Truma Combi, has anyone made an insulated enclosure/cover??

[Mr Plodd]

Just sat mulling things over in a spare five minutes (as you do) and it occurred to me that when I have my Truma combi heating the water a fair amount of heat escapes from the unit (toasty warm under the bench and warm air wafting up behind the seat proves that fact)

This heat is clearly energy that has come from somewhere, either gas, or more likely electricity when on site, and is therefore rather wasteful, and costly.

With the ever increasing cost of both gas and (possibly metered) electricity I thought I might make an insulated enclosure (cover) for it using Celotex or similar.

Has anyone already done this? if so have you any tips, advice or observations to pass on before I start work?



Thanks

 

[Dustydog]

Gas appliances are designed to be positioned in situations with adequate ventilation. I appreciate your point, it makes sense . However why not run it past Truma with a copy of your cabinet design and seek their advice?

 

[Mr Plodd]

Gas appliances are designed to be positioned in situations with adequate ventilation. I appreciate your point, it makes sense . However why not run it past Truma with a copy of your cabinet design and seek their advice?

Cracking idea. I haven't got as far as designing a cabinet. But running tge idea past Truma has to be a sensible thing to do.

 

[ProfJohnL]

Having been involved with the design of various gas and electric products I know how sometimes a product may seem to be poorly designed and the layman thinks they can do a better job.

But I do know that Truma and Carver (when they were operating in this field) both had to invest considerable sums to have their products assessed for conformance to design regulations and safety. What might seem an obvious adaptation to you , might contravene a regulation or an essential safety feature.

As part of gas appliance fitting instructions, the appliance manufacture has to specify essential gaps between the appliance and nearby furniture or other features. The fitting instructions should have been left in the caravan for the consumer to keep. I suggest you consult them.

 

[Buckman]

Having been involved with the design of various gas and electric products I know how sometimes a product may seem to be poorly designed and the layman thinks they can do a better job.

But I do know that Truma and Carver (when they were operating in this field) both had to invest considerable sums to have their products assessed for conformance to design regulations and safety. What might seem an obvious adaptation to you , might contravene a regulation or an essential safety feature.

As part of gas appliance fitting instructions, the appliance manufacture has to specify essential gaps between the appliance and nearby furniture or other features. The fitting instructions should have been left in the caravan for the consumer to keep. I suggest you consult them.

it is not the design of the unit, but the way it is installed especially in caravans where it seems the caravan manufacturer ignores the installation guidelines for the unit.

Many years ago we had that issue with a Lunar and the way the Alde system had been installed. Thanks to advice received on this forum from another poster who had a similar problem the issue was resolved by the dealer cutting vent holes at the front of the caravan. Problem solved.

 

[Mr Plodd]

Having been involved with the design of various gas and electric products I know how sometimes a product may seem to be poorly designed and the layman thinks they can do a better job.

But I do know that Truma and Carver (when they were operating in this field) both had to invest considerable sums to have their products assessed for conformance to design regulations and safety. What might seem an obvious adaptation to you , might contravene a regulation or an essential safety feature.

As part of gas appliance fitting instructions, the appliance manufacture has to specify essential gaps between the appliance and nearby furniture or other features. The fitting instructions should have been left in the caravan for the consumer to keep. I suggest you consult them.

To my mind Truma don't seem to have thought about, or addressed, the issue of insulation and therfore heat loss from the combi unit. Place your hand on it after it has been on for an hour or so and it feels very warm, so, expensive to generate heat, is being wasted/lost.

A modern home immersion heater has a thick jacket of foam around it to retain heat within it, the Truma unit appears to be somewhat lacking in that dept, so I find it rather difficult to believe that the matter of heat retention had much influence on the design process. If it had then surely, for such a compact item, effective insulation would be pretty easy to incorporate, but it doesn't seem to have been Hence my thoughts about improving matters. Some interesting comments so far, some raising points I hadn't thought of. Interestingly no-one appears to have done what I am contemplating.

 

[trevormonty]

If you are that worried about energy consumption turn it off when not needed for showers. For dishes its easy enough to boil a jug.

 

[Mr Plodd]

I am more concerned about excessive heat inside the caravan when in hot climes!
It's much less energy efficient to keep reheating water than it is to keep it hot.

I did email Truma asking their views, They didn't give me definitive answer, but advised it probably wasn't a a good idea as by doing so it might overheat. So bearing in mind the cost of possible repairs, and if course PCB's these days I have decided to abandon the idea.
Thanks to all those who responded with their thoughts.

 

[ProfJohnL]

To my mind Truma don't seem to have thought about, or addressed, the issue of insulation and therfore heat loss from the combi unit. Place your hand on it after it has been on for an hour or so and it feels very warm, so, expensive to generate heat, is being wasted/lost.

A modern home immersion heater has a thick jacket of foam around it to retain heat within it, the Truma unit appears to be somewhat lacking in that dept, so I find it rather difficult to believe that the matter of heat retention had much influence on the design process. If it had then surely, for such a compact item, effective insulation would be pretty easy to incorporate, but it doesn't seem to have been Hence my thoughts about improving matters. Some interesting comments so far, some raising points I hadn't thought of. Interestingly no-one appears to have done what I am contemplating.

