Hi Etta,

I found the discussion below in the DOE2 help manual. I would be happy to
look at your input if you want to send it to us/me. I couldn't do it until
the end of the day but would be willing to.

Carol

Volume 2r: Dictionary - Refrigeration
Systems>
Refrigeration Equipment
REFG-SYSTEM

This command is the foundation upon which you build a refrigeration system.
DOE-2 defines a refrigeration system to be a closed set of components
(circuits, loads, compressors, condensers, etc.) that share a common
refrigerant. The system is closed because the refrigerant in the system can
flow to any of the components in the system, but cannot flow to any
components outside the system (Figure ??). The common point in each
systemis the liquid receiver tank immediately downstream of the
condensers. From
here, one or more liquid circuits deliver refrigerant to various loads. The
loads evaporate the refrigerant, and suction circuits pass the
refrigeranton to one or more suction groups (compressor racks). Each
suction group has
one or more compressors. The compressors discharge into one or more
discharge circuits, which pass the refrigerant on to one or more condensers.
The condensers discharge liquid refrigerant into the liquid receiver.

The REFG-SYSTEM command is similar to the CIRCULATION-LOOP command in that
condensers attach to this component, and are controlled by this component.
However, compressors do not attach directly to the REFG-SYSTEM. This is
because a given REFG-SYSTEM may have multiple suction groups, each operating
at a different suction temperature, serving a different set of loads, but
discharging into the same condenser. In addition, different compressors may
discharge into different discharge circuits, some of which may be controlled
for heat reclaim, and others not. For this reason, suction-group/compressor
assemblies are defined separately from the REFG-SYSTEM.

You may define more than one REFG-SYSTEM. The only caveat is that multiple
systems cannot be cross-connected so that refrigerant leaves one system and
enters the other. In other words, refrigerant leaving the liquid receiver of
one system must return to the same receiver. Systems can be cross-connected
in the sense that refrigerant from one system can act on the refrigerant of
another system via a heat-exchanger. For example, a subcooler for a
low-temperature system can be fed with refrigerant from a medium-temperature
system, as long as the subcooler utilizes a heat-exchanger to keep the
refrigerant streams completely separate (Figure ??). The same is true of
desuperheaters, and refrigerant-to-refrigerant condensers.

The program checks to see if a load, such as a REFG-FIXTURE, is
cross-connected between two REFG-SYSTEMs. Such cross-connections will cause
the program to abort.

A REFG-SYSTEM can be quite complex, and REFG-SYSTEMS can be intertied in
manners which allow even greater complexity. For example, because a REFG-
SYSTEM may have multiple suction groups operating at different temperatures,
a single system can serve both low and medium-temperature loads. In
addition, suction groups can be staged so that the compressors of a
lower-temperature load discharge into a higher-temperature suction group.
When multiple REFG-SYSTEMS use refrigerants of different types, it is
possible to cascade the load of a lower-temperature system into a
higher-temperature system via a refrigerant-to-refrigerant condenser.
Examples are given that illustrate these concepts as well as others.

A condenser attaches to a REFG-SYSTEM from the CONDENSER command. The
program allows a refrigeration system to have more than one condenser.

While a REFG-SYSTEM normally expects there to be a condenser to reject heat,
you do not have to specify a condenser. In this case, the liquid and
discharge circuits will always be at the hourly condensing temperature
setpoint, the high-temperature energy in the discharge refrigerant will
simply disappear without the expenditure of any condenser energy. This
feature can be useful if you are in the process of constructing a refrigeration
system, and would prefer to specify a condenser after you know more about
the design refrigeration loads and system operating characteristics.
------------------------------