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  1. #1
    Join Date
    Feb 2013
    Posts
    7

    Energy cost efficiency - SEERS vs same SEERS + additional features

    Hi,
    I need to replace my AC unit (heat pump (air handler + compressor)) and I live in central florida. I have been wondering if there is, I think there is a difference regarding efficiency but so far I have not seen that information in numbers or a chart, a difference (% of savings) between a 16 SEER unit with Variable Speed and a 16 SEER with 2 stage compressor + variable speed. Basically what is the percentage of savings between 2 units with same SEER but one with 2 stage compressor and the other with just variable speed. The difference in price between both units is very low.
    It is worth money wise (savings and spending) to get 2 stage compressor vs only an air handler with variable speed and 1 compressor?

    Thanks in advance, Roberto

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,474
    Most 2 stage units run closer to 75-80% on low in actual use. About the only one that hits 60% is the A-S/Trane 20 with the dual compressors. The unloading scroll I've seen low capacities as high as 81% of total. Also gotta watch that some units on low don't have the greatest latent capacity so it may run longer on low but sucking out less water. Gotta look at all the numbers.

    As for operating costs, don't expect a major difference either way on single or 2 stage with the same ratings. Also in a hot climate, look at EER. A unit might have a nice SEER rating (fine at 70 out where much of the rating is based) but weak on EER which is at 95 out.

  3. #3
    Join Date
    Feb 2013
    Posts
    7
    Quote Originally Posted by BaldLoonie View Post
    Most 2 stage units run closer to 75-80% on low in actual use. About the only one that hits 60% is the A-S/Trane 20 with the dual compressors. The unloading scroll I've seen low capacities as high as 81% of total. Also gotta watch that some units on low don't have the greatest latent capacity so it may run longer on low but sucking out less water. Gotta look at all the numbers.

    As for operating costs, don't expect a major difference either way on single or 2 stage with the same ratings. Also in a hot climate, look at EER. A unit might have a nice SEER rating (fine at 70 out where much of the rating is based) but weak on EER which is at 95 out.
    Thanks.

    The units I was quoted were Goodman instead of Trane because my budget is limited so would you rather get a 16 SEER Variable Speed unit than a 2 stage compressor based on the fact that operating costs wont be major difference? I am even considering a 13 SEER unit but I want to have all the fact on the table just in case it would be better money wise going to a higher SEER with more features than a simple 13 SEER. btw .. I am replacing the original unit from my home that was built in 2002.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,599
    Moved to AOP Residential.
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    How-to-apply-for-Professional

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

  5. #5
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,537
    A 16 seer is a 16 seer. Meaning if rated at a 16 seer the unit will still yield the same electic bill if installed propely vs cost difference between the 2.

    I have seen (2) stage equipment with lower electic bills but that is due to temp and amount of time unit runs in lower stage. When 2 stage is installed properly and sized right. Your 1st stage unit will use less energy as the 1st of a compressor has higher seer and uses less energy. All units are rated on high speed/2nd stage compressor just like single stage units are.

    2 stage more for comfort then energy savings while it can inturn use less when in 1st stage. All units are regulated on 2nd stage/or single stage compressor. If you truly want a system that is 2 stage look at a Trane XL 20. This unit has (2) compressors compaired to others that only have 1 compressor that is staged. The payback is never really their but the comfort is. As long as you have system sized properly, installed properly and at least a variable speed indoor unit you can achive good numbers while increasing your comfort.

  6. #6
    Join Date
    Feb 2013
    Posts
    7
    Quote Originally Posted by duckman06 View Post
    A 16 seer is a 16 seer. Meaning if rated at a 16 seer the unit will still yield the same electic bill if installed propely vs cost difference between the 2.

    I have seen (2) stage equipment with lower electic bills but that is due to temp and amount of time unit runs in lower stage. When 2 stage is installed properly and sized right. Your 1st stage unit will use less energy as the 1st of a compressor has higher seer and uses less energy. All units are rated on high speed/2nd stage compressor just like single stage units are.

    2 stage more for comfort then energy savings while it can inturn use less when in 1st stage. All units are regulated on 2nd stage/or single stage compressor. If you truly want a system that is 2 stage look at a Trane XL 20. This unit has (2) compressors compaired to others that only have 1 compressor that is staged. The payback is never really their but the comfort is. As long as you have system sized properly, installed properly and at least a variable speed indoor unit you can achive good numbers while increasing your comfort.
    Thanks for the feedback.

    All the feedback I have received state a very important point that is sizing and I have a question regarding this because 3 different contractors are giving me a different sizes. Two are telling me 4 ton and other 5 Ton.

    Some details about my house. It was built in 2002 with an area of 2000 sf (not including garage) and the current unit I have is a 3 1/2 Ton outdoor compressor and a 4 Ton air handler. Then 2 years ago we added an extra room (almost 500 sf and it is in the rear of the house and the air handler is at the front) and we extended the ac ducts (it looks like a well done job) to the new extra room. The new extra room since the beginning is not getting enough cold air or even warm air in winter and I am guessing is because the current unit is not enough for the new 2500 sf.

    I am inclined in thinking that the 5 Ton is the right sizing based on the fact that we added almost 500 sf to the house. The guy that sized it to 5 Tons told me that 1 Ton - 12,000 BTUs per 500 sq is fine so that means 5 Ton unit.

    Any feedback about this.

    Thanks a lot.

  7. #7
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,474
    As the late Sherm would say: HORSEHOCKEY.

