Preventative maintenance of residential air conditioning units is known to restore performance capacity,
improve comfort and has been thought for years to lower utility costs. Extensive search of air conditioning
manufacturers, service personnel, university research and trade associations failed to provide information on the
magnitude of restoration of Btu capacity, whether it was latent or sensible heat, how much comfort was improved, or
to what extent if any utility bills could be lowered. Several trade articles dealt with the increase of energy
consumption from dirty condenser coils. Some of these articles indicated that head pressures were increased from
50 – 100 psi because of dirty condenser coils, thereby increasing energy consumption by the compressor by 10 –
20% to overcome these pressures. Likewise airflow across the evaporator coil was restricted by dirty filters, dirty
blower wheels, and with time dirty evaporator coils themselves, to reduce heat transfer to the coil.
This prompted personnel from the Louisiana Cooperative Extension Service to develop an air conditioning
maintenance demonstration that would illustrate what would happen to the head pressures and amp draw when the
condenser coils or evaporator coils were partially blocked. These demonstrations showed that energy consumption
could be increased 30 – 40% for the same amount of cooling when the coils were artificially blocked. This
demonstration, however, did not answer the ultimate question of the consumer. “How much can I save with
preventative maintenance?”
The homes were selected by personnel from the Cooperative Extension Service and Gulf States Utilities
Company. The following homes were selected.
Home #1 – 1211 Rue Crozat. Unit was thought to perform satisfactory, but cycled too frequently.
Home #2 – 1528 Louray. Heat Pump. No complaint, thought to be in average condition.
Home #3 – 549 Rodney Drive. No complaint. Unit thought to be in above average condition. Was
serviced less than a month before evaluation.
Home #4 – 563 Rodney Drive. Unit ran a lot and was selected because of a known dirty condenser coil.
Home #5 – 640 Broadmoor Avenue. Was selected because of excessive complaints of poor performance.
Unit had been serviced 2 – 3 times before evaluation with no results. It was known to be in very poor
condition.
(con’t) Louisiana Cooperative Extension Service Study
SERVICES PERFORMED
The following services were performed at all 5 residences.
1. Condenser coils chemically cleaned.
2. Evaporator coils chemically cleaned.
3. Filters cleaned or replaced.
4. Blower wheels cleaned.
5. Freon charged to factory specifications.
6. Inspected for return air leak.
7. Inspected and stopped duct leaks at the plenum chamber and return air.
METHODOLOGY
Homeowners were asked to set their thermostats at a comfortable level and leave it unchanged for
the duration of the evaluation. In addition they were asked to operate their homes in the usual manner. If
parties and other activities that were planned that would increase energy consumption, they were to advise
the investigators so that the evaluation period would avoid these times.
The technique used for the evaluation was to evaluate a home for a 24-hour period with outdoor
conditions of 88 – 92 °F. On the second day the unit would be serviced and on the third day a second 24-
hour evaluation would take place. In the event of rain or heavy cloud cover, the second evaluation would
be delayed until a similar day was available for the follow-up evaluation. The time of service was
coordinated with the service professional on a time available basis.
DATA COLLECTION
The following data was collected before and after service at each of the five residences.
1. Outside dry and wet bulb temperatures.
2. Inside dry and wet bulb temperatures.
3. Temperature at the return air grill, wet and dry bulb.
4. Temperature of the air discharged from the closest grill to the evaporator coil, both dry and
wet bulb.
5. Air velocities at and cross sectional area of return grill-filters.
6. Dry bulb temperature increase across condenser coils.
7. Running time meter on compressor.
8. Cycle patterns.
9. Power consumption.
RATING OF A/C COMPONENTS BY A SERVICE PROFESSIONAL
All air conditioning systems were serviced by the same service professional. During the servicing period
the service professional was asked to rate the condition of each component in each of the air conditioning systems
serviced. This was a five-category rating indicated by the key words poor, fair, average, good and excellent. Graph
1 is a summation of this rating effort. Of all the components evaluated, a fair rating was the most prominent rating.
The most prominent range was from poor to average. This information implies that if the 5 units evaluated are
typical, then service would perhaps restore at least ½ to 1 ton or more air conditioning capacity through each central
air conditioning unit.
DISCUSSION
Air conditioning systems seemed capable of giving reasonable performance when their state of
maintenance rated from fair to average. This is based upon the fact that as long as the home is comfortable, most
residential occupants feel that the air conditioner is performing satisfactorily. This is especially true since the trade
appears to have a tendency to oversize the system and then, if the family has made energy improvements such as
additional insulation and installed storm windows, the air conditioning system can be performing below its capacity
because of poor maintenance and maintain comfort while energy utilization increases.
As with most equipment, the maintenance of all components can influence the equipment’s’ performance.
However, there appears to be, in most cases, one to two components in “poor shape” that primarily limits the
equipment’s performance.
TABLE 8 Running Time Reduction (Hrs/Day) |
DEMONSTRATION | AFTER SERVICE |
#1 1211 Rue Crozat | 2.0 |
#2 1528 Louray | 0.05 |
#3 549 Rodney Drive | 0.75 |
#4 563 Rodney Drive | 2.90 |
| #5 640 Broadmoor Ave | 2.80 |
Average . | 1.70 |