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  1. #14
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    Jan 2004
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    68,776
    It can be brought in by time if you want.

    After X minutes, the stat energizes second stage.

    Not something I would recommend in general though.
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  2. #15
    Join Date
    Oct 2010
    Location
    Dallas/Fort Worth Texas
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    25
    thanks, I was hoping it would do that. The reason i ask is because my house is all foam insulated and we are getting way different opinions on the size of equipment needed from the foam guys to the HVAC guys. The foam guys basically say 3 tons and the HVAC guys say 5 tons. So in a way i guess they are meeting in the middle at a 5 ton two stage compressor unit.

    I honestly think that the 3 ton portion of the system will keep up with most of the days year round if not all the days. My builder and HVAC guys are skeptical on a smaller unit keeping up. And I am stuck in the middle.

    In theory it sounds good. My bills were way too high this past summer due to the oversize units I have now. I am hoping when they switch out the system that my bills will come in much lower. thanks again.

  3. #16
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    Jan 2004
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    PA
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    The spray foams guys are most likely correct. And your builder and HVAC subs have no real experience on spray foamed houses.
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  4. #17
    Join Date
    Jul 2008
    Location
    Rochester NY
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    4,763
    That doesn't sound like meeting in the middle to me!

    What does the j say? What infiltration assumption was used? (Make the spray guys promise you a leakage target of TIGHT and perform a blower door before rolling up the hoses! Walk through with smoke and spray paint, mark leaks missed for final application.)

    What shading assumption? On blazing hot days you'll draw shades.

    What ductwork are they proposing if 5 tons? 2000cfm requires BIG DUCTS and bottom/side or side/side return.

    Do everything you can to get your load to 3 ton, will make an amazingly comfortable house. Spend the equipment savings on an erv.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  5. #18
    Join Date
    Oct 2010
    Location
    Dallas/Fort Worth Texas
    Posts
    25
    Actually the system i have now is 6 tons, with an ERV. Both sides have done a manual J and both come up with two different systems. They have even come in with thermal equipment to see if there were any leaks and the house is very tight. Everything you have mentioned has supposedly been taken into account by both sides. It honelstly comes down to the HVAC guy being afraid to put in something that won't keep up with the DFW heat during the summer. They are talking about using carrier and their 5 ton two stage compressor system, so I am trying to get numbers regarding this system. If I can keep the other two tons from kicking in as often, then would that not work as a 3 ton system?

  6. #19
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    PA
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    Have both sides bring their load calcs to your house and have a meeting of the minds. And have each explain to the other how they came up with their loads.

    Bet the HVAC subs are using lower R values, and a higher infiltration value.
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  7. #20
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
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    BRILLIANT. Simple and brilliant.

    And if they settle on 4 tons it'll only need 1600cfm.

    Definitely figure out how much airflow your duct work can handle, not much point in buying a gallon and a half of milk if you only have a one gallon jug.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  8. #21
    This is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.

    Further infractions may result in loss of posting privileges.
    Last edited by beenthere; 09-24-2012 at 06:45 PM. Reason: Non Pro * Member

  9. #22
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,640
    Quote Originally Posted by cindyandwade View Post
    This is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.

    Further infractions may result in loss of posting privileges.
    Just curious. Do you have any controlled fresh air ventilation? If yes, what? What is your opinion of the need for fresh air? What is the typicall %RH?
    Only if you care to share.
    Regards TB
    Last edited by beenthere; 09-24-2012 at 06:47 PM. Reason: Removed quote of Non Pro * Member
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  10. #23
    This is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here. Please apply to the AOPC today, thank you.

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    Last edited by beenthere; 09-24-2012 at 06:45 PM. Reason: Non Pro * Member

  11. #24
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    Jul 2008
    Location
    Rochester NY
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    Impressive post cindy, thorough and thoughtful.

    Without the thermostat to tell the unit what stage to run at, the logic of the furnace is left to guess. This logic is oriented around time to satisfy, which makes your furnace turn on and off, on and off. This means it always starts in low then after a period of time it jumps to high. The analogy is starting really slowly at a green light, then hitting the gas to the floor as you approach the next red light. Bassackwards. Don't you want MORE acceleration if you are going too slowly, and less as you approach a red light?

    Ideally your furnace stage control would be what my new Ecobee refers to as reverse staging.

    Reverse staging

    If this option is enabled, the thermostat will cycle down from the higher stages so that as it approaches set point it will only be running in stage 1. The HVAC equipment will start in stage 1. As the stage 1 temperature delta is exceeded, the second stage will engage. Once the equipment has brought the current temperature back to within the temperature delta, stage 2 will disengage and stage 1 remain running until the set point is meet.
    This means your furnace attempts to run continuously if it can, keeping the house evenly conditioned and running at optimum efficiency. This reduces cycling losses, wear and tear, temperature fluctuations, etc... (Seems you may understand this already, but others reading may not.)


    Regarding your second post:
    Quote Originally Posted by cindyandwade View Post
    We do not. After air sealing our leakage is about 2500,

    2 young adult sons who are in and out and like to have their window open sometimes for no reason, and not open when it should.

    Fresh air is nice, except in allergy season.
    I don't think you've sleuthed out the open window thing. People usually have IAQ or comfort reasons for opening windows. The best fresh air, particularly for those with allergies, is fresh air that has been filtered before hitting your lungs. The type that doesn't leave dust all over your house. The kind that doesn't toss control to the wind by changing the pressure and flow balance of your hvac system.

    I audited a super insulated house with annual gas bill 3x what it should have been ($1500 yr v/s $500). People were opening windows because of an error in the fresh air management. Often this is an unconscious response to discomfort caused by stinky air. If people are opening windows in heating or cooling conditions, you may want to dig a bit further into why, and into what TB is alluding to.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  12. #25
    This is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.

    Further infractions may result in loss of posting privileges.
    Last edited by beenthere; 09-24-2012 at 06:44 PM. Reason: Non Pro * Member

  13. #26
    Join Date
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    Location
    PA
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    cindyandwade, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.

    Your post has been deleted.
    Further infractions may result in loss of posting privileges.


    Revived old thread, thread closed
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