Comparison of energy consumption in buildings with demand controlled ventilation and conventional CAV

A number of computer simulation case studies have been conducted with the objective of investigating the potential for energy savings in buildings with variable air volume (VAV) systems and demand controlled ventilation (DCV), compared to buildings with conventional constant air volume (CAV) ventilation systems. The simulation systems have been modelled on a modular form, they are generally very detailed and comprehensive, and they have shown to be able to provide very realistic results compared to real world conditions. Energy savings of DCV by CO2, temperature and decipol (indirect CO2 control) have been investigated, both for single zone and multi zone systems. Simulations show that parameters such as occupancy ratio, outdoor temperature, solar radiation, control strategy and minimum flow rates are important for the savings potential. Energy savings obtained from DCV are not only a result of decreased energy usage for air conditioning and fan operation. Such numbers have little meaning other than for a comparison among air conditioning systems. The coherent behaviour of different energy systems in the building is very important. Since energy usage of several systems in a building is affected by DCV, it is the savings related to the total energy usage of the buildings that is outlined. Simulations show that savings in the range of 30-50% of CAV easily can be achieved, even more in many cases. Energy savings can be increased further by introducing even more effective control strategies.