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Community and Q&A

Variable-Speed Air Handler Paired with Minisplit-Style Inverter Condenser

Zachary Wilhoit | Posted in Mechanicals on

Climate: 3A W/H.

Project: 2400 sqft 5 ton central air heat pump replacement.

Struggling to find a product on the market that meets the following criteria:

  • Minisplit-style air-source inverter condenser with full heat down to -5F or lower (LGRED, Mitsubishi Hyperheat, MRCOOL Universal etc.)
  • Variable speed ducted air handler

Due to the existing house geometry and air filtering requirements, staying with a ducted air handler is a must. Even concealed duct head units are a no-go.

And -5F full heat performance might allow me to eliminate backup resistance heating entirely in my climate, freeing up a huge amount of breaker space and further improving net energy consumption. We don’t have gas, and geothermal is too expensive.

Problem is, for all systems I’ve found so far featuring a low temp heat capable minisplit style inverter condenser… while the air handlers are typically multi-speed selectable ECM blowers, I don’t think that they are truly variable speed, like premium air handler units from Goodman, Trane, etc. Example product: LG LV480HHV…. Is my understanding correct?

Trane has introduced the XV19 which is about the closest I’ve found so far, but I can’t find any information on its low-temp heating capabilities.

Goodman has the GVZC20, and of course plenty of other US manufacturers have variable speed air handlers mated to inverter condensers with the  traditional US boxy form factor, but as far as I can tell, their low temperature performance are all pretty poor compared to the newest low-temp minisplit style condensers.

I’m guessing it’s probably a bad idea to, say, mate an LGRED inverter condenser to a Goodman variable speed air handler…..

If there is no such product on the market, how much comfort really would I be giving up by going with a multi-speed air handler as opposed to a true variable speed unit?

Thank you for your consideration.

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Replies

  1. Sean Cotter | | #1

    I looked at several of these, including Mr Cool Universal. In the case of the Universal, I don't believe it was the Hyperheat/extra low temp outdoor units. Midea makes HyperHeat units that pair up with the handlers. https://www.minisplitwarehouse.com/product/midea-48000-btu-16-seer-central-ducted-split-hyper-heat-pump-ac

    I don't believe the indoor units are variable speed and the communication between indoor and outdoor units is just general 5-wire, call for heat/cool. The indoor units do some work separately (air temp, humidity, etc) to start moving the air around.

    An older thread about a Mr Cool setup came back alive this week I noticed, someone successfully did a DIY install. This was in Chicago and, unless something has changed or was misrepresented on the Mr Cool site, I don't believe it was a extreme cold model (will run, but not at the best efficiency below 5 above or something).

  2. Charlie Sullivan | | #2

    Just in case you are not familiar with it, the NEEP database, https://ashp.neep.org/, is a great resource for finding units that are good candidates, even though you'll still need to look up more data to find whether it they meet your specific requirements.

    Another option to consider is a air-to-water heat pump, at which point you can go crazy mating it with your preferred air handlers and then layering on whatever controls you want.

  3. Zachary Wilhoit | | #3

    Thanks for the reply. The COP specs at different temperatures on the Midea unit you linked prompted me to dig a little further into the datasheets for the condensers I've been looking at.

    The COP difference at low temps wasn't as large as I expected, but the minisplit hyperheat style condenser moves a lot more heat at a given outside temperature, a difference equivalent to about 5kW resistance heat.

    A shame, because everything I've read suggests that a variable speed (i.e. variable CFM) air handler makes a difference in both comfort as well as energy consumption, if you leave the fan on all the time as I plan to do for enhanced indoor air filtration. (~150W delta 24/7/365)

    However, the COP favors the Goodman unit at high temps, and it's 100F a lot more often here than 20F, much less single digits....

    Trying to estimate yearly energy consumption based on tables of COP, degree days for my house, and thermal resistance of my house sounds like a lot of work, but now that I've seen this table I wouldn't be surprised if the Goodman came out on top between the superior high temp COP and fan=on energy savings.

    https://manuals.totalhomesupply.com/wp-content/uploads/manuals/LGRED-VAHU-Engineering-Manual.pdf

    https://www.goodmanmfg.com/pdfviewer.aspx?pdfurl=docs/librariesprovider6/default-document-library/ss-gvzc206ee64f0022fa6258827eff0c00754798.pdf?view=true

    Does anyone have a recommendation on which to pick? Or any other thoughts on equipment selection re: energy efficiency for an air-source ducted air handler in Texas?

