Heat Pump Water Heaters at Avant Garage

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The Avant Garage project has a unique site condition that has caused us to re-examine the method in which Postgreen Homes heats the domestic hot water in each of its homes. There is just enough shading surrounding the site on the roof of the Avant Garage to dissuade us from installing our typical two flat panel solar thermal array. For this reason, we put on our research caps and came up with a new water heating solution that still fits our strict requirements of budget and performance.

After a few days of research, we decided that some of the new Heat Pump Water Heaters being offered were the best fit for our homes. These water heaters use the same heat pump technology that our split ductless heat pumps used for heating and cooling our homes. Rather than creating heat from scratch from an electric element in the water tank, the heat pump water heaters exchange heat from the surrounding air. They are able to reach efficiencies as high as 235% compared to a typical electric hot water heater that will be between 90% – 95%.

The top two choices for Heat Pump Water Heaters on our list are the GE GeoSpring Water Heater and the Rheem Hybrid Electric Water Heater. Both come in 50 gallon options which should be sufficient for any family of four, bost nearly identical specs. Each model also costs about $1,200 – $1,400 according to our current research.

Table from the ACEEE (American Council for an Energy-Efficient Economy) on Water Heating Life Cycle Costs:

Water Heater Type Efficiency (EF) Installed Cost Yearly Energy Cost Total 13 Year Cost
Electric Heat Pump Water Heater 2.20 $1,660 $190 $4,125
Gas Tankless 0.82 $1,600 $256 $4,925
Condensing Gas Storage 0.86 $2,000 $244 $5,170
High-efficiency Gas Storage 0.65 $1,025 $323 $5,220
Conventional Gas Storage 0.60 $850 $350 $5,394
High-efficiency Electric Storage 0.95 $820 $439 $6,528
Minimum Efficiency Electric Storage 0.90 $750 $463 $6,769
Solar with Electric Backup 1.20 $4,800 $175 $7,072

This table above is actually quite sobering for us. We rearranged it to be sorted from lowest total cost of operation over a 13 year period to least. You can clearly see that the heat pump water heater is at the top of the list with our standard to date Solar with Electric Backup at the bottom of the list. This is due to the high install cost of Solar which is brought down by Federal and State incentives, but it’s reassuring to see these stats given our new direction in water heating technology.

These units will also serve double duty in our future homes with basements as they naturally cool and dehumidify the surrounding air. It’s almost like a free mini air conditioner in your basement during the summer that will help keep it from getting too damp and musty feeling.

That’s it for water heating for now. Let us know what you think of our new direction in the comments.

11 Comments

  1. Brad says:

    While these units are certainly a better choice than a standard electric unit, I really don’t think you can compare them in operating cost. Maybe things in PA are different than in the middle of the country, but that chart is based on natural gas rates that are very high. For example last month I paid 63 cents a therm for gas, but the ACEEE chart is based on $1.40 a therm! So basically the operating cost for all of the gas units is 45% of what is listed above. So currently, that 60% efficient, gas tank design is less costly to operate than your shiny new heat pump model. Furthermore, it is no worse on emissions because its gas and doesn’t have transmission loss like electricity.

    If you have to use electric, by all means please us the heat pump water heaters. If you have access to gas, it’s the most efficient in cost and energy usage, especially the condensing tanks which is my favorite.

  2. Chad Ludeman says:

    Brad, you make some good points, but your data on average gas costs seems to be off a bit. I’m not sure where you live, but the natural gas prices are much higher on the East Coast and the rest of the country for that matter. Here is a decent link to some data on average costs of piped gas and electric in Philly and the rest of the country – http://www.bls.gov/ro3/apphl.htm

    You’ll notice that the average in Philly has been above $1.50 per therm for years and has just recently dropped below $1.40. The rest of the country has not dipped below $1.00 on average, so if you’re paying $0.65, you are definitely an outlier…

    In general, you make good points about the efficiency of gas and I have no problem with builder’s taking this approach. We at Postgreen Homes have simply committed to an all electric house, at least for now, for two main reasons. One, it’s much easier and less costly to have electric only installed in Philly compared to electric and natural gas. Secondly, electric power has the possibility of being supplied 100% by renewable resources by the homeowner or in the future by the power supplier. Natural gas can never be 100% renewable as it is a fossil fuel. We’re splitting hairs a bit and getting into the minute details of the choices behind our homes, but this is why we do what we do for the moment. Thanks for the observant comment!

