Heat pump water heater size and brand
Andy Kahn| Posted inGreen Products and Materialson
我准备选择热泵水加热器r for the house I’m building. I was leaning towards Airtap but they seem to be gone. the house has 3 bedrooms and 2 1/2 baths with one fairly big tub. I am trying to decide on a reliable brand and looking to see what people recommend. I think I need at least a 60 gallon tank but it seems like the resistance electric would kick on a lot less if I got a 80 gallon tank. what are the disadvantages of the larger tank besides a little more surface area for heat loss?
Thanks for any feedback
Andy
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Replies
Andy,
An 80-gallon tank is always preferable to a 60-gallon tank. I recommend that you read this article:Heat-Pump Water Heaters Come of Age.
In that article, I wrote, “All of the researchers I talked to emphasized the benefits of a large tank size... ‘Bigger and hotter tanks are better,’ said Aldrich. ‘It’s counterintuitive.’ ”
Stiebel Eltron units cost more than other brands, but have an excellent reputation.
The new 80 gallon GE sold through box stores has been getting good reviews, and runs an EF of 3.0 (significantly higher efficiency than earlier models). If you're concerned about the newness of this particular model (or the endless problems they had with their original launch of that line over a half-dozen years ago when they were being built offshore rather than at GE's Kentucky manufacturing plant) the box stores have fairly cheap parts & labor extended warranty deals.
How big is the "fairly big tub"? The 80 gallon GeoSpring is good for 90 first-hour gallons. If the tub takes more than 70 gallons you may need something bigger to get satisfactory overall performance.
If most of the household uses showers instead of tub bathers it may be worth installing a gravity-film type drainwater heat exchanger downstream of the main shower(s), which will increase "apparent capacity" of the tank by half or more for showering, but not for tub-fills. Taller and fatter drainwater heat exchangers yields higher return efficiency- a 4" x 48" has about the same 53-56%+ return as a 3" x 60". For slab-on-grade homes this would really only work with the upstairs showers, since they have to be installed vertically. The best time to think about drainwater heat recovery is during the design & construction phase, since the higher efficiency versions don't fit neatly into a 2x4 framing bay, and it's easier to plumb-in the potable side from the get-go rather than as a retrofit.
The best thing about them beyond improving the hot water capacity is that they don't use power. It won't always "pay back" on energy costs in super-cheap power areas (especially with an EF 3 water heater) but the extended capacity can eliminate the need to go with a more expensive 100 gallon tank, if an 80 gallon tank can fill the tub.