Image Credit: Carrier
More Musings of an Energy Nerd
UPDATED on July 20, 2018, with new information from Carrier.
Mitsubishi and Fujitsu sell air-source heat pumps (ductless minisplits and ducted minisplits) that work well in cold climates. Many GBA readers report that these appliances are providing dependable space heating in climates as cold as Minnesota, Vermont, Maine, and Quebec, where temperatures drop to -20°F or colder.
Traditionally, U.S. manufacturers of air-source heat pumps have favored ducted units over ductless units. Most air-source heat pumps sold by Bryant, Carrier, Lennox, and Trane, for example, are designed to be hooked up to forced-air ductwork, just like a typical furnace.
Here at GBA, we often advise readers that ductless minisplits are a good way to heat and cool a compact well-insulated house. That said, ductless minisplits don’t work as well for large, spread-out homes or for homeowners who want uniform heating and cooling in every room, even when doors are kept closed.
Most U.S. homes have forced-air HVAC systems — that is, systems that distribute heat and cooling through ducts. Some GBA readers wonder, “Are there any cold-climate heat pumps that can be hooked up to conventional forced-air ductwork — the type of ductwork found in a typical American house?” We’ll do our best to answer that question.
Note that there is always an energy penalty associated with any heating or cooling equipment connected to ductwork. Equipment connected to ducts will never be as efficient as the best ductless equipment, because it takes a substantial amount of electricity to push air through ducts.
What about ducted minisplits?
Japanese manufacturers of ductless minisplits also manufacture ducted minisplits. Even though these units are designed to be connected with ductwork, they generally can’t be connected to the type of forced-air ductwork installed in a typical American house.
Most ducted minisplit systems lack the…
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24 Comments
Ecologix Heat Pump
You may want to include the Ecologix Cold Climate Heat Pump in this list. They have excellent support and respond to questions quickly. Any data not available on their website (which is very poor) is only an email away. Here is a link to their spec sheet. http://ecologix.ca/products/product-selection-tool/SpecSheet/?productcategory=3&modeltype=16
Other info on Carrier Greenspeed
Even though they don't provide the information in written form, they have a mathematical model for the Carrier Greenspeed, and an online tool that can allow you to estimate the capacity (but not the efficiency) at temperatures as low as -30F, at least for the 2 ton and 3 ton models:
http://www.tools.carrier.com/greenspeed/
Click on the Heating Capacities tab, then adjust the Heating Design Temp down to the temperature of interest.
For both the 2-ton 25VNA024A**30 and 3 ton 25VNA036A**30 the capacity at -15F is about half it's capacity at +5F, and the capacity at -10F is about half the AHRI rated capacity at +17F. The drop in capacity is fairly linear with temperature from +5F on down.
Regarding propane as "backup", that is more expensive to install than auxiliary resistance heaters (available for all the US manufacturers' goods, as well as Mitsubishi's MVZ and PVA air handlers), and may be more expensive to operate too, if the heat pump's capacity can cover the load down at least down to the 90-95th percentile temperature bin for most areas. (In areas with cheap electricity and expensive propane it's always cheaper to use the electric heat strips.) At +10F most heat pumps are running a COP of at least 2, and even at -10F most heat pumps are running a COP of about 1.5, and burning some heat strip to make up for just the capacity shortfall for just 10% of the load isn't going to destroy the average seasonal efficiency. When propane is being used for the "backup" when the heat pump is out of capacity 100% the heat is from the propane, none from the heat pump, so there is no COP leveraging the energy inputs.
Even in fairly expensive electricity areas it rarely pencils-out in favor of PROPANE dual-fuel systems (but it can for natural gas, in some areas.) Given the volatility of propane pricing, and the fact that electricity rates are regulated, it's a safer bet to skip the dual-fuel. Install enough heat strip to cover the shortfall in capacity down to maybe 15F below the 99% outside design temp, not more. (There are usually between 2-5 different sizes of auxiliary heat strip available for most models.) By not oversizing the heat strip you won't run into excessive cycling of the heat pump at low ambient temperatures, which could take an additional toll on efficiency almost as big as running the heat strip.
