When both heating and cooling systems are used in a building, which of the following statements is true?

When both heating and cooling systems are used in a building, which of the following statements is true?

• A. The smaller of two loads
• B. The larger of two loads
• C. The sum of both loads
• D. The average of both loads

Answer: (B)

When sizing for both heating and cooling, the amount of capacity you need is determined by the larger demand between the two. Heating and cooling loads represent opposite goals: heating tries to offset heat loss, while cooling offsets heat gain. At any design condition, you either need heating or cooling, not both at full power at the same time. Therefore the equipment (or the feeder/service that supplies it) must be sized to handle the worst-case scenario, which is the greater of the two loads. For example, if a building’s heating load is 40 units and its cooling load is 60 units, you design for 60 units. You don’t add them together because you don’t require both full heating and full cooling simultaneously. The system is built to meet the maximum demand, not the sum.

When sizing for both heating and cooling, the amount of capacity you need is determined by the larger demand between the two. Heating and cooling loads represent opposite goals: heating tries to offset heat loss, while cooling offsets heat gain. At any design condition, you either need heating or cooling, not both at full power at the same time. Therefore the equipment (or the feeder/service that supplies it) must be sized to handle the worst-case scenario, which is the greater of the two loads.

For example, if a building’s heating load is 40 units and its cooling load is 60 units, you design for 60 units. You don’t add them together because you don’t require both full heating and full cooling simultaneously. The system is built to meet the maximum demand, not the sum.