Bryant 50YEW Design Manual page 58

Water-to-Water System Design Guide
Part IV: Controls
User interface: Figure 4-1 shows the factory installed and
wired panel-mounted user interface for customizing the MPC
programming. A large dot-matrix style 2" x 2" [5 x 5 cm] back-
lit display is controlled by four arrow keys and a select key. The
main screen, as shown in fi gure 4-2, displays current outdoor and
water temperatures, and allows the user to change settings by
selecting one of the menus from the bottom of the screen. A
special installer set up mode allows the technician to change some
of the default MPC parameters. The user interface includes a
time schedule for DHW generation, Fahrenheit/Celsius selection,
vacation mode for DHW, and other user preference options.
Figure 4-1: 50YEW User Interface
Figure 4-2: 50YEW User Interface Main Screen
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Arrow Keys
Select Key
Bryant: Whatever It Takes.
12-point terminal block: Thermistors and external wiring are
connected to a 12-point terminal block for ease of installation. The
MPC, user interface, CXM board and other relays/components are
factory-wired to the terminal block. A blue/gray pattern is used for
ease of identifi cation.
DHW valve (optional): An internal three-way valve is available,
which allows the 50YEW unit to switch between heating and
DHW generation.
Internal source and load pumps / internal expansion tanks
(optional): Source pump(s), load pump, and expansion tank(s) are
available to help lower installation costs and labor. When installed
at the factory, pumps are wired and controlled by the MPC.
50YEW Series Control Features
The advantage of a programmable controller, as outlined above,
is the ability to integrate complex decision-making tasks with the
standard heat pump (CXM) controls and communicate with a user
interface. Below is a list of standard features that are included in
the 50YEW series controls.
CAUTION:
Maximum leaving water temperature of the 50YEW series
equipment is 145°F [63°C]. For domestic hot water tank
temperatures or heating buffer tank temperatures above
130°F [54°C], pump and pipe sizing is critical to insure that
the fl ow rate through the heat pump is suffi cient to maintain
leaving water temperatures below the maximum temperature,
and to provide water fl ow rates within the ranges shown in
the performance section of this manual.
Outdoor temperature reset: The heat pump capacity and water
temperature delivery to the heating system must be designed
for local weather conditions, usually at the 99.6% outdoor
temperature. Therefore, 99.6% of the heating season, the
heating load is less than it is at design conditions. As the outdoor
temperature decreases, the heat loss of the structure increases,
which requires more capacity from the heating system. If the
water temperature is reduced as the outdoor air temperature
increases (and vise-versa), the heat pump operates at higher COP
most of the year. The MPC has a built in algorithm that adjusts the
buffer tank temperature based upon outdoor air temperature to
maximize effi ciency and comfort. Temperature settings may be
adjusted at the user interface if factory defaults are not suffi cient.
The base setpoint for energizing the compressor in the heating
mode is determined by subtracting one-half the heating differential
value (HTD) from the buffer tank heating temperature setpoint.
The HTD is the differential used for controlling setpoint. For
example, if the buffer tank setpoint is 100°F [38°C], and the HTD
is 6°F [3°C], the compressor will be energized at 97°F [36°C] and
will be turned off at 103°F [39°C]. The HTD is the difference
between the compressor "call" (97°F [36°C]) and the "satisfi ed"
(103°F [39°C]) temperature. The buffer tank temperature may