    Don't buy from someone using a rule of thumb or so many tons per sq ft. Demand a load calc to get the right size. Oversized high SEER cycling too much can cause higher bills than lower SEER with long run times. Also causes higher humidity. Be sure complete duct system can handle 2000 CFM. The reason the new area isn't heating or cooling right is poor duct design. Very common with an addition. They probably tapped into an undersized main duct. Going bigger likely won't help.

  8. #8
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,537
    Quote Originally Posted by BaldLoonie View Post
    As the late Sherm would say: HORSEHOCKEY.

    Don't buy from someone using a rule of thumb or so many tons per sq ft. Demand a load calc to get the right size. Oversized high SEER cycling too much can cause higher bills than lower SEER with long run times. Also causes higher humidity. Be sure complete duct system can handle 2000 CFM. The reason the new area isn't heating or cooling right is poor duct design. Very common with an addition. They probably tapped into an undersized main duct. Going bigger likely won't help.
    I agree with bald on this. Poor duct design can be your problem? Has anyone looked at the ductwork? Rules of thumb for ductwork are just like rule of thumbs when sizing a system as most people that do this rule of thumbs don't have a clue to how to size ductwork or a system so use rules of thumb. Is there return in the new addition? Ductwork needs to looked at period before moving forward with any work!

    Quote Originally Posted by rzuluaga View Post
    Thanks for the feedback.All the feedback I have received state a very important point that is sizing and I have a question regarding this because 3 different contractors are giving me a different sizes. Two are telling me 4 ton and other 5 Ton.

    Some details about my house. It was built in 2002 with an area of 2000 sf (not including garage) and the current unit I have is a 3 1/2 Ton outdoor compressor and a 4 Ton air handler. Then 2 years ago we added an extra room (almost 500 sf and it is in the rear of the house and the air handler is at the front) and we extended the ac ducts (it looks like a well done job) to the new extra room. The new extra room since the beginning is not getting enough cold air or even warm air in winter and I am guessing is because the current unit is not enough for the new 2500 sf.

    I am inclined in thinking that the 5 Ton is the right sizing based on the fact that we added almost 500 sf to the house. The guy that sized it to 5 Tons told me that 1 Ton - 12,000 BTUs per 500 sq is fine so that means 5 Ton unit.

    Any feedback about this.

    Thanks a lot.
    The good old rule of thumb. Look at your thumbs and compare to your wife's are they the same size? While rules of thumb have worked for homes with poor insualtion, windows and air leakage when you get into newer built homes with good insulation, windows and low air leakage your load changes. Just throwing a bigger system in will not fix anything if anything can make worse along with decreasing comfort. For years now the building industry has been set on making homes tighter and better insulated only to have contractors still use rules of thumb to size equipment! Just doesn't make sense to spend money to improve homes building practices to have it washed by installing oversized equipment. There goes your investment on energy improving your home.

    Please get the contractor or contractors to perform load cal (manual j) on the home to find out how many btu's is needed to heat and cool your home. Size your duct system (manual d) to ensue proper sized supply and return. Then they can size equipment with (manual s). You find a contractor that does this and you can't go wrong. While it might seem to be a lot of work for the pros here it is a every day thing that needs to be done to ensure you we are doing our job correctly to size every aspect of your home heating and cooling system propely.

  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,390
    Who built the house?
    SF means something but not as much as Infiltration, total glass area, windows S.H.G.C. and orientation.

    What are your monthly electric bills for the last 24 months?
    Are you on FL Power & Light service?

    MANY Modern FL homes are likely adequately sized at 700 Sq.ft / ton.
    4-ton should be sufficient for nearly 3,000 Sq.Ft.

    Unless you have a 2002 D.R. Horton, First Choice or similar developer.
    In that case, You'll need a blower door test and window inspection (single pane - no tinting/ ?) to size properly.
    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

  10. #10
    Join Date
    Feb 2013
    Posts
    7
    Quote Originally Posted by dan sw fl View Post
    Who built the house?
    SF means something but not as much as Infiltration, total glass area, windows S.H.G.C. and orientation.

    What are your monthly electric bills for the last 24 months?
    Are you on FL Power & Light service?

    MANY Modern FL homes are likely adequately sized at 700 Sq.ft / ton.
    4-ton should be sufficient for nearly 3,000 Sq.Ft.

    Unless you have a 2002 D.R. Horton, First Choice or similar developer.
    In that case, You'll need a blower door test and window inspection (single pane - no tinting/ ?) to size properly.
    This is a Ryland home.
    Annual bill has been $2000 for the last 2 years so an average of $167 per month.

  11. #11
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    If you need a 5 ton system to cool a 2002 built 2500ish sq ft home in central Florida, and you don't have a glass wall or 3, you need to fix the house!
    Depending on the type of construction, even a 4 ton system may be over sized by a fair amount.
    If more government is the answer, then it's a really stupid question.

  12. #12
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    Quote Originally Posted by dan sw fl View Post
    Unless you have a 2002 D.R. Horton, First Choice or similar developer.
    So they are not just a local disease on the new home construction industry....
    If more government is the answer, then it's a really stupid question.

  13. #13
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,390
    Quote Originally Posted by rzuluaga View Post
    This is a Ryland home.
    Annual bill has been $2000 for the last 2 years so an average of $167 per month.
    Yearly cost tells me absolutely Nothing about your specific A/C use.

    It does tell me
    you use ~2 X what I use for 1,800 Square Foot residence (~ $90/month)
    with a 3 ton 10 SEER unit built the same year.

    I guess you probably have t-stat set to 72'F in the summer
    in support of
    your local utility.
    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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