Do immersun type devices work

Hi,
So basicly I could use an immersun to run a 1kw immersion and a couple of heaters in bedrooms, if total load is less than 3kw?

Thanks Rob

Yes, or use your exisiting 3 kw Immersion and when that is up to temperature let it roll over on to the heaters, or if you have a very large system PV and low base load, you can link two immersuns together to control up to 6kW proportionally.

If you link up 1kW immersion and 2 x 800W heaters on the same circuit, at the same time as you suggest, when the 'spare' output from the PV system is 1.3 kW then 500W will go to the immersion and 400W to each of the heaters. so the water will take loner to heat up, and you may just get everything luke warm.
Also if you wire a 1 kW immersion in 'roll over' mode, will take a lot longer to heat if you have spare PV generation > 1kW as the immersion won't take more that 1 kW.

MicraShed said:

Thats what I have been quoted plus a bit extra because Im outside the usual coverage area for te installer. I need to sort out a date for an install with them actually but Ive been in and out of damn hospital again this week.

Given the cost of the unit is roundabout the £380 - £400 mark from the company that makes them from what I did find out (Google be your friend here).
Add in materials (cable etc), travelling, VAT and other sundries then another £99 on top isnt really that bad for a qualified spark to fit it. Whilst it might sound a fair wedge for a box of bits, having researched the unit (all-right so far it does seem to be anecdotal evidence) they do two things - the make sure almost every scrap of electric you generate is used, and they reduce the energy (gas or electric) you use to heat your water.
Now for me, given that my domestic gas use is pretty much entirely water heating use between about March time and October time and given that Im using about 14kW/day between these months of gas.

So, gas at about 4.1p/kWh x 14kWh x 210 days (appx) = £120.40

Potentially in the months where I dont have the heating on for anything other than hot water that is a saving of £120. There should be additional savings through the year as well, so the "payback" time for me at least will be about 3 to 4 years, possibly less.

These are only rough calculations of course, but it certainly seems a viable proposition. My only concern is whether or not there are any "moving" parts (eg, power relay) that might have a limited lifespan and need maintaining during the payback period.

Of course I could be talking out of my bum here, so I welcome other peoples thoughts or experiences.

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The only flaw I can see in your calculations is perhaps not factoring in what time of the day the gas use takes place. Although I have never looked at the meter on a typical day I suspect most of my gas use takes place in the morning, first as the hot water is brought back up to temperature after cooling overnight, then after the first shower and then once more after the 2nd shower. These showers typically take place before 09:00 5 days a week when most PV systems will only have produced a few kWh. And even if a 4 kWp system is running at 100% at 08:00 it still isn't pouring as much heat into the hot water tank as your boiler will so the reheat time will be longer.

The surplus kWh from PV will help cover the cost of any hot water use during the day and early evening though.

Thus I think the payback time for something like the Immersun will be considerably greater for my hot water use profile which is probably not far different than many people's.

insulate your tank properly though and the water should remain hot overnight from the previous days heating.

Gavin A said:

insulate your tank properly though and the water should remain hot overnight from the previous days heating.

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Our hot water tank (3kW element, about average tank size) was without a jacket for a while earlier this year.

From almost cold, without the jacket (a basic red B&Q/Homebase-type), the heating time was about 75 minutes. With the jacket it was about 45 minutes.

If the hot water was unused, the amount of time before it began reheating went from about 75 minutes without the jacket, to about 120 minutes with the jacket.

In other words: by having a boiler jacket, the heating time was almost halved, and the time before reheating was almost halved. Half as much power usage to heat it, and half as much power usage to maintain it at a hot temperature.

So for those who don't have one; £10-15 for a boiler jacket should pay for itself after just several weeks.

Our tank is already insulated with foam jacket from the factory, but the tank cupboard was always really warm. Last week I fitted an additional red jacket from BQ and now the cupboard is cool so this must be a good thing.

When you say without a jacket do you mean just a bare copper cylinder? My post above is referring to a 20 year old copper cylinder with perhaps 1.5 inches of hard foam insulation bonded to the cylinder at the time of manufacture.

robertevans68 said:

Our tank is already insulated with foam jacket from the factory, but the tank cupboard was always really warm. Last week I fitted an additional red jacket from BQ and now the cupboard is cool so this must be a good thing.

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The tank I mentioned earlier had a tough foam-like, pale greenish coating on it, maybe 2cm thick. It wasn't bare copper.

Adding the jacket to the hard-foam-coating roughly halved the power consumption or roughly doubled the time between reheating.
Had it been bare copper I expect it would be doubled again.

