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  1. #1

    Replacement system need design help

    I got multiple offers on replacing the current 11 year old 3.5T Lennox system in central Texas. Main reason for replacement is inadequate cooling upstairs (5 degrees difference) and noisy compressor right next to bedroom. Overall, house feels warm and humid most of the time, especially upstairs. Home office I use all day is in one of the room upstairs, so lots of heat is generated by the computers.

    The house is 2000sqf (1400sqf down and 600sqf up), two levels, vaulted ceilings in living. It is facing E-W, so it gets lots of sun all day long. There are two returns, in the hallways up and down.

    Here are the options presented by three different contractors:

    1. 5T Trane XL15i 13.5 SEER, rebuilding ducts upstairs and putting a return in each room. With an option to zone upstairs and downstairs for 4K more, or to have 3 zones: downstairs, upstairs and office for 6K more.

    2. 5T Carrier Infinity 15.5 SEER, rebuild ductwork for upstairs, add returns in each room upstairs. Another options is to have 2 units, also Infinity 2T up and 3T down. But this is adding 7K to the price.

    3. 4T 16 SEER Lennox dual speed, rebuilding ducts, add return in each room upstairs, sealing vents, blow in insulation in attic to get to R38, solar screens on all windows facing west (not a big fan of looking out through those), weatherstripping doors. they claim to test the whole house for leaks.

    All options include MERV 12-16 air filter at the air-handler, instead of on the return grills.

    Our main problem is really getting even or almost even temperature throughout the house, and being able to cool down the office without freezing the rest of the house.

    To me, zoning makes sense, but I've heard that electric dampers are not really reliable. Also one problem I see is having to push 4-5T of air to cool just the upstairs in situation when downstairs is not calling for cooling.

    Option 3. makes sense also becauase it addresses other factors than just throwing big equipment at the problem.

    Not sure which way to go here:
    - zoning with one system
    - two systems
    - one system w/out zoning, but addressing other factors and preventing heat from entering the house.

    I would appreciate any advice.

  2. #2
    Join Date
    May 2007
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    DC Metro Area (MD)
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    What are the indoor unit model numbers for each quote? Are these heat pumps or air conditioners? Do you have a gas furnace? Who did a load calculation to determine sizing? The Lennox guy is quoting a different size, so somebody's wrong--and I wouldn't be surprised if it's the people who are quoting 5-ton units to replace your current 3.5-ton unit. A load calculation is needed to determine proper sizing. Just because your upstairs isn't cooling properly doesn't mean the system's undersized; you may just have inadequate supply/return upstairs. Unfortunately with 2-story homes it isn't uncommon to have a temp. difference between the two stories. It looks like the Lennox quote is actually trying to improve your envelope and lower your heat gain. And with a 2-stage unit you usually won't be pushing 4-5 tons of cooling upstairs when just one zone is calling--there are 2 compressor stages with different capacities.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,556
    Don't try to cool the office off of a central system. Put in a window unit to assist the central for the office.

    Your upstaris is warmer then the downstairs. And its humid in the house. Could have ductwork isues creating the problem, and not the size of rquipment.
    Get a contractor to do a load calc instead of guessing about teh size you need. And over sized system will make it more humid.
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  4. #4
    No gas, only electric. I guess we need a heat pump because unit would also need to heat the house during winter.

    1. TraneXL15i Out door M# 4TWX5060A1000A; A/H M# 4TEE3D65A1000A;
    Thermidastat M# TCONT803; Heat Strips M# BAYHTR1415BRKB

    2. Carrier Infinity Series - no model specified

    3. Lennox XC21

    I believe only Lennox guy did load any calculation. It took him 10-15 minutes with calculator to some up with design. The others were eyeing it and then just came up with a the quote.

  5. #5
    Join Date
    Jan 2004
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    Lancaster PA
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    If he didn't measure windows, doors, room or total house size. He may not have done a true load calc.

    Do the sizes vary.

    All the units you listed are ok. You just need to deside what level of comfort you want.
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  6. #6
    Join Date
    May 2007
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    DC Metro Area (MD)
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    The Trane air handler you specified has CleanEffects built in, which may be a plus for you. This matchup provides 13.75 SEER, 11.70 EER, and 9.00 HSPF (ARI Ref. #1427734). You may be able to cut the cost if you ask for a 4TEE3F65A1000A air handler instead (no CleanEffects--I'm not sure if this is something you requested or not). 10-15 minutes sound a bit short for a load calculation. You need the model numbers of the indoor units for the other two units to accurately compare the three.

  7. #7
    Join Date
    Dec 2007
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    Cedar Grove, Wi-Sheboygan
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    Why not go with 2 zones one up and one down, and move your office to the downstairs instead of up in a bedroom where it is warmer. Do the house insulation and seal door's, maybe upgrade your windows. There's alot of things a person can do to improve the heat load of a home themselves getting a new system installed is only gonna solve half your problems IMO.

  8. #8
    Whats your opinion on singe unit vs two units vs zoning?
    Is it possible, assuming all the right steps are taken, to have great comfort upstairs and downstairs with only one unit?

  9. #9
    Join Date
    Dec 2007
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    Cedar Grove, Wi-Sheboygan
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    IMO there's no reason why you can not cool down a upstairs of the home and the main living area of the home with one furnace using a VS blower and 2 zones as long as there is adequete duct work in place with the proper amount of return air thru out the home I don't see any reason not to ba able to do this with one system in place. Having to seprate systems = double the amount of maitience, and what do you do when the upstairs furnace were to take a dump on you what then???? or the downstairs goes on you???? The way furnace's are made today with the VS ECM motors and the right sized duct work= a complete system & Comfort !!!

  10. #10
    Join Date
    Aug 2003
    Location
    Lincoln, Nebraska
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    We put in zone systems all the time and have had no dampers fail as far as I can remember. I have a 11 year old zone system and it works great. I can get the upstaire to any temp I want even on the hottest days. As for the extra air there should be a bypass and freeze stat installed to help with that.

    As said I think you will need to adress the computer room seperately from the others. Probably a window unit or something like that.

    Unless you zone the system or put in 2 systems you will most likely always have a temperature diggerence between floors.
    Its a good Life!

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    Quote Originally Posted by DanW13 View Post
    and what do you do when the upstairs furnace were to take a dump on you what then???? or the downstairs goes on you????
    I'm not sure, but I think most people with half a brain would go to the area that the heat or A/C was still working in, and call for service.

    Of course your totally screwed if you only have one system. You half to wait until a tech gets out to fix that single system. And if it happens to be a holiday, you might get to pay triple time to have it fixed.

    Even with 2 systems, an office in a bedroom won't stay at the same temp as the rest of the house.

    Get a window unit, or ductless for it.
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  12. #12
    Join Date
    Sep 2006
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    Bagzi,

    Another option is to consider an inverter driven system where the compressor runs at variable speeds and the indoor air handler(s) do too. These systems are known as VRV or VRF and manufactured by several Japanese companies such as Daikin or Sanyo.

    http://www.daikinac.com/commercial/p...oducts&page=55
    http://www.sanyohvac.com/productList.php?cat1=3&cat2=13

    These are top of the line comfort systems that are used widely outside the US and are becoming more prevalent here as our energy cost continue to rise.

    There is a small single outdoor unit and up to nine indoor air handlers - one for each zone. System efficiency improves as more air handlers are added to the system. Air handlers can be ductless or ducted depending on your needs. The outdoor unit is extremely quiet.

    With your home facing East/West then it has a significant load difference within the home depending on the time of day. And the office area has its own needs. You may find that your home would be best suited with five zones. East zones up and down, West zones up and down and then the office on its own zone. They make air handlers as small as about 7,000 BTU. Each zones has its own temps and can even be turned off while not having any negative impact on the other zones. Can not do that with a typical US system.

    The beauty of these systems is that you do not require elaborate over sized duct work (by-pass ducts and such) for the zoning as each zone has its own dedicated air handler. The ducted air handlers are physically quite small and you may be able to use much of your existing duct work after some remediation.

    There is one central controller for the system and small sensors (size of a match book) in each zone. All units communicate with each other and the outdoor unit. Inverter systems are very efficient and can run as low as about 25% of nominal capacity and even exceed nominal capacity on those really hot days. It is hard to oversize one of these systems as they fully adapt to the load - whether cooling or heating.

    Good luck.

  13. #13
    Join Date
    Apr 2008
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    TEXAS
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    just my opinion, but i live in central texas and i prefer a seperate unit for upstairs. the upstairs unit takes a beating in our climate(103 today). a single unit even with zoning takes a real beating here. its not uncommon for us to replace 4 year old compressors in two story homes with a single system.
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