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  1. #1
    Join Date
    Apr 2009
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    Questions regarding HVAC-Calc

    I have a couple of questions regarding the HVAC-Calc program and admit I am on a steep learning curve regarding heat loss calculations. I downloaded the program and understand the basic operation, required input data is fairly straight forward. The design that I am trying to enter is a three level home with a finished basement, main living floor and a conditioned attic. The home will be SIP construction with 6” walls and 8” SIP roof. Five of the rooms on the main level will have vaulted ceilings, so there is not attic deck above. The remainder of the main level will have flat ceilings with the attic deck above.

    1. Since the program asks for a ceiling height, should I take the average ceiling height for the rooms with vaulted ceilings?

    2. The program does not have a SIP roof, should I just use the R-30 roof choice?

    3. Should the attic be included as a second floor or should I just include the attic as a vaulted ceiling over that portion of the home and adjust the wall height to account for the gable ends? The attic deck as well as the deck under the main level will be un-insulated.

    4. I entered the total length of each exterior wall and a room for each section of exterior wall, since the remainder of the walls are interior, I assume that I should be unconcerned with them since correct? The square footage I entered is the total for each level and not just for the rooms with exterior walls

    5. Finally, I have an attached garage that will also be constructed from SIPS with a SIP roof. The garage will be separated from the living areas by a SIP wall. The garage will be partially conditioned (abt 40 degrees in the winter) to prevent the freezing of water lines in our RV. How can this situation be handled by the HVAC-Calc program? I had originally modeled the living areas without the garage. Should I continue this way so that I have a more conservative model?


  2. #2
    Join Date
    Oct 2008
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    Being a bit more clear and specific will help with your problem - what program your using ? what kind of construction your dealing with ..,2 story, 3 story , in ground ..All of these are in my program and have done many .. Heat Gain & Loss are much easier than they use to be.. If your program has a training tool use it a few times.. There's probably areas in your program your missing ..

  3. #3
    Join Date
    Apr 2009
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    Thread Starter
    The Program that I have been using is HVAC-Calc. I have played around a little more with it and used the tutorial videos. I believe the results of the various model runs I have done are in the ballpark. It appears that I have a heat loss of about 52 kBTUh. The partially conditioned garage adds another 13 kBTUh for a total loss of about 65 kBTUh.

    In reading product specifications from the various GHP manufacturers, specifically the “Hydronic Heating Capacities”, how is the heat loss related to determining the size of the GHP needed? I know that I need to replace the calculated loss to maintain the interior temperature specified in the model and I know that the model is based on conditions that seldom occur in reality. Referring to the product performance data sheets provided the the various manufactures, which reflect the system performance under various conditions, how do I use this data to size an appropriate system for my home?

    General questions:

    Where can I find groundwater temperatures for a specific area?

    It’s the EWT listed on the specification sheets that groundwater temperature?

    Is Total Heating Capacity (HC) the number used to size the system or is Total Heat Extracted (HE) the number used or neither?

    How is the hot water storage tank sized?

  4. #4
    Join Date
    Feb 2006
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    Don Sleeth, author of HVAC-Calc, provides tech support last I checked. Google ground water or deep earth temps for a national map with temperature contour lines.

    EWT is only same as ground water temp on an open loop system

    System output (HC) is HE + power it uses in heating mode. In cooling power used is subtracted from Heat Rejected to determine nest cooling

    Best hot water tank arrangement is two tanks. Size the upstream buffer tank to a day's household use. Size the downstream finishing tank to the house's worst hour of use

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