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Community and Q&A

Need help finding an efficient heat pump (with “Hyper-heat”) for a small house

Hugh Weisman | Posted in GBA Pro Help on

I’m an architect (learning a bit about things like the STRETCH Code and HERS) involved in designing a carriage house on Martha’s Vineyard. The town requires meeting a HERS index of 55.  The project is pretty small with only 1,2oo square feet of conditioned space and two bedrooms.

Our initial thought was to use a Mitsubishi multi-zone mini-split system with Hyper heat. But we’ve found that the units with 4 or 5 zones are too big for our needs….only 18,000 BTU/hr at a design temperature of 10 degrees.

Then we thought about doing  a single zone ducted system, but Mitsubshi says that their air handlers with Hyper-heat need a larger ODU. One compromise is a two zone 22K BTU/h system with an 18K BTU/h ducted air handler and a 6K BTU/hr wall unit…But using Mitsubishi, the unit would only have a SEER of 16 and HSPF of 9.65. Our original rating calcs assumed a SEER of 20 and a HSPF of 11….. we would like to get as close to that as possible.

Any suggestions would be appreciated. Another manufacturer? Work-arounds, whatever. Basically, we prefer not to oversize the 18K Btu/h heating, and need that at 10 degrees or less, and we’re agnostic regarding a single zone or five zones.

Thanks, Hugh

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    There's no way to break it up into five zones and have it run efficiently.

    A single zone ducted solution:

    A Fujitsu 18RLFCD is good for over 20,000 BTU/hr at MV type 99% outside design temps of +11F to +13F. It uses the same compressor technology that Fujistu puts in their cold climate minisplits, but isn't sold as a "hyper heating" type. While it doesn't have a pan heater for managing defrost ice build up, at relatively temperate MV wintertime temperatures that's never needed, even during Polar Vortex cold snaps. That unit tests at SEER 19.7, HSPF 11.3 (close enough?):

    http://www.fujitsugeneral.com/us/resources/pdf/support/downloads/submittal-sheets/18RLFCD.pdf

    See the capacity tables on p.17 (PDF pagination):

    https://portal.fujitsugeneral.com/files/catalog/files/(DT)ARU9-18RLF-AOU9-18RLFC2015062.pdf

    At 70F indoors it's good for 19,700 BTU/hr @ +5F, and 18,400 BTU/hr @ -5F.

    Good luck finding a contractor willing to install the thing anywhere but an attic though. With advance planning you may do better than I did a few years ago when mounting one in the basement would have been an ideal solution for a friend's project in Vineyard Haven, but the local installers insisted that they would only put it in the vented attic, above the insulation. The homeowner was under the gun (it was late October and they needed an occupancy permit), and went with a less than optimal 2- ton 3 zone multisplit instead.

    The Daikin and Mitsubishi mini-duct units that size use compressor technology more suited for warmer climates. The 1.5 ton Midea Premier Hyper series ducted unit has somewhat comparable capacity specs to the Fujitsu, (18K @ +5F, only slightly smaller) but local support in Massachusetts might be of concern:

    https://us.midea.com/dam/jcr:858f7d94-63a0-4042-8c35-0df96d1c3ecf/US_PP-RAC_PROD_PREMIER-DUCTED_specsheet.pdf

    The Fujitsu unit can be mounted vertically in a micro-closet no bigger than 10 square feet if the architect designs for it. This one was a retrofit solution in Berkeley California:

    https://uploads.disquscdn.com/images/2ffa6e108a7ded9f51130ff14126239b275b1244b7d53138beb63b4182d68f13.jpg

    https://uploads.disquscdn.com/images/7843213f27734395e6ede8ea696552a8eafd3a2dd7f62c2b61241bb23189a293.jpg

    John Semmehack designs high performance homes using the xxRLFCD series Fujitsu on a regular basis, and would be a good resource to tap when going that route:

    https://www.greenbuildingadvisor.com/profile/user-626934

    http://www.phius.org/NAPHC2018/Think%20Little%20Slide%20Deck%20-%20NAPHC%202018.pdf

    https://think-little.com/home/

    1. Expert Member
      Akos | | #4

      Slight segway here, but something I've been trying to understand.

      I always see insulated interior duct runs south of the border. The only insulated duct run we do here is for HRV inlet/outlet.

      The air leaving the air handler is at worst case 100% rh with a 7C exit temp (say 20C house with 45%rh, so 7C dew point). As soon as the air leaves the AC unit, the interior of the house is warmer, the ducting will pick up some of this heat and will always be above the dew point temperature, so there is no chance of condensation either inside or outside the pipe.

      Am I missing something?

      1. Expert Member
        Dana Dorsett | | #6

        >"Am I missing something?"

        Insulated supply ducts are required under IRC code (whether air conditioning or heating). Most US codes are based on the IRC. Air conditioning ducts aren't always run through fully conditioned space either. In my insulated semi-conditioned basement the uninsulated (pre-IRC) ducts do fall below the dew point of my basement air regularly during the cooling season when the oversized central air conditioning runs (which is never more than an hour or two per day) but they don't get wet enough in locations that I care about to really matter.

        1. Expert Member
          Akos | | #10

          Thanks, that makes sense.

  2. Hugh Weisman | | #2

    Thanks... that's a possibility....we have attic spaces within the insulation envelope, but the preferred space is a "mechanical room" on the 1st floor. The house is basically a two bedroom apartment above a three car garage...also, I don't love doing the whole slim unit thing...seems kind of dinky compared to a "real" air handler like the Mitsubishi ( http://meus1.mylinkdrive.com/files/MVZ-A18AA7_For_MXZ_MULTI-ZONE_SYSTEMS_Product_Data_Sheet.pdf ) .. I haven't had the time to determine whether cfm, static pressure, etc. will be ok for the duct runs we need.

  3. Expert Member
    Dana Dorsett | | #3

    Fujitsu makes a 1.5 ton "mid static" version if it needs more boost, but the xxRLFCD is quite a bit beefier than most mini-duct cassettes, and can handle decently long runs.

    https://portal.fujitsugeneral.com/files/catalog/files/(D&T)%20ARU12-48RGLX.pdf

    The ranch house in CA was slightly bigger than the carriage house, and they even did it with FLEX. A hard piped solution (at least at the corners, with stretched flex for the straight runs) works fine. This is not a rocket science project taking it the edge of what's possible to fit one into a 1200' carriage house.

    MXZ compressors need at least two zones hooked up to work, and the MVZ air handlers don't modulate. The minimum modulated output of a -2C20NAHZ compressor is more than twice that of an 18RLFCD, and nearly half your design load- it's not going to modulate much and the nameplate HSPF efficiency with a 1.5 ton MVZ and a 6K head (where would you even put it that made sense?) is 17% less heat per kwh.

    http://meus1.mylinkdrive.com/files/MXZ-2C20NAHZ_Submittal.pdf

    The 2C20NAHZ would be a more expensive, less efficient, and less comfortable solution than an 18RLFCD, which is about as perfect a fit as you can ask for.

    [edited to add] It's at least possible to run with just the MVZ air handler as a single zone on an MXZ compressor if you hook it up through a branch box, but that configuration does not have an AHRI rating, which is probably necessary to have in your documentation to meet spec. (The branch box adds cost too.) A pair of MVZ could get you there, but it's an even lower HSPF, and even more expensive & bulky.

