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  1. #1
    Join Date
    May 2013
    Posts
    17

    New Trane System Question

    Our 15 year old mixed vendor A/C failed on us. The main failure was multiple leaks in the evaporate coil. Looking at the repair costs, rebates available, tax credits, and age of the system, I felt it was best to replace it with a new system rather than repair the old system in patchwork fashion.

    Based on what I have read here many times, it is more important to focus on the install contractor and less on the brand of the equipment. Using the local installers that were available and decent (based on reviews, ratings, recommendations, gut feel, etc.), we were down to the choice of a Trane or Lennox replacement system.

    For summary information, we live in mid-central Florida, non-coastal, have cheap natural gas available, and all of the Florida normal items apply (high humidity, summer heat, light winters, etc.) The house is 15 years old, 2250 square feet, has decent duct work (inspected by utility company and several contractors), has decent insulation (R30 in the attic and also inspected), and the heat/cooling load calculations show the load between 52k to 57k BTUs. As probably expected, our needs are driven more by the cooling load than anything else.

    Our old system was the following:
    - Goodman CLJ60-1 one stage condenser (replaced Carrier 38CKB060 condenser in 2004 due to repair costs exceeding replacement costs)
    - Carrier 58UHV100-1-20 variable speed furnace
    - Carrier CK3BXA060 evaporator coil
    - Carrier TSTATCCPRH01-B thermostat (thermidistat)

    The replacement system that was selected is as follows:
    - Trane 4TTX6060E1000B (XL16i) condenser
    - Trane TUD2D120B9V5VB (XV80) furnace
    - Trane 4TXCD063BC3H evaporate coil
    - Trane TCONT802AS32DA (802) thermostat

    The install contractor did a great job during the install, and the follow-up visit the next day. I have verified that DIP switches are set and equipment is wired for 2 stage cooling, 2 stage heating, and Comfort R is on. It has been several weeks since the unit was installed, and I have a couple of questions:

    1) The unit cools the house in 1st stage adequately so far. April has been a great weather month for us, but that also means it has been mild compared to the summer (humidity is lower, outdoor temps lower, etc.) For cooling, the unit cycles on for about 6 to 8 minutes and then back off. This happens 2 to 3 times per hour at the most during the hottest parts of the day (thermostat cycles per hours is set for a maximum number of 3 runs per hour). The old unit seemed to come on for longer periods of time, but since it was older, low on refrigerant, etc. I thought that may have been it. Since it has been mild weather, my thought is that the short run times was due to the mild weather and would get longer as we get into the heat of the summer. Is this OK for the new unit or would it be considered short cycling?

    2) The new thermostat seems to maintain the temperature within a .5 to 1 degree of the set point only, and does nothing about the humidity. The old thermostat maintain the temperature as well but also factored in the humidity, and would overcool by a few degrees (think it was 2 or 3 degrees) as needed to maintain humidity levels. Could the new thermostat be the reason behind the 6 to 8 minute run times as compared to the longer run times on the old equipment?

    Thanks.

  2. #2
    Join Date
    Dec 2002
    Location
    Arizona
    Posts
    4,411
    How was your new system sized?
    Make your expertise uniquely valuable.

    Make your influence uniquely far-reaching.

  3. #3
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,665
    you need the tcon803
    We really need change now

  4. #4
    Join Date
    May 2013
    Posts
    17
    Quote Originally Posted by jimj View Post
    How was your new system sized?
    It was a combination of things. 1) Old system was a 5 ton with no issues, and new system was 5 ton (I know that is frowned upon, but it was said by several of the contractors); 2) We are a tract home in a subdivision with multiple homes of the same model and the install contractor has done several of them; 3) Contractor did go through the home and verify ducts sizes, return air grill sizes, etc.; and 4) In order for me to feel comfortable, I did several different load calculations using an online site, spreadsheet someone published, and a program that was available. All of them came out in that 52k to 57k BTUs for cooling.

  5. #5
    Join Date
    May 2013
    Posts
    17
    Quote Originally Posted by catmanacman View Post
    you need the tcon803
    I know the main difference between the 802 and 803 is the humidity sensor. Is the 803 going to make a huge difference? Is the best one to get the 803, or do I go to something other than the Trane such as the Honeywell IAQ I see mentioned a lot?

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295
    Quote Originally Posted by cpeek View Post
    It was a combination of things. 1) Old system was a 5 ton with no issues, and new system was 5 ton (I know that is frowned upon, but it was said by several of the contractors); 2) We are a tract home in a subdivision with multiple homes of the same model and the install contractor has done several of them; 3) Contractor did go through the home and verify ducts sizes, return air grill sizes, etc.; and 4) In order for me to feel comfortable, I did several different load calculations using an online site, spreadsheet someone published, and a program that was available. All of them came out in that 52k to 57k BTUs for cooling.
    Best approach would have been to reduce the Heat Gain by improving the building thermal envelope.

    Furnace is not needed in a central FL residence.
    Think Heat Pump.

    Now you can convince yourself you need a whole house dehumidifier due to NOTICABLY Oversizing of the A/C unit.

    With Relative Humidity < 44%, Floridians would generally find that ~77'F is comfortable.

    http://www.acrsystems.com/products/trh1000/
    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

  7. #7
    Join Date
    May 2013
    Posts
    17
    Quote Originally Posted by dan sw fl View Post
    Best approach would have been to reduce the Heat Gain by improving the building thermal envelope.

    Furnace is not needed in a central FL residence.
    Think Heat Pump.

    Now you can convince yourself you need a whole house dehumidifier due to NOTICABLY Oversizing of the A/C unit.

    With Relative Humidity < 44%, Floridians would generally find that ~77'F is comfortable.

    http://www.acrsystems.com/products/trh1000/
    I appreciate what you are saying, however all of the contractors in this area recommended using the furnace because we have natural gas available. None of them would do a heat pump. I specifically asked this with each of them (over 6 contractors), and each had similar answers - natural gas heat is so cheap compared using a heat pump that it makes no sense to do anything but a furnace. There was also a large rebate from the gas company (which is a subsidiary of the electric company) for replacing a furnace. In addition, we have five neighbors that have replaced their systems over the last few years, and none of them could get a contractor to do a heat pump.

    As for the oversizing of the unit, does that mean the unit is considered to be short cycling? If everything I described pointed us to a 5 ton system (old system was 5 ton and worked fine, same model tract home with identical requirements, cooling load needs between 52k to 57k BTUs, etc.), what should I have done different to get the right sized system?

  8. #8
    Join Date
    May 2013
    Posts
    17
    Can anyone advise whether the 6 to 8 minute runtime averaging 2 to 3 times per hour during the hottest part of the day would be considerer short cycling? Is this normal?

  9. #9
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,049
    Quote Originally Posted by cpeek View Post
    Can anyone advise whether the 6 to 8 minute runtime averaging 2 to 3 times per hour during the hottest part of the day would be considerer short cycling? Is this normal?
    Yes, that would be considered short cycling. In milder temps this is normal but when the outdoor temp is close to, at and above design temperature for your area the unit should run nearly all day without shutting off, and catches up through the night and begins to cycle.

  10. #10
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,049
    Hvac equipment takes about 10 minutes of runtime to get up to its rated efficiency and work like its designed.

  11. #11
    Join Date
    May 2013
    Posts
    17
    In Florida, we are kind of in the mildest of our seasons (April/May). Yesterday the low was 61 and the high was 77, and today it was 59 and 73. Over the last week or two the average low was 63, the average high was 81 (with a handful of days at 87 to 88 as the high).

    The temperature has been very mild and close to our thermostat setting of 78. With this kind of weather, would it be reasonable that a unit would run short cycles or should that never happen (e.g. the run times must always been at least X minutes long)?

  12. #12
    Join Date
    Dec 2002
    Location
    Arizona
    Posts
    4,411
    I think you will have the answer to your questions in the next 90 days. If you never or very rarely see your system switching to second stage your system is over sized.
    Make your expertise uniquely valuable.

    Make your influence uniquely far-reaching.

  13. #13
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,049
    Quote Originally Posted by cpeek View Post
    In Florida, we are kind of in the mildest of our seasons (April/May). Yesterday the low was 61 and the high was 77, and today it was 59 and 73. Over the last week or two the average low was 63, the average high was 81 (with a handful of days at 87 to 88 as the high).

    The temperature has been very mild and close to our thermostat setting of 78. With this kind of weather, would it be reasonable that a unit would run short cycles or should that never happen (e.g. the run times must always been at least X minutes long)?
    It's reasonable for the ac to run short cycles in mild weather. When the highs get in the mid to upper 90s it shouldn't cycle much at all, if it does its oversized.

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