Mitsubishi Hyper Heat MSZFH09 vs 06 HSPF
First question to the site after (finally) creating an account. I’ve read countless posts over the past few years as I built my home, so I give thanks to all for that!
Regarding inverter mini-splits, I am quite familiar with the Fujitsu Halcyon series single units from RLS to RLS3 on, some with XLTH with good results.
My newest project involves a well insulated “tiny house” on the farm (highly insulated c container) for local kids to enjoy, plan to try a Mitsu unit due to exceptional turndown ratios compared to Fujitsus given the low btuh requirements at calculated winter design temps.
Regarding specs, the MSZ/MUZ-FH06 combination, as rated, would be near perfect, though even that one with its 1,600 btuh modulated minimum would endure some cycling losses when over 40 degrees in my “bulding.” What I don’t understand is why the FH09 unit has the same 13.5 HSPF despite being rated at 10,900 btuh vs the 06 @8700.
After poring over submittal data, it appears to me that both units are using the same hardware (heat exchanger/compressor, etc) with the heating/cooling output differences only due to software (manufacturer limits of compressor speed primarily). Nonetheless,and expecially if that is the case, one would normally expect the HSPF to increase somewhat when the rated output is lower, correct? That’s certainly my experience with the various series of Fujitsu Halcyons that I believe similarly differentiated their models, specifically the 9 vs 12kbtu units.
Lastly, if anyone is still reading this, the integral pan heater is potentially helpful in my climate (-NAH suffixed units), though I have no idea how that changes performance; I’d expect it to be a huge impact especially if it’s a “dumb” system that just draws 120 or so watts anytime it’s below 32F).
For those familiar with the Fujitsu units, as I am, their original pan heat implementation knocked the HSPF substantially, the newer units much less so, but at least with the Fujitsu units I had a rough idea of the price being paid to melt condensate!
Thanks!
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Replies
> with its 1,600 btuh modulated minimum would endure some cycling losses
I'm curious, do you have data that shows that modulating down to 1,6000 btuh isn't worse for efficiency than cycling?
So far as I know, modulation is always more efficient. Yes, that can be teased out directly from the data such as the original NREL article on the 12RLS...the first Halcyon unit I had: https://www.nrel.gov/docs/fy11osti/52175.pdf
Modulation is the rationale for inverter-driven (variable speed) compressors in the first place....and their resultant incredible efficiencies over a broad range of outdoor temps/outputs in comparison to old school single stage, or even dual stage, central units.
> modulation is always more efficient.
Almost all "conventional wisdom" about mini-splits sizing is sometimes false. A quick look at NEEP data for a FH06 shows that cooling COP at min capacity is ~11% less than at rated capacity. That's about the same as the typical loss from cycling. Some other models are much worse (exceeding cycling losses), others show better COPs at min capacity.
That is true in a few scenarios at min capacity modulation but those #s need to be taken with a grain of salt. My understanding of those discrepancies is the fact that at ultra low modulation, the baseline power use of the unit becomes a significant factor....meaning the wattage needed to keep the unit "alive."
But I'm primarily interested in heating season, where that also comes into play at lower temperatures. So yes, there are scenarios where the attendant inefficiencies of cycling can be obviated.
For example, in the Fujitsu units (which I'd also expect to be the case with Mitsubishi), when freezing or below outside the unit draws about 60 watts 24/7 (I've measured this) even when it's powered down entirely...so long as the breaker supplying it is active. This draw is apparently to keep the compressor lubricants adequately warm to prevent damage upon eventual startup in cold weather.
In our current camp, visited infrequently during January/February, I address this by leaving the circuit supplying the unit off. Prior to powering up the unit if I visit in January when it's 20 degrees out I flip on the breaker, wait 20 mins, then power up the unit.
Investigate "refrigerant migration" (or read the manual). Usually needs more like 20 hours of warming to get rid of the excess refrigerant diluting oil in the crankcase.
"20 hours" with 60 watts heat input and 15 feet of insulated 1/4"-ish lines is kinda comical thermodynamically. Fire anyone? No matter, I haven't killed the units in 10+ years of use, and currently keeping a 2,300 sq ft home at 72 degrees in January/February (pretty cold here then) with 800kwh usage during each of those two months. I guess something's working...
Pump/compressor efficiency is dependent on a lot of variables (especially with the vapor injection and wide range of loads, temps and pressures a ASHP runs at). If you slow down a compressor it will draw less power (watts), but the amount of work being done per watt may drop faster than the wattage drops (lower efficiency). Or in other words the compressor will have an optimal efficiency range and the further you move away from it the less efficient it will become.
The watts per hour might lower, but the BTUs/watt may be lower too.
This is evident on the LG units (that have the lowest min modulation of anybody I think), but the efficiency is documented to be lower at min modulation. This is no surprise and may still be a good compromise for performance overall.
"Regarding specs, the MSZ/MUZ-FH06 combination, as rated, would be near perfect, though even that one with its 1,600 btuh modulated minimum would endure some cycling losses when over 40 degrees in my “bulding.”"
Is dehumidification a concern? Just be aware that some of these mini splits with super low minimum operating capacities do a terrible job at dehumidifying under low load. I've got an FH09 that, as far as I can tell, does essentially zero dehumidification until it's operating at more than 50% capacity. I'm guessing b/c I can't measure that, but I don't really see any dehumidification until the outdoor temperature gets up to about 90. So yeah... an 80 degree day with a 65 degree dewpoint? I'd see very little dehumidification from my FH09 under those conditions and would probably be running my standalone dehumidifier.
The FH series has been retired by Mitsubishi and replaced by the new FS.
anyone else with thoughts on this? The FS specs seem virtually identical to the FH BTW but good to know. I find it odd, though, that the listed COP for the FS of 2.26 at maximum capacity is the same 2.26 at 5 AND -5 which is slightly worse than the FH at 5 (which is listed at 2.45). Leads one to believe there was a data entry error there.