# heat pump water heater



## Alaska (Jun 16, 2012)

Anybody out there using a heatpump water heater?


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## Ross (May 9, 2002)

Heard of them but sorry no experience!


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## SolarGary (Sep 8, 2005)

Hi,
I don't have any direct experience -- I've collected a little material here: 
Solar Water Heating Projects and Plans Heater

The video of Tom installing the Geyser HP water heater is very entertaining.

One thing to just be aware of is that they cool the air in the room they are installed in. In the summer, that's a plus, but in the winter, it just means your furnace has to reheat this cooled air. The last article at the link above is on arranging the ducting of air to the HP water heater seasonally to get around this.


Gary


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## wannabechef (Nov 20, 2012)

I looked at them at Home Depot...not sure if you live in Texas or Alaska, but the heat pump water heater would do well in Texas...not so much in Alaska.


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## WisJim (Jan 14, 2004)

I've been looking at them, and considering one instead of putting in solar water heating panels. The heat pump water heaters "seem" to be so efficient that it would make sense to run one from my PV system when the time comes to replace my LP burning water heater. But I also am hoping for more info from people with some experience with them. A recent issue of Home Power magazine did have an article about water heating and had a little about heat pump water heaters.


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## SolarGary (Sep 8, 2005)

WisJim said:


> I've been looking at them, and considering one instead of putting in solar water heating panels. The heat pump water heaters "seem" to be so efficient that it would make sense to run one from my PV system when the time comes to replace my LP burning water heater. But I also am hoping for more info from people with some experience with them. A recent issue of Home Power magazine did have an article about water heating and had a little about heat pump water heaters.


Here is an attempt at how the costs come out that I did earlier -- it first compares the solar thermal approach to just resistance heating with PV, and them running a heat pump water heater with PV: 

*Demand*
If you take a family of 2 with a total demand of 50 gallons of hot water a day, and heat it from 50F to 120F, thats (50 gal)(8.3 lb/gal)(120F-50F) (1 BTU/lb-F) = 29K BTU per day, or 8.5 KWH per day. That comes up to 3100 KWH per year.

*PV Reisistance Heating*
So, for just hot water you need PV array that generates 3100 KWH year. I don't know where you are, but if I run PVwatts for Springfiled, IL (a nice central place), it takes a 2.5 KW PV array to generate 3200 KWH per year -- just enough to fully satisfy hot water energy on a yearly basis.

Since PV panels produce about 13 watts per sqft of panel, you would need 2500/13 or about 200 sqft of PV panel to meet the yearly demand for hot water. 

Not sure what this 2500 watts array would cost today? Solar Today did a nation wide US study last summer and got an average of $6.80 a peak watt -- its probably down some from that, but at that price, it would be $17000 (installed and before rebates). In Mt (where I am) that would qualify for 30% federal + $1000 Mt credits for a total of $11000 out of pocket. 

*Solar Thermal*
This compares to a typical two 4 by 8 solar thermal collectors (64 sqft) that would satisfy about 80% of hot water demand. The panels are only 1/4 the area just because the thermal panels are about 4 times more efficient (about 60% vs 15%)

Our local solar water heating installer (Liquid Solar) does 2 panel thermal systems for about $5000. In MT they qualify for the 30% federal credit as well as an MT $1000 per couple credit, so end cost comes out $2500 out of pocket. I think we are a bit lucky to have this guy who does great work at somewhat lower than average prices, but shopping around might find a similar guy where you are.
If you are in to DIY stuff, you can make a good quality solar thermal system for about $1000.

*Heat Pump Water Heater Run By PV *
If you went with the heat pump water heater to improve the overall efficiency of making hot water, it would cut the required PV array for water heating about in half because the HP water heaters have a COP (efficiency) of about 200%. 
The down side is that it makes the system much more complex and expensive. There have been reports of short life and high maintenance on some of the models -- but, time help this. And, Its still quite a bit more panel area than a solar thermal system requires.

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Another approach that helps all of the above is to work on using less hot water -- good dishwasher, cold clothes washing, good shower heads.



Gary


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## wannabechef (Nov 20, 2012)

WisJim said:


> I've been looking at them, and considering one instead of putting in solar water heating panels. The heat pump water heaters "seem" to be so efficient that it would make sense to run one from my PV system when the time comes to replace my LP burning water heater. But I also am hoping for more info from people with some experience with them. A recent issue of Home Power magazine did have an article about water heating and had a little about heat pump water heaters.


You have to consider your incoming water temp...in WI it would use the coils more than the heat pump, not saving you a ton. They have a map that shows where they are most efficient. In your case a tankless might be a better option.


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## wannabechef (Nov 20, 2012)

SolarGary said:


> Here is an attempt at how the costs come out that I did earlier -- it first compares the solar thermal approach to just resistance heating with PV, and them running a heat pump water heater with PV:
> 
> *Demand*
> If you take a family of 2 with a total demand of 50 gallons of hot water a day, and heat it from 50F to 120F, thats (50 gal)(8.3 lb/gal)(120F-50F) (1 BTU/lb-F) = 29K BTU per day, or 8.5 KWH per day. That comes up to 3100 KWH per year.
> ...


Valuable information...


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