  4. Expert Member
    Dana Dorsett | | #5

    I couldn't find an AHRI submittal sheet for the 1.5 ton ARU18RGLX with the beefier cassette, but according to Tom Woodson the 2-tonner tests at SEER 17.5, HSPF 10.8:

    https://www.greenbuildingadvisor.com/question/fujitsu-mid-static-ducted-heat-pumps

    [edited to add] It's on page 4 of the DESIGN & TECHNICAL MANUAL:

    SEER 19.0, HSPF 10.9 for the 1.5 tonner. (That's ALMOST SEER 20, HSPF 11. )

    On p.28 the heating capacity at +5F is 18,880 BTU/hr, which meets your heating
    capacity spec.

    https://portal.fujitsugeneral.com/files/catalog/files/(D&T)%20ARU12-48RGLX.pdf

    The static pressure can handle 200 pascals (same as an MVZ) , which is 0.8 water column. You'd have to work overtime on screwing up the ducts to really need that in a 1200' house. Dialing it back to lower cfm and using a low-static pressure pleated MERV 10 or higher filter should make everybody happy.

    The minimum modulated output of 5400 BTU/hr is higher than the 18RLFCD's 3100 BTU/hr, but it's at least less than 1/3 your 18K design load number, so it would still modulate very well for most of the season.

  5. Hubi | | #7

    Hello, you may want to check out the Bosch inverter drive split system heat pump. Very efficient and draws only very low amps.
    There is a network of installers listed on their web page.

  6. GBA Editor
    Martin Holladay | | #8

    Hugh,
    If you are on Martha's Vineyard, you are lucky. Hire Marc Rosenbaum as a consultant -- he's worth every penny, and he has designed so many minisplit systems on Martha's Vineyard that he gives conference presentations on the topic. Here is the contact info:

    Marc Rosenbaum
    South Mountain Company
    Box 359
    Chilmark, MA 02535
    508-693-4850

  7. Hugh Weisman | | #9

    Thanks Martin.....good idea.

  8. Hugh Weisman | | #11

    I was able to obtain a spec sheet from Fujitsu for the ARU18RGLX, see attached....Now, I'm trying to determine if we're best off going single zone with the ARU18RGLX or a dual zone using one ASU7RLF1 and one ARU12RLF. The ASU unit would serve the main living space (kitchen, dining, living) and the ARU ducted unit would serve the two bedrooms (all on the 2nd floor above garage) and the entryway and utility room on the 1st floor. I don't mind having everything on one zone, but I'm a little nervous about whether the ARU18RGLX will have enough oomph to push all the air though the ducts (I don't have the experience to do the calcs and would rely on the installer to size ducts, etc).

    Does anyone have any thoughts on whether the ducted unit requires a ducted return. The unit would be in the utility room... it would be very simple to place a transfer grille into the utility room and the stair between 1st and 2nd floor. Using the Utility room as return plenum would reduce any static pressure losses in return ductwork, and would also provide sufficient ambient temperature air to the utility room to keep it well above freezing.

    A related question is deciding on a water heater.. Tankless would't be a good choice for this client. So choices (as I see it) are a propane or hybrid (heat pump) tank model (either 50 or 80 gallon). The "problem" with the propane is having to accommodate a tank outdoors aesthetically. The problem with the heat pump is that I would need to enlarge the utility room somewhat (not a problem) to have sufficient cubic footage, and that the heater would cool the utility room and eventually the entire insulated area. Actually, that's benefit in the summer when the carriage house is more likely to be heavily occupied, a negative in winter,

  9. Expert Member
    Dana Dorsett | | #12

    >" I'm a little nervous about whether the ARU18RGLX will have enough oomph to push all the air though the ducts "

    Seriously? So now even 0.8" water column static pressure is something to worry about? (NOT!)

    Even sloppy rule of thumb duct designers would have to work pretty hard to screw it up on a house that size.

    The 5400 BTU/hr minimum modulated output @ +47F is higher, and it's max capacity @ +5F is less than the AOU/ARU18RLFCD, but it still has reasonble margin. The higher minimum modulation going to limit the outdoor temperature range over which it modulates, cutting into the "as-used HSPF" efficiency relative to the 18RLFCD, but that's still a reasonable fraction lower than the 6100BTU minimum modulation of the AOU18RLXFZH multi-split.

    The bench tested 10.8 HSPF efficiency of the ARU18RGLX is also 20% higher, than the 9.0 of an AOU18RLXFZH with a pair of slim duct cassettes.

    >"The "problem" with the propane is having to accommodate a tank outdoors aesthetically."

    Not really. The real problem with propane on MV is the micro-monopoly of the suppliers extorting extreme pricing on low volume users.

    >"The problem with the heat pump is that I would need to enlarge the utility room somewhat (not a problem) to have sufficient cubic footage, and that the heater would cool the utility room and eventually the entire insulated area. "

    A Sanden heat pump water heater puts the compressor outdoors, and there are two form factors of 83 gallon tanks to choose from. It's not cheap (about 4 grand), but it's more efficient than a tank-top compressor hybrid unit, and would easily pay for itself in operating costs relative to an 80 gallon condensing propane tank at on-island pricing.

    https://www.sandenwaterheater.com/sanden/assets/File/SANDEN_CO2WaterHeater_12_18.pdf

    https://www.sandenwaterheater.com/for-professionals/

    It does introduce the visual "noise" of a second outdoor compressor. If two compressors is a deal breaker a 2 ton or 3 ton LG Multi V S with a Hydro Kit, and a TurboMax 65 (or 109) would work using LG's ARNU183BGA4 high static duct cassette for space heating/cooling, but that's probably going to be even more expensive than a Fujitsu + Sanden solution.

    http://www.lgvrf.ca/en/multi-v-s.aspx/Download?filename=EM_MultiV_S_OutdoorUnits_11_15.pdf&id=1508

    The 2 ton could cover it, but the 3 tonner would be a better bet for covering both the space heating + water heating load:

    http://www.lgvrf.ca/en/multi-v-s.aspx/ARUN024GSS4

    http://www.lgvrf.ca/en/multi-v-s.aspx/ARUN038GSS4

    http://www.thermo2000.com/pdf/en-US/specs/specifications_turbomax.pdf

    The Multi V S is a full-on VRF system and can simultaneously heat one zone (say the TurboMax on the Hydro Kit) while cooling others with a full heat recovery.

    This solution was featured in a recent This Old House series heating/cooling a Net Zero house in Rhode Island.

    https://www.thisoldhouse.com/watch/jamestown-net-zero-house

  10. Hugh Weisman | | #13

    Dana.
    Thanks so much...A lot to digest, but I'll dig into it...And you're right about the propane costs...We pay in excess of $500 per year for approximately 110 days of occupancy per year....that would work out to about $1,500 per year for full time occupancy, given that summer occupancy is heavy.

    Do you think that in any case, we shouldn't even consider a tank top hybrid unit?

    P.S. And how do you know so much about the Vineyard?

    1. Expert Member
      Dana Dorsett | | #15

      >"Do you think that in any case, we shouldn't even consider a tank top hybrid unit?"

