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low voltage immersion heater

 
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emordnilap



Joined: 05 Sep 2007
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PostPosted: Fri Jun 15, 2012 5:33 pm    Post subject: low voltage immersion heater Reply with quote

Note this is a different subject to the thread 'low wattage immersion heater, here.

It seems like our usual weather (going by the past few years as well as this) is going to be mainly cloudy during summer. Our two current sources of hot water in summer are a solar hot water panel (brilliant if only the sun shone) and an immersion heater (heavy on juice but the supply is largely from renewables, still, we shouldn't be consuming too much industrial electricity). Our leccy bill is small and most of it is accounted for by use of the immersion.

So what about a small wind turbine combined with a 12 volt immersion heater, with a regulator and battery? We live in a continuously breezy/windy spot, so the right components could provide 24-hour hot water for relatively small expense - a cheap Rutland, pole, wiring, battery, regulator and immersion for what, 500-600?

What do you think?

Read here for instance. I would have to get some reliable information on what turbine would match what heater but, other than that, what's to watch out for? Laughing
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mobbsey



Joined: 24 Nov 2005
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Location: Banbury

PostPosted: Fri Jun 15, 2012 5:41 pm    Post subject: Reply with quote

Wouldn't it be just as easy to plumb-in some additional panels? Leccy system would require Building Regs. approval, the costs of which are pretty steep compared to getting someone with plumbing skills to add another panel or two.

You'd have to put a pressure relief valve in the system because you'll boil the water on clear days if using evacuated tubes -- for which reason I've always favoured flat plate because, quite apart from being more physically robust, the stall temperature is about 70 to 80C.
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JohnB



Joined: 22 May 2006
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Location: Beautiful sunny West Wales!

PostPosted: Fri Jun 15, 2012 5:56 pm    Post subject: Reply with quote

Rocket stove? That's no volts Very Happy.
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emordnilap



Joined: 05 Sep 2007
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Location: Houǝsʇlʎ' ᴉʇ,s ɹǝɐllʎ uoʇ ʍoɹʇɥ ʇɥǝ ǝɟɟoɹʇ' pou,ʇ ǝʌǝu qoʇɥǝɹ˙

PostPosted: Fri Jun 15, 2012 6:01 pm    Post subject: Reply with quote

mobbsey wrote:
Wouldn't it be just as easy to plumb-in some additional panels?


Dearer than what I wanted - and still no sun!

mobbsey wrote:
Leccy system would require Building Regs. approval, the costs of which are pretty steep compared to getting someone with plumbing skills to add another panel or two.


No planning required up to a 13 metre mast (domestic) or 18 metre (commercial/agricultural), provided it's the same or further distance from a boundary. This is Ireland, remember, different regs.

mobbsey wrote:
You'd have to put a pressure relief valve in the system because you'll boil the water on clear days if using evacuated tubes -- for which reason I've always favoured flat plate because, quite apart from being more physically robust, the stall temperature is about 70 to 80C.


Yes, our SolarTwin is flat plate and the max we've ever had was a full tank of about 65 degrees Centigrade. As I say, if the sun shines, we're on the pig's back but we see the sun less and less these days.

The hot water system is a normal vented one. As I was thinking small (600 watt immersion heater?) it may never get so hot as to boil.
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emordnilap



Joined: 05 Sep 2007
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Location: Houǝsʇlʎ' ᴉʇ,s ɹǝɐllʎ uoʇ ʍoɹʇɥ ʇɥǝ ǝɟɟoɹʇ' pou,ʇ ǝʌǝu qoʇɥǝɹ˙

PostPosted: Fri Jun 15, 2012 6:01 pm    Post subject: Reply with quote

JohnB wrote:
Rocket stove? That's no volts Very Happy.


Can it be plumbed into the existing system?
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mobbsey



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PostPosted: Fri Jun 15, 2012 6:40 pm    Post subject: Reply with quote

emordnilap wrote:
This is Ireland, remember, different regs.

Your ID says "Way Out West".... in the UK that popularly means Acton or Ealing!
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adam2
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PostPosted: Fri Jun 15, 2012 8:05 pm    Post subject: Reply with quote

Low voltage immersion heaters certainly exist, I believe that they are available from the suppliers of the Rutland wind turbines that you mention.

Unless in a very windy district you may be dissapointed with the amount of hot water produced.
A low voltage immersion heater is normally considered as a dump load. More to safely dispose of surplus electricity, than to heat a useful amount of water.

A standard 240 volt immersion heater is about 3KW and heats a typical sized hot water tank in an hour or two.
A 24 volt 250 watt immersion heater would heat the same tank in about 10 or 12 hours. That would seem sufficient for a household that only needs two tanks of hot water a day.
In practice though even the largest Rutland turbine only produces that much in a high wind.
I achieve a winter average of about 60 watts from each Rutland 913.
And that is at good site.
So even with two I would not heat much hot water, except on a very windy day.
Ample for lighting etc.
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emordnilap



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PostPosted: Mon Jun 18, 2012 12:10 pm    Post subject: Reply with quote

adam2 wrote:
A 24 volt 250 watt immersion heater would heat the same tank in about 10 or 12 hours. That would seem sufficient for a household that only needs two tanks of hot water a day.
In practice though even the largest Rutland turbine only produces that much in a high wind.
I achieve a winter average of about 60 watts from each Rutland 913.
And that is at good site.
So even with two I would not heat much hot water, except on a very windy day.
Ample for lighting etc.


