[ASKNACHI]This question was posted on AskNACHI.org by john (from hope valley ri). [/ASKNACHI]cape style 2 story house
1800 sq ft
2 bedrooms, kitchen and living room 1st floor
2 bedrooms on second floor
i have a 3 ton central air, it is a a frame coil
and a blower directly above the a frame coil.
directly on top of the blower is
the supply plenum,
about 6 " above the plenum there
is an even split of 2 ducts ( 10w x 10 h)
one going left and 1 going right
the one going right has a 8 x 8 hard duct cut into it about 24 " from the split.
This 8 x 8 is all that feeds the 2nd floor.
Afer the 8 x 8 cut in the duct continues and has 3 flex hoses to feed 3 rooms on the first floor.
The 10 x 10 duct going left supplies cold air to the kitchen and living room on the first floor.
There are 3 zone dampers, 1 on the 10 x 10 duct going left, 1 on the 10 by 10 duct going right (this damper is AFTER the 8 x8 cut in and 1 zone damper on the 8 x 8 ductfeeding 100% to the 2nd floor.
The 8 x 8 hard duct is the only feed to the 2nd floor w/ 2 bedrooms.
It is always 10 degrees hotter upstairs
and the 2nd floor is always calling for cold air and the 1st floor cools off and the 2 out of the 3 zone dampers are shutting off the cold air to the first floor and all the 3 tons (1200cfm’s) are trying to get thru the 8 x8 (300cfm capacity) duct that feeds the 2nd floor
My coil is freezing us within 24 hours and there is plenty of gas
and it is a brand new unit.
When the 1st floor zone dampers shut, I want to put a dump to get rid of the xtra 900 cfm’s
and my hvac guy says the dump should be put on the
8x8 duct AFTER that duct’s zone damper.
It seems to me that there is 1200 cfm’s trying to get into the 8x8
from the 10 x 10 supply and the extra cold air is going to get pushed back towards the supply plenum and freeze up the coil.
I think we should put the dump after the plenum splits into the 10 x10" but Before the 8 x 8 cuts into the duct .
what do u think?
and should the dump be put on the 10 x10 on the right side which is the side the 8 x 8 is cut into it?
or should the dump be put on the left side
but of course before the left side zone damper.