Seer help

Discussion in 'HVAC Heating & Cooling' started by chaoster, May 29, 2009.

  1. chaoster

    chaoster New Member

    Messages:
    42
    I am considering getting a fujitsu mini-split system. If I get a cooling only unit it has a seer of 14.3. A unit with a heat pump would cost $400 more, but have a seer of 21.0. Is it worth spending the extra money for a higher seer rating? I would probably not use the heat pump, just need cooling. TIA
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    21,806
    Location:
    New England
    It could probably pay for itself in short order. Take a close look at the current draws, and compare. The scale is linear, so you're getting a nearly 50% increase in efficiency. Now, I'm not fully familiar with how they rate it when it is a heat pump...it may be the same thing as the a/c only version...just factoring in the increased efficiency when in heating mode. If that's true, it isn't worth the difference if you don't need heat. Do they list cooling only efficiency?
  3. jimbo

    jimbo Plumber

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    8,997
    Location:
    San Diego
    Double check the spec sheet. The heat pump may be 21 on heat, and something less on cool. But if it is 21 on cool, the energy savings are significant, and I suspect the cost difference is also large. SO you have to calculate your operating cost over say 5 years vs. the price difference.

    Depending on your application, the LG flex multizone units, with inverter-driven variable speed compressors are terrific.
  4. Thatguy

    Thatguy Homeowner

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    1,460
    Location:
    MD
    from Wiki

    ". . .consider a 5000 BTU/h air-conditioning unit, with a SEER of 10, operating for a total of 1000 hours during an annual cooling season (e.g., 8 hours per day for 125 days).

    The annual total cooling output would be:

    5000 BTU/h * 8 h/day * 125 days = 5,000,000 BTU
    With a SEER of 10, the annual electrical energy usage would be about:

    5,000,000 BTU / 10 BTU/W·h = 500,000 W·h
    The average power usage may also be calculated more simply by:

    Average power = (BTU/h) / (SEER, BTU/W·h) = 5000 / 10 = 500 W
    If your electricity cost is 20¢/kW·h, then your operating cost is:

    0.5 kW * 20¢/kW·h = 10¢/h"

    Seems like you need to first specify the size of the unit. Also, in general, more complexity = less reliability (= higher SEER).

    If your yearly cooling is 50 Therms then the 14.3 would use 350 kwh, with the 21.0 using 238 kwh.
    If you pay $0.15/kwh then your cost for the 14.3 is $53/yr and for the 21 is about $36/yr.
    53-36 = $17/yr, so it would take $400/($17/yr) = 24 yrs to make up your $400.
    At 500 Therms/yr it'd take 2.4 yrs.

    Do you know how many kwh you use for cooling each year? You may be able to figure it out using the cooling degree day data on this site
    http://www.degreedays.net/
    plus your yearly elec. bill record.
    You'll also need
    http://www.google.com/search?client=safari&rls=en-us&q="heat gain" house&ie=UTF-8&oe=UTF-8
    Last edited: May 30, 2009
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