Other Asian mini-split ducted manufacturers???
Are Mitsubishi and Fujitsu really the only players in the game for mini-split ducted systems that can be connected to typical ductwork in US homes? I seem to recall Dana Dorsett pointing me to a system by Panasonic on this website. Is my memory faulty or should I go back and check the static pressure requirements for that Panasonic air handler?
New home construction
Is there anybody that would recommend a whole house mini split system for a new construction home?
Other ducted Asian heat pumps @ Antonio Oliver
I don't believe Fujitsu makes full-sized air handlers that easily use pre-existing ducts designed US style AC & gas furnaces, but they make the most powerful mini-duct cassettes on the market. Almost all mini-split vendors sell mini-duct cassettes similar to the Fujitsu xxRLF "Slim Duct" units, but most of the competition's mini-duct offerings have fairly wimpy blowers compared to Fujitsu's.
LG, Daikin (who now own's Goodman), Samsung and several others have heat pumps with large-duct type air handlers, some VRF, others single-speed. I don't recall Panasonic having anything like that.
http://www.lg-vrf.com/vertical-ahu.aspx/ARNU123NJA4
https://cms.daikincomfort.com/docs/default-source/default-document-library/brochure/cb-hpahu.pdf
https://samsunghvac.com/products/cac_multi-position_ahu.html
Gree makes similar products sold into other markets, but I'm not sure if they've been marketed in North America yet (at least not under the Gree nameplate.)
James: "Is there anybody that would recommend a whole house mini split system for a new construction home?"
Yes.
Response to Yupster (Comment #1)
Yupster,
Thanks for the link to the page with information on the Ecologix heat pump.
I look forward to hearing reports from GBA readers who have installed or lived with this equipment.
Response to Dana Dorsett (Comment #2)
Dana,
Thanks for the further information on the Carrier Greenspeed heat pump, and for the link to Carrier's GreenSpeed Calculator. I have edited my article to include that helpful information.
Like you, I don't recommend installing a propane furnace as a backup heating source for a home with an air-source heat pump. That's why I provided a list of cities with outdoor design temperatures of 4°F or above. If you're going to install one of these American-made air-source heat pumps, you should live in a climate that is warm enough that you won't need a second heating system as backup. If you live somewhere colder, you should probably install Mitsubishi or Fujitsu equipment -- unless the GreenSpeed Calculator convinces you that Carrier equipment can cover 100% of your load at design conditions.
The propane-furnace-as-backup approach was used by a group of Minnesota researchers -- but it's not an approach that I recommend.
Response to Dana Dorsett comment #5
My mistake, Dana. It was LG, not Panasonic. That said, Martin is still only recommending Mitsu and Fujitsu as reiterated in comment 7.
Response to Antonio Oliver
Antonio,
I mention Mitsubishi and Fujitsu because I've heard many reports of successful installations with these two brands. I know much less about LG equipment.
That said, if LG provides performance specs at -13°F or -15°F, or whatever your design heating temperature happens to be, and if you can find equipment that meets your design load, I see no reason not to use LG equipment if that's what you want to install.
Thanks again Martin
Thanks, Martin.
I found a variety of data here for an LG outdoor unit for the air handler pointed to by Dana:
http://www.lg-vrf.com/multi-v-s.aspx/ARUN038GSS4
Operating temperature down to -4F, apparently. Good enough for where I live, but probably not for people requiring operation down to -13F. Although I recall reading that for a particular Mitsu unit, people had been satisfied with performance below the lowest recommended operating temp.
See page 10 of this document:
Engineering Manuals Outdoor Units Multi V™ S
Response to Antonio Oliver
Antonio,
Thanks for the additional information -- and good luck with your project.
The 5 tonner is good down to -13F (WB) -12.6 (DB)@ Antonio
See the capacity tables starting on p.97 of the manual- the 5 ton LG Multi-V is good for 43-44K @ -13F outdoors, 70F indoors.
