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  1. #1

    Hmm AC Units Consuming More and More (did some due diligence)

    Hello everyone,
    I have a done a great deal of research on AC units and am now a little overwhelmed and need to see if my diagnosis is correct.
    Note: I am in an apartment bldg (in the desert) and landlord states the AC units have been maintained (which I dont believe). Voltage 220

    We have 2 units for an apartment that is approximately 1200-1400 sq ft.
    Both units are RHEEM

    Unit #1:
    3-Phase, RLA 7.0, Min. Supply Circuit Ampacity 10
    With AC running at 22*C with outdoor temp at 30*C the amp readings were 11-12 amps per phase and 12 amps all together including fan
    Wattage measurement with unit set at 20*C with outdoor temp at 30*C (night) = 4400 watts

    Unit #2:
    1-Phase, RLA 13.7, MSCA 19 amps
    With AC running at 22*C with outdoor temp at 30*C the amp reading was 14 amps and 18 including fan
    Wattage measurement with unit set at 20*C with outdoor temp at 30*C (night) = 3000 watts

    I cant tell if the units are consuming more than they should but our electric bill has been increasing over the past 3 years. I was told by someone that the compressors may be shot or the motor is clogged up hence consuming more. The wattage measurements were accomplished using an electricity meter reading system that seems to be quite accurate as I got the exact wattage for my dryer as stated in the manual
    I have information overload now and cant tell if the units are consuming more than they should and any observations would be very helpful

    Thanks!!

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,242
    Quote Originally Posted by angryTenant View Post
    Note: I am in an apartment bldg (in the desert) and landlord states the AC units have been maintained (which I dont believe). Voltage 220

    We have 2 units for an apartment that is approximately 1200-1400 sq ft.
    Both units are RHEEM

    Unit #1:
    3-Phase, RLA 7.0, Min. Supply Circuit Ampacity 10
    With AC running at 22*C with outdoor temp at 30*C the amp readings were 11-12 amps per phase and 12 amps all together including fan
    Wattage measurement with unit set at 20*C with outdoor temp at 30*C (night) = 4400 watts

    Unit #2:
    1-Phase, RLA 13.7, MSCA 19 amps
    With AC running at 22*C with outdoor temp at 30*C the amp reading was 14 amps and 18 including fan
    Wattage measurement with unit set at 20*C with outdoor temp at 30*C (night) = 3000 watts

    I cant tell if the units are consuming more than they should but our electric bill has been increasing over the past 3 years.
    ... Do you deposit your check with the local Utility or are you able to use a bank account?

    I'd be moving!

    Your electric bill per month is nearly _ $x,xxx. ..?
    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

  3. #3
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,242
    Are you in the U.S. or Saudi Arabia?

    I would say having a thermostat set at 68'F (20'C) versus 77'F is going to increase the electric bill significantly more than 70%.
    One should expect a properly sized unit (Designed to normal 75'F set-point) to run CONTINUOUSLY for >> 3,000 hours in the Desert.
    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

  4. #4
    Quote Originally Posted by dan sw fl View Post
    Are you in the U.S. or Saudi Arabia?

    I would say having a thermostat set at 68'F (20'C) versus 77'F is going to increase the electric bill significantly more than 70%.
    One should expect a properly sized unit (Designed to normal 75'F set-point) to run CONTINUOUSLY for >> 3,000 hours in the Desert.
    Thanks for the input.
    Good call, I'm actually in Dubai. Utilities are cheaper here but I'm still paying more every month. We haven't changed the way we run our units but the consumption has increased drastically and regularly over the past 30 months...leading me to believe the ac units may not b serviced and thus are pulling more amps.
    Is that a fair assumption and do the numbers indicate any issues with the units?

    PS other people in the building have seen spikes in their bills as well that are proportional and higher than they should

  5. #5
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,156
    Anybody else miss the 3 phase vs. 1 phase?
    12A x 3 phases = 36 amps.
    18A x 2 phases = 36 amps.
    Sorry, but I don't see where one unit is using more than the other.
    If all 3 phases are even I don't see how a motor winding could be partially shorted.
    Did you verify both units are same tonnage?

    When units DO use more power it's typically because of airflow (especially dirty condenser coils) or overcharged system.
    If the ACs are both top discharge, check airflow pattern, air should be coming straight UP from the unit, not off to the sides.

  6. #6
    Quote Originally Posted by 54regcab View Post
    Anybody else miss the 3 phase vs. 1 phase?
    12A x 3 phases = 36 amps.
    18A x 2 phases = 36 amps.
    Sorry, but I don't see where one unit is using more than the other.
    If all 3 phases are even I don't see how a motor winding could be partially shorted.
    Did you verify both units are same tonnage?

    When units DO use more power it's typically because of airflow (especially dirty condenser coils) or overcharged system.
    If the ACs are both top discharge, check airflow pattern, air should be coming straight UP from the unit, not off to the sides.
    Thanks 54regcab for your response. There are 2 units. One is a 1phase and the other is a 3phase.
    They have different tonnage as I understand it you take the RLA rating and divide by 5-6 to get the approximate tonnage. The 3phase unit is a bigger unit
    As for air flow do you mean the unit that sits outside...do I look at whether it is blowing air straight up or from the sides?

    Thanks again for trying to help out

  7. #7
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,292
    When was the last time the condensing coils on these two units cleaned?

    Deserts are dusty. Dust clogs up condenser coils. Clogged up condenser coils elevate compressor work load. Elevated compressor work load demands more power to do the same job. More power means more cost.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  8. #8
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,156
    yes the outside units. coils load up with dust over time.

  9. #9
    Join Date
    May 2008
    Location
    Central Fla.
    Posts
    311
    There should be 2 copper lines that exit the outdoor unit(1 has black insulation the other is exposed) and go into the building. The smaller of the 2 lines (the exposed one)should be warm to the touch, not hot. touch the small line and let us know what the line feels like. If it is hot the condenser is either clogged or has become inefficient .Either of these conditions will cause high utillity bills.

  10. #10
    Wow, thanks guys!
    I will check the pipe as TwincamDave suggested and report back.
    Shophound, that I dont know. I asked if the units have been serviced and I was told yes but the trend suggests otherwise

    So based on the info that i gave in the initial post, can I go to the landlord and state that the units are consuming more than they should be? Or are those numbers inconclusive?

    Thanks again. You guys have given more info than the landlord and their AC technician combined

  11. #11
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,156
    Do the units keep your apartment reasonably cool on 100f+ days?

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
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    Quote Originally Posted by 54regcab View Post
    Anybody else miss the 3 phase vs. 1 phase?
    12A x 3 phases = 36 amps.
    18A x 2 phases = 36 amps.
    No one would use Your rule for current because I think you absolutely fell off the track.
    Now I'd like to see you tell us about the power in an inappropriate way.
    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

  13. #13
    Join Date
    Nov 2004
    Location
    SW FL
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    I think if I lived in the desert I'd have to clean the coils every time the wind blew more than 8 mph.

    In other words, wash the outdoor coils every 10 days. Then see what happens to the electirc bill$.
    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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