by François Durier (CETIAT)
Advanced controls for heating, ventilation and air conditioning (HVAC) systems can reduce consumption in unoccupied zones of a building. They can also continuously adapt the operation to fit the demand and detect needs for maintenance. They are based on sensors and use control strategies adapted to the technology of the system, by modulating temperatures, flow rates, capacity, etc.
Previous studies have assessed the energy savings linked to enhanced controls of HVAC systems in buildings.
The Buildings Performance Institute Europe- BPIE (2017) found that building automation reduces energy consumption by around 27% in households, and smart technology can save an average of 23% of energy consumption in offices.
In a recent report "Digitalization and energy savings" (2017), the International Energy Agency (IEA) states that digitalization could save around 10% of total energy consumption in residential and commercial buildings by 2040, with efficiency gains that are "largest in heating and cooling, particularly through the use of smart thermostats and sensors".
According to the IEA, the energy savings linked to smart control of HVAC systems are a consequence of the following:
- Smart HVAC systems allow demand control, by improving the response of systems to the heating, cooling and ventilation needs.
- Smart systems can also embed, in addition to sensors, learning algorithms in order to better fit with users behaviour or building's use.
- Another strength of smart systems is their ability to communicate information about their operation, energy consumption and energy efficiency. This information can be used by consumers, owners, building managers, maintenance staff and energy grid managers. This allows human or automatic actions to adjust the system, by changing for example temperature settings, times for on and off operations, length of preheating or precooling periods before occupation, etc.
There are many sensors that can make a HVAC system smart. They monitor temperature, humidity, presence of occupants, air velocities, air and water flow rates, pressures, electricity or gas consumption, etc. Most of them must be chosen and installed by professionals. Among these sensors, the most popular are probably connected thermostats because they are available to the general public. These are programmable connected devices intended to help residential building occupants to know and manage their heating and cooling loads, especially from a smartphones. Several programmes in the USA have shown that smart thermostats lead to energy savings of at least 8 – 10 % for heating and cooling. A report from the American Council for an Energy-Efficient Economy (ACEEE) estimates the electricity savings linked to smart thermostats between 8 and 15%. Another report from ACEEE on energy savings in existing building estimates HVAC energy savings from smart thermostats between 5 and 10%. These figures relate to the specific north-American context in terms of climatic conditions, buildings and HVAC systems, meaning that different figures could be observed in Europe.
In the USA, smart thermostats were added to the ENERGY STAR certification programme in January 2017. In order to get the certificate, manufacturers are required to provide heating and cooling data from at least 1,000 homes collected for over a year from across the United States. A minimum threshold of HVAC savings has to be met compared to a baseline home, i.e. 8% for heating and 10% for air-conditioning. In December 2017, the list of certified products included 8 products from three manufacturers.
Connected indoor air quality (IAQ) sensors are designed to inform about indoor pollutant concentrations and could be used to control ventilation air flow rates.
The Chinese certification programme RESET for healthy buildings relies on continuous monitoring data. RESET monitoring standards are presented as key to identify the difference between good and poor IAQ sensors.
Smart meters (i.e. intelligent electricity and gas meters) can also contribute to making HVAC systems smarter. Nevertheless, interaction between smart meters and HVAC systems is not yet often implemented. Smart meters could in the future become additional sensors used to monitor and control HVAC systems. A recent report of the European project USmartConsumer reminds that smart metering offers a potential for energy savings and peak load reduction, but that this "enabling technology […] needs to be coupled with innovative customer-oriented services to realise all its potential benefits […]".
Heat cost allocators or heat meters in multi-family buildings with centralised heating systems are also giving information to the user and increase the motivation of inhabitants to set up indoor temperatures and thereby reduce heat consumption, as shown in an ongoing study operated in the Basque Country (Spain).
These examples demonstrate how smart technologies linked to HVAC systems enable to control systems, inform users and contribute to more energy efficient operation and users behaviour.
The IEA emphasises in its report the risk that "new services and comforts brought about by digitalization - as well as greater use of standby power by idle devices and appliances - could offset potential savings".
Care must therefore still be taken that the unquestionable energy saving potential of smart HVAC systems translates into actual savings. This requires even more than usual well designed, well installed and well used systems.