Achieving Energy Efficiency in Building HVAC Systems

Our research is directed at developing a software based tool that provides the basis for re-optimizing a critical variable that determines energy use in a buildings HVAC system, the specified airflow rates for each VAV box.

Why worry about HVAC energy efficiency?SmCity_HVAC_photonics

Analysis of large and moderate sized buildings reveals that HVAC accounts for 50 % of the building energy use, and that the total building energy use and cost scales strongly with airflow. This strong correlation occurs particularly in older buildings which were typically designed when energy was cheap and it was easier to meet the multiple ventilation, thermal, and humidity objectives by using high airflow rates. These high airflows however are costly, not only due to the energy used to heat and cool the air, but also due to large electricity demand to move the air around the building.

How our approach works

Our system determines actual flow rates on a room-by-room basis by using the building automation system and measuring the system response. The information obtained can then be used to determine what new reduced airflow rates could be used in each room while meeting its ventilation requirements. Building-wide performance is achieved by aggregating empirically determined room-level loads, thus ensuring that the coupled performance objectives can be achieved while minimizing energy use for every space within a building. This approach determines actual airflow rates for each room without relying on labor intensive room-by-room manual experiments conducted by air balancers.

Further benefits of our approach

Our approach provides a basis to re-optimize an existing building’s HVAC system without the need to change any equipment and it addresses “hidden” HVAC energy use that can’t be found by de-trending. Since the system is designed to utilize the building automation system to obtain data and to implement the solution, it is essentially a software solution that can achieve large energy reductions at a low cost. Robustness of the solution is achieved since it is based on real data from room-by-room controlled measurements. Lastly, this approach is also useful for conducting part of the commissioning work of new buildings, as well as diagnosing VAV problems such as broken dampers and sensor errors without extensive manual tests.