Alternativa 2

The Kleberg building first underwent retro-commissioning in 1996. Prior to this, a faulty building pressure sensor caused nearly 100% outside air to enter the building. One exception was that a faulty carbon dioxide sensor on one AHU caused its outside air damper to remain fully closed at all times. The hot water control sequence in place for two of the AHUs caused simultaneous heating and cooling. All AHU cold deck temperature set points were a constant value.

During the first round of retro-commissioning, some programming changes were implemented in order to ignore the faulty building pressure sensor, and instead use two

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other sensors with calibrated output in order to regulate outside air intake. The building pressure set point was also lowered at this time. The faulty carbon dioxide sensor on one AHU was replaced. The hot water sequence on two AHUs was modified to eliminate simultaneous heating and cooling, and a dead band between operation of the valves was established. The cold deck temperature set point for all AHUs was changed to reset with outside air temperature. The economizer mode was made to operate when outside air dry bulb temperature was below 60°F, attempting to maintain a 57°F cold deck temperature. The chilled water pumps were programmed to stage on one at a time according to demand. A night setback was implemented to lower the AHU static pressure set point and raise the cold deck temperature set point.

After the first round of retro-commissioning in 1996, some follow up work was performed in the period between June 1998 and April 1999. This focused on air balance in laboratories, terminal box calibration, and improved exhaust control. Temperature sensors, static pressure sensors, and AHU VFD outputs were calibrated. The cold deck temperature reset schedule was modified slightly, although it continued to be based on outside air temperature. Thermostats and controllers were repaired, and the control program for laboratories and offices was modified. The static pressure set point in the exhaust duct was set much lower than it had been, and the pressure sensor was calibrated. The result of this follow up work was a slight increase in electricity savings. Hot and cold complaints in 2000 and 2001 in the building resulted in additional commissioning follow up work being performed. This further investigation found a combination of changed control parameters and maintenance problems that were causing excessive energy consumption and comfort problems. For one of the air handling units, chilled water valves would not fully close, creating colder than desired discharge air temperatures, and in turn causing the preheat valve to operate unnecessarily due to the way in which it was programmed to control. Failed CO2 sensors and a failed building pressure sensor caused the outside air dampers on some of the air handling units to remain fully open at all times. The chilled water pumps, which had been programmed to

stage on and off as needed, were in bypass mode and remained on at full speed at all times, resulting in excessively high loop differential pressures. These problems and others were identified and corrected. (Chen, 2002)

Since only minor programming changes occurred between 2000 and 2009, the resultant increase in chilled water savings during that time period can most likely be attributed to the follow up work already described. This allowed savings to even exceed what had been achieved originally by retro-commissioning. Hot water consumption continued to climb, however, noted in more recent years when metering was again installed. Electricity savings increased in recent years, most likely due in part to a building lighting retrofit that took place in March 2005.

Some follow up investigation was performed in 2007. At this time, numerous maintenance problems were identified in the building. The two large AHUs were both found to be operating as constant volume units because their fan blade pitch control mechanisms were stuck in one position. These units also had problems with return air and relief air damper operation, and their return air fans were therefore turned off. Only one chilled water pump was operating, but it had been commanded to remain at full speed. Only one of the three hot water pumps was operable. A sampling of terminal boxes in the building revealed that the majority sampled did not have operable fan motors. Numerous other problems were discovered as well, including dirty coils and a few leaking hot water valves. The decision was made by management to suspend retro- commissioning activities and instead invest in retrofits of the equipment.

Figure 5-5 shows the normalized consumption values over time of chilled water, hot water, and electricity for the Kleberg building.

Figure 5 - 5. Normalized energy consumption over time for the Kleberg building.

5.6 Koldus

The Koldus building first underwent retro-commissioning in early 1997. Prior to this, both the chilled water and hot water systems had constant differential pressure set points. However, both pumps were in manual control resulting in excessively high pressures in the two loops. The AHUs each had constant discharge air temperature and static pressure set points. The economizer mode on the AHUs was enabled at outside air temperatures less than 55°F and maintained a mixed air temperature of 55°F. During non-economizer mode, outside air intake was found to be higher than needed. AHU return fans were found to run continuously during occupied periods. Four of five AHUs

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already shut down each night from midnight to 5:00 AM. One AHU was commanded in manual override to a constant speed. Some hallways and other rooms were found to be colder than desired. Hallway thermostats were found to set in the mid to low sixties. During retro-commissioning, the chilled water and hot water differential pressure set points were set to reset based on flow rates. The chilled water and hot water pumps were set up to turn off and on based on outside air temperature. The discharge air temperature and static pressure set points for each AHU were set up with an outside air temperature based reset schedule. The return fans were given flow set points five to ten percent less than the supply air during normal operation, and 1,000 cfm less than supply air during economizer operation. Air leakage was measured to be high through the closed outside air dampers on the AHUs, so the outside air dampers were set to remain closed during normal operation. The AHU shutdown schedule was extended to 10 PM to 6 AM on weekdays and 9 PM to 7 AM on weekends. All thermostats were set to 73°F for cooling and 69°F for heating.

Another round of retro-commissioning was performed in 2001. At that time the differential pressure set points for both the chilled water and hot water loops were altered to utilize an outside air temperature based reset schedule. The static pressure reset schedule for five of the AHUs was altered to utilize slightly lower values than had been implemented during the initial retro-commissioning. Some mechanical issues were identified during this round of retro-commissioning, but it was unknown if they were ever repaired.

A building lighting retrofit occurred in March 2005.

A follow up investigation was performed in 2008. It was found that both the chilled water and hot water loop differential pressure set points were reset based on outside air temperature, but the limits were slightly different than what was implemented in 2001. The second chilled water pump and the second hot water pump were both inoperable. AHU static pressure and discharge air temperature reset schedules were still based on

outside air temperature, but were altered slightly from the 2001 values. The economizer cycle for the AHUs was activated when outside air temperature was three degrees or more below the return air temperature. All AHUs were found to run continuously. Numerous mechanical problems with terminal boxes were found, including bad flow controllers and some boxes without reheat valves.

The chilled water and electricity savings in the most recent years were very close to those achieved in the years immediately following the first round of retro- commissioning, while hot water consumption had increased to a level more than twice the value before initial retro-commissioning. This was very suspicious, especially considering the lack of changes in control programming and in chilled water and electricity consumption over time. A metering problem was suspected. The 2008 investigation had confirmed that the metering at that time was accurate, and consumption values were believable. Energy balance plots from the data from both metering systems appeared feasible, though they were obviously different. Guanjing Lin, a Ph.D. candidate in mechanical engineering, studied the data further using a simplified energy analysis procedure. From this procedure, she was able to conclude that the hot water data from the previous metering system was inaccurate, since models of the building would not produce the hot water levels recorded at that time. Hot water levels recorded from the newer metering system were determined to be feasible based on the simplified energy analysis procedure. Therefore, it was concluded that no comparison of savings for hot water consumption could be accurately be performed for this building.

Figure 5-6 shows the normalized consumption values over time of chilled water and electricity for the Koldus building, as well as the hot water consumption since the new metering was installed.

Figure 5 - 6. Normalized energy consumption over time for the Koldus building.