ASHRAE Journal - March 2013 - 36

owner’s current facility requirements (CFR) for the airside
economizer systems in the facility, and to learn about the history of the facility’s airside economizer systems. These requirements may be different from those established during the
initial design and construction of the facility, due to changes
in the facility over time. Examples of questions to ask the facility manager and building operators to help deﬁne the CFR
related to the economizer systems include:
• What is the intended control sequence of the system, including integration with the heating and cooling sections and
the building pressurization control strategy?
• Have there been any changes to the facility since the original design/construction to warrant changes to the original control sequence?
• Has the system ever been manually disabled? If so, what
were the reasons for that (e.g., pressurization issues, control
issues, etc.), and how were they addressed?
• Have any benchmarks been established related to performance of the system?
• What level of operator training is required for the system?
By the end of this phase, the EBCx team should have a good
understanding of the owner’s requirements for the airside
economizer systems. The team should also have performance

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criteria to use in determining whether the current performance
of the economizer systems meets each of those requirements.

Investigation Phase
The investigation phase includes a detailed site investigation, comparing actual building conditions to the CFR established during the planning phase. The goal is to determine current performance and identify opportunities for bringing the
systems into compliance with the CFR.

Test Performance, Identify Issues
This step includes testing the airside economizer systems
to see how they are performing, identifying issues, and determining opportunities for improvement. Examples of typical
activities include:
1. For each damper related to the economizer system, test
the damper command signal to see if the signal matches the
damper performance, i.e., when the damper is commanded
opened, does it actually open? When commanded closed, does
it close? This often requires one person at the building automation system (BAS) workstation to control the system, and
another at the dampers to observe the damper performance.
2. Test each damper for leakage when commanded closed.
This can be done using visual observations, temperature measurements, an anemometer, a combination of these, or other
methods for assessing damper leakage.
3. Check the sensors to see if they are calibrated and located
properly. When checking calibration, use a calibrated handheld meter and compare the reading from the meter with the
reading from the BAS.
4. Test the system in all modes of operation to see if the
operation matches the desired sequence. Include testing of all
safeties and interlocks. In each mode of operation, note how
each component of the airside economizer system performs
(e.g., dampers, heating and cooling sections, building pressurization systems). There are two general methods that are
typically used for this: functional performance testing (active
testing) and trend data analysis (passive testing).
a. Functional Performance Testing. Change setpoints
and/or override input values to cycle the system between
the various operating modes (e.g., heating, economizer,
integrated economizer, mechanical cooling). Observe and
document the resultant performance, and note whether the
system does or does not operate as intended in each operating mode.
b. Trend Data Analysis. Gather trend data, from the
BAS or from data loggers, across all modes of operation. With
this method, the length of trending must be long enough for
the system to go through all modes of operation; seasonality is a consideration when using this method. Typical data to
gather includes outdoor air temperature (OAT) or enthalpy, return air temperature (RAT) or enthalpy, mixed air temperature
(MAT), supply air temperature, supply air temperature setpoint, chilled water valve position (or cooling stage), heating
water valve position (or heating stage), fan status and speed
March 2013

ASHRAE Journal - March 2013

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