I've been using a home made proportional controller, similar to the Imersun, with my 4kWp system since April and can say they are definately worthwhile.
How much you can get out can vary a lot depending on how you set things up.
My system was a standard 120L tank with 27" immersion and because I have a toddler in the house I had to limit the thermostat to 60 DegC, which was probably still too high. For the last 3 1/2 months this setup has been shutting down at about 11 am on good days and 1pm on cloudy days. This was adequate without supplimentary heat for 2 x evening baths plus general kitchen use or 1 x evening bath and 1x morning shower. I've logged the (true) energy sent to the immersion and it's been pretty consistent at 185 kWh/ month from about 350 - 430 kWh/ month generated.
Two weeks ago I modified my system and it's made a big difference so far with 7 -11 kWh/ day now going to the immersion, conditions permitting of course.
The mods I made where to fit a larger 150L tank (second hand off Ebay), 36" immersion which reaches to within a few inches of the concave tank bottom and a thermostatic temperature control on the tank outlet so I can run the tank hotter without scald risks at the taps.
I also switched the washing machine and dishwasher to hot fill and carefully time there use. Currently the washing machine goes on about 9- 10 am as it will drain whats left of the previous days heated water before the rinse cycles.
The dishwasher which doesn't use anywhere near as much water goes on about 1- 2 pm and uses enough water to re-engage the immersion thermostat to use some more of the afternoon sun.
The thermostat will still cut out by about 5pm on good days but the only way I could store any more energy in my current setup would be to use a pump for tank stirring which would not be easy plumb in to my system.
I may put a second hand storage heater on a relay linked to the thermostat but I don't think there will be enough spare energy during the winter months when it will be needed.

Digon - thanks for sharing your actual results to date. Can you post a link to any design info on the controller?

It is a design by a member of this forum, Pmcalli. There was a long thread on here discussing the design of these devices but I can't find it right now. as I'm not on aPC.

liquidity said:

The only flaw I can see in your calculations is perhaps not factoring in what time of the day the gas use takes place.

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Both my heating and hot water are controlled by a thermostat only. No time clocks.
So when the room stat calls for heat the boiler fires up and delivers heat (with surplus heat being dumped into the cylinder via the gravity hot water set up) TRV's shut off when individual rooms get up to temp.

If however the cylinder calls for heat, then the boiler fires up and delivers the heat via the gravity feed set up to the cylinder.
The downside of the gravity set up is that there is a very long run on the pipes so heat is wasted there, and the boiler ends up cycling as the heat does not disappate fast enough into the cylinder.

The cylinder is 17 years old and insulated by both a foam jacket and red jacket.
Pipes are insulated as well as they can be by foam.

4 KW of PV produces 4 x 900 units in the south west 850 in norfolk 800 in scotland. 3600

ten units a day at best during the winter its going to be more like 3-4 units which is when you use any hot water for heating.
This device will certainly cover hot water usage in the summer but i dont think it will achieve as much. Ideally you need a heat store Large well insulated thermal store to keep the heat in. You also need a range of immersion heaters as most are at least 2KW most are 3 KW. So if your exporting 1 KW and your 3 KW immersion kicks in then your using two units of electricty at 14p per unit =28p rather than Gas ' 4.2 p per unit x 2 = 8.4p that means it could cost you 60p a day extra

nicksgonesurfin said:

You also need a range of immersion heaters as most are at least 2KW most are 3 KW. So if your exporting 1 KW and your 3 KW immersion kicks in then your using two units of electricty at 14p per unit =28p rather than Gas ' 4.2 p per unit x 2 = 8.4p that means it could cost you 60p a day extra

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@niskgonesurfin, That's the whole purpose of inmmersun type devices, the PROPORTIONALLY control the power to the immersun so YOU DON'T import, and if you've only got 751 watts available that's all it will send to the 3kW immersion:

This ImmerSun was installed on the 22nd December 2012:

nicksgonesurfin said:

4 KW of PV produces 4 x 900 units in the south west 850 in norfolk 800 in scotland. 3600

ten units a day at best during the winter its going to be more like 3-4 units which is when you use any hot water for heating.
This device will certainly cover hot water usage in the summer but i dont think it will achieve as much. Ideally you need a heat store Large well insulated thermal store to keep the heat in. You also need a range of immersion heaters as most are at least 2KW most are 3 KW. So if your exporting 1 KW and your 3 KW immersion kicks in then your using two units of electricty at 14p per unit =28p rather than Gas ' 4.2 p per unit x 2 = 8.4p that means it could cost you 60p a day extra

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Given that is you heat your hot water cylinder with electric, I thought most ppl used GCH like me ??

If you do use GCH - the benefit could be less but still rewarding, again its all about knowing your systems, your needs and whats possible with your system, especially figs like whats your export rate to grid to work out ultimately your ROI !