Results 1 to 4 of 4
  1. #1
    Join Date
    Jun 2008
    Location
    Potomac, MD
    Posts
    1

    Dual Fuel & Zoning a 3 level Townhouse...

    Hi,

    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.


    OLD SYSTEM:

    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.



    NEW SYSTEM:

    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.


    QUESTIONS:
    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,
    Greg

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,429

    Thumbs up ACCA Manuals J, D, S and T will provide the necessary assistance ...

    QUESTIONS:

    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.

    Use Manuals J & D and perform complete analysis.
    T&B will be required for multi-zone system.


    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?

    .........
    Why 0.05"?

    Check the blower performance curve!

    VS AHU should be capable of about 0.7".

    Single-blade, steel barometric damper used to bypass excess air when majority of zone dampers are closed.

    Features:

    Counter-balanced weighted arm to control bypass air for zoned systems.
    Available in rectangular/square and round sizes.
    Air pressure in duct system increases as zone dampers close, pushing the SPRD open automatically.
    Arm and weight both adjustable to control amount of air bypassed.
    Recommended for low pressure systems with less than 0.5 in. wc.

    .........

    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.)

    ....

    No question asked.

    ...

    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?

    Yes, dampers are integral with many return grilles.

    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 5 jumps the price of the zone controller a bit - but otherwise is there some good reason not to do this?

    ... ...

    What is the smallest zone?
    How does the system perform with only one zone calling?


    How are you going to determine the Minimum open position of each damper?

    ...

    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!
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #3
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,793
    MAUAL J load calc. Your probably going to be making a new thread after you have that 4 ton installed. Titled something like. " New system roars when it goes to second stage"
    Unless your redoing most if not all of your duct system, not just plenums.
    I think you can only use Tranes zoning system with the 19i.
    Before its to late, have them do a load calc.


    If I don't run my A/C in teh morning, it won't catch up in the afternoon to well either. And i can maintain 72 when it 95 outside.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    Sep 2006
    Location
    The depths of hell in PHX AZ
    Posts
    1,140
    Alot of my in laws think that they can wait until the humidity and heat load in the house reaches tropical conditions and then turn on their system. Then wonder why they have problems or the unit runs forever.

    It takes alot of energy to get rid of that humidity and heat especially when the outdoor temperature has gone up. Don't assume that the unit is undersized. Get a load calc and run your unit at all times during the humid season to help your unit work easier. You don't have to keep the temperatures down low at all times but at least keep it set in the 70s with the windows shut to keep the humidity down to a manageable level. You might find by changing your use habits things could improve without having to jump up in size.
    I will believe that the government is broke when the welfare checks start bouncing!!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event