Mueller Model D Fre-Heater Installation and Operation Manual
Effective March 1, 1993
Part No. 8800430
Revised November 6, 2019
2.5 REFRIGERATION CONNECTIONS (CONTINUED)
Consult Table 1 for the per circuit condensing unit capacity range of Model “D” Fre-Heaters. Stay within the
capacity range specified to assure proper condensing unit operation.
A condensing unit exceeding the single circuit capacity of a specific Model “D” or “DE” Fre-Heater may be
connected to two or more Fre-Heater circuits on one or more Fre-Heaters having a combined circuit capacity equal
to the condensing unit (see Figure 11).
When making multiple Fre-Heater circuit connections to a single condensing unit, piping to the Fre-Heater
circuits should be in parallel. Series piping (through one circuit into another) of the Mueller Fre-Heater should not
be used.
A refrigerant line discharge muffler is not necessary for proper operation or warranty coverage in a Fre-
Heater installation. However, if the Fre-Heater is to be installed in an area where any machine noise would be
objectionable, a discharge muffler should be considered as a method of eliminating the normal compressor
pulsation noise present in all refrigeration systems.
Typical condensing unit piping is shown in Figures 10, 11, and 12.
NOTE:
Horizontal installation may be used in ammonia refrigerant applications to provide a positive flow of oil
from the Fre-Heater.
If there is a hot gas defrost valve, an oil separator, and/or a discharge muffler in the compressor discharge line, the
Fre-Heater must be installed downstream of those items. See Figure 13 for an illustration of this.
In the event of extended compressor operation with little or no water usage, it is possible to generate water
temperatures that exceed the 210°F setting of the pressure temperature relief valve. This will result in repeated
dumping of hot water through the relief valve.
To avoid the repeated release of hot water by the pressure temperature relief valve, a correctly sized three-way
heat reclaim valve, a transformer, and an immersion Aquastat (or its equivalent) should be installed. Installation
and operation instructions for the above bypass system are included with these instructions for your reference. A
straight-through solenoid valve may be used in lieu of the three-way valve if it is rated for hot gas operation and the
port size is large enough to allow unrestricted refrigerant flow.
For maximum condensing unit efficiency and Fre-Heater heat recovery, head pressure controls must be used.
On air-cooled condensing units, head-pressure-operated fan controls must be installed; and on water-cooled
condensing units, a head-pressure-operated water valve must be installed, if one is not already on the condensing
units. On many low temperature applications, an auxiliary cooling fan must be installed on the compressor
if the condenser fan is cycled to maintain head pressure. Consult the compressor manufacturer for their
recommendation if in doubt of sufficient air flow for compressor cooling.
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