Specifications

124
component, the Main Control Unit. The Remote Sensing Unit uses a single
sensor that is capable of making the temperature and the relative humidity
reading. The sensor reports to the secondary microcontroller. The secondary
microcontroller is the central component of the Remote Sensing Unit and is
interfaced to the sensor and the wireless communication chip. The secondary
microcontroller receives the temperature and relative humidity information from
the sensor and takes care of any manipulation that must be done to put the
information into a form accepted by the wireless chip. The wireless chip is then
given the information by the secondary microcontroller, and the information is
reported to another wireless chip in the Main Control Unit.
The Remote Sensing Unit is located on the exterior of the building. Throughout
the design process we have kept in mind that installation of the system needs to
be kept as simple as possible. The purpose of a simple install is so that the
system will be able to be installed in a new building in the same manner that a
typical HVAC system would be installed or it can be retrofitted to an existing
structure without having to run new wire through an existing building. Since the
Remote Sensing Unit is intended to be installed on the exterior of the building,
three issues must be taken into consideration. First, there is no power supply
where the Remote Sensing Unit will be installed, therefore battery power is
needed. The battery needs to power the Remote Sensing Unit for a sufficient
period of time because changing the batteries on a regular basis is not realistic.
Secondly, the Remote Sensing Unit must be protected from the elements such
as rain, and snow. In order to protect the Remote Sensing Unit it will be placed
in a weather proof box. Although the box is weatherproof, it needs to allow air
flow so that temperature and relative humidity readings are accurate. The third
issue is installation. The Remote Sensing Unit needs to be housed in an
enclosure that is made to be mounted onto a wall using screws.
The Main Control Unit is the other main component of the system. The Main
Control Unit consists of the main microcontroller, a temperature and relative
humidity sensor, two wireless chips and, the LCD touch screen user interface.
This is the part of the system where the decision will be made about which
components of the HVAC system will be turned on. The main microcontroller is
interfaced with a temperature and relative humidity sensor, an 802.11b wireless
chip, a ZigBee wireless chip, control relays, and the LCD touch screen user
interface. The Main Control Unit Uses the current indoor and outdoor
temperature and relative humidity values, and the user selected settings as input
and determines what is necessary to heat or cool the building. The signals from
the main microcontroller goes to 24V relays which then send a 24V control
voltage to the appropriate component. The Main Control Unit updates the touch
screen display and the web server so that current and accurate information is
displayed at the two user interfaces.
The LCD Touch Screen display is the main user interface for the system. It is
composed of a display and a controller. The controller is what is programmed
and interfaces with the main microcontroller. The controller produces the image