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  1. #1
    Join Date
    May 2010
    Location
    New Jersey
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    1,309

    Can Sizing Make One Brand Preferred Over Another

    Example:

    1st Floor: 80mbtu heat, 36mbtu sensible heat
    2nd Floor: 45mbtu heat, 31mbtu sensible heat

    Constraints:

    1st floor requires 4-ton ac, which requires 1600cfm blower
    2nd floor requires 3.5-ton to reach sensible heat. The 60mbtu furnaces have 1200cfm blowers restricting them to only some 3.5-ton units.

    For the 1st floor
    Some brands (such as Rheem, Lennox, Goodman) have 90mbtu furnaces that handle the second floor with a small margin. Others have very high efficiency (such as York-98, Nordyne-97) that undersize just a little, with in the calculation error. Others (such as Trane) don't offer as 1600cfm blower in an 80mbtu furnace, requiring a 100mbtu model.

    On the 2nd floor, most manufactures have a 14-15 SEER single-stage 3.5 ton AC that can be used in the 60mbtu furnace. However, they differ significantly. Carrier has numerous models with 17-18.5 SEER in there 60mbtu ICS furnace. Others offer models that only obtain 13 SEER using a flat coil.

    Do the specific Manual J requirements favor one brand over another and leave others, for example Trane in this case, inappropriate because a furnace/ac combination can't be reached that has appropriate sizing for each?

  2. #2
    Join Date
    Nov 2004
    Location
    NJ
    Posts
    1,204
    Quote Originally Posted by DavidNJ View Post

    Do the specific Manual J requirements favor one brand over another and leave others, for example Trane in this case, inappropriate because a furnace/ac combination can't be reached that has appropriate sizing for each?
    Manual J determines the loss and gain on a room or structure, there is no chapter that guides you to select equipment. Read Manual S for equipment selection procedures, it will explain the correct way to do it.

    You seem so obsessed with finding a system to match your loss or gain at any given moment, yet you are skipping giant steps in the design process.

    Have you been adding any of your excess latent capacity to your sensible capacity when looking at what unit to chose?
    How do you know you need 1600 (400 p/t) CFM for a 4 ton unit?
    How do you know it's not 350 p/t or 425 p/t?
    Are you still using an exaggerated outdoor design temperature?

    To answer your question I quoted, no, Manual J does not favor any 1 brand.

    Manual J is just 1 step of many in the proper design process of a residential heating and or cool system.
    Ed J

  3. #3
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    First, Manual 'J' has absolutely nothing to do with sizing the equipment. That is done in Manual 'S'. However, even with Manual 'S', the sizing of the equipment is done by the manufacturer of the equipment, not the ACCA (Air Conditioning Contractors of America). Furthermore, the size of the blower in a furnace is determined by the necessary airflow across the heat exchanger in order to keep the temperature rise within the manufacturers set limits. In some instances, those temperature limits allow for more than one blower size. Most manufacturers today list their blowers as capable of handling CFMs that correlate closely to the AC and HP nominal sizes. However, due to the need to adjust AC and HP nominal sizes to local conditions, it's truely a rare day that the furnace blower and the AC/HP system match exactly. That's why the manufacturers test the various combinations of equipment and come up with multiple SEER/HSPF/EER ratings sometimes for the same system combination.

    Finally, don't be too paranoid. The manufacturers do not know what size equipment you need for your house and unless a trained, knowledgable person does the load analysis and equipment sizing for your home, you're likely to end up with the wrong size. Or you can skip the load analysis, save the money and just put the wrong size in from the get go.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  4. #4
    Join Date
    Jan 2002
    Location
    East Grand Forks, MN
    Posts
    1,373
    Quote Originally Posted by DavidNJ View Post
    1st Floor: 80mbtu heat, 36mbtu sensible heat
    2nd Floor: 45mbtu heat, 31mbtu sensible heat

    Constraints:

    1st floor requires 4-ton ac, which requires 1600cfm blower
    2nd floor requires 3.5-ton to reach sensible heat. The 60mbtu furnaces have 1200cfm blowers restricting them to only some 3.5-ton units.

    For the 1st floor
    Some brands (such as Rheem, Lennox, Goodman) have 90mbtu furnaces that handle the second floor with a small margin. Others have very high efficiency (such as York-98, Nordyne-97) that undersize just a little, with in the calculation error. Others (such as Trane) don't offer as 1600cfm blower in an 80mbtu furnace, requiring a 100mbtu model.