    One possibility is to use one-to-one minisplit cassette units for temp/dehumidification, combined with a separate air handler system for filtration that is NOT mated to a condenser whatsoever. That just feels weird and overly complicated though.

  4. Zachary Wilhoit | | #4

    Thanks for the link Charlie! That looks like a great database, and I'll see if one of those is a variable speed unit.

    A concern with an air-to-water system, impressive though they are from an engineering perspective, would be ease of maintenance and local installer familiarity.

  5. Expert Member
    Akos | | #5

    Most mini split manufacturers refer to the unit that looks like a standard furnace as either high static or multi position air handler. Almost all manufactures have something in their product lineup.

    Common ones, Mitsubishi Zuba central, Daikin Skyair, Fujitsu Multi Position Air Handler. There are some pretty good systems as well from domestic manufactures such as Carrier's Greenspeed units.

    The Midea unit linked to earlier are great value and performance. I recently install a pair of their mid static ducted units, simple install, well built and are working great.

    Usually the choice comes down to what brand your installer is comfortable with and which units have local support. I would not get lost in the weeds chasing COP if nobody will install the unit you select.

  6. Jon R | | #6

    > a variable speed (i.e. variable CFM) air handler makes a difference in both comfort ...

    Quite often not. While they could match CFM for compressor output and desired dehumidification, they don't. Excessive CFM/ton causes poor dehumidification comfort, often much worse than a single speed fan and compressor unit.

  7. Zachary Wilhoit | | #7

    Hi Akos -- agreed, I'm only looking at brands/systems our local installers would be familiar with.

    Hi Jon -- consider the Goodman AVPTC and Trane TAM9. When paired with the correct communicating condensers, I believe they do match CFM to compressor load. And when paired with noncommunicating condensers (for example, a 2-stage unit), I believe you can still generally expect some or all the following behaviour depending on the model:

    - High CFM value for high stage
    - Low CFM value for low stage
    - Selectable CFM for fan only calls
    - Selectable fan profiles for dehumidification calls
    - Smooth ramping of fan speed between different calls

    That last point is particularly useful for our use case, as we have family members that hate it when the HVAC vents suddenly start/stop blowing on them at full speed.

    Please let me know if any of my understanding here is incorrect!

    pg 14-15
    https://hvacdirect.com/hvac/pdf/AVPTC-Install.pdf

    pg 45
    https://resource.gemaire.com/is/content/Watscocom/Gemaire/american-standard_tam9a0c60v51da_article_676251580913610_en_ii.pdf

    1. Jon R | | #8

      Lots of settings, but I couldn't conclude anything for sure for a variable speed compressor and variable speed AH fan.

  8. Jeff Wasilko | | #9

    Have you looked at the Mitsubishi Hyperheat outdoor units and SVZ-KP indoor units?

    The indoor units are true variable speed. The fan on the indoor unit ramps up slowly. We're using the Thermostat Interface (PAC-US444CN-1) which ramps up the indoor unit and outdoor unit at ~5 minute intervals.

    http://ld3.melsup.com/sfiles/Application%20Note%203044%20ME%20-%20Thermostat%20Interface%20Sequence%20of%20Operations.pdf shows the full operation of the interface and how it stages the indoor/outdoor units.

    We've got a 48k btu outdoor unit and a 30k & 24k btu indoor units. We couldn't be happier. They're very quiet and heat evenly.

  9. Expert Member
    Akos | | #10

    You are in warm enough climate that you probably don't need a hyper heat unit even without backup coils.

    None the less, the hyper heat units do have significantly better cold weather performance and usually come with base pan heaters.

    Even in milder climates, there are plenty of nights when temperature will hover near freezing and without a pan heater the outdoor unit could freeze up especially if the air is humid.

    You can see the difference between the units:

    https://ashp.neep.org/#!/product/34582
    vs
    https://ashp.neep.org/#!/product/28144

    A 2.5 ton hyper heat delivers about the same heat as the 4ton unit at 17F.

    Whichever unit you go with, the important part is to make sure the unit is sized correctly as most hvac systems tend to be grossly oversized.

    A right sized unit will be cheaper to buy, run more efficiently, be quieter and provide much better comfort than the typical 2x to 3x oversized units.

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