Components Required For Specific Applications; Thermostatic Expansion Valve; Leaving Air Temperature Sensor; Heat Pump Temperature Sensor - Bryant ZONE PERFECT PLUS ZONEBB2KIT Zoning Design Manual

Installation Instructions provided by Bryant with the selected
heating and cooling equipment. Thoroughly test the installation,
following the instructions provided, to ensure that it is installed
and set up properly.
COMPONENTS REQUIRED FOR SPECIFIC
APPLICATIONS
The following components are required in all Zone Perfect Plus
installations:
• a TXV (thermostatic expansion valve)
• a LAT (leaving air temperature) sensor, provided with all Zone
Perfect Plus kits
In a heat pump installation (not a dual fuel application), an HPT
(heat pump temperature) sensor is required.
In a dual fuel application, or any installation using the low
temperature lockout feature, the auxiliary heat lockout feature,
and/or the automatic humidity level adjustment feature, an ODT
(outdoor temperature) sensor is required. In other Zone Perfect
Plus applications, this sensor is optional.
Information about each of these components is provided in the
following sections.
A. Thermostatic Expansion Valve
A TXV is required in all Zone Perfect Plus installations. The
TXV replaces the fixed metering orifice, which regulates the
amount of liquid refrigerant entering the indoor evaporator. The
TXV assures that no liquid refrigerant leaves the evaporator,
possibly returning to the compressor and causing damage.
The likelihood of incomplete refrigerant evaporation is much
greater in a zoning system than in a non-zoned system because of
the reduced airflow when only a few zones require conditioning.
Thus, the TXV protects the compressor from possible damage
when airflow is very low.
NOTE: The purpose of the TXV is not to protect the coil from
freezing. The leaving air temperature (LAT) sensor performs this
function.
B. Leaving Air Temperature Sensor
A LAT sensor is required for all types of equipment. When
used with fossil fueled furnaces and air conditioned systems, locate
the LAT sensor in the air supply duct downstream of the furnace
and cooling coil. The LAT sensor must be upstream of the bypass
damper, if one is included in the system, or the first zone damper.
The LAT sensor monitors the leaving air temperature during both
heating and cooling. The User Interface is programmed with
temperature limits and prevents equipment operation if the leaving
air temperature exceeds the upper limit during heating or falls
below the lower limit during cooling.
When used with a heat pump, locate the LAT sensor downstream
of the accessory electric heaters. The LAT sensor monitors the air
temperature leaving the accessory electric heaters during heating,
as well as the temperature leaving the indoor coil during cooling.
C. Heat Pump Temperature Sensor
An HPT sensor is required in a heat pump installation, unless it is
a dual fuel application. Locate the HPT sensor in the air stream
between the indoor coil and the accessory heaters.
This sensor serves a similiar purpose to the LAT sensor, but does
not sense the temperature of the air leaving the electric heaters.
The HPT sensor monitors the air temperature leaving the indoor
coil during heating by the heat pump, and prevents the operation of
the heat pump if the leaving air temperature exceeds the fixed
temperature limit of 115°F.
D. Outdoor Temperature Sensor
An ODT sensor is required in all dual fuel applications. An ODT
sensor also is required to use the low temperature lockout feature,
the auxiliary heat lockout feature, and/or the automatic humidity
level adjustment feature in any installation.
For dual fuel systems, this sensor is used to control the switch from
electric to fossil fuel operation when the outdoor temperature
reaches the preset temperature. When used with the low tempera-
ture lockout feature, the ODT sensor is used to prevent equipment
operation during cooling when the outdoor temperature falls below
the preset lower limit.
When used with the auxiliary heat lockout feature, the ODT sensor
is used to prevent electric heat operation in a heat pump installa-
tion when the outdoor temperature rises above the preset limit.
When used with the automatic humidity level adjustment feature
during heating, the system automatically reduces the humidity set
point by 1 percent for every 2°F reduction in outdoor temperature.
In other Zone Perfect Plus applications, this sensor is optional.

SPECIAL APPLICATIONS USING ZONE PERFECT PLUS

This section discusses special Zone Perfect Plus applications that:
• Emphasize energy savings or "setback."
• Include multi-stage equipment.
• Include variable-speed blowers.
• Include a barometric bypass damper.
A. Understanding the Requirements of Setback with
Zoning
If you are designing a zoning system for energy savings, it is
important to understand the additional challenges that you face
before you begin to design the air distribution system. The energy
savings achieved by setting zone temperatures back (lower for
heating or higher for cooling) can be substantial. However,
"setback" brings additional requirements to the system.
The zones that are not set back might be surrounded by zones that
are. This situation results in the need to deliver additional capacity
to the zone that is not set back since the zone duct and damper need
to deliver the capacity required to meet the zone's needs and to
compensate for the conditioning that spills over to the neighboring
zones that are set back.
Thus, the effective block load of any zone increases above the
value normally calculated for it when its neighboring zones are set
back. The amount of the increased load depends on the extent to
which the neighboring zones are set back. This need for additional
capacity increases the size of damper and duct required for the
zone.
When a zone has been set back, the system eventually must return
the zone to a more comfortable conditioning level. This need
increases the capacity that must be delivered to the zone. The
amount of additional capacity that is necessary is the capacity
required to match the zone's load plus the capacity required to
implement recovery within a reasonable time period. The amount
of capacity required for recovery depends on the extent to which
the zone had been set back and the desired recovery time. Again,
this need for additional capacity increases the size of damper and
duct required for the zone.
The improved insulation found in today's homes compounds the
demands imposed by setback. The better insulated the home, the
smaller the size of heating and cooling equipment required for the
home. However, the requirements of setback recovery are deter-
mined by the heat capacity of the zone, not by its losses, and heat
capacity is not changed by insulation. Improved insulation also
increases the challenge of maintaining different temperatures
between zones since the interior walls appear more transparent to
heat flow when the outer walls are better insulated. The opportu-
nity for energy savings in addition to the savings already achieved
through better insulation is reduced in a well insulated home.
B. Using Multi-Stage Equipment with Zoning
When dampers are closed in some zones and the air distribution
system becomes effectively smaller in a system with single-stage
equipment, airflow may drop below the system's minimum,
causing the equipment to shut down. In this situation, it is difficult
to maintain comfort in the home due to excessive equipment
cycling.
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