Heating Water Tank without EHU

[Smudger55]

I should know the answer but when without EHU, how do you heat water,? We have good solar panel but nothing else.

Is it just heat up on gas or battery will survive doing this?

I've done it before but, ha............... age thing, can't remember

Trouble I'm finding now into 70s I question everything, I was indecisive/ uncertain before but now, well

 

[funflair]

You would need a lot of solar to use it for water heating and your water heater may not be connected to the inverter anyway (assuming you have one) easiest and most reliable would be gas.

 

[NR]

Gas.

 

[Cush]

Gas. Should survive significant time on a full bottle. My turn on to 50 deg 20 min before needing it.

 

[Lizbiebrowne]

I heat the water in our Truma via the inverter. It draws about 38 amps (I think it’s a 600 W element). Takes about an hour to switch off and depletes my 400 Ahr batteries by about 8%.

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[Guigsy]

To heat water takes a large amount of energy. Mains electricity and gas can easily supply the power required.

To heat with solar would take a lot of panels. And would only work during the summer months. You could heat from a battery, but you'd need a large battery and a way to recharge the significant drain.

 

[Hezbez]

I'm amazed at how hot our water gets by default by just having the gas heating on (Truma 4e)

 

[Smudger55]

Further to my earlier post, heating. The last 2 nights at Port Solent I've restricted turning the heating on but it did get cold during the early hours. My main reasons for doing so, were gas bottle was low, didn't want trouble of changing it during the night and unsure how long to have it on have it on for fear of over USE. Summer and winter different, temp in van until say 2100 was good without any heating.

Bear in mind on this trip, I'm without management, I can go "light" with energy usage. When she returns, well, I will be advised accordingly, however I will need reassure her of a sensible approach to this.

So how do you agree heating usage when no EHU? or

 

[MisterB]

Motorhoming to me is about being just as comfortable as I would be when at home. It's not about being frugal to the point it becomes uncomfortable....that doesn't mean I haven't put an additional layer of clothing on or sometimes slept in pyjamas (shock/horror!), so make sure your comfortable whatever you use.

 

[Cush]

I’m always surprised how long a bottle I thought was low lasted! If it had been me, I would have used what gas there was for heating, not opened the fridge again and let it run out. At least the temperature would have been higher than not using any heating at all. You may be able to look in to an auto change over valve. Or change it before it runs out.

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[Carpmart]

It’s absolutely possible to heat water from excess solar. Once you have that setup, you can then, obviously, also heat water from the charge your DC DC charger provides. We only heat water through solar or when driving now days!

 

[Guigsy]

It’s absolutely possible to heat water from excess solar. Once you have that setup, you can then, obviously, also heat water from the charge your DC DC charger provides. We only heat water through solar or when driving now days!

Note: Most vans can't heat water from the 12v system. And even if they have an inverter, it's generally not wired to allow the inverter to power the 240v water heating elements. So most vans can't heat from excess solar.

 

[Jabstatt]

We went five days last summer using solar for hot water. No problem at all.

Tony.

 

[Carpmart]

Note: Most vans can't heat water from the 12v system. And even if they have an inverter, it's generally not wired to allow the inverter to power the 240v water heating elements. So most vans can't heat from excess solar.

I was, of course, referring to it being possible, as several Funsters, including myself, have adapted to enable solar hot water heating…

 

[Millcourt]

I heat the water in our Truma via the inverter. It draws about 38 amps (I think it’s a 600 W element). Takes about an hour to switch off and depletes my 400 Ahr batteries by about 8%.

I am a little puzzled by this and will be grateful to anyone who knows better correcting me.

I understood that the Truma Combi (6E) has 2 electric immersion elements, both rated at 900 watts. When the control panel is set to “Electric 1” the power consumption is 900 watts. On “Electric 2”, both elements are switched on and the power consumption is 1800 watts.

Presumably, if you have a sufficient power source the “Electric 2” option will heat up in half the time of “Electric 1”.

