Testing and Verification

Before the official demonstration could begin, various testing and verification processes were needed in order to validate the correct implementation of all software and hardware installed for this study. To do so, functional tests were needed for the installed TTR logic and the power readings of the VFD display, DDC system, and installed communication cards needed to be verified. Also, refinement of TM and RP calculations was needed due to observations of static pressure oscillation during initial testing.

Functional Mode Testing

With a variety of custom TTR programs installed by local contractors at the selected Iowa Army National Guard sites, a standardized functional test for the TTR control logic was implemented. The objective of the functional test was to verify the correct operation of the custom TTR programs in each of the DDC systems used. The test was provided by Taylor Engineering, Inc. and was performed on a dynamic, macro-enabled excel sheet, with the recommended TTR formula and settings installed in background functions. To complete the functional test, the DDC system and spreadsheet would run side by side in a live comparison. Using the test inputs provided from the spreadsheet, the response from the DDC system and the expected response from the spreadsheet were compared. Any discrepancies found were noted and resolved as soon as possible.

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The functional test began with the entering of site and AHU specific data: Date, Time, maximum and minimum static pressure setpoint limits, initial static pressure setpoint, TTR cycle time, and VAV boxes to test the most open damper position and static pressure setpoint calculation of the TTR programs. With these entries, the functional test spreadsheet would generate the recommended TM and RP rates, and asked the operator to verify if the results matched what was observed from the DDC system.

The functional test then progressed through several scenarios. This required manually overriding the test VAV box damper positions from the DDC system. With this information, the custom TTR program in the DDC system would output the newly calculated static pressure setpoint and send the appropriate command signal to the supply fan VFD. This was compared to the expected static pressure setpoint from the test spreadsheet and used to verify the supply fan response to the changing static pressure setpoints. The static pressure setpoint was first compared to the initial static pressure setpoint value from Step 1. In the proceeding steps, the test VAV box damper positions were altered to achieve an expected response from the DDC system. For example, with all VAV box damper positions at 85%, the static

pressure setpoint should remain unchanged the next following TTR step time cycle. If one of the VAV box damper positions was then adjusted to 92%, the static pressure setpoint should increase by an amount equal to TM1.

Along with the setpoint comparison, the functional test included a comparison for the limit check section of the custom TTR programs. By adjusting the test VAV box damper positions to 99%, this would increase the static pressure setpoint calculation by an amount equal to TM1+TM2+TM3. However, the resulting static pressure setpoint could not be greater than the predefined maximum static pressure setpoint.

For the remaining steps, the test VAV box damper positions were then decreased in order to simulate a reduction in building demand. This was to verify the correct summation of the RP1, RP2 and RP3 values and the limit check of the minimum static pressure setpoint. Once the testing was completed, the test forms were submitted for review.

Power Measurement Verification

To ensure proper readings of the VFDs studied during this study, a standardized testing procedure was created to verify the accuracy of the VFD display and DDC system trends and the accuracy of the VFD display and data logging systems. Using a Fluke 41B Power Harmonics Analyzer with a Fluke 80i-500s AC current probe, the VFDs at Des Moines MEPS, Boone RC and JFHQ were tested and verified.

The Fluke 41B had a listed accuracy for watt measurements of ± 1% + 4 digits and a resolution of 0.01 kW in the 1 kW range used for testing. The reference power meter was certified by the manufacturer to be properly calibrated during the time of the testing. The current probe had a listed accuracy for AC current from 1 to 20A of 10% + 0.3A for 10 to 45 Hz and 5% + 0.3A for 45 to 60 Hz. For AC current from 20 to 100A, the accuracy was 10% for 10 to 45 Hz and 5% for 45 to 60 Hz. The AC current probe was certified by the

manufacturer to be properly calibrated during the time of the testing.

To collect test readings from the VFDs using the reference power meter, the VFD panel control was selected to “hand” operation to freely adjust the speed command signal. Starting at the minimum allowed speed, typically 20 Hz or 30% and then rising by 10 Hz or 15% each interval to the maximum allowed speed, typically 60 Hz or 100%. The power

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readings were recorded after the VFD speed had stabilized, typically after one or two minutes. Table 3.1 provides sample results from JFHQ AHU-2 supply fan VFD.

Table 3.1 Power verification results from JFHQ AHU-2 supply fan.

In Table 3.1, the “VFD Efficiency” column is a comparison of the “Power Meter” input power readings and the “VFD Display” output power. The “Error” column is a comparison of the trended power data and the actual power data. For the JFHQ AHU-2 supply fan, this was a comparison of the data logger input power readings and the “VFD Display” output power.

While the tests included the full allowable range of speed of the VFDs, larger errors at low frequencies were acceptable as the supply and return fans do not normally operate in this range. All tested VFDs had limits of 18 Hz to 20 Hz as the minimum setting, while the maximum was either 60 Hz or indirectly limited by an external high static pressure alarm within the DDC system or AHU that tripped the unit if faulted. VFDs also inherently have losses resulting in error due to internal workings; a portion of the error was also attributed to the resolution of the VFD displays, typically ±.05 kW.

Output

Speed Frequency Power Meter Data Logger VFD Display Data Logger Reading

% Hz kW kW kW % % 30.00% 18 0.465 0.519 0.41 11.61% 21.00% 45.00% 27 1.33 1.38 1.3 3.76% 5.80% 60.00% 36 2.6 2.77 2.65 6.54% 4.33% 75.00% 45 3.85 3.98 3.8 3.38% 4.52% 90.00% 54.2 5.95 5.54 5.9 6.89% 6.50% 100.00% 60 - - - - - Error Input AHU-2 SF