If you've ever taken a calculus or physics class, you may have run across the Greek letter "delta" in the past. Science and engineering fields typically use delta to indicate a change in something, often some variable as part of a mathematical equation. In HVAC, delta has a somewhat more limited but similar meaning. Thankfully, you won't need any math prerequisites to understand how it works.
However, you may hear your technician talking about your "Delta T." The Greek letter might make you think you're about to get a complex technical lesson, but this term simply refers to the change in temperature produced by your air conditioning system. Your system should create an expected change (a drop) in air temperature, and it may indicate a problem if it can't reach this value.
How Do Delta T Measurements Work?
If your HVAC tech is investigating a problem with your system, they may check your Delta T as part of their diagnostic procedure. Multiple methods for performing this check exist, including inserting probes directly into your ductwork or simply checking temperatures at return and supply vents. Your Delta T is the difference between the high (return) and low (supply) readings.
There isn't a single value for Delta T that will work for every air conditioning system. The differential will depend on the system's design, and your technician will need to take these factors into account when using this diagnostic method. In every case, the expected values will fall within a range of a few degrees, and higher or lower Delta T values can both indicate a problem.
Why Does Delta T Matter?
Delta T effectively measures how much heat your air conditioner is removing from the air. If you have a 19-degree Delta T, it means that your air conditioner is expelling air that's about 19 degrees cooler than the air coming in through the return ducts. This measure gives your technician a reasonable idea of how much heat your refrigerant is absorbing.
A low Delta T means your system isn't keeping up with the amount of heat in your home, and you'll likely feel warmer air from your vents. This problem can have numerous causes, including physical damage to your condenser unit or excessive airflow over the evaporator coils. User error, such as keeping the central house blower running constantly, can also produce low Delta T.
While a high Delta T may sound like a good thing, an air conditioning unit that's running too cold is usually a problem, as well. High Delta T can indicate issues with refrigerant charge, inadequate airflow, or even more substantial problems with your home's ductwork design. In general, overcooling isn't something you should ignore.
If you notice that the air from your vents is too hot or cold, it may mean you have a problem with your Delta T. An HVAC technician can help you get to the bottom of the issue and get your air conditioner running effectively and efficiently again.
For more information on air conditioning repair, contact a company near you.