Electrode Water Heater

Hmmm.

The effectiveness of an electrode boiler is related to the conductivity of the medium into which the electrodes are immersed and the size of the electrodes.

Consider two identical wind generators and two identical boilers, one containing seawater, the other distilled water. The power dissipated within each boiler is related to the area of the electrode and the conductivity of the water, as these determine the electrical resistance of the boiler, and therefore its "match" to the wind generator. With similar wind speeds the windmill connected to the distilled water boiler will run faster than the one connected to the seawater boiler, as less power is being taken from the windmill on account of the higher resistance presented at the electrodes of the distilled water boiler.

Consider as a preferred option matching the output of the windmill to the known resistance of an immersed heater element, rather than to an electrode boiler. There would be no need to determine the electrode area accurately for each individual water and therefore the heat dissipated becomes independent of unknowns in water conductivity.

Consider carefully also the application to which the hot water is being put and therefore the need for antiscalants and acidity regulators within the hot water generated; these prolong the element and exend the effectiveness of the heat transfer surfaces. If the water is to circulated as the "primary" heat exchange circuit, like in a gas- or oil-fired central heating system, and the "secondary" side is used in contact with drinking or showering/bathing water, then the primary side needs to be kept at a slightly lower pressure, so that any leak is from the secondary side to the primary side; in the UK this is done by having the primary tank mounted in the loft space at a lower elevation than the secondary side.

If the application of the windmill is for domestic hot water storage, it may be possible as an alternative to couple the generator directly to the (often-underused because of the value of the electrical kWh) electric heating element found in the the typical domestic hot water storage tank, rather than going via an electrode boiler and a circulating loop as intermediate steps. Further, if a DC circuit is used it may be possible to arrange for a combined solar and wind energy collection and storage system, the two sources combining their contributions passively depending on the voltage at the terminals and the current coming from each source. Sizing such a system needs to allow for a maximum design dissipation in the element of 3kW at 240V in the UK, or a resistance of 19.2 ohms at the tank element electrical terminals.

Presently in the UK a major home improvement store chain is offering the purchase and professional installation of domestic wind turbines, subject to an approved Panning application, at <£1500 Sterling all-in. The arrangement suggested in the post, and any development of it, needs to compete with this figure and many home-brew solutions already do.

In economic terms it may be a better to export the electricity made from the windmill direct into the local electricity grid at the moment, thereby saving on electricity consumption at a higher value per kWh, rather than substituting the input from a lower value heat source in a hot water storage arrangement. Calculations using local data and circumstances and a measure of good judgement are needed at this point.

I already have a zone controlled system for heating my home with each room independantly controlled.

Heat is being provided by a heatpump 1.2KW with COP of 4, operating 24/7 with insulated hot water storage and with Oil-fired backup. It is my hope to compliment the system with a wind powered generator which would heat the water (having suitable electrolite in solution to enable the use of an "electrode" heater)

I very much apppreciate the contributions to this discussion and will welcome all further contributions

I would say that 5KW would work with enough battery capacity. My problem with this would be initial cost. There would be quite a long payback because of this.

Sorry I misread what you were doing. Standard indirect fired water heaters have a 4.5KW heating element. I would think that finding an element in the U.K. or Ireland would be doable at 220V-1PH-50Hz. Is this voltage avalable?? I would imagine a 30A circuit breaker as protection, wire size 3#10 + G would be needed. Does this wind generator have the capacity to produce this kind amperage needed? 20A??

I am about to order a 5KW wind generator if I am confident that the results will justify the investment

With a 20A breaker one might obtain a satisfactory calculation for short distances using 2.5mm² twin-and-earth [T&E] cable. The limiting distance for a 20A breaker on a 2.5mm² spur in free air according to the IEE Regs 16th Edition algorithms would be an interesting thing to calculate given that there is likely to be a distance between the generator and the storage location. For a 32A breaker, 4.0mm² or larger T&E would almost certainly be required.

Comment #1 questions the need for battery storage if a redundant electric immersion heater element were available, as the water being heated, which is what the post is seeking to do, provides the energy storage facility required in the post. Were the selected wind generator rated 3kW instead it would simplify things a little as immersion heater elements for domestic use at this rating are readily available in the UK. 3kW may be a little easier to obtain from the wind than 5kW, needing a smaller windmill with a more slender support structure. Then, the winds may be stronger in Eire...

My installation is located on the south west coast of Ireland where there is a consistent supply of wind energy which I feel would give me a realistic pay-back on my investment.I intend using 6mm cable from the generator to the distribution centre which will be a max. distance of 15 meters and should keep transmittion losses to a min.

Since heating other than domestic hot water will not be required for an average of 6 months each year I would need the inclusion of batteries and inverter to make the power supply suitable for normal domestic use including heatpump-- Air conditioning which we are led to believe will be neccesry with the expected Summer temperatures Due to Global warming.

I still would like to consider using an Electrode heater (for practical reasons) eventhough resistance heaters are readily available

Ever considered taking domestic hot water and passing it through a plate and frame heat exchanger on one side and transfer heat into the heatpump loop on the other? This may aid on those cold nights. This could be done using a small pump and aquastat on the heatpump return water side to compensate for drops in heatpump loop temperature. Do you have any reheat on the heatpumps?

I am considering doing as you suggest but also heating the residual liquid refrigerant in the receiver to improve COP and discharge water temp.

Nage,

I still don't get the decision for an electrode heater. Can you explain your choice?

Just use resistance wire/elements, if you add a system that can switch from series to parallel you can adapt the consumption to the available power.

I assume you will have a 3pH permanent magnet generator/alternator which you will couple direct to the heated tank?

Commonly available residential water heaters use 2.5 (+/-) KW. resistance heaters.

Would'nt it be easier & safer to use proven elements???

There might well be safety issues with an electrode heater connected

to a residential piping system.

I agree with most of the comments here, but if you are set on an electrode heater, do not use it directly in the water for the house, have a seperate water system with a suitable electrolyte in it to help boost efficiency and use the resulting warm liquid to feed a heat pump or via a heat exchanger to warm the water for the house.

Make sure that the electrode heater is correctly earthed and that there is no electrical path to the house water piping....eg. put in plastic or rubber pipes somewhere between the two....