Effect of sensor position on the performance of CO2-based demand controlled ventilation

Abstract

CO2-based demand controlled ventilation (DCV) can save energy while maintaining acceptable indoor air quality. CO2 concentration may vary within an occupied space and it is unclear how sensor location influences the ventilation and energy performances. The objective of the present study is to investigate the effect of CO2 sensor position on the performance of DCV systems under mixing and displacement ventilation. Experimentally validated computational fluid dynamics (CFD) models were simulated under representative indoor ventilation and occupancy conditions. The results show that the ventilation strategy, occupancy level, and air change rate have notable impacts on the CO2 sensing performance. Under mixing ventilation, CO2 sensors placed at the room exhaust can meet the requirements of sensor accuracy defined by ASTM E741 and California Title 24. However, the sensor errors associated with sensor location can be higher than the acceptable threshold under displacement ventilation, which exhibits vertical CO2 stratification with two separated zones (lower transition zone and upper uniform zone). The dividing height of the two zones is highly sensitive to the occupancy level. In such cases, exhaust sensors can overestimate the breathing zone concentration and result in additional energy consumptions for thermal conditioning as well as fan operation, especially for densely occupied buildings. The study findings suggest that for ensuring good performance of CO2-based displacement ventilation, it is necessary to develop quantitative relationships between CO2 concentrations at the breathing height and the room exhaust considering ventilation strategies. Keywords: indoor air quality; CO2 sensing; computational fluid dynamics; building energy; displacement ventilation Highlights • CO2 sensors near occupants result in large errors under displacement ventilation • CO2 sensors at breathing height perform well for constant occupancy conditions • CO2 sensors at breathing height yield errors with varying occupancy • Under mixing ventilation, CO2 sensors at the room exhaust yield a good accuracy Energy and Buildings, Aug. 2019 ! https://doi.

Effects of ventilation on the indoor spread of COVID-19

“…Other examples of stratification have been reported in mixing-ventilated spaces (Mahyuddin & Awbi 2010; Pei et al. 2019).

Figure 2.The concentration measured at different heights in a naturally ventilated office in London.

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“…CO 2 ), which is more than sufficient to counteract the density of CO 2 at the measured concentration. Other examples of CO 2 stratification have been reported in mixing-ventilated spaces (Mahyuddin & Awbi 2010;Pei et al 2019).…”

Spatial distributions of ozonolysis products from human surfaces in ventilated rooms

“…Due to the large temperature gradient between the human surface and the ambient air (>10°C), buoyancy‐driven thermal plume developed over the surface of the occupants. To simulate the turbulent flow due to this naturally convective thermal plume, Menter's shear stress transport (SST) k‐ω model was applied 32,33 . To capture detailed heat and mass transfer near the surface boundary layer, the first cell height of the human manikins was designed as 5 mm, which resulted in the average y + value (dimensionless wall distance of the cell centroid from the nearest wall) of 1.5 for the manikin surface 34 …”

“…To simulate the turbulent flow due to this naturally convective thermal plume, Menter's shear stress transport (SST) k-ω model was applied. 32,33 To capture detailed heat and mass transfer near the surface boundary layer, the first cell height of the human manikins was designed as 5 mm, which resulted in the average y + value (dimensionless wall distance of the cell centroid from the nearest wall) of 1.5 for the manikin surface. 34 The velocity field calculated from the CFD model was validated with previous measurements.…”

An Investigation of Indoor Air Quality in a Recently Refurbished Educational Building

“…Although CO 2 is denser than air, CO 2 stratification occurs because exhaled breath is warm, and is either immediately entrained into the main body plume or rises as a secondary plume where it typically settles at an intermediate height before being entrained and carried into the upper layer (Bhagat et al, 2020). Pei et al (2019) showed that temperature and CO 2 The objective was to sample the building and its typical contents to capture the combined effect of the following Furniture and numerous architectural models and model making equipment were present throughout the space…”