10 July 2002
Piping Insulation. Refer to ASHRAE Handbook Refrigeration and IIAR
Ammonia Refrigeration Piping Handbook.
Control Systems. Design control systems, including control software
applications, with safety interlocks, alarms, and shutdowns. Provide programmable
logic controller (PLC) based systems with ladder logic documentation. Alarms with
automatic notification must be integrated. Automatic alarm notification should be first to
the area supervisor onsite location. If no response, automatic alarm notification must
notify the 24-hour watch. This can be accomplished via a dedicated telephone line.
Control systems, having communication and data logging, permit systems
to operate at optimum conditions under transient load conditions. This should include
staggered startup of multiple compressors and other refrigeration loads. Due to this,
and stored product requirements, refrigerated control systems can become complicated.
Recommend simple installations if at all possible. Basic control systems for an
ammonia liquid recirculation system have approximately 100 input and output (I/O)
signals. These include evaporator pressure regulation, backpressure regulation,
capacity control, hot gas bypass, room temperature, and concrete slab temperature.
Control system designs should be reviewed and approved by the local O&M entities.
Before application of energy management systems/load shedders to
refrigeration systems, and related fans and pumps, the designer will ascertain that
application will be neither conducive to equipment damage nor counterproductive.
Safety trips, compressor slugging, freeze-ups, and loading of circuits may become more
likely to occur.
Defrosting. Spaces maintained at 2 degrees C (35 degrees F) will be
defrosted with ambient air. Spaces maintained below 2 degrees C (35 degrees F) will
use either a hot-gas or electric-heat defrost system. For safety reasons, electric defrost
should be avoided on ammonia systems. For a defrosting system, choose between a
timer defrost controller or a demand defrost controller.
Timer defrosting is a time initiated and time terminated control method that
has an adjustable defrost duration and number of cycles in a 24 hour period. The timer
defrosting is the most common method of defrosting control. Winter and summer
conditions require different defrost duration and cycles. Demand defrost is a defrosting
control method initiated by measuring the air pressure drop across the coils. Demand
defrost is a more efficient defrost control method.
Seismic Zone Requirements. The geographical location of a facility
determines its seismic zone. The seismic zone locations have requirements for building
design and restraint of equipment. Refrigeration facilities for cold storage must meet
seismic design requirements. Refer to TI-809-04 Seismic Design for Buildings at
Refrigerant Management. The Air Force document AF Refrigerant
Management Handbook may be of assistance during the preparation of a facility
refrigerant conservation and replacement program. The handbook is available on CCB.