Thanks adam2 for the usual informative message. Your first example is more than sufficient - two tanks of hot water is a lot.

So do you reckon it's not worth it - or does there come a point where it is worth it (ie, a certain size turbine)?
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adam2
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PostPosted: Mon Jun 18, 2012 1:42 pm    Post subject: Reply with quote

The "two tanks a day" that I quoted is the absolute maximum under conditions of continuall high wind, and no electricity used for anything else.
Under average winter conditions you would be lucky to get part of a tank of slightly warmed water every few days.

Still worth considering, but more as a way of safely disposing of surplus electricity, than as a source of significant hot water.

Electric water heating from a wind turbine can be very worthwhile, but to reliably produce significant volumes of properly hot water you will need something larger than a Rutland W/T.
Excellent though these machines are, they are primarily intended for lighting etc.

A reasonable amount of hot water can be produced with an average input of 500 watts, which is 12KWH a day.
This however implies a wind turbine of several KW capacity, perhaps as much as 10KW.

A very large hot water tank would be needed, several hundred liters.
This should have 2 elements, one near the top and one near the bottom.
When limited energy is available, the top element would heat the top of the tank to say 60 degrees, thereby ensuring some properly hot water.
Once the top of the tank is hot, then the bottom element would heat the whole tank, potentialy to nearly boiling point.
A mixing valve on the outlet is vital to avoid scalding.
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Last edited by adam2 on Mon Oct 08, 2012 12:27 am; edited 1 time in total
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emordnilap



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PostPosted: Mon Jun 18, 2012 1:57 pm    Post subject: Reply with quote

Thanks again adam2. I'm slowly learning but, as you can gather, I'm not a natural at this stuff.

Your post implies that it's not worth it using a small wind turbine; but then, you say a large turbine might boil the water! I want something in between, naturally.

I'm trying to determine at what size turbine (and matching immersion) would be optimum for some hot water, particularly as a solar hot water panel is already in place. A pre-heating where the immersion might only be needed as a top-up could be worthwhile.

I am also trying to work out how to match immersion to turbine, should we decide to go ahead.
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adam2
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PostPosted: Mon Jun 18, 2012 2:29 pm    Post subject: Reply with quote

A wind turbine large enough to heat a useful volume of hot water under average conditions, is likely to potentialy boil the water under conditions of sustained high wind or low hot water demand.

This needs to be allowed for, either by designing the hot water system to boil safely, or by having some other dump load, or running hot water to waste when it would otherwise reach a dangerous temperature.
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Last edited by adam2 on Mon Jun 18, 2012 4:20 pm; edited 1 time in total
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emordnilap



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PostPosted: Mon Jun 18, 2012 2:31 pm    Post subject: Reply with quote

adam2 wrote:
A wind turbine large enough to heat a useful volume of hot water under average conditions, is likely to potentialy boil the water under conditions of sustained high wind or low hot water demand.


Thanks.
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emordnilap



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Location: Houǝsʇlʎ' ᴉʇ,s ɹǝɐllʎ uoʇ ʍoɹʇɥ ʇɥǝ ǝɟɟoɹʇ' pou,ʇ ǝʌǝu qoʇɥǝɹ˙

PostPosted: Tue Jun 19, 2012 11:43 am    Post subject: Reply with quote

adam2, what do make of this article:

http://www.reuk.co.uk/Wind-Turbine-Water-Heating.htm

The sub-heading, "Heat water directly using a wind turbine generator (with or without a battery bank)" gives the impression that it's worth doing not just as a dump load. Indeed, there are two further divisions: "Diversion Load Water Heating" which is the dump load scenario and "Direct Wind Turbine Water Heating" which is using a turbine for the sole purpose of heating water, talking about matching the turbine closely to the needs of the heater. It's this section that intrigues me most.

This is a typical heater: http://www.ebay.co.uk/itm/ws/eBayISAPI.dll?ViewItem&item=180296507747&clk_rvr_id=355421416074#ht_4551wt_1206
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emordnilap



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Location: Houǝsʇlʎ' ᴉʇ,s ɹǝɐllʎ uoʇ ʍoɹʇɥ ʇɥǝ ǝɟɟoɹʇ' pou,ʇ ǝʌǝu qoʇɥǝɹ˙

PostPosted: Sun Oct 07, 2012 9:33 pm    Post subject: Reply with quote

There's a place not far from me that has a low-wattage immersion powered by a wind turbine; might have to have an excursion.

Adam2 (or anyone knowledgeable of course), what do you think:
http://www.glynns.ie/index.php?page=wind-turbines
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