Replies

1. 
   Ductme | May 13, 2018 06:34am | #1

   Would also do a PVA30/PUZ30 attic setup for 2nd floor (3 bed 2 bath) of our colonial. These units seem better than the MVZ/MXZ, am I missing something? Doc for MXZ is too big to attach: http://meus1.mylinkdrive.com/item/MXZ-4C36NAHZ.html .

   Thanks for your help!

   Scott

   
2. GBA Editor
   Martin Holladay | May 13, 2018 06:38am | #2

   Scogan,
   Common usage is to use the word "minisplit" for both ductless minisplit systems and ducted minisplit systems. But if you have a specific question about which units qualify for a Massachusetts loan program, the obvious way to get an answer is to contact someone who administers the loan program to ask for a clarification.

3. 
   Ductme | May 14, 2018 10:20am | #3

   Thanks Martin. I have tried contacting them and they are unable to give clarification until an application is submitted. I'll have to just get an estimate, submit an application for the loan program and see what they determine the system as. Then I guess I'll have to appeal it if they call it a mini-split!

   Thanks,
   Scott

4. Expert Member
   Dana Dorsett | May 14, 2018 03:53pm | #4

   The PVA and MVZ air handlers should qualify as central heat pumps every bit as much as a modulating Bryant Evolution or Carrier Infinity w/Greenspeed. The differences are primarily cosmetic- the orientation of the coils and fan in the outdoor unit.

   Get a competent qualified third party to run an aggressive Manual-J load calculation for EACH zone separately.

   With both the 2.5 ton PVA-A30AA7 / PUZ-HA30NHA5 AND a PVA-A36AA7 / PUZ-HA36NHA5 system in the house you're looking at a huge oversizing factor that will take away from both efficiency and comfort. The modulation range is not infinite, and it's better to size them where they modulate most of the season, even if it means that at the 99% outside design temp it might need the heat-strip options to cover the additional load.

   Just one PVA-A36AA7 / PUZ-HA36NHA5 can deliver 38,000 BTU/hr @ +5F, which is more than the heat load of my entire 2400' 2x4 framed house + 1600' of insulated but not directly heated basement at +5F. And at +47F it's minimum modulation is 18,000BTU/hr well above my heat load at +47F. That means it would only modulate during the winter months, and then only if it's the sole heat source for the house (which it could be.) The minimum output of the PVA-A30AA7 / PUZ-HA30NHA5 at +47F is also 18,000 BTU/hr, which is half my design heat load. With a pair of them at my house they would effectively never modulate, and only cycle on/off, which is bad for efficiency, bad for comfort.

   The MVZ air handlers on an MXZ compressor should qualify as a central heat pump too, but unlike the PVA/PUZ setups there is no modulation, which makes sizing it correctly even more critical, since you want them to run nearly continously during the coldest weather for maximum comfort.

   If you have a heating history with your oil burners, run a fuel-use heat load calculation, which can be used to sanity-check the Manual-J. The loads for the 2 zones added together should add up to something similar to your fuel-use calculation. For details see:

   https://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/out-old-new

5. 
   Jon_Lawrence | May 14, 2018 10:39pm | #5

   Dana,

   Why is there no modulation with the MVZ/MXZ combination? The MXZ submittal shows a capacity range down to 7,200 BTU's. If I recall, the linear expansion valves are located in the branch boxes and if this is a single indoor unit with no branch box, then I could see how the refrigerant flow could not be throttled back, but couldn't the compressor speed at least be reduced since it is inverter driven?

6. 
   Ductme | May 15, 2018 08:12am | #6

   Great info thanks Dana! I will try the fuel use heat load calculation. My other option was SLZ ceiling units for each bedroom, capping off ductwork to the 2nd floor, still with a PVA or MVZ for 1st floor/basement. I have been told by several contractors now that the ducts are too small and would never get the airflow needed on the 2nd floor to effectively cool and remove humidity of i had just one heat pump/air handler. I like the idea of individual zones for each bedroom, but long term just sounds like more potential repairs. That's why I was thinking air handler in the attic, but now I'm leaning back towards the SLZ's, PVA, and AeroSeal 1st floor ducts. Depending on my load calculation, the MXZ-48 might handle an MVZ and 3 SLZ units. SEER is 16.8 and would qualify for the heat loan, again only if it is a "central heat pump".
   Thanks for all of your expertise. I'm just an auto tech trying to figure out this large, long term investment.

7. 
   Ductme | May 15, 2018 08:45am | #7

   Also considering the new MLZ ceiling units that fit between joists, saving on some labor.

8. Expert Member
   Dana Dorsett | May 15, 2018 11:59am | #8

   When you run the room load numbers, and you'll see that the bedroom loads are small relative to the output of MLZ or SLZ cassettes, which means a LOT of cycling on/off, with lower comfort & efficiency. The head/cassette per room approach leads to truly grotesque oversizing issues.

   MXZ compressors are not full-on VRF systems. They will support a number of different heads/cassette capacities, but as I understand it even those heads/cassettes that can modulate when married to a dedicated compressor do NOT modulate when on an MXZ compressor. That means the heads have to be reasonably sized to their room/zone loads to hit the efficiency numbers, and provide reasonable comfort.

   For very small loads like individual bedrooms you'll be better off using a mini-duct cassette sized for the combined load, whether it's on it's own modulating compressor, or an MXZ multi-split. Sizing the heads/cassettes to the room/zone loads becomes even more critical when they aren't modulating. An FH09NA mini-split on a dedicated compressor (not a multi-split) will modulate between 1600 - 18,000 BTU/hr @ +47F, an 11:1 turn down ratio, which offers a lot of flexibility. But when on an MXZ compressor it's locked to the step size capacities of the compressor, with no real modulation.

   Unlike the MVZ air handlers, the PVA air handlers are fully modulating, but unlike most mini-splits they don't have a very large turn down ratio. It varies from model to model, compressor to compressor, but for PVA/PUZ systems it's typically between 2:1 and 3:1. If you oversize a system with just 2:1 turn down ratio by even 50% it almost never modulates- it can be better (higher seasonal efficiency and more comfortable) to undersize it slightly for the 99% design load, and add the properly sized heat-strip option (there are several sizes) for augmenting capacity for the coldest weather. Sized to where it's still modulating during the shoulder seasons it'll deliver a COP of about 3.5, but when cycling it won't be much more than 2.5. Using heat strips trades a hit in efficiency for the coldest few percent of winter hours against higher modulating efficiency during the bulk of heating season hours.

9. 
   Jon_Lawrence | May 16, 2018 08:02am | #9

   Thanks Dana. It has been a frustrating task trying to design a multi-zone system for my current project that will modulate more often than not. I will post a new thread with the specifics.

10. 
    Jon_R | May 16, 2018 09:17am | #10

    Also be careful of the fan modulation rate (which effects AC dehumidification/comfort). For example, only 1.4:1 on the PVA-A36AA7.