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  1. #1
    Join Date
    Jul 2004
    Location
    South Alabama
    Posts
    24

    Homeowner question: Comparing cost vs efficiency

    I hope it is ok to post this.. I'm not asking for pricing advice from anyone.. but for reference, I want to post some relative figures for what I'm looking at.

    Someone please tell me if this is not ok, and I'll pull this right away.

    Ok... First off... I'm not rich, so money is definetly an object. I currently have a 5-ton Goodman 10seer (Straight-A/C) unit manufactured in '99 I with a Bristol Scroll compressor. The compressor has a pin-hole in it on the side at an internal weld.

    New compressor installed - (**Edited: about twice the price of a 5-ton compressor)
    (I have no problem with this figure.. I know they don't give out free 5-ton compressors)

    Or I could get a new outside unit installed for about the same price and use the same evap coil/AH that is in place now, I'm guessing this would still put me somewhere in the 10 seer range.

    Or I could get a new 13 seer Heatpump inside/outside installed for roughly twice this. (I don't believe this has variable speed fan)

    Or.... I could go with a 16 seer unit with 2-stage compressor and variable speed fan for just a little more than 3x as much.

    I am in the deep south, the temps in the summer months are in the mid 90's and humidity runs very high. May-Aug are the big summer cooling months here. Winter's are relatively mild. I may have 1 month where the power bill gets up a bit in January, but nothing like the stretch we see in the Summer months. For heat it is just using the Internal coil heater, no air pump at this point. My summer cooling costs is prob $250-300 a month in the hottest months.

    I'm very confused on what to do here... the people I have talked with have all been straightforward, and I know it's probably impossible to determine what savings I would see from going with the higher seer units, but I'm just looking for an idea of how much more efficient would the higher priced units be over what I have installed now. I have to do something anyways.. with a hole in the compressor

  2. #2
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    If you edit out the price of the compressor, the post should be OK.

    I just read somewhere that replacing a 10 SEER system with a 13 SEER system would provide a 30% savings in operating costs. 14 SEER would be 40%, etc. I would take this as a ballpark estimate.

    If you replace the whole system, I would step up from the 13 SEER to the Goodman 14 SEER. Make sure you get the optional TXV (thermostatic expansion valve) for the air handler coil. It provides maximum cooling efficiency under all operating conditions.

    In my opinion, a 14 SEER offers the best combination of purchase price and true operating costs.

    A good installation is critical for a properly performing, long lasting system.

    Good luck.

  3. #3
    Join Date
    Jul 2004
    Location
    South Alabama
    Posts
    24
    Done...
    I like the idea of the variable speed fan, I do have some issues with humidity in the house. It is 2400sq ft of living space with single pane windows. The tech recommended to stay with a 5-ton... he said that the variable fan would help with the humidity. It is a Carrier Infinity system BTW.
    But... that's a lot of money... One good point is I could get a low interest loan from the local power company, the other options I'm just going to have to put it on the Credit card which is not low interest.

    I hope I'm not being too much of a goober by asking these questions, but I've been reading these forums for a long time.

  4. #4
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by bmilam View Post
    Done...
    I like the idea of the variable speed fan, I do have some issues with humidity in the house. It is 2400sq ft of living space with single pane windows. The tech recommended to stay with a 5-ton... he said that the variable fan would help with the humidity. It is a Carrier Infinity system BTW.
    But... that's a lot of money... One good point is I could get a low interest loan from the local power company, the other options I'm just going to have to put it on the Credit card which is not low interest.

    I hope I'm not being too much of a goober by asking these questions, but I've been reading these forums for a long time.
    Goodman makes a variable speed air handler - the model# starts with AEPF. It can be used with any Goodman heat pump from 13 SEER to 18 SEER. Model# ARUF is the 3-speed air handler, ASPF is the 5-speed air handler.

    www.GoodmanMFG.com

    Carrier Infinity is the Cadillac of the line. Carrier also makes a mid-level Performance series which has excellent efficiencies when paired with the right air handler.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,770
    Hot and humid.
    A single stage with VS will make it feel better then what your old system did.
    A 2 stage with VS will be able to lower the humidity more yet. Possibily allowing you to set the stat a degree or 2 higher, and still feel as comfortable.

    Not sure how cold your area gets, or how long your heating season is. But a heat pump does help to lower the bill compared to strip heaters.
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  6. #6
    Join Date
    Jul 2004
    Location
    South Alabama
    Posts
    24
    Another thing I just thought about
    The tech said there wasn't any real reason to replace the evap coil.... (currently 10 seer) if I replaced the outside unit... I'm guessing it would be a 13 seer unit since thats the minimum. He explained that I certainly would not be seeing 13 seer.

    I understand that it would not be as efficient , but would I have anything close to my current 10 seer performance if doing this?

    I've been browsing/searching the forums for hours now... and have read some scary stuff now on mismatches. Should I be worried about this option?? Would it make sense to go ahead and replace the inside unit ?

    Sorry for the stupid homeowner querstions

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,770
    If you reuse your old indoor coil. You could have anything from a 9 SEER to a 12 SEER.

    If your compressor fails, and the distributor or manufacturer ask for the mod and serial of the indoor coil, and it doesn't match, they will void the compressor warranty.

    Read the mismatch performance.
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  8. #8
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    I am a homeowner in a hot-humid climate too. I have a 2-stage AC but it is strictly a luxury, when money is a sizable concern you will get better use of your dollars by buying a 1-stage unit. They are available up to 15-16 SEER, although the 5-ton size usually drops a point or two in efficiency.

    However... infiltration of outside air is a big enemy in climates like yours and mine. It will add serious humidity load to your AC and generally just run up your bills. Back in 1975 almost nobody built tight houses so I would assume there are many opportunities for improvement. The good news is sealing up air gaps is cheap to do. The bad news is it is labor intensive and very difficult to find people to do it for you. There exist some sophisticated methods for measuring your house tightness but they may not be widely available in your area. When you get tight enough, there is a need to pay attention to explicit ventilation systems, but that is probably academic when you start with a 1975 house.

    For the subject of windows (also mucho expensive), let me observe that so much of the time the temperature difference between indoors and outdoors is 10-15F or so. That is the basis for some saying double pane is not so important. The real reason for double pane windows in the South these days is the anti-heat-ray coating is fragile and needs to reside on the *inner* surface of a double pane where it cannot be scratched off. I suggest you look into solar screens as a cost effective thing to do first.

    Sales people always say "more insulation". Well insulation is usually good but if it is applied over a leaky ceiling with many cannister lights, I think it is the wrong answer to the problem. If you don't have radiant barrier in a ventilated attic, you should get some unless your house is nearly always shaded. Radiant barrier can reliably save 8-12% of your AC usage in our climate, it will make your attic cooler in a way you can really feel.

    A high efficiency AC will save *some* money, but the way to make sure your house is not an energy hog is to get better sealing. I would not feel ashamed of 13 SEER but the money saved should go into making your house tighter, if you can.

    Hope this helps -- Pstu

  9. #9
    Join Date
    Apr 2007
    Posts
    6,285
    Or heck use HVAC Calc and do the figuring yourself....then you can instantly see what upgrading insulation or windows may do for you. With that info you might be able to choose the best option where you get a more efficient system and were also able to choose the best envelope upgrades to compliment that for your money.

  10. #10
    Join Date
    Jul 2004
    Location
    South Alabama
    Posts
    24
    Thanks so much guys... I have learned a ton in the last two days by pouring over the archives. I never knew how important some things were that my house is lacking.

    I know there are some areas in the ceiling lights that are not sealed properly. I didn't know how important this was before. I've replaced 7-8 recessed fixtures already and will replace them all now. I know that anytime in the past when I've had a fixture removed, I could feel a lot of hot air coming out of the hole into the living space. So.. I'm going to get to work on fixing those items. I also need a vapor barrier in the crawl space.. that can't be helping Also think I want to install a radiant barrier on the joists to try and keep the attic a little cooler. The Duct-work is in the attic, so that might help. I think I could stand to save a good bit of money with some diy grunt work to make my house tighter.

    I think I've pretty much decided on the Bryant System, just not sure on which one yet.

    It's either a 13 seer Bryant heat-pump unit
    or the 16-seer Bryant Evolution (W/ 2stage compressor & Var Spd Fan) heat pump system for 2grand more (after rebate).

  11. #11
    Join Date
    Apr 2007
    Posts
    6,285
    Attic access doors can be pretty bad also.


    Hopefully this works....it's some good reading material about the humidity and comfort in the south. It's from 2002 but still worth reading.
    http://www.fileden.com/files/2008/6/18/1965139/DOE%20Building%20Science%20Case%20Study.pdf
    Last edited by BigJon3475; 06-26-2008 at 02:16 PM.

  12. #12
    Join Date
    Jul 2004
    Location
    South Alabama
    Posts
    24
    Thanks Bigjon.. good stuff, I've been using the portable dehumidifier like they describe in option 1, it didn't stack up to poorly with the other options except operating expense wasn't wonderful.

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