PV immersion heater proportional control

[Earthstore]

You mean not to use one at all and rely on gas/wood boiler to heat water up??

No that is not what I asked, If you have some free energy IE surplus PV then you should use it, but use it wisely.
Why pay £500 for something that will only save you £50 per year, when if used differently could save you £200 per year.

The figures are not exact of course, they are just examples.
The same as my MPG example, if you only had one device which car would you put it on, the one that gains you 10 MPG or the one that gains you 30 MPG?

 

[Gavin A]

I have put this before, but I will ask again, Why is everybody obsessed with heating their hot water from excess PV?

Domestic hot water is only 5%-10% of you heating cost, so that leaves 90%-95% which is to heat your home, surly if you are going to the expense of controllers it would make more sense to run some small heaters to reduce your heating costs, this way the sums might add up too.

Once your hot water tank is hot that's it, you still export if you have a surplus, however if you could raise the temperature in your house a couple of degrees that would be more beneficial.

If you owned two cars and there was a device that would save you 50% on your MPG Would you put it on the one that does 20MPG giving you a 10MPG gain, or would you put it on the one that does 60MPG giving you a 30MPG gain?

Before anyone buys a controller, do the mathematics first.

presumably because most of the excess generation occurs at the time of year when heating isn't required, and adding electric heaters will add around £3-500 on top of the cost of the Immersun or similar device vs an existing immersion circuit.

We have done both, and in some situations it can be worthwhile to feed excess to a small storage heater eg in a room that doesn't get any sun in the afternoon if the rest of the house is being warmed by the sun later in the day, but it's only really going to reduce boiler use for relatively small periods in the year when just a little supplementary heat is wanted in a single room.

 

[jason121]

I have put this before, but I will ask again, Why is everybody obsessed with heating their hot water from excess PV?

Domestic hot water is only 5%-10% of you heating cost, so that leaves 90%-95% which is to heat your home, surly if you are going to the expense of controllers it would make more sense to run some small heaters to reduce your heating costs, this way the sums might add up too.

Once your hot water tank is hot that's it, you still export if you have a surplus, however if you could raise the temperature in your house a couple of degrees that would be more beneficial.

If you owned two cars and there was a device that would save you 50% on your MPG Would you put it on the one that does 20MPG giving you a 10MPG gain, or would you put it on the one that does 60MPG giving you a 30MPG gain?

Before anyone buys a controller, do the mathematics first.

Kinda disagree
Why not install a TMV and up immersion stat to 70-80 degree
That way immersun will always input into tank

 

[methley]

Yep, that's what I'm doing. However my home built controller was much cheaper than an Immersun anyway. I've also wired in a couple of electric elements to towel radiators also. It's useful to have those hot during the day in summer to dry out towels in the bathrooms. If you don't use it you lose it so why not!

 

[Gavin A]

Kinda disagree
Why not install a TMV and up immersion stat to 70-80 degree
That way immersun will always input into tank

waste of time, effort and money IMO with most cylinders as you'll lose most of that additional heat overnight anyway as the delta T between the tank and ambient air pretty much doubles.

plus it turns a nice simple job into one where you're into messing around with the plumbing around the tank which is usually in a pretty confined space, and opens up all manor of other potential problems once you work out that the isolation valve is buggered etc

 

[methley]

I've also fitted a secondary tank jacket to counteract this. Cost a fiver ;-)

 

[jason121]

waste of time, effort and money IMO with most cylinders as you'll lose most of that additional heat overnight anyway as the delta T between the tank and ambient air pretty much doubles.

plus it turns a nice simple job into one where you're into messing around with the plumbing around the tank which is usually in a pretty confined space, and opens up all manor of other potential problems once you work out that the isolation valve is buggered etc

open the door and warm the hall way

 

[Gavin A]

I've also fitted a secondary tank jacket to counteract this. Cost a fiver ;-)

that's always worth doing, but as an example, we've got a monitored solar water heating system at home with a 50mm insulated jacket, which overnight will drop from 80deg to 70deg C. This isn't really an issue with our system as all the plumbing was needed anyway, but I don't see it being worthwhile most of the time when all you're doing is putting a controller on the existing immersion circuit as it's just opening up a whole different can of worms for minimal benefits and adding at least 50% to the installed cost of the immersion controller.

