A001_Kulis_Theater_HVAC_Study_-_17y11m01d.pdf

ANCHORAGE

2700 Gambell Street, Suite 500

Anchorage, AK 99503 907.743.3200

FAIRBANKS

1028 Aurora Drive

Fairbanks, AK 99709 907.452.1414

PALMER

125 W. Evergreen Avenue, Suite 102 Palmer, AK 99645

907.707.1215

SOLDOTNA

170 E. Corral Avenue, Suite 2

Soldotna, AK 99669 907.420.0462

JUNEAU

6205 Glacier Highway

Juneau, AK 99801 907.780.6060

November 1, 2017

Gerald Romig Project Manager 176th Civil Engineer Squadron 7252 Gibson Ave.

JBER, AK 99506

SUBJECT: Noise from HVAC system at Kulis Theater, 3rd floor Hangar 18, JBER

PDC# 17340AN

Jerry, Below is our report on the Operations Theater HVAC noise issues for your use. We appreciate the opportunity to provide engineering expertise for this study. Please keep us in mind for future projects you may have in the works.

Purpose

The Kulis Operations Theater at Hangar 18 on JBER provides an important meeting place to present and discuss critical information. The HVAC system serving the space has become increasingly noisy, to the point where it is distracting to personnel and limits the effective use of the facility. Kulis contacted PDC Engineers and requested investigation, study, and recommendations for how to address the noise issue.

On October 9th Randy Williams of PDC met with Gerald Romig at Hangar 18 to conduct a site investigation. This report describes the existing HVAC system, what was observed that day, analysis and discussion of the sources of the noise(s), and recommendations for addressing the issues.

Description of System

The 3rd floor of Hangar 18 houses the Kulis Operations Theater, previously known as the Briefing Room on older plan drawings. It is about 40' deep and 48' wide (about 1920 SF) in size and seats about 200 people in sloped theatre-style seating, facing a stage area with multimedia presentation capabilities. A moveable divider separates the back of the room from similar adjacent space to the south. Per staff, the divider is kept closed. Heating is provided by two wall-mounted recessed cabinet unit heaters, controlled by individual thermostats. Ventilation and cooling is via overhead air ducts to ceiling-mounted supply air diffusers, with corresponding return grilles and ducts. The air system is controlled as a single zone, with a single room temperature sensor and a CO2 monitor to enable of the fan system, and control of the temperature.

The supply and return ducts exit the west wall of the room through fire dampers, then travel through the west hangar to the Ventilation Unit (untagged) on the west mechanical mezzanine. The unit was installed around 1997 and has not been significantly altered or upgraded. It is a packaged 100% outside air system, consisting of separate supply and exhaust fans, a heat-pipe type heat recovery system, Noise from HVAC system at Kulis Theater

P:\2017\17340AN-Kulis_Thtr_HVAC\5Rprts\HVAC Study\17340AN-Kulis Theater HVAC Study.docx filters, and a heating coil. Approximately 5080 CFM of Outside air and Exhaust air are ducted from the unit to the exterior of the building.

Findings / Data

Noise levels were measured in the Theater using two smartphone apps to characterize sound levels with the HVAC system running. An example reading, and a chart of the results are below. Note that these applications are not calibrated, and should be used for comparisons and relative values only.

Figure 1 – Raw noise reading at front of Theater (App #1) Figure 2 - Noise measurement data summary (uncalibrated)

Measurements were also made at the supply fan with open cabinet door, and included on the results summary chart above (orange bars in Figure 2).

Noise levels appear high in the middle octave bands from 250 to 1000 Hz. In the front of the room, directly beneath a supply diffuser, the 2000 Hz band also appears somewhat high. Note that human speech is in the 500, 1000, and 2000 Hz frequency bands.

Specific issues potentially contributing to noise generation were investigated as described below.

1. Diffuser type. The supply diffusers in the theater ceiling are perforated face with stamped steel fixed deflectors. These are a poor choice for this application due to poor horizontal diffusion performance and lack of direction control. They are also noisy at high airflow volumes.

2. Diffuser rattle. Several of the diffuser deflectors have worked loose from the perf face and are rattling when the system is on. The noise is very specific frequency and is qualitatively annoying.

3. Airflow hiss / turbulence. Air movement noise is evident at each diffuser, some worse than others. This is likely due to balance dampers or excessive flow causing turbulence near the outlets.

4. Airflow uneven among diffusers. Airflow felt higher from some diffusers compared to others.

Noise was correspondingly higher at higher flows.

