feedback on a fujitsu cassette mini-split design

[cooper5114]

I'm an owner-builder. Building a detached garage w/a room over. I'd like to make this room nice enough that the LOML and i would live there if her folks ever move in when they get really old :).

the room is roughly the shape of a T and is open except for the bathroom and a pantry/closet (shown in grey off to the right of the kitchen).

Total sf = 1300 and a lot of the ceiling area = roof (12x12 pitch).

I'm working with a HVAC contractor and would just like some others to give me some feedback on our approach.

We're planning on putting 3 fujitsu cassette units -- the smaller ones (9K BTU units i think). I don't think we quite need that much cooling capacity but he believes due to the distances we need 3 to circulate the air throughout.

To get air in/out of the bathroom i think we're going to have some type of in wall fan/return -- i don't think the smaller Fujitsu cassette units have a way to run an aux duct from them.

In this picture the blue boxes show the approximate location of the units.

What do you think? Seem rational? Concerns?

[tedkidd]

How is it insulated? What is the air leakage? Is the storage area inside or outside the thermal boundary (my inclination would be to have it inside, unintentionally conditioned or buffer space. I think good design means your weather and thermal boundaries are the same.).

What is the load calc? Since you live in Hawaii that's probably a lot!

Seriously, where is this building (you didn't put zip code in your profile, which makes even the most general comments possibly inappropriate to your location)? Feel free to suggest to the site owners that they require SOME entry in the location field...

Those are inverter units, right? So I suppose if you go with 3 instead of 2, if you don't mind the extra money, it doesn't matter.

[BURL-REF]

Casettes are essentially mounted in a dropped ceiling. You will need to service the units at some point. The electrical box and drain connection would be above the ceiling. Are you using a dropped ceiling ? or providing an access panel to service.

How high are the side walls , use those if possible.

[cooper5114]

I apologize for being pretty short on relevent info -- didn't even think about the profile not having my city.

I'm in Columbia SC. So it can get to 100 in the summer and low teens in the winter.

Insulation - i'm probably not going to be able to afford foam but the rafters are 2x10's so i have some room for decent insulation. Also there are 4' knee walls but i'm planning on running the insulation all the say along the rafter so teh area behind the knee walls shoudl be w/in the building envelope -- as will the pantry area on the right.

Access -- there's only about 3' of space above the ceiling to the peak of the roof but i'm planning on putting in attic access for service. The tech said that he could have the drain/service lines all pointing toward the center of the room so that he shouldn't need to climb over the units.

Using side walls -- i ruled against putting units on the side walls since the knee walls are only 4' high. There are taller walls where the windows are...but this tech prefers to run the lines on the outside of the wall in this instance which i don't aestetically like. He's concerned (though he'll do it) with putting wall mount units above the windows and routing the lines around header, etc. and then having drywall issue in the event we need service. I can understand that as on one wall there's likely be be kitchen cabinets against that wall.

[tedkidd]

I apologize for being pretty short on relevent info -- didn't even think about the profile not having my city.

I'm in Columbia SC. So it can get to 100 in the summer and low teens in the winter.


This is all too common, and not your fault. Hopefully we'll get enough pro's to lobby for the "Location" to be a required field at membership. That would save a lot of people time and reduce the length and useless noise of many threads.



On the foam, if you are going to condition the space you will pay more not foaming than you will by foaming, and the space will be noisier, less comfortable, and you will be less happy. Take this from someone who deals with home energy issues every day, or don't.

People who foam don't regret doing it (if it's done right). People who use fiberglass, particularly when knee walls are present, tend to have problems.

[BURL-REF]

You say 3 9,000 casettes, is your heat gain 27,000btu's ? I believe the smallest casette is 18,000. Installing these in a sheet rock ceiling, the drain could be problem due to the joists your using. You can not go any higher with that drain outlet. It comes off the side and must slope down from there.

Also using 3 evaps on one on Fujitsus Flex systems will require a primary zone box. Individual systems might be a better choice, incase of compressor failures etc.

[cooper5114]

Burl

It seems that Fujitsu carries two lines of cassettes. These are smaller "mini cassettes" which measure 2'x2' and they are available in 9K BTU.

On the drain issue, you bring up a good point that i'll disucss w/my HVAC pro. I do notice though that one of the features mentioned is a "condensate pump" which makes me wonder if it doesn't have be drain based on gravity alone.