Some Mini Split Questions

[pcmeiners]

"but normal output is actually 300% "rated" output. It's marketing spin."

With Fujitsu, the rated output is 100% at -26, the highest output is not 300%, more like roughly 150% over the rated output. Which would you rather have, as you call a market spin, or down right false output, incapable of supply enough heat below zero. I will take 100% at -26 with an average COP of 4.

 

[American Locomotive]

This just tells me that Mitsu underrates their equipment. They still lose capacity as the ambient temperature drops. The solution is to simply upsize your equipment so that at very low temperatures you are still making sufficient heat.

If there is no oversight for the data sheets that knife cuts both ways. Meaning we can't trust any of them.

I didn't know how much capacity they lose.. Well, I didn't realize how much it was going to hurt until we had "serious freezes" in 2021. It's just odd-ball (to me) that they are rating units to "100% output" at -20C, but normal output is actually 300% "rated" output. It's marketing spin.

Yes, Hyper Heat units are technically oversized compared to their rated nameplate, but there's a lot more to it than that. They are NOT simply just larger units with a smaller sticker attached.

Let's take Mitsubishi's 9,000 BTU Hyperheat unit.
- 12,000 BTU/hr maximum cooling.
- 18,000 BTU/hr max heating @ 47F.
- At -13F, the unit is still providing 8,000 BTU/hr worth of heat at a COP of 1.9

Compare it to Mr. Cool 4th Gen 12,000 BTU "non Hyperheat"
- Maximum cooling of 12,850 BTU/hr
- At -13F, the unit is providing 3750 BTU/hr worth of heat @ COP of 1.37

Compare it to the Mr. Cool 4th Gen 18,000 BTU "non Hyperheat"
- Maximum heating of 21,640 BTU/hr @ 47F
- At -13F, the unit is providing 6320 BTU/hr worth of heat @ COP of 1.4

Compare it to the Mr. Cool 4th Gen 24,000 BTU "non Hyperheat"
- At -13F, this unit provides 10,300 BTU/hr of heat, @ COP of 1.28

So by cooling, the Mitsubishi 9k is more like a "standard" 12k BTU unit, but absolutely demolishes the 12k unit in heating. If you compare by maximum rated heating, the Mitsubishi 9k is like a Mr. Cool 18k, but still handily beats the Mr. Cool at -13F. It's not until you step up to the 24K Mr. Cool that the -13F heating performance starts to out-class the "9k" Mitsubishi. But the biggest thing to pay attention to is the coefficient of performance or COP.

The COP basically relates how many watts in of electricity, to watts out in heat. At -13F, the Mitsubishi is typically over 50% more efficient than the Mr. Cool. The 24k Mr. Cool is so inefficient at -13F, that it's only marginally better than just running an electric space heater. It's basically just heating your space with heat from the compressor instead of actually extracting heat from the air.

That is the "Hyperheat" difference. They are not just oversized units with smaller stickers. There's some real engineering in there to make them extract as much heat as possible at low temps, and do it efficiently.

 

[dcg9381]

Thank you for the explaining it. My first set of mini-splits I focused on cooling capacity.. Which is probably the right thing for our climate. In 2021 we had a record freeze and I was shocked at how little heat these things put out (at all). Note, it's not just about heating capacity in the cold (and yes, as you mention there are big differences in design / efficiency) - but a heat pump with a spinning fan does not do well when faced with a lot of freezing precipitation that tends to mis-balance fan blades arranged vertically. I caution everyone in cold climates to pay attention to heat capacity on these because if it bit me in TX, it's likely to bite someone else.

I eventually shut the units down. They did not sound good running and were going into defrost frequently. We got by with electrical resistance heat and propane. Lesson learned.

 

[rlitman]

I didn't know how much capacity they lose.. Well, I didn't realize how much it was going to hurt until we had "serious freezes" in 2021. It's just odd-ball (to me) that they are rating units to "100% output" at -20C, but normal output is actually 300% "rated" output. It's marketing spin.

Not odd at all. That's how "design temperature" works.

 

[pfettig77]

Ok. I'm still waffling between two separate units and on multi zone. I noticed one of the systems I'm looking at has a 28K BTU condenser and 12k and 18k indoor units. I realize they can't run to full capacity at the same time, but I want the option of 18k for the garage. It's got a lot of windows and 2x4 walls and 10' ceilings, so it'll be harder to heat. I'd like to be safe and have more heat available there. The bonus room will has the same square footage but far fewer cubic feet - so 12k should be more than enough.

When they're both running, will I get 16k BTUs from the 18k head and 12k BTUs from the 12k head?

 

[pfettig77]

.

 

[American Locomotive]

The capacity will be split it up in some proportion to the heads. If both heads are demanding maximum heating/cooling, I am not sure which one gets "priority". My assumption is the system would balance the refrigerant flow between the heads in some proportion to their maximum capacity.

 

[pfettig77]

The capacity will be split it up in some proportion to the heads. If both heads are demanding maximum heating/cooling, I am not sure which one gets "priority". My assumption is the system would balance the refrigerant flow between the heads in some proportion to their maximum capacity.

I emailed someone at AA minisplits and they said this (it doesn't make a ton of sense to me - and not just the grammar):

"Because they both dont run a full capacity. for example the 18000 btu will cool the room down to the diser temperature and then it will power down to 60-30% and then send full power to 12000 btu. because of the you can run more btu then the out side making them alot more efficient then traditional AC units. thank you"