Passive first, equipment second

A building's energy demand is largely fixed by decisions made before any equipment is selected: which way the long elevation faces, how much glass is on it, and whether that glass is shaded.

In most Indian climates the west elevation is the problem. Glazing there gains heat through the hottest part of the afternoon and keeps releasing it into the evening. Shade it, reduce it, or accept a permanently higher cooling bill.

Only once the envelope is doing its job does equipment selection matter. A well-specified system on a poorly oriented building runs harder for the same comfort, forever.

The order matters because the passive decisions are cheap at design stage and impossible later. You can upgrade an air-conditioner in year five. You cannot rotate the building.

You can upgrade an air-conditioner in year five. You cannot rotate the building.