Critical load is the electrical capacity available to the tenant's own equipment, measured in kilowatts, and in these leases it's the unit rent is calculated on. A tenant taking 500kW at $130 per kW per month is paying $65,000 a month regardless of how many square feet that gear occupies. The landlord is selling delivered, conditioned, redundant power, and the floor space is how it gets described.
PUE stands for power usage effectiveness, the ratio of total facility power to the power that reaches the computing equipment. A PUE of 1.4 means every kilowatt of computing draws 1.4 kilowatts from the utility, with the extra 0.4 going to cooling and losses. It matters in the lease because the electricity bill is usually passed through to the tenant. If the landlord's plant runs inefficiently, the tenant pays for that inefficiency, so tenants negotiate a target PUE with a credit or a cap when the building misses it. That clause is the landlord taking operating performance risk that a normal net lease landlord never touches.
The other exhibit to read in a lease like that is the service level agreement on uptime, because the remedy for a power interruption is usually a rent credit tied to how long the outage lasted and how many nines were promised. Redundancy language (N+1, 2N) tells you how much spare equipment stands behind that promise. Those two exhibits together, the PUE adjustment and the uptime remedy, are where a colocation landlord's real risk sits, and neither one appears in an office or industrial lease at all.
