PV immersion heater proportional control

[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!!

 

[yorkshiremike]

Brian, do you think your 17.6kWh of gas saved daily is a bit optimistic? For example, how many kWh has your Immersun indicated that it's putting into the HWC each day? The reason I'm asking is that I'm wondering how inefficent (in terms of gas energy to energy in hot water) the indirect gas water heating is. Certainly a modern condensing combi boiler can manage 80%+, but it is directly heating the water so I was sort of assuming that a modern condensing system boiler would be making 70%+ after allowing for heat loss in pipes to the HWC etc. But this would still mean that 17.6kWh should be more than enough to fully heat the HWC from cold twice a day. Energy to heat water in Wh at 100% efficiency = 1.16 x number litres x temperature rise, so 130 litres through a 35 deg temp rise = 5.28kWh. The immersion should be close to 100%.

Mike

We've fitted several Immersuns now, though a couple of the customers needed rewiring as they had other stuff connected onto the immersion circuit. I've one fitted at home, but it is only heating a towel rail - we have a combi - currently planning to have a thermal store fitted, unless anyone has a better idea.

 

[sly_dog_jonah]

I went through some very similar calculations yorkshiremike when weighing up whether to invest in an immersun. I think Brian must be basing his calculations on reduced gas usage, not the amount dumped into the immersion by the immersun. But I'll let him answer your question.

Our hot water usage via a modern Gas boiler (non-combi) averages 13/14kWh/day for 1 shallow bath (for a toddler) and 2-3 showers/day. Our dishwasher and washing machine both have cold supplies only. The tank's thermostat (for controlling the boiler) is set to around 45C. Since we have a large tank I'm hopeful that sufficient heat will be retained from good PV days even if they are followed by rubbish days, and negate the need for any gas water heating except for during poor weather spells. However I'm realistic and expect that on most days of the year we'll have to use some gas, but less than we currently do.

 

[brian wright22]

Brian, do you think your 17.6kWh of gas saved daily is a bit optimistic? For example, how many kWh has your Immersun indicated that it's putting into the HWC each day? The reason I'm asking is that I'm wondering how inefficent (in terms of gas energy to energy in hot water) the indirect gas water heating is. Certainly a modern condensing combi boiler can manage 80%+, but it is directly heating the water so I was sort of assuming that a modern condensing system boiler would be making 70%+ after allowing for heat loss in pipes to the HWC etc. But this would still mean that 17.6kWh should be more than enough to fully heat the HWC from cold twice a day. Energy to heat water in Wh at 100% efficiency = 1.16 x number litres x temperature rise, so 130 litres through a 35 deg temp rise = 5.28kWh. The immersion should be close to 100%.

Mike

We've fitted several Immersuns now, though a couple of the customers needed rewiring as they had other stuff connected onto the immersion circuit. I've one fitted at home, but it is only heating a towel rail - we have a combi - currently planning to have a thermal store fitted, unless anyone has a better idea.

Yes it is the amount of Gas in kwh that I am not using by having the Gas central heating boiler on water heating only.This was based on the gas bill from EDF over the period of time that the boiler was not used for the Central heating.
The thing to remember here is that the Gas boiler loses a significant amount of heat through its casing anf the 1 inch pipes that feed the tank indirect coil.It was originally thermo syphon but is now fully pumped but not a condensing boiler.
With the Immersion heater every bit of power goes into heating the water.
From my EDF Gas Bill, the meter is measuring the gas by cubic M, this is then converted to Units and the value equals Kw/h with a calorific value of 38.4. Whereas the electric bill quotes the Units are equal to Kw/h.The units of Gas does not equal units of Electricity
I hope this helps

 

[brian wright22]

I went through some very similar calculations yorkshiremike when weighing up whether to invest in an immersun. I think Brian must be basing his calculations on reduced gas usage, not the amount dumped into the immersion by the immersun. But I'll let him answer your question.

Thanks Sky, you are correct it is based on my reduced gas consumption.

 

[sly_dog_jonah]

Brian, The Immersun can display it's daily/weekly/monthly/lifetime kWh's delivered to the immersion: Main Menu>View Savings then cycle through the time periods). Would be interesting to compare those figures with your Gas savings over the same period (or similar period depending on when your meters were read by you/EDF).

http://www.immersun.co.uk/downloads/immerSUN Installation and User Guide v1.0.pdf Section 5.4

 

[brian wright22]

Brian, The Immersun can display it's daily/weekly/monthly/lifetime kWh's delivered to the immersion: Main Menu>View Savings then cycle through the time periods). Would be interesting to compare those figures with your Gas savings over the same period (or similar period depending on when your meters were read by you/EDF).

http://www.immersun.co.uk/downloads/immerSUN%20Installation%20and%20User%20Guide%20v1.0.pdf Section 5.4

Yes Sly, Its been averaging 3.3kw hours per day for the past 32 days.


By this comparison, either the gas boiler is very inefficient or the calculation of the Immersun is somewhat inaccurate? I must say that using recognised formular to calculate the heat required to raise the amount of water in my tank seems to indicated that I need more kwh's than the Immersun indicates!

 

[pwboston]

I have dual immersion as only source of heating hot water, on E7

so i can easily tell each day what my water took to heat it. currently using between 4 and 8kw per night at 6p per unit to heat my water, so my savings wont be that huge, and its a lot harder to guage what gas or oil would be saved, but this system does give an accurate saving on electric (if i installed one)

 

[pwboston]

Incidentally with this being a fit after an install job does it still come under the 5% VAT?

 

[brian wright22]

Incidentally with this being a fit after an install job does it still come under the 5% VAT?

Very interesting question. Immersun are certainly adding 20% vat!!! via their suppliers. If it does qualify for a 5% vat then they are making a 15% extra profit.

 

[yorkshiremike]

By its self, it doesn't qualify for the 5% rate (see HMRC site):
[h=2][/h][h=2]The reduced rate applies to installations of:

• controls for central heating and hot water systems (see paragraph 2.6);
• draught stripping (see paragraph 2.7);
• insulation (see paragraph 2.8);
• solar panels (see paragraph 2.9);
• wind turbines (see paragraph 2.10);
• water turbines (see paragraph 2.11);
• ground source heat pumps (see paragraph 2.12);
• air source heat pumps (see paragraph 2.13);
• micro combined heat and power units (see paragraph 2.14); and
• wood-fuelled boilers (see paragraph 2.15).

[/h]


If you argue that it is ancillary to fitting PV and the Immersun is fitted at the same time it's possible that it should be 5%. So far, we've just fitted for existing customers who have already had PV, so charged at 20%. If the bill you get shows VAT, then the legally the rate shown is what they have to account to the Tax man at.