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  1. #1

    Questions on upgrading from a 2.5ton to a 3ton AC Unit

    Little Background:

    I live in north Florida in a 1492sqft one story house built in 94. I have a Carrier split heat pump system. I work from home and like the temp to be set at 73-74. During the summer days the AC runs non-stop and the temp still climbs to 78-80. I have lived in the house 7+ years, and had every inch of the AC checked and cleaned, windows tinted, and personally examined every inch of duct work for leaks. All the companies/people who have looked at it say the unit is undersized for the house, and I need to go to a 3ton unit to maintain the temp I want. The air handler is located near the center of the house. It is a Carrier FB4ANF030, R22, with a piston size of 70 which matches the outside condenser. The blower motor has 3 speeds that can be hardwired. I went from medium speed to high in an effort to try to cool better. Did not help. On top of all of this energy cost have skyrocketed, and my bill was over $400 last month with only 2 people living in the house.

    Questions:
    1. I know just having the outside unit upgraded to a 3 ton could lead to the inner coil freezing. However would having the blower still on high and a addition of a TXV on the coiling coil prevent that?

    2. If it would still freeze, can I just upgrade to a 3ton coil that would still fit in my current air handler?

    3. Is it worth just upgrading to a TXV valve for energy savings and or any enhanced cooling?

    4. Can the compressor just be replaced with a far more efficient one without replacing the whole outside unit?

    5. If the only way is to upgrade to a complete new unit, will I need all new duct work as well? Currently there is only one main return, and no individual return to each room, per new home construction specifications.

    6. Has any ever heard of replacing a Central AC unit with a Mini Split system like LG's Art Cool? I really like the idea of controlling AC temp in each room.

    I apologize if my lack of understanding has lead me to ask some very wrong or crazy questions.

  2. #2
    Join Date
    Jul 2011
    Posts
    354
    this is JMHO, if your going to upgrade your unit to 3 tons replace a/h,cond,line set. get a 16 seer unit with a energy efficient motor! you will probably have to increase the return size. as far as mini splits in each room, people do that, but some times cost becomes a concern, the problem with hvac today is there are MANY choices available and some people just get confused. most people will tell you to get a load calc of your house, get some quality co's to give you a estimate and express your ideas,see about possible rebates, and go from there . this is JMHO, i leave actual advice to the pro's .

  3. #3
    Join Date
    Jul 2011
    Posts
    354

    Confused

    Quote Originally Posted by LucidLight View Post
    Little Background:

    I live in north Florida in a 1492sqft one story house built in 94. I have a Carrier split heat pump system. I work from home and like the temp to be set at 73-74. During the summer days the AC runs non-stop and the temp still climbs to 78-80. I have lived in the house 7+ years, and had every inch of the AC checked and cleaned, windows tinted, and personally examined every inch of duct work for leaks. All the companies/people who have looked at it say the unit is undersized for the house, and I need to go to a 3ton unit to maintain the temp I want. The air handler is located near the center of the house. It is a Carrier FB4ANF030, R22, with a piston size of 70 which matches the outside condenser. The blower motor has 3 speeds that can be hardwired. I went from medium speed to high in an effort to try to cool better. Did not help. On top of all of this energy cost have skyrocketed, and my bill was over $400 last month with only 2 people living in the house.

    Questions:
    1. I know just having the outside unit upgraded to a 3 ton could lead to the inner coil freezing. However would having the blower still on high and a addition of a TXV on the coiling coil prevent that?

    2. If it would still freeze, can I just upgrade to a 3ton coil that would still fit in my current air handler?

    3. Is it worth just upgrading to a TXV valve for energy savings and or any enhanced cooling?

    4. Can the compressor just be replaced with a far more efficient one without replacing the whole outside unit?

    5. If the only way is to upgrade to a complete new unit, will I need all new duct work as well? Currently there is only one main return, and no individual return to each room, per new home construction specifications.

    6. Has any ever heard of replacing a Central AC unit with a Mini Split system like LG's Art Cool? I really like the idea of controlling AC temp in each room.

    I apologize if my lack of understanding has lead me to ask some very wrong or crazy questions.
    one follow up. forget the new txv,forget replacing the compressor,your unit is a 94, time to give it the heave hoe! you'll need the upgrade, talk to some quality co.s, tell them your ideas and concerns,get a load calc on your house and go from there! this is just my humble opinion, good luck.

  4. #4
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,490
    Quote Originally Posted by LucidLight View Post



    Questions:
    1. I know just having the outside unit upgraded to a 3 ton could lead to the inner coil freezing. However would having the blower still on high and a addition of a TXV on the coiling coil prevent that?

