A split-system heat-pump water heater
Locating the compressor outdoors and using CO2 as the refrigerant eliminates some of the biggest concerns builders have with typical hybrid water heaters have.
We’ve chosen an air-source heat pump for hot water. The Sanden water heater is a unique product. The compressor is mounted outside with the minisplit compressors and it shares many of the same features: slimline construction, inverter motor, and ability to operate to -20⁰F. The outdoor compressor is able to heat water to 175⁰F. The compressor on more-conventional heat-pump water heaters is located with the tank and typically means cool air is dumped in the house during the heating season. The Sanden’s split system means that there’s no energy penalty in the winter. There’s no electric resistance back up element (comparatively inefficient), so we installed the 115 gallon tank for a high first-hour rating. Also, the larger tank will allow for better tank stratification, which improves the performance of all heat-pump water heaters. For our house the Sanden only provides domestic hot water, but in other houses we’ve used the water heater to provide radiant heat as well.
We think it’s important when we select products to consider their life cycle implications not just their operating performance. That’s why we really like the CO2 refrigerant Sanden uses. It has a global warming potential of 1—compared to commonly used R138a that has a global warming potential of 1,438.
More from the 2018 FHB House project:
- Locally-Sourced Shiplap Cedar Siding
- Why Do Most Passive House Projects Use European Windows?
- Installing Rockwool for Continuous Exterior Insulation
View Comments
Doesn't locating the compressor outside mean that in cold temperatures the heater is less efficient than a comparable unit that is located inside? Does this efficiency hit negate the benefit derived from not dumping cold air into the conditioned interior? I'd assume the net benefit/detriment depends on climate zone. If course, as is noted, there are other advantages to the Sanden heater. Getting a noisy appliance outside is a plus, especially in a small house.
Yes, there's a good chance they'll be as dependable as refrigerators....as long as they don't add on an ice-maker to the outdoor unit.
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Liked it. good work..
I think you intended to compare to R134a.