      There is nothing wrong with going with a tank top hybrid unless you're marginal on how much room-volume it has to draw from. A Sanden takes up a very minimal amount of indoor space and is more efficient, but not necessarily efficient enough to "pay off" the ~$2000 difference in upfront cost between a tank top heat pump water heater and a Sanden. At 5o cents/kwh the Sanden would be an obvious choice, at 25 cents it requires a more careful analysis. What the $2K difference would be buying is indoor space and higher efficiency number for the spreadsheet.

      >"P.S. And how do you know so much about the Vineyard?"

      I don't- I just make it up as I go along! :-)

      As mentioned in response #1 I was advising on a project in Vineyard Haven a few years ago helping specify and negotiate the HVAC solution. (I was brought less than 2 months ahead for the heating season-it was a real scramble.) They eventually went with a pair of 2 ton 3
      zone Fujitsu multi-splits- not my first choice, but time was running short. An -18RLFCD would have been a better choice than the second multi-split, but all contractors they were negotiating with refused to install it anywhere but in the attic, above the insulation, despite ample room for installing it in an unfinished but insulated basement. At that time several other options were on the table, including condensing propane + split AC solutions which I investigated and advised very STRONGLY against on financial grounds, an overpriced overkill 4 ton Carrier Greenspeed + 1 ton Daikin, and at least one other. I still get updates from the homeowners a few times per year. Since that time they have topped a row of trees on the south side of the house to light up a decent amount of shiny new rooftop PV- enough to offset most of their utility costs.

  11. Jan Juran | | #14

    Hi Hugh: I recently installed a Rheem Performance Platinum heat pump HW heater in my Long Island NY home zip code 11976. Uniform Energy Factor 3.55; 67 gallon first hour rating; $1299 at the local big box store for model XE50T10HD50U1; plus $500 for my plumber to install it. Energy Star's protocol estimates a yearly electricity use of 915 KwHr. PVWatts estimates that 650 watts of PV added to my grid tied PV array will produce these 915 KwHrs per annum; the local PV installer will do it for $2.10 per watt after 30% tax credit=$1365 for enough PV to run it for 30+years. Total: $1300+500+1365=$3165 installed, or significantly less than the low end installed cost of a Sanden CO2 system. Benefits include zero electricity cost/GWG/pollution plus the PV system will still generate long after the HW heater wears out. The value of the free AC during summer and basement dehumidification exceeds the winter heating energy penalty for the air source heat pump HW heater in my case. Alternatively one could install a bit more PV to cover any incremental winter space heating need (or to cover any electric resistance hot water heating by the hybrid HW heater during the year's coldest days). The local recycling center provides proper disposal and refrigerant recapture for $5. If your site is appropriate for PV, a tank top hybrid unit plus PV would appear to be the better solution. Bonus: if/when the hybrid HW heater wears out, you could replace it with a Sanden unit if the Sanden price becomes more competitive at such future date; the PV system should still be producing the needed kilowatts.

  12. Hugh Weisman | | #16

    Jan, what would you estimate as the amount of cooling is in Btu/hr? is it significant enough to affect the mini split sizing?

    Dana, We see that the Sanden unit actually runs water at the exterior and requires heat tape protection. Are there backup power supplies (battery, not generator) that work with these in the event of a power failure.

    1. Expert Member
      Dana Dorsett | | #17

      I'm not aware of a Sanden-specific heat tape power backup system for freeze protection in the event of an extended power outage, which IS an issue with that solution.

      There is some arm-waving discussion of the LG Multi V S solution used in the RI project in this video:

      https://www.youtube.com/watch?v=Ag1tmOCgcdE

      There are plenty of LG mini-splits in evidence on MV, but I'm not sure if any of those contractors are familiar with the Multi V (larger commercial systems running on multi-phase power) or Multi V S (single phase power and smaller) VRF systems.

      Later this year I'll be exploring that system a bit deeper as a possible solution for a house in Sherborn MA where they are planning to replace an existing oil fired water heater and oil-fired furnace with heat pumps + solar, but only after performing more retrofit weatherization and build out of fully conditioned basement space, etc. Early in the planning a pair of Fujitsu -xxRLFCD (or-xxRGLX) ducted system + tank top heat pump water heater have been sketched in as realistic place holders, pending the final Manual-J, but a Multi V S might work better (TBD). The available space in that basement is more than adequate for a tank-top compressor water heater, but the net efficiency of the Multi V S is probably better, and takes up less space indoors. (It ain't yer grandma's multi-split, appearances notwithstanding.)

  13. Hugh Weisman | | #18

    Yeah, and the last thing I want to do is try and tell a GC how to rig up some car batteries or a computer UPS to power heat tape in the event of a power failure. The Sanden sounds great but for a project that's supposed to be simple just seems to create as many problems as it fixes.

    I'm starting to zero in on using a hybrid water heater with the utility room having enough cubic footage (700-800) for it to work ok even if that was all. But the utility room will also be vented in some fashion, either by having a supply and return from the central ducted unit, or being part of a plenum return to the unit, which is looking more and more like it will be the Fitjutsi ARU18RGLX.

    I've attached are some drawings showing our design. Present intention is to lengthen the utility room to extend across the back of the garage, excepting for an indentation at the end in the garage side wall for the outdoor unit. We'll have individual ducts from the indoor unit running in insulated spaces at the back of the first floor and up into the insulated attic spaces at each bedroom and then discharge to the bedrooms. The main living area will have a duct going straight up in a chase to be added behind the toilet... then across the bath ceiling to discharge into the living area. There will probably be a single whole house return to the utility room in the partition it shares with the stairway.

  14. Jan Juran | | #19

    Hi Hugh: the Pacific Northwest National Laboratory did a detailed study of the interaction of a heat pump hybrid HW heater and mini split HVAC equipment in July 2014 which includes the relevant sets of equations to estimate the BTU effects: https://labhomes.pnnl.gov/documents/HPWH_SpaceConditioning_Report_PNNL_23526_FINAL.pdf This PNNL study also includes several estimates of cooling BTU savings, by various climate zones.
    Basically, the conclusion is that if you use the MV home for 110 days primarily during cooling season, you should realize measurable cooling BTU benefits, on average. However the variables include where the HW heater is placed (in conditioned space or in an unconditioned basement); is it fully ducted to outdoors or not ducted or partially ducted; hot water usage amount; the HW heater COP and EF; etc.
    While you should gain meaningful BTU savings on average during cooling season, the absolute sizing of the mini splits will probably not be affected. For example you probably may want to size the cooling capacity to cover the peak cooling BTU need assuming you might draw only a negligible or small hot water amount during those several peak hottest hours/days of the season.

  15. Hugh Weisman | | #20

    We've now gone out to bid for this project specifying a Fujitsu 18RGLXD system (single zone, high static duct air handler). It gives us just what we need in terms of SEER and HSFP efficiency, and full heating down to at least design temperature of 8 degrees. One bidder has just asked us if they could substitute Mitsubishi for Fujitsu, stating that they have maintenance issues with Fijutsu.... my inclination is to say yes provided they can propose an equivalent unit, but I haven't been able to identify one.

    We received a preliminary HERS rating of 48 (required by code in West Tisbury MA by the STRETCH code to be 55 or less)....very pleased by this. Our intention has always been to meet code and have an efficient house, but without some of the more intensive measures often prescribed on this site.