    The TXV will not help with that. It maintains a specific superheat, but does not maintain a specific refrigerant pressure (therefore refrigerant and coil temperature). If the indoor coil is too small the refrigerant cannot pick up enough heat, and it will get colder and colder until frost forms.

    2. If it would still freeze, can I just upgrade to a 3ton coil that would still fit in my current air handler?

    Typically no. The blower is also sized for up to a certain tonnage (in your case 2.5). It comes as one unit.

    3. Is it worth just upgrading to a TXV valve for energy savings and or any enhanced cooling?

    No.

    4. Can the compressor just be replaced with a far more efficient one without replacing the whole outside unit?

    Compressors themselves aren't that much more efficient than they used to be. Switching from a recipricating to a scroll will gain a little, but most of the efficiency comes from coil surface area (new units are much larger than they used to be). More airflow = more heat transfer, which leads to lower compression ratios: less work, less power.

    5. If the only way is to upgrade to a complete new unit, will I need all new duct work as well? Currently there is only one main return, and no individual return to each room, per new home construction specifications.

    Every home is unique. A salesman will need to see the house and the system, take some measurements and calculate what you need. Sometimes everything is fine, sometimes minor modifications are all that is needed.

    6. Has any ever heard of replacing a Central AC unit with a Mini Split system like LG's Art Cool? I really like the idea of controlling AC temp in each room.

    It would be expensive. You would be looking at refrigeration linesets and electrical run to each head, and depending on your construction you might also have exposed lines and electrical that you will have to deal with. This is usually done for older homes with no ductwork at all.

    I apologize if my lack of understanding has lead me to ask some very wrong or crazy questions.

    No problem... we all like what we do, thats why we're here.
    .

  5. #5
    Join Date
    Jun 2011
    Location
    Seattle WA
    Posts
    1,238
    IMO I wouldn't go replacing single components on a 17 year old system (IE outdoor unit) I would make the leap and replace the whole system with properly sized equipment, or tough it out until you are forced to replace.
    America; first we fight for our freedom,
    then we make laws to take it away.

    -Alfred E Newman

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,271

    Hmm

    Quote Originally Posted by LucidLight View Post

    I live in north Florida in a 1492sqft one story house built in 94. I have a Carrier split heat pump system. I work from home and like the temp to be set at 73-74.

    I have lived in the house 7+ years, and had every inch of the AC checked and cleaned, windows tinted, and personally examined every inch of duct work for leaks.
    On top of all of this energy cost have skyrocketed, and my bill was over $400 last month with only 2 people living in the house.

    I apologize if my lack of understanding has lead me to ask some very wrong or crazy questions.
    Ducts should be inspected via duct pressure test.

    Why would one wait 7 years to address VERY High energy costs?
    $400 may be about 2 to 2.5 X what would be considered "normal"?

    My bill runs about $140 max during 3 high cooling months ( June, July, August) for 1,800 square foot. $100 for a few months (May, September, October). $60 for several months in the winter. ... I might be 200 to 300 miles South of you.

    I would expect noticably lower [ Not significant] bills in the summer when I replace my 10 SEER system with a 15 to 20 SEER unit in a couple years.
    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
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Keep in mind that a 17 y/o 2.5 ton unit is not likely running at full capacity anymore. I have a 17 & 18 y/o 3.5 ton units and based on my ariflow estiamtes and air temp, they are only operating at around 2 - 2-1/2 tons.


    Don't assume you'll see massive drops in your energy bill. R22 units do a great job of dehumidifying wiht their older smaller surface area coils. I've foudn that I'm more comfortable at 2-3F high temps on my old R22 systems than the one time i upgraded to a new 410a system. I saw only a small drop in my energy bills. Maybe 20% at most. You wanto look at EER not SEER when comparing peak summer energy bills. Thsoe 10 SEER unit I beleive are usualy like 8.5EER. The 20 SEER systems are actually usually only 16-18 SEER and I think 12.5-13 EER. That is as much as 35%, but it's not 1/2. Even my least effecient unit, I calculated that at a 80F outdoor temp was operating at a COP of 2.6. (using a power factor of 0.8) The other unit was a COP of 3.2 including estimated indoor pwoer consumption by the blower.... which has a ECM. It also helps that the system has a TXV and a newer cased coil on a newer furnace.

    So I'm running at a 9-11 EER. Not suprisingly, my bill for the first 13 days of July was only $119. (we just moved in). Which was a welcomed relief. So repalcing my equipment, would probably have a payback of something like 12-15 years.

  8. #8
    Quote Originally Posted by dan sw fl View Post
    Ducts should be inspected via duct pressure test.
    I have never heard of Duct Pressure Test. What is involved, and what is the typical cost?

    Quote Originally Posted by dan sw fl View Post
    Why would one wait 7 years to address VERY High energy costs?
    $400 may be about 2 to 2.5 X what would be considered "normal"?
    The energy costs have just recently skyrocketed. This month $416, same month last year $280. Even at that time $280 was a lot more than my neighbors I talked to. However they tended to have a the thermostat set on 78, opposed to my 73. So I have been dealing with the indoor 78-80 summer heat for 7 years, and now the monthy bill is far larger, it is just more motivation to finally do something about it.

  9. #9
    Join Date
    Dec 2003
    Location
    Citrus County, Florida
    Posts
    1,508
    Some excellent suggestions here. Your ducts need to be tested to ascertain that they are able to handle the amount of airflow you are trying to push thru them. A properly designed duct system is key to both comfort and efficiency. You may find tha your present duct sysem can not handle a 3 ton system; you may find your present duct system can't handle your present 2 1/2 ton system. A competent contractor will test your system and make a decision for you. I have been told approximately 80% of duct systems are too small.
    Doug

  10. #10
    My idea would be a window unit for your office. Or to go first class, a split unit. I have a split and the lack of noise is very nice--although you pay for it.

    Here's my reasoning:

    You never, ever replace a working unit just for the sake of so-called high efficiency. This is because claimed energy savings are like claimed gas mileage: they have little to do with the real world. In real life the payback time for high efficiency is longer than the life of the unit.

    Apparently you've had your existing unit checked by...well, everybody. Or were all of the tests done by the same person or company? I can't too strongly suggest getting a second opinion. A key fact is that it seems your unit was cooling fine, but now it's not. This did not just happen for no reason. As a quick check look at the outside unit. It has two copper pipes connected to it. The small pipe should be warm or hot (careful!), the large pipe should be cool and sweating.

    I'm sorry to tell you this, but the piecemeal fixes you contemplate are going to nickel and dime you to death, and might never work to your satisfaction. That's unless you're talking to a guy who's been in the business for 20-30 years, and absolutely knows how go about the risky business of modifying the thing. But you don't have such a guy, or you wouldn't be asking these questions.

    When a system is getting on toward 20 years old, then replacement might be the best idea. But if it's checked by more than one person--working for more than one company--and found to be working OK, then I can't imagine replacing it. I vote for the add-on window or split idea.

    By the way, an expansion valve (TXV) won't do anything for you, they're for conditions of widely varying heat load, which a house is not. And a different/wrong compressor is quite likely to screw the works entirely, since all the parts in your system were very, very carefully matched by the engineers who designed it. Whoever suggested these to you doesn't sound to me like the 20-30 year guy.
    Last edited by picbuck; 08-16-2011 at 12:21 PM. Reason: clarity

  11. #11
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    "OUCH ouch ouch, I keep burning my hand on that pot!!!"

    --- "Hey dummy, use the potholder!"

    Apply this thought process to your home, it needs to better protect you from outdoors.

    How about taking a look at deficiencies in the HOUSE? If there were 3 windows open would you;

    A: close the windows, or
    B: get a bigger heat pump?

    Assuming your answer is A, imagine your house has 3 INVISIBLE windows open, do you;

    A: call someone who specializes in finding and closing invisible windows, or
    B: assume there is nothing you can do to improve the house, so settle on a bigger heat pump.

    BTW, Closing the windows is the only way to significantly reduce cooling costs... Getting a BIGGER unit is not the answer to your energy problem.
    Last edited by tedkidd; 08-16-2011 at 10:47 PM.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,271

    Thumbs up I love a REALITY CHECK !

    Quote Originally Posted by tedkidd View Post
    "OUCH ouch ouch, I keep burning my hand on that pot!!!"

    --- "Hey dummy, use the potholder!"

    Apply this thought process to your home, it needs to better protect you from outdoors.

    How about taking a look at deficiencies in the HOUSE? If there were 3 windows open would you;

    A: close the windows, or
    B: get a bigger heat pump?

    Assuming your answer is A, imagine your house has 3 INVISIBLE windows open, do you;

    A: call someone who specializes in finding and closing invisible windows, or
    B: assume there is nothing you can do to improve the house, so settle on a bigger heat pump.

    BTW, Closing the windows is the only way to significantly reduce cooling costs... Getting a BIGGER unit is not the answer to your energy problem.
    TED,


    WELL SAID IN A CONCISE MANNER !
    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

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