PV immersion heater proportional control

[methley]

...I have attached a photo of the one I'm trailing at the moment.

Mmh, my home brew version isn't looking quite so tidy just yet!

 

[brian wright22]

I'm sure it looks fine when the lid is on!!

 

[pwboston]

You can wire it to both immersions if you have two. It has output 'load sensing' and a 'changeover relay' with several different software selectable options on how the relay is used. So with 2 immersions, you wire the top one as the primary via the relays NC contacts and the lower immersion as the secondary via the relay's NO contacts. The immersun then (proportionally) feeds to the top immersion until such time the top of the tank gets to temperature and the thermostat in the top immersion goes open circuit. The immersun then detects there's no longer a load on the primary output, so it switches the relay and now applies proportional output to the secondary (lower immersion). It periodically checks the primary load and will restart supplying it when it comes back in circuit.
We've wired one up similar to this so that it first heats the HWC via the immersion then switches to the element in the towel rail.

If the bottom one is wired off the E7 and is switched on by your electricity meter through an MCB in the board, would the Immersun allow the off peak element to come on in the 7 hours overnight if the water wasnt hot enough, can it be wired to allow this, or would you simply wire through this and setup the on board timer to run for the 7 hours of the economy 7 period for that element. If you get what i mean?

because during the day it wouldnt allow any immersion to be switched on unless it had enough power, so will it allow the power through during the night when there is none?

 

[brian wright22]

There is a volt free pair of change over relay contacts that you can route to the bottom immersion heater and have the common connected to the immersion heater live ,the normally closed contact would be connected to the E7 and the normally open would connect to the CU 240 ac.
When th immersun was satisfied for heat by the top immersion heater then the bottom immersion would be supplied by 240 v normal CU supply. When the immersun was not supplying any surplus power and both immersion heaters were satisfied then then the E7 supply wiring would always mimic the way before the Immersun was installed.So after dark (no Solar PV) your E7 would operate as normal.

I hope this helps

 

[Scobo]

Mmh, my home brew version isn't looking quite so tidy just yet!

View attachment 14276

Looks the business.
Is it a proportional controller ?

 

[methley]

Yes it is. In the photo above you can see it is feeding 647W into the immersion. It works by keeping the export between 30W and 70W wherever there is an excess being generated. It will work with any sized resistive load up to about 5.5kW. At the moment it's driving the immersion but will shortly have a couple of towel radiator elements hanging off it too.

 

[Scobo]

Excellent job !
Could I ask how much the parts cost ?

 

[methley]

Around about the £120 I would have thought.

 

[Scobo]

Not bad !
Give us a shout if you ever decide to market it. :wink_smile:

Scott.

 

[sly_dog_jonah]

I can now give an update to the Immersun device I have been testing. The device has exceeded my expectations and can report after a month of testing that it does everything it says in its specification.

Sounds very encouraging results. Our Immersun is getting installed Wednesday. Currently we have the gas boiler programmed to heat water for 1hr in the morning and 1hr in the evening, with the thermostat set to 55C. The 3kW immersion is at the bottom of the 200litre tank (new build so well insulated, 1C loss per day) but was until now just a backup in case of boiler failure. Once the Immersun is installed the initial plan is to keep the boiler programmed, but only for the evening in case it's been a rubbish day, but to reduce the thermostat to 45C and to set the immersion thermostat to be 55C.

After a while of testing that out, the next stage will be ramp up the immersion's thermostat much higher, to increase the energy we can dump, but to fix a blending valve to mix down the hot water to a safer 50C or so. This should reduce the probability of needing to 'top up' with gas heating, and also solves our issue of having our thermostat too low currently to prevent Legionnaires (because we have a toddler in the house and another on the way).

Throughout all this we will monitor the gas usage to monitor the effectiveness of the Immersun as well as tracking how many kWh it dumps into the tank. Hopefully it will be at least another month or two before the central heating (gas) has to be put back on, prior to then our gas consumption will be solely for water heating (and will hopefully be negligible).

 

[brian wright22]

Quote Sounds very encouraging results. Our Immersun is getting installed Wednesday. Currently we have the gas boiler programmed to heat water for 1hr in the morning and 1hr in the evening, with the thermostat set to 55C. The 3kW immersion is at the bottom of the 200litre tank (new build so well insulated, 1C loss per day) but was until now just a backup in case of boiler failure. Once the

Read more: http://www.electriciansforums.net/p...ter-proportional-control-6.html#ixzz25Oudjnnx​

Yes, the only downside to me setting the immersion heater thermostat hight to 65 degrees C is the very hot water I like the idea of a blending valve.Fortunately we don't have full time youngsters in the house only visiting Grandchildren which we can keep an eye on.

 

[sly_dog_jonah]

Yes, the only downside to me setting the immersion heater thermostat hight to 65 degrees C is the very hot water I like the idea of a blending valve.Fortunately we don't have full time youngsters in the house only visiting Grandchildren which we can keep an eye on.

If anyone has both hot and cold water pipes near to each other in the airing cupboard, and sufficient pressure for each then a blending valve should be a relatively trivial job for a plumber to fit.

I look forward to comparing results with you Brian. Do you have any estimate of the Gas kWh's saved in the first month?

 

[brian wright22]

I look forward to comparing results with you Brian. Do you have any estimate of the Gas kWh's saved in the first month?

So far I have managed to get enough hot water to enable the Gas Boiler to be turned off for 32 days since the installation of the Immersun. It also depends on the total size of the hot water tank and the depth that the immersion heater (Top Mounted) extends down into the tank.Ours is 1050 mm high and the immersion heater is 36" in length. Hence it does heat virtually down to the bottom of the tank which gives about 130 litres capacity. The tank is rated at total water capacity of144 litres.
The savings in Gas over the 32 days is @ 3.556pence/kwh x average gas consumption x 17.6 kwh = about 62.6 pence per day to heat the water. There is a 21p / day standing charge but I have to pay this anyway so this is not included in the calculations.
Multiply this by 32 days so far = £ 20 total gas saved.
Obviously it won't be as high as this in the winter months but there will be a saving.
I have attached the installation shot. I'm trialling this device and found the MK grid switches very conveinient.

 

[sly_dog_jonah]

Thanks for the information Brian. Our 200 litre tank is 1.45m tall, but the immersion is positioned around 35-40cm from the bottom so there is plenty of water above the element to heat (about 150 litres by my reckoning). It's only a 13" element but I don't think this should affect things too much as it is horizontally mounted in the tank.

It's a shame 'No Standing Charge' tariffs are few & far between these days, otherwise we could eliminate that pesky 21p/day during the warmer quarters of the year (assuming you don't cook with gas).

 

[brian wright22]

Yes we do cook with gas so its not all wasted!!