Damper tests provide valuable insights, Part 7A; Test Proceedure and a First Look at the Results

In our last post, we talked about the results of the test Brent
and Abdi ran on the Pacific Energy Center AHU1 and the
recommendations they made based on those results.  Those
recommendations and the test they developed became the foundation
for the test Wayne Jin and I ran that yielded the surprising
results.  In this post, I thought I would give you a quick
look at the procedure Wayne and I used and then give you a first
look at our results.  The procedure we used included elements
typically found in most functional testing procedures.  A
general discussion of these elements can be found in the
Functional Testing Basics chapter of the Functional
Testing Guide
in Section 10 – Elements of a Functional
Test
.  I’ll discuss these elements as the pertain to
the test we did at the PEC.

Statement of Purpose

Our statement of purpose was as follows:

This test documents the minimum outdoor air flow into the
system at the current setting under different supply flow
conditions. It also checks the outdoor air damper leakage and
characterizes the economizer dampers.

Instructions

Our instructions provided some basic information regarding how
the test was to be performed and highlighted a few important steps
and techniques, including the way the load on the fan would be
ramped up extra procedures that would be included in some steps to
assess hysteresis and the
impact of the kitchen exhaust hood.  I’ll discuss these items
further when I discuss the actual test procedure.

Equipment Required

For our test we needed several specialized pieces of
equipment.  One was an airflow multimeter (the one we
used was manufactured by Shortridge)
and
clinometers (ours came from ACE hardware)
.   
The airflow multimeter allowed us to measure air flow based on
louver, filter and damper face velocities and area.  The
clinometers allowed us to measure damper blade angles.  We
also hooked up analog sensors that we hoped would allow us to log
damper blade angle as we went along.  Here is a picture of the
set-up we were using, which coupled a angle sensor with an AEC Microdata
logger
, and a close up of the angle sensor, which was
manufactured by Crossbow
Inertial Systems
.

Acceptance
Criteria

Typically functional tests have acceptance criteria that tie the
results back to the design intent.  In our case, our test was
run for information gathering purposes, so there were not formal
acceptance criteria.

Precautions and
Prerequisites

Our test would be run with a “live” building, as is the case for
many retrocommissioning projects.  Thus, we needed to be sure
that we would minimize the impact of the test on the building and
its occupants.   Towards that end, we took the following
steps:

We scheduled the test for a day when the building had no
events scheduled. 
This minimized the potential for
generating complaints as a result of the test.  It also
minimized the need for operating the kitchen exhaust fan. 
This was important because we wanted to keep the fan off for most
of the test steps.

We scheduled the test for a time when we anticipated mild
weather.
  Since our test would frequently drive the
system towards a100% outdoor air condition and operate in that mode
for significant amount of time, we wanted to do the test on a day
where this would not over-cool nor over-heat the spaces served by
the system.  thus we targeted a time when outdoor temperatures
would be in the range typically associated wtih the
system’s required discharge temperature.

Preparation

Preparation on the day of the test consisted of gathering up our
equipment, reviewing the procedure, verifying that our
prerequisites were met, and making sure we documented the building
operating condition, especially the state of things that might
impact outdoor air flow, like toilet and kitchen exhaust
fans.

Procedure

The goal of the test was to document the performance of the
outdoor air dampers with the supply fan operating under different
load conditions.  At first blush, it would seem like we could
simply command the speed of the supply fan up incrementally to
achieve this.  However, in a working VAV system, the supply
fan speeds up as the result of the need to provide additional flow
while maintaining the desired duct system static pressure. 
Simply increasing the fan speed is not the same thing; rather, it
would tend to increase the duct system static pressure if there was
not a demand for increased flow since the VAV terminals would need
to throttle harder against the available supply pressure if the
loads they served had not increased. 
To realistically simulate different load driven flow conditions,
our procedure planned to incrementally raise the discharge
temperature set point.  This would reduce the cooling effect
available from the supply air and the terminal units would have to
open and provide more flow in order to maintain set point, all
other things being equal.  We discovered that it took a while
for the system to react to this change and elected to modify our
procedure to speed things along.  Specifically, we took
advantage of the empty meeting spaces and adjusted their set points
down into the low 60’s (F) to cause the terminal units to drive to
full cooling.  This simulated the effect we desired and had a
much faster response time.

I seem to have reached the character limit for a post at this
point, so I’ll just start another and pick up there where I left
off here.

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