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Damper tests provide valuable insights, Part 7A; Test Proceedure and a First Look at the Results
June 29, 2007
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.
Posted by David Sellers on June 29, 2007 | Comments (0)
