Digital timer for hot water

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timmmay

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#189298 23-Dec-2015 07:19

I'm looking for a digital timer for my hot water (3000W / 13A element), as with Flick power is cheaper overnight. I already have a Theben TR 608 Top2 for my underfloor heating timer (data sheet here), from memory it was around $100. Apparently saving a guy $5 per week / $250 / year.

I've seen a reference to someone using something like this, which is $30. Any reason not to use one of those?

Obviously I'm going to check with my regular electrician (my neighbor) before I buy anything, interested in thoughts first, especially from people who are qualified in this area.

Notes: new cylinder, with a cylinder wrap (probably unnecessary, had it for the old one), well insulated older house, two people living here, with the water heater turned off the hot water would last us around 36 hours regular use.

Update: you can see my estimated savings from this on this post.

UPDATE: according to the Ministry of Health residential hot water must be kept at 60 degrees or above at all times to prevent the growth of Legionella Bacteria. This bacteria can prove fatal. My current thought is heating water only at night could increase the changes of catching the bacteria. Instead I may look at turning off the hot water cylinder during periods of typical high load (7-9am and 5-8pm), but will likely leave it on other times. That's a shame, as I think it was contributing to decent power and money savings.

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#1455768 23-Dec-2015 07:25

Are you sure your hot water isn't already on ripple control?

timmmay

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#1455773 23-Dec-2015 07:36

lxsw20: Are you sure your hot water isn't already on ripple control?

Yes we have a new ripple control receiver beside the new digital meter. My understanding is this turns the hot water off in times of high usage, but that's for the benefit of the grid/supplier not for me. It could be that power is very expensive for some reason but there's plenty of capacity so ripple control leaves it turned on.

I want the hot water on only between say 2am and 6am, in addition to ripple control, to reduce costs. The timer will sit behind ripple control.

mdooher

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#1455818 23-Dec-2015 09:23

This is not going to work as well as you think. For example if your cylinder was 100% efficient (it isn't) the timer would have zero effect.

Assuming you have a new cylinder (and this is a far better way to increase efficiency) it probably uses about 1.6kwh per 24 hours just to keep the water up to temp.

If you turn it off it will of course slowly cool down but will need warming up again before use. (I' cant be bothered with the calculations...It's the last day of work!) but at 26 cents per kilowatt hour the losses equate to 42 cents per day (just to keep it warm) so you might save $150 a year ... if you didn't have to heat it up again, but you do have to heat it up again don't you?

You will save almost nothing using this technique, add to that the cost of the timer and the Electrician to wire it in ...

Matthew

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#1455821 23-Dec-2015 09:28

My parents are looking for timer for their hot water cylinder.
They have solar panels, but not batteries (feeds back to grid).

It makes sense for them to be heating hot water during daylight, and turn it off overnight. I will look into the timers in the OP.

timmmay

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#1455822 23-Dec-2015 09:28

The cylinder is brand new, which means it's well insulated, and it also has an extra wrap on it just because I had one lying around. I've kept it turned off for 3246 hours, while it was in use (4 showers a day), and the water was still very warm at the end of that. Sure there will be losses, but there's more than enough water to last ages for us, and if the losses are 42c/day at regular rates they're more like 15c/day at off peak rates. Plus there is the direct experience of someone already doing it, and Flick have said they're planning on introducing it as a service for all their customers at some point.

Given peak rate electricity can be around 26c/hr or sometimes higher during peak times with Flick, and off peak electricity can be 10c/hr, I believe there can be very real savings.

I'm doing it, the only question is what timer to use.

mdooher

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#1455823 23-Dec-2015 09:30

timmmay: The cylinder is brand new, which means it's well insulated, and it also has an extra wrap on it just because I had one lying around. I've kept it turned off for 3246 hours, while it was in use (4 showers a day), and the water was still very warm at the end of that. Sure there will be losses, but there's more than enough water to last ages for us, and if the losses are 42c/day at regular rates they're more like 15c/day at off peak rates. Plus there is the direct experience of someone already doing it, and Flick have said they're planning on introducing it as a service for all their customers at some point.

Given peak rate electricity can be around 26c/hr or sometimes higher during peak times with Flick, and off peak electricity can be 10c/hr, I believe there can be very real savings.

I'm doing it, the only question is what timer to use.

If you really want to use cheap night rate power get Flick to setup your ripple control/second meter/ smart meter etc to do that.

Matthew

timmmay

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#1455831 23-Dec-2015 09:44

mdooher: If you really want to use cheap night rate power get Flick to setup your ripple control/second meter/ smart meter etc to do that.

I just called Flick - they can't do that. Ripple control is under the control of lines companies, Flick can't even find out when / under what conditions they do things. So it's timer or nothing. Flick are still doing research into this, apparently there is a risk (probably small) that the lines company turn off water heating overnight with ripple control and people end up with no hot water. A company may not want to take that risk on a wide scale, but I can take that risk for my house.

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mdooher

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#1455838 23-Dec-2015 09:58

timmmay:
mdooher: If you really want to use cheap night rate power get Flick to setup your ripple control/second meter/ smart meter etc to do that.

I just called Flick - they can't do that. Ripple control is under the control of lines companies, Flick can't even find out when / under what conditions they do things. So it's timer or nothing. Flick are still doing research into this, apparently there is a risk (probably small) that the lines company turn off water heating overnight with ripple control and people end up with no hot water. A company may not want to take that risk on a wide scale, but I can take that risk for my house.

Ok, from what I gather people that put timers in find that they tend to use less hot water, I suppose the "worry" about it going cold changes their habits. Might increase the savings for you too.

That timer will work but it seems cheap to me. Personally if I was going to put one in I would pay more for a nice Schneider one (maybe I'm being snobby but I prefer well known brands in my switchboard) or you could add a quality contactor to the output.

Don't get me wrong if the one you are looking at has the appropriate documentation it should be fine ....but that's what F+P said before their Chinese made washing machines started burning down houses.

Matthew

timmmay

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#1455840 23-Dec-2015 10:02

True. I'll probably just use one like I already have, or whatever my electrician recommends. I have to have the whole switchboard rewired some time before long anyway, it's just old.

mdooher

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#1455841 23-Dec-2015 10:05

timmmay: I have to have the whole switchboard rewired some time before long anyway, it's just old.

Ooohh...Start saving now...It pretty much means having your house rewired too

Matthew

timmmay

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#1455846 23-Dec-2015 10:10

mdooher:
timmmay: I have to have the whole switchboard rewired some time before long anyway, it's just old.

Ooohh...Start saving now...It pretty much means having your house rewired too

The house has been rewired, it's just the old switchboard. The neighbor said $1000 - $2000 depending on choices made, equipment used, etc.