GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted Hamburger/Search Icon

Community and Q&A

Fujitsu Multi-Position Air-Handling Unit

Patrick OSullivan | Posted in General Questions on
I’m trying to find the goldilocks indoor unit for part of my home (NJ, climate zone 4A). Total load calc is 19,306 Btu/h (heating) and 15,947 Btu/h (cooling). Air flow is 741 cfm @ 0.6 in. wc.
I do not want to oversize the system. At first glance, an 18,000 Btu/h unit would seem to be most appropriate, but it seems none of them can produce the required airflow for this situation. The downside of stepping up to 24,000 Btu/h is that the modulation capability of many of those units seems to not be ideal.
Another ‘design constraint’: if I can get to 18 SEER, 12 EER, 10 HSPF, and COP of 1.75 @ 5 F, I get $2,000 from the state.
I had thought the Fujitsu ‘mid-static’ unit (24RGLXD) was going to be a good option, but it misses out on the SEER requirement for the rebate.
Enter the AMUG24LMAS, a unit that is more like a traditional air handler, but seems to have decent modulation characteristics (minimum heating of 5,400 Btu/h @ 47 F).
Has anyone seen these in the wild or heard anything about them? Information is scarce online (I can’t even find a dealer that advertises selling it), so I’m wondering if it’s new product that’s not really made its way out yet.
Also open to recommendations of other units I may have missed in my research!

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. Expert Member
    Akos | | #1

    The CFM requirement is just for sizing your ducts. You size the unit for the heat load. So if the 1.5 ton unit works, I would go for it.

    For mid static units, you can also check out Mitsubishi, LG or Midea.

    If this is a new build, it doesn't take much to decrease the duct losses a bit, which can get you down to a low static unit. There are many more options for these and are cheaper.

    1. Patrick OSullivan | | #3

      > The CFM requirement is just for sizing your ducts.

      Well, at the end of the day, doesn't the system need a certain volume of air at a certain temperature in each room to adequately balance the heat flux in/out of the envelope?

      So, there must be some minimum CFM for each room, and therefore a minimum CFM for the entire zone, and therefore a minimum CFM for the particular unit, no?

      1. User avatar
        Jon R | | #5

        Less CFM just means that the duct air has to be hotter or cooler to satisfy the load. And with cooling, a common problem is too much air (unless some of it bypasses the coil).

        Too little air will effect efficiency and can cause room-to-room balance to shift excessively (although that often happens anyway).

      2. Patrick OSullivan | | #7

        After I posted this, I think I realized my error. I was thinking of CFM as more of an output from the design rather than as an input to it. I think I should be instead thinking in the sequence of:

        1. My design load is X Btu/h per room
        2. The sum of the design loads for the zone is Y Btu/h.
        3. The indoor unit selected provides up to Z Btu/h capacity by means of Q cfm of air at R in. wc.
        4. Ducts then get sized to flow the proportional amount of Q per room without excessive pressure loss.

        1. Expert Member
          Akos | | #8

          Exactly.

  2. User avatar
    Jon R | | #2

    A spec to consider is how well the air handler matches the compressor output (CFM/ton) at low cooling loads. Most do poorly, almost eliminating dehumidification. But they don't publish this, so you don't know until you notice the dehumidifier running.

    1. Patrick OSullivan | | #4

      If they don't publish it, what's the best way to evaluate it? :-)

      1. User avatar
        Jon R | | #6

        One can get some clues by looking at the compressor modulation range and compare to the air handler modulation range. But then there are things like "dry mode" and frequent manual adjustments.

  3. Jonathan Lawrence CZ 4A New Jersey | | #9

    Rebates aside, I have 2 - 12RGLX's in a 1:1 setup serving my 2nd floor and conditioned, unvented attic and I could not be happier with them. They are silent, they sip energy, they do not short cycle and they have done a very good job of managing humidity.

    1. Patrick OSullivan | | #11

      Great to know! Care to recommend your installer? If you'd prefer to share offline, I can provide contact info.

  4. Deleted | | #10

    Deleted

  5. Jonathan Lawrence CZ 4A New Jersey | | #12

    Yes, I can share offline if you provide contact info.

    1. Patrick OSullivan | | #13

      Shoot me an email here if you don't mind: [email protected]

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |