[Greenbuilding] small in line heat pump

[John Straube]

Just FYI, the small (2 ton and under) ducted heat pump systems that work at near or below 0 F that I have looked at over the last few years have included

Daikan FTQ-18PAVJU / RZQ-P (the only real air handler unit) and  FDX512 with RXS-12DVJU "Slimduct"
Mitsubushi SEZ-KD25VA among what seems to be a dozen variations, and their ZUBA which solves essentially all of this (but costs 10K or more)  Their hyperheat product, though not very efficient, do work down to -13F and lower.
Fujitsu ARU9RLF up to ARU24RLF or similiar.  Have very good performance to 5F.
Sanyo has some decent ducted units (still around .25" w.c), but all bigger than 2 tons except 26uw72r.
LG seems to lag behind in low temperature (below 5F) operation, but that may just be them not reporting their specs in detail: I only have cooling experience with LG units and they seem good.

Some of these come close to doing what you might want, eg some have static pressure capacity of up to 0.35" (still less than North American standard units which give over 1" wc) and most have fans that are in the 3 cfm/W or better range.
It has always been cheaper and higher performance in my experience to use these small duct systems as intended: with a small direct duct run to one or two rooms, drawing from a third.  Use 2, 7 kBTU/hr units (as in the Fujitsu model I mentioned) and you get really good performance.
I am pretty sure there are some good combinations out there, and I keep me eye open because eventually we will have one.

For price and performance it is hard to beat wall mounted units: just bought a 12 KBtu Fujitsu (rated SEER26) that has over 12K output at -5F for $1300 (the ASU12RLS2, COP=2.45 at 5F and COP=3 at 23F).  Separate HRV ducting makes all kinds of sense at those prices but people may need to live with wider temperature variations between rooms with those wall mount units.

The nice idea of a central handler, a modulating low-temperature heat pump with peak outputs of 9 to 20 kBtu/hr, able to integrate an HRV, and circulate air through a good filter and modest-sized duct system over a typical 1400-2000 sf two storey house at cost less than twice that of a standard furnace/AC eludes us.  The product could be made in a heartbeat if any of the producers wanted to, but that is the problem, not technology. Nobody is willing to make a 20 kBTU/hr furnace for gosh sake; the smallest condensing gas furnace with ECM fan motor is 40 kBtu/hr and has been for almost 20 years.


Prof. John Straube, Ph.D., P.Eng.
Faculty of Engineering
Dept of Civil Engineering / School of Architecture

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