The Effect of Air Sampling Tube Material on Ozone Measurements
1Energy and Environment Group, Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, QC, Canada; 2Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST), Montreal, QC, Canada
Ozone is a highly toxic reactive gas that has an increasing application in wide industrial and environmental operations. The exposure limits of ozone for workplaces are low as commonly in 100 ppb or less; therefore, accurate measurement of ozone concentration in workplaces is crucial for protecting workers’ health and safety. Ozone can be readily decomposed within the sampling tube due to chemical reactions with the tube’s inner surface or other contaminants inside the tube. The tube material should be resistant to ozone and, more importantly, inert to ozone reaction. PTFE, FEP, and austenitic stainless steel are suggested to use for ozone sampling. Besides, silicone and Viton—common soft tubing materials—are known to be ozone-compatible. In this paper, we tested eight different tubing materials—PTFE, FEP, stainless steel 316, stainless steel 304, Viton, Silicone, Tygon PVC, and FEP lined Tygon PVC (Tygon SE200) — to investigate how they affect the ozone measurements. We monitored the ozone concentration from the inlet and the outlet of each line for 1 h. At 100 ppb of ozone, the ratios of the outlet ozone concentration to the inlet are measured between 0.27 and 1.0. The effects of ozone concentration and humidity are also investigated. Except for PTFE, FEP, and Tygon SE200, the rest of the tested tubing materials showed reductions in the ozone monitor readings, causing false assurance of ozone exposure.
Field Measured Data on Ventilated Attic Performance to Validate the Code Requirements
National Research Council of Canada, Canada
Ventilating attics is a common practice to remove built-up moisture and heat from inside the attic. However, the effectiveness of attic ventilation on moisture accumulation and energy consumption remain in question. Investigating the hygrothermal and energy performance of ventilated attic is a significant step towards sustainable buildings and Net Zero Energy Construction. Therefore, under the ongoing research on Energy Performance of Residential Roofs (EPRR) at the National Research Council of Canada (NRC), this paper aims to consider the relevant parameters to determine the moisture changes and energy consumption of residential roofing under Canadian climatic condition. An experimental platform is designed to test temperature, moisture, air flow, heat flux, and pressure differences to analyze heat gain and energy consumption of vented attic. This holistic approach provides solid bases for architects and residential building designers to analyze the performance of ventilated attic. Findings from the current study indicated that the temperature, air flow, and humidity are, to some extent, constant with a minimal changes inside the attic throughout the day showing a static condition. The attic air temperature is nearly 2oC higher that the ambient air temperature during the early mornings and late evenings indicating the heat flow from indoor heated spaces into the attic room in cold season. However, during the afternoon, the attic temperature is slightly less than the ambient temperature reflecting the impacts of solar radiation. When the air temperature drops, more moisture intrudes to the attic space and since there is no way to lessen the humidity, the moisture accumulates and thus the relative humidity becomes higher than the ambient humidity. The energy consumption is nearly 20% more in the warmest week compared to that of the coldest week indicating the higher cooling energy demands.
Efficiency Increase of Air Handling Units by Parallely Operated Fans
Institute for Energy Efficient Buildings and Indoor Climate, Germany
To meet the rising comfort requirements of non-residential buildings like office buildings mechanical ventilation in the form of e.g. air handling units (AHU) is needed. As of today, the fans in AHUs are designed for a specified operating point. The real operating range does rarely match this design point, which causes the fans operating in ranges with suboptimal efficiencies. This leads to higher electrical consumption than needed and therefore higher emissions of CO2.
In this work we propose a control strategy which can be applied to an AHU where several smaller fans are operated in parallel. We show that when this fan array as a whole is operating in a suboptimal operating point, it is beneficial to switch off one or more fans. This shifts the remaining fans to a operating point with higher efficiency, resulting in an overall higher efficiency.
The experimental AHU is equipped with four parallely mounted radial fans and additional dampers upstream of the fans to prevent backflow in case a fan is switched off. The electric consumption of each fan is measured separately to calculate a global system efficiency. Several fan performance maps are generated from measured data, which enable the controller to predict the system efficiency and decide on the optimal number of active fans.
We benchmark the new control strategy against the standard strategy with no fan-shutoff. The use case covers a demand controlled load profile, which is based on a generic office building with parallel ventilation branches which can be shut off separately.