Capacity tables for their smaller units all stop at -4F.
http://www.lg-vrf.com/multi-v-s.aspx/Download?filename=EM_MultiV_S_OutdoorUnits_02_18.pdf&id=1508
Mitsubishi System
Thanks to a lot of help from Dana and others on this forum, we decided to go with a Mitsubishi zoned system using a MVZA18AA7 multi position unit downstairs and SEZKD12NA4R1 horizontal ducted unit upstairs for our new house. I found the "mylinkdrive" website very helpful when making that selection.
The price for the Mitsubishi system installed with ducting is $17,050 using the Hyper Heat MXZ-3X24NAHZ2-U1 external unit or $15,600 using the Non Hyper Heat MXZ-3C30NA2-U. We live in the Seattle area and so will likely go with the non-hyper heat external unit. The price for the Carrier Green Speed 3-ton, 25VNA036 Infinity Series was $18,600. Our design peak heat load is 22,000 btu/hr in our mostly code built, 2,200 sq. ft. house. We will have back-up propane heat only because we wanted to have a cozy free standing propane stove in the kitchen.
The Mitsubishi unit had a number of advantages important to us including better sound performance inside and out, high efficiency DC motors, and 3 speed fan speed on the internal units. We were able to design around the low static pressure performance of the horizontal ducted unit. We plan to run the units continuously and connect our HRV supply piping to the intake ducting.
NVH, etc. From Ducted System
We've been using a Carrier 2.5 ton, 8.5 HSPF, 13 SEER, single stage heat pump since Dec. 2001. Installation cost was $4,575, which included a new variable speed air handler, 5 kW + 10 kW staged strip heat package, programmable thermostat, and large pleated air filter that is changed yearly. It still works great with minimal maintenance. A defrost circuit board failed at year 10 ($700-dealer) and thermostat's humidistat lost accuracy in last year and was replaced with new Carrier COR TS ($75-me).
With a combination of greater home insulation and leak sealing over the years, plus learning the ins and outs of the unit (hidden settings), I can happily report that the HP provides over 98+% of necessary heating and the backup strips only come on (as auxiliary- for short time) when the outside temperature is between 0F to -5F. Some years this doesn't happen. Our design temp. is 9F and home is 2200 sf split foyer.
As the unit is now on year 17 and uses freon based refrigerant (never leaked), I'm keeping abreast of better and more efficient units for future replacement. One that has caught my eye is Daikin SkyAir Inverter Ducted. 1.5 ton, 20 SEER, 12 HSPF, and capable down to -4F, with strip kits also available. Downsizing is the goal for efficiency sake, plus modulation with the inverter and better turn down ratio most of the time. Let the strips handle the 2-5% on the left side of the curve. Also, it has very low NVH with swing rotary compressor and horizontal mount. Or maybe go with 2 ton unit, no backup strips, and less turn down ratio? Need to do some math on this.
NVH- our unit is moderately loud and turns on and off all the time. I congratulate Copeland Scroll Compressor engineers, as this part is old-school durable. I took care of the 'rattle trap' nature of the outdoor Carrier unit with self installed sheet rubber bushings between metal panels and proper leveling, as it had settled a bit over the years. I desire an outdoor unit that is quieter- 50 dB range. Unless Carrier has improved them, the GreenSpeed units sound loud (higher pitch) in severe cold at high operating capacity.
Finally, our single speed unit is excellent at humidity control, especially with the new, more precise COR thermostat. It lowers the air handler fan speed , combined with 3 degrees "cool to dehimidify" range, to keep RH around 50% all summer long. This does lower the daytime set point from 78F to 75F or 76F, especially in the morning or after a period of heavy rainfall. It's back up to 78F and 50% RH in the late afternoon and/or during dry periods. I'm willing to use a little more energy to keep the indoor air dry, especially downstairs which is 50% below grade.
So my last question is- Do ducted mini-splits, especially smaller more efficient units, have less ability to dehumidify the air as the older units?
It depends on the cooling mode @ Joe Dwyer
>Do ducted mini-splits, especially smaller more efficient units, have less ability to dehumidify the air as the older units?
