Electric shower in van???

[Gybe]

The heater doesn't use its X litre of water cotent and then heat another X litres does it. As water in the heater is replaced it's geting heated. If you get a balance between flow out and flow in you should get a reasonable amount of time for a shower.
The warmer the water coming in to the heater the quicker it will reach a good temperature. An inboard tank will often provide warmer water than an outboard tank if you have the choice of where to draw water from. On hot summer days external aquarolls can provide fairly warm water if they have been under drirect sunlight. We have both options, the inboard tank is a far better option in the winter.

 

[ProfJohnL]

Hello gary and Gybe,

There is a flaw in your thinking gary, based on the manufacturers figures of 22 mins for 55C rise for 13L may mathematically give your 2min per litre, but under heating there are considerable thermal convection currents inside the tank which means you don't just heat the top 1 litre, the whole 13L tank starts to warm up. Its not perfectly evenly distributed there will be some hotter water at the top but the temperature gradient from top to bottom under heating will be much less than 70 to 15C you suggest.

The thermal currents inside the tank are driven by the heating effort and with 1.25kW gas input (approx 1kw into the water with about .25kW heat losses through the flue assuming an 80% efficiency) and 1.5kW electric a total 2.5kW heating will cause quite some mixing.

The first litre of water will only reach a super elevated temperature provide no water is drawn off. This is through stratification which can only occur when the water in the tank is largely undisturbed. So after a couple of minutes you may have water at the top of the tank which is several degrees warmer than the bottom, BUT as soon as you start to use the water in the heater the inrush of cold water very quickly starts to mix the whole tank and it starts to assume a more even but lower temperature.

Hi Gybe, I agree the heater will continue to try raise the water temperature even when water is being used, and it is quite true the warmer the water on entry, the less energy is needed to raise its temperature to the desired level, but shower usage typically between 3 to 4 Litres a min. this still rapidly out strips the heaters ability to maintain the desired water temperature.

The concept of storage water heaters and showers, relies on the fact that water from a fully heated tank is too hot to use undiluted. Typically the top temperature of a heater is 68 to 70C and a common shower temperature is is roughly 40C the shower mixer tap allows the user to proportion the amount of hot and cold water to achieve the comfortable shower. 13 Litres of water at 70C is roughly capable of providing enough hot water for three showers when mixed with cold water. - the biggest problem is water storage both of fresh cold and waste.

 

[Gybe]

We have two baths and three showers at home and two huge water tanks supplying them and then there is a huge immersion heater tank linked to a two boiler system plus a solar system.
Obviously in a caravan you are never going to have the same capacity or flow water or heating output. If you want a long or multiple showers you are obvioulsy going to have to compromise. After a day in our wetsuits we normally both want a hot shower when we get back to the caravan.
As I put in a previous post on this subject, we have a water saving small fine jet shower head in the caravan and it's not exactly a water blaster

, but we can both get a good shower and warm up when the heating is directed to the bathroom as well.
When we're not connected to a mains water supply we have about a 150 litres of water too draw on wth inboard tanks and two aquaroll's.
With a little compromise and trial and error we have the comfort we require

. It's not the full body massaging power shower of our home ensuite but it does the job.

 

[joeby]

i have been showering in my caravan for 17 years , what a lot of gobbly **** over a shower , get a life

 

[colin-yorkshire1]

i have been showering in my caravan for 17 years , what a lot of gobbly **** over a shower , get a life

AH but if you were bothered about a life you wouldn't spent so much time on the computer writing on a forum,
would you!!!!!

 

[Guest]

I know theres a flaw John but we are only talking 22 minutes in total so the flaw cannot be significant. So keeping it simple, the fact remains it heats water very quickly and that's what the OP is on about
Speaking of efficiency though and you'll know this, early tests surprisingly proved Carvers 'side' heating is just as efficient as housing the burner within the tank!

 

[Gabsgrandad]

Quote "i have been showering in my caravan for 17 years ,"

------Now that is a 'slow' shower.!

 

[ProfJohnL]

Hello gary,
All gas appliances of this type must reach a minimum of 70% thermal efficiency before they can receive the essential CE approvals mark for sale in the EU. The fact that the Cascade 2 had the CE mark means it must have been at least 70% despite its side heating arrangement.

 

[Guest]

I know John, it was meant in way of a complement to Carver for coming up with it, actual it's in the mid 80%'s, 87% i think?, certainly no worse than internal heating from a heating chamber set within the tank