http://www.nrel.gov/docs/fy11osti/49881.pdf

Check on the duct work in Fig 4 & 6 on pages 16 & 17.
I know it's just for testing, but it's interesting nonetheless.

You're making my head hurt (doesn't take much), but that's an interesting experiment. It would be interesting to see the temperature deltas between the attic peak and ground level throughout the day and we get further into winter.

The average outdoor temp since sunup, has been about 40F
(it's only 42F right now, in the later part of the heat of the day)! ;)

Last 24 Hours Weather: , read this fast, before it changes!

My attic temp right now is 66.4F (overnight min=40.9 max=68.0).

So, 66.4 - 42 = 24.4 deg F of difference (at this second)..


Anyways, since we had Sanyo #1 set for 68F most of the day,
when we were heating, the addition of some warmer air to the intake
would have likely mean less watts would have been used..



Would there be a break-even point within 5 or 10 years??
What does your kW hours cost you? Are you using PV and a GTI? :p
(I've been running this PC on solar all day).

Since I'm using high performance heating machines already,
I would be somewhat reluctant to add-on a hack like this, for a small gain.
Even if it saved 15%! That's not a heck of a lot of money,
when you are only burning 60-70 bucks a month on heating..
(We spend more than $60 on candle-pin bowling)! Prices
Heck, we could cut out bowling and our heat would be "free".. LOL!!

My heating cost is ready way lower than anyone else on this side of town...:D

And, another large duct down the side of our house would not likely be approved by my wife. :eek:

I think it looks pretty darn strange.

In the introduction, it looks like they are trying to establish a methodology for measuring the COP of mini-splits.

But in this photo:


...they are clearly trying to account for ALL of the air that is coming into the mini-split...

And in this picture:


...it is clear that the incoming air duct that is being implemented is MUCH smaller that the opening in the front of the mini-split for air expulsion, so the duct itself is a significant bottle neck to the flow of air, and would significantly diminish the COP of the system.

And this! What the heck is this? It looks like a college freshman's bad-beer nightmare...


I think NREL has some explaining to do.

But the incoming air duct is something for you to keep in mind when you build your attic hear reclaimer duct.

Good luck on this project.

-AC_Hacker

Hey, it's funded by OPM, other people's money.. (Taxpayers), so they don't have to use their
noggins, just hook up a million and one bucks worth of equipment and trash bags..
Presto, another big wad of "study" funding is in the pipeline.. ;)

That duct-work behind the ODU was what I was looking at. BUT, in my goofy brainstorm,
I visualized the warm air output port much smaller. An opening size, about the size of the IDs of wall duct.

When I was reading their paper, it seemed like some of stuff they wanted to
do was a bit out of date for doing a study of modern technology..
It had me wondering if some of their text was recycled from some
older study they did a few years back.?. Before inverter mini-splits.

Looking at what they wanted to start off with, their data collection ideas
are what might be called the "Shot Gun" or Kitchen Sink method.

I half expected to see something like, "Be sure to get the installer's wife's maiden name".. :p

I'm getting ready to install a Mitsubishi 2-zone mini-split and decided to mount the outside unit on a small platform outside the second floor on the north side of the house. Here in South Carolina, the cooling season is longer than the heating season, so having the unit on the north side keeps it out of the hot summer sun. A second reason for having it "upstairs" is to keep it above the approx 8 foot deep cold air drainage flow that flows past the house on clear windless winter nights. This location also requires shorter power and tubing runs than a ground level installation and makes it more difficult for potential copper thieves to make off with the outside unit (not that this is a problem yet in my rural location).

That sounds good, but you want to be sure the unit is mounted so it motor vibration won't be transmitted into your home.

I used some coroplas (stuff used to make signs) to block snow and rain, (gutter over-flow)
and it conducts sound into the house.
http://i46.photobucket.com/albums/f1...0slot/R072.jpg

The top edge is now taped to the siding. Our bathroom is on the other side of the wall.
There are times when the Sanyo is really cranking, the low frequency vibrations are very noticeable.
Especially when you are in the bathroom. Loud enough, so I wouldn't want it near my bedroom..

It's not that Sanyos make a lot of noise, they don't.
But, the motors and their conducted vibrations, can turn the wall into a big speaker-like surface.
Stand next to the Sanyo outdoors, you can hardly hear it.
But in the bathroom it's really drumming on the wall..

This isn't a problem with my other Sanyo, it's case is free standing.
Not connected to a rain roof..

That sheet of coroplas isn't that big of a conductor. It's not rigid, it's very flexible.
But, it's enough to make me want to replace it with a free-standing roof..

I plan to mount the unit using rubber grommets to damp any vibration that might reach the platform.

I've got the rubber shocks on the mounting feet, but they can only do so much.

I've seen a lot pics of wall mounted units, and most of them were on very
solid looking walls. Sometime brick walls.

I live in a 1956 wood frame house and if you hit the outside wall with
a tennis ball, it sounds like baseball @ 600 fps from inside the house..
A 6,000 BTUh window AC vibrates the whole bedroom wall.. :o
That's another reason we like the Sanyos, they are pretty quite..

I like your idea, a few pages back, To have the outdoor unit under a open air Carport or the such,great idea, Worth doing. A simple Structure, With a plywood roof would work well. Keep the snow ,rain and leaf debris from impacting its performance.
Probably 2 sheets of 4x8 plywood would be enough for the roof area.
I have a 10x10 Gazebo that stays dry and snow free easily all but 2 feet in.