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HVAC Systems - Internal Loads


Internal loads can come from occupants, appliances, as well as plants since watering plants requires moisture to be introduced into the home.

Determining Occupants - According to ACCA, there is only one acceptable method for determining the number of occupants in a home and that is to take the number of bedrooms and add one. ACCA assumes the master bedroom is occupied by two people and the remaining bedrooms are occupied by one person each. This is why we ask for the number of bedrooms on the project screen. 

When performing a room-by-room load calculation, ACCA does not recommend placing the occupants in their respective bedrooms. They suggest placing them in a kitchen or living room as that would represent a worst case scenario when everyone is congregated together.

Determining Appliances - One common mistake is for a user to simply count all of the appliances and lights found in a home. ACCA only recommends to account for appliances and lighting that is likely to be operating in the early evening of a design day. Typically this includes appliances that never turn off (like a refrigerator) and a few ancillary appliances such as the dishwasher, laundry, TV, and a small amount of lighting.

ACCA created default scenarios with all of these appliances bundles already to make this selection easier. Cool Calc allows a user to select from one of the default scenarios or select individual appliances.

Determining Plants - If a home contains a significant amount of plants, they should be totaled up and accounted for in the internal load section of Cool Calc. Plants require water, and water evaporates into the air which causes air conditioning systems to work harder in the summer to maintain adequate humidity levels in the home.

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    Rafael Cecena

    Hi my name is Rafael,
    Is there a customer Service line or tech support line, I created a profile but Cool Calc seems to have calculated way below of what it should have been. I can be reached at 805-761-8089

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    Cool Calc Support

    Hi Rafael,

    Thank you for taking the time to connect. Please feel free to send us a note at info@coolcalc.com if you have additional inquiries.

    Cool Calc.

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    James Bowser

    When I entered my first project, CoolCalc allowed me to enter my unusual number and type of lighting appliances. I'm no longer asked to enter my extreme BTU appliances in any project. Is it based on what I enter in ACCA? How do I control entering appliances?

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    James Bowser

    I found out that YES, you do have to enter "Custom or Other" for the ACCA question to get asked for the types and number of appliances. HOWEVER, when an appliance type is "Other or Custom" the wattage entered is NOT used in the BTU calculations. I had to select a Microwave to equate for the type of appliance I needed to enter. So I entered 70 microwaves in order to make the BTU calculator work correctly. Please fix this error.

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    Mahendra Naidu

    hey bill i send a report of my house 1421 sandy ct ,modesto,ca,95355 can i put a 4 ton ac unit it shows i need 3 ton ac thanks.

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