Setting up the Immersun Vs Central Heating - Help!

[MicraShed]

stick a timer in the circuit to the cylinder stat, jobs a goodun. (I think, but I'm not entirely familiar with this set up - is the heating circuit pumped or gravity fed as well?).

Its a home brew affair. The hot water is gravity fed, only the heating is pumped.
The cylinder stat is a strap on type:-

The control box is basically a power relay which switches depending on whether there is a "call" from either room stat or cylinder stat.
This one is the original prototype - the one I have on the boiler now is neatened up a little and in a plastic case but is essentially the same:

Power is sent to the boiler controls for the water / heating depending on whether there is a call from the thermostats. A neon on the top of the unit indicates if its the water & heating or just the water that is active (ie if the pump is running or not).

No doubt people will exclaim WTF? But at the time this was necessary to ensure I had hot water when i needed it and heating when I needed it as I work erratic shifts (I might have mentioned Im a nurse these days?) So the house (quite well insulated) remains at a background temp of 17 degrees, when I get up I simply put the heating up to 20, when i go to bed or go out I shut it back down to 17.

Sounds horrific? Well by maintaining a background heat it takes less time to get the house up to a comfortable temperature. Gas use for a four bed semi over 2011 averaged between 13kWh/day (Summer) to 33kWh day (winter).

 

[Gavin A]

that's a lot in summer.

the problem I'd suspect is that the stat probably has a 2 deg hysterisis setting, so will be cycling the boiler fairly frequently every time the cylinder drops 2 deg, which won't take that long with only 25mm insulation (if that). Each time it cycles it has to heat up all the fluid in the presumably 22mm or higher pipework, plus the pipes, plus the boiler etc not just the water in the tank, so the efficiency of this operation is fairly low.

I think this is a question we really need to be asking people, as it'd be a simple process to put even a basic inline timer into the system on the same circuit as the switched live for the stat, plus extra jacket to keep the heat in (I know, sorry it's somehow still in our warehouse and didn't make it to your cylinder).

 

[MicraShed]

I think this is a question we really need to be asking people, as it'd be a simple process to put even a basic inline timer into the system on the same circuit as the switched live for the stat, plus extra jacket to keep the heat in (I know, sorry it's somehow still in our warehouse and didn't make it to your cylinder).

Meh! Dont worry about the jacket, its not the end of the world.

Some of that gas use is cooking, but not much - you are of course bang on with the cycling of the gas boiler. So an inline timer is possibly the simplest option at this point, though I have to say having read up a bit about unvented systems I wonder if ultimately that may be the way forward in the future. Not this year though as Im still paying for the PV install. And whilst I have the width Im not sure about the height in the existing cylinder cupboard (though thats a fairly simple matter of removing the ceiling and utilising some of the loft space above.

 

[Worcester]

Just as a comment, you can get programmers just for the cylinder stat. We are oild fired and the hot water and heating are linked to the same time so if we have heating on in the am, then it kicks in the hot water adding a progarmmable cylinder stat timer to just the cylionder stat circuit lets us programme a completely different regime for the hot water (within the bands of heating on / off) and allows us to alter the temperature as well, so it's not just when it's on / off, it's also what temperature we want it at. That allows us to give the ImmerSUN the 'priority'.
Have a look at this as the 'ultimate' - less expensive options that do the same thing are available.

WP75-RF
http://danfoss-randall.co.uk/PCMPDF/34248v06.pdf

 

[Worcester]

p.s. we had a custom built unvented dual cylinder made espcially for us as a one off due to height restrictions, so it's short and fat ... it actually ended up costing less than an off the shelf unvented dual cylinder.

