Air Conditioning equipment that is “too big” will NOT keep people comfortable when there is a large cooling demand (see below), and will hurt performance and be a burden the rest of the time.
Air Conditioning equipment that is “too small” will not satisfy the cooling needs.
Builders and contractors often oversize air conditioners because they think it will reduce service calls. Field studies show that central air conditioners are, on average, being oversized from 24% to over 100%. Oversizing has a bad effect on energy use, comfort, equipment life, and system costs:
Oversized air conditioning equipment often runs for very short periods and may not reach its steady-state “cruising speed” where it operates most efficiently. Oversizing by 50% has been shown to increase seasonal energy use by 9%.
Very short runtimes mean indoor air doesn’t get mixed, and uncomfortable “hot spots” occur in kitchens and sunny rooms.
Very short runtimes can leave too much uncomfortable humidity in the air.
Comfort problems lead homeowners to lower the thermostat, leading to unnecessary energy use and increasing the risk of condensation problems.
Homeowners spend more time on the outside fringes of the comfort zone and often reset the thermostat.
Wear and tear on equipment results from too-frequent stopping and starting.
Costs of equipment, installation, and maintenance are all higher.