Retrocommissioning Findings Summary: Building X #1 Priority: Major Comfort/Control Problems

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1 IMPORTANT NOTICE: This sample document is provided for instructional purposes only. CCC is not rendering advice concerning any commission project or practices. This document is neither approved nor intended to serve as a standard form. The user of these documents should confer with qualified advisors with respect to its commissioning and other documentation Retrocommissioning Findings Summary: Building X #1 Priority: Major Comfort/Control Problems Finding Description of Problem Recommendation Benefits and Payback 1 Building pressurization A pressurization test was performed on the building in mid November to determine building pressure with respect to outside and quantify the air flow necessary to positively pressurize the building. Spaces that are negatively pressurized will draw unconditioned outside air into the building (infiltration) through gaps in the exterior shell, causing energy waste and comfort problems. The building pressurization test demonstrated that approximately 250,000 CFM of air must be delivered to the building in order to achieve positive pressure throughout the building (lobby at neutral). Minimize outside air infiltration by ensuring that the building is positively pressurized. 1. Find and repair building envelope leaks. Begin by focusing on the areas of known infiltration (floors 2&3 and the mechanical rooms). 2. Turn off the return fans associated with AHU1 and AHU2 when the outside air temperature is below 60F. These units serve the negatively pressurized floors. Further tests are necessary to optimize this control strategy. Comfort, Reduce heating and comfort complaints associated with infiltration. Reduce the recirculation of building exhaust air into the outside air stream (Finding 6) Savings: $14,400/year Payback: 0.3 year 2 Chilled water/ahu control: Chilled water valve instability Chilled water/ahu control: Chilled water pumps 6,7,and 8 speed Chilled water/ahu control: Chiller cycling The measured discharge air temperature for AHUs 1-4, ranges from 55 F to 62 F, with setpoint at 55 F. The rapid opening and closing of the cooling control valves to meet discharge air temperature setpoint appears to be causing significant instability in the entire chilled water plant, particularly operation of the chilled water distribution pumps and chillers. Trend data indicated operational problems with the chilled water distribution pumps: 1) typically two pumps operate continually; 2) pump speed rarely dropped below 60% speed; and 3) the third pump cycles ON and OFF at 20 min-1 hr intervals. Trend data shows that chilled water supply temp varies from 42 F to 63 F as chillers cycle OFF and ON at minute intervals. The fluctuation in chilled water temperature can also contribute to the instability of the cooling coil valves and distribution pumps. Primary chilled water pump sequencing problems may also promote this instability. Improve chilled valve control to improve stability of chilled water plant and discharge air temperature. Start with tuning the PID control loop that controls each cooling coil valve. There may also be other problems with chilled water pump sequencing and the differential pressure sensor that could contribute to this instability. All sequences must be fully identified and brought under control. Comfort, Maintenance, Reduction in comfort problems Maintenance savings from reduced cycling of control valves, pumps, and chillers. Reduced pumping and chiller energy. $2,600/year energy savings plus maintenance savings, 1.2 year payback (energy only) 2005, Portland Energy Conservation, Inc. (PECI). All rights reserved. 1

2 Finding Description of Problem Recommendation Benefits and Payback 3 Heating air handler control: Hot water valve control and hot water distribution pump speed control Boiler temp sensor placement 4 Cooling AHU discharge air temperature reset Trend data indicates that a majority of VAV boxes are not calling for heating when the outside air conditions are mild, yet the heating coil valves serving AHU5 and AHU6 are 100% open. The reason for this is because the hot water temperature and heating air handler temperature reset schedules do not correspond. A discharge air temperature of 120 F will never be met with 113 F water temperature, so the heating coil valves are always 100% open. As a result, two secondary hot water distribution pumps are running at 95% speed and the third pump cycles to 95% speed at 15-minute intervals even though there isn t load on the system. The over pumping of the systems contributes to improper boiler operation and staging as well as hot water temperature setpoint control problems. The boiler plant hot water supply temperature sensor should read from the main supply pipe, but based on the operator workstation graphics and field observation, the sensor is located within the Boiler 3,4,5 loop. If the hot water control loop uses this sensor, the boiler plant controls to an incorrect supply temperature. Trend data indicates that a discharge air temperature setpoint of 55 F is maintained and appears to be contributing to comfort complaints and increased reheat. Control programming for AHU3 was evaluated in depth and it was determined that several of the courtroom zone setpoints were driving the discharge air temperature setpoint when the courtrooms were unoccupied. This is most likely occurring in some of the zones used to control AHU1, 2, and 4 as well. Lower the discharge air temperature reset schedule at hot deck air handlers. Further lower the hot deck low limit discharge air temp down to 70F, so the hot deck can be satisfied by the return air temp when reheat loads are small. Lower the maximum hot deck temperature to 105F (the max design temperature). Address infiltration issues first since heating capacity is a problem. Eliminate overpumping by addressing control sequences and potential pump impeller trimming. Reducing overpumping will improve heating capacity. Investigate the controlled sensor in the hot water control loop. If incorrect, install temperature sensor in the correct location. Change operator workstation and hot water control programming to account for the correct sensor. Evaluate each zone that is used as part of the reset control programming. Some zones may need to be eliminated while others may be better candidates to give an accurate representation of building load requirements. In addition each zone control parameters should be reviewed. Comfort, Energy savings from reduced hot water distribution pump speed, run fewer pumps, fewer boilers. Maintenance benefits: reduced cycling improves life of pump motor. Save heating plant energy by using the return air to serve reheat loads. Energy savings: $4,800/year Payback: 0.1 year Comfort, Potentially improved boiler plant and hot deck air handler control. Comfort, Zones will be more comfortable when the discharge air temperature reset is functioning. Energy savings not quantified. 2005, Portland Energy Conservation, Inc. (PECI). All rights reserved. 2

