plus the space taken for the extra heater, wildly outweighs any minor gain in reduced gas consumption.

Now, a Truma with a built in engine fed water to water heat exchanger really would be useful.  I wonder if they've ever considered making one?

[colin]

Or maybe chuck the Truma and fit a Atwood 3 way, all that free hot water and it must be less than £1000 to fit? :-S

[flicka]

Thanks for all the input especially derek & brian.

I maybe didn'y explain myself enough, cos ot seems to be getting complicated.

The option of "free" hot water produced whilst travelling and especdially when camping without EHU appeals, as it will also extend Gas supply.

I have tried to illustrate what I visualise in the attachment.

Regarding Dereks comment of 2 Water system the only extra water I anticipate is to fill a small Exchanger and it's associated supply/delivery hoses.

 

I think that the hot water would move itself by thermal transfer from the Heat Exchanger to the Truma boiler tank. ?????

 

The problem I foresee is regarding expansion as the Water as it is heated, but I anticipate the Truma will be capable of handling that.

 

I would be very pleased to have your opinions.

 

 

Heat Exchanger.ppt

[Derek Uzzell]

Brian K:

 

I doubt if Truma has considered adding an 'engine coolant' heat-exchanger to their products. This is not because it would be technically impossible, just that, since 1997, Truma has owned Alde and the latter company's "Compact" air/water heaters (introduced in 1993) have included an exchanger option within their design brief. So, if motorhome manufacturers wish to make 'free' air/water heating a selling point for their vehicles, they can do it via the Alde system and the Truma parent company will still benefit commercially. Besides which, it's a lot simpler to incorporate an exchanger into Alde's 'spread all around the motorhome' heating system than it would be if the exchanger were embedded in an 'installed in one position' heater/boiler of the type Truma has always concentrated on.

 

Colin:

 

I'm not familiar with the appliance you mention, but I assume it's a heater fitted to USA RVs. As far as I'm aware there is no European commercial support for Atwood products (Truma subsumed Atwood's European arm in around 1999 when it went bust), so that might present problems. Is there anything on the internet to describe the Atwood heater, please?

 

Flicka:

 

Unfortunately I've no Powerpoint-reading capability - all I can see of your attachment is a tiny line drawing. However, if you've got your heat exchanger separate from the boiler, however small the amount of water within the exchanger, it effectively becomes a 'New Storage Vessel' and (as far as I can see) will have all the NSV-related drawbacks I mentioned earlier. Proof of the pudding is in the eating. If you build your proposed system and it works as you anticipate then you are right: if it doesn't work then you aren't.

[flicka]

Hi Derek

Thank you for your comments, as you say it appears to be a trial & error build. That's why I am so iterested in others views.

 

I have copied the previous attachment to word, hopefully this will be readable.

 

Another point - I found that there are some very compact Heat Exchangers for HVAC applications (4-6" dia & 18" long) built with Copper tubing within a cast Alluminium body. I think that radiators used to be built with copper tubes but not sure, does anyone know if copper would be detrimental to the engine cooling system?

Heat Exchanger.doc

[flicka]

Thanks to Derek identifying Alde's system, I found their website which shows the very thing I am interested in :-

 

http://www.alde.co.uk/itemdetails.php?itemId=58

 

Will investigate in more detail, as it would appear to also use their "mini-radiators" in the loop, at reasonable prices and on-line order facility.

 

http://www.alde.co.uk/products.php?itemCat=alde%20convectors

 

[Derek Uzzell]

flicka:

 

Thanks for the different format diagram.

 

I'm 99.99% certain that your scheme as shown is not going to work as the 'natural' thermal tranfer it assumes will move heat from the exchanger to the boiler just won't happen. The only time you might get some heat transfer is when water is drawn from the boiler (ie. when a tap was opened), but that would be of minimal value. Even though you've introduced a dinky loop into the pipework between exchanger and boiler, the system is still an 'NSV in series' one as far as I can make out.

 

Much of my career was as a computer systems analyst and, while I was not great at being able to identify processes that would work, I was red hot at identifying ones that wouldn't (always a lot easier!)

 

Not sure about the copper effect nowadays, but it was certainly the case that vehicle radiators used to have copper cores.

