What to do with Hot Water?

[The Rok]

Right, but most won't have 415V.

I guess I just don't think about these things. We have gas but last time I went for a month and left on the hot water, 2 fridges, some lights on auto.

Had the leave the fridges on, couldn't come back from a months holidays to a fridge full of warn Corona! I'd be suicidal!

 

[medhead]

Haha, looks like it's solar ftw.

What do i do for the 4 months in melbourne there's no sunshine.....

The systems are electric boosted. Manual switch in your meter box.
. Had this in Cairns in the 1980s, had to use it about 3 times.

 

[Austman]

Can't see many houses having 415V though.

More than you might think. Many people wouldn't even know that they had it. I didn't know until today.

I knew my ACs were 240V and thought the water heater was too. But nope - the heater is 415V, 3-phase. There are 12 of these in my apartment building, all installed nearly 9 years ago. A large AC is another reason why 415V might be already connected.

 

[The Rok]

More than you might think. Many people wouldn't even know that they had it. I didn't know until today.

I knew my ACs were 240V and thought the water heater was too. But nope - the heater is 415V, 3-phase. There are 12 of these in my apartment building, all installed nearly 9 years ago. A large AC is another reason why 415V might be already connected.

Ah, apartment building. That makes sense as lifts and central air con systems are usually 3 phase. I was thinking more of residential houses in the suburbs. Not many will have 3 phase power.

 

[UP4014]

Ah, apartment building. That makes sense as lifts and central air con systems are usually 3 phase. I was thinking more of residential houses in the suburbs. Not many will have 3 phase power.

You're right not many, the ones that have it also have the advantage that they have two circuits from the street so when a tree branch takes down a single wire two streets away they still have half their house working. Yes I have 3 phase originally for the three hot water systems in the house.

matt

 

[docjames]

OK, I dont have 415V.


@ munnitalP - Three weeks? Wow, that's quite a change. You actually looked at the numbers?

 

[oz_mark]

You're right not many, the ones that have it also have the advantage that they have two circuits from the street so when a tree branch takes down a single wire two streets away they still have half their house working. Yes I have 3 phase originally for the three hot water systems in the house.

Some years ago, I lived on a street where one of the phases stopped working one night. I lost power to half the house, my neighbour lost lights but could watch TV.....

(Back when Perth had 440V power!)

 

[munitalP]

OK, I dont have 415V.


@ munnitalP - Three weeks? Wow, that's quite a change. You actually looked at the numbers?

I crunched the numbers before Xmas regarding my service in Sydney (house in Melbourne is solar/gas so never worried) as we were away getting toward 3 weeks. Rough & ready calcs based on my personal circumstance (off peak demand supply) made it cheaper to leave on rather than reheat on return by around 45%

My service is quite new and very well lagged (insulated) as the main bathrooms are upstairs, but I also have a shower at the far end of the house. I have hot water within 10 seconds at any time of the year at any point in the house.

If you get your cylinder volume, your power cost, element size, I'll crunch the numbers for you. Will need Resistance / Watts from element

 

[docjames]

Ok, so, read an ECG, X-ray, ventilator, no worries. Understand hot water - problematic.

These photos is what I can see on the side that might have the info you need. It's a rheem - looks average size, fuse box says "off peak hot water".....

The off peak price here is around 12c/kwh + gst (so make that 13.2c/kwh).

Thanks!!

 

[Sprucegoose]

Sounds like false economy. The greenies propagate this sort of rubbish.

 

[docjames]

I'm mostly interested in cost (and its an interesting theoretical exercise).

The "climate change" impact per year on a global scale is negligible. I don't want this to be a political thread - let's leave it at that.

 

[irv]

I live on the mid north coast of NSW, we have solar HW, great aspect, good location but in mid winter Solar does not live up to expectations so in Melbourne in winter. However dependent on your location great in summer with zero power used in off peak back up. Alternative head to the northern hemisphere in winter (if you can)

Haha, looks like it's solar ftw.

What do i do for the 4 months in melbourne there's no sunshine.....

 

[AVC]

400 litre is a reasonable size. It's obviously off peak, as it has two elements (upper and lower). One iis off peak and one is the booster element (if you run out during peak period).

I personally would leave it on. The price of off peak is hell cheap.

To heat an average HWS from cold, your looking at least an hour to two hours, depending on the thermostat setting and ambient temps. Multiply your tariff at the time x 4.8 (kW) x 1.5 (hrs). to get the price to heat your water tank.

Now, being an off peak unit, you would have to switch on the booster element to get hot water once you returned from a trip, but the booster (top element) only heats part of the tank, so you would not have a full tank of hot until after the next off peak period.

 

[chrisb]

My gas one has a 'vacation' setting which would seem to be a logical choice. It's basically as cold as it goes while still being on.

 

[SFSC]

Ours is off peak heat pump only. We turn ours off if > 1 day.

Our thinking is this: Given any amount of insulation, heat energy loss to surroundings depends on the temperature difference (Δt) between the water and the surroundings. As Δt falls because the tank is not being reheated, the rate of energy loss reduces until eventually Δt and thus the heat loss is zero. No matter when it is turned back on the amount of energy used to reheat it will always be less than if it was left on.

 

[docjames]

My gas one has a 'vacation' setting which would seem to be a logical choice. It's basically as cold as it goes while still being on.

Except there's no gas main, and no vacation setting on the service....

 

[AVC]

I personally leave mine on. As I want hot water when I get home. That and I am not going to rummage about in the bushes to get our (gas) HWS lit up.

A few months ago, our hot water ran out. Strangely, on the very same day that there was a plumbing fridge magnet left in our mail box. I go to investigate. Ends up the pilot light went out, so I relit it. No problem. As it turns out they has to turn off the gas to the estate to do an emergency repair. I wonder how many people called a plumber to get their pilot light lit.

 

[Pushka]

If you've sorted the hot water issue, do you also clean out and turn off your fridge?

 

[j.espoir]

In my experience if turning the hot water tank is that, if 30 day away, yes. But the problem is, if the hot water tank got turn off in a long period of time, it might have some strange smell of the water! Eg, dead water smell from the swam.
Solar hot water system could be a option!

 

[docjames]

@ Pushka

No - it has a vacation setting!