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Community and Q&A

Do I really need 4 minisplits?

Gordon Taylor | Posted in General Questions on

My wife and I own a lot in a development in the Pacific NW (Zone 4c), and we are planning to build our retirement house on it. We have never built a house before. Our projected house (which we designed ourselves) is 1,833 sq. ft. on one story, a modified California-style bungalow, as simple in geometry as we could make it.

The developer of this neighborhood is a good guy, and he wants to work with us; however, he is not really into “green” building per se. He aims at giving solid value for money, and he succeeds. We tend to prefer going with him, opposed to getting an outside bid, since he lives in his own development (built on land his family has owned for generations) and stands behind his product. He is listed as an Energy Star builder, but that standard is too wimpy for my tastes.

He has quoted us an affordable price for the house (VERY important, since this is all the money we have), but basically he would put up a stick-built house (well-built we have no doubt), in the traditional West Coast manner: ventilated crawlspace, under-floor R-19 insulation, 2×6 walls, plenty of wood (no Advanced Framing), R-19 fiberglass walls, truss roof with R-38 attic.

For HVAC we prefer minisplits (the local minisplit dealer lives in the same development), and for our 1,833 sf house the builder has budgeted for 4 minisplit units (probably the smallest Mitsubishi Mr. Slim). I, on the other hand, would like a sealed, insulated crawl space (and rim joist) per BSC recommendations, 2×6 walls (well-sealed) with R-23 Roxul rock wool or R-21 fiberglass, 1.5” to 2” polyiso sheathing (yielding a nominal >R-30 wall), and the attic insulated to R-49 or R-60.

The sealed crawl I think I can talk him into: the price should be a wash. And the sealing of air leaks is something he’ll surely do. But I think the polyiso foam with siding nailed to vertical battens will be a sticking point. I don’t think he’s ever built that way before, and I’m pretty sure he’s going to tell us it will cost a lot more money, what with the added trim-out details around the windows, etc.

My thinking is this: why should we put 4 minisplit units into a small house if we can put part of that money into improving the thermal envelope? (I know another builder, by the way, who is hungering to build us a hybrid ICF foundation-SIP wall structure. But he doesn’t live in the neighborhood.)

Your advice, please, especially about the minisplits. How many do I really need in a house of this size?

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Replies

  1. TJ Elder | | #1

    Gordon,

    Just to confirm your suspicions, the cost you would save by installing only one mini-split should more than pay for the envelope improvements. As the envelope improves, there's less need for mechanical equipment. Do some further reading to educate yourself about best practices for green building--this list is a great resource: https://www.greenbuildingadvisor.com/blogs/dept/musings/how-do-everything.

  2. Gordon Taylor | | #2

    But would one mini-split suffice?

  3. User avater GBA Editor
    Martin Holladay | | #3

    Gordon,
    Q. "Would one mini-split suffice?"

    A. There are two issues here: your total heating load and distribution effectiveness.

    The only way to know your total heating load is to calculate it. If your and your builder don't know how to calculate your home's heating and cooling load, you'll probably need to hire an energy consultant.

    Concerning distribution: if you leave your bedroom doors open for most of the day, you'll probably be fine. If privacy requirements mean that your bedroom doors are closed during the day, you may need one or two ducted minisplit units -- or backup electric resistance heaters in the bedrooms.

  4. Bruce John Stracke | | #4

    Gordon...

    Unless your home site is too far out from a good selection of builders I would recommend finding one who builds with the methods that support your goals for your home. Sound green and energy efficient building requires starting at the bottom of the pyramid and working your way up. Leaving out some of the steps or mixing and matching doesn't work well. Worse, what is acceptable in a traditionally built home may lead to unintended consequences in one trying to be energy efficient.

    Trying to make a cow be a horse is really difficult. Yeah, they both graze and look good in a pasture, but riding a cow is less than optimal.

  5. Jeff Nelson | | #5

    I agree completely with Bruce. My first thought was to find and hire a contractor who you don't have to drag kicking and screaming into the 21st century. Especially in Portland. Gordon, it seems you like this guy for a variety of reasons, but if you want to build responsibly, you may do better with a contractor who (if he's not experienced at green building) is at least willing to try some of the methods that are detailed on this site. And be open minded. Ignorant people who are willing to learn are a world away from ignorant people who prefer to stay ignorant. I know I'm making some generalizations here, but attention to detail is paramount in green building and I, for one, would not want to be working with someone I not only had to teach, but had to convince!

