We were recently shocked to learn from a group of twenty top commercial HVAC contractors that up to 80% of commercial economizers were found to be non-functional in the field. As we reviewed the business opportunities available by renovating economizers it became clear that this is a niche market and few contractors are harvesting from this wide-open opportunity. Let’s take a look at typical repairs needed to restore an economizer to full and effective operating condition.
Basic Economizer Functions
Before reviewing economizer repair and adjustment opportunities, consider the use and application of this essential equipment accessory. In many parts of the country according to code demands, economizers are required to be installed on commercial and light commercial HVAC systems that exceed 5 tons of cooling.
The primary driver is to provide buildings with a source of fresh air that enters the system through the equipment by utilizing an economizer accessory that connects directly to the equipment or by pulling air through a fresh air duct. A common fresh air number used is 15 CFM per occupant in the building, although this number can vary from county to county.
Another reason for specifying an economizer is to capture free air conditioning when the outside air conditions are cooler than the inside of a building and cooling is needed. Controls are used to limit operation to times when dry bulb and wet bulb outdoor temperatures fall within the established control settings. When conditions are right the economizer may open to maximum position and pull free cooling from the outside that’s used to condition the building. The cost of operating the fan only compared to the cost of running the compressor represents a significant savings opportunity. This may save thousands of dollars per year in operating costs.
A surprising percentage of economizers were found to be intentionally disabled. This action is taken on the warmest days when the cooling system is unable to keep up with the load of the building. When the building is uncomfortably warm, an inexperienced or unaware technician goes to the unit, conducts some very basic tests and discovers what appears to be a gaping hole in the side of the unit pulling hot air into the building.
Under this set of conditions, eliminating the fresh air being pulled into the building appears to the inexperienced technician to be a temporary solution to the discomfort in the building. The technician may make the mistake of disabling controls or screwing shut the economizer and failing to return when the cooler weather returns. It may be months or years until a knowledgeable technician may discover the defect and restore the economizer to it’s intended operating state.
Other defects include attaching an economizer accessory to a system, which doesn’t match the heating or cooling equipment. The installation of undersized or oversized economizers is an additional problem that should be corrected. We received reports of economizers that were placed on the roof or in equipment rooms that have never been removed from their original packaging.
Some manufacturer’s economizers appear to be an afterthought and seem to be included only as a poor quality temporary accessory shipped to meet a compliance measure. An inspection and assembly of a poor quality economizer will confirm this notion. On the other hand, several manufacturers still provide quality louvers, controls and eyebrows intended to remain functional throughout the life of the equipment.
Poor quality economizers may need to be replaced with new ones, or components may need replacing to return the device to full and effective operation.
Adequate Airflow Adjustments
Ideally, the engineering expressed on the original building plans may still meet the fresh air requirements of the building. Once this is verified the economizer function can be tested as follows:
1. Manipulate the system controls to drive the economizer to minimum air position. This will verify the basic louver functionality.
2. Measure the airflow through the economizer by performing a traverse of the airflow entering the system. (See the economizer test procedure offered at the end of this article.)
3. Compare the actual economizer airflow to the specified airflow.
4. Adjust the airflow by adjusting the louver position and retest to confirm required airflow is being delivered.
5. Manipulate the system controls again to drive the economizer to maximum position.
6. Measure and verify airflow volume. Adjust airflow if needed.
7. Also be sure the check the blower motor amp draw and compare operating amps to full load maps to verify the motor operating amps do not exceed motor rated full load amps. This may occur when the fan suction pressure is reduced by opening the economizer, increasing fan airflow and motor amp draw.
Another set of tests and adjustments focuses on the economizer controls. Surprisingly the most common defects found in controls, are that the controls are unplugged. Connect the economizer controls to the equipment and then test and diagnose economizer operation.
The durability and quality of the controls should be considered when selecting or specifying an economizer. There is a current trend to lower the price of economizers by installing controls. The controls have life spans so short that the argument can be made that economizers are built and installed only to satisfy the requirement of compliance.
Several better contractors are replacing cheap and ineffective economizer controls at startup.
Run the economizer controls through a full sequence of operation and verify the opening and closing of the louvers at the control system set points. If the equipment and controls provide for multi-stage operation, also verify the set points activate at each stage of operation and agree with control settings.
Opportunity exists in the realm of the economizer and remains wide open to a contractor that will take the time study and learn economizer repair and adjustment.
Rob “Doc” Falke serves the industry as president of National Comfort Institute an HVAC based training company and membership organization. If you're an HVAC contractor or technician interested in a free procedure on how to measure economizer airflow, contact Doc at firstname.lastname@example.org or call him at 800-633-7058. Go to NCI’s website at nationalcomfortinstitute.com for free information, articles and downloads.