The fundamental notion of ‘smart’ in building materials discourse is responsiveness—the ability of materials to react to environmental stimuli by manifesting a noticeable physical change when there is a difference in the conditions of their immediate surroundings. This notion, however, is also interchanged with ‘intelligence’, which involves an array of control protocols. Notwithstanding, both notions are used synonymously and as occupant comfort and energy efficiency strategies in buildings.
The energy efficiency and comfort strategies concerned with intelligence involve machine components of learning and control algorithms, actuators working under a governing central intelligent system, an integrated system of sensors complementing each other, as well as integrated circuits to help increase the accuracy of measured data and convert the same into digital signals that can be transmitted wired or wirelessly to a control system. These control systems require the application of information and communication technology (ICT) to facilitate the implementation of advanced sensors and control algorithms. Thus, the measure of energy efficiency and comfort is largely dependent on the degree or level of automation and sophistication of the control system, which has also been described as complex and expensive, requiring high operational energy and a payback period, in some cases, of up to 20 years.
So-called ‘hybrid systems’ featuring human-in-the-loop approaches enabled by human-centric computing, smart devices and machine components of intelligence complementing each other have been suggested. However, the machine components still require continuous monitoring technology, computers for supervisory control, and other associated hardware, including data transmission systems, which would consume power, increase equipment costs and decrease the overall system efficiency. Consequently, systems with zero additional energy demand remain the best approach to the issue of energy use, and passive systems were identified as meeting these criteria, with smart materials able to respond independently to environmental stimuli without any external or induced input. Additionally, their installation is easy and reliable. However, direct user control according to occupant/user preference is not possible. Indeed, while smart/passive systems comprise advanced materials with multiple functionalities able to respond to the emerging environmental-energy problems in the society, it is practically impossible to have intelligent/hybrid/active systems without additional computer control and its resulting implications. Moreover, user control (an identified problem with smart systems), still presents a problem in intelligent systems, with some occupants still reporting feeling uncomfortable with the deployed optimized solutions, especially with mechanical heating, ventilation and air conditioning (HVAC). Studies reveal that as many as 43% of occupants are actually dissatisfied with mechanical HVAC, and 56% to 89% of government workers regard it as a problem in Europe and the US [27], and thus a mismatch between building systems and occupant comfort. Since energy savings in intelligent systems are largely determined by the degree of automation of the control system, and system performance depends on user behavior or acceptance, the personal preferences and requirements of each user would need to be taken more into account when optimizing control algorithms to achieve better system performance and thus higher energy savings. This, however, still presents a problem, because occupant behavior is not a precise and quantifiable science. Even with passive sensors (widely used because they are cheaper and consume less energy than active ones), an external power source is needed, ‘false-off’ readings may also occur frequently in systems as sensors may fail in detecting a stationary body, and so on [28]. Generally, now, building occupants actually accept a larger range of temperature variation in naturally ventilated buildings than in computer controlled air-conditioned ones [3].
It was found that both notions were often used interchangeably even though they have distinct implications. On the one hand, while smart materials could be connected to computers to provide building occupants with control, the resulting intelligence, on the other, adds complexity to the system and ultimately increases the demand for energy. It has been argued that this ‘additional energy’ could be supplied from renewable sources. However, renewable energy systems still fall short because of their high upfront cost, intermittency and general low capacity. Additionally, sensor feedback is necessary to deploy comfortable solutions and energy savings in intelligent systems, but only after they have ‘sensed’ or detected all environmental variables. Monitoring, calculating, analyzing and transmitting all this data across a range of users with different needs would consume a lot of power, increase equipment as well as associated (installation) cost, and decrease the overall system efficiency. Consequently, until the global community finds more considerable alternatives, focus and attention should indeed be on zero energy demand technologies and systems.
Buildings remain the biggest energy consumers in the world, and thus present a huge opportunity for significant savings in global energy use, especially when the focus is shifted to address the issue from the point of demand. With smart materials, the requirement of zero additional energy demand and occupant comfort can be achieved without the need for computer-controlled intelligence. In fact, the current study revealed that while smart materials and systems independently manifest direct responses to external stimuli by altering their physical state and reverting back when the stimuli is removed, intelligent materials and systems provide occupant/user control of the environment and technological appeal, rather than comfort and energy efficiency. The prevalence of information and communication technology, interconnected devices and IOTs, enabled by even faster internet speeds, inadvertently positioned intelligent buildings as the next logical step in the evolution of buildings, and is now gradually expanding the current approach to building design to include automation and computer-based (control) systems, which will require machine learning and human-in-the-loop approaches with computers able to predict behavior and deploy solutions after close monitoring. The world is experiencing an increase in energy demand. From energy use charts, energy use is on the increase, and this is largely due to the demand from electrically powered technologies that are presented as clean or efficient. The current study makes the case that focus should be on reducing or eliminating demand altogether with less pressure on existing sources of energy production. Thus, when assessing the key challenges of buildings in making them truly smart, the focus should be towards zero additional energy. Interventions in old and new buildings alike can come in the form of advanced, high-performance, passive smart materials that use their (material) properties to respond to the changes in their environment, resulting in significant energy savings by eliminating demand and ensuring overall occupant comfort. The approach to design and overall solutions to environmental problems should be region specific. Technology is not a one-stop approach to issues, and the ‘one size fits all’ approach is no longer feasible. Instead of changing energy use, the focus should be on eliminating demand altogether. The properties of existing advanced smart materials with multiple functionalities can be further modified so they are able to respond to the emerging environmental-energy problems in our society.