Air Quality In Rooms Research Articles

Total air age: an extension of the air age concept

Air age is an important index to evaluate indoor air quality in ventilated rooms. Current definition of air age is limited to indoor part, i.e., the air age at the inlets of air supply diffusers is assumed to be zero. This work extends the air age concept to the so-called “total air age” by considering the impact of air delivery process on air age. The air age in duct is solved using one-dimensional flow characteristic, which includes the mixing process between airflows with different ages. It is then coupled with the room air age which is solved using computational fluid dynamics technique. An iterative algorithm is proposed to calculate total air age in general ventilation systems and a direct method is further derived for systems with only one air handling unit. Two examples are given to demonstrate the calculation of total air age and the distributions of total air age are compared with those of traditional air age.

Video exposure assessments demonstrate excessive laboratory formaldehyde exposures.

Video exposure assessments were conducted in a comparative anatomy laboratory using formaldehyde-preserved sharks and cats. Work in the facility using time-integrated samplers indicated personal and area concentrations generally below the current OSHA permissible exposure limit. However, complaints about room air quality were frequent and routine. Using a photoionization detector with an integral data logger, total ionizables present were sampled as a surrogate for formaldehyde. After synchronizing time tracks from the datalogger concentrations with simultaneously created videotapes of laboratory tasks, composite video exposure overlays were generated. Use of this video exposure method revealed very short-lived, excessively high peak exposure events, whereas conventional time-weighted averages indicated the majority (30/32) of personal exposures were below the OSHA limit of 0.75 ppm. These legally acceptable exposure levels were associated with self-reported symptoms of burning nose and eyes and eye irritation. Thus, transient peak formaldehyde concentrations not detected by longer term averaging studies could be responsible for the health effects reported. The video exposure monitoring method demonstrated that close dissection work, opening peritoneal cavities, and specimen selection activities were most likely the causes of elevated student exposures. Teaching assistants' exposures were the highest, exceeding OSHA limits on several occasions. The utility of the video monitoring method for conducting enhanced, critical task exposure assessments is discussed.

Revised Air-Exchange Efficiency Considering Occupant Distribution in Ventilated Rooms

Air-exchange efficiency is widely used to indicate the ventilation effect and indoor air quality in ventilated rooms. However, it does not take occupant distribution in the room into account and is thus limited. In this paper, a revised air-exchange efficiency (occupant air-exchange efficiency) that differentiates between different zones by considering different occupancy in each zone is developed. Results from studies of a large-space ventilation case, a personalized ventilation case, and a displacement ventilation case show that occupant air-exchange efficiency can better be used to evaluate the ventilation effect of a room.

Protecting service and maintenance workers during laboratory chemical hood repairs

Laboratory chemical hoods may be the single most important engineering control for protecting laboratory workers from chemical exposures, but their maintenance and repair can present potential health and safety hazards to facilities staff. We performed a comprehensive survey of chemical hood systems in laboratory intensive buildings here at Yale University, including an assessment of air quality in Chemistry Department mechanical rooms where fan systems must be accessed by service and maintenance staff. Air monitoring in these mechanical rooms showed intermittently measurable concentrations of many laboratory chemicals, but their magnitudes when present were very low, ranging from about 10 to more than 6,000 times below their applicable permissible exposure limits. Despite the perception by many facilities staff that chemical exposures are their greatest hazard, we found that traditional physical safety issues are the most prevalent source of risk to those responsible for laboratory hood maintenance.

Strömungsmessumformer zur Luftvolumenstrombestimmung in Stallanlagen

Other than heating, air volume flow in animal houses is currently the only method for adjusting the desired room temperature and air quality. With the development of anemometers, sensors are available, which make it very simple to measure the air flow and can easily be incorporated into the ventilation control system. Possible uses for these measuring instruments in animal houses are discussed in the following.

Indoor air quality in rooms with cooled ceilings.: Mixing ventilation or rather displacement ventilation?

Experimental investigations and practical experiences in Europe have proved that hydronic cooled ceilings are able to remove high cooling loads without impairing thermal comfort. As hydronic cooled ceilings cannot remove latent loads and pollutants, e.g., CO 2, VOCs, odors, additional ventilation has to be applied. Often, displacement ventilation is used, which is able to provide lower pollutant levels in the occupation zone than mixing flow systems, if the occupants are causing most of the pollution. Unfortunately, the advantage of the displacement flow, in respect to the air quality, can vanish when cooled ceilings are used to remove the major part of the sensible cooling load. For these applications, a combination of a cooled ceiling with a mixing ventilation system might be more appropriate. This paper presents the results of an investigation examining the distribution of tracer gas in a test chamber which is equipped with a radiant cooled ceiling. There is both a displacement flow system and a mixing flow system available, so that the concentrations of the tracer gas within the occupation zone characterizing the air quality can be compared directly and evaluated under similar conditions. The vertical air temperature rise is taken into consideration as well, as it influences the displacement flow and is an important issue for assessing thermal comfort. The results show the interaction of the portion of the cooling load being removed by the supply air, the air quality in the occupied zone and the vertical air temperature rise. The figures and tables presented show which of the two supply air systems investigated have advantages over the other.

Dynamic Model to Tune a Climate Control Algorithm in Pig Houses with Natural Ventilation

Algorithms for environmental control in livestock buildings have to be tuned for optimum response of actuators. For tuning, a simple, but dynamic, climate model for a pig house was formulated and validated to predict the environmental changes in a pig house with natural ventilation under varying conditions. A control algorithm was included in the model and tuning of the algorithm has been performed with the model. The tuned algorithm was implemented in a climate controller and data on the results are presented. It was concluded that the model can be used to simulate room temperature and carbon dioxide concentration in heated pig houses with natural ventilation. The dynamics as well as the actual levels of climate parameters showed agreement between simulation results and actual results. The model can be used to find gain factors and time constants for PID-controllers in algorithms for control of room temperature, air quality, and ventilation rate in natural ventilated pig houses. This would enhance fast and accurate tuning controllers in livestock buildings with natural ventilation as compared to on-site hand tuning.

ROOM-TYPE AIR CLEANER DESIGN CRITERIA AND PROTOTYPE PERFORMANCE

ABSTRACT Two rules-of-thumb for minimum performance of a room-type air cleaner have been developed from consideration of a first order model for room air quality. By adopting a criterion that the use of an air cleaner should cause the particle concentration to be at least cut in half, the rule-of-thumb for a room with no smokers is that the product of filter efficiency and flow rate should be ≥.8 m3/min (≥30 cfm). If the particle concentration is dominated by smokers or other sources, the product of filter efficiency and filter flow rate should be = m3 /min (= 100 cfm) Tests were conducted to determine the efficiencies of candidate filter media. The selected media, Filtrete G-0115, has a fractional efficiency for 1 μm particles of 97 percent when clean, and an efficiency of 78 percent when fully loaded. This drop in efficiency is due to the masking of the electrets on the surfaces of the filter fibers. A fibrous filter room-type air cleaner was designed to perform in accordance with the rules-of-thumb. Wh...

The use of moments for assessing air quality in ventilated rooms

A comprehensive theoretical framework is presented, based on the use of moments of concentration histories, i.e. multiplying concentration readings by time of reading and then integrating with regard to time. The concept is applicable to characterize either the diffusion of the supplied air or a contaminant released within the room. Results are presented from about 50 measurements demonstrating the usefulness and practical applicability of the approach for assessing air quality in ventilated buildings. Different experimental procedures have been explored and are discussed.