Energy Efficient Commercial Buildings Act of 2021 This bill temporarily modifies the tax deduction for energy efficient commercial buildings for taxable years beginning after December 31, 2021, and before January 1, 2032. Among other provisions, the bill provides for a lower (25%) reduction of annual energy and power costs for certain energy systems, revises the maximum amount of the deduction, and allows an alternative deduction for costs relating to energy efficient retrofit building property.