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  1. #40
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,025

    Lightbulb

    Quote Originally Posted by adamt View Post
    My 1978 house is 3200 sq ft, 2700 finished. Walls are r13, weak vapor barrier with brick veneer. Thermal pane metal windows. R38 in the ceiling(except "cathedral" ceilings).

    I was pretty impressed with the HVAC Calc program, it generalized and itemized in the right areas. All of my supply ducts were exactly what the program called for and my return drop was almost exactly half of what it called for.

    The previous unit was 5 tons and didn't usually make it more than 1 night before freezing solid. I purchased a new 16.5" x 20" drop to be installed with the new furnace. Additional returns will be added later.
    The installer insists that 600 sq ft per ton works for this area and this altitude.

    He was also concerned about my "water problem". I'm still a little confused about this comment, I was planning on installing a humidifier with the ac. He said that the 100 grains that the program defaulted to for Denver was unrealistic.
    I am a Carpenter(Local #55) and he is a Tinner on the same sight. I like his work and his work ethic. The price is also unbeatable, even though he keeps increasing it. Adam

    This is very interesting...

    Denver, CO., is at 5,280 ft El., 2.5% summer design is 91 dry bulb; 59 wet bulb; an extremely low 15% relative humidity. Grains of moisture per/lb dry air is only 39.87; dew point is a low 37.3-F.

    Therefore, the heatload is nearly all sensible; unless there is a waterfall in the conditioned area...

    A mere 600-sf to the ton seems outrageous to me!

    If you end-up with 3200-sf, seems to me a 4-Ton @ 800-sf to the Ton, ought to be more than adequate.

    Remember what ACCA Manual D says about RA filter sizing; with 4-Ton, in that dry climate I'd probably go 450-cfm per/ton or 1800-cfm / 300-fpm is 6-sf of free-air-area (Ak).

    So, 6-sf * 144 is 864-sq.ins. / a .70% cheap low velocity throwaway filter, is 1234-sq.ins of physical filter area. That's at least two 24X26's with deep boxes to the RA duct.


    Now, don't pay any attention to those realities, do it their way & your way, - because I take NO responsibility for any unhappiness later.

    I will say, that when we undersize a little, we can always do Retrofit work to drop the heatload to fit the equipment. That doesn't work the other way around...

  2. #41
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,981
    Quote Originally Posted by MLeonhardt View Post
    Judging by the area I am in this summer, 27 days straight of over 100 degree temps. I have 4 neighbors that did the energy audit and did the recommended. Guess what ! Not one of them can hold less than 85 in the house with the units running 24/7. Expensive lesson in electricity usage and equip cost.

    So much for design temps..
    Its actually not an expensive in electricity usage.....just because its running 24/7 doesn't mean it's using more electric.

  3. #42
    Join Date
    Dec 2008
    Location
    Littleton, Co
    Posts
    54
    udarrell, Thanks for the reply, the waterfall is outside. I agree with you on the sizing, I wish my installer/seller was a little more confident on these calculations. I have an Aprilaire 2210(2000 cfm) and a 16.5" x 20" return drop ready to be installed. I would like to go with a two stage 4 ton a/c, if I can afford it.

    Adam

  4. #43
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,756
    Quote Originally Posted by beshvac View Post
    Its actually not an expensive in electricity usage.....just because its running 24/7 doesn't mean it's using more electric.
    "NY neighbors used that diet, they're still fat. Must be the diets don't work."

    When someone makes an ignorant post, is it incumbent on us to determine if it's uninformed or stupidity? If you play good cop, should I (or someone) play bad cop?

    Part of me thinks maybe you ignore and allow them to learn their assumptions are backwards at their own rate. All the information they need has been covered before, all they need do is spend a little time with search.
    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. #44
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,756
    Quote Originally Posted by adamt View Post
    I have an Aprilaire 2210(2000 cfm) and a 16.5" x 20" return drop ready to be installed. I would like to go with a two stage 4 ton a/c, if I can afford it.

    Adam
    Adam, that doesn't sound even close. for 4 ton you need bottom side or side side (two return drops).
    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.

  6. #45
    Join Date
    Mar 2010
    Posts
    195

    I Know Bud

    Quote Originally Posted by tedkidd View Post
    Boy ac, my post and jimj's totally teed you up to talk about comprehensive cost/benefit analysis software, did you miss that?
    Kidd,

    Of course I saw that, and I appreciate it.

    As you know, there are a lot of parts swappers and price shoppers hanging around. Guys defending dry ship R 22 units, then talking about how you should do your load calc dog and pony show to "size" them. Lots of silliness.

    When you get to close to talking about System Efficiencies, Sealing/Insulating, and the dynamics of looking at the house as a whole, you start to hit the nerves of the "swap the AC" and the "customer can't afford it" gang.

    If you take a poll of the past 10 ACCA presidents you will find all of these companies now focus on the house as a whole.Since last years ACCA president is in your town, you know this first hand.

    The obstacles to this change in focus are well vetted as well. Cost Structure, Time Frames involved, Overselling Savings, and Contractor Mindset.

    As you are also aware, AC contractors are losing lots of work due to not moving in this direction. They loose lots of work, but they don't see that. You don't see the jobs you lose to other companies and trades where you were never even invited to participate.

    The nice juicy fish are increasingly being caught upstream from them. Then they will tell you about all they see are price shopper fish, parts swapper fish, fish with no credit, etc.. No Sht. The good ons were caught upstream.

