Page 1 of 2 12 LastLast
Results 1 to 13 of 23
  1. #1
    Join Date
    Oct 2019
    Posts
    13
    Post Likes

    What is [Moisture Removal: 1.3] in a [Manual J Heat Load] evaluation?

    In the end of the [Manual J Heat Load] worksheet there is [Moisture Removal: 1.3]. Why would this multiplier be present? **Note: we live in a Phoenix, AZ... it's very dry.

    ------------------------------------
    SUB-TOTAL BTUH GAIN (ROOM SENSIBLE ONLY)........................33,150
    DUCT LOSS/GAIN FACTOR (TABLE D)..........................................x 1.1
    SUB-TOTAL BTUH (SENSIBLE GAIN).........................................36,4 65
    MOISTURE REMOVAL (SUB-TOTAL x 1.3).....................................x 1.3
    .................................................. ..........TOTAL BTUH GAIN...47,405

  2. #2
    Join Date
    Mar 2009
    Location
    Mount Holly, NC
    Posts
    7,707
    Post Likes
    In a tight home, occupants breath can build up humidity.
    Cooking, bathing etc adds up as well.
    The TRUE highest cost system is the system not installed properly...

    Find a HVAC-Talk Contractor by clicking here

    Click below to BECOME a pro member
    https://hvac-talk.com/vbb/forumdispl...ip-Information

    Do you go to a boat repairman with a sinking boat, and tell him to put in a bigger motor when he tells you to fix the holes?

    I am yourmrfixit

  3. #3
    Join Date
    Oct 2019
    Posts
    13
    Post Likes
    Thread Starter
    The Manual J Heat Load calculation takes into account the number of people living in the house.
    As far at the kitchen and bathing... this 1.3 multiplier would then turns our needs from a 3 ton to a 4 ton HVAC. Note that oversized AC will not take out humidity.

    36,465........./ 12,000 = 3.04 ton
    36,465 x 1.3 / 12,000 = 3.95 ton

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,495
    Post Likes
    Quote Originally Posted by azhvacsys View Post
    In the end of the [Manual J Heat Load] worksheet there is [Moisture Removal: 1.3].
    Why would this multiplier be present?

    **Note: we live in a Phoenix, AZ... it's very dry.

    ------------------------------------
    SUB-TOTAL BTUH GAIN (ROOM SENSIBLE ONLY).. 33,150 ___ Q.s
    DUCT LOSS/GAIN FACTOR (TABLE D).........…...… x 1.1
    SUB-TOTAL BTUH (SENSIBLE GAIN).....................36,465
    MOISTURE REMOVAL (SUB-TOTAL }......………....x 1.3
    .............................. TOTAL BTUH GAIN...47,405
    Looks like a REALLY OUTDATED Worksheet

    +++ 1.3 IS NOT AT ALL APPLICABLE TO ANY DRY REGIONS.
    _______

    WHAT IS THE ROOM TEMPERATURE AND RELATIVE HUMIDITY IN YOUR RESIDENCE?

    ________ i.e. 78'F @ 42% R.H.

    BASIC : SELECT EQUIPMENT BASED on Q.s & ODT in DRY REGIONS which
    _________ includes the calculated duct heats / gains
    _________ FOR YOUR DUCT LENGTHS AND LOCATIONS.
    … governed by ACCA Manual S.

    --- ODT Outdoor Temperature

    ALL DUCT WORK AND AIR HANDLER should obviously be within Conditioned space.
    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

  5. #5
    Join Date
    Feb 2010
    Location
    On the water but near the hood
    Posts
    1,808
    Post Likes
    Quote Originally Posted by azhvacsys View Post
    In the end of the [Manual J Heat Load] worksheet there is [Moisture Removal: 1.3]. Why would this multiplier be present?
    Because your calculation only arrives at a sensible heat gain figure and doesn't account for latent loads. The equipment capacity is a budget and if a certain amount of work is budgeted for latent work (removal), that leaves less available to do sensible heat removal
    **Note: we live in a Phoenix, AZ... it's very dry.
    July, August, and september are monsoonal months...all very warm months with high humidty. These are the months that a swamp cooler is useless

    ------------------------------------
    SUB-TO
    See the edits.

