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Community and Q&A

Cold Climate Central Ducted Heat Pump Recommendation

j_prescott | Posted in General Questions on

Hello,

I have a net-zero-ready renovation project where we’ll be selecting HVAC equipment soon. We have low overall loads but a need for distribution with a zone for each floor of a 3-story house.  So, I have a “problem” with low loads and a need to select ducted cold climate heat pump equipment (ducted minisplits?) that won’t be oversized.

What manufactures / equipment would you recommend for air-to-air cold climate heat pumps for my scenario?

Here are the details. 

Net-zero-ready renovation of a historic home in southern Vermont (zone 6).

HVAC design (Manual J, S, D, etc.) will start soon. My HVAC (and plumbing) contractor is agnostic about specific equipment vendors. We expect to purchase equipment from our local supply house (FW Webb here in New England) but can consider other sources too. Vendors who have good records for reliability, and parts and support availability when needed are preferred.

I’ve performed some preliminary load calculations and expect my heat load will be somewhere around 35~40k BTUs/hr total for 4,000+ sq. ft. of living space. The house has three floors of living space (1st, 2nd, 3rd floor) and lots of smaller rooms. Our plan is to have ducts in the basement with an air handler to hit the first floor and ducts around the perimeter/eaves of the 3rd floor with air handler(s) on the 3rd floor to hit the 2nd and 3rd floor rooms.  Basement is in the insulated envelope and the heat load includes it, but it’s storage/mech only and we don’t plan on conditioning it directly.

I anticipate we’ll end up with either an air hander for each floor or, perhaps, one for the first floor and a single air handler with a zone control for the 2nd and 3rd floors. 

Here are the preliminary heat load calcs for each floor (= each zone). This is from spreadsheet work, not an actual Manual J (yet), with -4F outdoor, 70F indoor design temps.
3rd Fl: 11k
2nd Fl: 10k
1st Fl: 16k (6k of which is basement)

So, yeah, about 1 ton each for the 2nd and 3rd floor, and 1.5 ton for the 1st floor including basement load.  If we had an open floor plan this would probably be a “just get a mini-split for each floor and call it a day” scenario.

What do you recommend? Are there some ducted mini-split options that would be a good match for this house?

Thanks!

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Replies

  1. insaneirish | | #1

    Mitsubishi and Fujitsu tend to be the highest regarded units. Daikin is also liked by a lot of folks. The rest of the manufacturers seem to be okay usually, but get less play.

    You can likely cover the 2nd and 3rd floor with a single unit. If you do that, I wouldn't try to zone anything, which adds lots of complexity. Low load houses with well designed ducts will balance pretty well without zoning. And if you were thinking of zoning because the 3rd floor isn't used that much, I think the savings of not conditioning it full time will be negated by the complexity of zoning or a third system.

  2. Expert Member
    AKOS TOTH | | #2

    I think the more important thing than brand (assuming all proper cold climate units) is about local support. You want to pick a brand that your installer is familiar with and you can get it serviced down the road if needed.

    A heat pump in your climate might be outside the comfort zone of lot of installers, you might get magical pricing where the cost well above a furnace+AC. The BOM cost of even the best cold climate heat pump is a couple dollars more than a furnace+AC plus if you take into the account the lack of gas piping, venting and CO alarms, it is cheaper. One way to work around this is to only have the HVAC tech quote installing the equipment and have the ducting and commissioning done by others. This will more likely get you closer to time+materials type of quote.

    Outside of the main players previously mentioned there is also Gree and Midea. Gree is the OEM for GE cold climate units and Midea for Carrier. Both make products with excellent specification. I've used Midea ducted units in a slightly warmer climate than you (north edge of zone 5), great performance and better price point than most.

    In terms of comparing units, this is a great resource:
    https://ashp.neep.org/#!/product_list/

    Once you select a couple of units you'll have to do some digging for the engineering manuals to see the performance in your climate. Most cases you can get by with no strip heater but adding a small one in for those polar vortex days is not a large additional cost.

    A couple of general pointers. If you are looking at multiple indoor units, go for dedicated outdoor unit for each. These tend to be more efficient and have much better modulation range than most multi-splits, plus you get a bit of redundancy.

    A well insulated and sealed basement should be very low heat loss. Running the basement at 60F or 75F would barely budge your yearly energy usage but running it warmer will make the floors above much more comfortable. Think of it as budget heated floors.

    Figure out what you are looking to do for ventilation as it will also drive your zoning a bit. Generally for two air handlers, you are looking at two ERVs which adds a bit of extra cost.

