Block load represents the total HVAC system capacity required to simultaneously serve all zones at their peak individual loads, without considering load diversity. This conservative approach assumes every zone reaches maximum cooling or heating demand at the same time. Block load establishes the upper capacity threshold for central plant equipment like chillers or boilers.
Calculation Process
Block load calculation sums individual zone peak loads regardless of time of occurrence. If Zone A peaks at 50 tons during 2 PM and Zone B peaks at 40 tons at 4 PM, block load totals 90 tons. This method does not account for time-of-peak variations or occupancy patterns. Building code requirements and industry standards like ASHRAE 90.1 often reference block load for equipment selection to ensure adequate capacity. Commercial buildings typically calculate block load in addition to more refined methods.
Equipment Sizing Impact
Central cooling and heating plants must accommodate block load to prevent inadequate capacity during simultaneous peak conditions. Chiller capacity, boiler output, and main distribution lines are typically sized to block load specifications to maintain design conditions throughout the facility.
Economic Implications
Block load sizing often results in oversized central plant equipment that operates at part-load efficiency most operating hours. Advanced controls and load diversity analysis can optimize equipment selection to reduce capital costs while maintaining reliability.