Manual J Calc Question - Page 2
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  1. #14
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
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    209
    Cem-bsee, I did not see any duct work or CFM data on the architect's report, just "6 tons".

    I'm beginning to see that I have over estimated the load based on the number of people.

    No home theaters. My goal for the last half of my life is less TV and more reading.

    Dan, thanks for the comments. I agree that I need to be more realistic, but I needed some feedback and knowledge so I could assess realistic input.

    Parking? Make 'em hike. We car pool here in Bakersfield. Our infrequent get togethers probably involve 7-8 cars.

    On the zoning issue, I have gone back and forth on the issue and it has been difficult to even speak to a contractor who would consider it. But now it looks like a 5 ton single unit would handle the cooling load. That was the point of the J calc.

    The contractor and I are still looking at the XL19 vs. XL16 question. He prefers the 19 but is willing to entertain my desire for a R-410A system.

    Thanks again for all the information.



  2. #15
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    You old timers crack me up.


  3. #16
    Join Date
    Apr 2001
    Location
    san jose,ca.
    Posts
    5,285
    OLD TIMER? I heard that.
    Nathen i designed my systeme for 2 people only,me & wife,I don`t allow any guests over.If 25 people showed up at my house i`d charge admission, then i`d leave.It`s called anti-social bigbird................

  4. #17
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    Irascible, I'm only(?) 52, and Buck doesn't look like that anymore.

  5. #18
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    One last question.

    The HVAC Calc. Residential 4.0 Manual expresses the opinion that the the heat loss calc for heating should include a safety factor, maybe 20% extra, when selecting equipment but that cooling should not include the same safety margin.

    Is that the recommendation of the professional participants?

  6. #19
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    do you want to contol humidity? if not, then oversize

  7. #20
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,233

    Thumbs up AZ

    Originally posted by cem-bsee
    do you want to contol humidity? if not, then oversize
    I hope ONLY the " Arizona climate " people would be listening to hint of oversize.
    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

  8. #21
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    There's no need to add a safety factor, especially if you're in Arizona. Your furnace size will probably be dictated by your air conditioner's size. In other words, the smallest heating capacity that you can buy with your five ton furnace will probably be much more than you need. I think some other OEMs are wising up and changing just a bit. But with Trane the smallest BTU input that I can buy from my wholesaler in a 5 ton furnace is 100K BTUH. That's probably much too big for your house. This is one reason why I like two stage furnaces. The first stage is often all the house ever needs.

  9. #22
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,233

    Thumbs up Heating Eq Selection

    Originally posted by nathan9999
    .. for heating .. include a safety factor, maybe 20% extra, when selecting equipment
    Is that the recommendation of the pros?
    No Experienced recommendation from me.

    SW FL doesn't need much ( or some years, Any) heating.
    .........

    For a gas furnace, it is quite easy to provide an oversized unit.

    I really doubt that 'short cycling' may be as much
    of a Heating equipment concern as it is for A/C.
    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. #23
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    Irascible, so I assume from your post that I cannot necessarily match a 5 ton XL16i with the smallest XV80 or XV90 from the Trane website. is that correct? I have viewed the ARI website but haven't managed to figure out how to see which products can be matched.

    From the J Calc the smallest XV90 is way too big for my house and even the smallest XV80 would probably be too big. The 1st stage would probably be the only stage I would ever use in Bakersfield.

  11. #24
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,233

    Heating Eq Selection

    Originally posted by nathan9999
    From the J Calc the smallest XV90 is way too big for my house and even the smallest XV80 would probably be too big. The 1st stage would probably be the only stage I would ever use in Bakersfield.
    Do Heat Pumps ( or straight A/C) with electric strip (10 or 15 kW, in your case) generally make sense for the Bakersfield heating season?

    Electric Rate ?
    Heating Hours ?
    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

  12. #25
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    The smallest furnace you should put on a 5 ton AC is a 5 ton furnace... meaning that the blower is rated to push 5 tons of air. You could get away with a 4 ton furnace under VERY unusual (almost non-existent) circumstances. But I'm not going to get into that. It wouldn't be worth the expense and it's not smart for dry climate AC anyway. You want BIG airflow in dry climate AC. So a BIG blower is in order.

    The smallest BTU input that I'm aware of for a Trane furnace with a 5 ton blower is 100K BTUH. So it's quite likely you'd only need your first stage most of the time. Though realize that you'll still get second stage quite often during any sort of recovery.

    Dan:
    Electricity is almost as precious as gold out here. Gas makes most sense for California.

  13. #26
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    Dan, electric rates here are about 11-13 cents/kwh. Very few heat pumps. Everybody seems to go with gas furnace. Irascible is in northern CA so he would probably be more informed why heat pumps are so rare (perhaps not so rare in Northern CA).

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