Split system AC units.

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Split system AC units.

Postby offgridQLD » Tue Oct 01, 2013 2:45 pm

A little while back I was on the hunt for some spit system AC units for our offgrid house. I wanted one for the clean room in the shed and the other for our home theater/rumpus room in the house.

The little clean room (walled off and insulated 4m x 4m corner in the shed) At just 16m2 and heavily insulated Was a perfect match for a small 2kw reverse cycle split system.

The home theater/rumpus room at 50m2 also heavily insulated and only a few south facing windows was a perfect mach for a 4kw spit system.

The next thing to do was to find the most efficient units out there. After doing some hunting around I found the Mitsubishi SRK20ZJ-S 2.0kW split system was by far the most efficient 2kw unit. It has a EER value of 5.71 :shock: This means that while consuming 1000w it will output 5700w of cooling . Or when scaled to its size it will consume 350w and output 2000w of cooling.

After settling the SRK20ZJ-S for the shed I was expecting it to be a simple matter of picking the 4kw version of this unit for the home theater/rumpus room. First thing I found was they didn't make a 4kw version it jumped from 3.5kw to 5kw. Ok then I would go for the SRK50ZJ-S 5.0kW unit. Looking at the specs though they didn't add up. The efficacy or EER value was not even close to the 2kw SRK20ZJ-S in fact it was 40% less :?

It turns out that most manufactures only produce two evaporator sizes for there entire model line up 2kw up to 8kw. The size of the evaporator has a huge effect on the efficiency of the system. So the little SRK20ZJ-S 2.0kW uses the same size (295x798x232) indoor evaporator unit as the SRK50ZJ-S 5.0kW

With there 6kw up to 8kw units they used the same size (325x1100x238) evaporator. Why would they do this I can only put it down to esthetics and cost.

If the 8kw unit was to have the same ratio/size evaporator surface area as the 2kw unit (295x798mm) The 8kw unit would have to have a evaporator with a frontal surface area of (3129 x 1180mm) No one would accept a unit that large hanging off there wall it would look ridiculous !

Considering 5kw was a little over sized for the home theater/rumpus room . I decided that two 2kw systems at each end of the room would be a much better option and I get a 4kw system and keep the amazing 5.71 EER value :D . The price of two 2kw units ($700 each was the same as one larger unit $1400). The only extra expense using two small units is instillation. Though having my own vacuum pump and other refrigeration gear made the insulation cost minimal and the long term cost of installing two is well worth it aether way.

I just thought this might help a few people out when looking for the most efficient AC units. Evaporator size is very important!

You cant go past the Mitsubishi SRK20ZJ-S its great for off grid 350w is nothing on a sunny hot day. Even if you just use one and create a oasis room to escape the mid day heat.

Kurt
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Re: Split system AC units.

Postby Gordon-Loomberah » Tue Oct 01, 2013 3:44 pm

I bought myself a couple of the Mitsubishi 2.5kW units a while back, although I haven't yet installed them. They aren't quite as efficient as your 2kW unit, but I thought those were a bit small for the job, and I can easily run both 2.5kW units on a sunny day.
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Re: Split system AC units.

Postby jimbo » Tue Oct 01, 2013 4:22 pm

I installed the 2.5kw unit in our bedroom early this year and it's fantastic. We initially only ran it for a few hours at night but then started leaving it all night set to around 22-23 degrees. I can't remember how much current they pulled but it was hardly noticeable by the morning in our internally insulated room!
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Re: Split system AC units.

Postby offgridQLD » Tue Oct 01, 2013 4:29 pm

Yes there is a little bit of " what the hell " on a sunny day if your off grid system is large enough. My thinking was just to limit the loads a little on the inverter as things sure do add up.

The 50m 2 room with the two units was a double garage in the past so thick concrete floor with just a narrow strip of windows on the south side were the old garage door was. 2.4 ceiling but a good 2.4 again in the roof cavity double insulated. Its a cool escape room to start with so doesn't need much to cool it .

We do get a reliable breeze and don't really need AC for most of summer but when the weather doesn't want to play nice and there is no breeze and a good storm is building up over a summers day. Having a escape room that's kind of darkish to escape the bright sun and has AC to escape the humidity is bliss.

Jimbo,
They are very quiet on silent mode I think it was 25 DB from memory. Haven't needed one in the bedroom though as that hangs out over a valley and gets the cool breeze.

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Re: Split system AC units.

Postby jimbo » Tue Oct 01, 2013 4:41 pm

We never thought we needed one being at just over 400m elevation and plenty of windows and doors to open but last summer was very long and we had quite a few hot, humid nights with no breeze. A few times we had the AC set at the same temp as outside but just using it to dehumidify the air which makes it a lot easier to sleep.

I don't mind the noise of AC, even on high fan (used to it from work) but the mrs is a bit picky and was fine with the unit.

Cheapest price i found was $900ish from memory.
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Re: Split system AC units.

Postby offgridQLD » Tue Oct 01, 2013 4:55 pm

That's it some times you just get weather that's hard to work with no matter how well your house is located or set up. I am reasonably tolerant to the odd bit of hot or cold weather and can rug up or go for a swim in the creek and see the bad weather out But when you have guests its nice to throw all that to the wind and be able to create a comfortable environment no matter what the weather throws at you.

Ac units last a long time. I have a spit system at the city house that's over 15 years old (gave up a side trip to Easter Island to pay for it hmm the silly decisions you make when your young :roll: It wouldn't surprise me if it was working in another 10 - 15 years. Unfortunately its not the super eco kind like the Mitsubishi. considering the service life of a good split system is so long its even more important to pick one that's efficient or you could be regretting it for a long time before a opportunity to replace it comes along :roll:

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Re: Split system AC units.

Postby bpratt » Tue Oct 01, 2013 7:28 pm

Thanks for the timely thread on split systems.

We've just sold and are going to build the next place, so we won't be far away from working out what split systems to get.
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Re: Split system AC units.

Postby scottyf » Tue Oct 08, 2013 7:56 pm

Thanks for the info Kurt.

The Government's Energy Rating website is pretty handy for selecting appliances but it is always good to hear from people who have actually used and installed the systems.

I have a small reverse cycle installed in my unit and the installer told me that it was "undersized and wouldn't be able to cope with the size of the area".

Proper insulation and decent shading over my windows and screens means that we rarely need to use the ACU and when we do, it is only operated with a reasonable thermostat setting (23*C). Compressor operates at full bore initially but after a few minutes (up to 15 on really hot days), the compressor cycles on and off as it should (more off than on).

If we are using the oven in the kitchen, it does cycle on more often than not...but we got around that by getting a small convection oven so we can cook outdoors is summer (we use the convection oven indoors in winter as it doubles as a heater - it's a lot cheaper to run than a conventional oven). Insulation and draft-proofing are the key!
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