 

[hawgraham]

I had an ImmerSun unit installed 2 days ago. I have now had a chance to analyse how it works. Unfortunately there is a problem in that the unit outputs bursts of 3kw sine waves. In otherwords part of the power being put to the immersion heater is coming from the mains not your PV panels. Over a period of time the unit does output the average power quoted, but because of the way it works it would not be able to run off grid. If you think about i,t if your immersion heater is 3kw then that is the power it will take unless the voltage applied to it is reduced (like when you run it from an 110v transformer). This unit does not reduce the voltage it just outputs 3kw pulses, if you have 500w to spare from your panels the unit will still output 3kw pulses with a gap inbetween so that over a period of time the average power output is 500w. Most of the time you are still putting 500w into the grid. Your household meter does not run backwards so when the 3kw pulses are used 2.5kw of it is coming from the grid (in this case) so over a period your meter will clock up power used.

If you want to see what I mean just stick a current clamp on the cable and stick an oscilloscope on the end.

 

[BruceB]

.............. Your household meter does not run backwards so when the 3kw pulses are used 2.5kw of it is coming from the grid (in this case) so over a period your meter will clock up power used.

If this is the case then the people at Immersun have made a fairly basic mistake which would surprise me. I suggest you ask them before being critical of the product. If the burst firing of the triac is within the averaging period of the meter electronics then there should not be a problem.

 

[Worcester]

@hawgraham,

You're both right and wrong here.

An understanding of the various power control methods and how meters work is important.

Yes the Immersun uses burst fire so 20% would mean in very simple terms that 1 cycle in 5 is passed through at full power and the other 4 at zero, (so the system exports during those cycles). The alternative to burst fire is phase angle control.

Lets assume that the voltage is 230 volts that the immersion is a 3 kW unit (13.04 Amps) and that there is 720W of power available
So in say a 1 second period, over 50 cycles, the current flow MAY look like this: (see attached AMPS)
and the cumulative energy consumed from the grid is therfore: (Cumulative Watt hours) - i.e NET consumption = 0 (Zero) Wh

The little light that flashes on your meter is recording 1/1000 of a kWh, i.e 1 Wh or 1 Watt Hour (1 cycle passes 0.0166r Wh @3000w)

The meters actaully measure AVERAGE energy consumed over a short period of time, and hence they take into account both the forward and reverse flow during that period.

The system was configured to use burst fire after extensive discussions with the meter manaufacturers and a large number of tests with different meters, and the manufacturers of the ImmeSUN unit have yet to come across a meter that works any differently. If you can prove otherwise I am sure that they will help you out.

So, all you ImmerSUN customers can rest at ease.

 

[Graeme Harrold]

I was listed last week as an installer on their site, and have quite a few in the pipeline already. Previously I was fitting the Parsons Switch, unit cost is comparable, but Immersun is easier to fit as you dont need to change the immersion. The first Parsons I fitted ended up with a new tank as the copper ripped as the old immersion was being removed.....Immersun all the way now......

 

[MicraShed]

Does the "pulsing" explain why my immersion switch neon looks like its at a 1990's illegal warehouse rave?
(Click on pic for video)

 

[Gavin A]

yes.

I'll have to add that to our web page - now with add rave effects in your airing cupboard.

 

[Worcester]

You guys obviously don't remember the 70's party trick of shoving a flourescent starter in series with a normal (coloured) 60W incandescsent bulb and creating great random flashing lights for home parties. -- But then no self respecting spark would ever admit to knowing about that trick!

 

[Gavin A]

we had lasers and video projectors at our parties....


well actually I do remember one party where the lighting effects somehow ended up involving a torch and a christmas baubble being spun by hand.

There was also one party that involved some electrical work on the fly using tin can fuses and plugs being ripped off the decks and them being wired direct into the socket before I erm sorry my friend had to switch to that deck before the record ended on the other deck.... which probably wouldn't pass muster on the old risk assessment. Or maybe I imagined it.

 

[MicraShed]

I was running round in short pants in the 70's but have been guilty of occasional iffy electrical lighting effects for the Venture Scout disco in the 80's.
Then I moved to Manc in the 90's and the less said about the electrics in the nurses digs the better really.