3 #2 Priority: Major Energy Waste Finding Description of Problem Recommendation Benefits and Payback 5 Courtroom Fan-powered VAV box operation There are 15 courtrooms located on the 9th through 16th floors and each courtroom is currently served by either two or three series fan-powered, dual duct VAV boxes. In order for a series fan-powered dual duct VAV box to maintain space temperature correctly, the series fan must operate continually during building operation. Currently, the fans in the courtroom VAV boxes are turned ON manually based on complaint calls. If the fan within each VAV box does not operate, the air supplied goes directly back into the return plenum. In effect, the main air handler supply fans are unnecessarily circulating air that never reaches the space. When the VAV box fans are OFF, the zone temperature control is poor and bringing the space to comfort conditions can take over 6 hours. Trend data shows that zone temperature typically comes under control within 15 minutes to an hour when the VAV box fans are ON. Ensure the VAV box fans operate as intended to achieve zone temperature control and improve comfort while saving fan energy at the main air handlers. Option 1 (preferred): Command all VAV box fans ON during scheduled building operating hours regardless of occupancy within the courtroom. Control minimum airflow based on CO2 in the courtroom to avoid excessive reheat loads. Option 2: Command each VAV box fan ON when the respective courtroom lights are turned ON. Comfort, Option 1: Eliminate airflow when the courtroom is unoccupied. Courtroom temperature will be controlled for immediate occupancy during building schedule. $10,100 energy savings Payback 1.5 years; Best control Option 2: Save energy only when lights are ON. Potential for energy waste since the fans would operate if the lights were left ON during unoccupied times. Improved temperature control. $3800 energy savings Payback 2.7 years 6 Eliminate exhaust air recirculation Currently the air being exhausted from AHU1, 2, 3, and 4 recirculates back into the outside air intakes. Because of the blending of exhaust and outside air, the measured outside air temperature increases by 10 F when the real outside air temperature is 45 F or less and increases by 5 F between 50 F and 70 F. The elevated outside air temperature means the economizer cycle is less effective and the chilled water plant is required. If the return fans will be turned off as a result from implementing Finding 1 to resolve the building pressurization problem, air will be relieved through gaps in the exterior shell and will not be concentrated at the outside air intakes. Chilled water energy savings and free cooling. $6,800/year Payback: 0.4 years 2005, Portland Energy Conservation, Inc. (PECI). All rights reserved. 3

