There is a concept called “the
three-legged stool” of refrigeration cycle performance. What it means is that a unit that is running
well balances three factors. These are efficiency, capacity and reliability.
My experience is that people
responsible for HVAC units primarily want reliability. They bought the unit and are willing to spend
money on energy to run it and will even pay to repair it when it is not
working. They generally will not think
about efficiency until they have reliability.
They are not interested in any more capacity than they need to maintain
comport. Reliability is the important
issue to most people responsible for air conditioners.
When an air conditioner is reliable,
those responsible for them often would like them to be efficient. Efficiency means how much capacity it is
delivering for the energy it is using.
Air conditioners that are running poorly very often use about the same
amount of energy as those that are running well, they just deliver less
capacity. Therefore have to run longer to satisfy the set point and shut
off. The additional runtime uses more
energy and reduces the unit’s total efficiency.
There are some refrigeration cycle faults and degradations that cause an
air conditioner to use more energy while it’s running. I have found that the units that are the most
efficient tend to also be the most reliable.
My experience is that units that perform as similar as possible to the
way they performed when they were new produce the best balance between
efficiency, capacity and reliability.
