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Old 11-09-13, 09:50 AM   #21
Servicetech
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Originally Posted by NiHaoMike View Post
The payback can be quite a bit quicker if you make use of the air conditioning/dehumidification features. That said, it's surprisingly easy to build your own for less than half the cost of buying one. And if you run a R410a compressor on R290 or R433b (the "Davuluri Treatment"), it would very easily attain the 140F or so for dishwashing. I'm also using a dsPIC and OpenWRT platform for system control, currently developing the firmware for it.
Nice homebrew window AC conversion

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Old 11-09-13, 11:03 AM   #22
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Servicetech,

There will come a day that natural gas prices will rise to their previously heavenly levels. The major oil companies are "fracking" up the planet in search of whatever cheap energy they can find. The current low cost of natural gas carries an enormous environmental cost, which not all of us bear, yet. Sooner or later, they will have to change their model. Cuz nothing lasts forever (except a dollar).

Also bear in mind that lots of ecorenovators are generating their own heat and/or power. The payback on the investment does not always compare to the current market value of x.

Point in case: Pinballlooking has installed 10kW+ of solar PV and signed up for net metering. The power company in his area will only let him carry forward a discount for his generated power, to be used against his consumption. As a result, he's installing heat pumps and electric water heating to consume his generated power. He also drives an electric car, which gets charged at home with solar power. End result: no electric bill, no natural gas bill, highly reduced fuel costs, increased home equity.

Worth it or not? Doesn't matter, it's not your house.
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Old 11-09-13, 11:49 AM   #23
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Is his electric bill really gone or is he still responsible for paying the minimum customer/meter charge? PV will become more cost effective as more power companies go to smartmeters and Time of Use pricing. On summer afternoons when demand (therefore rates) is highest PV will be producing close to maximum potential. At 44 cents per KWH the savings could really add up.
Variable Peak Pricing Plan
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Old 11-09-13, 12:36 PM   #24
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The problem with heat pump water heaters is they work harder as the incoming water tempatures drop. In summer when a heat pump water heater would be most effective incoming water tempatures are in the 70's. Payback time for heat pump water heater is simply too long. If you have natural gas, forget it. No way a heat pump water heater will ever pay for itself when compared to gas.
It is very interesting what you have said.

It looks like you have a solid understanding of payback time, which some other people understand as break-even.

Could you please show us your calculations (graphical would be even better) so that we can understand your point?

Sincerely,

-AC
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Old 11-09-13, 02:03 PM   #25
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It is very interesting what you have said.

It looks like you have a solid understanding of payback time, which some other people understand as break-even.

Could you please show us your calculations (graphical would be even better) so that we can understand your point?

Sincerely,

-AC
Give me the COP specs for the unit you are considering. COP falls as ambient tempature drops and more work is needed as incoming water tempatures drop. If you have to use a lot of resistance supplimental heat at low tempatures then a lot of the savings get wiped out.

Also consider that payback time gets extended if a repair on the unit is required. Keep in mind there's no running down to lowes and picking up a thermostat/heatign element if one goes out. Parts are special order from the manufacturer and I doubt they are cheap. Lowe's used to sell the heat pump water heaters but discontinued them because they weren't selling. A homebrew solution that you DIY could have a significantly shorter payback time than a commercailly made unit depending on what the parts cost and what your time is worth.

I've even looked at Natural Gas tankless water heaters and the payback time just isn't there when compared to an old school tank water heater. Natural gas prices need to double before payback time becomes reasonable.
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Old 11-09-13, 03:17 PM   #26
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Give me the COP specs for the unit you are considering.
Well, since you did say, "No way a heat pump water heater will ever pay for itself when compared to gas", I'm, guessing that you have run the numbers already. I mean that level of certainty doesn't come from nowhere... right?

Just in case you haven't run the numbers, how about a Geyser PRO-125. I picked that one because it has a published COP curve, which should give you enough information for your analysis.


...and HERE is a list of pages that Google thinks have pricing information for a new Geyser PRO-125.

Additionally, HERE is a table of national natural gas prices, so that you can pick various scenarios. By the way, this link updates itself, so the information will continue to remain valid.

Certainly can't neglect electricity use, so HERE is a table of national electricity rates. As in the paragraph above, the link updates itself, so the information will continue to remain valid.

