## Motorola: Cleanroom Declassification from Class 10,000 to Class 100,000[^1]

Project Benefits Summary

+-------------------------------------------------+--------------------+
| ### *Estimated Annual Energy Cost Savings*      | ### *\$154,940*    |
+-------------------------------------------------+--------------------+
| ### *Actual Project Cost*                       | ### *\$89,700*     |
+-------------------------------------------------+--------------------+
| ### *Project Payback*                           | ### *7 months*     |
+-------------------------------------------------+--------------------+

### Facility Description

The Motorola AIEG facility in Northbrook, Illinois is part of the
Motorola Automotive and Industrial Electronics Group. The facility
includes a 6,700-ft^2^ class 10,000 cleanroom used for test and assembly
of automotive electronics controllers. The building also contains office
space and another production area. A single air handler serves the
cleanroom and includes two parallel supply fans and two parallel return
fans that supply the cleanroom through ceiling mounted HEPA filters.
Each of the fans has adjustable pitch fan blades. Twelve steam
humidifiers and thirteen duct-mounted electric reheat coils humidify and
reheat the supply air to each room to maintain the 70°F ±2°F dry bulb
and 45% ±5% relative humidity setpoints for the cleanroom.

#### Project Description

The purpose of this project was to reduce operational costs and energy
use by reducing the cleanroom classification from class 10,000 to class
100,000. To accomplish this airflow was reduced but the ceiling grid and
number of HEPA filters remained the same to allow for future flexibility
in the cleanrooms. The facility currently operates at class 100,000 or
better. Measures were also implemented to improve temperature and
humidity control to reduce unnecessary dehumidifying when the outside
air is already below the cleanroom humidity setpoint.

The air handling unit supply volume (return air and outside air) was
reduced from 67,000 cfm to approximately 30,000 cfm (10 cfm/ft^2^ to 5
cfm/ft^2^) by shutting down one each of the supply and return fans. The
pitch of the blades on the existing fans were modified to further reduce
the airflow and decrease energy use. The supply air temperature setpoint
had to be decreased from 67°F to 63.7°F with the reduction in supply
airflow because the heat load in the room remained the same. Since
dehumidification demand requires the cooling coil to cool the air to
48°F, much less energy is needed to reheat the air to meet the lower
supply temperature setpoint. As a result of this improvement, the peak
load for reheating the supply air is expected to drop from 412 kW to 150
kW. The actual savings are still being measured but the estimated energy
use impacts are shown in table 1.

####### Table 1 ‑ Estimated Energy Savings

  ----------------------- --------------- --------------- ---------------
  *Operation*             *Previous       *Current        *Savings
                          (kWh/y)*        (kWh/y)*        (kWh/y)*

  Fan Operation           825,700         130,700         695,000

  Reheat During Cooling   1,795,100       549,000         1,246,100

  Cooling                 615,800         301,600         314,200

  Heating                 557,700         314,000         243,700
  ----------------------- --------------- --------------- ---------------

There are huge energy savings due to the reduction in fan power and and
reheating of the supply air. Obviously, turning fans off saves energy,
but adjusting the pitch of the fan blades also contributes to the energy
savings. When the pitch of the blades is modified, the fan will only be
able to supply the amount of air required and motor energy can be
minimized. Adjusting blade pitch also results in a change in fan
efficiency (up or down, depending upon the original blade position),
however this impact is small relative to the overall reduction in motor
power required to deliver less air.

More precise control of cooling coil dehumidification was achieved by
installing a dewpoint sensor after the cooling coil. When the outdoor
air dewpoint is below 45°F (the room setpoints require a dewpoint of
about 48°F) during cool, dry seasons like spring and fall, the air does
not need to be dehumidified. Adjustment of control of the cooling coil
to only cool the air down (if cooling is needed) to meet the required
70°F dry bulb temperature setpoint then saves by reducing the energy
needed to cool the air all the way down to 48°F and reducing the energy
needed to reheat the air back up. This control also prevents unnecessary
dehumidification by the cooling coil that, in turn, requires more steam
to raise the relative humidity of the air to the required 45% setpoint.

###### Applicability to the Cleanroom Industry

Significant energy was saved on this project because all of the
recirculated and outside air is dehumidified and reheated. Therefore, a
50% reduction in airflow not only reduces fan energy but also greatly
decreases the amount of energy needed to condition the smaller quantity
of air. The energy use benefits of changing cleanliness classification
are vividly demonstrated by the work at Motorlola. However, very few
facilities are capable of changing cleanliness classification. It is
worth considering primarily for facilities that have modified operations
to include less sensitive processes or in facilities where the original
classification has proven far cleaner than is actually required for the
manufacturing process that was implemented. The Motorola facility is
quite small and this type of conversion is likely to be much more costly
for a large facility, however, the energy use benefits are so large,
that it is likely to be a worthwhile investment with a very short
payback even in the largest facilities.

Typically, cleanroom HVAC systems use separate makeup air and
recirculation units and only the makeup air from outside needs to be
conditioned. This method is much more efficient because only the makeup
air is dehumidified and reheated to meet the appropriate temperature and
humidity setpoints when mixed with the recirculation air. Since the
recirculation air is already close to the room setpoints (typically
slightly warmer), it can provide a large portion of the heating needed
for the makeup air when the air mixes and the amount of reheat required
for the makeup air can be further reduced.

[^1]: Based on "Motorola AIEG, Northbrook, Illinois, Cleanroom
    Conversion Study." Prepared by Black &Veatch ATD; April 29, 1999.