Heat pump water heater moisture issues
Recently saw this article from BSI:
BSI stuff is usually well researched but there are some real issues with the article. When they are doing the calculations for heat extracted from the house air, they don’t take into account that all exterior walls are radiating heat into the house, a large volume of air like that barely budges in temperature.
They also don’t mention that a HPWH in a 60F dewpoint place is actually dehumidifying the basement, the issue is there is not enough mixing with house air.
It is good they are pointing out that there can be issues with installs and installation instructions could be better to avoid some pitfalls.
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I read the article and didn't find anything I disagree with. Can you excerpt particular passages you have issues with?
As a side note, I wish he had taken up the issue of outdoor venting of HPWH's. Somehow people seem to have gotten the notion it's a good idea; it's not.
Fig2 shows a wall with 45F air on one side. With a properly sized enclosure with sufficient wall area, the walls radiate heat, so the air won't be at 45F assuming house at 70F. Locally, if the exhaust is blowing at a wall directly, that wall will be cold though but that can be fixed by ducting or turning the water heater.
"The best-case scenario for installation in an enclosed space
would be a closet the size of an entire house. For example,
a 1625 ft² room with 8’ ceilings has an air volume of
13,000 ft³. If that volume of air enters the water heater at
an airflow rate of 120 cfm (typical for many HPWHs)"
This bit also doesn't work in real life since the house air is touching exterior surfaces plus we also have your favorite thermal mass also adding heat.
A HPWH will not be able to budge the temp of any large volume simply because it is essentially only a 4000BTU AC unit, which I know will barely cool a larger room.
Some of the text also implies that HPWH won't work no matter the room size. This is absolutely wrong.