Energie thermodynamic water heater. Claim 80% saving. Anybody have them?

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Forums › Finance and wealth management › Energie thermodynamic water heater. Claim 80% saving. Anybody have them?

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#2345711 29-Oct-2019 10:20

Well, they have some case studies now but they're not too informative. There's an installation in Nelson with the system heating both the hot water system, and hydronic heating in concrete slab. But very little detail is provided.

The only power required is from the 390W compressor which presumably doesn't run 24/7 since once the water reaches the set temperature the compressor doesn't need to run.

As for heat losses from the HWC, I wonder why people don't leave the HWC in the living room (decorated appropriately) so the heat losses from the cylinder provide some space heating.

And if you have PV panels .. surely that lowers the cost of ownership?

gchiu

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#2345960 29-Oct-2019 18:32

Another question for the science guys. If it just uses environmental heat to evaporate the refrigerant, why couldn't you just install it in the roof cavity of a steel pitched roof at build time? That's hotter than outside due to greenhouse effect.

gchiu

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#2346629 31-Oct-2019 09:37

Indicative costs were given above of $8-10 k for a typical installation which includes a 250L mains pressure hot water cylinder.

If you empty your HWC daily, then Mercury says it takes at least 3 hours to reheat.

If you have a typical 3kW immersion heater in your HWC, then the cost per year of heating the water daily is 365 * 3 hrs * $0.30/hr * 3kW * 1.15 which is $1133.32 inc GST per year. That doesn't include the Legionella sterilizing which probably you don't need if you're emptying your tank daily. But usually that's only done weekly.

If you add the cost of a 500W PV panel to cover the operating costs of the 390W compressor (which only operates when the water needs reheating ) say $500, then the payback period is

$9500 / $1133 = 8.38 years.

HWCs last about 8-12 years some longer. So, over 12 years you might save about $4k. That's assuming there's no refrigerant leak, and the compressor doesn't need replacing.

Does that sound right assuming a North Island climate where the day time temperature doesn't drop below -5 deg C.

gchiu

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#2346633 31-Oct-2019 09:49

As a comparison, BRANZ's 2005 report Cost Benefit Analysis for Solar Water Heating Systems EC1112 says that for Wgton a new solar hot water system with new HWC, the pay back period was 19.5 years or 15 years if you imported the components yourself.

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#2346708 31-Oct-2019 11:19

gchiu:

Indicative costs were given above of $8-10 k for a typical installation which includes a 250L mains pressure hot water cylinder.

If you empty your HWC daily, then Mercury says it takes at least 3 hours to reheat.

If you have a typical 3kW immersion heater in your HWC, then the cost per year of heating the water daily is 365 * 3 hrs * $0.30/hr * 3kW * 1.15 which is $1133.32 inc GST per year. That doesn't include the Legionella sterilizing which probably you don't need if you're emptying your tank daily. But usually that's only done weekly.

If you add the cost of a 500W PV panel to cover the operating costs of the 390W compressor (which only operates when the water needs reheating ) say $500, then the payback period is

$9500 / $1133 = 8.38 years.

HWCs last about 8-12 years some longer. So, over 12 years you might save about $4k. That's assuming there's no refrigerant leak, and the compressor doesn't need replacing.

Does that sound right assuming a North Island climate where the day time temperature doesn't drop below -5 deg C.

That doesn't sound right.

Try a calculator for the HWC heating e.g. http://processheatingservices.com/handy-heating-calculators/water-heating-time-calculator/

Say you heat 250 litres from 15C to 65C (difference of 50C) then a 3kW heater takes 5 hours or so not the 3 hours you quoted.

The difference is probably due to a smaller average cylinder size than the 250 litre example. I imagine that the average is still below 200 litres. Older, mainly low pressure cylinders, used to average less than 150 litres e.g. 30 gallons is ~110 litres.

Edit: I should have the following.

While it is easy to empty a cylinder with mains pressure using 10 litres of hot water a minute, is that what normally happens? That would only mean only 25 minutes of showering to empty the cylinder. I don't hear my friends and family saying that they do that. But maybe it is reasonable that a tank full of water would be used over the entire day.

Agood mains pressure cylinder should last more than 20 years. Cylinder life expectancy is partly correlated with water pressure so a low-medium pressure copper cylinder typically lasts 30 years. You possibly mean vitreous- or glass-lined steel cylinders which are about 12-15 years - they are susceptible to cracking e.g. in earthquakes. But perhaps you mean steel cylinders where corrosion protection is not maintained, maybe that is quite normal.

gchiu

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#2346780 31-Oct-2019 13:33

I've gone through 3 HWC in the last 30 years. Two were gas heated and the other electric. Don't know what the linings were.

Another HWC is rusting on the outside though not leaking and the plumber says we should replace it. It's only 12 years old.

Regarding the heating, maybe Mercury's calculation is based on the base temperature being much higher. Once it gets down to 40 deg C I won't shower as it's too cold for me.

But both of these points you raise improve the cost benefits of using thermodynamic water heating. If your stainless steel water heater lasts 20 years, then you potentially get 12 years of free hot water.

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#2346800 31-Oct-2019 14:04

gchiu:

As a comparison, BRANZ's 2005 report Cost Benefit Analysis for Solar Water Heating Systems EC1112 says that for Wgton a new solar hot water system with new HWC, the pay back period was 19.5 years or 15 years if you imported the components yourself.