4 Finding Description of Problem Recommendation Benefits and Payback 7 Modify pump flow rates Almost all of the balancing valves serving the chilled water, condenser water, and heating hot water pumps were only 50% to 60% open. This imposes a significant pressure drop. Many of theses pumps are also controlled by a VFD to modulate flow-rates. In addition, pump data indicates that the design pump head may be unnecessarily high. As a result, excess water may be circulating through each system, which wastes energy and may also be contributing to the system control and instability problems discussed previously. Instability problems must be fixed first before any pump modifications are made. Open each throttling valve to 100% and provide design flowrate from each pump by either adjusting the VFD, trimming the existing or installing a new pump impeller, or a combination of both measures. Energy savings is achieved since the system moves design flow and the pressure drop is eliminated at the balancing valve. Energy, Control. Pump energy savings $10,000/year; 3 year payback More definitive savings and implementation costs will be calculated when actual pump tests are performed. Improved control of hot water supply temperature when the system is not overpumped. 8 Nighttime Lighting Sweep Control After a nighttime walk-through, a significant contributor to the building s 300 kw nighttime and weekend load determined in the utility data was found to be the main lighting on the 3 rd through 7 th floors. Relocate the override switches (add some switches if necessary), reprogram the lighting control system to optimize light operation during unoccupied hours, and reimplement the lighting sweep control for all of the lights on the 3rd through 7th floors. Lighting energy savings $14,200/year Payback: 0.7 years 9 Optimal Start of Air Handling Units The central air handling units are scheduled to start around 3:00 am on Monday mornings and between 5:00 am and 5:30 am Tuesday through Friday mornings. When high outside air temperatures are expected, the air handlers are set to start earlier (approximately 1 am). The early start-up may be a consequence of system control problems as identified in previous findings (Finding 2 and Finding 5). Trend data indicated that a many of zones were brought to desired temperature within 1 hour of system start-up. By solving the root causes of the space temperature control problems, the operators should be able to start the air handlers later in the morning. Implement an optimal start control sequence for the building. Estimate that system operation can optimally start around 6:30 am. Limiting the hours of supply, return, and exhaust fan operation will save fan energy and central plant pumping energy. Estimated energy savings: $8,700/year Payback: 0.3 years (Savings by avoiding 1 hour of operation a day; does not account for extra summer hours of operation avoided) 2005, Portland Energy Conservation, Inc. (PECI). All rights reserved. 4

5 Finding Description of Problem Recommendation Benefits and Payback 10 AHU3 economizer control The economizer control for AHU3 has been overridden at 30% outside air because the return fan motor breaker was continually tripping when the dampers were allowed to fully modulate. The problem is most likely due to improper sequencing between the outside and return air damper interlocks. With the outside air at 30%, chilled water is required even at cold outside temperatures. As a result, the chiller lockout temperature was lowered to 47 F compared to original design sequence of 56 F. A wall adjacent to the outside air damper was sucked in and is now braced (mid-november). Address the damper interlocks and allow economizer to modulate. Allow chillers to run when OAT>56F. Chilled water and free cooling energy savings. Savings if exhaust air recirculation is eliminated: $8,400/year; 0.4 year payback Savings if exhaust air recirculation is not eliminated: $5,400/year; 0.5 year payback 11 Warm-up mode modifications The warm-up sequence is intended to raise building temperature rapidly by closing all outside air intake dampers, shutting off exhaust fans, and supplying warm air to the zones. A warm-up sequence typically occurs before the building is occupied so that ventilation air and exhaust can be reestablished prior to actual occupancy. The current building warm-up sequence is not working correctly warm-up is programmed to occur whenever the return air temperature is less than 70F. Excessive infiltration in the mechanical rooms and shortcircuiting of supply air to the return air plenum (refer to Finding 5) causes the return air temperature to be less than 70 F a significant amount of time when the building is occupied and has a cooling load. As a result, the air handler requires chilled water to meet the cooling load since the economizer is locked out. Shutting off the toilet exhaust fans while the building is occupied leads to an indoor air quality problem. Modify the warm-up control sequences. Potential control strategies include: 1) Base warm-up on discharge air temperature reset to enable warm-up only when there is no cooling load 2) Base warm-up on a lower return air temperature; or 3) Limit warm-up to occur between startup and 8:00 am. Reducing infiltration, short circuiting from courtroom VAV boxes, and improvements to the discharge air temperature reset control sequence should be implemented before a final warm-up control strategy is selected. Energy, Indoor air quality. Fan and cooling energy savings. $7,600/year Payback: 0.4 year 2005, Portland Energy Conservation, Inc. (PECI). All rights reserved. 5

6 Finding Description of Problem Recommendation Benefits and Payback 12 Over Ventilation Outside air in excess of ventilation requirements takes energy to heat and cool. Based on an occupancy of 400 people plus an estimated 200 person transient occupancy, the dedicated outside air fans bring in at least 32,000 cfm more than is required for ventilation. Option 1: Turn off 1 ventilation fan per pair of air handlers. Verify flows at remaining fans. Option 2: Change fan sheave diameters to achieve the desired flow-rate. Option 3: For maximum flexibility over time, add a variable speed drive to control each outdoor air fan (4 fans, 10 hp each). Fan, heating, and cooling energy savings: $4,700/year Payback Option 1: immediate Payback Option 2: 0.2 years Payback Option 3: 4.2 years 13 Chiller 3 operation Chiller 3 is should operate when building loads are 115 tons or less, but chiller s internal controller was set to prevent the unit from operating above 50% full load amps. As a result a second chiller would come on-line and contribute to the chilled water plant instability outlined in Finding 2. Operating personnel eliminated the 50% limit and programmed the chiller to operate at 100% full load amps. With this setting, the chiller will not stay on-line. Investigate Chiller 3 operation with chiller manufacturer (McQuay). Once Chiller 3 becomes operational, it should be used as the base chiller to serve low building cooling loads. Energy, Maintenance. Cost savings and implementation cost have not been estimated for this measure at this time. 2005, Portland Energy Conservation, Inc. (PECI). All rights reserved. 6