Unless you know the regulations concerning the design of a heater, you are not in a position to say whether Truma did or did not consider the insulation of the product.

There could be components that need ventilation to be compliant with the approvals for the appliance. The appliance manufacturers fitting instructions will specify clearances and ventilation requirements.

Just as an example there used to be a two regulations that forced heater manufacturers to use steel for gas pipe, even though it would rust! The reason was that copper pipe was not allowed to be used if it passes through panel if the panel could reach or exceed 100C. Most members of the public would not be aware of that regulation so to them it would seem better to use a copper pipe.

There are numerous similar limitations that have to be applied, yet to the public may seem to be inappropriate.

The caravan manufacturer should comply with the appliance manufacturers fitting instructions which. Unfortunately we have seen many instances where that does not always happen.

 

[Raywood]

Cracking idea. I haven't got as far as designing a cabinet. But running tge idea past Truma has to be a sensible thing to do.

Do patent it if you manage, as if it is good Truma could pinch it.

 

[Beardy]

It's much less energy efficient to keep reheating water than it is to keep it hot.

Sorry, that's a myth.
When ever the water is hotter than the ambient temperature it will be loosing energy in the form of heat (unless it's 100% thermally insulated...... which is impossible). That energy has to be replaced to raise the temperature to the required level. The most efficient way to use any water heater is to heat the amount you need at the time you need it.

 

[Mr Plodd]

I did email Truma asking their views /opinion. Their response was pretty much as I expected and very non committal. Basically.ly they said that they didnt think it was a very good idea because the whole thing could possibly overheat and possibly damage the PCB.
Bearing in mind the cost of PCB's I have decided to abandon the whole idea.

Sorry, that's a myth.
When ever the water is hotter than the ambient temperature it will be loosing energy in the form of heat (unless it's 100% thermally insulated...... which is impossible). That energy has to be replaced to raise the temperature to the required level. The most efficient way to use any water heater is to heat the amount you need at the time you need it.

But doesn't it take more energy to get to a certain temperature rather than maintaining it? Think of a car, it uses far more fuel accelerating up to a certain speed than it does maintaining that speed? Energy is energy.

 

[Sam Vimes]

Its not as straighforward as you think and your analogy is a little off - your car will need to slow down at some time and then speed up again.

The amount of energy to heat a liquid is:-

Mass x Specific Heat x Temperature rise.

If you have 8kg of water in your tank at 20degC and want to heat it to 70degC then as the specific heat and actual mass in this comparison is constant, then its a factor of 8 x 50 = 400

If you get your tank to 70degC but don't draw any hot water off for a while then lets assume it drops 5degC and needs raising by 5degC to get it back to 70degC. Then this equates to 8 x 5 = 40

Yes less energy but if your tank has to do this 10 times before you draw off the water then thats 10 x 8 x 5 = 400. Same amount of energy as if you'd just let it cool right down and started again.

So factors like how well its insulated, how much hysterisis has your thermostat and how often you want to draw water come into play. Also how much heat loss actually matters. Running off water at 60degC may be just as useful as 70degC.

Crudely put would you leave your home immersion heater on if you went away for a year or would you turn it off and start again when you got back.

 

[trevormonty]

I did email Truma asking their views /opinion. Their response was pretty much as I expected and very non committal. Basically.ly they said that they didnt think it was a very good idea because the whole thing could possibly overheat and possibly damage the PCB.
Bearing in mind the cost of PCB's I have decided to abandon the whole idea.


But doesn't it take more energy to get to a certain temperature rather than maintaining it? Think of a car, it uses far more fuel accelerating up to a certain speed than it does maintaining that speed? Energy is energy.

Still more energy efficient to heat on demand. The only reason HW cylinders exist is most domestic circuits can't provide enough power for instantaneous heating to have a decent shower. Yes there are heaters for showers but wouldn't call it a decent shower. Also they help to reduce peak energy demands on network. Gas doesn't suffer from these problems which is why on demand water heaters are more common.

In caravan dual fuel HW cylinder is cheaper and simpler to implement than 2 separate on demand heaters. Especially if you can combine it with room heating.

Just google energy equations they will be on web for heating water and losses in typical HW.

 

[Mr Plodd]

Crikey! I wasn't expecting a degree level lecture on thermodynamics chaps!!

All superfluous anyway, it ain't gonna happen (the insulated box that is)

 

[trevormonty]

Water Heating Calculator

Use the water heating calculator to determine how much time and energy you'll need to increase the temperature of the water.

www.omnicalculator.com

For 10lpm to take water from 10C to 40C requires 2kw.

 

[trevormonty]

Crikey! I wasn't expecting a degree level lecture on thermodynamics chaps!!

The full Monty is all part of service.

 

[ProfJohnL]

...
But doesn't it take more energy to get to a certain temperature rather than maintaining it? ... Energy is energy.

If you leave a typical caravan water heater running for more than about 5 hours just to keep the water hot, you will spend more on the energy than if you only turn the heater on about half an hour before you need the hot water.

Typically it needs about 500Wh of energy to heat the tank from cold, but a typical heater will consume up to about 100Wh per hour JUST to maintain a tank full of hot water to offset the heat losses.