Buildings account for approximately 40 % of energy use in the European Union, as well as in the United States. In light of the European Energy performance of buildings directive, efforts are underway to reduce this energy use by targeting zero or nearly zero energy buildings. In such low energy buildings in cold climates, ventilation to ensure suitable indoor air quality is responsible for half or more of their energy use. The use of heat recovery and demand-controlled ventilation are potential solutions to reduce ventilation-related energy consumption. Demand-controlled ventilation can be utilized to realize energy savings by maintaining the concentration of CO2 below a control setpoint. This control approach can reduce ventilation airflows when possible to reduce energy use.
This paper presents a study of a corridor of offices ventilated with constant airflow in Norway over two weeks of normal occupancy. Measurements of temperature, relative humidity, carbon dioxide, particles and occupancy levels were used to calibrate a simulation model. These measurements were used to validate a coupled energy, airflow and indoor air quality model. Co-simulation between EnergyPlus and CONTAM was used to evaluate the baseline energy use and develop a CO2-based demand-controlled ventilation strategy which took into account other pollutants and recirculation airflows. A parametric study was performed to evaluate energy use and occupant exposure. The main findings from the simulations reveal:
- Interactions between recirculation of air and increased ventilation rates to maintain low CO2 levels are not always intuitive. In some cases, increased ventilation rates were unable to maintain acceptable CO2 levels when using recirculation of exhaust air, and the increased fan power of the demand-controlled ventilation system prevented very large energy savings.
- DCV based on multiple pollutants must be carefully programmed to avoid control problems. For instance, reducing outdoor air intake when outdoor particle levels were high was effective so long as occupancy was below 100%.
- Occupant health and building energy use are strongly correlated, and the ventilation control needs to be programmed considering this interdependency. Here we propose to use reduced exposure to pollutants as a performance parameter for comparison to reduced energy use. The study presented herein serves as the initial phase of a project to study in greater detail how to reduce ventilation while ensuring indoor air quality using a comprehensive analysis method.