Low temperature heat pumps
user-1137156
| Posted in Energy Efficiency and Durability on
Ductless Minisplits are no longer the only answer to efficient heating in relatively cold climates!
There are, finally, air handlers that allow a fully ducted air to air heat pump system for small heat requirements in cold climates! Mitsubshi now offers the MVZ series, 12,000BTU/h,18,0000BTU/h,24,000BTU/h,30,000BTU/h,and 36,000BTU/h ducted air handlers that pair with their MXZ-C hyperheat outdoor units and together offer 80% + of rated heat output at -13degrees f.
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Replies
Jerry,
I discussed the Mitsubishi MVZ series in my June 2015 article, How To Buy a Ductless Minisplit.
There are disadvantages to the MVZ series; the main disadvantage is that it isn't as efficient as a single-zone ductless minisplit approach.
I am in Zone 5 (East Central Illinois) and I am seriously considering replacing the current AC split system with the Mitsubishi HyperHeat connected to one MVZ indoor. Per the below manual:
"Single unit connection is possible only with MVZ model. Connect 2 or more units for models other than MVZ."
https://meus.mylinkdrive.com/files/MXZ-4C36-5C42-8C48NAHZ_PAC-MKA30-50BC_TechService_OCH573_08-14.pdf
I heard the single-MVZ/MXZ combo is not AHRI-listed but is possible.
I am aware that the outdoor MXZ units are variable speed systems. However I am confused by the fact that the MVZ blower fan can run only at 3 speeds. Does that mean it can modulate only at 3 "stages"?
Thanks in advance.
The range of output is indeed limited by the range of the MVZ blower speeds, a turn down ratio lower than what is typical for wall-coil type mini-splits (or better class mini-duct cassettes.)
Dana,
Dhanyavad :)
I am a layperson/homeowner. I am trying to understand the "turn down ratio". Let's say an MVZ-A30AA4 is paired with a MXZ-8C48NAHZ. The CFM on the MVZ is 613-744-875 at the 3 speeds according to the below:
https://meus.mylinkdrive.com/files/MVZ-A12-36AA4_Service_HWE1407A_03-15.pdf
1. Can you explain the ratios and how they compare to the wall-coil type?
2. I am confused by the fact that even at the highest speed it's only 875 CFM. I heard each ton requires 400 CFM?
3. Are the blower speeds controlled by the thermostat or the outside unit?
4. I am thinking of employing zoning, in which case, would the zone controller be able to call for different speeds based on the ESP of the zones that are calling?
5. Any cons with the 4 ton MXZ verses a 2.5 ton MXZ since both can modulate down to 7200 BTUs?
6. I am confused that Mitsu did the MVZ with 3 speeds only. What could possibly be the reason for this considering many majors have variable speed blowers? COuld this impact humidity control?
I have no trust in what Mitsu tech support line says since when I first called asking if a single MVZ could be connected, the answer was NO. It was only after I pointed out the wording in the service manual that the person I spoke to put me on hold for 5 mins, then got back saying yes, it's indeed possible although the single unit connection isn't AHRI listed. Should I be concerned that it's not AHRI listed?
Thanks in advance.
I don't understand why the fan speed range is so limited on the MVZ. From the service manual, it sounds like they are using a dc motor, which means they should be able to modulate down to very low fan speeds without any significant added cost. I am also bothered by the fact that they don't specify the power consumption of the fan--that can indicate a) that they are embarrassed to admit how bad it is, or b) that they didn't pay any attention to it in design or testing. In any case, the capability of that blower to deal with pressure drop in long ducts inherently means that it will have more power consumption than the blower in a minisplit.
FWIW, the below states the "Minimum Circuit Ampacity" to be 1. Does that mean the maximum consumption is 230W?
https://meus.mylinkdrive.com/files/MVZ-A36AA4_For_MXZ_MULTI-ZONE_SYSTEMS_Product_Data_Sheet.pdf
I'm following this closely... why is the rated output (of 80%) only noted at a low of -13f... the competing mini-splits are rated to -25f... that is a big deal in zone 7... is it still producing useful heat at -25f?
Also what COP are they stating at -13f
I see Dana is back at GBA. I would be grateful for Dana's input on the questions I have above.
zzzz...zzzz... zzz...
...huh? Kya hua? Mention not, mera dost! ;-)
I really haven't dug into the MVZ specs enough to make even a good guess at it, but a high efficiency small air handler that maxes out at less than 230W total draw seems credible. The current isn't usually going to be in phase with the voltage on equipment, so max power is probably on the order of 200-215 watts, not the full 230.
Rules of thumb for CFM per ton used by the air conditioning folks don't really apply to modulating equipment. I don't know for sure, but if it's like their other coil types you probably have the option of either setting a fixed cfm or letting the system modulate for best efficiency/capacity, which possible for most of their wall-coils.
Oversizing the capacity of the compressor by more than ~1.5x beyond the design load is likely to result in somewhat lower average efficiency, but as long as it can still modulate down to the same level the efficiency hit shouldn't be very big (single digit percentages would be my guess.)
Most cold climate mini-splits will still be putting out useful (but unspecified) heat at -25F/ -32C. But Mitsubishi specs typically claim they automatically shut down somewhere around -18F, and won't re-start until it has warmed up to a few degrees warmer than that. Check the submittal sheets for this verbiage:
System cuts out at -18º F (-28º C) to avoid thermistor error and automatically restarts at -14º F (-26º C).
(Clipped from the FH09NA submittal sheet: https://meus.mylinkdrive.com/files/MSZ-FH09NA_MUZ-FH09NA_Submittal.pdf )
In reality, based on reports of others, most are still going at temps below -20F. The -18F is probably the upper bound temperature of where it might cut out, but you're certainly not guaranteed to have heat at temps below -18F, and are forewarned of that possibility in the documentation. If that's a show-stopper, either look at Fujitsu's cold climate equipment, or install the auxiliary strip heating option if using the MVZ. I don't see that verbiage in any of the MVZ documentation, what little of it there is online.
Tim: Which mini-splits are now specifying output at -25F, or is that just the "operating range", with unspecified output at that temp? Even the Fujitsu RLS3H series specifies -15F as the low end of the operating range, though the experience of others indicates they definitely keep going at -25F and colder, (but at around -30F outdoors the exit air temperature at the heads feels pretty tepid, as reported by Jin Kazama, in Quebec, who sometimes posts here.)
I know I'm resurrecting an older thread here, but just wanted to clear something up that I've been hung up on while trying to decide on which mini-split system to go with.
I just got off the phone with mitsubishi tech support, and they verified that while the fan speed only moderates between 3 different levels, the cooling/heating capability of an MVZ air handler is attached to the modulating capability of the outdoor compressor. So while the fan on the air handler might be set to always run on the high setting (maybe to overcome static pressure in a poorly ducted system), the air handler could still vary anywhere between 6,000 and 36,000 btu's (if that is what the compressor is capable of)
And they also confirmed (according to this link), that a 1:1 pairing is possible between the MXZ and MVZ units (at least for the higher capacity outdoor units)
http://meus1.mylinkdrive.com/sfiles/Application_Note_1029-MVZ_MXZ_configurations_v1.3.pdf