Ducted mini-splits have a "dehumidify" or "dry" cooling mode that can be selected, which will do most of much what your current thermostat is doing when set up for "cool to dehumidify", but without over-cooling. A mini-spit in "dry " mode automatically adjusts the latent-to-sensible cooling ratio by running the coils a bit cooler via a combination of refrigerant volume & blower speed adjustment, but some still operate to the temperature setpoint, others not. Operated in "dry" mode the SEER is lower and it's sensible cooling capacity is lower, but that's the nature of physics, eh? (Cooling to 3F colder than you normally would just for better latent cooling has an even bigger penalty.) When the latent loads are low you can always run it in the normal cooling mode. See the ultra-brief discussion on p.8
& 9 of the manual regarding DRY mode for the SkyAir units. If I'm parsing the English correctly it still operates to a temperature setpoint, but you can't adjust the setpoint while it is in DRY mode:
http://www.daikinac.com/content/assets/DOC/OperationManuals/FTQ_PBVJU%20Operation%20Manual.pdf
Like most large air handler mini-splits the 1.5 ton Daikin SkyAir has a limited turn down ratio of barely over 2:1: 9,000BTU/hr min, 20,000 BTU/hr max in heating mode). The 2-tonner has the same 9000 BTU/hr minimum, but a 3:1 ratio (27,000 BTU/hr max), which is better than most! Depending on your actual outdoor lows it may have sufficient capacity to dispense with the heat strip kits altogether. Since it's HSPF was tested at 27,000 BTU/hr (instead of 20,000 BTU/hr for the 1.5 ton unit) and has the same 9K min-modulation as the 1.5 ton version, the as-used efficiency will probably be higher than the 1.5 tonner, since it'll be running closer to it's mid-range sweet spot most of the time. That is despite having slightly lower SEER and HSPF numbers at the "rated" modulation level.
http://www.daikinac.com/content/assets/DOC/Product%20Brochures/CCFFTUSE12-05R%20FTQ%20RZQ_P%20-%20SkyAir%20Consumer%20Tri-Fold.pdf
The capacity tables only go down to +14F, but the 2-tonner delivers a bit over 24K @ +14F outdoors, 70F in, the 1.5 tonner delivers 20K. See p88:
http://www.daikinac.com/content/assets/DOC/EngineeringManuals/2017/Engineering%20Manual-SkyAir-web.pdf
You can safely probably infer it's capacity at your design temp of +9F and +70F indoors by the capacity numbers at 75F indoors, +14F outdoors (5F warmer than both the indoor & outdoor design temps, for the same delta-T), which is 18K for the 1.5 ton, 24K for the 2 ton.
Do you happen to have the capacity tables for your aging 1-speed 2.5 ton Carrier handy?
@ Dana Dorsett
Thanks for your thorough reply. I previously looked at the engineering manual, but not the brochure showing the turn down ratios. The 2 ton model seems the way to go, having the same low end capacities for heating and cooling and a higher top end heating capacity for really cold weather events (-5F common to -10F max). It will probably also work without heat strips, so we can get back a little money up front to offset the higher cost of 2 ton versus 1.5 ton system.
I'm not familiar with how SEER and HSPF are calculated for variable speed units, as it's easier to understand with a single speed like ours. So you are saying that a larger inverter compressor can be more efficient in real world conditions due to running more often at moderate speed instead of high speeds, which isn't accounted for in the ratings for such units?
Our unit is Carrier 38YRA030320 outdoor and 40FKA002300 indoor. The company that installed it claimed 30K BTU and 13 SEER, with no HSPF rating. When I said 8.5 HSPF, this is really just a best guess for similar era units and it could be lower. I couldn't find a combo rating, but the 38YRA unit with slightly newer air handlers (circa 2004) does come up in a search:
http://dms.hvacpartners.com/docs/1009/public/00/38yra-4si.pdf
The balance point table goes down to -3F, but it uses a 3 tons air handler with 2.5 tons HP. Our AH is only 2.5 tons. Anyway, our current balance point is around 0F to possibly -3F, based on observation of the unit a few years ago operating on a very cold morning with old thermostat and "aux" symbol+ higher fan speed+ hot air from register. With the new thermostat, such data is logged to a web portal!
