GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Ducted split or heat pump model advice

John Ranson | Posted in Mechanicals on

Hi,

My house is built, and the manual J is 26219BTU @ 6F design conditions, done by a independent energy efficiency design firm. The house is near rochester NY, zone 5.

The heating system will be ducted due to my preference for closed bedroom doors. Can anyone recommend a ducted split system or air source heat pump that will have good load modulation and give the output needed?

I’m looking at the Mitsubishi  PVA-A30AA7 & PUZ-HA30NHA5 pairing, but the modulation doesn’t seem great.

Best regards,

John

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. Patrick OSullivan | | #1

    PVA-A30AA7 is more of a traditional air handler, so the lack of modulation doesn't surprise me.

    A bit more info would be useful. Some general information about the size and shape of your house will be helpful in determining if one or more compact ducted units would be more suitable.

    And though I suspect your sizing might be driven by the heating load, perhaps you can share your Manual J cooling load as well.

  2. Jon R | | #2

    Be careful - a wide modulation range doesn't mean much of anything (why do you want it?). It might provide worse dehumidification and worse efficiency than a system with less modulation (or possibly even a single speed system with no modulation).

    Do give some preference to a system that will allow some zoning without creating problems - loads vary and zoning can improve comfort.

  3. Expert Member
    Akos | | #3

    John,

    This is your best resource to figure out your options:

    https://ashp.neep.org/#!/product_list/

    If you get a decent duct design done up front (less than 0.4" water drop), you can go with a pair of low profile ducted hyper heat units to get some zoning.

  4. John Ranson | | #4

    Here's the basic house layout.

    The cooling load is 12675BTU @85C design temperature. This is one reason why I want a unit with good modulation. Any heat pump that can heat the house will probably be around 2x oversized for cooling.

  5. Expert Member
    Dana Dorsett | | #5

    The 2.5 ton mid-static Fujitsu mini-duct unit (has blower power comparable to full-sized air handlers) would cover those loads, with about a 3.5:1 turn down in cooling mode at your 1% outside design temp of ~85F:

    https://ashp.neep.org/#!/product/25351

    The heating capacity margin is a bit thinner than the PVA-A30AA7 & PUZ-HA30NHA5 though:

    https://ashp.neep.org/#!/product/29005

    The 3 ton Fujistu mid-static mini-duct unit has a big bigger modulation range, and a bit more heating capacity than the 2.5 ton Mitsubishi solution at temperatures that matter:

    https://ashp.neep.org/#!/product/25352

    The max static pressure ratings of that series Fujitsu mini-duct cassette is the same 0.8" w.c. as the Mitsubishi PVA air handlers. Duct systems designed for one will work with the other, except for the details at the air-handler/cassette unit itself.

    https://hvacdirect.com/hvac/pdf/36RGLXD.pdf

    http://meus1.mylinkdrive.com/files/PVA-A30AA7___PUZ-A30NHA7-BS_Product_Data_Sheet-en.pdf

  6. John Ranson | | #6

    Thanks Dana.

    The 30kBTU Fujitsu unit looks great. I can't find a technical manual for it, but I found one for the AUU30RGLX, which uses the same outdoor unit. It confirms the maximum heat output at 5F should be sufficient for my needs.

  7. Expert Member
    Dana Dorsett | | #7

    While the ARU30 would do, the ARU36 isn't oversized for the heating load- it's only a 1.25x oversize factor using the max at +5F, and that doesn't account for defrost. The ARU36 also modulates about 10% lower than the ARU30 in cooling mode at the temperatures that matter, per the NEEP data sets (which sometimes contain typos and other errors.)

    Even if your Manual-J has slightly inflated load numbers the 3-tonner is probably the "right" one. They both modulate down to the same 9.6K @ +47F - it's not giving up any modulation range in heating mode to go with the ARU36RGLX.

    With either of them you're going to have to run it in "DRY" mode to keep humidity bounded on the stickier days. The COP at minimum-modulation in cooling mode is an insanely high 15+ at 82F, which usually translates into very little latent cooling, and your calculated cooling load isn't much higher than the minimum modulation.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |