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  1. #1
    Join Date
    Mar 2009
    Location
    Central Ky.
    Posts
    47

    Temp Rise Question

    Good Evening,
    I've spent a couple of days at my daughters trying to lower her elec. bill. Sealing attic ductwork, more insulation etc. I caught the outdoor temp. @ 47 this morning so I checked the temp rise at the air handler and 18 degree is all it would do.
    She has a 2 ton 10 seer unit. I phoned the only HVAC guy I know and he seemed to think its performing as it should. I've done some online research and the output should be 22k btu @ 47 degrees, which on paper is a 24 degree temp rise.
    I'm sure there's variables, but would 18 degrees be considered an acceptable temp rise? Any response welcomed, and thanks.

  2. #2
    Join Date
    Aug 2001
    Location
    Pavilion, NY
    Posts
    2,186
    Did you happen to measure the temperature of the large insulated line?
    ...

  3. #3
    Join Date
    Feb 2013
    Location
    Joliet, IL
    Posts
    1
    This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

    You can find the rules for posting and qualifications here.

    Additional infractions may result in loss of posting privileges.
    Last edited by jpsmith1cm; 02-06-2013 at 09:29 PM.

  4. #4
    Join Date
    Mar 2009
    Location
    Central Ky.
    Posts
    47
    Kanga, Thanks for your reply. Didn't have a good therm. for the suction line but I'll get it tomorrow and repost. It was hot very hot all you could do to keep your hand on it.

  5. #5
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    549
    22 BTUH at 47F ODT sounds a little optimistic to me, but it may be possible if all is tuned correctly.

    I am curious though, how you calculated your expected temp rise without knowing your airflow

    Either way, it sounds like it may be possible for a tech to tune up your HP and squeeze a few BTU out of it. It's probably well worth your money for a service call if you can shed some $$ off your hydro bill

    Use the contractor locator map to find an Htalk guy, there are lots of guys here that are really good with HPs

  6. #6
    Join Date
    Jul 2005
    Posts
    5,576
    As has been mentioned, you must know the cfm in order to calculate the expected temp rise. If this system has a 3 ton air handler set for 3 tons of airflow (1200 cfm) then the numbers would be pretty close. That being said, if that was the case, then lowering the airflow to 800 cfm would actually reduce the heating capacity and could potentially reduce the efficiency in heating mode as well, and this depends upon several factors. The good news is that it's a 2 ton system, how much electricity could it possibly be using?

    ROI should be taken into account before energy saving projects are begun. It's difficult to recoup improvement costs when the heating and cooling expenses were already relatively small. What's the model number of the air handler? Are the ducts running through an unconditioned space? Did you measure the temp rise at the return and supply grilles, or at the air handler inlet and outlet?

  7. #7
    Join Date
    Mar 2009
    Location
    Central Ky.
    Posts
    47
    LK & Medic,
    True airflow is unknown, but I did go to emerg. heat w/10k strips and had a 39 degree TR. With that known info I looked up the online heating data which was 22k btu. @ 47 amb. A lil math later I had 24.8 target TR. Unfortunately 18 degrees only means about 16k if my math is right. AH is 2 ton on hi speed. Temp readings were @ filter & 12" off supply plenum.
    Last edited by MrDodge; 02-06-2013 at 08:48 PM. Reason: add info

  8. #8
    Join Date
    Feb 2010
    Location
    Ohio
    Posts
    562
    If you had only the electric heat strip on at 10kw = 34,120 btuh. 34,120=1.08xCFMx39. Therefore, CFM = 810 if you got a good accurate TR (approximately). It's probably running at the same speed as when the HP is running, right? Do you know if that's true for a certainty?

  9. #9
    Join Date
    Mar 2009
    Location
    Central Ky.
    Posts
    47
    Chris, Yes confident about the strip TR, & yes fan speed is same strip or HP. Thanks

  10. #10
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,863
    tbone18

    This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

    You can find the rules for posting and qualifications here.

    Additional infractions may result in loss of posting privileges.

  11. #11
    Join Date
    Mar 2009
    Location
    Central Ky.
    Posts
    47
    Kanga, I took an accurate temp at a coil today. Suction line was 106 degrees @ 35 degrees ambient with a 13 degree temp rise. If the online data is correct I should have a 20 degree TR even with a 10 seer.
    I cleaned the indoor & outdoor coil yesterday. Are these numbers in line for a 10 seer or should I have someone look at it? Thanks in advance.

  12. #12
    Join Date
    Aug 2001
    Location
    Pavilion, NY
    Posts
    2,186
    You have something going on there. Your line temp should be about 30 degrees warmer. I would have someone check the refrigeration circuit.
    ...

  13. #13
    Join Date
    Mar 2009
    Location
    Central Ky.
    Posts
    47
    Thanks Kanga, For your timely response. Monday I started this endeavor with temps near the same as today (35). The HP wouldn't keep up (aux. would kick in). Today, after sealing the ducts, 36 bags of cellulose etc. the lil unit is off more than its on. But I'd like it to be a lil closer to spec so I'll have it serviced.
    Thanks again

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