Mini Split Heat Pump and Distribution Ducts

[tucsonjwt]

I have a small 1400 square foot duplex in Tucson, Arizona. I would rather not have two packaged units on the roof, so I am looking at mini-splits.
My problem is the larger unit (about 1000 sf) (where I live) has 3 small bedrooms, 3 small bathrooms, an open living room/kitchen area, and a small (90 sf) study. The other unit is a small studio (about 400 sf), including a small bath and study.
I am curious about the ceiling cassette units (Mitsubishi, Fredreich, etc.) that have two knockouts for distribution ducts. Would this be an inexpensive way to cover 4 rooms with one indoor unit? These units also refer to a fresh air intake for the ductwork which requires a "fan" - does anybody know how that works?
The house is undergoing remodel and is all open, with an attic that will not be accessible after completion and a crawlspace the has about 30" of height.
Thanks for any information I can get.

[dan sw fl]

[QUOTE=tucsonjwt;1487316]I have a small 1400 square foot duplex in Tucson, Arizona. I would rather not have two packaged units on the roof, so I am looking at mini-splits.

I am curious about the ceiling cassette units (Mitsubishi, Fredreich, etc.) that have two knockouts for distribution ducts. Would this be an inexpensive way to cover 4 rooms with one indoor unit? [QUOTE]

Yes, if the proper amount of air distribution is known.

What is the size of the ceiling cassette unit?
Does it fit in your ceiling?

[tucsonjwt]

I have ceiling joists on 2' centers and the building is completely gutted - no drywall - and I am looking at a Fredreich C24YF (22,200 BTU) heat pump. This is an old territorial roof, with something like "homemade" relatively flat roof trusses - all made of 2 x 4s with a lot of bracing.

But, I see what you mean - it would require opening two joist spaces at 33" square:

INDOOR UNIT:
W x H x D in: 32 5/8 x 9 5/8 x 32 5/8
Net Weight: lbs 75
Shipping Weight: lbs 97

Are there smaller units that would fit in one joist space of about 20-21"?

Also, what is the requirement for "fresh air intake" when using the distribution ducts, and how are they connected?

Thanks.

[Shophound]

Since you've gutted the building, consider framing in a drop ceiling and mounting the air handler below the existing ceiling (attached to existing ceiling joists) and then ducting in the supply and return runs (best not to use enclosure formed by drop ceiling for return as it could lead to infiltration if not sealed). Daikin makes a very flat air handler that can be used on their mini-split or multi-split condensers that is ideal for a drop ceiling installation. An additional benefit is that it gets the ducts out of the attic...the absolute worst place to run ducting.

[tucsonjwt]

Thanks for the information.
Do you have the model number on the Daikin unit? I see a multi wall mount or ceiling mount unit system, but no ducted system.
I'm still wondering what that "fresh air intake" is all about.
If possible, I would like to keep the original 9' high ceilings, but I suppose I could just drop the hallway ceiling and punch out holes into the walls over the bedroom/bathroom doorways - that is very common here in "modern" construction. That would leave me with a very small study about 25' away to supply with heating/cooling -possibly with an attic duct.

[Shophound]

Thanks for the information.
Do you have the model number on the Daikin unit? I see a multi wall mount or ceiling mount unit system, but no ducted system.
I'm still wondering what that "fresh air intake" is all about.
If possible, I would like to keep the original 9' high ceilings, but I suppose I could just drop the hallway ceiling and punch out holes into the walls over the bedroom/bathroom doorways - that is very common here in "modern" construction. That would leave me with a very small study about 25' away to supply with heating/cooling -possibly with an attic duct.

Try this link:

http://www.daikinac.com/residential/productsUnits6.asp?sec=products&page=55

[tucsonjwt]

Looks interesting - but 10-11 EER is less than the 13-16 SEER which seems to be almost standard for modern heat pumps.

I don't see how the air is distributed out of the air handler. Do refrigerant lines flow to each wall unit or ceiling diffuser?

