CEMP-E
TI 810-10
1 February 1999
design guidance from both ASHRAE and manufacturers' literature prior to designing these
systems, as they have many unique design characteristics.
3-7. DESSICANT DEHUMIDIFICATION. Both the ASHRAE Handbook Fundamentals and
Handbook Applications describe several applications where desiccant dehumidification should
be considered. These applications include instances where the latent load is large in
comparison to the sensible load, instances where the energy costs to regenerate the desiccant
is low relative to the energy costs required to dehumidify the air by chilling it below its dewpoint,
missile assembly buildings, waveguide housings, and radomes.
3-8. THERMAL ENERGY STORAGE. Consider using thermal energy storage (TES) where, for
example, it could reduce peak power demand charges, provide additional cooling capacity
where it is more life cycle cost effective than adding cooling equipment, or provide life cycle cost
effective redundancy necessary to ensure reliability for critical applications.
In many instances, utility deregulation is changing the cost structure of the power purchased by
our customers. Subsidies for installing thermal energy storage and incentives for reducing the
peak demand are not as prevalent as they were just a few years ago. It is imperative that the
designers obtain the current utility rate structure and become knowledgeable about probable
future utility costs so that accurate assumptions are used when determining the feasibility of
using TES. Other factors of note include the unique methodology required to size a TES
system, including both the hourly cooling load for the facility along with the hourly power
consumption of the installation.
Where "ice-on-coil" is used as the method for TES, the loss in efficiency that occurs when
chilling water to a lower design temperature must be factored into the life cycle cost analysis.
This loss in efficiency may be somewhat offset by the lower temperature of the air entering the
condenser during the hours when the system is "recharging." For facilities where a water tank is
required, it may be advantageous to specify a tank suitable for storing chilled water. Regardless
of the type of TES system specified, ensure that the supply water from the storage tank is at or
below the required entering water temperature of all cooling coils during the last hour that the
TES will be used at the outdoor design conditions specified.
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