    I have to be careful not to go to far addressing solutions as you know.

    thanks bud, keep swinging

    ACBD

  7. #46
    Join Date
    Jul 2009
    Location
    Independence
    Posts
    197

    Cool

    you guys already know the right way to do it is to use manual J - it makes a big difference what kind of insulation, windows, and the angle the sun hits your specific sized overhangs that shade the windows. and do you have a fat shade tree on the south side , and how many of the windows are on the south compared to the north ect. and also the design temp for your area. summer in arizona is gonna take on a lot more btu of heat than summer in Detroit.
    even then , the design temp for us in KC is 95 degrees, but for the last two years its been over 100 most every day for nearly three months.
    when i come home from working on a roof all day, or in an attic i want to see the sweat on my nose solidify into ice.

    the rule of thumb I've seen though is not 1ton per 1000sqft -- but
    1 cfm per sqft, then you figure 400 cfm per ton and --
    viola 1000 sqft is 2 1/2ton. of course this is completely wrong for some houses and a little closer for others, given all the real conditions of the heat gain of the structure.

    myself id use manual J but figure it for 100 degrees anyway (cant remember off the top of my head what the design wb for this area is)
    The average person has one testicle, and one ovary.

  8. #47
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,591
    If people learned how to use manual J and Manual S like they are suppose to. they wouldn't have to worry about how small the manual j load is.
    Contractor locator map

    How-to-apply-for-Professional

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

  9. #48
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,025

    Smile

    Shophound, as usual is right on target; when U add up all the BTUH losses some systems barely deliver half their laboratory Ratings.

    By the way I believe Fort Worth TX is around 670 El., 105-F DB; 71-WB yields 18.3% RH; & only 62.44 grs. moisture per/lb dry air.

    Indoors: 75-DB; 62-WB; 48.5% RH; & 64.46 grs moisture per/lb air & colder air is heavier. Therefore, infiltration air has less grs of moisture than the indoor air.

    Go to high humidity areas with very high sensible, plus very high heat Indexes & you will have way over 100 grains of moisture per/lb of air for the A/C to deal with. A high to even medium air infiltration rate will cause a very high latent load, - that must be accurately calculated when sizing equipment...
    Last edited by udarrell; 07-30-2011 at 11:03 AM. Reason: 18.3 RH...

  10. #49
    Join Date
    Jul 2009
    Location
    Independence
    Posts
    197
    Ah...
    they taught us manual J, D, and P, but id never seen S until now,
    very interesting

    http://www.constructionbook.com/acca...cca-standards/

    "Why the "400 CFM per ton rule" is a myth, why the blower CFM is exclusively defined by the sensible heat equation, why lower DX coil air flow rates are compatible with humid climates, and why water source refrigeration cycle equipment should not be sized to satisfy the design heating load"
    The average person has one testicle, and one ovary.

  11. #50
    Join Date
    Mar 2010
    Posts
    195

    Thanks for this. You are right.

    Quote Originally Posted by VAV616 View Post
    you guys already know the right way to do it is to use manual J - it makes a big difference what kind of insulation, windows, and the angle the sun hits your specific sized overhangs that shade the windows. and do you have a fat shade tree on the south side , and how many of the windows are on the south compared to the north ect. and also the design temp for your area. summer in arizona is gonna take on a lot more btu of heat than summer in Detroit.
    even then , the design temp for us in KC is 95 degrees, but for the last two years its been over 100 most every day for nearly three months.
    when i come home from working on a roof all day, or in an attic i want to see the sweat on my nose solidify into ice.

    the rule of thumb I've seen though is not 1ton per 1000sqft -- but
    1 cfm per sqft, then you figure 400 cfm per ton and --
    viola 1000 sqft is 2 1/2ton. of course this is completely wrong for some houses and a little closer for others, given all the real conditions of the heat gain of the structure.

    myself id use manual J but figure it for 100 degrees anyway (cant remember off the top of my head what the design wb for this area is)
    Hey,

    So, the first thing you (and most other guys ) do is override the primary design condition. If this tool is gospel why would you override the first entry. But yet almost every guy I know does this. It's called CYA. It's also part of the use the values that give the answers you want school of load calculations. Then your right, and smart. Gotta love it.

    But you better do load calc....just let me know what load you want, I'll give it to you.No problem.

    ACBD

  12. #51
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,025

    Thumbs up

    Quote Originally Posted by adamt View Post
    udarrell, Thanks for the reply, the waterfall is outside. I agree with you on the sizing, I wish my installer/seller was a little more confident on these calculations. I have an Aprilaire 2210(2000 cfm) and a 16.5" x 20" return drop ready to be installed. I would like to go with a two stage 4 ton a/c, if I can afford it. Adam

    Glad to hear you're going to keep the air clean.

    Regarding the equipment over-sizer crowd, Tell them what you want, it's your money...

    Wish we were all multimillionaires, we could afford to do whatever we wanted to do...

  13. #52
    Join Date
    Jul 2009
    Location
    Independence
    Posts
    197
    Id just hate to see somebody spend a whole lot of money, and then on a hotter-than-usual summer the guy is calling me because it wont keep up, or to him it seems like its not cool enough, or some guy who likes to keep it at 72.
    your right though , its called CYA.


    how about 700 fpm and < .5 in ESP is that still a good standard?
    The average person has one testicle, and one ovary.

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