    Rant over.

    edit: Looks like you never mentioned Portland. Sorry.

  6. Gordon Taylor | | #6

    Many thanks to all who posted replies. I really appreciate it. No, I did not mention Portland, Jeff. Nor did I name a state or province. I'm deliberately being vague about location because I sincerely like and respect the developer in question. I'm certainly well aware of all Martin's posts, though I can't always (to say the least) follow the levels of nerditude to which the discussions rise. (There's a squiggly line under that word, so I must have come up with a new coinage.) I was just trying to get a ball-park estimate for my heating needs, and I was trying to do it without spending as much money for a consultant as I would for another mini-split. (Yeah, I'm cheap.) In any case, this helps. Thanks again.

  7. John Brooks | | #7

    In Texas we usually(not always) occupy our bedrooms at night...and we often close the doors.
    I think a multiple ductless mini-split concept could work....
    The problem is ....the "heads" are all oversized for reasonable size bedrooms.

    I think What we need are MICRO-Minisplits

    I know there are multiple head VRV systems ... but the heads still seem to be oversized for bedrooms and the "lines" still have to be run back to the main outdoor unit.

    I think It would be better if each Micro-head had a very short "line" to it's own outdoor heat exchanger.

  8. David Meiland | | #8

    There's no need to spend "as much money for a consultant as I would for another mini-split" in order to get a heat loss calculation. You could actually waste a lot of money by not doing this particular part of your project correctly.

  9. User avater GBA Editor
    Martin Holladay | | #9

    John,
    In Massachusetts, people usually close their bedroom doors at night, too. But Carter Scott, a builder in Townsend, Mass., isn't getting any complaints from homeowners who have bought his homes, which are heated with two ductless minisplits -- one in the downstairs living room, and one in the upstairs hall. The bedrooms have no heat.

    The key is to have a very well insulated thermal envelope with a low rate of air leakage. If you don't spend daylight hours in your bedroom, just leave your bedroom door open during the day.

    All I'm saying is, it works in Massachusetts.

  10. David Butler | | #10

    Gordon, lots of good advice thus far. John's comment about mini-split heads being too large for bedrooms is spot on, but mostly a summer issue. Martin is also correct in that suggestion that you may not need a head in each bedroom. Here's the rest of the story...

    If a house has enough insulation and tight enough, it may not need direct distribution in smaller bedrooms, and maybe not even in the master, depending on design loads (especially glazing area and u-factor). On the other hand, in cooling climates, even a super insulated home may need direct distribution to bedrooms, especially those facing south and/or west. Much depends on personal preference. I know plenty of folks who are ok with 60F at night during winter and don't mind sleeping with only a ceiling fan in summer, even if the bedroom reaches 80F! Personally, my wife and I have trouble sleeping if the bedroom is above 73F in summer. If you have kids, their tolerance depends on what they're used to. Infants are another matter. So I reject blanket statements about what works and what doesn't. All that being said, I don't believe the specifications you indicated are nearly enough to get away with a single centrally located head, at least not in your climate zone.

    Regarding John's point about minimum head capacity... Mini-splits with variable refrigerant flow (VRF) technology are able to ramp down capacity depending on load. However, the operating range of an individual head is rather limited, with minimum capacity typically 60% to 70% of maximum. So in a bedroom, where the peak load might only be 1k or 2k BTU/hr, you can end up with what I refer to as "motel room syndrome", especially under part-load conditions, whereby you end up freezing when unit is on and feel warm in comparison when it cycles off. This is less of an issue in heating mode since heat pumps naturally have a more moderate supply air temperature and longer runs times.

    Assuming a mini-split is the best solution for your home (I'm not convinced of that), the best way to resolve the distribution problem is to use a ducted head for the bedrooms (requires a ultra-low static duct system). But I can't imagine a variable drive mini-split system with four heads would cost less than a conventional ducted system. Any gain in efficiency VRF provides is unlikely to offset the additional cost. In my experience, the best use of mini-split systems is in a super-insulated home with design loads of less than 15KBTU/hr, or in disconnected rooms such as a garage apartment or bonus room.

    I specialize in designing mechanical systems for high performance homes. At the expense of appearing self-serving, you should give serious consideration to hiring a 3rd party designer for your envelope and mechanical systems. Without careful modeling and expert HVAC guidance, you'll likely spend far more than you should, or end up with sub-par performance, or both.

