7
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AE4-1395 R5
shown in
Table 2
. A tandem circuit with a charge over
this limit must have crankcase heaters applied to both
compressors.
Tandem compressor assemblies are available for
purchase from Emerson. In lieu of purchasing the
assembled tandem, the OEM has the option to
purchase the tandem-ready compressors to assemble
the compressors into a tandem configuration in
their manufacturing plant. Drawings of the tandem
manifolds are available by contacting your application
engineer.
Figure 7
illustrates a typical tandem
compressor assembly using ZPD34-ZPD54K5, ZPD61-
ZPD83KC, ZPD91KC, ZPD104KCE, ZPD122KCE,
and ZRD36-81KC scroll compressors. Note that only
one compressor in the tandem assembly is a digital
scroll compressor.
Customers that choose to design
and build their own manifolds for tandem and trio
compressor assemblies are ultimately responsible
for the reliability of those manifold sets.
For more information on tandems, please refer to the
non-modulating compressor Application Engineering
bulletins listed on
Page 4
.
Modulation Control
Two different controls are available from Emerson to
provide digital scroll modulation control, the Copeland
Scroll Digital Compressor Controller and the Emerson
Commercial Comfort Controller.
The Copeland Scroll Digital Compressor Controller is
an open loop controller that provides control, protection,
and diagnostics for the digital scroll and is suited for
OEM applications. The system controller supplied by the
OEM calculates the required compressor capacity and
communicates that capacity to the digital scroll controller
via a 1-5 VDC analog signal. For more information on
the Copeland Scroll Digital Compressor Controller please
refer to
AE8-1328
.
The Emerson Commercial Comfort Controller is a closed
loop controller that provides modulation control based
on space temperature and is suited for both OEM and
retrofit applications. This controller is typically located in
the conditioned space and controls the modulation cycle
of the compressor without the need for an additional
system controller. For more information on the Emerson
Commercial Comfort Controller, please refer to
AE8-1393
.
NOTICE
For OEMs that choose their own controls
package, the controls must include the protection
features incorporated into the Copeland Scroll
Digital Compressor Controller. Please consult
with Application Engineering for a list of these
requirements.
APPLICATION TESTS
Oil Level Verification
If the system configuration is more complex than a
single circuit packaged system with one compressor,
evaporator, and condenser, an oil return test is highly
recommended during system development testing.
For this test a sample compressor with a sight-tube
should be used to observe the oil level over the
entire operating range of the system at the expected
compressor modulation rates, to ensure an adequate
oil level in the compressor at all times. The oil level
should not go below the weld points of the lower bearing
bracket for the ZPD34-ZPD54K5, ZPD61-ZPD83KC,
ZPD91KC, ZPD104KCE, ZPD122KCE, and ZRD36-
81KC compressors. For the ZPD103KC, ZPD120KC,
ZPD137-182KC and ZRD94-125KC digital scrolls the
minimum oil level is 1.5" (40 mm) below the center of
the standard oil sight-glass on the compressor. If the
oil level falls below the prescribed level for more than a
few minutes either more oil is required in the system or
an oil recovery cycle is needed. For more information
on what an oil recovery cycle is, please consult with
Application Engineering.
If the system contains more than 20 pounds (9 kg) of
refrigerant, it is our recommendation to add one fluid
ounce of additional oil for every 5 pounds (15 ml/kg)
of refrigerant over this amount. This is a starting point
and oil should be added as determined through system
testing or as required by the end use application in the
field.
The compressor oil level should be checked with the
compressor 'off' to avoid the sump turbulence when
the compressor is running. Manifolded compressors
should have their oil levels checked after 20 to 30
seconds of off time, to allow oil balancing between
the manifolded compressors.
Excessive Liquid Flood Back Tests
It is expected that the design will not flood during
operation at all of the varying loaded and modulation
