Nowadays, reducing energy consumption is the fastest way to reduce the use of fossil fuels and, therefore, greenhouse gas emissions. Heating, Ventilation, and Air Conditioning (HVAC) systems are used to maintain an indoor environment in comfortable conditions for its occupants. The combination of these two factors, energy efficiency and comfort, is a considerable challenge for building operations. This paper introduces a design approach to control an HVAC, focused on an energy consumption reduction in the operation of the HVAC system of a building. The architecture was developed using a Raspberry Pi as a coordinator node and wireless connection with sensor nodes for environmental variables and electrical measurement nodes. The data received by the coordinator node is sent to the cloud for storage and further processing. The control system manages the setpoint of the HVAC equipment, as well as the turning on and off the HVAC compressor using an XBee-based solid state relay. The HVAC temperature control system is based on the Predicted Mean Vote (PMV) index calculation, which is used by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to find the appropriate setpoint to meet the thermal comfort of 80% of users. This method combines the values of humidity and temperature to define comfort zones. The coordinator node makes the compressor control decisions depending on the value obtained in the PMV index. The proposed PMV-based temperature control system for the HVAC equipment achieves energy savings ranging from 33% to 44% against the built-in control of the HVAC equipment, when operating with the same setpoint of 26.5 grades centigrade.
Global warming and climate change effects have been of such impact that several countries around the world are enforcing public policies to mitigate them. Mexico has shown a strong commitment to the environment and rational use of energy, as signed on the General Law for Climate Change (GLCC) and stating, in its second article, the goal of a 30% reduction of greenhouse gases by 2020. To add to this goal, the Hermosillo Institute of Technology is implementing a pilot energy saving program that mixes retrofitting of academic buildings and the implementation of automatic controls for lighting and heating, ventilating, and air conditioning (HVAC). The retrofitting is performed by replacing fluorescent T8 tubes with high efficiency LED T8 tubes in a new arrangement. To increase the energy saving obtained by the retrofitting, a building automation and control system (BACS) has been developed and installed. The BACS is implemented using two different networks, the first one communicates a central control unit with the building control node using a private Ethernet network. Inside the building, the control actions are transmitted using a ZigBee network. The energy savings have been estimated as 4864 kWh/year, representing a 36.42% saving, the environmental and health effects are calculated using emission parameters of the nearest power plant to our site, and the procedure presented in Harvard’s Six Cities Study by Dockery. Results show a total CO2eq equivalent to 0.000409% of the national goal. The economic impacts of the carbon social cost and health benefits are $745.26 USD/year and $4017.71 USD/year while the direct billing savings are $3700.56 USD/year, and these results are based on only one building of the campus.
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