Thanks

[beenthere]

Looks interesting - but 10-11 EER is less than the 13-16 SEER which seems to be almost standard for modern heat pumps.


Thanks


Don't confuse EER, and SEER, they are 2 different ratings.

[johnsp]

Such a small studio would probably be easily done with a single mini-split. You want to keep the air handler on an outside wall to avoid using a condensation pump. Or put a small package unit outside and duct under the house for the first floor.

The upstairs unit could be done with a cassette unit. The take-offs are 4" rounds . Not a ton of air comming out of those. Are the joists running in the right direction to bring the ductwork in the direction of the rooms? Look into package outside also and duct it upstairs. Sounds like you're gonna have finished sheet-rock walls and ceilings. I hate having mechanicals up between joists. A cassette might leak condensation some day.

I say do ductwork since all the walls are open. Tie into a package unit outside or see if a split air handler can be mounted under the house.

[tucsonjwt]

The studio and main unit are all on one floor - side by side, next to each other on the same level.
The ceiling joists (and floor joists) mostly run perpendicular to the orientation of the rooms, so no help there.
I won't need much air out of the 4" side knock outs - mostly supplying 5' x 7' bathroom and 6' x 12' study.
I still don't get what the "fresh air intake" is all about. Do I need to run a separate duct directly from outdoors to the ceiling cassette in order for the distribution ducts to work?
Most houses here use a gas pack on the roof - by I have a flat roof which are notorious for having those roof mount units leak. I am looking for an option which will keep the unit off the roof. I suppose a multizone wall mount system would work - I just thought the ceiling cassette would be a more attractive (i.e. conventional) look.

[johnsp]

Yes a fresh air intake would require a duct from the outdoors to the intake of the unit.
Would lower the effectiveness of the unit, fighting the hot summer outside air and the cold dry air in winter. It's not needed. The cassettes and larger wall units are still loud IMO. If you put the cassette unit in the middle of the house, you must still run the lineset and condensation line to the unit. Any leaks will not be repairable without tearing out sheetrock.

Minisplits also have the floor mount fan coils that would look like PTAC or radiator units on a wall. These would be very easy to pipe down into the floor and under the crawl back to the condenser unit. Nothing on the roof or ceilings

[tucsonjwt]

OK - it looks like a ducted system might be the most cost effective way.

How about a conventional split system, with two small compressors mounted on a pad outdoors (a neighbor's small duplex has two tiny Rheem units- maybe 2' square) and some sort of ceiling mounted air handler with heat pump capability.

I could drop the ceiling in a short hallway run for the larger unit, and build a ceiling soffit for the small studio. So, who knows of a small air handling heat pump split unit that can suspend from the ceiling (horizontal and compact) with decent SEER rating?

I really want to stay off the roof and out of the attic if I can.

Thanks.

[johnsp]

Checkout Goodman's website. They have air hadlers that could be ceiling mounted or installed between between wall studs (24" on center). Don't think you'll get seers over 12, since the units are small. The hallway wall would have to be brought out to cover the air handler. Maybe build a closet around it.

Aonther option would we the vertical PTAC's. They come in smaller sizes.
Basically you'd have to build a closet against an outside wall.

http://www.geappliances.com/products/introductions/zoneline/download/vertical_series_spec_brochure.pdf

http://www.retroaire.com/products_vpac.asp

[johnsp]

Checkout Goodman's website. They have air hadlers that could be ceiling mounted or installed between between wall studs (24" on center). Don't think you'll get seers over 12, since the units are small. The hallway wall would have to be brought out to cover the air handler. Maybe build a closet around it.

Another option would we the vertical PTAC's. They come in smaller sizes.
Basically you'd have to build a closet against an outside wall.

http://www.geappliances.com/products/introductions/zoneline/download/vertical_series_spec_brochure.pdf

http://www.retroaire.com/products_vpac.asp