    David Butler
    http://optimalbuilding.com

  11. Gordon Taylor | | #11

    This is great advice. Thanks to you, David, and to Martin H. and the rest. I now have a much clearer idea of how to proceed.

  12. Gordon Taylor | | #12

    By the way, I went to the Taunton Store last night and spent $20 on old issues of FH, the better to acquaint myself with the topics at hand. (1/2 price sale)

  13. Jesse Lizer | | #13

    interesting read David. That is the sort of feedback I have been searching for for a long time as I too debate between a mini split system or a geo system for our new home.

  14. Nathan Spriegel | | #14

    Why not just use a transfer grille (motorized or not depending upon the supply air setup) between the large spaces with minisplits and the bedrooms? What little energy is used by the motorized versions would be more than recovered in the higher efficiencies of the wall-mounted versus ducted minisplit systems.

  15. David Butler | | #15

    Nathan, I've seen this work in a Passive House, but using jump ducts with in-line axial fans. Keep in mind that when circulating room-temperature air, it takes a LOT more CFM to satisfy a given load than with direct distribution, where you're working with 55F or 110F supply air. For this reason, this strategy would only work in super insulated, extremely tight homes. In any case, there's no way a couple of transfer fans (which aren't available with ECM to my knowledge) would be more economical than a ducted mini-split.

  16. David Butler | | #16

    Jesse, ironically, the more efficient the envelope, the more difficult it becomes to justify the additional cost of high efficiency equipment. Once you 'do the math' as many times as I have, it becomes obvious that mid-efficiency single-stage air source heat pumps nearly always have lower lifecycle costs than multi-stage, gshp, or mini-splits. Whole house mini-split systems, in my opinion, are only appropriate when conventional equipment won't work, for example, homes with extremely low loads. They're still too expensive to compete on efficiency alone.

  17. User avater GBA Editor
    Martin Holladay | | #17

    David,
    There's one more justification for considering a minisplit: they are appropriate for very cold climates, whereas most American air-source heat pumps don't operate at cold outdoor temperatures.

  18. Mojave Disaster, 3B | | #18

    There's one more justification for considering a minisplit: they are appropriate for very cold climates

    Hmmmn... do you happen to have a handy consolidated chart of different mfr's minisplits operation at "very cold" temperatures? Because from what I remember, hunting around, they're not typically brilliant. I'll go back and look--in the meantime, can you share your insight & sources?

    (If I'm wrong, I'll be happy to know it, because perhaps I'll get a minisplit.)

  19. User avater GBA Editor
    Martin Holladay | | #19

    Minneapolis,
    Model number PUZHA36NHA Mitsubishi Mr. Slim Hyper-heat -- $6,286 on the Internet.
    Nominal rating is 38,000 Btuh. Actual output at -13°F is 30,000 Btuh
    Variable speed. 20 amp maximum amp draw.
    COP at 5°F is 1.9. Obviously the COP is less at -13°F, but is still above 1.0.

    More specs here:
    http://www.mitsubishicomfort.com/media/226460/h2i_brochure.pdf

  20. David Butler | | #20

    Martin, interesting that you would make that point. I think you have it backwards. All mini-splits, at least the ones I'm familiar with, have hard cut-offs, typically between 0F and 10F. On the other hand, conventional (American) air source heat pumps have no hard cut-off. For example, Trane's expanded performance tables go down to 2F, and Carrier's go down to -3F. And these values don't mean they won't operate at much lower ambients. Case in point - the tables for my Lennox go down to -20F, and its design is not much different from the other majors.

    In practice, for homes with access to natural gas, I specify an external hard cut-off at the economic balance point, which depends on local electricity vs. gas prices. In order to calculate the economic balance point, it's necessary to refer to the expanded performance tables to estimate the COP curve. For example, my Lennox has a COP of 2.5 at 17F (rated) and 2.0 at 0F (estimated).

    Edit: I just read your subsequent post, and yes, the Hyper Heat is one example of a mini-split that operates below 0F. But to say American heat pumps don't operate at cold temps is simply wrong.

  21. Gordon Taylor | | #21

    Fantastic. A down-to-earth answer. Thank you, AJ Builder!

  22. Aj Builder, Upstate NY Zone 6a | | #22

    " Do I really need 4 minisplits?"