 

[Gavin A]

open the door and warm the hall way

just what's needed on those hot summer nights....*






*and now I've got John Travolta / Olivia Newton John singing away in my head

 

[Greenday]

Just chatting to a customer who we fitted an immersun for. He turned his boiler off for hot water 4 weeks ago and has enough hot water for his needs since via just the immersun.
The reason for his call was that he wants us to fit an electric heater to the relay. I had to discourage him a little and have asked him to monitor to check that the immersun is showing water hot at some stage during each day!
Must admit I'm surprised he is getting enough hot water at this time of year even if he is a small user.

 

[echase]

Why is everybody obsessed with heating their hot water from excess PV?

Before anyone buys a controller, do the mathematics first.

Here is some maths and some hard facts.

Intelligent Immersion Ltd has done a detailed analysis of several of its proportional controllers that have been in service for more than a year, based on logging their power flows. It is concluded that a fair average figure for energy put into an immersion heater is 1400kWhr per year for 4kW PV systems. Based on a gas cost (plus boiler inefficiencies due to short cycling in summer) of 7p per unit that amounts to £100 per year saved. With oil, bought wood, LPG or full priced electricity that might be double. So with a £200 device price it pays itself back in 1-3 years, not including any installation cost (which should be zero for DIY install). That is an excellent payback for a green device with many, such as double glazing and PV, taking much longer. It would be good even at a base 4p per unit gas cost. That is good reason to be obsessed with water heating.

The biggest reason for not exceeding 1400kWh is because the water temperature on summer days reaches its set temperature part way through the day.

Of course there are things that can be done to extract more than 1400kWh out of it such as heat a towel rail, second immersion, underfloor heating, etc, but 2 problems:-

1. Our data shows that there is only significant excess export from say Mar to Sept and only then on very sunny days, which are pretty rare in UK. That is not the days when you normally want underfloor heating, etc. A towel rail is about the only summertime use for the heat and personally I never need to heat my towel rails in that period. Battery charging is about the only thing I can think of that can be done with any excess year round.

1. It incurs costly additions to the basic immersion application, whose payback will be long as their benefit is small (e.g. due to the short period when they are useful).

So to adapt your car analogy a car that does 60mpg is good. One that does 80mpg is better but not if it costs 50% more to buy, as the extra will never recover itself in saved fuel.

There are some strange claims being made by some in this market area. You can generate very optimistic numbers that lead to marketing statements like “save £250” but only if you assume at least 2 out of 4 of the following factors: 100% of the generation goes into water heating (i.e. no house usage), fuel is >15p, it is a large household using lots of water and is in south of England. It is disingenuous to claim that it applies to all.

For stepped contollers and 1kW immersion elements the payback is much longer.

 

[echase]

1. Our data shows that there is only significant excess export from say Mar to Sept and only then on very sunny days, which are pretty rare in UK.

Just to be clear, by that I meant more export than the immersion can absorb because it is up to temperature or the export is over 3kW. Of course it can carry on powering the immersion all year round, albeit with much less export available to be absorbed in the depths of winter. At the moment it is cold and sunny and my unit is putting 1kW into the immersion. There will though not be enough input over the short day to have any spare for say towelrails, unless I am very abstemious with water usage.

 

[Worcester]

.
The same as my MPG example, if you only had one device which car would you put it on, the one that gains you 10 MPG or the one that gains you 30 MPG?

It depends how often and far you drive each of the vehicles, ....

 

[Worcester]

Here is some maths and some hard facts.

Intelligent Immersion Ltd has done a detailed analysis of several of its proportional controllers that have been in service for more than a year

Here are some more hard facts, available publicly from Companies House

Name & Registered Office:
INTELLIGENT IMMERSION LIMITED
THE GREETINGS
GRANGE ROAD
WINCHESTER
ENGLAND
SO23 9RT
Company No. 08271212
Date of Incorporation: 29/10/2012

Some I'm not quite sure how it can have done 12 months analysis?
Or perhaps Edward Chase, sole director of Intelligent Immersion Ltd was working with and selling his products through a different company?

 

[Gavin A]

I think he's been running and monitoring some pre-production pilot systems for a while, I'm aware of the evolution of his design from concept through to this stage as he basically documented it on the Navitron forum prior to eventually being banned when he commercialised it.

I have no reason to doubt that he has the years worth of data that he says he has, though I do think the savings figures he's supplying look quite high, and probably relate to relatively high hot water consumption levels eg family houses rather than single or 2 people households.