Hotwater Insulation for a modern (already insulated) cylinder

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cshaun

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#100070 2-Apr-2012 19:39

Can't really find any information on if it's at all worth while insulating a new "A grade" cylinder. It's cold to the touch... But I'd be willing to make the small investment if it did eventually pay for itself in say 5 years?

Pipes aren't insulated so will definitely be doing that.

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#604136 2-Apr-2012 20:42

Another way of looking at it - at 30c per kWh you would need to save 40 kWh per year to pay for a $60 wrap in five years.

I do not have the MEPS standard for hot water heating - but a BRANZ report online says "A 140 litre A-grade cylinder has a standardised Water Mark heat loss of 2.1kWh/day including 0.7 kWh/day for pipe losses from the cylinder".

The actual loss depends on the environment where the cylinder is installed and the average ambient temperature. The standards will no doubt state what those assumptions are for the validation tests.

If a wrap can reduce the standard 'a grade' 766kWh loss by 5.4% then a $60 wrap will pay for itself in five years at 30c per kWh.

If you are on ripple control a wrap will deliver a marginal benefit of hot water for slightly longer.

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keewee01

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#604137 2-Apr-2012 20:44

We had a new cylinder installed 2 years ago and the plumber insisted that it wasn't worth insulating the cylinder as all newer ones are very well insulated to start with.

That's what he told me at least. :)

springheal

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#604150 2-Apr-2012 21:04

Agree with keewee01.

Also, the fact that the cylinder is cool to touch proves that the internal insulation is more than sufficient.

Cylinder wraps were designed for the earlier cylinders with no built in insulation!

gzt

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#604168 2-Apr-2012 21:28

keewee01: We had a new cylinder installed 2 years ago and the plumber insisted that it wasn't worth insulating the cylinder as all newer ones are very well insulated to start with.That's what he told me at least. :)

This is the standard advice, you will find it everywhere. There are many cases where the standard advice is absolutely not correct.

A few years ago I added a wrap to a cylinder installed in a ceiling space provided with exactly this standard advice and the difference was massive. Hot water lasted a lot longer in the winter.

I'm sure the bill came down as well but that was not the main objective for that one.

springheal: Agree with keewee01. Also, the fact that the cylinder is cool to touch proves that the internal insulation is more than sufficient. Cylinder wraps were designed for the earlier cylinders with no built in insulation!

It proves the temperature is being dissipated over the metal surface of the cylinder faster than it is escaping from inside, but that is all. Depends a lot where you touch it as well. Also depends when it was last in an active cycle and how much it had to heat during that cycle. The top horizontal surface of the cylinder will always be warmer. The lower you get, the cooler it is for most of the day.

Most of the earlier cylinders do have built in insulation, just not very good.

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keewee01

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#604192 2-Apr-2012 22:03

gzt:
keewee01: We had a new cylinder installed 2 years ago and the plumber insisted that it wasn't worth insulating the cylinder as all newer ones are very well insulated to start with.That's what he told me at least. :)

This is the standard advice, you will find it everywhere. There are many cases where the standard advice is absolutely not correct.

A few years ago I added a wrap to a cylinder installed in a ceiling space provided with exactly this standard advice and the difference was massive. Hot water lasted a lot longer in the winter.

I'm sure the bill came down as well but that was not the main objective for that one.

springheal: Agree with keewee01. Also, the fact that the cylinder is cool to touch proves that the internal insulation is more than sufficient. Cylinder wraps were designed for the earlier cylinders with no built in insulation!

It proves the temperature is being dissipated over the metal surface of the cylinder faster than it is escaping from inside, but that is all. Depends a lot where you touch it as well. Also depends when it was last in an active cycle and how much it had to heat during that cycle. The top horizontal surface of the cylinder will always be warmer. The lower you get, the cooler it is for most of the day.

Most of the earlier cylinders do have built in insulation, just not very good.

Yes I agree that that advise would not be correct in every situation, but as stated - it was a new cylinder so the advice given is relevant for that. This is why I made the point it was a new cylinder so as to not mislead anyone, rather than just saying "Oh, out plumber told us not to insulate because it is already". ;)

In our old house we wrapped the old cylinder and it made some difference. No where are much as I was told to expect - but then the cylinder was in an extremely awkward location that made complete wrapping impossible.

timmmay

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#604369 3-Apr-2012 10:35

My cylinder's about five years old. I put a wrap on it, I had to take part of it off recently and it was quite warm underneath. It does add insulation, the only question is payback period.

Jaimita

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#604383 3-Apr-2012 10:52

If you are looking at saving money from hot water: Make sure your cylinder is set at 60 degrees and coming out of the tap at 55 degrees. If it is set hotter you are wasting money and you risk burning yourself (even more so if there are little children or older folk living in or visiting the house).

Also if you have a big enough cylinder you may profit from putting it on nightrate. There may be a fee to set that up. Test whether your cylinder is big enough by switching off in the morning and switching back on at night. Do that for a week, and if you don't run out of water you may benefit from the nightrate setting.

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keewee01

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#604386 3-Apr-2012 10:57

Jaimita: If you are looking at saving money from hot water: Make sure your cylinder is set at 60 degrees and coming out of the tap at 55 degrees. If it is set hotter you are wasting money and you risk burning yourself (even more so if there are little children or older folk living in or visiting the house).