    1. Expert Member
      Dana Dorsett | | #22

      With Mitsubishi you'd have to go with a 1.5-2.5 ton SVZ/SUZ combination to hit comparable capacity & efficiency as the Fujitsu 0.8" static pressure.

      The 1.5 tonner delivers an SEER 18/HSPF 12.6 efficiency and a bit over 12,200 BTU/hr @ +5F, about 600 -700 BTU/hr less than what an -18RGLXD delivers:

      https://meus.mylinkdrive.com/files/M_SVZ-KP18NA_SUZ-KA18NA2_SUBMITTAL-en.pdf

      If that's not enough capacity the 2 ton equivalent doesn't have whole lot more capacity than the 1.5, but, but the 2.5 tonner would probably cover about as much load at +8F as the 1.5 ton Fujitsu. You'd have to look up the capacity tables for the 2 and 2.5 ton SVZ/SUZ pairings- the AHRI submittal sheets on those sizes don't specify a +5F capacity. But the 2.5 tonner which delivers SEER 18/HSPF 13.6 efficiency, with a capacity of 21,400 BTU/hr @ +17F, and almost certainly more than the 18RGLXD capacity at +5F.

      https://meus.mylinkdrive.com/files/M_SVZ-KP30NA_SUZ-KA30NA2_SUBMITTAL-en.pdf

      The modulation range on those units aren't as wide as with the Fujitsu xxRGLXDs, but if the slightly lower output of the 1.5 ton Mitsubishi still has enough margin it's not a bad choice.

  16. Lance Peters | | #21

    The Rheem Hybrid compressors are 4200 BTU/Hr. Since the contribution of the compressor would be directly proportional to how much hot water is used, I'm not sure it would be a good idea to count on it for space cooling?

    http://cdn.globalimageserver.com/FetchDocument.aspx?ID=673cb60e-0940-4d67-a487-948dfcb3db8c

  17. Hugh Weisman | | #23

    Dana,
    I've looked at the various tables and agree with you that it looks like the 2 ton won't have enough heating capacity at +8 degrees design temp...We need about 17,000 btu/h heating and the table for the 2 ton shows only 14,600 at 17 degrees, which obviously will be less at 8 degrees. Sounds like we'd have to go with the 2.5 tanner...That's a lot of overcapacity for most conditions. My client would probably like faster heat-up on winter weekend if the house has been unoccupied, and faster cool-down in the summer, but I'm aware of short cycling issues (but certainly not an expert). Should I dismiss the 2.5 Mitsubishi out of hand, or consider (or prefer it) if the delta in cost is minimal?

    1. Expert Member
      Dana Dorsett | | #24

      If the heat load is 17K @ +8F the heat load at +47F is about 6.3K- about half the minimum modulated capacity of the SVZ-KP18NA / SUZ-KA18NA2 at that temp. A 50% duty cycle during the shoulder seasons isn't terrible. The cycles will still be pretty long, not short-cycles.

      At the mid-winter mean temp of ~+32F the load will be about 10-11K, and the minimum modulated output is likely to be around that number or lower, so even though it will be duty-cycling during the shoulder seasons and warmer winter afternoons it will modulate pretty well during most of the winter, and would still hit pretty close to it's HSPF numbers (and might even beat that by a small amount.)

  18. Hugh Weisman | | #25

    Thanks....that helps....and the reality is this Owner may have the place shut down in winter completely, or keep it at around 50 degrees. A lot of the time that probably means the system is not working much at all....but there's always the chance of a year round caretaker occupying so we want to do this right. What's the consensus about maintenance issues on Mitsubishi vs Fujitsu? I don't know whether the GC is saying more problems with the FIjutsi or just that the local support is not good....well get into that with him when we evaluate bids.

    1. Expert Member
      Dana Dorsett | | #26

      Both vendors are pretty reliable and have reasonable support in MA, though Mitsubishi seems to have more than half the market share, and a regional design center in Southborough MA. I have no experience or real world data on either of those model lines.

  19. Stephen Sheehy | | #27

    I lived on MV for several years in The 70s. I've been in Maine for 25 years. The coldest winters I ever experienced were on MV. Windy, damp, awful. Those days at 35° with 25 mph wind and rain were far worse than a nice clear, still -18° here.

    1. Hugh Weisman | | #28

      you've got it Stephen, unless you want to try my corner of Riverside Drive and 86th Street in Manhattan. On a 15 degree day with maybe 10-15mpg winds in the rest of the city, we can get winds on our corner of 45mph +. It just destroys you.

      1. Tom May | | #29

        Weisman, an architect, any relation to Jamie? If so I would think some solar would do you some good especially on the island, unless you are deep in the woods of WT. Yup those cold, damp wind blowing days when the whole island stays home. Why not just a small conventional hot water boiler with baseboard heating, especially being just a garage or carriage house apartment. Hot air systems sitting stagnant during the off season can get a little nasty. Appliances outside are subjected to corrosive salt air. Solar hot water for heavy summer time use, especially outside showers, and free auxiliary heating in the winter, when the apt. is not in use, should be something to think about. An indirect HW heater can work off both the solar and boiler. Most HW systems there are winterized with antifreeze for winter conditions and power outages so marrying the two shouldn't be a problem. A small PV set up could power the solar for those outages, to prevent frozen pipes in the winter, and guarantee HW the rest of the time.

        1. Hugh Weisman | | #30

          Yup...Jamie's older brother. How did you know him.

          Actually, the project is "deep in the woods of WT" but a small HW system ain't in the cards. Although the owner is not thinking right now about winter see, there's every reason to think that she'll have a caretaker there year round at some point. And summer A/C is absolutely a given. So a mini-split it will be.... but thanks for the thought. We've specified a Fujitsu system (with Dana's advice), but one contractor who's bidding says he will only install Mitsubishi, having had bad experiences with Fijutsi support on-island.

          1. Expert Member
            Dana Dorsett | | #31

            >"We've specified a Fujitsu system (with Dana's advice), but one contractor who's bidding says he will only install Mitsubishi, having had bad experiences with Fijutsi support on-island."

            Does that mean you're also getting a bid for the SVZ-KP18NA / SUZ-KA18NA2 ?

            Regarding off season stagnation, with a modulating mini-splits long cycles even at low load and a low static pressure pleated MERV 13 or higher filter the ducts stay pretty clean, unlike the crummy 1" thick lousy filters seen in most ducted systems. With hydronic rads/baseboard heating and a standard split AC the off season stagnation through the heating season can result some pretty funky stuff on the ducts too. Nothing is perfect, but ducts that are used year round at low cfm with a high MERV stay pretty close to pristine.

          2. Tom May | | #32

            My brother, Mike the plumber, and his family have been there for nearly 40 years. I lived there seasonally from the early 80's til the late 90's working along with my brother during the boom. Jamie was looking at renting out space one winter at the house he had on Look St, and being into solar myself, I stopped in to check it out. I then lived a few houses down one summer in another somewhat passive house he helped design. He's a character.
            My brother has a compound off Pine st, with a legal "way" with our family name in VH and built a house in GH where he resides now. Back then everybody knew each other, especially in the winter.
            Just figured if you were related, and since he was into solar, I would mention it as an alternative, but obviously it's up to the client. As you mention, getting any type of service there is tough, which is why you should keep it simple and use ready available products.

