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Old 09-04-15, 11:12 PM   #1
UNCSoc
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Default A better heat pump water heater?

Ecorenovators,

I am wondering what you think of the interesting claims made about this (newer?) heat pump water heater. They seem to make sense, but really? and do they make that much difference in efficiency and longevity?

Even if all of the claims are right, does it all add up to being worth $2400 for the larger unit? Seems like a lot, but maybe the efficiency would pay it back in a few years.

stiebel-eltron-usa.com/accelera (would have to paste in your browser search engine)

If you can't get to the link, here are some of the claims:

A true heat pump water heater that can satisfy 90 percent of hot water needs

Each watt used for compressor and fan results in 3-5 watts worth of hot water generated.

The backup heating element is placed at the top of the tank so it can be smaller and more efficient

During a draw, the cold water enters at the bottom and is kept from mixing with the hot water, so you can use all the hot water stored in the tank (rather than seeing a rather quick decline in temperature with the remaining hot water as the cold water is drawn in).

The "coils" surround the outside of the tank for greater efficiency and to eliminate any chance of mixing with water.

Glass tank for longevity

In may case, it would sit in my basement utility room (the company claims that would be best in colder climates). I could also put it in a rather large insulated crawl space if there was some efficiency advantage there.

Wow, it sounds perfect (except for the price of course--I know some of you are building your own heat pump hot water heaters, but I don't think I am at that level just yet so may have to spend the money)

Thanks.

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Old 09-05-15, 11:01 AM   #2
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Here is a live link to the 80 gallon model:
http://www.stiebel-eltron-usa.com/accelera.html

Looks like a well built unit. The thing I like most about this unit is that the incoming water is plumbed in at the bottom. When hot water is drawn from the top, the cold water naturally stratifies and stays at the bottom. Also, the unit doesn't have multiple modes to set, it just works like it was designed to all the time. Less gadgets inside means less chance for malfunctions.

As far as payback goes, hpwh are not much cheaper to run than natural gas. Due to the fracking craze, natural gas is cheap for the time being. This may or may not change anytime soon. Also depends on your grid power rates and local gas utility.

Last edited by jeff5may; 09-07-15 at 10:11 AM.. Reason: more info
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Old 09-05-15, 12:27 PM   #3
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Default Burning Down The House...

Quote:
Originally Posted by jeff5may View Post
As far as payback goes, hpwh are not much cheaper to run than natural gas. Due to the fracking craze, natural gas is cheap for the time being. This may or may not change anytime soon. Also depends on your grid power rates and local gas utility.
I had a dear friend, now deceased, who had been hit very hard by the vicissitudes of life, and although he remained a good and dear friend, his ability to think 'long term' and in regards to his ability to see 'the whole picture' was damaged.

I clearly remember going over to visit him on a fiercely cold winter day, and I watched him tear off boards from the interior walls of his house and throw them in the wood stove to keep warm.

It was a sad sight to see, this dear man behaving in this way... destroying his house to keep warm. Clearly a very sad symptom.

* * *

Reason I mention this true story, is that this story is exactly parallel to fracking. It's no coincidence that Dick Cheney managed to have congress pass a law that would indemnify and hold blameless for environmental damages, the actions of the companies, BEFORE FRACKING STARTED. They already knew what would happen.


Essentially, the fracking companies are pumping hazardous, carcinogenic, chemicals deep into the ground that will contaminate the deep aquifers, in some places this realization is already beginning to happen.

And we get cheap natural gas in return.

The stories of flaming water taps are only the very tip of the iceberg.

My point here is that making simplistic economic decisions, without seeing the bigger picture is no different than my deceased friend burning down his house... because in fact, we are piece by piece, burning down our house.

We need to widen our view and consider the consequences.

Best,

-AC
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Old 09-05-15, 06:47 PM   #4
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CIA puts Cheney at about $40B with most of it gained since 2001. Hmmmmm

Fracking will be the end of any area that allows it. Alberta just had a 4.3 magnitude earth quake in a place where they were not seen before. Even the regulator said it was due to fracking. I think there should be a cull of the human race.....oh wait....we are seeing it in Syria

That said, back to the Stiebel Eltron. I know these guys and have bought a lot of stuff off Frank Stiebel for years. Their stuff comes from the parent in Germany and is well respected there so I think that the quality would be better than the GE Chinese stuff. That's my $.02
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Old 09-07-15, 11:43 AM   #5
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Whoa! This thread went off the deep end fast! Great analogy, AC_Hacker.

One of the reasons my wife and I left Appalachia, was to get away from the fracking. Most people were salivating at the prospect of a company drilling on their property, not considering the long term effects on their water supply or personal health. In many cases, the property owner has no right to refuse to allow the gas drillers to extract it.

ABOUT WATER HEATERS!! My friend in SW Pennsylvania has a HPWH very similar to the one you describe. I helped him carry it in the house. We were going to attempt installing it in the closet of his upstairs bathroom, right behind the shower, it was simply too big to fit through the bathroom door. He wanted it close to the shower for the short plumbing run, but he also hoped to recover some heat from the steamy air during a shower. Alas, we had to install the WH in his laundry room.

