Switching geyser off?

Wiring, circuits, batteries etc.

Re: Switching geyser off?

Postby Greystoke on Tue Jun 02, 2009 9:18 am

windgat wrote:USB logger - I imagine there are devices out there which record various inputs (like amps, volts etc) which you can later connect to a USB port and download all the data for analysis on a PC.
I "Googled" USB-loggers. They're a bit limited, and the really useful ones are far too expensive (±$500 :!: )

windgat wrote:Probe sounds a hassle - and it needs to be deep in the water to get the core temp. As you say, maybe its less important than the power.
Agree. I've decided to buy a new kWhr-meter and install it at the geyser permanently.

windgat wrote: We could test a thermostat to find the hysteresis, and then we would know the on and off temperature points, so the current would tell us the temperature at the thermostat on and off points. That would be enough to get the model perfectly tuned.
Correct. Perhaps we can also ask the manufacturers for info.

windgat wrote:PS: This forum went down yesterday for about 12 hours - did you notice?
Yeah :impatient:
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Re: Switching geyser off?

Postby windgat on Fri Jun 05, 2009 11:19 am

One thing is clear - to minimise energy use the geyser should be at its coldest overnight. That means the best would be to switch off just BEFORE the evening use of hot water, and to switch on in the morning long enough before the first need for hot water. That means the thermal gradient is minimised during the cooler night temperatures.
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Re: Switching geyser off?

Postby Greystoke on Fri Jun 19, 2009 7:16 am

I've bought a kWhr meter (Only R99 :!: and made in Image)
The boys will help me install it this week-end.

I'l start recording on Monday (@ 6AM and 6PM)
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Re: Switching geyser off?

Postby Derek on Fri Jun 19, 2009 11:01 am

I have a solar panel on my roof. I switch the geyser on for 1 hour in the morning from 5am to 6 am. In winter from 4-30am to 6am and again for half an hour at 7pm. The geyser and pipes are all very well insulated. This works like a charm. :D
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Re: Switching geyser off?

Postby Greystoke on Fri Jun 19, 2009 11:08 am

I can't use solar panels, because my geysers(2off) are all installed at window level. To use solar panels I'd be needing hot water pumps at frightfull prices. Instead I'm planning on using a windcharger (still in design) to power the geysers. But after that I'm planning on doing precisely the same thing as you do. :D
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Re: Switching geyser off?

Postby Derek on Fri Jun 19, 2009 11:19 am

I also found the pump prices and solar panel to supply them very expensive. What I use is a normal cheapie pump which I run for 10 seconds every 3 minutes only when the solar panel temp is higher than 45 degrees c. I used a 555 timer circuit and two relays and it works like a charm..
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Re: Switching geyser off?

Postby windgat on Fri Jun 19, 2009 11:31 am

Sounds good Derek. It would be great to hear what pump you use, how you connected it, and where they can be bought...

I got a price of R2600 for a pump with standard brass fittings. :shock:
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Re: Switching geyser off?

Postby Derek on Fri Jun 19, 2009 11:58 am

The pump is a Pedrollo. You can get them at any farmers co-op. It is similar to a swimming pool pump only much smaller. They say in the specs that it cant handle above about 70 degrees, but mine seems to handle it ok. I want to build a big windcharger of about 3-5kw. Any ideas where I can get plans from. Wouldnt mid some reasonably priced solar voltaic panels either. The chinese ones dont live up to the spec's they advertise.
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Re: Switching geyser off?

Postby Greystoke on Fri Jun 19, 2009 12:31 pm

Derek wrote:I also found the pump prices and solar panel to supply them very expensive. What I use is a normal cheapie pump which I run for 10 seconds every 3 minutes only when the solar panel temp is higher than 45 degrees c. I used a 555 timer circuit and two relays and it works like a charm..
What an idea :!: Never ever thought about that. Image
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Re: Switching geyser off?

Postby windgat on Fri Jun 19, 2009 1:40 pm

Thanks Derek. Does that run of mains? If so, do they have a 24V version?
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Re: Switching geyser off?

Postby Greystoke on Fri Jun 19, 2009 5:10 pm

A 555 is an integrated circuit. I think its max supply voltage is ±15V (not too sure!). You need an extra output transistor to operate a 12V relay. The timing is done by an external trigger voltage, which then engages a time-delay operation under the effect of an external resistor-capacitor circuit.
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Re: Switching geyser off?

Postby windgat on Fri Jun 19, 2009 8:02 pm

I was asking about the pump!!
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Re: Switching geyser off?

Postby Greystoke on Sat Jun 20, 2009 5:12 am

Huh :?:
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Re: Switching geyser off?

Postby windgat on Sat Jun 20, 2009 8:00 am

Derek wrote:The pump is a Pedrollo. You can get them at any farmers co-op...

I was asking if this is an AC pump. I would want to run it off my 24V wind charged system, of course. Or alternatively directly off a small solar panel - that way it only pumps when the sun shines, so its like passive control - no need of a control circuit.
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Re: Switching geyser off?