    On the 2nd floor, most manufactures have a 14-15 SEER single-stage 3.5 ton AC that can be used in the 60mbtu furnace. However, they differ significantly. Carrier has numerous models with 17-18.5 SEER in there 60mbtu ICS furnace. Others offer models that only obtain 13 SEER using a flat coil.

    Do the specific Manual J requirements favor one brand over another and leave others, for example Trane in this case, inappropriate because a furnace/ac combination can't be reached that has appropriate sizing for each?

    With what I sale and install; I can meet and match any Heat-Loss/Heat-Gain numbers.
    I'm not sure if it's possible to meet and match with other brands, I never tried or had too, thank goodness.

    With your heat load calcs: it is not a problem, it just means bigger duct system and more cost!

    My Load calc software is a independent program; there are no ties with any equipment or brands!

  5. #5
    Join Date
    May 2010
    Location
    New Jersey
    Posts
    1,309
    Having talked to a few installers of different brands over the past week, the answer is yes.

    For most brands you can configure 'a system' to meet any load. However, different brands have different strengths. While brand 'Y' may have the highest efficiency furnace, its second tier single stage AC units may not be efficient enough to quality for an ES credit. While brand 'C' may not introduce a 10+ stage modulating furnace until the fall, its current high-end may have a 1400cfm blower and have an ES qualifying 3.5ton single stage furnace that can run it. To meet a 31mbtu sensible heat gain and 45mbtu heat loss using the high end furnace, brand 'T' may need a 100mbtu furnace with a 38mbtu lowest stage, while brand 'Y' uses an 80mbtu furnace with a 27.4mbtu lowest stage, while brand 'C' can do it with a 60mbtu furnace with a 22mbtu lowest stage.

    This happens with other items also. You may prefer a Honda Civic over a Corolla, but a Camry over an Accord; a Canon point-and-shoot over a Nikon but a Nikon DSLR over a Canon, etc.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    Load calc looks off, for a 2 story house.

    Redo it. And don't fudge.
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    How many times must one fix something before it is fixed?

  7. #7
    Join Date
    May 2010
    Location
    New Jersey
    Posts
    1,309
    It s been redone 6 ways from Sunday. Breaking it down room by room and two vendors have said they will put it in Wrightsoft's MJ8 software for comparison, refine some of the approximations (such as ducts) that are a bit part of the numbers.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,171
    And what infiltration rate did you use.
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  9. #9
    Join Date
    May 2010
    Location
    New Jersey
    Posts
    1,309
    The default was 0.4/0.7 summer/winter. I tried those and 0.7/1.0. Right now it is set to 0.5/0.8.

    The blower door test was 5100 cfm50 with 3200 sq ft and 31,000 cu ft.

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    So your using an infiltration rate 60%more then the BDT says you have.

    Your house is loose. So why are you spending so much time on looking at high efficiency units. Instead of lowering your infiltration rate. Which will save your a whole lot more money every year. Then a high efficiency unit will.
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  11. #11
    Join Date
    May 2010
    Location
    New Jersey
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    How does the BDT say my infiltration rate is lower? Depending on EIN the ACH0 should be between .5 and .7, shouldn't it?

    The HVAC-Calc number is says it is based on area, and although the tool has the external wall area, it doesn't have the building volume. The house has a high ratio of exterior wall area and ceiling area to total area, is separated from other houses by at least 100 ft, and is in a valley between two ridges, each about 1/2 mile away, at about 300ft.

    What infiltration rate do you think is appropriate...and why?

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,296

    Thumbs up

    Quote Originally Posted by DavidNJ View Post
    How does the BDT say my infiltration rate is lower?

    What infiltration rate do you think is appropriate...and why?
    Correlate the stated BD TEST Value to the actual ACH.
    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

  13. #13
    Join Date
    Jun 2010
    Location
    Houston, TX
    Posts
    178

    That seems to be the approach of the contracts I met/talked to!

    Help me understand (I know NOTHING about Manual J..):
    Manual J just tells you how many BTU of cooling and heating you need? It doesn't take into consideration the A/C you may already have?
    I would like a Manual J but I am going to change only one A/C-Furnace..
    Does it still make sense to get one done?)
    If I don't change anything in my house (I mean sealing, windows etc) will the Manual J calculation still be fairly accurate -say 2 years from now- if I decide to change my other unit?

    Quote Originally Posted by skippedover View Post
    Finally, don't be too paranoid. The manufacturers do not know what size equipment you need for your house and unless a trained, knowledgable person does the load analysis and equipment sizing for your home, you're likely to end up with the wrong size. Or you can skip the load analysis, save the money and just put the wrong size in from the get go.

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