Page 113 - Zero Net Energy Case Study Buildings-Volume 1

SCIENCE & ENGINEERING BUILDING I
This mispositioning of the pressure sensors is not an uncommon experience; the location of pressure sensors in laboratory supply air ductwork should therefore be checked and evaluated during the commissioning process to avoid the resulting failure to meet design airflow require- ments along with excessive energy use.
Correction of Design Air Flow Rates
As part of best practices in laboratory design required by UC Merced for maintaining minimum ventilation rates for safety and maximum ventilation rates for energy efficiency, the design ven- tilation rate was set at six air changes per hour (6 a.c./hr). The design engineers set this rate for the supply side of the system. The exhaust side operated at an air flow rate higher than that es- tablished as the maximum design flow rate at the exhaust fume hood. By adjusting the exhaust air flow rate to 6 a.c./hr as originally intended, energy was saved by reducing the ventilation fan speed to achieve this rate.
Correction of Supply Fan Speed Controls
It is noted in the HVAC system description that two fans serve each floor of the building; the second fan assures that airflow will continue through the lab spaces if the first fan fails. When the two fans are both normally operating, they each are supposed to operate at comparable lower speeds to provide the required ventilation air. These fans were designed with a control logic known as “PID loop”, which is basically a type of “cruise control” for the fan and which should result in this equal fan power operation.
However, measured data from these fans showed that the design of the control system’s PID loop was erroneously causing one fan to operate at 100% full power while the second fan was operating at 30% full power. This operation had a major impact on the energy used by the two-fan combination since higher fan power operation literally has an exponential effect on the energy demand for that fan. The fan operating at full power was responsible for an exaggerated amount of energy use compared with the other fan.
Once alerted by the measurements, the controls engineers changed the control logic so that both fans operated at the same speed, still moving the same amount of air as required for the laboratory space. This simple adjustment resulted in an energy savings for all fans in the build- ing of about 35% compared to the pre-correction operation. See the accompanying chart, which shows the comparative energy use under the two conditions of fan operation.
Discovery and Replacement of Failed Exhaust Fan
Another advantage of close monitoring of the energy use using the installed meters and online viewing of the data analysis is the discovery of system problems that normally go undetected, at least for long periods of time, because of the backup systems in place to cover for system com- ponent failure. These failures often result in a significant increase in energy use that are normally only detected through diligent review of energy bills.
An example of this occurred in Science & Engineering Building I six years after the building was occupied. As described in the description of the design of the HVAC system, there are four ex- haust fans that are constantly operating at various speeds to remove exhaust air via the labora- tory fume hoods. These exhaust fans are linked together so that in the event of failure of one fan, the other three fans increase their speed to make up the difference. Again, because the energy use by a building fan increases exponentially with the increase in fan speed, such a failure will result in a sizable jump in energy use.
Such an exhaust fan failure occurred in early 2012 and the increase in fan speed of the other three fans was not detected by the building control system. The failure would have gone unno- ticed except that the building energy-use metering system picked up the spike and was noticed by the UC Merced facilities staff who were monitoring the energy performance on a routine basis.
CASE STUDY NO. 5
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