    My preferred method of ducting ERVs with fully modulating heat pumps is a hybrid ducted setup. This has the ERV delivering fresh air to the return of the air handler and the stale air pickup is ducted to kitchen, bathrooms and basement. Depending on the overall size of the ERV, this can save you between 2 to 4 bath exhaust fans which helps offset some of the extra ducting costs. This setup works best if you select an auto balance unit such as Zehnder Q series, Broan AI or Panasonic Intellibalance.

    The air handler on modulating units runs 24/7 so it will help with distributing fresh air through the house plus it also tampers the ERV fresh air supply which can get chilly even with a high efficiency unit in those sub zero temperatures.

    1. cococchio | | #4

      Hello Akos I am thinking to use the hybrid ERV system you just described with a single ducted VRF heat pump in a 5ooo SQFT 3 story house in 4a zone and 2 zones (2 floor and 1+basement).
      With a ducted high pressure air handler, the flows from a ducted ERV can be affected by the air handler so going with ERV fully ducted might not make sense because actual room by room flow rate will vary depending on the status of the air handler.
      Going back to ERV selection. You mentioned Zehnder Q, Broan AI and Panasonic Intellibalance. The respective max flows are about 350 CFM, 160CFM and 200CFM. For my house only the Zehnder would provide enough CFM to roughly double the airflow the 170 CFM ASHRE requirement in boost mode. So my question is: do you use boost mode in your design? I am trying to avoid two separate ERVs (not even sure it is a possibility with a single air handler). Zehnder seems like the only option but does Zehnder design hybrid ERV systems?

      1. Expert Member
        AKOS TOTH | | #5

        "single ducted VRF heat pump in a 5ooo SQFT"

        I don't think that is the best idea. I would split the house up on two air handlers and use that as zoning.

        I'm not following your question. With any type of zoned setup, you still have to watch flow rates for zones that are off. You don't want to fully shut a zone off when not calling for heat, enough airflow should be maintained to ensure air changes in all the rooms.

        There is no requirement for boost, not sure where this is coming from. First you need enough airflow to meet code. From there you look what that unit has on max. You take that max and take out about 60 CFM for your kitchen stale air, 15-30CFM for a basement, what is left over you can use as bathroom exhaust. To clear a bath typically you want between 50 to 100CFM, so this means most ERVs are good for 2-4 bathrooms. The rest of the bathrooms need an exhaust fan.

        1. Deleted | | #8

          Deleted

      2. deucevantage | | #15

        Zhender is NOT your only option..you could buy 2-6 Panasonic intellibalance ervs for price of average zhender installl!

    2. aunsafe2015 | | #6

      "My preferred method of ducting ERVs with fully modulating heat pumps is a hybrid ducted setup. This has the ERV delivering fresh air to the return of the air handler"

      ERV delivering fresh air to the HVAC return could be problematic in humid climates during the summer months. It would be picking up lingering moisture from the a/c coils and delivering it back into the house, no? Kind of like running the HVAC fan all the time.

      1. Expert Member
        AKOS TOTH | | #7

        A properly sized modulating system should be providing some minimal cooling all the time so the system blower is running, the air from the ERV won't matter.

        Say we do shut down the air handler. The pressure drop across a the air handler filter, A-coil and supply ducting is much larger than the return, most of the fresh air would be supplied to the house through the return grill. A small amount would be sent through the supply but I doubt it would be anything major.

        The hybrid ducted ERV is definitely not a good idea with interlocked single stage AC system. In that case air handler will run the same time as the ERV and if there is no cooling need, re-evaporation could be an issue. Definitely not great for humidity removal during shoulder season.

        1. aunsafe2015 | | #9

          Interesting, thanks for the reply. You've convinced me.

    3. maxwell_mcgee | | #11

      Akos -- I'm curious if you can elaborate on your preferred ERV ducting methodology. From what I've read, it seems that the gold standard is a separate dedicated duct network for the ERV that's not connected to the rest of the H/AC ducting. (e.g., a Zehnder Q with its own ducting)

      Is your preference driven by cost / complexity complexity considerations (i.e., it's easier/cheaper to do it this way?) Or is this truly a better option?

      1. Expert Member
        AKOS TOTH | | #12

        Maxwell,

        A fully ducted ERV is always the best setup if the budget allows.

        The hybrid ducted setup gets you most of the benefits of a fully ducted erv for much less cost. It also conditions the fresh air supply which can be a fair bit bellow room temperature in cold climates and a bit muggy in the summer time in places with high humidity.

        For the money saves, when using a modulating heat pump, I'm strugginging to come up with a reason why not to use it.

        Maybe I should start calling the hybrid ducted ERV and modulating heat pump as pretty good house HVAC system. Not passive house, but good enough for us normal folk.

