Ceiling-Mounted CO2 Sensing: Effect of Location and Stratification Temperature

IF 4.3 2区 环境科学与生态学 Q1 CONSTRUCTION & BUILDING TECHNOLOGY
Indoor air Pub Date : 2024-09-27 DOI:10.1155/2024/1840021
Tewe Heemstra, Marc van der Schans, Joanna Gibas, Jean-Paul M. G. Linnartz, Roger Delnoij
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引用次数: 0

Abstract

Carbon dioxide is an important parameter for indoor air quality (IAQ) monitoring and demand controlled ventilation (DCV). Usually, CO2 sensors are wall-mounted at 0.9–1.8 m (3–6 ft) height as prescribed by LEED, although ASHRAE standards seemed to relax this requirement. In this work, we investigate whether positioning these sensors in the ceiling is effective and advantageous. We studied CO2-level measurements for HVAC control in configurations with mixing ventilation and found that CO2 from human exhalations experiences buoyancy from several factors. We calculated buoyancy from air properties, and we introduced the notion of “stratification temperature” for exhaled air. By simulation, we test the sensitivity to temperature, and we conducted in situ in vivo measurements to acquire more detailed insights in the feasibility of ceiling sensor positions. Buoyancy calculations show that in exhaled air, the positive buoyancy of H2O approximately compensates for the negative buoyancy of CO2, so that thermal buoyancy is the most dominant factor. Exhaled air, containing CO2 to be measured, will rise towards a ceiling that has a temperature below the stratification temperature. Computational fluid dynamics (CFD) simulations of a small office space indicate that this can also be the case in the presence of air flows induced by a mechanical ventilation system. The measurement results support that using “properly mounted” CO2 sensors in the ceiling gives lower variability in CO2 measurements and faster response than wall-mounted sensors and yields slightly higher values than wall sensors. Our results highlight the need to update the standards and regulations for sensing CO2 to include ceiling-mounted sensors.

Abstract Image

吸顶式二氧化碳传感:位置和分层温度的影响
二氧化碳是室内空气质量(IAQ)监测和按需控制通风(DCV)的重要参数。通常情况下,按照 LEED 的规定,二氧化碳传感器安装在 0.9-1.8 米(3-6 英尺)高的墙壁上,尽管 ASHRAE 标准似乎放宽了这一要求。在这项工作中,我们研究了将这些传感器安装在天花板上是否有效和有利。我们研究了混合通风配置中用于暖通空调控制的二氧化碳水平测量,发现人类呼出的二氧化碳会受到多种因素的浮力影响。我们通过空气特性计算浮力,并引入了呼出空气的 "分层温度 "概念。通过模拟,我们测试了对温度的敏感性,并进行了现场活体测量,以便更详细地了解天花板传感器位置的可行性。浮力计算显示,在呼出的空气中,H2O 的正浮力大致补偿了 CO2 的负浮力,因此热浮力是最主要的因素。含有待测二氧化碳的呼出空气会向温度低于分层温度的天花板上升。对一个小型办公空间进行的计算流体动力学(CFD)模拟表明,在机械通风系统产生气流的情况下,也会出现这种情况。测量结果表明,与安装在墙壁上的传感器相比,"正确安装 "在天花板上的二氧化碳传感器能降低二氧化碳测量值的变化率,并且响应速度更快,测量值也略高于墙壁上的传感器。我们的结果突出表明,有必要更新二氧化碳传感的标准和规定,将安装在天花板上的传感器纳入其中。
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来源期刊
Indoor air
Indoor air 环境科学-工程:环境
CiteScore
10.80
自引率
10.30%
发文量
175
审稿时长
3 months
期刊介绍: The quality of the environment within buildings is a topic of major importance for public health. Indoor Air provides a location for reporting original research results in the broad area defined by the indoor environment of non-industrial buildings. An international journal with multidisciplinary content, Indoor Air publishes papers reflecting the broad categories of interest in this field: health effects; thermal comfort; monitoring and modelling; source characterization; ventilation and other environmental control techniques. The research results present the basic information to allow designers, building owners, and operators to provide a healthy and comfortable environment for building occupants, as well as giving medical practitioners information on how to deal with illnesses related to the indoor environment.
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