Page 1 of 2 12 LastLast
Results 1 to 13 of 19
  1. #1
    Join Date
    May 2005
    Location
    TN
    Posts
    8
    I have carefully run the numbers using the HVAC-Calc Residential program and have the following numbers.
    Sensible Gain 19,857
    latent Gain 1,827
    Total heat gain 21,684
    Total Heat loss 34,159
    Nashville, TN area
    Program says use a 2 ton. I understand this is based on 12,000 BTU's per ton, but what about the heat pumps capacity to heat? Do you size the heat pump just using the heat gain numbers and an AUX heat strip for the high total heat loss btu's?

    My home will be an all elec of aprox is 2329 sq ft with 4 1/2" SIP (strucual insulated panels) wall construction. Downstairs is aprox 1500 sq ft, 2nd floor 829 Sq ft. Joists between floors will only be 12 inch in height. Home on 40" sealed and conditioned crawl space. All windows low-e with argon.

    I asked 3 companies in the area to give me a quote and design a system for me.
    2 recommend a 3 ton zone system with one zone for each floor
    1 said a 2 system plan with a 2 1/2 ton for 1st floor and a 1 1/2 for the 2nd.
    I don't think any of them really ran a Manual J.
    Additional Question?
    Should I run the 1st floor ducts in the crawl space, and the 2nd floor between the floors? Or try and squeeze them all in the area between floors. Have been given both ways by different contractors. Have learned a lot from the forum, thank you.
    John

  2. #2
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Heat Pump and A/C are the same unit,size by the A/C required,so as not to oversize the A/C.

    Makeup the lackof capacity on the heat pump side with electric heaters installed in the air handler.

    I'd use a 2 zone ,zoning system,and I'd put all the ducts between floors,and insulate the outside walls between the floors so there is no heat gain or loss from the ducts.Problem is with 12" space ,there may not be enough room.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    The first and second floor combined came out to 2 ton, what are you using to condition the crawl space?
    Contractor locator map

    How-to-apply-for-Professional

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

  4. #4
    Join Date
    May 2005
    Location
    TN
    Posts
    8
    Dash says: The first and second floor combined came out to 2 ton, what are you using to condition the crawl space?

    Under duck sizing, the program calls for 97 CFM for the crawlspace. So in answer to your question, It is included in the calculations.

    I did find an error with my calcs. I did not enter a factor for crawlspace floor that would account for heat loss thru the ground. I have since added the closest thing I could find, a basement floor more than 2 foot below grade. It added another 2016 BTU's for heat loss.
    Brings the new total for heat loss to 37320.
    Heat gain is 21967
    Please set me straight if I have gone wrong here.
    Remember, this is a very tight well insulated house: Sip walls are a true R-17

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    I used a crappy program I have at home, and came up with 2120 heat loss, and 608 for gain, for your crawl space.

    Its good enough for ball park calcs, and close to what you recalced.

    So you answered my question.

    I agree with Dash on duct work in the ceiling.
    Contractor locator map

    How-to-apply-for-Professional

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

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,273

    Lightbulb SWEET Selections for 2,329 S.F.

    Originally posted by dash
    Heat Pump and A/C are the same unit,size by the A/C required,so as not to oversize the A/C.

    Makeup the lack of capacity on the heat pump side with electric heaters installed in the air handler.

    I'd use a 2 zone ,zoning system,and I'd put all the ducts between floors,and insulate the outside walls between the floors so there is no heat gain or loss from the ducts.Problem is with 12" space ,there may not be enough room.
    Dash hit the nail on the head As Always.

    You should review use of 16" trusses which may give you > ~ 12.5" clearance.

    Evaluate TRANE XL15i 2.5 Tons ... 2TWX 5030 with TWE037E and TWO Zones.

    http://www.trane.com/Residential/Pro...mps/XL15i.aspx

    AND Get someone who KNOWS and has applicable Zoning Experience ... ask for references + Follow-up with actual site reviews with at least two of the references.

    Alternate: XL16i 3.0 Tons ... 4TTX 6036 with 4TEE 040E.

    http://www.trane.com/Residential/Pro...mps/XL16i.aspx

    JT, Your " GREEN House " type of building is Fantastic.

    .. THOROUGH PLANNING and
    Trying to Do it Right the First Time
    will make you MUCH more satisfied
    with your Home Comfort selections.

    [Edited by dan sw fl on 05-28-2005 at 09:52 AM]
    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

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,273

    Lightbulb Housing Envelope .. Energy Comparison

    John,

    You may wish to review

    .. Resource Efficient and Affordable Demonstration
    .. (READ) project in East Lansing, Michigan

    ... which is 1800 ft2

    http://www.johnbarrie.com/read.htm
    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. #8
    Join Date
    May 2005
    Location
    TN
    Posts
    8
    When should the number of registers for a room be increased?
    I know you all hate rules of thumb, but for a given CFM load for a room, when should you split it into more registers?

    I have decided that I need to increase my truss size between floors to 16". That should allow more room for ducts.

  9. #9
    Join Date
    Nov 2004
    Posts
    2,927
    Originally posted by jtalbert
    When should the number of registers for a room be increased?
    I know you all hate rules of thumb, but for a given CFM load for a room, when should you split it into more registers?

    I have decided that I need to increase my truss size between floors to 16". That should allow more room for ducts.
    When only one duct will not handle the required cfm.
    When the room is too large for only one register.
    When you think you need or want to.

    Is that the answer you want to hear?

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,273

    Register Size, Noise Criteria NC

    Originally posted by jtalbert
    When should the number of registers for a room be increased? ... when should you split it into more registers?
    12" Sq. Diffuser will easily handle 300 CFM.
    So at > 300 CFM, if you do not wish to use a 14".

    Of course, there are an infinite number of Opinions on diffuser sizing.

    I usually limit the Dining room diffusers to 10" x 10" and use two in a few cases. Also, the master bedroom is quite frequently split to lower the velocity and minimize the noise.

    Review the diffuser mfg specs and limit the NC to < 30.



    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
    May 2005
    Location
    TN
    Posts
    8
    To Review: HVAC-CALC 4.0 gives me:
    Sensible Gain 20705
    Latent Gain: 1954
    Total Heat Gain: 22659
    Total Heat Loss: 38163
    Calc program Recommends a 2 ton system
    Heat pump to be installed for AC and heat

    Just talked to one of the HVAC contractors I have asked for bids and he said that the TVA here in Tennesee recommends to size system up to 125% of the sensible heat gain. That is to keep the heating element from coming on too early in the heating mode (aprox 35 dgrees) and degrading efficiancy.

    Does anyone know of this recommendation? I have not read anything on the forum regarding upsizing the system tonnage according to heat losses. I would appreciate any clarification on this issue. Thank you

  12. #12
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    There is a section in manual J that allows that for heat pumps.

    But, depending on the HSPF of your heat pump, you don't need to, and it could do alot worse humidity control in the summer.

    The higher seer equipment doesn't have good humidity removal, wothout using A VS blower and humidity control.

    What are your summers like. Dry. or humid?
    Contractor locator map

    How-to-apply-for-Professional

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

  13. #13
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    HSPF is the effiency,not anything to do with when the heat strips come on,which is more to do with capacity.


    1.25 times your sensible,is 24,821btus,so really still a two ton,without oversizing,even if you add the latent,it's not a 2.5 ton.


    I've heard of 1.25 times total ,for sizing heat pumps in cold ,Dry climates,I avoid it ,due to needing dehumidification in your area for cooling.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event