    Centralize a mini split or two in a superinsulated home. Install interior doors with 1" gap at floor. Add undertile electric radiant floor heat to daily AM used bathrooms. Add ceiling fans to bedrooms. Now you have comfort in all your rooms summers and winters. Cost effective strategy and simple.

    Perfection

  23. User avater GBA Editor
    Martin Holladay | | #23

    David,
    I accept your point: American air-source heat pumps can operate at cold temperatures, so my earlier comment wasn't quite correct. I don't know of any American air-source heat pump that can match the specs of the Mr. Slim Hyperheat, however.

    Furthermore, I'm confused about why you write, "For homes with access to natural gas, I specify an external hard cut-off at the economic balance point, which depends on local electricity vs. gas prices." If you're also installing a gas furnace for cold temperatures, you're installing more equipment than necessary. Why bother with a gas furnace AND an air-source heat pump?

    Natural gas is so cheap, that if you have a furnace, don't bother with the heat pump.

    [LATER EDIT] Oh, I just realized -- the heat pump is mostly there for summer cooling, and only incidentally for a little bit of heating during the swing seasons...

  24. John Brooks | | #24

    Undercut doors are not adequate for return air in most rooms

    and it is certainly not a "solution" for air distribution

  25. Daniel Ernst | | #25

    Gordon - I don't think Martin and David's suggestion should be overlooked. If you really want to know the heating / cooling load for your house, it's going to take some homework. Hiring a consultant that's well versed in this type of discussion will allow you to create a house design that's optimized for your climate, and a heating / cooling system that's optimized for your house. Yes it will cost some money, and take some time, but it should result in a more thoughtful design . . . and hopefully a more rewarding outcome.

  26. Daniel Ernst | | #26

    One thing that hasn't been discussed here is ventilation. HVAC - Heating, VENTILATION, and Air Conditioning.

    To John Brooks - I'm guessing that your skepticism of a centrally located minisplit has less to do with heating, more to do with cooling, right? Have you thought about a single point source for heating / cooling (a centrally located minisplit) coupled with an HRV / ERV? The minisplit provides the conditioning, the whole house ventilation system provides the distribution and mixing.

    The MICRO Mini-split you talked about is the ERV fresh air port located in each bedroom ;-)

    Martin - Do you know if Carter Scott's houses have balanced ventilation? I remember seeing what appears to be a Lifebreath HRV in this video:

    https://www.youtube.com/watch?v=ySPp4XECFf0

  27. John Brooks | | #27

    Daniel, My concern is more about cooling...
    And of course we need ventilation.
    I don't know how practical or affordable it would be ... but my understanding from a few sources including John Struabe's BSI Insight 022 (The Perfect HVAC) is that discrete components would be the most efficient.

  28. Gordon Taylor | | #28

    To Daniel Ernst: You point about the heating load calculation is well taken. I will certainly not neglect the advice. Thanks for your input.

  29. Aj Builder, Upstate NY Zone 6a | | #29

    Brooks, not thousands but millions of homes are lived in as I type this without distributed HVAC. Every hot water baseboard home. Every camp on the hundred lakes here in the Adirondacks.

    And as to the need for super well ducted cooling for bedrooms, I am sure those of you living in the south think its mandatory, but in my area not.

    My earlier spec is perfect for my area. And if Daniel Ernst's HRV is combined with it, then it is better than perfect.

  30. David Butler | | #30

    Martin wrote:
    "I don't know of any American air-source heat pump that can match the specs of the Mr. Slim Hyperheat"

    As I said before, my Lennox heat pump (mid-tier 15 SEER, 8.5 HSPF) has COP of 2.0 at 0F, a tad better than the mini-split you referenced. A lot of what I'd call 'conventional wisdom' regarding US-manufactured heat pumps is based on outdated information.

    Martin wrote:
    "Why bother with a gas furnace AND an air-source heat pump?"

    You're making me work hard today!

    A lot depends on local electric rates. In markets with average or better electric rates (say, 11 cents or lower), a mid-efficiency HP will cost less to operate above freezing than a high efficiency furnace. Keep in mind that in cold climates, in fact, especially in cold climates, there are far more heating hours above freezing than below. Referring to TMY2 bin tables for Minneapolis, we see that 2/3rds of the heating hours on average are above 30F. This surprises many folks. At $0.11/kWh, my HP has a COP47F of 3.95, so the average operating cost in the 30F to 65F heating range is about $0.82 cents/therm (electric rate * 29.3 / COP47F). I assume you know how to estimate the operating cost for a furnace. Just don't forget to account for blower energy. If blower is ecm/variable, we're talking 5 to 8 cents/therm (depends on electric rates). Roughly double that for a psc blower.

