Page 1 of 2 12 LastLast
Results 1 to 13 of 19
  1. #1
    Join Date
    Aug 2003
    Posts
    501

    Changing coil on undersized system

    I was brought in as a second set of eyes on this one.Got a 2 ton r410 txv system 10 degree s/c 13 degree s/h with a 15-16 degree temp drop across coil.the system will only cool down to 74 degrees on a 80-85 degree day.i checked everything,airflow,filters,coil and all were good this is the first season the customer used this system as they just bought the home and of course it was a as is sale.the customer wants a little more out of the system but funds are an issue.they were told the system was a tad undersized which i agree with.there fix was to put a 2.5ton condensing uniton the coil that was there i said i would change coil to 2.5 ton,so which is going to get more bang for the buck and again a system changout is not in the works and all the customer is looking for is about 3-4 degree colder inside temp

  2. #2
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,944
    I really tried, but I still don't think I quite have the full situation straight from the way it is worded.

    Did they already have a 2.5 ton outdoor unit installed without changing out the indoor coil? If so, you may get away with changing the txv to match the outdoor unit.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  3. #3
    Join Date
    Aug 2003
    Posts
    501
    Nope its a 2 ton condensing unit and 2 ton ac coil

  4. #4
    Join Date
    Dec 2011
    Location
    New Zealand
    Posts
    2,202
    Fit a suction/liquid line heat exchanger by the indoor coil. Move the bulb of the TXV to the outlet of the of the heat exchanger.
    This will give an increased wetted area of the evap. Lifting the SST slightly, increasing the LMTD of the coil as whole, and reducing the refrigerant pressure drop through the evap slightly.
    Fair cheap option
    As with both options you have given i would not guarantee any specific performance gains.
    Changing the outdoor will give additional cooling, but you may have consequences when ambient is not so hot. (freezing coil and or condensation on outlet grills)
    Replacing indoor only will give increased cooling, higher SST, but could reduce humidification. (good dry bulb temp, poor wet bulb)

  5. #5
    Join Date
    Aug 2003
    Posts
    501
    i am leaning towards a coil change,it cools to 74 degrees at an 83 degree and under outdoor temp so i just need a little more cooling.

  6. #6
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,944
    I see no capacity gain in changing the indoor coil.

    I would try lessening the load and increasing the delta-t by reducing airflow.

    I am not familiar with what barbar is talking about....or I am just having trouble understanding posts tonight.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  7. #7
    Join Date
    Aug 2003
    Posts
    501
    i put airflow on low and adjusted the charge that was my first move

  8. #8
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,559
    Give them the proper way to fix it in the most economical matter. Changing coil isn't going to do much IMO. It's their house and their money. If you start messing with it by changing coil, moving txv or whatever. You're gonna own their POS. Sometimes it's better to walk away and not make money than trying to help and losing money and your reputation. I've walked away from several because they didn't want to do what my recommendation was to fix it.
    I like DIY'ers. They pay better to fix.

  9. #9
    Join Date
    Aug 2003
    Posts
    501
    They totaly understand i am only going to offer maybe something that might work and it will be in writing/also i do see alot of systems around here with a 1/2 ton larger coil.

  10. #10
    Join Date
    Dec 2011
    Location
    New Zealand
    Posts
    2,202
    Quote Originally Posted by RoBoTeq View Post
    I see no capacity gain in changing the indoor coil.

    I would try lessening the load and increasing the delta-t by reducing airflow.

    I am not familiar with what barbar is talking about....or I am just having trouble understanding posts tonight.
    The present coil produces superheat, this part of the coil has minimal effect on net cooling, but could be upto 20% of the coil surface area. (sorry do not know the specific of the coil). By adding a suction line heat exchanger and moving the bulb, the coil becomes fully wetted (liquid refrigerant boiling) better heat transfer.
    The superheat is given from the liquid line "increased sub cooling"
    The better heat transfer slightly increases the the SST at the comp giving an increased refrigerant mass flow. (increase nett refrigeration effect)
    The sub cooling reduces the the flash gas entering the evap, less flash gas, reduces the pressure drop across the refrigeration circuitry.So the boil refrigerant temp is more even across the coil.

  11. #11
    Join Date
    Dec 2011
    Location
    New Zealand
    Posts
    2,202
    Quote Originally Posted by splus View Post
    i put airflow on low and adjusted the charge that was my first move
    So when you lowered your airflow, did your suction pressure drop?
    If so then you reduced the nett cooling effect, even though your air temp would seem to be colder.

  12. #12
    Join Date
    Aug 2003
    Posts
    501
    pressure dropped 4psi air temp only dropped 1 degree though

  13. #13
    Join Date
    Dec 2011
    Location
    New Zealand
    Posts
    2,202
    So you actually lost about 3-4% in nett cooling by reducing your airflow. Due to reduced refrigerant mass flow.

Page 1 of 2 12 LastLast

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