Alternative way of fitting a Willis immersion

iwb

I read this thread with great interest but decided I wanted to try something different. Like many others, I have a (300L) tank with an immersion element nearer the top so I only heat 100L max. I also have an Eddi (with addon relay board) and a Zappi. I give away quite a bit of energy to the grid when the car isn't here or doesn't need a charge and I don't have a smart meter.

Similarly to others, I want to use the first Eddi output to heat the 100L using the in built immersion and have the Willis heat the lower part of the tank when that's done. My tank has a solar coil at the bottom which was never used as I didn't spend the money on the collectors.

As you can see, I put the Willis into the spare coil with a circulating pump. I have only done this in a temporary way for now but would really like to get peoples thoughts on this and what the upsides and downsides are in your opinion.

So far, I have run it for a few hours at a time giving the heater the full 3kW and raised the temperature of the tank from 12C to about 47C and all seemed to go very well. I have done this manually by switching on the pump first and then the immersion. I haven't insulated it yet so I know i'm losing heat. I found it very difficult to bleed the system so I didn't fit the expansion vessel to the top. You can see a plastic bottle screwed on there instead which is just a water reservoir. When I run the pump, there is still a small amount of air coming out into the bottle.

I have spent about €100 to date as I had the circulating pump already. It would be another €100 or more to but one I think.

Some questions;

Does this setup need a permanent water supply to allow for leaks or anything else, or can I just close it once all the air is out and put on the expansion vessel? Do I even need the expansion vessel if I pipe a feed into it? The whole system is between 2L and 3L of water.

What is the best way to manage it automatically? I think I can start the pump with the relay output from the Eddi but how do I manage when the pump starts and stops on temperature? Should it always run once the Eddi is heating, even if only very minimally?

John.G

Good thinking but the immersion is mounted incorrectly, it should be mounted with the immersion head on the bottom, in its present orientation air can be trapped bretween the outlet and the immersion top which may (although unlikely, burn out the heating element) and the thermostat may not be sensing the correct temperature, however, as you have forced circulation (circ pump) you will probably be OK, its certainly far easier to adjust the stat in its present position.

You do need either a expansion vessel or the top up bottle, you may have to extend the bottle higher up if setting the immersion stat cut out at 65C/80C,

What make/model and setting pump are you using? and do you feel much difference in the flow/return temps on the immersion?.

Automatic Running?, pump should IMO be started/stopped with the eddie relay wired in series with the immersion stat.

iwb

Thanks for the comments. I don't feel much difference in in flow and return temperatures. I think that's because the pump is fast, so it equalises it. The pump is one I had for recirculation of hot water as our cylinder is in the garage. I never installed it, so it was hanging around. Not sure what sort of pump I will use permanently as I do want to install it to circulate the hot water in the house at some stage. I would say the flow for the Willis can be very low and still be very effective.

I have no idea about pump settings. I didn't change anything.

John.G

That may be a bronze pump, if not leave as is and buy one when you install the secondary circulator otherwise it will corrode and possible discolour the hot water. If it is bronze and you replace it, something like my 6M Wilo Yonos Pico ar ~ £120 will circulate at say 8 to 10LPM ro give around a dT of 5C or less and consume only 20/25 watts or less.

I wouldn't be too happy leaving the Immersion as is as it will more than likely lead to premature failure of the heating element as air/vapour will definitely build up in the that top space which the AAV will not get rid of IMO.

Your pump is a 2M stainless steel one so you should replace that and reuse it for recirculation.. You can still use a 4, 5 or 6M Wilo as you can run them at any head you like, right down to 0.5M. The 4M would be quite adequate and probably a few bob cheaper than the 5 or 6M models

This is your Grundgos Pump.

https://product-selection.grundfos.com/ie/products/up-ups-series-100/up-ups-n/up-20-15-n-150-59641800?tab=variant-curves&pumpsystemid=2120449068

tnegun

As you have the relay board for the Eddi it can be configured to run the circulation pump for 5 minutes every time max temp is reached it would be a bit start-stop with the closed loop but would give you some automation over the running of the pump. See page 50/51 here

John.G

Maybe? a advantage with this system vs a destrat pump or even the convection type only willis immersion is that this bottom coil will act exactly in the same manner as a solar coil (which it is) and will only influence the cylinder top temperature when the "store" temperature exceeds the cylinder top temperature.

There is/should be a sensor pocket located just above the solar coil top (the "store" temperature) which usually has a PT1000 temperature sensor, if the Eddie cannot use this signal then a pipe/cylinder stat can be strapped on and set to the required max cylinder temperature, this way, the solar coil/willis can still give the maximum cylinder temperature attainable. With no other heating, the cylinder temperature and the store temperatures will be the same with a fully charged cylinder, of course, a strap on cylinder stat can be positioned lower down near the bottom of the solar coil and will call for heating once ~ 10/15 litres or so of hot water is drawn off even from a fully charged cylinder. Interesting, to say the least.

10-10-20

Very interesting application OP. Don't forget the corrosion inhibitor!

Drewgt

I like the Good Alternative thinking. Id removed my thermal collectors to fit PV so am in a similar position.

I understand you've created a separate sealed system similar to a thermal solar with the collectors replaced by an immersion. If it works great! However, if you used Willis in its intended fashion imo you'd get better efficiency as you've only one energy transfer although you've none of the Willis convection issues. As you've a sealed system I wonder what the effect of glycol would be instead of water as the thermal solar uses glycol due to better thermal capacity and as your bottom coil is designed for?