    In cold climates, I frequently specify heat pumps supplemented by a hydronic fan coil. A high efficiency hot water source serves double-duty for dhw. It's worth noting that a HP outdoor unit only costs a few hundred more than the equivalent AC-only condenser. The air handler costs considerably less than a furnace, although the hydronic coil offsets part of that difference.

    The benefit of this approach vs a dual-fuel furnace (furnace + HP outdoor unit), is that the HP and hydronic coil can operate simultaneously. This is not the case with a dual-fuel furnace (the HP must shut down when furnace turns on, else the freon will not condense). Why is this important? In markets with low electric rates, it makes sense to keep the heat pump on, even below freezing, taking advantage of it's lower operating cost. Also keep in mind that a HP's output doesn't fall off a cliff below freezing. It's a gradual slope. In high performance homes, it's not unusual for the thermal balance point to be in the mid-twenties. Assuming a balance point of 25F, the HP will still dispense with 80% of the load at 20F. This also seems to surprise a lot of people.

    Of course, in areas with high electric rates, a HP may not be the best choice (unless natural gas isn't available). However, utilities with high electric rates tend to have seasonal rate schedules, with much lower rates in winter. The marginal winter rate is what's important in this type of analysis.

  31. Gordon Taylor | | #31

    To Martin, Daniel Ernst, and others: Perhaps I should ask this in a new thread; however, I have just found the DIY heat load calculation software at hvac-calc.com. It looks good to me, and it costs $49 for an individual homeowner to use. Has anyone used this program?

  32. User avater GBA Editor
    Martin Holladay | | #32

    David,
    Thanks for your lengthy, detail-filled response; I appreciate it.

  33. Jesse Lizer | | #33

    Martin or anyone else familiar with the Mitsu hyper heats. I was reading some product literature and it appears, at least on the 36k H2i units you can "twin" the heads and use two. I assume this might be an option if one would want to have better air distribution? Any thought if it could be done on the 12k BTU unit?

  34. User avater GBA Editor
    Martin Holladay | | #34

    Jesse,
    I don't know. I suggest you call Mitsubishi and talk to a technical rep.

  35. Gordon Taylor | | #35

    Hello, can someone answer my question about HVAC-calc?

  36. David Butler | | #36

    Gordon, the s/w you referenced is not compliant with Manual J 8th edition. AFAIK, only RHVAC (Elite) and Right-J (Wrightsoft) are MJ8 compliant. The previous version (7th Ed.) was published in 1986 and doesn't even include support for low-e windows. The evolution from MJ7 to MJ8 was a huge step and long overdue. (The MJ book itself increased from 120 to 540 pages!) For example, MJ8 includes several computer procedures that greatly improve estimates of duct losses and solar gain through glazing. I could go on.

    The learning curve for the RHVAC and Right-J software programs is steep, and in my experience, those who use any load calc software without owning the book and being familiar with the Manual J procedure are destined to make serious errors. These programs are only tools and cannot replace knowledge and experience.

    In the design sequence, Manual S (equipment selection) follows Manual J. Here's a link to an article I wrote on Manual S: http://hub.am/pmwigX

  37. Gordon Taylor | | #37

    David, thank you. I'm trying to fight my way out of a jargon vortex. So you're saying HVAC-calc is useless, correct? Remember, this is a small house in Zone 4c.

  38. John Brooks | | #38

    Gordon, I think the best advice was at post #25......

    If you just want to save money up front....
    You can toss a coin and decide if you need one or 2 minisplits, add some ceiling fans, undercut all your doors and cross your fingers

  39. User avater
    John Semmelhack | | #39

    Gordon,

    For $49, you could muddle your way through a poorly organized piece of software that isn't up to speed with the current industry standard for residential load calculations and hope the result is accurate enough. Or for something like $249, you could have a professional (such as David Butler, for instance) run the load calculations.

  40. Aj Builder, Upstate NY Zone 6a | | #40

    Almost Brooks. Add the radiant bath floors and the HRV as Daniel mentioned and perfection finger crossing optional.

    Of course as I said before this design is for a cold climate not the south.

