Significance of temperature control in evaporator
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Sporlan Evaporator Pressure Regulating valves (EPRs)
are designed to provide an economical means of
accurately maintaining evaporator pressure and
temperature under varying evaporator loads. The
primary function of an EPR is to prevent the evaporator
pressure from falling below a predetermined value
or setting. A consistent evaporating temperature is
maintained at the valve setting as evaporator loads
decrease. When the evaporator load increases, the
valve Opens on a Rise of Inlet pressure above its
setting. Controlling evaporator temperature, by
maintaining the saturation pressure of the refrigerant
in the evaporator, provides more consistent evaporator
temperature than a conventional thermostat or suction
pressure cut-out control.
These methods of control allow the evaporator
pressure to decrease as the load drops off; lowering
the evaporator temperature and decreasing evaporator
performance, while increasing evaporator frost build
up.
Sporlan offers three types of evaporator pressure
regulating valves, covering applications from small
spot coolers to large multiplex supermarket systems.
The ORIT-6 and ORIT-10 EPRs are direct acting and
offered with standard adjustment ranges and fitting
options. The (S)ORIT and (S)ORIT-PI pilot operated
EPRs provide more capacity at lower pressure drops,
and offer additional features including solenoid shut
off for defrost applications.
Sporlan evaporator pressure regulating valves are used
in many applications to provide:
• Consistent evaporator pressures and temperatures
(during decreasing load conditions) for excellent
system temperature control.
• Allow multiple evaporator systems to operate at
different temperatures when piped to a common
suction group.
These applications are categorized as single evapora-
tor or multiple evaporator systems.
Single evaporator/single compressor systems:
There are many single evaporator systems which
utilize EPRs for precise evaporator temperature control
(see Figure 1). However, there are several factors
to consider. Proper valve selection is critical. Since
pressure drop in the suction line is lost efficiency,
EPRs are commonly oversized to reduce suction line
pressure drop. Single evaporator systems can allow
as little as 2 psi drop across direct acting EPRs (0.5 psi
drop across SORIT and 1.0 psi drop across SORIT-PI
pilot operated EPRs,) and still maintain acceptable
control. Severely oversized valves can cause pressure
hunting and negatively impact temperature control.
In addition, special consideration must be given to
single compressor systems. In these applications
the suction pressure can drop to an undesirably low
level as the EPR throttles to maintain the evaporator
pressure. In these cases, a discharge bypass valve must
be used to maintain acceptable compressor suction
pressure. These valves are typically piped with the valve
outlet feeding the suction line downstream of the EPR.
Special considerations must be taken to protect the
compressor from overheating when using a discharge
bypass valve. These considerations and the application
of the discharge bypass valve are discussed further in
Sporlan Bulletin 90-40. Bypassed discharge gas can be
introduced at the inlet of the evaporator or upstream
of the evaporator pressure regulator to maintain a
minimum suction pressure. But, the discharge bypass
valve must be externally equalized, and the external
equalizer connection must be downstream of the
evaporator pressure regulator.
Multiple evaporator systems:
Many supermarket applications use multiple
evaporators piped to a common suction header (see
Figure 2). These evaporators can be operated at
different temperatures for the various products being
refrigerated. This is the most common application for
pilot operated EPRs. Any group of evaporators where
the desired saturation temperature is higher than the
saturation temperature corresponding to the common
suction pressure will require an EPR. For example, if
evaporator A in Figure 2 is designed for -10°F (24.0
psig for R404A), and evaporator B for -20°F (16.0 psig),
an EPR would be used to maintain evaporator A at the
24.0 psig setting. In addition, if the common suction at
are designed to provide an economical means of
accurately maintaining evaporator pressure and
temperature under varying evaporator loads. The
primary function of an EPR is to prevent the evaporator
pressure from falling below a predetermined value
or setting. A consistent evaporating temperature is
maintained at the valve setting as evaporator loads
decrease. When the evaporator load increases, the
valve Opens on a Rise of Inlet pressure above its
setting. Controlling evaporator temperature, by
maintaining the saturation pressure of the refrigerant
in the evaporator, provides more consistent evaporator
temperature than a conventional thermostat or suction
pressure cut-out control.
These methods of control allow the evaporator
pressure to decrease as the load drops off; lowering
the evaporator temperature and decreasing evaporator
performance, while increasing evaporator frost build
up.
Sporlan offers three types of evaporator pressure
regulating valves, covering applications from small
spot coolers to large multiplex supermarket systems.
The ORIT-6 and ORIT-10 EPRs are direct acting and
offered with standard adjustment ranges and fitting
options. The (S)ORIT and (S)ORIT-PI pilot operated
EPRs provide more capacity at lower pressure drops,
and offer additional features including solenoid shut
off for defrost applications.
Sporlan evaporator pressure regulating valves are used
in many applications to provide:
• Consistent evaporator pressures and temperatures
(during decreasing load conditions) for excellent
system temperature control.
• Allow multiple evaporator systems to operate at
different temperatures when piped to a common
suction group.
These applications are categorized as single evapora-
tor or multiple evaporator systems.
Single evaporator/single compressor systems:
There are many single evaporator systems which
utilize EPRs for precise evaporator temperature control
(see Figure 1). However, there are several factors
to consider. Proper valve selection is critical. Since
pressure drop in the suction line is lost efficiency,
EPRs are commonly oversized to reduce suction line
pressure drop. Single evaporator systems can allow
as little as 2 psi drop across direct acting EPRs (0.5 psi
drop across SORIT and 1.0 psi drop across SORIT-PI
pilot operated EPRs,) and still maintain acceptable
control. Severely oversized valves can cause pressure
hunting and negatively impact temperature control.
In addition, special consideration must be given to
single compressor systems. In these applications
the suction pressure can drop to an undesirably low
level as the EPR throttles to maintain the evaporator
pressure. In these cases, a discharge bypass valve must
be used to maintain acceptable compressor suction
pressure. These valves are typically piped with the valve
outlet feeding the suction line downstream of the EPR.
Special considerations must be taken to protect the
compressor from overheating when using a discharge
bypass valve. These considerations and the application
of the discharge bypass valve are discussed further in
Sporlan Bulletin 90-40. Bypassed discharge gas can be
introduced at the inlet of the evaporator or upstream
of the evaporator pressure regulator to maintain a
minimum suction pressure. But, the discharge bypass
valve must be externally equalized, and the external
equalizer connection must be downstream of the
evaporator pressure regulator.
Multiple evaporator systems:
Many supermarket applications use multiple
evaporators piped to a common suction header (see
Figure 2). These evaporators can be operated at
different temperatures for the various products being
refrigerated. This is the most common application for
pilot operated EPRs. Any group of evaporators where
the desired saturation temperature is higher than the
saturation temperature corresponding to the common
suction pressure will require an EPR. For example, if
evaporator A in Figure 2 is designed for -10°F (24.0
psig for R404A), and evaporator B for -20°F (16.0 psig),
an EPR would be used to maintain evaporator A at the
24.0 psig setting. In addition, if the common suction at
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