Postby Greystoke on Wed Jul 15, 2009 11:56 am

OK,
I’ve checked the kWhr readings of my geyser for about 4 weeks, trying to interpret the results. It wasn’t as easy as I thought it would be.
The thermal resistance was by far the most difficult to nail down. The trouble was that when the geyser is on standby (during the night) it would come on only once during the night, giving me the problem of determining the time interval over which to average the consumed power (because the thermal conductivity equals the average power required to maintain the temperature of the geyser). I overcame this problem by leaving the geyser on standby for an entire weekend while we were away. This way I got a far more accurate number, ie:
Best estimate = ±0.46 °C/Watt

The water usage was mainly derived from the power consumption, which has its own little problem, because some of the power to heat the cold intake water also has be to used to compensate the natural cooling. I now know that this factor equates to a loss of 125 Watt to the geyser heater element. So instead of 2kWatt, it must be derated to 1.875kWatt

BTW: The average power consumption of the geyser over a period of about 4 weeks was equivalent to an element of 315Watt burning 24/7!


Image
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Re: Switching geyser off?

Postby windgat on Thu Jul 16, 2009 4:32 pm

Great! Did you try plugging any of that into the spreadsheet I posted?

Idea is that one could then model the savings/extras that would result from a timer switch. First step is to see if the model matches the existing behavior.

The time slice could be smaller - ideally one needs to write software to work with a tiny time slice for greater accuracy. The spreadsheet can also use a smaller timeslice, although it becomes a bit cumbersome.
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Re: Switching geyser off?

Postby Greystoke on Thu Jul 16, 2009 4:55 pm

windgat wrote:Great! Did you try plugging any of that into the spreadsheet I posted?

Idea is that one could then model the savings/extras that would result from a timer switch. First step is to see if the model matches the existing behavior.
No, I didn't. I'm gonna leave that to you for the time being. Meanwhile, I'm carrying on with more measurements. (I'm introducing a timer !)

windgat wrote:The time slice could be smaller - ideally one needs to write software to work with a tiny time slice for greater accuracy. The spreadsheet can also use a smaller timeslice, although it becomes a bit cumbersome.
No need to reduce the timeslice. I have an algorithm that will improve the accuracy without reducing the time increment.


BTW: My geyser uses 315 Watt 24/7, which means that if I could design a wind turbine generator that produces ±300 Watt on average in PE winds, it would power a 100L geyser !
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Re: Switching geyser off?

Postby windgat on Thu Jul 16, 2009 9:25 pm

Greystoke wrote:
windgat wrote:The time slice could be smaller - ideally one needs to write software to work with a tiny time slice for greater accuracy. The spreadsheet can also use a smaller timeslice, although it becomes a bit cumbersome.
No need to reduce the timeslice. I have an algorithm that will improve the accuracy without reducing the time increment.

Aha, an improvement on the linear formula? I'd be interested. Problem with largish time slices is that modelled geyser can only switch off or on at the end of a time slice.

Greystoke wrote:BTW: My geyser uses 315 Watt 24/7, which means that if I could design a wind turbine generator that produces ±300 Watt on average in PE winds, it would power a 100L geyser !

That is a thought! You should be able to get around that with 1m blades. Whats yr average wind speed?
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Re: Switching geyser off?

Postby Greystoke on Fri Jul 17, 2009 6:18 am

windgat wrote:Aha, an improvement on the linear formula? I'd be interested. Problem with largish time slices is that modelled geyser can only switch off or on at the end of a time slice.
Sorry, its an improvement on the accuracy of the fit. The timeslice stays the same (or can be enlarged for the same accuracy).
I misunderstood.


windgat wrote:That is a thought! You should be able to get around that with 1m blades. Whats yr average wind speed?
I think we went over that already :D The average of the winspeed-cubed is 4.3m/s. So, to get 300Watt (311 to be exact) you need 2m blades ! Image
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Re: Switching geyser off?

Postby windgat on Fri Jul 17, 2009 8:13 am

Hmmm, thats not so rosy then. Another factor is speed of heating after using hot water. A 3kW element will heat up the water 10x faster than a 300W generator. So you could save the 'maintaining' spikes of element usage, but not really the longer element use (to warm up a batch of cold water). That means not much power saved....

So, to salvage something positive :yay: ...

A much smaller turbine would be able to provide 'maintaining' power, which would keep the geyser hot indefinitely as long as no hot water is used.
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Re: Switching geyser off?

Postby Greystoke on Fri Jul 17, 2009 8:28 am

Great minds think alike :lmao:

I also came to that conclusion. For that to be successful, you need about 100 - 150 Watt (that still needs 1.4m blades !). However, . . .
If you mount the turbine above a sloping roof you gain a ±200% improvement due to the concentration of the airflow. That means that I can use 1m blades :D
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Re: Switching geyser off?

Postby windgat on Fri Jul 17, 2009 4:37 pm

Great! So you started building yet?
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Re: Switching geyser off?

Postby Greystoke on Fri Jul 17, 2009 5:39 pm

Nahh !
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Re: Switching geyser off?

Postby Greystoke on Sat Jul 18, 2009 8:31 am

I have a few things to sort out first before I can start on the design of this turbine.
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Re: Switching geyser off?

Postby windgat on Sun Jul 19, 2009 10:20 pm

:lol: Where do you find all these icons!?

Well perhaps someone coming on the course next week will make one and want to sell it... that should allow you plenty of time in that beach chair!
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