  41. Aj Builder, Upstate NY Zone 6a | | #41

    Gordon, read the Service Cavities blog. And even better check out a site mentioned in that blogs post #62. I think your builder and you will love the information.

    http://blog.lamidesign.com/p/usa-new-wall.html

  42. Jim Hassi | | #42

    We had a similar dilemma on a smaller (1120 sq/ft), very energy efficient house that we are just wrapping up: Do we use a 3 head mini-split, or use an HRV to help distribute the heat. In the end, we used a 2 head mini-split - but: We used a ceiling unit and ducted it into the 2 bedrooms. All of this is overkill in a house that has a heat load of less than 10K btu/h by Manual J and 0.6 ACH BEFORE BIB and drywall.

  43. Jesse Lizer | | #43

    Jim
    can you comment on how the system is performing, a long with your location?
    thanks

  44. David Meiland | | #44

    Jim, you could have skipped the heating equipment and gotten a medium-sized dog to heat the house.

  45. Gordon Taylor | | #45

    AJ, I am well acquainted with the jargon vortex contained within the Service Cavities blog, as well as the orgy of technical delights in that PassivHaus blog. It felt like the old Johnny Cash song, "I fell into a burnin' ring of acronyms." I assume that's what you're referring to. Your other points are well taken. I have read the USA New Wall blogposts by Mr. Vardera several times. Why, specifically, did you recommend that? Maybe I didn't read it carefully enough. That happens quite often. By the way (or BTW, if you guys prefer), the underfloor bath heating you recommend was already in our plans.

    And thank you, John Brooks, for your insights as well. Even if I end up following AJB's advice, I'll still look in the phone book.

    Last, I just want to say, like a modern Scarlett O'Hara, starved and grubbing in the dirt of modern verbiage, "As God is my witness, no matter what happens, I'll never use AFAIK in a written communication!"

  46. David Butler | | #46

    Gordon, one suggestion regarding bathroom heat. I typically recommend electric heat for small problem areas like baths and the knee-space of an oft-used desk. Adding a bit of supplemental heat to these areas can improve comfort AND save energy, assuming main thermostat is thus kept lower than otherwise.

    In areas where the supplemental heat may be needed over a period of hours, radiant heaters are best (as opposed to convection), combined with mass. I use one of those oil-filed radiators (DeLonghi) in my home office. But in a bathroom, where you need heat quickly for brief periods, convection is good, while mass provides little benefit. A low-wattage baseboard or "toe kick" heater would be a good choice, controlled by a wind-up timer. Just be sure to get the lowest wattage available. I've also used 250-watt IR bulbs (requires a special housing, with local fan) to good effect. These used to be fairly common in hotel baths. It's really more of a lifestyle choice, but these options are less costly than in-floor heat, and should use less energy since they would likely be energized for shorter periods.

    Attached is a resource list I compiled.

  47. Gordon Taylor | | #47

    Even better. Thank you, David.

  48. Aj Builder, Upstate NY Zone 6a | | #48

    Cold bathroom. Cold tile. Wake up, enter, burr. Wind up Davids timer. Jump in shower. Get out, warm air, cold tile.

    Radiant tile heat set on digital clock timer comes on warms tile before you wake up. Warm feet, happy feet, happy human, overall pure joy. Your first week you like it so much that you get a divorce from fighting over who gets to the bathroom first.

    Davids idea is a nice 1950s hotel idea though.

  49. David Butler | | #49

    Warm tiles are nice. I got around the 'cold tile' syndrome by placing a small mat in front of the vanity. The bath mat takes care of shower exit. Just pointing out options. As I said, it's a lifestyle choice.

  50. Keith Gustafson | | #50

    RE: David Butler

    I wonder if you could tell us the model number of your Lennox heat pump, I could find no info on lo temp performance of their products, most run on heatstrips in low temps

  51. Jesse Lizer | | #51

    I just reviewed a submittal on a project the engineer is using Lennox XP16 heat pumps for an assisted living facility. It said on the technical sheets from Lennox that the XP16-024 (2 ton) has a COP of 2.54 @ 17 degree. THe heat output at 17 is 12900 BTU, so quite a drop. Heat output at 47 degrees is 21600 btu with a COP of 3.48. SEER is 16, and they have other models said to get up to 19.

  52. Aj Builder, Upstate NY Zone 6a | | #52

    2.54 at the unit. Then figure your distribution efficiency losses.

