Dehumidification Control - Daikin Maverick I MPS A03C Installation And Maintenance Manual

Burners
Burners for these units have been designed so that field
adjustment is not required. Burners are tray-mounted and
accessible for easy cleaning when required.
Manual Reset Overtemperature Control
Do not jumper this device! Do not reset the overtemperature control without
taking corrective action to assure that an adequate supply of combustion air
is maintained under all conditions of operation. Failure to do so can result
in carbon monoxide poisoning or death. Replace this control only with the
identical replacement part.
Two manual reset overtemperature controls (one on 80,000
Btuh) are located on the burner shield. These devices sense
blockage in the heat exchanger or insufficient combustion
air. This shuts off the main burners if excessive temperatures
occur in the burner compartment.
Operation of this control indicates an abnormal condition.
Therefore, the unit should be examined by a qualified installer,
service agency, or the gas supplier before being placed back
into operation.
Pressure Switch
This furnace has a pressure switch for sensing a blocked
exhaust or a failed induced draft blower. It is normally open and
closes when the induced draft blower starts, indicating air flow
through the combustion chamber.
Limit Control
Do not jumper this device! Doing so can cause a fire or explosion resulting
in property damage, personal injury or death.
The supply air high temperature limit cut-off is set at the factory
and cannot be adjusted. It is calibrated to prevent the air
temperature leaving the furnace from exceeding the maximum
outlet air temperature.
Important: Replace this control only with the identical
replacement part.
IM 970-2 • MAVERICK I ROOFTOP
DANGER
DANGER

Dehumidification Control

With the factory installed reheat option, in addition to a
thermostat or space temperature sensor that is normally
present, an indoor relative humidity sensor is installed in the
occupied space and connected to the Rooftop Unit DDC
Controller which (see illustration) then controls the capacity
of the cooling coil to remove moisture from the supply air and
maintain space relative humidity below an adjustable limit. The
default value is the ASHRAE recommended limit of 60% RH.
With this option, a refrigerant reheat coil is installed
downstream from the evaporator coil. When the space humidity
is too high and reheat is energized, this coil uses some of the
heat that is normally rejected to the outside by the condenser
coil to instead reheat the cold air from the evaporator coil just
enough to avoid overcooling the space. Providing "neutral
air" to the occupied space extends the run-time of the unit to
provide better dehumidification than an air conditioner without
this option.
Because the demand for dehumidification can be different
from the cooling demand, the unit will first satisfy the demand
for cooling and then if the space humidity is still too high,
reheat mode is energized. When in reheat mode, the supply
air leaving the unit will be near the entering air temperature,
but at a much lower humidity. The unit will exit the reheat
mode when the humidity setpoint is satisfied; or if the load is
increased, it will return to normal cooling mode. Reheat is not
available during the gas heating mode. For two-stage units
with independent refrigerant circuits, reheat is only available on
the first stage.
Figure 37 shows the refrigerant path during the normal
cooling mode. The liquid refrigerant leaves the TXV with
the sudden pressure drop causing the liquid to expand to
a vapor and absorbing the heat from the supply air going
through the evaporator coil. The refrigerant vapor then travels
to the compressor where it is elevated to a higher pressure
and temperature. The superheated refrigerant vapor is then
rejected and the refrigerant condenses into a subcooled liquid
where the process repeats itself.
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onTrols and PeraTIon
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