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  1. #1
    Expert opinions please:

    I have low performance and high electric bills. Moved in to the house 4 months ago.

    3.5 Ton system 11 SEER Rheem (7 years old)
    Horizontal A coil
    Outdoor Ambient 78 DB 66WB
    CFM 1585
    RAT DB 71
    RAT WB 65
    SAT DB 60
    SAT WB 59
    Evap TD 11


    Condensing Unit
    Suction P 59
    Suction T 45
    Liquid P 199
    Evap temp 33
    Superheat 12
    Subcooling 22
    FLA 19.9 - Unit running at 18

    Evap coil is fixed orfice.
    Evap coil has been hacked into with what could only be described at the jaws of life. Opened panel observed clean coil, no air bypassing coil (no missing baffle or anything unusual other than the crappy patch job on the coil casing). It's like the previous owner had a problem but either did not have it fixed or the tech didn't know what to do.

    Would appreciate any help, it's been about 15 years since I was in the mechanical side of the business (been in the controls business since then).
    Mike Patrick
    The opinions stated here are mine and may not reflect those of my employer Siemens Industry, Inc.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,750
    How did you measure your CFM?

    Slow it down.
    Pump the unit down, and check for the right piston.
    Check for a restriction in the liquid line.

    Post the model and serial #s of your units.
    That may help.
    Is this a heat pump.
    Contractor locator map

    How-to-apply-for-Professional

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

  3. #3
    Join Date
    Oct 2003
    Posts
    2,866
    Originally posted by mpatrick Expert opinions please: I have low performance and high electric bills.
    I aint fallin for it. She said it wasn't that good and ever since you've had to keep the lights on.

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    Without knowing more about your system, such as coil size and whether it's matched correctly with rest of system (since it was "hacked in"...who knows what was done?), sounds to me like you have excessive liquid stacking up in condenser (high subcooling) but at the same time a low superheat. Higher SEER rating could account for this partly, but you're reporting subpar performance and high utility bills.

    How clean are all the coils and blower wheel? And did I read your outdoor ambient temp right as being 78 degrees dry bulb? TO be pulling near FLA at that mild of an ambient...something's up.

    Post more info such as model nos. of coil, air handler, and condensing unit. And condition of all coils, dirty or clean. Just casually you look overcharged but not enough info to say with more confidence.

  5. #5
    Join Date
    Feb 2004
    Posts
    114
    Just so you know im still a new tec

    check your filters, and make sure your condenser is clean.

    is the blower cleaned and door closed

    last is ther any frost on the line

  6. #6
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,505
    Originally posted by mpatrick
    FLA 19.9 - Unit running at 18
    Is that a FLA on the unit or RLA? Ruud, Rheem same difference usually measures theres in Rated Load Amps so 18 would be ok.
    “Reality is merely an illusion, albeit a very persistent one.” –Albert Einstein
    “Experience is a hard teacher because she gives the test first, the lesson afterwards.”-Vernon Law

  7. #7

    More Info

    Conventional split system (not a heatpump)
    Rheem Model RALB042JAZ
    Serial 535fo7960712
    Blower filter and coil clean, blower door closed.
    Cleaned condensor, not perfect but reasonably clean.

    Estimated CFM from fan curve on inside of gas furnace door using .5" static.

    No frost on line.

    System appears to be original as everything matches the other system (2 ton).

    The evap coil is missing the model tag due to the hacking, but appears to be the same brand/model as the 2 ton only a little bigger. The 2 ton coil is a Benchmark B34d24-h.
    Mike Patrick
    The opinions stated here are mine and may not reflect those of my employer Siemens Industry, Inc.

  8. #8

    Little more info

    Just to calibrate what I mean by high electric bills.

    $543 last month for a 2700 sq ft house in Houston. Rate is 11.1/kwh, usage is average of 145kwh per day. Other large loads have like the pool pump etc have been investigated and every thing points to this unit as the energy hog.
    Mike Patrick
    The opinions stated here are mine and may not reflect those of my employer Siemens Industry, Inc.

  9. #9
    Join Date
    Jul 2003
    Location
    Texas
    Posts
    457

    Re: Little more info

    Originally posted by mpatrick
    Just to calibrate what I mean by high electric bills.

    $543 last month for a 2700 sq ft house in Houston. Rate is 11.1/kwh, usage is average of 145kwh per day. Other large loads have like the pool pump etc have been investigated and every thing points to this unit as the energy hog.
    Check out electric rates by other providers. Here in Dallas area, I use Reliant, (used to use TXU) monthly rate is currently around 8.0 to 8.4 cents per kwh. Thats a big percentage difference from your 11.1/kwh.

  10. #10
    Join Date
    Feb 2004
    Location
    Maine
    Posts
    483
    Even if the A/C unit was malfuntioning this wouldn't cause you to use 145 kwh a day! At 18 amps at 220 volts this would be 4kw per hour, if unit were to run 10 hours a day thats 40 kwh per day. Figure in another 20 to 30 kwh/day to run the rest of your house and you would only be at 70kwh/day. Have you had your electricity supplier check this out for you? Maybe you have a bad meter, or a problem thats allowing current to flow to ground. Have power company check stuff out, then get a good electrician. There is something really wrong here and I don't think its your A/C. Try turning off all appliances and unplug everything in your house and see if that disc inside your electric meter stops moving, it should. Make sure you unplug everything as small plug in transformers will use some juice while plugged in. If meter disc keeps moving after everything is unplugged and turned off you have problem for the power company or an electrician to figure out. Hope this helps.



  11. #11
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,505
    That seems to be a lot of home for a 3.5 ton to try and cool
    especially if your in Houston, I am paying 10 cents pkw in Houston right now unless they have gone up since last bill with reliant. You said 71 RAT you keep it pretty cool in there, I find with the majority of my customers that 78 is an average setting and it will make a difference on the light bill every degree you go down, how much? to many varibles but Reliant has some sort of average they say For every one degree you set the thermostat warmer in the summer, you can save 2 to 3 percent off your monthly cooling bill.I don't know pressures look ok but I just think you keep it to cold and personally 3.5 tons in Houston for that size home I just don't think will work unless you have no heat load.
    “Reality is merely an illusion, albeit a very persistent one.” –Albert Einstein
    “Experience is a hard teacher because she gives the test first, the lesson afterwards.”-Vernon Law

  12. #12
    I have managed to lower the KWH usage to 80/day, by doing the following:
    1- Run pool pump early in the morning so the pool is clean when the wife and kids get in. I found that they were manually turning it on when they got up because I had it running in the evening.

    2. Raised programmable stats to 76 during the day from 73.

    3. Hot tub has an electric heater(50 amp/230v)- when the power flashes (happens often) it defaults to 100 degrees and can not be reprogrammed. I designed/installed a lockout circuit that shuts the controls down on a power failure. Requires manual restart.

    4.Replaced 80% of incandecent bulbs with compact flourescent.

    5. During the investigation of all of this, I discovered that this particular AC only had a 10 degree Delta T and warranted more investigation.

    6. I am in one of the few regulated sections of Texas and cannot change power companies.

    7. Electrical system/meter is in good working order. Verified with digital KWH meter I have access to.

    8. This is one of two AC units. I have a 2 ton upstairs.

    9. I know 71 is cold for the return air, I had it turned down low while I was taking measurements. It has been cool and rainy for 3 weeks here.

    [Edited by mpatrick on 07-01-2004 at 09:42 AM]
    Mike Patrick
    The opinions stated here are mine and may not reflect those of my employer Siemens Industry, Inc.

  13. #13
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,505
    Sorry I did not catch the other unit on my first cup of coffee, of course TEV would be better I am surprised that rheem could get 11 seer without one but maybe so. I tell you have a lot of power consuming stuff going on, my home is about 200 sq.ft. smaller than yours single level and other than a/c the only other power consumers i use is my MIG Welder sometimes, and my air compressor and a fridge in the garage and i run a blower out of a furnace in my garage 110 volt i think it runs around 6.8 amps probably run all this an average of 8 times a month for a short period and my bill last month was 245.00 and i felt pretty blessed. I know I have a lot of customers that have those 500.00 light bills but they have bigger homes and keep it a lot cooler than i do but none of us in my home really like it real cold 78 during the day is fine and we turn it to 75 at night.
    “Reality is merely an illusion, albeit a very persistent one.” –Albert Einstein
    “Experience is a hard teacher because she gives the test first, the lesson afterwards.”-Vernon Law

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