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  1. #1
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    I just completed my first try at the HVAC-Calc Residential 4.0 for a new home. My results came out as:
    Sensible gain: 53,545
    Latent gain: 14,030
    Total heat gain:67,575 (5.5 tons)
    Total heat loss: 33,464

    I have been trying to determine if a zoned system is a good option, and that is one reason why I wanted to do a Manual J calculation, to see if one unit could handle the house. Based on my first try the heat gain is too much for one 5 ton AC unit.

    Here's my question (don't laugh too hard):

    When the program asks for how many people are in a particular room I estimated maximum head count for each room at any particular time, although it is highly unlikely that that many people would ever be in the house at the same time. For example, I put 5 in the kitchen, 4 in the nook, 10 in the family room, 8 in the dining room, 2 in a hallway, etc.

    The total heat gain for the "people" component is 29,150, and that is what prompts the question. 29,150 represents 43% of the total gain, so I'm thinking maybe I should not use the total capacity for each room simultaneously.

    If I have mistakenly loaded up each room too high then perhaps the total heat gain may fall into a 5 ton range.

    I would appreciate your advice.

  2. #2
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    One other topic relating to the J Calc. I am working with a Trane dealer and was considering the XV90 furnace. The first stage of the smallest XV90 (on the Trane website) is 37K, 2nd stage 56K.

    If my J Calc. is correct at total heat loss of 33,464 does that mean I would rarely, if ever, use the 2nd stage on the XV90?

    The smallest Trane XV80, on the other hand, shows 31.2K first stage and 48K 2nd stage.

    How would the heat loss result affect the choice of furnace? I want a VS.

    Thanks

    [Edited by nathan9999 on 06-11-2005 at 06:46 PM]

  3. #3
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    People input is usually 2 per bedroom,so yes it will reduce the load a lot,by correcting it.


    Smaller furnace isa better match,but the 90 is more effiecent,as you likely know.Larger furnace shorter run times,common problem when needing a small furnace.

  4. #4
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    I changed the "people" input to 1-5 people per room and it dropped the total heat gain to 55,585. The program indicates 4.5 tons.

    Dash, thanks for the advice. I'll show this to my contractor.

  5. #5
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,387

    Exclamation House S.F. + Windows determines

    Originally posted by nathan9999
    My results came out as:
    Sensible gain: 53,545
    Latent gain: 14,030
    Total heat gain: 67,575 (5.5 tons)
    Total heat loss: 33,464

    .. although it is highly unlikely that that many people would ever be in the house at the same time.

    The total heat gain for the "people" component is 29,150, and that is what prompts the question.

    29,150 represents ___
    29,150 BTUh sounds like > ~50 people.
    MAX that I use =~ DOZEN.
    Something like
    Dining 4
    Kitchen 1 ..+. = 1.0 appliance ( 1,200 BTU)
    Laundry 0 ..+. > 0.5 appliance
    Family 4
    Bedroom 2
    Bedroom 1

    S.F. Floor ___
    S.F. Glass ___
    Wall Height ___

    My Standard Selection = ~90% of Total.
    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

  6. #6
    Join Date
    Jul 2000
    Location
    NW IL.
    Posts
    3,935
    With such a small heat loss and such a high heat gain wouldn't a heat pump be more in line?

    Aircraft Mechanical Accessories Technician. The Air Force changed the job title to Air Craft Environmental Systems Technician. But I've decided I'll always be a Mech Acc.

  7. #7
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    has ManJ changed? seems like ASHRAE suggests 2 people for M bdrm, one for each other bdrm. However, place the heat load where most people will gather at one time, probably now days the entertainment rm (family rm) -- or split between family & dining.

  8. #8
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    MechAcc, electricity rates her around 12-13 cents/kwh, so heat pumps have never made much of an inroad, but I must admit that it has crossed my mind to look into one.

    cem-bsee, the programs helps did not make it clear (at least to me) if I should be going with (1) a cumulative maximum number of people in all rooms simultaneously, or (2) just the maximum number of people in the largest room.

    So, let's say i speculate a maximum of 25 people in the family room/kitchen/nook at any one time. Would I enter that number and leave out any other rooms?

    Thanks

    [Edited by nathan9999 on 06-12-2005 at 12:29 AM]

  9. #9
    Join Date
    Apr 2001
    Location
    san jose,ca.
    Posts
    5,285
    25 people in the familt room? What you having a buck owens reuniun?

  10. #10
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    2 per bedroom,and yes for the load put them in the living area.If you entertain a lot maybe a couple extra.Adding to many (10 or more,maybe even 5 extra)will oversized the system.



    Party load,use two systems or a two stage/speed compressor.

  11. #11
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    Bigbird, I actually know Buck (related by marriage) but I routinely travel with a much cheaper crowd. But we do have family holiday dinners with 20-25 in attendance.

    Dash, as of now I'm looking at 2 stage AC unit.

    If my calc is correct at 4.5 tons then I would be looking at a 5 ton unit with 3 or 4 zones for 3139 sq ft.

    Just as an example of the validity of the posts on this forum on oversizing, consider this:

    The architect drew the plans (approved by the county) for 6 tons. The local Carrier dealer said he would not install less than 7 tons. Every other dealer (with the exception of 2) recommended a "so many tons per 400-500 sq ft approach".

    So, subject to verification of the calc, the actual load calls for 4.5-5 tons, not 6 and not seven.

    Many thanks to the originator and participants in this site.

    Without the information on this site I would have accepted a builder's grade system and never even been aware of the options for higher efficiency and comfort.

  12. #12
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    how many families have 2 per bdrm?
    how many times will someone have a big party?

    so, set the temp down/ up 3h before the party. Or, if couple does this often, go with Dash

    esp if putting in hi seer --

    did Arch compute loading & cfm? just curious -- any of it agree with your calcs?

    yes, just put people in 1 or 2 rooms, none in others.

    BTW, are you doing houses with theaters? but, probably no more load than my 2 400w cmptrs, + monitor + printer + scanner + ...

    [Edited by cem-bsee on 06-12-2005 at 04:09 AM]

  13. #13
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,387

    Realistic Loads

    Originally posted by nathan9999
    (1) a cumulative maximum number of people in all rooms simultaneously, [Edited by nathan9999 on 06-12-2005 at 12:29 AM]
    Why design a system for that "one-a-year party"? Are those 25 people gathering for a mid-afternoon ( exactly at 4 PM - 6 PM peak load) event on a day when it is ~94'F?

    Your residential design is using simultaneous that may occur for ~2 Hours per Year. Plus, How much is the infiltration load when 30 people are Opening All the doors! ?

    I probably would estimate 32 people total for a 9,000 S.F. residence. TRANE XL19i's are always used for this type of load in my designs.

    You may wish to be somewhat more Realistic about developing this Simultaneous Load in any other designs you may perform.

    ... Do you have room for parking 20 cars?

    Another equipment selection combination may be:
    2 A/C systems ...
    No Zoning
    with a 2-ton XL16i bedroom area system
    and a 4-ton ( or 5)XL19i common area.

    NOTE:
    Costs for Zoning may nearly be the same as adding a small system.
    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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