Page 1 of 2 12 LastLast
Results 1 to 13 of 25
  1. #1
    Join Date
    Apr 2007
    Posts
    46

    Understanding Electric costs with Rheem 2-stage

    Ok... I have a 2 stage RHEEM 16SEER 4ton R410A system. I believe its an RARL-JEZ unit.

    I am trying to figure out how much it costs me to run my unit. My KW/h rate is 17 cents per KWH. But I can't figure out how many KWH each of these units use (air handler & condensor) when in stage one mode and stage two mode.

    For example, I had my AC set to 69 overnight (I like it cool). I leave for work at 8am and don't get home till 6pm. I have two choices:

    Leave it set at 69 or whatever temp during the day. It will probably stay in stage1 for the entire day, but it will be on for most of the day.

    Or I can do what I have been doing and remotely turn on the unit at around 3pm. It will kick into stage 2 15 minutes after I turn it on and it will run for a few hours in stage 2 to get the temperature down from 75 (since it went up with no air on) to 69.

    I would love to find out what the KWH usage on these units are because my thermostat is Proliphix and it has built in counters to tell me how long stage1 is on for and how long stage2 is on for.

    Thanks in advance.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,063
    Never heard of anyone needing it 69* in their house with a properly sized, and functioning 2 stage.

    You would need to also know the relative humidity in the house, and convert that to WB and then compare it to the extended data chart to know how many KW's it uses in what stage at those conditions.
    Contractor locator map

    How-to-apply-for-Professional

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

  3. #3
    Join Date
    Jan 2007
    Location
    Minneapolis, MN
    Posts
    415
    Measure the power use,add your power cost and it tells all.
    http://www.powermeterstore.com/p4124/eml_2020.php

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,063
    So he would need 2. One for the indoor unit, and one for the outdoor unit if he wants to be acturate.

    One if he just wants to guess.
    Contractor locator map

    How-to-apply-for-Professional

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

  5. #5
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,286

    Confused Derate about 20 - 30%

    Quote Originally Posted by DjPiLL View Post
    Ok... I have a 2 stage RHEEM 16SEER 4ton R410A system.
    I believe its an RARL-JEZ unit.

    My KW/h rate is 17 cents per KWH.

    For example, I had my AC set to 69 overnight (I like it cool).
    You definitely need to be paying a Higher electric rate!
    A/C needs to be derated a very large amount
    since the 4-ton rating (ARI) is based on 80'F.

    What is your location?
    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

  6. #6
    Join Date
    Apr 2007
    Posts
    46
    Quote Originally Posted by dan sw fl View Post
    You definitely need to be paying a Higher electric rate!
    A/C needs to be derated a very large amount
    since the 4-ton rating (ARI) is based on 80'F.

    What is your location?

    I am not sure what you mean by derating. Why do I need to be paying a higher electric rate? My electric bill is broken into two sections and the total rate comes out to about 17cents a KWH.

    I am in Long Island, NY.

    Right now I have it set at 70 degrees and its comfortable enough and i'll probably leave it at 70 overnight.

    My house gets extremely hot whenever the outside temperature goes past 70 degrees. My upstairs was 78 degrees and my downstairs was 75 degrees before I turned the air on.

    I just thought there would be an easy way to tell how much electric this thing uses. If I know the wattage of the two units, my electric company gave me the formula to calculate the amount of KWH it uses.

  7. #7
    Join Date
    Jun 2007
    Location
    Bucks Co PA
    Posts
    364
    Quote Originally Posted by DjPiLL View Post
    I am not sure what you mean by derating. Why do I need to be paying a higher electric rate? My electric bill is broken into two sections and the total rate comes out to about 17cents a KWH.

    I am in Long Island, NY.

    Right now I have it set at 70 degrees and its comfortable enough and i'll probably leave it at 70 overnight.

    My house gets extremely hot whenever the outside temperature goes past 70 degrees. My upstairs was 78 degrees and my downstairs was 75 degrees before I turned the air on.

    I just thought there would be an easy way to tell how much electric this thing uses. If I know the wattage of the two units, my electric company gave me the formula to calculate the amount of KWH it uses.
    I have tried contacting the manufacturer (I haven't purchased yet), but it seems this info is TOP secret. LOL

    I understand the equipment uses electric at different rates at different times but I also would like to know the "max" current draw of a particular unit.
    .

  8. #8
    Join Date
    Apr 2007
    Posts
    46
    Yeah. It's just going to be difficult to figure out how much this CAC is going to cost me.

    I am getting a hot tub installed this month so my electric is already going to spike from this. It will be difficult to gague what my CAC is going to cost when this summer I will be introducing a new CAC and a new Hot Tub during the same season.

  9. #9
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by DjPiLL View Post
    Yeah. It's just going to be difficult to figure out how much this CAC is going to cost me.
    You need to contact Rheem/RUUD and get some Technical Operating Data for your system.

    Goodman, www.GoodmanMFG.com, provides outstanding technical data on their website for their products including condenser power consumption for each stage under various outdoor/indoor temps.

    Good luck.

  10. #10
    Join Date
    Feb 2007
    Posts
    999

    Derating

    Originally Posted by DjPiLL
    I am not sure what you mean by derating.

    The manufacturer's specifications are listed as ARI cooling specifications, which are:

    95 degrees outdoor temperature, 80 degrees (Dry bulb); 67 degrees (Web bulb) indoor temperature.

    A Rheem RARL-042-JEZ unit w/ matching coil and furnace* might list its full capacity as 35,900 BTU (sensible) and 11,100 BTU (latent). Total is 47,000 BTU.

    However, since your thermostat is set at 70 degrees, you loose 840 BTU sensible capacity for every degree below 80, per 1000 CFM, or 10 x 840 x1.6 = 13,440 BTU lost (400 CFM x 4 ton = 1600). So at 95 degrees OD and 70 ID, your total sensible cooling would be 33,560 BTU.

    This illustrates the importance of a heat calc with a/c sizing based on house's sensible heat gain.

    AM

    *depends on specified coil and furnace

  11. #11
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,286

    Angry HUGE DeRating

    Quote Originally Posted by ampulman View Post

    Originally Posted by DjPiLL
    I am not sure what you mean by derating.

    ... Rheem RARL-042-JEZ unit w/ matching coil and furnace* might list its full capacity as
    35,900 BTU (sensible)
    11,100 BTU (latent)
    47,000 BTU total

    However, since your thermostat is set at 70 degrees, you loose 840 BTU
    sensible capacity for every degree below 80, per 1000 CFM, or 10 x 840 x1.6
    = 13,440 BTU lost (400 CFM x 4 ton = 1600).

    So at 95 degrees OD and 70 ID, your total sensible cooling would be 33,560 BTU.
    Math Check
    35,900 Sensible
    13,440 Derating
    22,560 Net

    Total cooling capacity ... 33,560

    So actually the 4-ton acts more like a 2-ton or 2.5-ton in VERY Heavy latent load conditions with such a low thermostat setting.

    Pay me now or pay me later ... local utility company.
    _____________________ I appreciate your business!
    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

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,286

    Smile Comfortable

    Quote Originally Posted by DjPiLL View Post
    I am in Long Island, NY.

    Right now I have it set at 70 degrees and its comfortable enough and i'll probably leave it at 70 overnight.

    My house gets extremely hot whenever the outside temperature goes past 70 degrees. My upstairs was 78 degrees and my downstairs was 75 degrees before I turned the air on.
    L.O.L.

    78'F is quite comfortable here at 40% R.H.
    Last edited by dan sw fl; 05-28-2008 at 11:25 PM. Reason: sp
    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
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,063
    His math is ok, except, he's using 1600 CFM on a 1400 CFM unit. And he's missing another part of the Manual S, that would regain 5,550 BTUs sensible. Meanig the 3.5 ton would be working more like a 3 ton.
    Contractor locator map

    How-to-apply-for-Professional

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

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