    Seems like we should store heat pump output during the high temperatures of a day to distribute during the low temperatures.

    Could jump up to COP 3 doing such.

    I bet where I live it works out to 10 cents per 3200btus delivered at best and at a low temperature and high flow rate that feels drafty and cold.

    Would love to visit an install of a mini split that has happy owners within. Any near the Adirondacks?

  53. David Butler | | #53

    @Keith, I have an XP14 with CBX27 air handler (non-variable ECM).

    Attached are screenshots of the AHRI ratings database page for the 2-ton XP14 and XP16 with 2 different sizes for the air handler. Unfortunately, COP is no longer included in AHRI's certification database, but it's 3.98 at 47F and 2.60 at 17F for the XP14.

    Bottom line: The single stage XP14, actually has better heating performance and only slightly lower cooling performance than the 2-stage XP16, which is considerably more expensive. Note that the XP16 has HSPF of 8.5, compared to 9.0 for the XP14. Also note that the XP14's COP is 15% higher at 47F and heat capacity at 17F is 10% higher. This furthers save by reducing supplemental heat demand.

    The reason I'm drilling down on this is that it serves as a perfect example of why it's important to look beyond the nameplate ratings to find the best performing system. Even in cooling-only climates, the small (3% to 6%) bump in SEER for the XP16 isn't going to save nearly enough to justify the additional cost.

  54. David Butler | | #54

    AJ, distribution losses for the blower fan are already factored into the COP (assume 0.50" external static), and the remaining distribution losses for the duct system (conducted loss and leakage) are irrelevant if ducts inside the envelope. In poorly designed homes where ducts are relegated to an attic or unconditioned crawl, I'll grant you that the additional distribution losses will handicap a ducted vs. a non-ducted system.

    As for your comment about cost (10 cents forr 3200 btu delivered), I have no idea how you arrive at this. Please be specific. But for a fair comparison, no de-rating for distribution losses unless you're advocating ducts outside the envelope.

  55. Jesse Lizer | | #55

    David
    What is your building shell like? It is very interesting what you have been pointing out about these US heat pumps.
    2 ton geo quote is 20k (prior to credits), XP16 quote was 12k (prior to some credits), and 2 12k btu hyper heat units is around 5k installed. PLus around 2k for an HRV. Geo and HP include HRV. Load is roughly 9k btu each floor.

  56. Keith Gustafson | | #56

    Thank you David

    I still don't see data on very low temp performance,

    I believe that the Mini splits also lose a lot of capacity at low temps, but will still function.

    I have not seen the Americans claim similar ability

    of course the web is not all knowing

  57. David Butler | | #57

    @Jesse, my house is a mid-range slab-on-grade production home built in 2005 (I didn't design or build). I converted to all electric and added 5.4 kW of PV, to achieve net-zero plus 20% as it turns out. I could provide envelope specs, but don't want to drag this thread any further off topic.

    GSHP prices vary dramatically by location and dealer. Last year, a northern AZ dealer quoted $43k for a 2.5 ton project I was working on (two bores @ 275' each). Price included dhw with desuperheater and ERV. There are several reasons for high GSPH prices in that particular market: only one local geo dealer, an insanely generous utility rebate (sad, but true that this translates to higher prices), but most importantly, drilling costs are also insane at $20 to $25 per foot. Client ended up with a 15 SEER ASPH installed by top-notch dealer for under $8k, plus $5k for a solar dhw (under $2k with incentives) and $400 for supply-only ventilation (no way an ERV or HRV could ever recover its cost in that climate).

    If your home design and envelope is such that you can get by with two ductless mini-splits, sounds like that's the best option. I'm surprised you can get two Hyper Heat H2i splits installed for $5k, but I'm not doubting you. I'm guessing you're referring to the single zone version (MSZ-FE12/MUZ-FE12)? AFAIK, the only way to do multi-zone with H2i technology is to step up to City-Multi (P series), but prices are much higher and smallest outdoor unit is 3 tons.

    @Keith, low temperature performance can be found in the expanded performance tables. I've attached a sample page for the XP14. You can find some residential models on the commercial site here: http://www.lennoxcommercial.com/technical-documents/product-specifications.asp

    BTW, I am very impressed with the output capacity of the H2i at 17F. Very impressed, especially given the price point for two systems mentioned by Jesse.