I've set our AH to operate in 'comfort' mode, which means 700 CFM versus 875 CFM for cooling and 785 CFM versus 875 CFM for heating. Thus, both SEER and HSPF need to be down rated slightly versus factory rating. Finally, I did a search for the rating of aging units and came across "Building America Performance Analysis Procedures for Existing Homes," which has a formula:
EFF = (Base EFF) * (1-M)^age
EFF= 100 * ((1-.01)^16.5)
EFF= 84.7%
I need to pin down our heat loss at balance point more precisely, but I think it's around 8K-11K BTUs/hr at -3F. I also need to extrapolate 2 tons SkyAir HP capacity at very low temps. Does this sound reasonable?
Sorry, wrong Carrier 38YRA link. Here it is:
http://dms.hvacpartners.com/docs/1009/public/0b/38yra-7pd.pdf
Yes, lower speed means higher efficiency (mostly) @ Joe Dwyer
Manufacturers of modulating equipment get to choose the modulated level at which efficiency is tested at 47F for the AHRI "rated" or "nominal" heating output as long as it has enough capacity at +17F to hit that range. Manufacturers play marketing games a bit, and can even inhibit the unit from exceeding a given output at any temperature, which is what Daikin seems to have done with the SkyAir products:
If you look at the capacity charts in the engineering manual, the nominal 20,000 BTU/hr heating capacity AHRI conditions for 1.5 ton SkyAir is also it's total capacity at 70F indoors at all temperatures, from +14F to +50F a curve flatter than a skating rink!
The chart for the 2 ton unit indicates that at 70F indoors the total capacity is almost the nominal 27,000 BTU/hr at +23F, but only 24,000 BTU/hr @ +14F, but limited to 27,000 BTU/hr from 32F through 50F. That's not quite as flat a curve, but 20% more capacity at +14F than the 1.5 ton unit, and probably 20% more (unspecified outputs) at 0F or -5F. They could have kept it a flat 24K from +14F to 50F, but probably needed to call it 27,000 BTU/hr for marketing purposes, to distinguish it more from the 1.5 tonner.
But since they both can modulate down to 9000 BTU/hr @ +47F the 2 ton unit is probably going to be operating in the high efficiency sweet spot over a wider range of temperatures than the 1.5 ton unit. I doubt that it's the same unit, just being controlled differently- the coils.)
Looking at the capacity tables for your existing Carrier you have ove 18K max capacity @ 17F (17K net defrost), just shy of 13K @ -3F (12K after defrost), and if it's running the heat strips at around 0F it means your load is probably something like 14-15K @ 0F. It's not clear if the 1.5 Daikin would be able to deliver that much at 0F (since it's unspecified) but maybe. It's almost certain (though still unspecified) that the 2 ton Daikin would, (with margin!), if it's delivering 24K @ +14F.
A 2 ton GreenSpeed also puts out about 24K @ +14F, which drops to about 17K @ 0F, and 16K @ -3F. Click on the Heating Capacities tab on this page, then play around with the outdoor design temperature setting for eyeballing the capacity:
http://www.tools.carrier.com/greenspeed/
If it's about the same proportionally the 1.5 ton Daikin's 20K @ +14F would become 13K @ -3F, 14K @ 0F, which could be marginal. But the 2 ton would be delivering about 17K at -0F, 16K @ -3F, which should cover it without engaging heat strips.
So, if comparison shopping, compare the up front cost of the 1.5 ton + heat strips to the cost of the 2 ton with no heat strip. I suspect the difference is pretty small.
Age derating curves have wide error bars, so I'm not sure you should be using the derated capacity value for your heat load analysis, then specify the new equipment based on that derated number. The new equipment will age too, perhaps at a different rate, or maybe the same. But if you use the fully rated value of the old equipment in the analysis you'll do just fine specifying the new equipment without needing to upsize from there.
Mitsubishi and Trane
I recently had a conversation with an HVAC contractor who carries both Trane and Mitsubishi. He indicated the two companies have formed a joint venture.
https://mehvac-blog.com/joint-venture-mitsubishi-electric-trane/
I'm wondering if we will be seeing better cold weather performance from Trane in the future?