He is quite pleased with its operation in the summer months, when the house is warm and humid, but in the cold winter months he switches back to resistive heat, since he hates that powerful blast of cold dry air coming from the laundry room.

My recommendation, is to first reduce the amount of water you use; install a water meter! If you choose to install a HPWH, get one smaller than you think you'll need, locate it somewhere with a reasonable source of heat, and such that a blast of cool air is not an issue. Also, install a waste water heat exchanger to recover that valuable energy going down the drain!

My TRUE recommendation, is to look at what others have built and shared on this forum, and set out with us to build your own. We'll help, I promise!
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Old 09-07-15, 04:51 PM   #6
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Default Getting Back On Track...

If I recall correctly, you posted the idea of using an ASHP for most of the water heating, and then supplementing the final heating with a demand gas boost.

In effect you would be using the ASHP as a water pre-heater for the gas demand water heater.

I've been turning the idea over in my head for several days now to consider the merits of such a system.

First of all, a properly set-up ASHP water heater is less expensive to run than electric, because the same power would be used at a 150% to 300% advantage, no matter what the price of electricity.

It would also be likely to beat gas, because much of our electricity is generated not just by coal, but also by gas. There would be some comparison calculating to do, depending on the relative costs of each fuel.

Build It Solar, has some very useful calculators available, and one of them is for comparing the various fuels for heating a house. The calculator stays pretty up to date on fuel costs, but they can be changed by inputting your own value. One very interesting aspect is that the calculator also calculates the CO2 resulting from the various fuels, as well as the cost.

So 'heat a house' is essentially the same as 'heat domestic water'... you can see which one will be the most advantageous, but the calculated costs will not apply.

Back to your pre-heat idea, I usually see the pre-heat idea applied to solar preheating, with the final lift being done with electric or gas. In this case, the pre-heat is essentially free, so the advantage is very easy to calculate.

But your idea was to combine ASHP which already is quite efficient, with a demand heater, which is also efficient.

Tankless efficiency is predicated on avoiding standing heat loss. if your hot water is being used constantly, it may not be much more efficient. If it it is used infrequently, with long intervals in between, then avoiding the losses that would occur during that non-use period would be a big advantage. For instance, I am the only one using my hot water, so the tankless is really great. So, you'd need to factor this in to your consideration.

Also to consider it that the lower the lift that a heat pump needs to make, the higher it's efficiency. So by reducing the cut-off temp of the ASHP water heater, you could improve efficiency.

There are so many variables here that it would be pretty difficult to predict mathematically where the 'sweet spot' would be, or if there would even be one. But you could build the beast and try it out by varying the cut-off point of the ASHP water heater and measuring the fuel used. For that, you would need a device to measure the electricity used by the ASHP water heater alone. And you would also need a device to measure the gas used by the demand heater, which is a project by itself.

Yous should also be aware that for this setup, your gas demand water heater would need to be aware of incoming water temperature. I'm not convinced that the small inexpensive demand heaters have this feature.

Good luck!

Best,

-AC
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Old 09-08-15, 10:48 PM   #7
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To answer the question, yes this model is a bit better than other models for a typical homeowner.

Most heat pump water heaters are hybrids in order to meet the wide array of demands. They tend to fall back on using electric heating elements quickly. A prior reply noted a situation in which a homeowner did this and why. The heating elements are old school style so they must be mounted lower in tank


If you know you have a location where the heat pump can work year round, and you won't typically empty the tank, but use a fair amount of hot water (family) then this model is optimized to take most advantage of heat pump savings.
Keep in mind it is a MASSIVE 80 gallon model with a heat pump on top, 6 Feet tall and close to 1 Ton in weight filled with water.


This model is effectively an ASHP with an on demand electric element at it's outlet.
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Old 09-16-15, 08:08 AM   #8
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Has anyone in the Ecorenovator world seen a residential HPWH that recovers energy from a home's waste water stream? It always seemed to me, that the time a water heater "calls for heat", is likely when the warmest water is draining from the home.
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Old 09-17-15, 04:58 AM   #9
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The heat from waste water goes mainly into the pipework close to the house and in cold climates it prevents freezing.

For water heating the best choice is evacuated tubes even in countries like Ireland that have only one day of clear skies in six. In winter water supply is usually much colder which means the panels work with weaker sun. The gain in the coldest six months can be around 50% of the summer gain. In any case houses should have an efficient heating system for winter that also tops up the water temperature.

Heat pump water heaters that use internal house air as a heat source are really only for summer use. In winter the heat has to be replaced from other sources that could heat the water directly instead.
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Old 09-17-15, 09:43 AM   #10
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Quote:
Originally Posted by marx290 View Post
Has anyone in the Ecorenovator world seen a residential HPWH that recovers energy from a home's waste water stream? It always seemed to me, that the time a water heater "calls for heat", is likely when the warmest water is draining from the home.
There are heat recovery systems for the waste pipe, basically big bits of copper.

The issue besides cost recovery, is you need headroom, a good 5-10feet of vertical drop from the drain to install the device.

google is your friend

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