Timer on hot water cylinder?

[Smifffy]

I don't believe it would use considerably more power over a 24 hour period. In fact I believe the opposite, it costs more to try and keep your water heated to a set temperature, than it does to allow it to cool and just re-heat it once.

It takes 4.2 Joules of energy to raise the temperature of a gram (or mL) of water (liquid) 1 degree C.

Ye cannae change the laws of fuzzics Jim.

As you say, you do have a (limited) choice of rates you pay for your Joules, and control over how many mLs you want to heat.

[bogan]

Remind me never to shake your hand...

At that temperature your HWC is a perfect breeding ground for bacteria - even 55 deg is not entirely safe. From a health point of view, it's better to store water at 65-70 deg, and use a tempering valve to bring it down to a safe temperature at the tap.

+1 And considering the main use of having hot water at all is for hygeine, you may as well do a proper job of it.

I don't believe it would use considerably more power over a 24 hour period. In fact I believe the opposite, it costs more to try and keep your water heated to a set temperature, than it does to allow it to cool and just re-heat it once.

If it costs significantly more to hold the water at temperature, check and improve your insulation. Also, if you have a decent temperature ripple, and are running it to a low temperature, you might get bacteria buildup during the day.

One thing you could look into for power saving (probly going off on a bit of a tangent here), put a heat exchanger in your shower, so the cold water going in is heated by the warm water going down the drain. Or solar etc, better to lower your total usage than just get into a lower price bracket.

[Smifffy]

A whole swag of polyethylene farm piping on your roof would heat a HW cyclinder on sunny days

You would need to set it up so that it doesn't:

• Radiate heat to atmosphere on cold days
• Freeze

[scissorhands]

Remind me never to shake your hand...

At that temperature your HWC is a perfect breeding ground for bacteria - even 55 deg is not entirely safe. From a health point of view, it's better to store water at 65-70 deg, and use a tempering valve to bring it down to a safe temperature at the tap.

Mines instant gas so no hygiene issues I think

Its digital temp adjust only goes from 37-50 degrees C

p.dath if your intent on switching your HW circuit via timer, an inspector or regulating authority enquiry may be prudent as electricians like myself have not normally come across this, a manual on off has the advantage of human modulation in regard to load/guests, but the timer is the no brainer esp if manual switch access is poor.

[Virago]

Mines instant gas so no hygiene issues I think

It's a major hygiene issue for someone with a HWC who may follow your advice. At 45 deg the cylinder would basically be a bacterial incubator.

But yeah, instant (non-stored) low temp is fine.

[bogan]

You would need to set it up so that it doesn't:

• Radiate heat to atmosphere on cold days
• Freeze

Temperature controlled valve or two would sort it, only let water through if it's hotter than the alternative.

[Hellzie]

Modify usage and turn down temp, I'm at 45 degrees C

Careful with that, if you turn it down too much you increase the risk of evil legionella bacteria growing in your cylinder and possibly getting pneumonia by breathing in the little critters. There are different recommended temperatures, the majority recommend a temperature of at least 49 degrees C.

[Smifffy]

One thing you could look into for power saving (probly going off on a bit of a tangent here), put a heat exchanger in your shower, so the cold water going in is heated by the warm water going down the drain. Or solar etc, better to lower your total usage than just get into a lower price bracket.

I think the HX concept would struggle, at the flow rate to fill the cylinder, the exchange surfaces would need to be very large indeed, particularly with respect to the limited duration of operation of the warm side.

Keeping the surface clean of soap scum, hair and other detritus would also be difficult I'd imagine.

Without running the calcs, I'd hazard a guess that cutting one's shower shorter by a minute would save more than an HX, and of course the shorter the shower, the less effective the HX becomes.

Temperature controlled valve or two would sort it, only let water through if it's hotter than the alternative.

Yes, I'm not saying it can't be done, just that there's a little more involved than simply hooking up a length of poly pipe. Depending on storage I'd say it's a good option for the incoming water, if the cylinder is used during the day a lot - better than a heat exchanger on the shower drain.

[bogan]

I think the HX concept would struggle, at the flow rate to fill the cylinder, the exchange surfaces would need to be very large indeed, particularly with respect to the limited duration of operation of the warm side.

Keeping the surface clean of soap scum, hair and other detritus would also be difficult I'd imagine.

Without running the calcs, I'd hazard a guess that cutting one's shower shorter by a minute would save more than an HX, and of course the shorter the shower, the less effective the HX becomes.



Yes, I'm not saying it can't be done, just that there's a little more involved than simply hooking up a length of poly pipe. Depending on storage I'd say it's a good option for the incoming water, if the cylinder is used during the day a lot - better than a heat exchanger on the shower drain.

Indeed, and the bigger the surface the longer it wuld take to heat, so a fair few temperature adjustements during the shower may be required. Still, essentially free energy once impolemented though.

I guess living in palmy, you get the idea that sun isn't common enough to bother harnessing, wind on the other hand....

Or another idea, just make a water brake dyno, and feed it into a well insulated storage tank. Hell, if I put the bros on there you could have a steam supply for days

[NighthawkNZ:Me]

Make sure you have good insulation on the cylinder, as it could cool quiker than expected and to heat it again evey day could cost more...

Remember when the cylinder is up to temp the element only has to keep it on the simmer at that temp, if it cools it has to actually heat it for longer periods of time and may cost more.

When they had the power shortages in the 90's and the power company's in their wisdom decided to save power by turning off the cylinders... peoples power bills went up, and it actually used more power...

I would also look into solar heating, gas, wetback...

Example our coal range is a form of warmth, hot water on wet back (and boiling water for coffee) as well as cooking... (not saying install a coal range a modern one is around 10,000g) over all saves money on power bill but some of the money is spent on coal... But there are other options that can lower your power bill

I am not sure on the instant gas thingy neighbor has it in conjunction with Solar... but don't know much about it.

[p.dath]

P.Dath mentioned a legal minimum, I thought it was 55^C ? 45 is a tad risky no?

Yes. At that temperature legionella can grow - and that can kill you!

It takes 4.2 Joules of energy to raise the temperature of a gram (or mL) of water (liquid) 1 degree C.
...
As you say, you do have a (limited) choice of rates you pay for your Joules, and control over how many mLs you want to heat.

Ahh yes, that is to raise the temperature, but that doesn't take into account the constant heat loss, and constant heating required to maintain the temperature in the tank.

Mines instant gas so no hygiene issues I think

Its digital temp adjust only goes from 37-50 degrees C

p.dath if your intent on switching your HW circuit via timer, an inspector or regulating authority enquiry may be prudent as electricians like myself have not normally come across this, a manual on off has the advantage of human modulation in regard to load/guests, but the timer is the no brainer esp if manual switch access is poor.

I think you might be right. I might ring my power company and ask them.

I have a manual switch - but I don't want to wait up till 11pm every night to turn it off.

[MisterD]

It's a major hygiene issue for someone with a HWC who may follow your advice. At 45 deg the cylinder would basically be a bacterial incubator.

Mains supplied water will be chlorinated though won't it?

[p.dath]

Mains supplied water will be chlorinated though won't it?

Heat destroys chlorine. Warm water grows bacteria faster than cool water.

[p.dath]

I am not sure on the instant gas thingy neighbor has it in conjunction with Solar... but don't know much about it.

We have a lot of people in the household. I think instant hot water with gas would suit small users better.

[pete376403]

Have you investigated the heat-pump type HWCs? I'm guessing that they use the heat pump to initially warm the water and then an element to raise the water temp to its final setting.