  6. #6
    Join Date
    Oct 2019
    Posts
    13
    Post Likes
    Thread Starter
    Here is the finish to the worksheet:

    ------------------------------------
    SUB-TOTAL BTUH GAIN (ROOM SENSIBLE ONLY)........................33,150
    DUCT LOSS/GAIN FACTOR (TABLE D)..........................................x 1.1
    SUB-TOTAL BTUH (SENSIBLE GAIN).........................................36,4 65
    MOISTURE REMOVAL (SUB-TOTAL x 1.3).....................................x 1.3
    .................................................. ..........TOTAL BTUH GAIN...47,405
    .................................................. ................................................
    ........TOTAL GAIN....47,405...........BTUH x 1.2....56,886...........4.8 TON

    This [x 1.2] multiplier accommodates the latent load?

    So a 3 TON base need is now a 5 TON need?

    Note what was originally on the house was a 3.5 TON HVAC.

  7. #7
    Join Date
    Oct 2019
    Posts
    13
    Post Likes
    Thread Starter
    Thank you Dan for your response.
    Could you point me out to literature/website that shows why/when this [Moisture Removal: 1.3] would be applied. Thank you.

  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,495
    Post Likes
    Quote Originally Posted by azhvacsys View Post
    Thank you Dan for your response.

    Could you point me out to literature/website that shows
    why/when this [Moisture Removal: 1.3] would be applied.

    Thank you.

    Review any/all manufacturers EXTENDED PERFORMANCE DATA.

    S.H.R. is dependent on YOUR ROOM TEMPERATURE & R.H.
    If one does not know their room conditions [ post # 4, line 3],
    one should Not expect Any real further assistance.

    Just perform the Manual S calculation.
    https://www.acca.org/HigherLogic/Sys...&forceDialog=0

    SENSIBLE HEAT RATIO

    OVERALL CAPACITY IS DEPENDENT on OutDoor Temperature

    _____________
    ___ I.E. ___ GSX16
    .... PAGES 6 - 30

    https://www.goodmanmfg.com/pdfviewer....pdf?view=true
    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

  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,495
    Post Likes
    Quote Originally Posted by azhvacsys View Post
    Here is the finish to the worksheet:

    ------------------------------------
    SUB-TOTAL BTUH GAIN (ROOM SENSIBLE ONLY)........................33,150
    DUCT LOSS/GAIN FACTOR (TABLE D)..........................................x 1.1
    SUB-TOTAL BTUH (SENSIBLE GAIN).........................................36,4 65
    MOISTURE REMOVAL (SUB-TOTAL x 1.3).....................................x 1.3
    .................................................. ..........TOTAL BTUH GAIN...47,405
    .................................................. ................................................
    ........TOTAL GAIN....47,405...........BTUH x 1.2....56,886...........4.8 TON

    This [x 1.2] multiplier accommodates the latent load?

    So a 3 TON base need is now a 5 TON need? NO.!

    Note what was originally on the house was a 3.5 TON HVAC.
    Piling on the ESSENTIALLY NON-Applicable factors for DRY region 1.3
    & 1.2
    on top of it leads to REALLY EXTENDED CRAZINESS.

    ~ 36,000 NOT 56,886

    + WHY would one use 1.1 factor for ducts when they are in conditioned space?

    + DERATE OF OVERALL Capacity IS REQUIRED for 110'F in PHOENIX
    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. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,495
    Post Likes

    REAL CONDIITONS per ASHRAE FUNDAMENTALS

    MCWB = 69.3 'F

    _________ Mean
    ___________ Coincident
    _____________ Wet
    _______________ Bulb
    Attached Images Attached Images  
    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

  11. #11
    Join Date
    Oct 2019
    Posts
    13
    Post Likes
    Thread Starter
    Hi Dan,

    Thank you for your help here.

    Just to clear up the layout of the system...
    The HVAC is a split system between the compressor outside and the air handler in the attic.
    The duct work is in the attic, sitting in basically outside air.
    The 1.1 factor for ducts don't apply here?

  12. #12
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    31,460
    Post Likes
    If your ductwork is not in the conditioned space, and neither is your air handler, that's going to change everything.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist
    Member, IAEI

    AOP Forum Rules:







  13. #13
    Join Date
    Oct 2019
    Posts
    13
    Post Likes
    Thread Starter
    By how much?
    I don't think it justifies a 70% increase (1.1(duct) x 1.3(moisture) x 1.2(latency, maybe)) in base size?
    Note the 5 ton on there now does not pull humidity out of the air. We have to open our windows and doors to dry out the house. What was original to the house was a 3.5 ton HVAC.

Page 1 of 2 12 LastLast

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •