Background -

March 2010 - The large window air conditioner shown above was installed May 1984, in the second floor dormer window, replacing an old 10,000 btu 120v Admiral window unit. The 185 pound Sears 18,700 btu 240 volt window air conditioner did its job well, but not very quietly and certainly not without a lot of electric consumption. I serviced it every year, including making repairs to the steel bottom pan, which started rusting away, after about 15 years. As the summer of 2010 approached, it was clear that this old machine might not make it another year, nor was the racket it was now making going to allow us to put up with the noise for another year.

 

In fact, the bottom pan broke in half, when the Mitsubishi dealer/installers (2 men) removed it from the window and placed it in the back of their truck. No doubt that it was time to replace it! Now, I could finally deal with the dormer window, to get it ready to support the installation of a ductless system... a Mitsubishi MSY system, model GE12NA which is a 12,000 Btu/h system (capacity range is 3,800-13,600 Btu/h) with a SEER rating of 20.5. Due to the many improvements we've made to the energy efficiency of the house, a system as large as the 18,000 Btu/h unit being replaced is not needed.

 

Info about 'Inverter Compressor' technology and Mini-Split systems

Here are several links to articles that discuss the benefits of this technology, used in most split system ductless air conditioning systems... Article 1, Article 2, Article 3 and a .pdf file format article. Lastly, here is an 8 minute video from Mitsubishi, which talks about and shows the benefits of their Mr. Slim system.

 

A very recent article asks... Will Minisplits Replace Forced-Air Heating and Cooling Systems?, addresses the questions associated with the new January 2012 Energy Star Version 3 Specs and mandatory commissioning, not previously required for home HVAC installations. And another recent article... It's Air Conditioning, Not Air Cool-ditioning, talks about systems that deal well with humidity control in humid areas, like our own Virginia location.

 

If you find additional articles that you consider very informative, please send me links to them so I can post them here, for others to benefit from.

 

The old cabinet will go to the dump, its guts removed by the Mitsubishi dealer for freon recovery. You can see that this was not a small window air conditioner.

 

The window frame opening wasn't very bad at all, (thanks to old growth wood) since we didn't do anything to it at the time we removed a very old 10,000 btu Admiral 120v unit and installed the new larger capacity 240v Sears unit. The 1 x 2 solid maple piece at the top of the frame helped support the bigger unit, along with vertical braces below the unit. In this picture, a piece of 1-inch ridged green insulation panel has been placed on the inside of the window opening, to keep the bugs out, while the exterior window trim is restored and refinished. The original window sash has been used in the front door, as shown elsewhere on this web site.

 

The house in 1984 was not very energy efficient... one of the two attic vents (south side) had been covered over with cement asbestos siding sometime in the late 1950's, preventing any attic flow-thru ventilation, there was no soffet ventilation, no bathroom ventilation fan, no knee wall insulation in the bedrooms, very leaky original windows (we could actually see the light weight window curtains move with strong wind gusts outside) and many air leak areas around the entire house, which is why the 18.7k btu unit was installed to help overcome the situation. Of course, all of these issues have since been corrected. The upstairs rooms now only needs 12k btu cooling capacity due to the many energy efficiency improvements we've made since 1984.

 

With the old paint scraped and sanded off and a coat of primer ready for caulking, the window was simply enclosed using 3/4-inch exterior plywood and framed with 2 x 3 material, using screws so that the frame can be removed easily, if desired by a future owner. The vertical center support is glued to the plywood, to provide a solid mounting for the new air handler and prevent potential vibration noise. Double foil faced 2-inch R-16 polyisocyanurate foam board is used to insulate the frame, seen below.

The plumbing lines and a 14-3 120v supply line from the outside compressor run into the house through a 3-inch hole in the window box. The outside exterior plywood cover has been attached and primed... the gray spots are caulking, waiting for the second coat of primer and two finish paint coats.

 

The hole position for the plumbing and electrical lines is specified by the air handler mounting bracket, for both left and right side plumbing access. The 14-3 electrical line is not yet in, which provides power from the outside compressor unit. The three tabs at the top of the mounting bracket is what the 23 pound inside unit hangs from, secured at the bottom lip. The old original 20 amp 240v outlet for the window air conditioner can be seen in the right hand corner.

 

With the inside air handler mounted, this is its cover showing where the air filters are located. The small panel on the right is where the 14-3 cable is connected, in the close-up below. In looking at the door on the right and its hinge placement, if you're thinking it will hit the air handler, you're right. It will be moved to the inside of its frame and open into the room.

 

I did all of the electrical wiring for both systems, running two 240v 15 amp circuits to the outside compressors and the 120v lines from the compressors back to the air handlers. Getting the wire into the air handler cabinet and through the back and up into the area where the connections are made is very tight. Further, the terminals are not positioned for todays current flat 14-3 cable, but were meant for round 14-3 cable. I was unable to locate any round 14-3 exterior grade cable!

 

This is a front view of the cabinet with its front access panel closed. Below are pictures of the two rooms it will blow into. One slightly to the left of the cabinet, the other directly in front of it. There are two sets of air direction vanes in the air handler, so air flow can be directed into each room. In the pictures below, you can see the painting and bathroom door change has been completed. We didn't move the original solid door, but decided to install a wooden bi-fold louver door, to assist in cooling the bathroom when the door is closed. This has turned out to be a very good door solution, allowing both privacy and ventilation. Note that the louver openings are positioned as they would be for an external shutter when closed, facing down.

 

Looking out the door of bedroom #1 at the Mitsubishi interior air handler.

Looking out the door of bedroom #2 at the Mitsubishi interior air handler.

Looking into the dining room from the living room, you can see the other air handler at the upper right corner of the window. It is also a Mitsubishi MSY system, model GE15NA which is a 14,000 Btu/h system (capacity range is 3,100-18,200 Btu/h) with a SEER rating of 21. It replaces a 14,000 btu 120v window air conditioner that sat in the window next to the new air handler. During the summer, you had to shut the window unit off during meals, because of its direct air flow across the table. Not a good idea to have friends over for a meal, on a hot summer day!

 

Work in progress, with the insulated plumbing shown going into the upstairs window cover, to connect to the upstairs interior unit.

 

Update July 2010-

During our very hot 100F temps during early July, I noted that the cooled air temp at the face of the outlet vents (measured with a Fluke 8060A and thermal probe, 1% accurate) of the upstairs unit was 4F-6F degrees warmer, then the downstairs unit, 46-48F versus 42F at maximum cooling and the same differential at lower cooling levels. (IE: 56-58F versus 52F) Upon inspecting the black insulated plumbing, where it comes out from beneath the roof overhang and up to the new window cover, I found that the black plumbing insullation was very hot to the touch, because it is on the west side of the house with the afternoon sun beating down on it, versus the downstairs unit plumbing which is on the north side and no sun exposure.

 

I decided to try additional insulation on the plumbing to see if that might help. I added a larger diameter insulating pipe cover, painting it white to help reflect the sun light. Fortunately, this did the trick! Had it not, my next step would have been to have the charge level checked, because this unit is a much greater distance from the compressor, then the other unit.