          3. Hugh Weisman | | #33

            Dana. We specified the SVZ-KP30NA indoor unit and a SUZ-KA30NA2 outdoor unit...figured that was necessary to get the design temp performance needed.

          4. Hugh Weisman | | #34

            tom...good to hear from you. actually, I built a (somewhat) passive house in Chilmark for ourselves a couple years after Jamie. it wasn't quite as extreme as his, but has triple glazed windows, heavily insulated walls (for that era, anda sun space with a blower system to take heated air into a concrete block duct system below the slab on the bottom floor. We've since removed the blower system and installed a Sanyo multi-split heat pump...but all-in-all very efficient.

        2. Tom May | | #35

          Thanks Hugh, yeah it was fun times back then. Did a lot of funky solar stuff down there, I'm sure you remember Anna E. from Sol Viva. Dealt with a lot of crazy "celebrity" clientele, and crazy building going on back then. Place just isn't the same......especially with no more Johnny "Seaview" at the Ritz....

          1. Hugh Weisman | | #36

            or Loretta at the Seaview.

        3. Tom May | | #38

          Yup, she was a sweetheart, had to be, to put up with Johnny and his antics...... joking of course. It was a good dive bar/ hotel that unfortunately got torn down and rebuilt. Used to hang around with her daughter JoAnne and her husband Mario, aka Chachi, in that big house on Ocean Park that This Old House got their hands on. Haven't been down there for some time, just getting reservations and the cost of the ferry makes things worse. Had many a day waiting on standby, hanging at the Leeside, when you were guaranteed a ride, but I'm sure I'll get back down there at some point to visit and see some old friends. Plus like I said, it's not what it used to be. Thanks for bringing back some old memories.

  20. Moe Hirsch | | #37

    Hi, the biggest issue you run into with "oversized" units is the turn down ratio. Take a look into the Mitsubishi PUMY-HP36NKMU.

    SEER rating between 18 and 22 depending if you have ducted or non ducted units connected.

    turn down ration for the cooling is 29% low end which is 10,440 btu.
    The heating turn down is as low as 17% which is 6120 btu.

    The only indoor machines that clean air well are the ducted units with oversized pleated filters. The wall hung and cassette units do a mediocre job at best.

    connected load 50-130% of outdoor unit capacity.
    I like that these units DO NOT USE A BRANCH BOX. Less wheels on the bus to break.

    Pretty much a like a hydronic heating system with brazed Ts on the suction and liquid lines.

    some more info from Mitsubishi.
    Connects up to 9 indoor units • Single-phase outdoor unit with Variable Refrigerant Flow Zoning (VRF) technology • Service accessible through both a front and side panel • Up to 984 ft. of total pipe length • Base pan heater standard • 100% heating capacity at 5° F • 78% heating capacity at -13° F utilizing flash injection technology • ENERGY STAR® certified units1

    I'm not in bed with Mitsubishi. Carrier green speed is another good system and probably less expensive. We are an install and consulting company out of Pomona NY called TurnUpTheComfort.com . We gravitate to Mitsubishi for the great tech info on the mylinkdrive site.

    feel free to DM me any specific questions

  21. Expert Member
    Dana Dorsett | | #39

    >"We specified the SVZ-KP30NA indoor unit and a SUZ-KA30NA2 outdoor unit...figured that was necessary to get the design temp performance needed."

    That's a mistake.

    Seriously- don't install it, even if it comes in as the lowest bid.

    It's minimum modulation at +47F is 12,640 BTU/hr, well over half your design heating load, and it's turn down ratio is pretty limited. You'll note that (unlike the 1.5 tonner) they don't even spell out the +5F capacity in the AHRI submittal sheet:

    http://meus1.mylinkdrive.com/files/M_SVZ-KP30NA_SUZ-KA30NA2_SUBMITTAL-en.pdf

    The KP/KA18 might need a small amount of heat strip to handle cold snaps, but it is FAR more appropriately sized for the actual load, and would run more efficiently and comfortably (a much higher shoulder season duty cycle) than the 2.5 tonner, even when factoring in the use of heat strip to cover Polar Vortex coolth (or even the 99% load.)

    https://meus.mylinkdrive.com/files/M_SVZ-KP18NA_SUZ-KA18NA2_SUBMITTAL-en.pdf

    With turn down ratios this low it's better to undersize slightly than to oversize by more than 1.25x (and that's what you'd be doing with the KP/KA30.)

    Curiously, the 2-ton KP/KA24 has an even lousier turn down ratio, and higher minimum output at +47F than the 2.5 tonner, along with lower HSPF test numbers.

    It's fair to say that none of the KP/KA series pairings are a really great fit for your loads.

  22. Hugh Weisman | | #40

    Dana, Somewhere along the line, I seem to have misinterpreted your recommendations. Back when I indicated the island contractors do not like (meaning will not install) Fijustsi, you recommended this.

    "If that's not enough capacity the 2 ton equivalent doesn't have whole lot more capacity than the 1.5, but, but the 2.5 tonner would probably cover about as much load at +8F as the 1.5 ton Fujitsu. You'd have to look up the capacity tables for the 2 and 2.5 ton SVZ/SUZ pairings- the AHRI submittal sheets on those sizes don't specify a +5F capacity. But the 2.5 tonner which delivers SEER 18/HSPF 13.6 efficiency, with a capacity of 21,400 BTU/hr @ +17F, and almost certainly more than the 18RGLXD capacity at +5F"

    I responded. "I've looked at the various tables and agree with you that it looks like the 2 ton won't have enough heating capacity at +8 degrees design temp...We need about 17,000 btu/h heating and the table for the 2 ton shows only 14,600 at 17 degrees, which obviously will be less at 8 degrees. Sounds like we'd have to go with the 2.5 tanner...That's a lot of overcapacity for most conditions. My client would probably like faster heat-up on winter weekend if the house has been unoccupied, and faster cool-down in the summer, but I'm aware of short cycling issues (but certainly not an expert). Should I dismiss the 2.5 Mitsubishi out of hand, or consider (or prefer it) if the delta in cost is minimal?"

    To which you responded "If the heat load is 17K @ +8F the heat load at +47F is about 6.3K- about half the minimum modulated capacity of the SVZ-KP18NA / SUZ-KA18NA2 at that temp. A 50% duty cycle during the shoulder seasons isn't terrible. The cycles will still be pretty long, not short-cycles.

    At the mid-winter mean temp of ~+32F the load will be about 10-11K, and the minimum modulated output is likely to be around that number or lower, so even though it will be duty-cycling during the shoulder seasons and warmer winter afternoons it will modulate pretty well during most of the winter, and would still hit pretty close to it's HSPF numbers (and might even beat that by a small amount.)"

    Since I said that I had said that it looked like we needed to go with the 2.5 tonner, and your response talked about half the modulated capacity, I somehow thought you were saying the 2.5 tonner was ok. Now, I see that you actually were talking about the 1.5 ton unit, but that only delivers about 12,000btu/h at design temp and we need about 18,000. Now, I'm complete in a fog about how to proceed.

    1. Expert Member
      Dana Dorsett | | #41

      >Now, I'm complete in a fog about how to proceed.

