minisplit Inverter vs Standard compressor

AndyG · May 07, 2012, 07:56:24 AM

I was looking at minisplits on minisplitshop.com and decided to compare the load amperage of the inverter type compressor versus the standard type. I am looking at 9000btu heat pump units. Their specs show less than 1amp difference. There is $215 difference in price. I will be in places where power is very limited so efficiency is important to me. $215 is a lot to spend for 1 amp. What am I missing?

dukegrad98 · May 07, 2012, 08:02:11 AM

Others with more experience will surely respond, but here's how it was explained to me... Apparently the inverter units require a much lower start-up amperage / load, compared to standard units, and even after start-up they have more variable speed options in the compressor than traditional units, which are either on or off. Inverter units instead will settle into a low-speed cooling function. Put together, that all reduces strain on your generator or main inverter.

I wound up going with three mini-splits -- two 12,500btu inverter heat pump units at 240V, and one 9,000btu unit that can run on 110V (for the bedroom, and in case I am somewhere with only an extension cord!). We're working on the installation now. It's a lot of capacity, at nearly three tons, but summer days can easily run over 100 degrees down here. It will take a good bit to cool the bus down. I've got a 20KW generator just in case...

Cheers, John

robertglines1 · May 07, 2012, 09:03:37 AM

The big differance is the starting surge. Inverter builds up to load. the other demands it rite now! full on. Also inverter only uses what it needs to maintain. I have both in the 45 the std dims lights when it comes on. the other two are inverter type ;you never see a differance when they kick on. 20 20 hindsight if I knew what I know now I would not have shopped price on the front one and pd extra for the inverter type. Also you will find the inverter type have a higher efficiency rating. For you who don't know Andy is my son. He has a toter home and shares our coach &work on it. He is planning on putting a mini-split in his Toter. Others please share your experiences. Bob

dukegrad98 · May 07, 2012, 09:29:25 AM

Quote from: robertglines1 on May 07, 2012, 09:03:37 AM
For you who don't know Andy is my son. He has a toter home and shares our coach &work on it. He is planning on putting a mini-split in his Toter.

Ha! I didn't know. Geez, Andy, your old man is the voice of experience that has been educating me in this area. Good luck outfitting your toter -- I'll stay busy upgrading your old '89 coach with the three new minisplits I've got here. I hope the '98 project is going well, too, Bob.

Cheers, John

Midwilshire · May 07, 2012, 09:32:36 AM

Quote from: AndyG on May 07, 2012, 07:56:24 AM
I was looking at minisplits on minisplitshop.com and decided to compare the load amperage of the inverter type compressor versus the standard type. I am looking at 9000btu heat pump units. Their specs show less than 1amp difference. There is $215 difference in price. I will be in places where power is very limited so efficiency is important to me. $215 is a lot to spend for 1 amp. What am I missing?

Thanks for asking, Andy. We had the same question over the weekend.

And thanks for answering, Bob. You two make a good team!

robertglines1 · May 07, 2012, 01:35:23 PM

Andy is a Engineer. recently is the power production industry. Mostly for Navy. will say no more. He has the knowledge. To question the cost benefits. Probably in a ample power situation it would take awhile to recover the initial cost. But if you plan on running on limited power source or inverter the start up surge or extra amps would limit your run time. Bob

luvrbus · May 07, 2012, 02:34:07 PM

A friend has 3 inverter type AC units in his rig he like them the problem he has if he leaves a unit on cool when he unplugs and starts his generator it blows the circuit board he has blew all 3 and his boards are not cheap 395.00 each

They don't like power spikes like a generator will give you sometimes on startup the factory rep told him and they would not warranty the parts so be careful when changing over cost him over 1200 bucks for that lesson.

robertglines1 · May 07, 2012, 04:29:04 PM

Thanks for the info: Haven't had the occasion to transferr power yet but will remember to start with them off then add load. Will also bring that question up to Duwayne (Mci8tin tent) he is a hvac guy. Bob

robertglines1 · May 07, 2012, 07:04:37 PM

Talked to my ac guy. A bad relay in the changeover or a a neutral bonding issue between gen set and shore power causes problems. He is agreement best practice is to shut off to be safe and restart after change over. The model I have have a surge protector built in and a auto reset feature. I did check on that. New lesson for the day. Bob.

AndyG · May 09, 2012, 09:28:12 AM

I know about Dad's experience with the minisplits. We even looked at my toter yesterday to get an idea of where we would place the indoor and outside units. I posted to the board to see if anyone else had opinions or experiences to share.

mc8 tin tent · May 14, 2012, 10:20:30 PM

Andy
Inverter units are more energy eff. however they can be a lot more expensive to repair from operating in a low volt condition.( via 4-H ctr.). With both systems, shut all off allow pressures to equalize(3 mins.)restart each unit one at a time and keep an eye on the volt meter( over 10% volt drop don't operate). Good Luck.
Dwayne

AndyG · May 17, 2012, 12:50:59 PM

Thanks Dwayne. You know exactly the kind of conditions I will be seeing. Tractor shows like the 4-H Center and Thresherman's park in Boonville. I think that (1) 9000btu unit will be plenty for my 12' toterhome. I was thinking that the minisplit will be perfect for the limited power availability.

pvcces · May 17, 2012, 10:53:24 PM

Hi, Andy.

The inverter unit will have an advantage over the non-inverter type because you will not have enough room for air throw in the Toterhome; they need 12 to 15 feet of clear area to keep them from short cycling and being uncomfortable. With the inverter type, it will be able to slow down and increase it's cycle time.

In any event, even if the air conditioner doesn't pull the temperature all the way down, the lower humidity will make you feel much better.

When we installed our first heat pumps, I was worried about not having enough capacity. I oversized our units, and will be replacing them with the next lower capacity when I get the chance. The right size is the best choice for good performance.

Tom Caffrey

Oonrahnjay · May 17, 2012, 11:47:58 PM

Quote from: pvcces on May 17, 2012, 10:53:24 PM(snip) When we installed our first heat pumps, I was worried about not having enough capacity. I oversized our units, and will be replacing them with the next lower capacity when I get the chance. The right size is the best choice for good performance.

Yes, Tom, I recently went through this with my house (coastal NC, reasonably hot summers with high humidity for most of the year). A "smaller unit" that works harder and takes time to bring the temp down has longer to dehumidify. Since the current draw/cost is similar between a big unit that blows lots of cold air for a short time and smaller one that takes a little longer to do the cooling job, the longer cycle times give you more stable temps and dehumidification. If you were measuring the cool down time with lab instruments, you might be able to measure a little difference for that particular situation (and this might be a bigger factor in super-hot places, Clifford) but the real-life difference for most of us is so small we'll never notice it.

This is one place that bigger is NOT always better!

(Note: The compressor unit that I ended up specifying for my 18 SEER home unit has a two-stage compressor motor. In conditions of heavy cooling, it kicks in both stages of the motor; for lesser cooling needs or just "maintenance" when it's not a lot warmer outside, it only runs the second, smaller stage. It's seemed to make a good bit of difference in my home electricity costs -- I don't know if such a thing is available in a unit suitable for bus use but if it is, I recommend you consider it.)