Helpful? 0

Are you familiar with the ducting option for heat-pump water heaters?

Since Alex has been pointing out the energy advantages of using a heat pump water heater (HPWH), I thought some readers might be interested in the approach I've taken with the technology. Instead of just scavenging heat from where this unit is located, I added duct work and a centrifugal fan to draw air from the two upper level bathrooms in my home so that the heat pump was "seeing" air from the occupied space. I also added duct work on the discharge side. In this installation, in addition to the energy savings, the following benefits accrue:

1) Higher winter time temperature "seen" by HPWH,

2) Improved moisture management in a tight envelope home as significant hot water use is followed by increased ventilation,

3) Demand-based mechanical ventilation based on hot water use, which in turn is related to occupancy, and

4) Summertime 42 F air returned to living space to provide some "free cooling".

Any questions?

Asked by David Bearg, PE, CIH
Posted Sat, 03/15/2014 - 08:33
Edited Sat, 03/15/2014 - 08:54

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2 Answers

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1.
Helpful? 0

David,
As you may know, at least one heat-pump water heater (Air Generate, the manufacturer of the AirTap) allows an option for ducting. Here is a link: http://www.airgenerate.com/ati66dv.html

The main disadvantage of these arrangements is that the duct and fan increase energy use, so the installer has to calculate whether the thermal benefits are greater than the fan energy use.

Answered by Martin Holladay, GBA Advisor
Posted Sun, 03/16/2014 - 06:40

2.
Helpful? 0

Actually I suspect that it's even more complicated than that, as the duct work and fan can increase the temperature of the air stream entering the HPWH and can thereby offer offsetting benefits in overall energy efficiency of the installation.

Answered by David Bearg, PE, CIH
Posted Sun, 03/16/2014 - 09:59

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