7 #3 Priority: Controls Optimization Finding Description of Problem Recommendation Benefits and Payback 14 AHU1 and AHU2 Static pressure reset AHU 1 and 2 static pressure setpoint of 3 inches never resets, although the control sequences call for reset. Implementing static pressure reset reduces supply fan energy as static pressure setpoint is lowered to the minimum value. Reset discharge air static pressure per the original design sequence of operations. A few zones may be driving the system to maximum static pressure due to zone control problems or the sequence itself may not be programmed correctly. Reduced fan energy. $2,400/year Payback: 0.6 year 15 AHU5 and AHU6 Hot deck static pressure control Trend data indicates that AHU5 and AHU6 discharge air static pressure is maintained 0.5 in.wc. higher than setpoint, which wastes fan energy. Review the static pressure reset control sequence and tune the PID loop so that actual static pressure meets setpoint. Reduced fan energy. $2,500/year Payback: 0.6 year 16 Turn off Minimum ventilation air fans during economizer mode 17 Cooling tower controls Dedicated outdoor air fans (for ventilation air) run even in economizer mode, when excess outside air is provided for cooling. Currently there are three cooling towers serving all of the chillers and each cooling tower contain two fan motors a 7.5 HP motor for low speed and a 25 HP motor for high speed operation. cooling tower fans typically cycle between low and high at 8 minute intervals at relatively mild outside air conditions. Only one or two cells are typically used during normal operation, which results in increased fan energy usage. The difference in the condenser water supply and return temperature is typically 4 F, with the lowest condenser water supply temperature at 70 F. Reprogram to turn off outdoor air fans when economizing. The ventilation fans will still operate when outside air temperature is above 70 F or below 40 F. Option 1: Adjust cooling tower control strategies as necessary to optimize condenser water supply temperature and reduce fan cycling. Control optimization includes: Allow condenser water to flow across all three cooling towers. Lower minimum condenser water temperature setpoint to 65 F (per original design sequence). Improve fan staging Option 2: In addition to opening all three isolation valves and lowering the condenser water setpoint (see above), install VFDs on each 25 HP cooling Fan energy savings. $2,800/year Payback: 0.8 year Control, Energy, Maintenance. Improved motor life by eliminating cycling. Improved condenser water temperature control for chilled water plant stability. Option 1:$1,300/year Payback: 1.1 years Option 2: $2,700/year Payback: 7 years 2005, Portland Energy Conservation, Inc. (PECI). All rights reserved. 7

8 tower fan motor to improve control. Finding Description of Problem Recommendation Benefits and Payback 18 Isolation valves on the cooling tower Due to the cooling tower configuration, a shut down and draining of the condenser water system is required to clean the tower sumps or repair a leak in them. To separate the sumps so that one sump can be drained while the others remain active, knife valves need to be added to the flumes and isolation valves must be added to the return water connections from the basins. Maintenance Because shut down of the cooling towers makes a critical system nonoperational, the work must be scheduled during non-normal working hours. Adding isolation valves makes the system less susceptible to a total outage if any one tower fails. $2000 savings per maintenance cycle Payback: 5.8 years. 19 Minimum VFD speed on Hot Deck Supply Fans Trend data shows that AHU5 and AHU6 supply fan speed never dropped below 40%, which indicates this is the minimum programmed speed for the VFD. Investigate the lowest speed for efficient VFD operation and change VFD settings. Reduced fan energy. $800/year Payback: 1 year 20 Perimeter office occupancy sensors: floors 4, 5, 6, and 7 The lights in the majority of private offices located on the 4th through 7th floors are controlled by both wall switches and occupancy sensors. Due to problems with the lights turning off even if the offices were occupied, most of the occupancy sensors have been disabled. These problems could be resolved by moving the occupancy sensors to better locations within their spaces. $1,800/year Payback: 2.8 years 2005, Portland Energy Conservation, Inc. (PECI). All rights reserved. 8