        1. maxwell_mcgee | | #13

          That makes sense to me. Thank you!

  3. adrienne_in_nj | | #3

    Akos,
    Can you elaborate on how you would find somebody to install the ducts and do the commissioning only? I assume that most of these workers are either licensed HVAC contractors or they work for licensed HVAC contractors? And either the tech installing the equipment or the contractor installing the ducts might be upset that they weren’t offered the entire job. I can see how a general contractor might have somebody in mind because of existing relationships, but how would an ordinary homeowner accomplish this?

    1. deucevantage | | #16

      Good luck finding a contractor who will do ductwork but not install HVAC units-most tors hate-and are dropping-duct installation. They want to quickly install equipment, get you in a service contract and sell you your next unit in 15 years.they HaTE ductwork-it requires real manual skill, hard labor and climbing ladders squeezing into tight spaces , and in the dc metro arae, less than 5 % of HVAC contractors even do this when you DO buy equipment from them !!

  4. walta100 | | #10

    I have the 3 stage Rheem 17 SEER heat pump that heats my house down to 9°F with the strips locked out.
    It is not listed in the NEEM index but its 20 SEER cousin is, the only differences are software and the outdoor fan motor.

    https://www.rheem.com/group/rheem-heat-pumps-classic-plus-series-three-stage-rp17

    Walta

  5. j_prescott | | #14

    Thanks for the replies and discussion here. I've been evaluating options with the help of the NEEP site. I've modeled what modulation and heating design coverage would look like for my expected loads for mid-static ducted single zone options from several manufactures that my HVAC contractor can source via their supply house.

    Mitsubishi has a great reputation on GBA, however the modulation for the mid-static ducted options doesn't seem quite as good as some other options I'm seeing.

    GE/Haier has received some positive feedback from contractors here, but their stats on NEEP seems to shows some challenges with minimum output / modulation vs what I need. Frustratingly, their sales materials seem to claim lower mins (they claim an output range... but without any indication of the temp where that range is applicable) and, more helpfully, their max outputs down to -22F. The number I'd really like to validate is the min output at 47F and how that will impact cycling during shoulder seasons but I've yet to find that in their materials. NEEP's data seems to indicate their 47F minimums are somewhat high --> turndown ratios are not what I would hope them to be.

    Bosch, per NEEP, seems to have good modulation, but their then COP numbers are not as good as others in comparison across the board, and look pretty bad at the low end, dropping to <1 at 5F!

    Finally, Samsung seems to have some very intriguing options in their light commercial line - pan heaters, great modulation / turn-down, decent COP numbers, etc.

    Is anyone able to offer some perspective on these, especially Samsung?

    Thanks!

    PS - Some links to the Samsungs I'm considering for loads in the 9~12k range:
    https://ashp.neep.org/#!/product/53967/7/25000///0
    https://ashp.neep.org/#!/product/53968/7/25000///0

    1. Expert Member
      AKOS TOTH | | #19

      Mini splits are pretty mature technology well before they become popular in North America, as long as you can get support I would not worry too much about brand. I'm starting to see some Sumsung units installed around me, hard to compete in market where almost everything is Mitsubishi/Fujitsu.

      Mid static units are great for small space but they could be challenging to install as they don't look like standard air handlers. High static units are a bit bulkier but they are a more straight forward install for most HVAC techs.

      The low turndown on lot of units at 47F are mostly a problem with high efficiency at low load, which is a good thing. There is only so low most compressors will turn down (~200W to 500W) and when you run units at such low load with the very high COP they put out a lot of heat. Fujitsu/LG/Samsung/Midea seem to do a better job with this and generally have much lower turndown at 47f.

  6. greenright | | #17

    You really should look at the Fujitsu Airstage. Better numbers than the Mitsubishi and a full VRF with great turn down which is what you are looking for. The only thing currently Mitsubishi has on Fujitsu is marketing.

  7. deucevantage | | #18

    Greenroght- what is “full turn down “ refer to. Also do carrier trance Lennox make/sell full vrf models? Is a variable speed scroll compressor coupled with a variable spied ecm fan always “vrf”?

    1. greenright | | #20

      All inverter- driven systems are de facto VRF as the compressor has variable rpm and consequently variable refrigerant flow. However in hvac lingo full VRF is when the expansion valve is usually in the head (and not in the condenser) and is a modulating type- ie not just “on” “off” but has different degrees of open and corresponding btu output. The fan speed in the head has no bearing on VRF. The Fujitsu VRF has a turndown of 2.5 to 3. Mitsubishi also has full VRF (the PUMY series), but is at a (much) higher price point. Also Fujitsu has some pretty low BTU heads/ cassettes/ ducts that can be matched to smaller rooms.

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