What it takes to create a net zero energy building
Techno-social advancement in HVAC systems is key for the successful development and operation of net-zero-and positive-energy buildings, says Dr Tushar Jain
Heating, Ventilation and Air Conditioning (HVAC) are now ubiquitous in air conditioning systems for most non-residential buildings in cold as well as warm temperate climates and will likely remain so in the coming future. This dominance in the market of HVAC systems has emerged over the past twenty years due to the perceived comfort demand of occupants, low cost and advances in building management systems. However, HVAC systems which are an integral part of modern buildings consume most of the energy resources. According to a report by India energy securities scenarios 2047 (IESS2047), Govt. of India in the year 2015, HVAC consumes about 55% of all the energy consumed by commercial sector buildings in India.
Of the many variants of HVAC systems available in the market, namely fan-coil unit (FCU)-based, variable-air volume (VAV)-based, commercial buildings typically employ the use of centralized systems. In these systems, the heating and cooling along with ventilation are performed at a centralized location outside the building by an Air Handling Unit (AHU) which results in better maintenance and lesser indoor noise. The processed air is distributed to every room with the help of controlled ducts. The required heating/cooling is then achieved by supplying processed air to individual rooms and is regulated by a terminal device under the control of a thermostat at the user premises. The excess air in the room is recirculated through AHU to ensure the energy-efficient operation of HVAC systems.
For the centralised scheme to work effectively, numerous components of the HVAC have to be orchestrated carefully. It has become a widely accepted fact that measures and changes in the building modus operandi can yield substantial savings in energy. A faulty component may negatively hamper the efficient operation of HVAC and the life of the entire system. The faulty component forces the other healthy components to put in extra effort to meet the objective of thermal comfort for the user. However, all the while, a user may not even experience the effect of a fault due to thermostat enforcing user comfort over energy consumption or component safety. It has been reported that the energy wastage in US commercial buildings is in the interval of 32.4–171.4 Billion kWh/year costing $3.3–17.3 billion/year. This energy wastage is due to only 13 most commonly occurring faults. The issue of early detection of faults in commercial buildings becomes very crucial because the occurred fault in a specific component appears to propagate to other subsystems and may result in cascaded failure. Currently, the commercially available building energy management systems (BEMS) lack the ability to accurately pinpoint the location and magnitude of fault that has occurred in the HVAC. The inability not only leads to high service time but also require human effort and expertise. There is a need for commercial BEMS which automatically diagnose the fault and tells the maintenance crew precisely what is the severity and where to head. The information from BEMS would greatly aid in finish servicing and significantly reduce the turnaround time of HVAC fault maintenance.
In order to incorporate a supervisory control scheme for HVAC systems in existing BEMS, there are several key areas that require immediate attention thanks to the rapid progress in advanced and low-cost technology. The sensor measurements, for example, temperature, humidity, illuminance, etc., in a control scheme play an important role. Due to the large size of commercial buildings, the sensors have to be deployed and their measurement should be monitored automatically over the complete building with very less human intervention. Since a hardwired connection may not be possible, reliable wireless communication between the controllers and sensors should be setup. However, with networked infrastructure, the issue of cyber security becomes highly relevant as it may expose the building to vulnerabilities, thereby, impacting the occupants and energy consumption directly. Numerous research works have been reported for the automatic mitigation of faults in a networked architecture, however, it still seems farfetched commercially. In particular, commercially available solutions generally seek for hardware redundancy for fault mitigation. This not only increases the operation cost but the maintenance cost as well during the building recommissioning. A striking approach is to use analytical redundancy by carefully designing the failure modes and effects analysis.
Apart from the technological solutions, another important aspect is the users’ actions and the effect they have on the building performance. It has been observed that users are slow in adapting to new technologies. In actual practice, users’ behaviour, governed by their subjective comfort feeling and their actions have a significant impact in the building’s performance. It is advocated that improvement on the effect of users’ behaviour can be obtained through enhanced energy awareness. Extracting the benefits of networked infrastructure, a possible solution is to make users communicate at a lower level infrastructure with the overall energy management system. Using user web interfaces the occupants can communicate their comfort preferences to the system. The occupants’ preferences should be recorded on a daily basis via for example electronic data- sheets available on the building’s intranet.