Understanding Heat pump Water Heater Specs
When a water heater specification says that, e.g., the UEF is 3.39 and the recovery rate is 21 GPH, which mode(s) are those for? Are they both for the default mode? Or are they allowed to pick and choose the best-looking mode for each value so the UEF is 3.39 if you use the heat pump only mode but the recovery rate is 21 GPH only in the HP + electric mode?
Here are some example specifications:
Bradford White AeroTherm: https://s3.amazonaws.com/bradfordwhitecorp/wp-content/uploads/brochure_aerotherm_athrmb.pdf,
Rheem PROTERRA https://s3.amazonaws.com/WebPartners/ProductDocuments/FABA4C3B-688B-48B7-820D-C2179C539B04.pdf
The main impetus behind the question is wanting to know the actual first hour and recovery rates we’re likely to see in practice so we can ensure the unit is the right size and have an idea of how long it’s going to be running each day.
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See https://www.law.cornell.edu/cfr/text/10/appendix-E_to_subpart_B_of_part_430
"This operational mode shall be the default mode (or similarly-named, suggested mode for normal operation) as defined by the manufacturer in its product literature for giving selection guidance to the consumer. For heat pump water heaters, if a default mode is not defined in the product literature, each test shall be conducted under an operational mode in which both the heat pump and any electric resistance backup heating element(s) are activated by the unit's control scheme, and which can achieve the internal storage tank temperature specified in this test procedure; if multiple operational modes meet these criteria, the water heater shall be tested under the most energy-intensive mode."
UEF is tested on "default" mode, which uses both heat pump and electric resistance. However, based on the "medium-usage" draw testing pattern, it is very unlikely that the resistance heating elements will be engaged much.
Generally speaking with HPWH, it's better to oversize and set a lower hot water temperature. That increases efficiency and lowers the chances of running out of hot water or running resistance elements.
Thank you! That's what I wanted to know.