 

 

 

 

[flicka]

Thanks for your prompt reply Derek

 

(As my other half says - there's another one of my ideas down the Thetford)

I will have a rethink regarding introducing a circulation pump between the Heat Exchanger outlet & the Truma Boiler inlet , but I suspect that's were the economic vaibility dissapears.

 

[colin]

Derek Uzzell - 2008-01-08 8:50 AM

Colin:

 

I'm not familiar with the appliance you mention, but I assume it's a heater fitted to USA RVs. As far as I'm aware there is no European commercial support for Atwood products (Truma subsumed Atwood's European arm in around 1999 when it went bust), so that might present problems. Is there anything on the internet to describe the Atwood heater, please?

From one of my CAK catalogues, 2005 I think

[Derek Uzzell]

Colin:

 

There doesn't seem to be anything Atwood-related in CAK's 2007 catalogue.

 

I'm aware CAK was once a major supplier of Atwood products, but I was fairly sure they had stopped this by 2003. I don't remember an Atwood "3 way" heating system, although Atwood did market a "Confort 3".

 

This was an Italian-made combination air/water heater that competed directly with Truma's C-series appliances. The Confort 3 found its way into a few UK-built motorhomes - some Heralds and Autocruise models had them - but its electrical side could prove troublesome (I speak from bitter personal experience!) However, Confort 3 had no engine-coolant heat-exchanger capability of the type flicka is interested in and the only 'free' hot water came as a by-product of air-heating (exactly like a Truma C-series).

 

Perhaps you could check through your CAK documentation (I've chucked my earlier CAK catalogues away), please? If there is (was) an Atwood product available that heats water via gas, 230V and engine waste-heat it would be useful to have details.

[John S]

Many years ago when I was employed as an Electricity Board engineer one of my colleagues had a meeting with a development engineer employed in the petroleum industry. He described to me a project being experimented with which involved transferring engine waste heat to a thermal block presumably contained within a coil of piping carrying hot radiator water.

Upon returning home after a drive with a hot engine the block would be removed and transferred to a sort of domestic storage heater whereupon it would proceed to give up it's stored heat thus warming the house. That was the idea anyway.I wonder if it ever got further than the drawing board.

John S

[Guest peter]

I doubt it John, because if you can carry it into the house, it won't have enough density to store much heat.

[Guest peter]

Just an idea. As I don't know how Truma heaters are constructed. But it might be worth a try if you have an old one. The idea is this....cut off/open the top and put in a copper coil with suitable tank fittings and nipples. Then connect up a feed and return to the engine cooling system with isolation valves and you then have free hot water as per boat installation. This bypasses all of the aforementioned drawbacks of the two vessel layout. You never know it might be possible. But I'm not going to try it on my good working Truma system, but if it goes kapput I would certainly give it a go, as I've also been pondering this on and off for a while having free hot water on my boat albeit with a 1Kw immersion when on shore power. But with a good battery backup and inverter it's also possible when wild camping. I use a 1.2Kw genny on my boat when I'm moored up for a while with no 240V supply. You would be surprised how quickly 25Ltrs of water is heated up by a 3.7 Ltr 200HP diesel engine, even at only 1500 RPM.

[Brian Kirby]

flicka - 2008-01-08 10:29 AM Thanks for your prompt reply Derek (As my other half says - there's another one of my ideas down the Thetford) I will have a rethink regarding introducing a circulation pump between the Heat Exchanger outlet & the Truma Boiler inlet , but I suspect that's were the economic vaibility dissapears.

John

The Alde heat exchanger seems unlikely to generate an adequate thermo syphon effect.  However, if a circulating pump could be installed in the secondary circuit (i.e., if primary = to/from engine) to push that water around, the heat transfer should be OK. 

If the connections were taken from the heat exchanger flow tapping to the Truma c.w inlet side via a tee connection (tee 1), but the return is instead taken via a second tee (tee 2), inserted into the hot water supply outlet on the Truma and back to the exchanger return tapping, the general circulation would be through the Truma in the "normal" direction. 

There should be a non return valve between the c.w tank and the Truma.  You'd need to make sure this was between the tank and the tee as above.  You may need to insert a separate drain point in the secondary system at its low point, to prevent any possibility of a freeze up in the heat exchanger.  The circulating pump could presumably be one of Alde's wet system pumps, wired to operate only when the engine is running - but you'd need some kind of manual interlock to make sure it was protected against operation with no water in the cw tank.  Circulating pumps don't like running dry!  Have fun!