  58. Jesse Lizer | | #58

    David
    that is correct, 2 of the single head units. A google will show they run from around 1600-2000 online each. However the more expensive P series does have a single 36k unit, but according to Mistu, it can be "twinned". You can add a 2nd head and it splits the load between the 2. However this is still considered the same zone, and each head does not have independent control. This would cost more however, around 6800 for the unit plus a 2nd head (not sure on that cost, couple k maybe?) plus install. This price is starting to rival the cost of a HP central unit w/ distribution.
    I do not have gas in my area (would have to be propane) so that makes the choices slightly more limited. However with the net cost of geo only a couple k more then a air to air heat pump in zone 6, that makes geo something to really think about hard.

  59. David Butler | | #59

    @Jesse, as you've already discovered, there's no upside to the P series in your case. But just as a technical point, twinning the heads would not be appropriate for a two-floor home. The P series supports true zoning, where each head is independently controlled, but supplied by a single outdoor unit. Full-function heads cost well under $1k.

    I've specified multi-zone M series systems for high performance homes with small loads, typically using one ducted head (SEZ) and one or two ductless heads (MSZ) with one MXZ outdoor unit. The inverter compressor ramps down to supply whatever combination of units is calling, but as noted in my initial comment, the heads have a fairly limited capacity range, and the ducted SEZ only has 0.2" available external static. The duct designer really needs to know what they're doing.

    Like I said before, as long as you feel comfortable with ductless, the MSZ/MUZ system, which has a SEER of 23 and a COP-47 of 4.2, seems like the ticket for your project. No way geo can compete with that. And if you can get away with the 9k size, the SEER jumps to 26 and COP to 4.5. I recommend you sharpen your pencil when you do the load calcs.

    BTW, the federal tax credit for geo only applies to the heat pump itself and the loop. Congress delegated responsibility to the EPA/Energy Star to define which systems and components are eligible for the tax credit. There's a FAQ on the Energy Star website that specifically says duct systems, supplemental heat and other components not specifically related to the high efficiency rating do not qualify (http://bit.ly/qZiVyG). Unfortunately, most geo dealers are either unaware of this guidance or choose to ignore.

  60. Jesse Lizer | | #60

    thanks.
    I will have to separate my model out and rerun the main floor different from the basement level in my Revit MEP. I would assume the 9k unit would be more then enough for the basement level with 75% underground. The main level I will have to focus closer on. I assume the 12k unit is what I will have to use though due to the eff. drop off at low temps to hit my design loads. (however I would plan on a couple backup baseboards)
    Current calcs are based on a 4" urethane SIPs panel with an inner 2x4 insulated "utility wall", getting me mid r35s. For just 2k more then the 4" panel, I can ditch the inner wall and bump up to the r40 6" SIP panel. My current assumed infiltration I have been using has been 1 air change. Obviously the goal is under that, but I think that is a realistic goal.

  61. Jim Hassi | | #61

    @Jesse (re comment 43): We are in Bellingham, WA - Marine (c) 4. The house will be occupied starting March 1, so it will be a while before I can really say how well it performs. We will be installing energy monitoring devices, so I should have some decent data after that.

    @ David (re comment 43):- Maybe!

    We did some interesting things on this project - You can find out a little bit at:
    http://netzerohomes.blogspot.com/

    Our blog needs some updating and is pretty bare bones right now.

  62. Aj Builder, Upstate NY Zone 6a | | #62

    David Butler. I bet most here feel as I do that your posting here is very helpful and needed. Please help us all out in the future as much as you may and know that I for sure read your posts with great interest.

    Someday I will have to see if anyone in my area is doing any heat pump work for reasonable install prices. Still we have higher than average electric rates and I see that only getting worse. Solar panels may be the answer for that part. Not sure what effect my 43 degree ground temperature has including mountainside water flowing through the near surface most of the year.

    As I type this we hit 65 degrees today and the lake is absent the foot of ice we might have had other years at this time.

  63. David Butler | | #63

    Thanks for the kudos, AJ. Last year I wrote a two-part series on heating strategies for high performance homes for Energy Vanguard. Part 1 explains why I eschew furnaces for high performance homes. In Part 2, I discuss heat pumps in cold climates and hydronic supplemental heat. And here's an excellent article written by Allison about the thermal balance point for heat pumps. Be sure to check out my somewhat lengthy comments that follow.

  64. Aj Builder, Upstate NY Zone 6a | | #64

    Will browse on, thanks David.

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