Heating and Cooling Energy - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 244

systems with larger variations in load. The emergence of variable speed
drives and DDC control systems made the operation of these systems
much more effective. Newer chillers with digital control panels are able
to operate effectively and safely with variable flow. Another significant
advantage of the primary-secondary system is the system flexibility that
it offers. This type of system makes it easier to incorporate hybrid sys-
tems, as well as thermal storage systems and water-side economizers.
Depending on the piping and valving arrangement, the system can load
chillers evenly or sequentially. They also allow for the preferential load-
ing of particular chillers as required in a hybrid system to gain the maxi-
mum benefit. The complexity of these systems requires a well developed
sequence of operations to ensure that the control system will provide the
proper operation.
Condenser water systems for electric chillers are usually designed
with a 10°F temperature differential. Absorption chiller systems may oper-
ate with higher temperature differentials due to the greater amount of heat
rejected from these units. There may be benefits for electric chiller systems
in using a larger temperature differential for the condenser water system.
The primary benefit is the reduction in the quantity of water to be pumped
for the condenser water system to reject the same amount of heat. This al-
lows the use of smaller piping and pumps. The higher temperature will
improve the efficiency of the cooling tower, but will reduce the efficiency of
the chiller. There is a reduction in first costs due to the smaller pumps and
piping with no change required in the cooling tower or the chiller.
An oversized cooling tower is generally beneficial. Since it provides
additional capacity and an allowance for equipment problems. For oper-
ating costs, there is a reduction in pumping energy, possibly a reduction
in cooling tower energy, offset by an increase in chiller energy. The net im-
pact depends on the size of the system, amount of pumping, climate and
hours of operation, but generally results in a net reduction in energy con-
sumption.
EXHAUST AIR
Exhausting air to outside is an effective way to provide a safe and
comfortable working environment for industrial workers. Many exhaust
systems are designed for peak demand and operate 24/7 with little or no
controls. Normally, one fan controls several exhaust inlets. There are no