So in the example given by Lizbiebrowne, assuming it was switched to “Electric 1” to limit the current draw from the 12v supply via the inverter, a 900 watt load at 12v would draw a current of 75 amps. Allowing for some inefficiency in the inverter conversion to 240v, perhaps the actual draw on the 12v battery would be around 80 amps. If 80 amps is drawn for an hour, this equates to a usage of 80 Ah. With the 400 Ah battery installation mentioned, this would be around a 20% discharge and not 8% as mentioned.

Very happy to stand corrected either on my maths or understanding.

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[Otter Spotter]

Consider a heat exchanger fitted to your engine which will heat up your water whilst you are driving and store it in your existing hot water tank, free hot water

 

[Jimbohorlicks]

Off grid we use gas for hot water heating for a shower.Kettle for washing up as required but to heat the van we have a deisel heater. Wouldn't do without it now brilliant . Ours is plumbed into the main tank.

 

[Millcourt]

Thinking further about my previous post above, I have tried to approach this in another way. This is really stretching my recollection of “O-level” physics (well it was over 60 years ago!!!).

The Truma 6E boiler holds 10 litres of water. For practical purposes…. 10 kg.
The specific heat of water is 4,200 joules per litre. (I.e. the energy required to raise the temperature of 1 kg of water by 1 deg C.)
To raise the temperature of 10 kg of water (as stored in the Truma heater) by 1 deg C is 42,000 joules (or 42 kj).
If the ambient temperature is 15 deg C (say) and the Truma boiler heats the water to 60 deg C, this is a rise of 45 deg C.
So, to heat a full boiler of water in the Truma heater by 45 deg C, the energy needed (ignoring any heat losses from the boiler) will be 1,890 kj.
In electrical terms (according to Mr Google), 4.2 kj is equivalent to 1.17 Watt-hours (Wh).
So, the 1,890 kj needed equates to 527 Wh.
With a 12 volt supply, 527 Wh will need a current draw of 43.9 amps for a period of 1 hour. (Approx 44 Ah.)

Even allowing for heat losses from the boiler whilst heating up and inefficiencies with the Inverter, this is somewhat less than the 80 Ah which I calculated in my earlier post.

So…..I am either confusing myself with my mathematical calculations or I am demonstrating my misunderstanding of these matters.

Please can someone who is better informed correct me!

 

[Guigsy]

Thinking further about my previous post above, I have tried to approach this in another way. This is really stretching my recollection of “O-level” physics (well it was over 60 years ago!!!).

The Truma 6E boiler holds 10 litres of water. For practical purposes…. 10 kg.
The specific heat of water is 4,200 joules per litre. (I.e. the energy required to raise the temperature of 1 kg of water by 1 deg C.)
To raise the temperature of 10 kg of water (as stored in the Truma heater) by 1 deg C is 42,000 joules (or 42 kj).
If the ambient temperature is 15 deg C (say) and the Truma boiler heats the water to 60 deg C, this is a rise of 45 deg C.
So, to heat a full boiler of water in the Truma heater by 45 deg C, the energy needed (ignoring any heat losses from the boiler) will be 1,890 kj.
In electrical terms (according to Mr Google), 4.2 kj is equivalent to 1.17 Watt-hours (Wh).
So, the 1,890 kj needed equates to 527 Wh.
With a 12 volt supply, 527 Wh will need a current draw of 43.9 amps for a period of 1 hour. (Approx 44 Ah.)

Even allowing for heat losses from the boiler whilst heating up and inefficiencies with the Inverter, this is somewhat less than the 80 Ah which I calculated in my earlier post.

So…..I am either confusing myself with my mathematical calculations or I am demonstrating my misunderstanding of these matters.

Please can someone who is better informed correct me!

Maths looks fine. It's a theoretical minimum energy requirement.

With electrical conversion losses, and heat losses from the Truma losing a fair amount of heat to warming itself and stuff around it, I'd consider the figures to be pretty close.

Either way, it's quite a lot of electrical energy just to have one shower. If I had that much to throw away, I'd be wondering how much money I'd wasted on far too much solar and battery.