  3. Ian Watson says:

    That looks like a really cool (hot?) system, but I’m confused about one thing: where does the heat come from? Is it just sucking it out of the room? If so, I can see that being great in climates where the cooling season is dominant. However, in climates with large heating seasons wouldn’t it just be stealing the heat you want in your air? What are the efficiencies once you account for the fact that the heat has to be first generated by a furnace?

  4. […] it for water warming for now. Let’s know what you think of our new direction in the notes.Heaters garage – Google Web-log Search by Steve Kay http://www.air-n-water.com Transform the chilly garage, store, or perhaps workspace with the […]

  5. The garage is possibly the best place to put a heat pump water heater, if you’re sure it won’t freeze.
    Some geothermal heat actually enters the garage through the slab. Other strategies are discussed at:
    http://greenbuildingindenver.blogspot.com/2009/08/heat-pump-hot-water-heater.html#comments

  6. Rob says:

    The GE model requires 700 cubic feet of space from which to draw the air. Is that possible in he AG project? I do like these type of water heaters though, especially as replacement of a typical electric water heater.

  7. Gary says:

    If you’ve ever lived with an electric water heater, you’d know that there’s no way a 50 gal tank heater isn’t even close to being adequate for a family of 4; I think it’s even iffy for two people. The advantage non-electric tank units have is quick “recovery” (industry lingo for how quickly hot water can regenerate). This is one of the reasons I was sold on gas tankless many years ago; there is no recovery, just endless hot water. Also, there’s no tank to fail at an inopportune time.

    Typical lifespan of tank water heaters is 7-10 years; maybe a bit longer if maintained, which no one ever does. The warranty on your GE and similar heaters is 10 years, most likely pro-rated, and that probably covers only the unit itself, not installation labor. Assuming a 13 yr life is pushing it.

    Based on my experience with 10 Takagi gas tankless in rentals I built, own and manage, and in single family homes I and relatives own, I expect them to easily last 50% longer than tank units; maybe 100% as we’re fastidious about maintenance (flush out mineral scale every 3-4 yrs, that’s it). You’re chart erroneously assumes the same lifespan for all units.

    There are quite a few gas tankless units Takagi, Rinnai and others with EFs of 0.91-0.96. Higher efficiency may mean high unit cost, but that’s more than outweighed by the fact that they can be more cost effectively vented with PVC rather than double-wall stainless.

    Dial in the efficiency of higher end tankless units, markedly longer lifespan than tank units, and far superior real world performance vs electric tank/tankless and the “best choice” conclusion changes.

  8. Imagine an insulated box of PCM (phase change material) built as a platform for the front-loading washer and dryer and running the hot water through it to saturate the PCM up to 185F. Let the HPWH lope along all day pulling hot air out of the HVAC’s return air, extracting the heat out of it, putting it into the PCM energy storage box. Now run the cold 55F street water through that PCM box to get the heat to the bathtub and dishwasher.
    The HPWH’s exhaust is dehumidified cool air that is then pushed back into the home’s HVAC’s duct work and cool the high-performance house. www,airgenerate.com has a HPWH that is roughly equivalent to a 1.5 ton air conditioner and it heats an 80-gallon water tank on a 120VAC circuit pulling the same amp load as a microwave oven.
    Think outside the box (or tank).

  9. jason says:

    chad, i’d like to hear more about what you used and why. i want more on this topic.

  10. JC says:

    I like the technology of HPWH but many folks seem to think it’s better suited for warmer climate where # of cooling days exceed # of heating days. It’d also help too if the weather doesn’t go below 40F in the winter. I’d say it’s perfect for FL, CA, AZ and the likes, but I wouldn’t risk it on the East Coast where the few past winters have been rather harsh and it’s considered a mild if it reaches 40F during the day. The forum at GBA has an insightful discussion on this very topic – http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/heat-pump-water-heaters

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