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.