      Shall we start a club for that? :-)

      The "real" answer is to go with a Fujitsu, which has a sufficient modulation range.

      Per the submittal sheet the minimum output of the KP/KA18 @ 47F is 8300 BTU/hr (8120 per NEEP data), so it will modulate pretty well at the average winter temp of ~35F when the load is ~7800 BTU/hr. (If it's being maintained at 50F the load will be a lot less, and it will cycle, but at a reasonably high efficiency.)

      https://ashp.neep.org/#!/product/29080

      The minimum modulated output of the KP/KA30 at +17F is probably around 10K, but since it's data hasn't been submitted to NEEP and it isn't specified in the AHRI submittal we really don't know. If you have access to the extended temperature capacity tables or other engineering data you might be able to infer something. But at +47F when the load is in the 6-6.5K range it's minimum output is twice that. If it's modulating at 35F (unknown, but not likely) that wouldn't be terrible, but it's also not great.

      The 2.5 ton PUZ-A30NHA7 + PEAD-A30AA fills the bill, modulating down to 8,800 BTU/hr @ +47F and 17,700BTU/hr @ +5F, which is reasonably good sizing for both the design and average heat loads:

      https://ashp.neep.org/#!/product/28997

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

      Whether the comparatively lower HSPF 10.8 is a show stopper for this project or not isn't something that I can speak to, but it's a better fit, and the as-used efficiency will likely be higher than the KP/KA30. The COP of 5+ at minimum modulation at +47F is QUITE good, very close to that of the KP/KA18 at that temp & modulation level.

      Note that the cfm ratings of the PEAD series cassettes are at 0.4" water column, half the max of a Fujitsu or one of the full sized Mitsubishi air handlers.

      Still in a fog? (Me too...)

    2. Tom May | | #42

      Throwing a bunch of numbers around and making guesses based on manufacturers charts, doesn't really comply with real world situations. Laboratory testing does not equate to the many variables associated with installations in the field. Trying to design a system based on manufacturers numbers can leave you in a fog if you take them as absolute. Modulating this and modulating that can make things even more confusing. Keep it simple. For the price you are going to pay for systems that have only been around for a couple years that have not been time tested my end up costing you even more if they do not perform or break down with the many components and computer electronics involved compared to conventional time tested solutions. There were times when a simple fire is all one needed.

  23. Hugh Weisman | | #43

    Thanks Dana....Interesting that we've had two different GC's bid on this project. In both cases, they indicated that they "will not agree to install the Fujitsu system." I went with the SVP-SUZ 2.5 ton because of the full size air handler. Once, my client decides on a GC, we'll schedule a meeting with them and their mechanical contractor...hopefully, the PEAD cassette will have enough oomph for what's needed. Weird that the cassette will modulate to 8,800 but the full size air handler only to 12,000 every though the outdoor unit is the same.

  24. Expert Member
    Dana Dorsett | | #44

    >"Weird that the cassette will modulate to 8,800 but the full size air handler only to 12,000 every though the outdoor unit is the same."

    Mini-duct cassettes all have bigger modulation ranges than full sized air handlers. This is by design- the efficiency of driving a more powerful 0.8-1" water column air handler falls off at lower modulation levels due to the fraction of the power that is devoted to the bigger air handler.

    For a 1200' house just about ANY mini-duct cassette "... will have enough oomph for what's needed..." if the duct designer is competent, but it will be easier with the Mitsubishi PEAD or Fujitsu RLF with the cfm rated at 0.4" w.c. than it is for the wimpier SEZ-KD series Mitsubishi units (rated at 0.2"). The bigger "full sized" air handlers are for retrofits, or bigger houses with longer more complicated duct systems, or tin-banger trades-people designing ducts by rules of thumb.

    While you're at it you might as well have somebody quote on a 2-ton Carrier Infinity w/ Greenspeed with the FE4ANB006 air handler, which delivers ~23K @ +10F, ~20K @ +5F. It has a 2.5:1 turn down ratio, and isn't any worse a fit than the 2- 2.5 ton full size air handler Mitsubishis:

    https://ashp.neep.org/#!/product/29393

  25. Hugh Weisman | | #45

    really? minimum modulation at 47 degrees is 14,500Btu/H. Seems like the PEED unit is the answer if the duct designer gives his/her blessing...the last thing I want to do is get out my plastic Ductulator from architecture school.

  26. Hugh Weisman | | #46

    Dana....I have another small project that I'd sure like your recommendation(s) regarding, This one is an extension to our own home on Martha's Vineyard. The existing house was built in 1982 as what was then a close to state-of-the-art passive house. For years, we had no mechanical system in the house other than some electric wall space heaters in the bathrooms. 10 years ago we installed a Sanyo (now Panasonic) multi-zone 3 ton mini-split. All is well with that, and ancient history.

    The extension will consist of a new master bedroom & bath and a den connecting with the main house first floor (about 750 square feet) with a walkout basement of about 500 square feet under two-thirds of the extension. There willl be a substantial amount of floor to ceiling south (and ocean) facing glass...we'll insulate to MA code standards with CCF.

    I've done a quick coolcalc analysis, which comes to a total 20,000btu/hr at 10 degree design temp. The coolcalc program seems a bit haywire though in several respects, It shows a 2,400btu load for ducts although I input a ductless system, and the individual room loads only total about 18,000btu, not 20,000. The load is split approx. 7K for basement (seems way high), 7K for Master bedroom/bath, and 4K for the den. That said, we should certainly be fine with an 18K system. But which one? Given what I've heard on the island, I should stick with Mitsubishi, although I do intend to investigate Fijitsu further. In the immediate future, the basement (whose walls are mostly above grade) will not be used, but it may well become an office for me, or additional play or sleeping space for grandchildren. Thus, it should have HVAC, but best on a separate zone.

    My thinking is that ideally, I can find a multi-zone unit that works, perhaps the Mitsubishi MXZ-2C20NAHZ2....I don't know enough at this point if I could put a 6K head on it for the basement and a ducted 12K unit for the main floor. Alternatively, I could buy a separate 6K ductless unit for the basement and a 12K ducted unit for the main floor, or even 3 separate units....My head is hurting with all the combinations and permutations, and hyper heating, and compatibility of various indoor and outdoor combinations...At the end of the day, we need separate zones for the 6 or 7K basement load, and the 12K main floor. I'd appreciate your thoughts.

  27. Expert Member
    Dana Dorsett | | #47

    >"The load is split approx. 7K for basement (seems way high), 7K for Master bedroom/bath, and 4K for the den. That said, we should certainly be fine with an 18K system."

    A 3/4 ton ducted Fujitsu 9RLFCDgets you there with margin for the first floor with 15,400 BTU/hr @ +5F at max speed, a bit more at +10F.

    If it has to be Mitsubishi it takes a 1.5 ton SUZ-KA18NA2 / SEZ-KD18NA, with 12K out @ +5F (with the caveat that it needs to be pretty central without long duct runs, and a an extremely low static pressure filter.)

    https://ashp.neep.org/#!/product/29056

    The 1.8 ton Mitsubishi tests at a very high HSPF 13.1 provided you can find somebody who can do ducts right.

    That is WAY better than the HSPF 9.65 delivered by the MXZ-2C20NAHZ2 in mixed ducted/ductless configurations:

    https://ashp.neep.org/#!/product/29024

    A 1-ton Carrier/Midea 38MAQB12R--3 / 40MBDQ12---3 might be a good option if the local Carrier folks are supporting it:

    https://ashp.neep.org/#!/product/26455

    Any 2-ton Carrier Infinity w/GreenSpeed 25VNA024A*030* (with any of a half-dozen air handler options) would cut it too, but usually more money, and it's sub-optimally oversized.

    If you're not finishing out the basement you defer that, but if you want to do it all in one go..

    A half ton Mitsubishi FH06NA is good for 8.7K @ +5F with an HSPF north of 13:

    https://ashp.neep.org/#!/product/25906

    For $200 more the FH09 is good for 10.9K @ +5F, not that you need anywhere near that much for an insulated basement:

    https://ashp.neep.org/#!/product/25894

    >"...we'll insulate to MA code standards with CCF."

    What means CCF in MV dialect? Closed Cell Foam?

    R20 code-min closed cell foam in a studwall underperforms cheaper & greener R20 open cell foam due to the more severe thermal bridging through ~3" of stud (R3.6-R3.8) rather than 5.5" (6.6- R6.9). While the center-cavity losses are the same, the framing losses are nearly twice that of an open cell foam solution. The air tightness of R20 closed cell and R20 open cell is the same. The cost (both environmental & cash) is dramatically lower with open cell.

    The vapor permeance of the open cell is higher, but if the siding is rainscreened it doesn't matter, in fact it's better. If the siding is NOT rainscreened, half-perm "vapor barrier latex" paint on the wallboard is cheap, works fine for limiting wintertime moisture loading, and offers more drying capacity than 3" of closed cell foam.

    Insulating the basement is better done with EPS- even an R20-ish ICF (insulated concrete form) is usually cheaper than a code-min R15 closed cell foam. With an 2.25" + 2.25" ICF cantilevering a 2x6 framed wall off the concrete an over the exterior EPS to align the planes of the wall sheathing/WRB with the exterior of the foundation foam works great, but you have to plan for it.

  28. Hugh Weisman | | #48

    Thanks Dana,

    If I decide to go all ductless, would it best to look for a 3 zone unit, or do a small 6k single zone unit for basement and a 2 zone 18K unit for main floor?

    "What means CCF in MV dialect? Closed Cell Foam?" Yes

    "R20 code-min closed cell foam in a studwall underperforms cheaper & greener R20 open cell foam due to the more severe thermal bridging through ~3" of stud (R3.6-R3.8) rather than 5.5" (6.6- R6.9). "

    Code minimum is R30, not R20. Can't do that with open cell foam. With CCF, you need minimum 4-1/2" which reduces thermal bridging significantly. And yes, we'll have a 3/4" rain screen. For a variety of reasons, I don't want to use exterior insulation. But I'm curious, why do you say "if the siding is rainscreened it doesn't matter, in fact it's better"? wouldn't there be condensation at the sheathing regardless without a vapor barrier.

    "With an 2.25" + 2.25" ICF cantilevering a 2x6 framed wall off the concrete an over the exterior EPS to align the planes of the wall sheathing/WRB with the exterior of the foundation foam works great" Yes, it does. And actually that's what I did 35 years ago with the main house (only then it was 2" of pink styrofoam), but in the extension, for a variety of architectural reasons, I don't want to cover the (largely exposed) concrete with insulation and siding....I want the concrete exposed thus needing to use interior insulation. I'm planning to fur the inside of the wall with 2x4 spaced 1" from the concrete and use a total of 3" of CCF to achieve the required R20, for what's technically a basement wall although in some ways its effectively a regular exterior wall due to the amount exposed.. The overall R factor won't be that much different though due to the continuous R-6.5 insulation between the studs and the wall.

  29. Expert Member
    Dana Dorsett | | #49

    >"Code minimum is R30, not R20."

    Massachussets code does not call out R30 for walls. The MA residential code is based on IRC 2015, and there were no amendments statewide to N1102.1.2 (R402.1.2) Insulation and Fenestration Criteria.

    https://up.codes/viewer/massachusetts/irc-2015/chapter/11/re-energy-efficiency#N1102.1.2

    https://www.ase.org/sites/ase.org/files/massachusetts_2015_iecc.pdf

    There may be a local town "stretch code" of R30, but that isn't too likely.

    >"With CCF, you need minimum 4-1/2" which reduces thermal bridging significantly. "

    4.5" of stud is a about R5.4- R5.6, which is a HUGE thermal bridge undercutting the R30 center-cavity performance. Even at 5" you're looking at a "whole wall R" of about R15.5 due to the thermal bridging. At 4.5" it's a whole-wall R of about R13.5, (about the same as a 2x6/R20 open cell wall), but I'll leave it for you do the math on it:

    https://www.finehomebuilding.com/2017/07/10/closed-cell-foam-studs-waste

    https://s3.amazonaws.com/finehomebuilding.s3.tauntoncloud.com/app/uploads/2017/07/05111418/cell-foam-chart.jpg

    >"But I'm curious, why do you say "if the siding is rainscreened it doesn't matter, in fact it's better"? wouldn't there be condensation at the sheathing regardless without a vapor barrier."

    With a rainscreen in a zone 5A location (especially the warm edge, like MV) there is some drying to the exterior even in winter. While there is moisture adsorption (not condensation) in the sheathing from interior moisture drives, some of that is passed on to the exterior even in winter, and the additional drying capacity of being able to dry in both directions keeps the moisture levels from reaching mold/rot levels during the spring season when temperatures rise a level that will support mold.

  30. Hugh Weisman | | #50

    "Massachussets code does not call out R30 for walls. The MA residential code is based on IRC 2015, and there were no amendments statewide to N1102.1.2 (R402.1.2) Insulation and Fenestration Criteria."

    R20 vs R30. you're right. me bad. I was going from memory on that one. I'm going from memory on this also, but if interior moisture passes through the open cell foam and hits the cold sheathing, I thought that produced condensation....you say absorption. so even with open cell foam, no interior vapor barrier?

  31. Jon R | | #51

    Re duct condensation/ #4 (reply link isn't working):

    I checked and IEC code does not require supply ducts within the thermal envelope to be insulated.

    Another solution is to put a partial air bypass around the AC coil. This brings the supply air up to something above the interior dew point. And in many cases, it will improve latent performance.

  32. Expert Member
    Dana Dorsett | | #52

    >"..if interior moisture passes through the open cell foam and hits the cold sheathing, I thought that produced condensation....you say absorption. so even with open cell foam, no interior vapor barrier?"