Thanks for this thorough analysis of a topic that's hard to get info on and seems uncommon where we live. We're currently planning an addition to our 1920 house in the northeast. The house is currently 1600 sq. ft 3 bedroom colonial. With addition it will be 2400 sq ft. 4 bedroom. Current system is the original single-pipe steam pipe with a natural gas broiler. Winter running costs are not too bad. No ducting or central air yet.
Despite the cheap prices of gas, would love to modernize the HVAC, go electric, remove the steam system and introduce a heat pump, but having trouble deciding which way to go. Will be adding insulation and sealing to the house regardless. Got a proposal for a ground-source heat pump with ducting, but the total cost is high, and they want to put the air-handler in the attic which seems to be an efficiency no-no. A centralized air-source system might be the best compromise, the contractor I spoke to worked primarily with Fujitsu equipment, but I worry about the efficiency and load in the winter. Would love to be able to go able to go ductless, with the ceiling-mounted cassettes in bedrooms, and larger units on the first floor, but it seems like it would be a lot of units & equipment in total if we have one in each bedroom.
Curious if anyone has been in a similar situation with a renovation/addition and what direction they headed in. Of course going with a gas furnace (or keeping the steam heat and just adding mini-splits to the addition) would be the simplest and cheapest but we want central air, and would love to be able to get away from gas. Already have solar, but it covers our current usage, with window A/C units, so most of the heat pump electrical would not be covered, so increased running costs is a concern.
User-7146350,
First of all, can you tell us your name? (I'm Martin.)
I don't think it's possible to generalize about the best type of heating and cooling equipment for an old 1920s house. Every house is different, and for the best advice, you'll need to talk to an HVAC contractor or mechanical engineer who can make a site visit.
If you are thinking of installing a forced-air HVAC system in an older house that has an existing steam heating system (and no central air conditioner), the first two questions are:
1. Where will you put the mechanical equipment?
2. Where will you run the ducts?
If the answers to these questions are daunting, you may want to take a closer look at ductless minisplits -- especially since your big PV system seems to indicate an interest in all-electric solutions.
Hi Martin, I'm Martin as well actually!
Yes I've had HVAC contractors come by, they tend to want to put the air handlers into our unfinished attic as that is the simplest retro-fit, common in our area, with ducts coming down through closets into the first floor ceiling. Our basement has a low ceiling and is mostly finished. If we rip out the steam equipment and pipes, we would have some pathways for ducts along the basement, but I could not see an easy pathway for the ducts to get up to the second floor, as there are not many closets on the first floor to easily run them through and access all the upstairs bedrooms. However with our addition planned for next year, that could open up some more options.
Yes, I'm interested in the mini-splits, it just seems like we would need a lot of them to get adequate coverage when bedroom doors are closed. Perhaps the 3 small bedrooms would have a mini-centralized air handler in the attic with short ducts.
Martin,
Good luck. You're right, of course, that HVAC contractors often make inappropriate suggestions (like putting equipment in a vented unconditioned attic). Don't go down that path -- unless you are willing to pay the considerable cost of converting the attic into an unvented conditioned attic.
For more information, see "Solutions to the Attic Duct Problem."
Attics are just so tempting and convenient for this sort of work that we' re fighting a losing battle here. All that empty space for equipment and ductwork, with access to all the rooms below.......But air handlers and ductwork in the attic will cost you for the life of the house, in terms of both comfort and $$. It's just a bad practice that's got to be stopped.
You did mention that you are doing some insulation and air sealing. Where you are, and how much you are doing is important. If you get your heat and cooling loads down enough, it makes the minisplit solutions much more affordable and comfortable.
At 2400 square feet with more 'normal" levels of insulation, a two-zone solution could work. You could put the air handler in a mechanical closet in the new addition, with only the supply ducts running through the attic and buried in insulation, per Martin's article. This would also give you another reason to add more insulation to the attic, and that's not a bad thing. The first floor mechanical equipment and ducts would be in the basement. Whatever you do, make sure that your HVAC contractor makes the ducts airtight.
What about the new Daikin Fit? https://daikincomfort.com/products/heating-cooling/whole-house/heat-pumps/daikin-fit-heat-pump
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