Digital timer for hot water

Forums › Home Workshop DIY › Digital timer for hot water - which one?

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#1455982 23-Dec-2015 13:47

timmmay:
DarthKermit: Take a step back for a moment. Do you have a modern, insulated cylinder? Or if not, one that's got insulation wrap around it?

I suggest you read the whole thread, this has been covered. I'm not an idiot.

Never said you were dude. I missed that post about your new cylinder, my bad.

DarthKermit

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#1456007 23-Dec-2015 14:01

How big is your cylinder?

timmmay

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#1456010 23-Dec-2015 14:16

Not 100% sure. It's as tall as me and about as wide. It's up in the ceiling cavity so bit difficult to check. Rheem mains pressure, from memory. It's not the smallest available, it's not the largest. Why does it make a difference? 3000W element.

DarthKermit

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#1456015 23-Dec-2015 14:30

The bigger the cylinder, the more HW it can store (obviously!

). Also, the mass of said water should help it stay warmer for longer, the greater that mass is. I'm sure there are probably all sorts of formulas for calculating thermal mass if you really wanna get geeky with it.

Couple of other Qs:
Do you have a bath tub? And if so, do you run it very often?
Do you often have extra people staying in the house, thus increasing the HW usage?

timmmay

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#1456023 23-Dec-2015 14:38

Thanks for the thoughts, but I'm not really needing advice on whether it's a good idea - I know from my experimentation that the cylinder stores enough hot water for 24 - 36 hours. Using the bath will reduce that, but that's always in the evening so it can heat overnight.

FYI cylinder is something like this, I checked but it's fully wrapped and I can't see. It's around 5'8" high and a mans shoulder width wide, if you want precise measurements! It's pretty hot up there in the ceiling cavity, which probably reduces heating requirements in summer and increases them a bit in winter.

gzt

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#1456025 23-Dec-2015 14:44

Most if not all these timer switches have a 'manual' on button you can press for additional use , guests, etc. It is not really a problem in practice.

timmmay

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#1456050 23-Dec-2015 15:21

gzt: Most if not all these timer switches have a 'manual' on button you can press for additional use , guests, etc. It is not really a problem in practice.

In the one (which is pretty good quality) I have it's well into the sub menus.

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gzt

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#1456062 23-Dec-2015 15:35

That would be a pita. The cheap one you linked has a 'manual' press.

timmmay

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#1456090 23-Dec-2015 15:53

It's pretty rare we'd need to do that. If we had people staying I'd just have it on all the time, wouldn't matter for shorter periods.

gzt

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#1456113 23-Dec-2015 16:17

Yeah. Simple enough for a sparky to install an override if required somewhere convenient.

DarthKermit

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#1456145 23-Dec-2015 16:48

A manual over ride can be as simple as using a two way switch:
Wire the phase output of the timer to terminal 2.
Wire the phase input that goes to the timer to terminal 1.
Wire the load (the HW cylinder) to the common terminal.

That way the timer is always supplied power, but you can supply power to the cylinder at any time by simply flicking that switch over.

(Of course, get the sparky to do this work for you.)

timmmay

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#1456153 23-Dec-2015 17:22

Yeah not a bad idea thanks.

bfginger

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#1456345 23-Dec-2015 23:22

If a cylinder is on a timer it needs to be turned on long enough to make sure it goes over 60 degrees or else you're risking legionnaire's disease.

gzt

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#1456359 24-Dec-2015 00:02

Once every 72 hours is the standard I believe. The time on period will be more than long enough for that to occur. Temperature reached is a function of he thermostat not the timer.

timmmay

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#1456381 24-Dec-2015 07:01

Yep I know. Standards are here. Once a day or once a week, depending on how/where you measure the temperature. Remember this will be heated to 60 degrees for 5 hours a day, probably from 2am to 7am, so the risk is zero.

3.5 Protection from Legionella bacteria
3.5.1 To prevent the growth of Legionella bacteria, solar water heaters must either: a) have a continuously energised heating element fitted within 55% of the bottom of the water tank (by volume) and a thermostat set to 60°C or higher, or b) be controlled so that the water above the element is heated to 60°C once a day, and the element is in the bottom 20% of the water tank (by volume) and no more than 150 mm from the bottom of the tank, or c) be controlled so that all of the stored water is heated to 60°C or higher, once a week for not less than 1 hour. The temperature must be measured by a probe in the bottom 20% of the water tank (by volume) and no more than 150 mm from the bottom of the water tank. For open loop systems the stored water includes the water in the solar collector and water must be circulated through the collector during the heating period.
3.5.2 Where the solar water heater stores potable water and is used as a pre-heater for an instantaneous water heater, either: a) the hot water storage tank connected to the solar collector must be fitted with supplementary heating and a controller operating to meet the conditions outlined in Paragraph 3.5.1, or b) the instantaneous water heater must heat all water passing through it to not less than 70°C.

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