9 Other Findings Identified Finding Description of Problem Recommendation Benefit 21 Ventilation air Preheat control Each primary cold-deck air handling unit is served by its own dedicated ventilation air fan, and each ventilation fan has a pre-heat coil that temper the air when outside air temperature is cold. During a site visit, the ventilation air fan pre-heat control was observed to be functioning incorrectly, leading to simultaneous heating and cooling. The air temperature downstream of the pre-heat coil was approximately 85 F when it should have been controlled to the discharge air temp setpoint of 55 F. This condition caused the economizer to bring in more outside air to meet the 55 F discharge temperature setpoint. Investigate the control strategy and tune the preheat coil control loop. Reduced heating plant energy. 22 Chilled water temperature reset The chilled water supply temperature is to be reset between 42 F and 48 F based on chilled water valve position and return air relative humidity. With poor humidity sensor calibration in combination with poorly controlled chilled water valves, the chilled water supply temperature does not reset properly and is always 42 F. A lower-than-necessary chilled water temperature may also be contributing to some of the instability problems outlined in Finding 2. In the fall and winter, facility operators typically override the chilled water setpoint to 45 F. Modify the chilled water temperature reset control strategy to maintain return air relative humidity at 60% rather than 50%. This provides a reasonable amount of tolerance without sacrificing space comfort. In addition, only two of the current four return air relative humidity sensors should be used in the control strategy i.e. one sensor to serve AHU1&2, and one sensor to serve AHU 3&4. Annual maintenance costs are saved due to the reduced calibration requirement. Energy savings not estimated at this time due to chilled water plant instability. 23 Relative humidity sensor scaling factors The outside air and return air relative humidity sensors associated with AHU3 do not have the correct scaling factors programmed into the BAS. As discussed in Finding 22, relative humidity sensors require frequent calibration to ensure accurate measurement of air conditions and these values can cause operational problems since several control strategies are based on Corrected the scaling factors for return air relative humidity sensor completed by BRCS and JCI during PECI investigation. Do the same for the outdoor air RH sensor. Schedule calibration of all relative humidity sensors at least twice per year and minimize the number of sensors Energy savings not estimated at this time. Energy savings associated with this measure could impact the chilled water plant and economizer control. 2005, Portland Energy Conservation, Inc. (PECI). All rights reserved. 9

10 relative humidity. used in each control strategy. Finding Description of Problem Recommendation Benefit 24 Extended surface area filters 25 Elevator standby operations 26 Return fan VFD control Currently the outside and supply air streams for all air handling units are filtered multiple times before being delivered to the space. Each filter imposes a pressure drop on the air stream, which increases fan energy. Depending on the frequency of replacement, and the type of filters used, energy and material savings may be possible by removing some of the filters and installing more efficient ones with decreased pressure drop. The potential exists that all elevators in the courthouse remain in stand-by mode during typical unoccupied hours (6pm to 6am Monday Friday and 24 hours per day on weekends and holidays). There could be significant energy waste associated with stand-by modes. During the building pressurization test, the supply and return fans for all central air handling units were shut off at each individual VFD using the hand-off-auto switches. However, when the supply fans were turned back on and fan speed was being adjusted at VFD keypad, building staff indicated that the return fans turned ON as well, even though they were in the OFF position at the VFD. The recommendation is to evaluate potential for installation of extended surface area filters and removal of some of the existing pre-filters. Extended surface area filters typically have a lower initial pressure drop and have larger collection capacities, which allows for less frequent replacement. This measure requires further investigation with facility personnel to ascertain feasibility of implementation. Where banks of elevators exist, during unoccupied hours, schedule 1 elevator in stand-by mode and turn the others OFF. Further investigation and testing is needed to verify and correct the problem. Energy, sustainability. Energy savings not estimated at this time. Safety. 2005, Portland Energy Conservation, Inc. (PECI). All rights reserved. 10

11 27 VAV box operation A variety of problems with VAV box operation have been identified through trend analysis: Simultaneous heating and cooling Incorrect minimum heating airflow setpoint Incorrect minimum cooling flow setpoint Oscillating air valve at night Leakage through the hot deck dampers may exist. Further review and investigate all VAV boxes throughout the building and correct operating parameters as necessary. For example if a regular maintenance program were implemented to check 20% of boxes each year, within 5 years all of the boxes could be checked and maintained. Comfort, Energy, IAQ. Reduce comfort complaints. Correcting simultaneous heating and cooling. Correct ventilation airflow setting. Reduce damper actuation frequency for longer life. 2005, Portland Energy Conservation, Inc. (PECI). All rights reserved. 11