Example Retrocommissioning Measure: Opening Throttled Discharge Valves

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Lambert Wood
9 years ago
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1 Opening Throttled Discharge Valves This 21-story building, constructed in 1997, is located in Oregon and contains 589,000 gross square feet of mostly office occupancy. The HVAC system includes six large air handlers, 400 variable air volume terminal units, five boilers, three chillers, and three cooling towers. The RCx investigation revealed that the discharge valves for the nine condenser water pumps were all set at approximately 50% closed. This indicated that the pumps, ranging from 10 HP to 40 HP, were oversized and could generate more pressure than the system actually requires. When the facility s condenser water system was originally tested and balanced, each pump s discharge valve was gradually throttled down until its design flow rate was achieved. This method of flow control consumes more energy than using properly sized pump impellers and open discharge valves. As part of this RCx measure, pump tests were conducted to determine the impeller size necessary for achieving design flow with the discharge valves 100% open. The impellers for all of the condenser water pumps were trimmed to the appropriate diameter, and the discharge valves were opened. Total condenser pump power was reduced by 38% as a result of reducing the pressure drop across the discharge valves. Water Pressure (Energy) Wasted energy due to oversized impeller and throttled discharge valve. System curve before impeller trim. Discharge valve is partly closed to absorb excess pressure produced by pump. Curve shifts down after impeller trim. Pump produces less pressure, no throttling required. Location in System (see diagram below) Estimated annual electric savings $7, ,053 kwh Implementation cost $6, years From Cooling Tower Pump Discharge Valve To Chiller

The RCx investigation revealed that the discharge valves for the nine condenser water pumps were all set at approximately 50% closed.

2 Modify VAV Box Flow Setpoints The campus consists of four buildings, totaling 805,000 square feet of offices and computer software development labs. The HVAC systems include 34 air-handling systems, hundreds of variable air volume (VAV) terminal units, two chiller plants, and two heating water boiler plants. Investigation of building occupancy trends and design assumptions revealed an actual occupancy of 1,850 people, much less than the original design s assumed continual occupancy of 6,000. This large difference in occupancy impacted the HVAC system in two ways: 1. The actual cooling load was less than design, which caused the VAV boxes to operate at their minimum flow setting for much of the time. At minimum flow, these boxes were often reheating the air just to avoid overcooling the space, causing simultaneous heating and cooling and wasting energy. 2. The actual ventilation load was less than design, leading to overventilation of the spaces, even with the VAV boxes operating at their minimum airflow setting. Design cooling load with 24/7 occupancy and operation With scheduled operation, design cooling load is greater than actual cooling load VAV box minimum flow settings can be lowered to save energy The flow settings for the VAV boxes were recalculated and adjusted based on actual observed conditions. On average, the minimum flow settings were reduced by 40%. This modification helped the facility reduce its fan energy (lower fan speeds) and heating and cooling energy (reduced simultaneous heating and cooling). Estimated annual electric savings $24, ,980 kwh Implementation cost $20, years

Investigation of building occupancy trends and design assumptions revealed an actual occupancy of 1,850 people, much less than the original design s assumed continual occupancy of 6,000.

