
33
System Protectors
Emerson Climate Technologies
Schematic of a basic heat pump system.
Filter Driers for Heat Pumps
A heat pump is essentially a refrigeration sys-
tem that can ow in either direction. The key to its
operation is a four-way reversing valve that routes
the discharge gas from the compressor.
Depending on whether the system is cooling or
heating, the indoor and outdoor coils swap roles,
taking turns serving as the condenser and evapo-
rator.
Since conventional refrigerant control compo-
nents are designed for unidirectional operation,
their use in heat pumps requires installation in
pairs, one for each direction, with check valves
routing the ow through or around them. Today,
because of the growing use of heat pumps, com-
ponents such as thermostatic expansion valves
are available in bi-directional versions, as are lter
driers.
Removing Contaminants
Just like any other refrigeration system, heat
pump system components need lter drier protec-
tion to remove solid and soluble contaminants.
This may be handled several ways.
First, in systems with one-way expansion
valves and check valves, a one-way lter drier
might be installed in series with a check valve.
This would be a “part-time” arrangement, in that
ltration would be provided in only one direction.
Second, a one-way lter drier might be installed
with each of the check valves, so that one pro-
vides ltration in each direction.
Third, the simplest arrangement is to install a
bi-directional lter drier in the common liquid line.
Used in combination with a bi-directional thermo-
static expansion valve such as Emerson’s HF se-
ries, the complexity of multiple expansion valves,
check valves, and lter driers can be completely
eliminated.
Emerson BKF bi-directional pump lter drier
One-Way Flow, Both Directions
Inside a bi-directional lter drier the refrigerant al-
ways ows in the same direction through the dessicant
core regardless of which way the refrigerant is owing
through the system. The internal ow in this case is
controlled by an inlet apper valve and an outlet poppet
valve on each side of the desiccant core. As the liquid
enters the lter drier from either direction, the inlet ap-
per valve routes it to the outside of the desiccant core.
After it ows through to the inside of the desiccant core,
it exits through the opposite poppet valve.
The purpose of the arrangement shown below is to
prevent contaminants collected in one direction from be-
ing ushed back out when the ow reverses.
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