I'm trying to get a nice, comfortable system in our townhouse. We're going to be here for another 10 years or so - and I'd like to do this right.
This is on a 3 level townhouse (about 24' x 40', interior unit).
It's near Washington DC 20854 zip (hot & humid!)
Tall ceilings: 9' on ground floor, 10' on middle, and 8' to 12' cathedral on top.
It has 109 sq.ft of East facing glass and 175 sq.ft of West facing glass.
We've removed our 12 year old "builder grade"
York 80% gas furnace and POC* 3 ton AC.
(* = Piece of Crud )
The old 3 ton AC had been checked previously and was barely adequate.
If we didn't start running the AC in the morning, it couldn't catch up.
We're in the middle of switching to a "dual fuel" setup -
and already replaced the galvanized vent with PVC vent.
We've selected a two stage variable speed blower gas furnace,
~96% efficient. On top of that we've selected a 4/5 ton coil matched to
a two stage (2.5 & 4 ton) high efficiency heat pump using R-410 refrigerant.
It's got good filtration, steam humidifier, and UV lights over the coil.
1) A previous thread quoted something like "many evaporators have been ruined by 0.1 FR. Can someone explain that? The guy making my return & supply plenum is using a cardboard slide calculator that is based on 0.1.
2) I'm considering adding zoning - and the Honeywell SPRD literature also suggests that a 0.05 is the desired operating difference. I was planning a 4 zone system. The basement zone will usually close off early on the cooling cycle. What would I need to change to get a 0.05 operating difference?
3) There were two supply trunks - one 8x16 rigid running vertically to the attic, then to insulated flex duct. I was planning on adding two dampers in the attic - one to zone the MBR & bath, and one for the rest of the upstairs. The other supply trunk was 8x20 feeding the middle floor & ground floor, plus a 6" round supply taken off just at the beginning of the 8x20 to feed two registers on the middle floor.
My plan was to separate the ground floor registers and add a new round supply just for them running back to the plenum. (Relatively easy access to that supply trunk as it runs through the garage.)
4) If I zone the supply side, I've also heard it's desireable to put dampers on the return registers on each floor. I currently have a return on all three floors. Is this worth doing?
5) The middle floor is fairly open with East windows & West windows & patio doors. It picks up the early morning sunlight, but it's the afternoon sunlight that is really brutal. Plus, the kitchen is on the west side - adding to the heat load. I'm considering breaking the middle floor into two zones (East & West) - with the West zone including the kitchen. Going from 4 zones to jumps the price of the zone controller a bit - but otherwise is there some good reason not to do this? The open layout of the middle floor seems like it might be overkill to attempt to zone it East to West, but it might really help if cooking in the kitchen in the afternoon!
FLOOR LAYOUTS & HEAT LOADS:
Overall - this is your basic 3 level towhouse, so 24' wide x 40?' deep, ceilings of 9' on the ground floor, 10' on the middle, and cathedral ceilings sloping 8' to 12' on the top floor. The eastern exposure is red brick, the west exposure is vinyl siding. Proposed zones include:
Zone 1: Ground Floor = Family Room & interior bathroom, 9' ceilings, tile floor with area rug over much of the tile. About 480 sq.ft and 4,224 cu.ft with 73 sq.ft of West facing windows.
Zone 2: Middle floor = Kitchen, Fam Rm, LR, DR, 1/2 Bath, 9 to 10' ceilings - 960 sq.ft or 9,120 cu.ft with 60 sq.ft of East facing glass and 60 sq.ft of West facing glass.
Zone 3: MBR, Master Bath & Closet: about 384 sq.ft 3840 cu.ft, with 40 sq.ft of West facing windows.
Zone 4: Other BR's on top floor (cathedral ceilings up to 8' to 12') so about 576 sq.ft or 5,760 cu.ft with 46 sq.ft of East facing windows.
So I'm hoping that with the new system, if I run it all day - it would run with relatively longish cycles on the 2.5 ton "low cool" setting, and the 4 ton "high cool" setting would allow it to "catch up" and cool the house down as needed. Duct speeds should be within the recommended ranges for velocity on either the 2.5 or 4 ton setting.
I'm a little concerned about the duct pressure - and especially in regards to the one users comment about 0.1 FR being hard on the evaporator coil. Since we're in the middle of remodeling the house, I'm actually willing to re-size the ducts to a limited extent. The upper floors are served by an 8x16 supply to the attic and insulated flex from there to the registers.
The 8x20 supply trunk that serves the middle floor and ground floor is currently supplemented by a 6" round supply coming off the plenum to serve two registers on the middle floor as well. The plan is to turn this 8x20 into Zone 3 and use it just for the middle floor - in which case it ?might? be too big. If I move the 6" round to the 8x20, I'm thinking it will be "close enough" to properly sized.
The plan was to add a separate 8" round supply trunk to pick up the Zone 1 ground floor registers. (2 in the family room, 1 in the bath, 1 over the garage entry door "hall")
But... considering that the ground floor was always cold in the summer - I was thinking that Zone 1 (8" round) would normally be OFF for most of the cooling cycle. This means that the normally open portion of the supply trunk would be 8x16 and 8x20, with the 8" round to the ground floor closed off. Is this adequate for both 2.5 & 4 ton cooling ?
Last question (for now):
I got a new lineset for the 4 ton Heat Pump - it's 1 1/8" diameter, where the old freon line looks like 7/8" diameter. To do it right, I know I should replace it - but... to just get it working, it would a lot easier to re-use the old 7/8" line set. Do I need to flush the old lineset out since it used the old Freon and the new system uses R-410? Is oil in the lineset a problem?
Thanks for any advice,