3 Reduce Simultaneous Heating & Cooling This 300,000 square foot silicon wafer fabrication facility in Oregon, constructed from 1997 to 1999, includes class 1, ,000 clean rooms. One of the building s main clean room make-up air handling units, a large 100% outdoor air system delivering 42,000 cfm, was adequately maintaining the clean room s tight temperature and humidity requirements (68ºF ± 1-1/2ºF, 45% RH ± 5%). Even though the system was ultimately delivering air at the proper temperature and humidity, the air handling unit s individual heating and cooling components were competing with each other by operating simultaneously. The preheat coil heated the 81ºF outdoor air to 115ºF, then the cooling coil cooled the air down to 40ºF, followed by the reheat coil heating the air to 46ºF. Since cooling the air to 40ºF also dehumidified it too much, the steam humidifier was then injecting steam into the airstream. To eliminate this simultaneous heating and cooling and unnecessary humidification, the following minor adjustments were made to the system: The preheat coil shutoff valve was integrated with the main control system so that the valve shuts off steam to the coil when it is not needed. Temperature sensors that were out of calibration were replaced. The control sequence was revised for more stable and efficient operation. Outside Air Damper Steam Preheat Coil Chilled Water Cooling Coil Steam Reheat Coil Humidifier Supply Fan HEPA Filters 81 F Pre-RCx: 115 F Post-RCx: 81 F Pre-RCx: 40 F Post-RCx: 46 F 46 F 54 F Pre-Filters Final Filters Temperature, F Pre-RCx Estimated annual total gas and electric savings $84,000 Implementation cost $7,000 Post-RCx Hatched area represents wasted energy due to simultaneous heating and cooling Point in Air Handler 0.1 years

requirements (68ºF ± 1-1/2ºF, 45% RH ± 5%).

4 Disabled Economizer Control This 21-story building, built in 1997, contains 589,000 gross square feet of mostly office-type occupancy. Its HVAC system includes six large air handlers, 400 variable air volume terminal units, five boilers, three chillers, and three cooling towers. The outside air damper related to a 120,000 cfm air handling system was locked at 30% open to remedy return fan operational issues that occurred when the system went into economizer, or free cooling, mode. With the economizer disabled, the system was requesting chilled water at outside air temperatures as low as 45ºF. At this temperature, the system could be using 100% outside air alone to cool the facility. If the economizer system were in operation, the air handler could use a higher percentage of outside air to provide cooling, rather than relying on mechanical (chilled water) cooling. This would reduce the energy used by the HVAC system. The operational issues related to the return fan were addressed and the airside economizer system was returned to fully modulating automatic control. Mixed Air Temperature, F Performance with damper locked at 30% Hatched area represents times of additional chiller energy use due to locked outside air damper Estimated annual electric savings $5,465 74,857 kwh Implementation cost $2,800 Outside Air Damper Performance years Outside Air Temperature, F Performance as fully modulating economizer

The outside air damper related to a 120,000 cfm air handling system was locked at 30% open to remedy return fan operational issues that occurred when the system went into economizer, or free cooling,

5 Modify Heat Pump Schedules This seven-story, 125,000 square foot office building in California holds 85 different tenants. Its heat pump HVAC system includes 175 water source heat pumps, two water loop circulating pumps, and two fluid coolers. The regular HVAC operating schedules had been modified to accommodate temporary after-hours occupancy, rather than operating the system under a temporary override. As a result, the entire heat pump system was operating when the building was unoccupied, even after the temporary occupancy period had passed. This savings opportunity was identified through system trend analysis and use of data loggers that revealed the modified heat pump schedules. The schedules for the heat pumps, water loop circulating pumps, and fluid coolers were modified to reflect actual building occupancy schedules. The building operators were trained on how to accommodate temporary after-hours occupancy requests. System operation was monitored through trending of the building control system and use of data loggers to confirm that the HVAC system was operating in accordance with the new schedules. Utility interval data also confirmed a reduction in operation during weekends and other unoccupied periods. Power (kw) Fluid Cooler Spray Pumps Pre- and Post-RCx Average Daily Load Shapes Pre-RCx Post-RCx 0 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 Weekdays - Pre-RCx Weekdays - Post-RCx Estimated annual electric savings $17, ,460 kwh Implementation cost $240 Immediate Weekends and Holidays - Pre-RCx Weekends and Holidays - Post-RCx

The regular HVAC operating schedules had been modified to accommodate temporary after-hours occupancy, rather than operating the system under a temporary override.

Commissioning - Construction Documents (Page 1 of 6)

Commissioning - Construction Documents (Page 1 of 6) A. General Information Climate Zone: Building Type: Conditioned Area (sf): Reviewer's Name: Reviewer's Agency: Note: Design Review for each system/subsystem