    It's ADsorption, not not AB-sorption, which aren't exactly the same thing. Adsorb is neither liquid nor vapor, but a 1 molecule thick layer of water on the pores in the wood as well as the microscopic tubular structures of the cellulose fibers in the wood. See:

    https://www.greenbuildingadvisor.com/article/professor-straube-moisture-physics

    Yes, moisture will accumulate in the wood when the wood is cold, which also increases it's vapor permeance, allowing a good fraction of the moisture to escape to the exterior while it's still cold. At a moisture content high enough to support mold the vapor permeance of OSB is comparable to that of standard latex paint on wallboard, so it's essentially a flow-through in climates as temperate as zone 5A.

    https://www.energyvanguard.com/blog/76574/Moisture-and-the-Quirkiness-of-OSB

    That's why the IRC (and MA code) allows using Class-III vapor retarders such as latex on wallboard on wood sheathed houses in climate zone 5, under the "Vented cladding over wood structural panels" exception to the requirements for interior vapor barriers:

    https://up.codes/viewer/massachusetts/irc-2015/chapter/7/wall-covering#R702.7

    https://up.codes/viewer/massachusetts/irc-2015/chapter/7/wall-covering#R702.7.1

    As long as it's reasonably air tight to the interior (5.5" of open cell foam is extremely air tight) the moisture risk to the sheathing is very low when using standard interior latex paint as the vapor retarder.

  33. Hugh Weisman | | #53

    Dana, I’m still working trying to figure put the best system for my expansion. I’ve now done coolcalc and manual calculations and I’m pretty confident the heating loads are as follows:

    6,000btu/hr Mostly above ground basement - needs to be a separate zone.
    9,000btu/hr Master Suite
    5,000btu/hr Den
    20,000btu/hr TOTAL

    Den and Master suite can be separate zones on ductless heads or same zone on duct or ductless. That results in five options as I see it….all using Mitsubushi.

    #1 MULTIZONE UNIT W/ (3) DUCTLESS HEADS -- MXZ-3C24NAHZ2 + (2) MSZ-FH06NA. & (1) MSZ-FH09NA. Total Heating Capacity at 5 degrees 25,000btu/hr, modulates (total) to 7,200btu/hr at 47 degrees

    #2 MULTIZONE UNIT W/ (1) DUCTLESS HEAD & AIR HANDLER -- MXZ-2C20NAHZ2 + (1) MSZ-FH06NA. & (1) SEZ-KD15NA4 (or PEAD-A12AA7). Total Heating Capacity at 5 degrees 22,000btu/hr, modulates (total) to 7,400btu/hr at 47 degrees

    #3 (3) SINGLE-ZONE DUCTLESS UNITS – (2) MUZ-FH06NA(H)/ MSZ-FH06NA + (1) MUZ-FH09NA(H)/ MSZ-FH09NA. Total Heating Capacity at 5 degrees 28,300btu/hr, modulates (total) to 4,800btu/hr at 47 degrees

    #4 (1) SINGLE-ZONE UNIT W/DUCTLESS HEAD + SINGLE-ZONE UNIT W/AIR HANDLER -- (1) MUZ-FH06NA(H)/ MSZ-FH06NA + SUZ-KA18NA2/SEZ-KD18NA4. Total Heating Capacity at 5 degrees 12,000/hr for ducted system, modulates to 4,900btu/hr at 47 degrees

    #5 (1) SINGLE-ZONE UNIT W/DUCTLESS HEAD + MULTI-ZONE UNIT W/(2) DUCTLESS HEADS -- (1) MUZ-FH06NA(H)/ MSZ-FH06NA + MXZ-2C20NAHZ2/MSZ-FH06NA & MSZ-FH09NA. Total Heating Capacity at 5 degrees 28,300btu/hr, modulates (total) to 4,800btu/hr at 47 degrees.

    If that’s the lineup, I’m trying to figure out the best way to go. My sense is that the various combinations all result in similar equipment costs. Presumably, installation of any of the combinations with ducts will cost more (#2, 4) and any combination with more than one unit will also cost more (#3, 4, & 5). That would make #1, the least expensive system to buy and install. Option #4 is about 20% shy of the design heat load for the ducted portion. So, is it worth considering #2, #3, or #5? Seems that #3 and #5 with two or three separate units (all with ductless heads) have no real advantage over #1 with three separate heads on a single unit other than having redundancy if a unit fails. That leaves #2 vs. #1….#2 will likely cost a bit more (due to ductwork), will treat all of the Master Suite & Den as a single zone vs. the advantage of separate zone, but doesn’t provide heat and cooling directly to the oversize master bathroom and a powder room, perhaps requiring some supplementary electric radiant heating. One additional factor is that the ducted unit will result in a quieter bedroom.

    What think you, Dana? Does my analysis make sense? What’s your recommendation?

  34. Expert Member
    Dana Dorsett | | #54

    In practice it's usually cheaper (and more efficient) to go with three separate mini-splits than a 3 zone multi split, strange as that may seem.

    A multi-zone version may be necessary if there simply isn't a reasonable space for installing multiple compressor units. If you have the space three separate units would deliver higher efficiency with a slight edge in comfort. With three separate units you also have the option of turning one or more completely off, increasing the effective modulation range at the low end during the shoulder seasons.

    If you don't have the space the -3C24NAHZ with ductless heads (with a modest amount of low-voltage radiant floor in the bath) would be preferable to a multi + single, and will still work out OK, since the loads of all zones are reasonably well matched to the capacities of the heads, and the whole house load at +47F will still be roughly the minimum modulated output of the compressor at that temp. It'll cycle a bit when it's in the 50s outside, but that's a lot better than having it cycling a lot even when it's in the 20s.

    Get it quoted both ways (from multiple installers) just to see. It's almost always more expensive to go the multi-split route, but not always.

    Ducted units aren't necessarily quieter than a high-wall coil like the FH heads. At it's absolute highest speed the FH09 head is still only 42dB(A) in heating mode- that's quieter than your refrigerator. At low speed (where it will run most of the time is 20dB (A), which is barely louder than a conscious adult breathing (and much quieter than a snoring human). At low speed a KD15 is 30dB(A), high speed 37dB(A), which is comparable to the medium-high blower rate of an FH09 at 36dB(A). The sound pressure levels at different cfm rates are included in the submittal sheets:

    http://meus1.mylinkdrive.com/files/SEZ-KD15NA4_SUZ-KA15NA_Submittal.pdf

    https://nonul.mylinkdrive.com/files/MSZ-FH09NA_MUZ-FH09NA_Submittal.pdf

  35. Hugh Weisman | | #55

    Thanks, Dana.. we will have quoted both ways, including electrical. It is surprising to me that separate units might cost less, but we will see. We certainly do have space for the compressors. I'm not surprised that a ducted unit is noisier than ducted units, but assumed that the remote location (over the bath ceiling and behind the common wall with bedroom) would make it quieter than a ductless unit within the room. If using the ductless, we would probable mount approx eleven feet above floor so it would have a bit of distance....also, our bed is a platform bed very low to the ground. and I do like the option of turning one or more units completely off during shoulder seasons. ...I can envision wanting to keep den at 70 degrees and bedroom substantially cooler. Chances are, we might have wanted some radiant floor in bath regardless.

    1. Expert Member
      Dana Dorsett | | #56

      >"...we would probable mount approx eleven feet above floor so it would have a bit of distance..."

      At 11' off the deck you will DEFINITELY want to spring for a wired or wireless wall thermostat. The temperature offsets at the outdoor temperature extremes will be to high otherwise, and you'll be constantly adjusting the setpoint up/down with the remote to stay comfortable. Without the wired or wireless remote/thermostat the room temperatures are normally sensed by the intake air at the head, which can easily be more than 5F different from the temperature at bed-blanket level even of a "normal" height bed.

      1. Hugh Weisman | | #57

        thanks....makes sense.

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