5. Duct oil-can. At the main supply fan outlet, the rectangular duct sides flex in and out with fluctuations in airflow, causing a distinct "oil-can" metallic noise under certain operating conditions.

6. Fan speed irregularities. Airflow through the main supply duct varied irregularly, causing changes in the amount and frequency of the air turbulence noise in the duct.

7. Fan belt loose. The supply fan belt tension is out of adjustment, causing the fan speed to be erratic, and the motor load to be inconsistent. The motor/fan combination generates fluctuating levels of noise.

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8. Pulleys out of round. Contributing to the erratic fan operation, the drive pulleys appear to be irregular or possibly damaged.

9. Fan speed high. Design of the fan system appears to have selected a relatively high fan speed, which would result in a higher production of noise compared to a slower fan.

10. Air volume total. The HVAC system runs at full speed when ventilation is called for. Volume control based on CO2 levels does not appear to be in place. This means that the room is likely over-ventilated and therefore noisier than it needs to be.

11. Fan wheel out of balance. In addition to the erratic fan speed, the fan appears to be out of balance, causing the fan assembly to vibrate. The fan supports are not adequately preventing the vibration from affecting the AHU casing, causing some noise transmission to the ductwork.

Discussion

From Figure 2 it appears that fan noise in the speech octave bands (500-2000 Hz) is a large contributing factor to the perceived noise in the room. Noise from the fan discharge travels down the inside of the duct and exits the diffusers directly above the audience. Additional contribution is likely from turbulence within the distribution ductwork above the room. Possible remedies for this type of noise include, in increasing order of difficulty and expense:

• Address the existing fan operational issues (items 5, 6, 7, 8, and 11). Mostly these are adjustments or repairs that should be done regardless of their noise generation potential.

• Slow down the fan speed (item 9) (will require design calculations to determine minimum airflow)

• Change the control strategy for the fan operation (item 10) (use CO2 for demand control ventilation, add variable speed drives and motors)

• Change fans (item 9). The noisy supply fan can be replaced with newer, quieter fan, and keep the existing ventilation unit cabinet and ductwork. The exhaust fan should also be replaced at the same time.

• Add sound attenuators in the ductwork; or possibly add sound lining to the existing duct.

Operational and maintenance issues should be addressed before more aggressive measures are attempted. The first 3 items in the bullet list above can be accomplished for relatively little expense, and will not only reduce the noise, but will improve the ability to provide comfortable conditions in the theater. Changing fans or adding attenuators should only be considered if further reductions in noise level are necessary.

Within the theater, diffuser self-noise and noise from balancing dampers or unbalanced flow rates are the primary contributors. Potential remedies here include:

• Replace air outlets and inlets with units selected for better air distribution performance and low noise generation (item 1 and 2)

• Re-balance supply and return air systems. Add balance dampers to each branch duct. (item 3 and 4)

Like with the work at the fan, both comfort and noise issues will be improved by the work described above.

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Operationally, the AHU system controls should be verified to be functioning properly:

• The ventilation system does not appear to run continuously when occupied. There should be at least a minimum airflow provided at all times during occupation, then increase airflow as needed to satisfy cooling and ventilation requirements.

• Are the unit heaters and ventilation system coordinated to not operate simultaneously?

• Heat recovery system – does heat pipe control work as intended?

• Heat coil – is sequence of operation appropriate and is valve functional?

These operational points are more for comfort and energy efficiency than for noise, but should be addressed as part of the control strategy work described above.

Summary & Recommendation

Investigation of the noise complaints at the Operations Theater uncovered maintenance and operation issues and system design shortcomings that together are causing the unacceptable levels of noise in the occupied space. Repairs and adjustments to the fan components would address many noise issues;

upgrades and adjustments to the air system in the theater would take care of several others. Further improvements in noise and comfort levels are possible with some additional effort.

Our recommendations are as follows, in sequential order:

1. Calculate system airflow requirements based on current use of space

2. Replace fan motors and add speed control drives

3. Clean and rotationally rebalance supply fan

4. Replace drive belt sheaves on supply fan

5. Adjust fan belt tension

6. Replace temperature controls at AHU and theater, to include CO2 demand controls and fan speed controls

7. Repair/replace controls for AHU heat recovery and heating coil

8. Replace supply air diffusers and return air grilles in Theater

9. Rebalance airflows in Theater, including adding balance dampers where none exist

We are available to discuss this report in further detail and answer questions you may have. Please contact Randy Williams or Danny Rauchenstein at your convenience.

On request, we will provide an engineering fee proposal to include the above recommended work in a design package for competitive bidding.

Sincerely, Randy Williams, PE

Senior Mechanical Engineer