Campsite Showers Water Heating. For Chris P.

At current prices electric water heating, whether by grid electricity or from local generation might not be the best option.

Grid electricity is at least 60 pence a unit. Local diesel generation from white diesel will be about 50 pence a unit under favourable conditions.

Propane is about 20 pence a unit from the larger cylinders, or say about 25 pence per unit of delivered hot water, to allow for the heaters not being 100% efficient.

Either use a hot water heater that heats a tank, or an instantaneous water heater for each shower. The very substantial peak loading of several showers is easily met with propane. 30 kilowatts is achievable for continuous use, and at least 100 kw for intermittent use. 6 showers each with a 14 kw heater will be fine on a single 47 kilo propane bottle. Automatic changeover valves are usual to prevent interruptions when the first cylinder is empty. A 14 kw gas water gives a far better shower than any common size of electric shower.

If a hot water tank is used, heat the bottom half from solar thermal sources and the top half from a propane boiler. This will save gas. 

Do not forget frost protection for plumbing.

Just a thought here Zoom lad. You mention 3 phase and you mention different available KW rating of immersion heaters. Might it open up your options for KW loading of the whole system at start up for example using a 2 or 3 x 3KW bog standard heaters across 1 or 2  phases would effectively give you a better range to play with than non standard (more expensive and less readily available stuff).

Example two 3KW heaters at 240 V wired in series would give you 2 x 0.75KW heaters equivalent. at 400V would give you 1.25KW x 2 heaters. Obviously i heater open circuit would cause the other heater to go open circuit, therefore switch off but I feel it might be easily mitigated. Worth a thought I think

Note I`m working on 240/415 real volts rather than 230/400 perceived volts but the principal thinking is the same.

Timing the fire up/shut down delays if using a few combinations could be beneficial too!

The world is your lobster (or haddock) 

It takes around 4200 Joules to raise the temperature of 1 litre of water by 1ºC - (1J = 1 Watt for 1 second) - so to raise say 1000l by 50ºC would take 210,000,000 J or around 58kWh - say 3off 3kW immersions for about 6.5 hours (someone please check my maths!) Plus a bit for losses.

As a starting point, perhaps think in the region of 10 litres/minute for a decent shower, but low flow fittings can reduce that considerably,

Thermostatic values are usually set to prevent scalding - either one TMV at the tank or individual thermostatic values on the showers, with an upper limit stop.

   - Andy.

AJJewsbury said:

As a starting point, perhaps think in the region of 10 litres/minute for a decent shower, but low flow fittings can reduce that considerably

I think that 5 l/min for 10 minutes would be perfectly adequate, though Andy's 10 l/min would be more luxurious and what people might expect nowadays. (If the flow is lower, people might not stay in any longer than they need to.) So the capacity of the tank needs to be 50 l per shower (in the sense of washing 1 person, rather than 1 cubicle).

The power of the water heater depends upon how many people will use those 4 showers. If there is a queue, supply will have to match demand. So 5 l/min = 83 ml/s = 83 g/s. Each g of water requires 4.2 J per deg C, so to go from 10 to 40 deg C requires 126 J for each g. Multiply that by our 83 g every second and you get 10,500 J/s = 10.5 kW.

Zoomup said:

or are they all uni-sex these days?

That reminds me ...

About 30 years ago I met a female Royal Netherlands Navy officer. I asked her whether all their ships had female personnel and she said that they did. I said that we were in the process of converting ours and she wondered what we were converting. Heads and bathrooms was my reply. She thought that was completely unnecessary because they used one lot of showers, but if you were shy, you could draw the curtain. 

Chris Pearson said:

The power of the water heater depends upon how many people will use those 4 showers. If there is a queue, supply will have to match demand. So 5 l/min = 83 ml/s = 83 g/s. Each g of water requires 4.2 J per deg C, so to go from 10 to 40 deg C requires 126 J for each g. Multiply that by our 83 g every second and you get 10,500 J/s = 10.5 kW.

So on a 3-phase supply, that sounds like 3 off 3kW immersion heaters.

It seems like a ridiculous idea to me.

My starting point would be to consider a solar thermal heating system.

That is a very interesting suggestion ebee. I wanted to have a perfectly balanced load to keep the generator happy. I have seen small rated immersion heaters used in small unvented hot water tanks, but have not investigated this fully.

The generator plate states 380 Volts.

Z.

A few years back on a campsite in Spain I noticed a small hill mound had been built to lay a hosepipe type thingy at say 45 degrees from flat , the hose was as big as a fireman`s hose and i assumed they trickled water thru it in the sunshine to heat it up. crude but maybe it worked some

I watched one of the Grand Designs TV shows, I cannot remember where it was, I think it was Australia, the house had a very long driveway and the services had to be dug in alongside it, so they buried a 100 mm plastic pipe in the same trench.

So, there's several hundred metres of buried pipe and the air for the ventilation system is brought into the house through it and arrives at ground temperature, which means it is cooled in the summer and warmed in the winter saving on the cost of running the air conditioning that provides cooling and heating.

So simple.