Specifications

7
The system is intended to be able to be retrofitted to an existing HVAC system,
and therefore several requirements must be taken into consideration. In order to
avoid running wire inside an existing structure, the temperature and relative
humidity measurements are required to be transmitted to the main control unit
wirelessly. In order to achieve wireless data transmission the sensor must make
its measurements and pass the data to a microcontroller which then must pass
the data to a ZigBee wireless chip that will communicate with another ZigBee
wireless chip on the main control unit.
The wiring for the air conditioning units to be controlled is already installed in the
building, and therefore controlling the power relays that turn the air conditioning
units on and off can be done via wire. AC units typically run on 220 Volts AC. To
supply the units with this voltage, a power relay must be switched to essentially
complete a circuit connecting the units to the main 220 V power supply for the
building. Our control system has to switch control relays to send 24 Volts to the
220 V power relays which turn on the AC units.
If a dehumidifier is not already installed in the HVAC system, the control system
is required to wirelessly control the dehumidifier. Ducts must also be controlled
by the main control unit in order to route new air into the building and old air out
when the system determines this is necessary. In this case, a remote unit will be
installed that will communicate to the main control unit the same as the remote
sensing unit, but will control a relay instead of reading temperature and relative
humidity.
The LCD touch screen user interface is required to allow the user to manipulate
every setting of the system using only their fingers. The LCD touch screen is
also required to display current temperature and relative humidity conditions both
inside and outside the building. The requirements of the LCD touch screen are
as follows:
 Display current temperature and relative humidity conditions at the main
control unit
 Display current temperature and relative humidity conditions outside the
building
 Display the logos of the sponsors
 Allow the user to input desired temperature and relative humidity settings
 Allow the user to view their current power costs
 Display the current percentage of total system energy being used via
“energy usage” bar
 Allow the user to select between “maximum savings” and “maximum
comfort” settings that specify a +- tolerance level for the user selected
temperature and humidity settings
 Update the settings on the LCD panel when the settings are changed
remotely from a mobile device