Mitsubishi HVAC -- residential v. commercial systems?
October 11, 2019 4:15 PM   Subscribe

HVAC nerd question: long tragic story how this happened, but our Mitsubishi installer just completed the job for our house (New York City, northern Bronx). Only then did we learn what actual systems were installed: a commercial system in a residential deployment.

It's 2x PUMY-P60NKMU outdoor systems for a 3000 sq foot house, hooked up to nine PKFY-P12NHMU-E2 units (some 12K, some 9K) for the various small areas/rooms in the house. They seem to work ok, and seem to be sized ok, though they are noisier than we were led to believe when we were shopping around.

In researching the noise, I discovered that these are P-series "commercial" systems from Mitsubishi, as opposed to the M-series "residential." Indeed, the residential systems have a Quiet Mode around 19dB as opposed to the 38 or so with lowest fan setting for what we've got.

Questions:
-- why would an installer use the commercial P system in a residential deployment?
-- can anyone explain the real differences between commercial and residential Mitsubishi systems? (Mitsubishi phone reps could not)
-- does this seem like it might be a consequential error?
posted by cloudscratcher to Home & Garden (2 answers total) 2 users marked this as a favorite
 
HVAC engineer here (but not your engineer, not in your state, etc) and I specify systems like these every day. If I were selecting systems for my own home and I had a lot of money to spend on HVAC I might pick similar equipment. If you had hired me to design your HVAC system and told me to give you something very efficient that would give you good control of temperature in each individual room, I might have picked the exact same thing.

The commercial systems tend to be more robust and more expensive, and often offer more features such as low ambient cooling, higher efficiencies, and the ability to provide heat to some rooms and cooling to others within the same system.

Also, those model numbers aren’t straight-up P-series units. The PUMY is marketed for large residential applications. It is an appropriate choice for a residential application.

The rated sound from the indoor units is not outside the range of good design practices. See page 13 here for more granular data on the rated sound levels and see here for more information on recommended design noise criterion levels.

It doesn’t sound like your contractor did anything wrong here, except maybe fail to manage your expectations about sound levels. 19 dB strikes me as really implausible, unfortunately.

If you want to read more about this type of system (which is kinda new and still gets HVAC engineers excited about how neat it is!) a good search term is “VRF” for “variable refrigerant flow.”
posted by beandip at 9:02 PM on October 11, 2019 [6 favorites]


He probably got a better deal on the commercial version; and didn't read deep into the spec sheet beyond the basic BTU and power load specs.

As above; 19dB does seem misprint low.

Worst case scenario; you change out the interior room units for the commercial ones you mentioned; in the rooms where the noise is critical.

Not an HVAC engineer; but with my Type III universal cert; guy could have been thinking for you in getting the more durable commercial units? It does read as a good sized project - lots of tubing; lots of wiring; and certainly not a simple one outdoor unit and two indoor wall units journeyman type of install.
posted by buzzman at 9:11 PM on October 11, 2019 [2 favorites]


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