Also if you have a big enough cylinder you may profit from putting it on nightrate. There may be a fee to set that up. Test whether your cylinder is big enough by switching off in the morning and switching back on at night. Do that for a week, and if you don't run out of water you may benefit from the nightrate setting.

That sounds like really good advice, thanks. :)

cshaun

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#604420 3-Apr-2012 11:35

It proves the temperature is being dissipated over the metal surface of the cylinder faster than it is escaping from inside, but that is all. Depends a lot where you touch it as well. Also depends when it was last in an active cycle and how much it had to heat during that cycle. The top horizontal surface of the cylinder will always be warmer. The lower you get, the cooler it is for most of the day.

Nicely said. That's what I was thinking too: cool to the touch - doesn't mean heat isn't escaping - just not enough to keep the outside warm. (BTW couldn't detect a temperature difference anywhere, top, bottom middle etc)

It is located outside under my house. So any escaped heat really is wasted (not in a drying cupboard or anything like that).

And yes realize almost everyone would say "it's already insulated enough, you don't need to insulate the newer type etc". Hence the post. Insulating again can't hurt... but quite pointless if it's a 50 year break even.

Guess there will definitely be a point were the wrap deteriorates to the point of being useless too - so break even would need to be before that happens.

I do not have the MEPS standard for hot water heating - but a BRANZ report online says "A 140 litre A-grade cylinder has a standardised Water Mark heat loss of 2.1kWh/day including 0.7 kWh/day for pipe losses from the cylinder".

Based on your numbers and removing the pipe losses. Scale to 180ltr. You get a loss of 550kWh/year. Wrap needs to reduce heat loss by 10% to give 5 year payback.

This seems similar to the info you manged to dig up - page 113: http://www.branz.co.nz/cms_show_download.php?id=b869c9c110a8b41d4a022b78f6898033994040b7

They actually mention in that report: "Cylinder wraps and pipe insulation could also give energy savings for A or B grade
systems, although the savings would be smaller. Assuming a conservative 0.3kWh/day saving."

Interesting how in their table a 'wrapped' cylinder is 2.1 vs A or B grade. Could be because of the B's dragging it down. And wrapped may include A's that are wrapped.

My costs are 22c per kWh so using that and $60 for a wrap.

Just based on the 0.3kWh/day saving (which includes pipe) - payback = 2.5 years.
Or 0.1kWh/day difference between wrapped and A or B grade = 7.5 years.

Based on the above I'm guessing payback would be 4-10 years. (Probably bit better if cylinder is outside like mine.)

gzt

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#604421 3-Apr-2012 11:39

It is unusual to have an electric cylinder outdoors. What was the reason for that installation style?

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cshaun

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#604423 3-Apr-2012 11:41

Jaimita: If you are looking at saving money from hot water: Make sure your cylinder is set at 60 degrees and coming out of the tap at 55 degrees. If it is set hotter you are wasting money and you risk burning yourself (even more so if there are little children or older folk living in or visiting the house).

Also if you have a big enough cylinder you may profit from putting it on nightrate. There may be a fee to set that up. Test whether your cylinder is big enough by switching off in the morning and switching back on at night. Do that for a week, and if you don't run out of water you may benefit from the nightrate setting.

Thanks yes good advice - should have mentioned that too I guess. I set it to 60 degrees yesterday.

Why 55 degrees specifically out at the tap?

I guess the lower this setting will result in less heat loss in the pipes on the way to the tap? So low as possible but high enough for washing dishes and anything else you may want hot water for.

cshaun

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#604424 3-Apr-2012 11:43

gzt: It is unusual to have an electric cylinder outdoors. What was the reason for that installation style?

Yes all used to be all indoors. But putting them outdoors is becoming far more common now days. Primary reason being space - why have it indoors when it doesn't need to be. And I guess they feel insulation good enough to put it outside now.

timmmay

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#604426 3-Apr-2012 11:46

Can you put a water heater in a ceiling cavity? I have heaps of space up there, and see no reason to have it in the body of the house taking up space, and I have no space around my house for it. I guess if it leaks there's a big problem, and it'd have to be well insulated.

cshaun

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#604431 3-Apr-2012 11:54

timmmay: Can you put a water heater in a ceiling cavity? I have heaps of space up there, and see no reason to have it in the body of the house taking up space, and I have no space around my house for it. I guess if it leaks there's a big problem, and it'd have to be well insulated.

My understanding is that's reasonably common too. My ceiling gets incredibly hot - would almost think you'd need less insulation. Though not sure how cold it gets during the night. I think the biggest negative would be it's more difficult to get at when anything needs to be done.

gzt

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#604435 3-Apr-2012 11:57

The standards state: "The delivered hot water temperature at any sanitary fixture used for personal hygiene shall not exceed: 55C* and "the storage water heater control thermostat shall be set at a temperature of not less than 60C to prevent the growth of Legionella bacteria".

In practice this means a tempering valve is required to ensure the (minimum) 60C storage temperature is always a maximum of 55C when it arrives at the tap.

The standards indicate it is acceptable to supply higher temperatures to kitchen appliances and laundry appliances. The standard also needs to be applied when installing new showers/basins/etc.

* but must be 45C for early childhood centres, schools, old people's homes, institutions for people with psychiatric or physical disabilities, hospitals.

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