Lastly HERE is a collection of regional climate maps that you can use to plug in values to the COP tables.

I'm looking forward to your findings.

Best,

-AC_Hacker
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Old 11-09-13, 03:28 PM   #27
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Ok then, consider this:

The OP has a (somewhat) super-insulated house and an unlimited supply of free firewood, but has become tired of chopping wood. He uses propane for a backup heat source. He is considering a heat pump for primary hydronic / domestic water heating. He has bought a small (1/2 ton) air source heat pump which installs into a standard electric water heater to experiment with. He plans on running the air source heat pump in the same location as the hydronic heat store, to maximize his COP.

Now tell me this: where in the world does a natural gas fired water heater fit into this plan? Anyone?
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Old 11-09-13, 08:30 PM   #28
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Pricing link for heat pump water heater not working, wasn't able to get a cost basis. Similiar product was running $1,500 @ Lowes when they used to stock it. NG water heaters run about $400. You need to save $900 in energy costs just to break even.

Power and gas rates vary considerably based on region. The chart for gas prices is incorrect for those of us in Oklahoma on ONG. Gas is $4.67 per Dth, Electricity is 10 cents per KWH (close to the 9.9 the link shows) A COP of SIX is required simply to break even with NG. ONG builds most of the cost into a flat $28/mo delivery fee and sells the NG "for cost". In Oklahoma if you have NG hooked up it makes sense to use it for everything you can.

All electric homes is where it could get interesting...
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Old 11-09-13, 10:47 PM   #29
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Pricing link for heat pump water heater not working, wasn't able to get a cost basis. Similiar product was running $1,500 @ Lowes when they used to stock it. NG water heaters run about $400. You need to save $900 in energy costs just to break even.
I just used the link from my post, and it did work. However, I wasn't able to get pricing info as I thought. The unit is a commercial water heater, built for very heavy use. That's probably why the COP curve was published, for use by engineers designing a whole commercial installation. I'll call on Monday and get a price.

But back to your post... I think I understand now.

When you say, "No way a heat pump water heater will ever pay for itself when compared to gas", your horizon only extends only as far as Oklahoma, even though this forum is read by people throughout all of North America, and also Europe, and we have had some very resourceful, informed and intelligent readers in Australia, and New Zealand, and even a few rare readers in South America.

Also, your idea of break-even is that the payback must be in the first year of use. I have never known anyone to consider that if a break-even period that is beyond the first year, it isn't worth considering.

If you were to do a real break-even analysis, you would be able to calculate the length of time it would take for one alternative to break even as compared to another... for any area, for any gas price and any electricity cost.

Using the Oklahoma Method, CFL lighting does not break even... Ditto LED lighting, Ditto insulation of any kind, Ditto any recognized energy saving method, except maybe bubble-wrap window insulation.

I think this kind of thinking is extremely limiting, but it certainly does explain a lot.

-AC
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Old 11-09-13, 11:34 PM   #30
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Other things matter too. In my area, CenterPoint Energy Minnesota Gas, has decided to essentially penalize low gas usage for those of us who use little due to our careful water use, heating, and those of us who actually insulate beyond code requirements.

I used 173 therms of gas from the 12 billing periods from the middle of 2011 to 2012 and spent $236.93 for the gas and that included $126 of service fees($10.50 per month). The utility filed a rate case to increase the service fees another $7 per month to $17.50. So basically my $236.93 that I paid before is nearly impossible to beat with efficiency savings because now if the rate case gets passed I'm paying $210 per year just to be connected to natural gas. In the summer, my cost of natural gas will actually be only about 12% or so of the amount I'm paying. The $236.93 that I paid before will now probably be roughly $300+ per year. Of course now if I add additional insulation, it becomes even less worth it for me so what I plan to do is once I get my house wrapped in additional insulation, a heat pump water heater will make sense and I will transition off the natural gas and be using a super efficient ASHP for building heat and the service fees from the natural gas company help my case. On top of all of that I'm installing solar PV to offset driving by the use of an electric car and all of this will be at least partially covered by energy sourced from my roof.

There are other motivations but if you are looking to lose natural gas or if natural gas is unavailable, the heat pump water heater can be financially beneficial. ..even in an area like mine where the natural gas is super cheap, but with the fees, only super cheap if you use a pile.

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