Evaluating the Effects of Common Faults on a Commercial HVAC Packaged Rooftop Unit

The goal of this project is to quantify the impacts of common single and multiple faults on a typical small commercial packaged rooftop unit (RTU) air conditioner in a laboratory setting. Air conditioner maintenance is a commonly overlooked service. As a result, a variety of faults present themselves in air conditioners throughout California businesses. These faults pose considerable strain on the economic resources of Southern California Edison (SCE) customers and add to the ever-increasing demands on the electrical grid. The California commercial sector consumes approximately 67 billion kilowatt-hours (kWh) of electricity annually. Heating, Ventilating, and Air Conditioning (HVAC) equipment accounts for 19 billion kilowatt-hours (kWh) in the California commercial sector (8.6 billion kWh in SCE commercial sector), or roughly, 28% of the energy consumed in the California commercial sector (29% of the energy consumed in SCE commercial sector).1 HVAC also accounts for approximately 300 Megawatts (MW) of non-coincident peak demand in California (99 MW of non-coincident peak demand in SCE commercial sector).1 At least 10% of energy consumed by HVAC equipment is expended from excessive run time, poorly maintained equipment, and controls problems. Given these challenges, a laboratory test environment offers a viable and controlled means for a better understanding of the impacts of various faults. Using the test method developed in a concurrent project (ET13SCE7030, “Development of a FDD Laboratory Test Method for a Commercial Packaged RTU”), a series of faults were imposed on an R410a 5-ton commercial packaged RTU. A total of forty-seven test scenarios were conducted, comprised of varying single and multiple fault iterations. All faults under steady state conditions demonstrated potential for significant performance degradation without causing outright failures. Condenser airflow reduction caused the most significant performance impacts for single faults; at The Air Conditioning, Heating and Refrigeration Institute Indoor (AHRI ID) and Outdoor (OD) conditions, total power increased 38%, air-side cooling decreased 12%, and air-side efficiency decreased by 36%. The most significant multiple fault impact observed was that of a 3-fault combination of low charge, evaporator and condenser airflow; this combination was able to reduce cooling and efficiency by 50% at AHRI ID and OD conditions while total power consumption remained roughly unchanged. This project successfully conducted a laboratory evaluation of a variety of faults scenarios commonly encountered in the field, under a range of climatic conditions representative of SCE territory. However, the data presented is not intended to be the final and universal map of fault impacts. There exists an overwhelming amount of permutations of fault severities, fault combinations, indoor/outdoor conditions, and HVAC equipment characteristics to explore. Current and any future lab data generated should work closely with simulation efforts in order to use numerical or mathematical models to “fill in the gaps” that do not necessarily need to be quantified with expensive lab testing. Additionally, current lab test methods have room for improvement and need widespread industry acceptance. Any data generated from different lab test entities must be ensured to be truly comparable and reasonably representative of field conditions. For example, current fault impact lab test methods do not appropriately capture the effects of air-side economizers, RTU cabinet leakage, or differences in non-steady-state performance. Industry acceptance of an FDD laboratory test method should continue to be a priority for key stakeholders in the HVAC maintenance/FDD industry (utilities, HVAC manufacturers, HVAC service contractors, FDD developers, etc.), with a clear understanding of how it fits into a combination of other diverse efforts. California utilities should continue their efforts to lead and support these activities. Ideally, field efforts, lab efforts, and simulation efforts across all stakeholders will be cohesively orchestrated and leveraged to best understand and enhance FDD and HVAC maintenance. In this scheme, a larger variety of scenarios can be explored, in an informed, effective manner.