Depending on the function of a space, the number of people using it will vary over the course of a day, week, or month. In most academic and commercial buildings, even when the rooms are empty they are using power.
A study by MIT explores the inefficient energy usage in buildings based on how and when they are occupied. Using data from two of the university's own buildings, the research could help designers and building managers make better decisions and optimize energy usage.
The researchers, part of the SENSEable City Lab, analyzed a laboratory classroom building and a more typical office building for all four seasons of 2006. The data showed that both buildings have daily cycles of electricity usage and seasonal cycles for heating and cooling. The research also found that in both buildings, while electricity use closely corresponded to the occupancy, the HVAC (heating, ventilation and air conditioning) loads did not relate to occupancy.
The reason? It takes a large amount of energy and a considerable amount of time to condition large spaces. So while the turnover of people in spaces is fairly fast, the energy needed to heat or cool the space lags behind.
The findings suggest potential for optimizing energy usage by creating a better match between space and occupancy. Co-author of the study, Carlo Ratti notes "You can move the people to the energy, in which case the architecture can help a lot, or you can move the energy to the people, which is more futuristic.”
“This paper is very much in harmony with our recent efforts to design and modify building infrastructure and systems to match varying occupancies,” says Jay Phillips, senior director of operations for Harvard University’s Faculty of Arts and Sciences, who was not involved in this study. He adds: “There is no question that matching building and equipment schedules with dynamic occupancy patterns is a significant conservation opportunity.”
Possible design based solutions include
- rearranging plans so that heat from larger, less used spaces can seep into more rooms
- using sensing based thermometers that regulate temperatures according to the number of people
- repurposing large spaces for more intensive and improved use
Wondering how the researchers measured the occupancy of the buildings for a full year? They tracked WiFi connections as a proxy. The data provides a reasonably reliable indication of occupancy. The researchers propose that their WiFi proxy idea be used for further research on energy usage in buildings since it is a low cost method that can be replicated easily.
“ENERNET: Studying the dynamic relationship between building occupancy and energy consumption” was published in the April issue of the Energy and Buildings journal.
The heat is on [MIT News]
Image: MIT News