That's not really comparable because that is for evacuated tube solar water heating (p.35) whereas the system in this topic is an air-source heat pump and the more relevant alternative you mention is PV panels.

Although the evacuated tube had a similar coefficient of performance (COP) to the heat pump (p.12) in that report, 1.73 vs 1.64, the research was actually from 1996. Today, air-source heat pumps typically have COPs well above that, e.g. 2.0-3.0 below 5C and COP 2.5-5.0 above 5C (see BRANZ report SR 329 (2015) Heat pumps in New Zealand).

As an aside, I actually installed a solar hot water system with a new HWC in the Werllington region during 2006. My pay back period is still 18 years which is not much different from their estimate.

Over the same period, price inflation has been a lot lower at 2% and interest rates a lot lower at 6% so the NPV and IRR are much more favourable.

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#2346806 31-Oct-2019 14:10

gchiu:

I've gone through 3 HWC in the last 30 years. Two were gas heated and the other electric. Don't know what the linings were.

Another HWC is rusting on the outside though not leaking and the plumber says we should replace it. It's only 12 years old.

Ah yes, cylinder life expectancy is a lot lower for outdoor units the more they are exposed to the elements. Where I live a lot of the outdoor units have additional shelter from the elements - under broad eves, under a separate roof, so they're more like an indoor unit which wouldn't normally rust on the outside.

gchiu

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#2346815 31-Oct-2019 14:32

Sorry, I meant there is some rust on the outside of a HWC affecting some of the fittings, and the HWC is inside an apartment.

I installed a solar hot water system 8 years ago as well in Wellington and this year all 20 tubes were replaced under warranty as they all had lost their vacuum. Modern evacuated tubes aren't supposed to do that as the glass is sealed differently now and doesn't use seals.

I don't know about the COP of these things (another manufacturer claims 4.55) but if I can get a payback for a thermodynamic system within 9 years I can't see any good reason not to do this for a new build.

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#2346822 31-Oct-2019 14:53

gchiu:

I don't know about the COP of these things (another manufacturer claims 4.55) but if I can get a payback for a thermodynamic system within 9 years I can't see any good reason not to do this for a new build.

The actual payback term depends on the actual performance of the system and not on the vendor's claims for the product. Go for it if you are confident that the system will perform as claimed or that the vendor will compensate you in the event that performance is not so good.

raytaylor

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#2346961 31-Oct-2019 21:04

gchiu:

Another question for the science guys. If it just uses environmental heat to evaporate the refrigerant, why couldn't you just install it in the roof cavity of a steel pitched roof at build time? That's hotter than outside due to greenhouse effect.

Noise.

I have seen one that sits in a semi detached shed. Hot air from the top of the attic is pumped out to a shed using a small auxilary fan which is switched on by the air movement of the heat pump cylinder kicking in.
The slightly cooler air is then returned to the attic for reheating in the large roof cavity.

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#2346966 31-Oct-2019 21:11

Sometimes i have wondered, how much faster would my heat pump be if the outdoor unit was on the sunny side of the house. Instead of blowing cold outdoor air across the heat exchanger to warm it up, what if the sun could do some of that work too?

Then the heat can be transferred inside quicker.

And on a freezing cold morning, which is still sunny or reasonably bright, the unit wont need to go into defrost mode.

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#2347010 1-Nov-2019 05:25

raytaylor:
Sometimes i have wondered, how much faster would my heat pump be if the outdoor unit was on the sunny side of the house. Instead of blowing cold outdoor air across the heat exchanger to warm it up, what if the sun could do some of that work too?

Then the heat can be transferred inside quicker.

And on a freezing cold morning, which is still sunny or reasonably bright, the unit wont need to go into defrost mode.

I attached a couple of old car radiators around mine and when the temp goes below 5, trickle water through it which is about 12-14 in winter. Works a treat. I was always going to automate it but never got around to it as we also have a fire and that stores heat overnight so it wasnt a biggy. It would also work better if it was in some form of cowling with a single ingress through a large radiator.

We dont have water meters so no cost there, but flow isnt much anyway and not for long.

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#2347073 1-Nov-2019 09:48

We installed one of these systems late last year, a 300ltr system (just over 9k). I can’t comment on the efficiency of the system as I have not kept a close eye on it but we are a family of 5 and the water was always hot and I noted no spikes on the power bill when randomly looking at the hourly total power used through the meridian website.

I had read that case study mentioned earlier but I had read others that latter contradicted it. I believe that in the UK the system was added to the register for tax rebates for efficient systems. I read many forums, mainly in the UK and watched a few YouTube videos with people running them including guy in the Scotland who was using the panel as an awning for his front door.

We are happy with the system; we are happy that the panel is not that big and blends into our roof (it does go white when the system is working hard) and we don’t believe that we are consuming a large amount of power to keep our family in hot water.

Time will tell but we are happy with the decision that we made to install one of these systems.

gchiu

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#2347119 1-Nov-2019 11:10

I presume that you're using the 390W compressor. Do you have an idea of how often that runs?

I think it goes white when running as the refrigerant is being pumped into the panel, and ice temporarily can form on the surface if the ambient temperature is low enough.

What part of the country are you in?

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