Zone Ventilation Research Articles

Workplace NO and NO2 during combined treatment of infants with nasal CPAP and NO

To determine the workplace concentrations of NO and NO(2) in and around a paediatric incubator during inhaled NO (iNO) treatment and during an accidental emptying of NO cylinders into room air. We simulated iNO-nasal CPAP treatment in order to assess the impact on the occupational environment. Furthermore, two full NO cylinders for therapy, 1,000 ppm, 20 litres, 150 bar and 400 ppm, 10 litres, 150 bar, were emptied as rapidly as possible into an intensive care unit (ICU) room. University hospital ICU. To correctly gauge the contribution from iNO-CPAP we constructed a system measuring breathing zone and room ventilation inlet-outlet values during a 10-ppm iNO treatment of a simulated infant. Maximal breathing zone values were 17.9 +/- 7.0 (mean +/- 95% CI) ppb for NO and 25.2 +/- 4.8 ppb for NO(2). If room inlet values were subtracted, the contributions to breathing zone values emanating from iNO-CPAP were 14.8 +/- 4.6 ppb for NO and 14.6 +/- 4.6 ppb for NO(2). At the ventilation outlet the maximal contributions were 4.2 +/- 2.9 ppb NO and 9.6 +/- 4.3 ppb NO(2). During rapid total release of a gas cylinder in the ICU room, simulating an accident, we found transient NO levels comparable to the high therapeutic dosing range, but only low NO(2) levels. Neither 8-h time-weighted average (TWA) nor 15 min short-term exposure limits (STEL) were exceeded during normal operation or during a simulated accident. The contribution of nitrogen oxides from treatment to workplace air were minor compared to those from ambient air.

An attic-interior infiltration and interzone transport model of a house

A detailed model is developed for predicting the ventilation rates of the indoor, conditioned zone of a house and the attic zone. The complete set of algorithms is presented in a form for direct incorporation in a two zone ventilation model. One of the important predictions from this model is the leakage flow rate between the indoor and attic zones. Ventilation rates are predicted from a steady state mass flow rate balance for each zone where all individual flow rates through leakage sites are based on a power law expression for flow rate versus pressure difference. The envelope leakage includes distributed leakage associated with background leakage, localized leakage associated with vents and flues, and active fan ventilation. The predicted ventilation rates agree quite well with field measurements of ventilation rates in houses and attics with different leakage configurations, without the use of any empirically adjusted parameters or constants.

A study of energy use and satisfactory zone ventilation of different outdoor air ventilation strategies for terminal reheat variable air volume systems

Increased building indoor air quality (IAQ) complaints due to reduced outdoor air ventilation rates led to ASHRAE Standard 62–1989. Even though the stipulated standard total outdoor ventilation flow rate may be drawn into the HVAC system, thermal imbalances in the various zones of the building can lead to certain zones being starved of the specified ventilation flow rate, thereby creating localized IAQ problems. The objective of this paper is to compare the differences in energy use and ventilation air flow rates supplied to different zones in the building for three different practical outdoor air ventilation strategies all of which are identical in performance at design conditions but which differ under part-load operation. A simplified simulation methodology (which past studies have demonstrated to be useful for field evaluation of actual buildings) has been used to predict the heating and cooling energy use of a two-zone terminal reheat variable air volume (TRVAV) system during part-load operation specified by varying outdoor temperature and humidity conditions. The trade-off between outdoor air intake and energy use are studied for the following ventilation strategies for a typical 10,000 m 2 commercial building: (i) constant outside air intake based on a value 20% higher than the ASHRAE minimum ventilation rate, (ii) constant ventilation air intake fraction, and (iii) ventilation air intake based on the unfavorable zone requirements (even though the other zone may be over-ventilated). How this trade-off is impacted by bullding size has also been investigated. Finally, we use bin data for Dallas, TX (a moderately hot and humid location) and Seattle, WA (a mild location) in order to study the differences in energy use and zone ventilation flows of different ventilation strategies due to building location. The effect of economizer cycles and of varying ventilation strategies depending upon diurnal building schedules have not been considered in this study. The results of this study which are based on a simplified HVAC simulation approach are consistent with conclusions reached by other researchers Using more detailed simulation models. This suggests that sound and meaningful diagnostic insights of actual building performance and operating strategies can be obtained from such simplified simulations.

The functional significance of ventilation frequency, and its relationship to oxygen demand in the resting brown long-eared bat, Plecotus auritus

Mean oxygen consumption and simultaneous ventilation frequency of nine non-reproductive brown long-eared bats (body mass 8.53-13.33 g) were measured on 159 occasions. Ambient (chamber) temperature at which the measurements were made ranged from 10.8 to 41.1 degrees C. Apneic ventilation occurred in 22 of the 59 measurements made when mean oxygen consumption was less than 0.5 ml.min-1. No records of apneic ventilation were obtained when it was over 0.5 ml.min-1. The relationship between ventilation frequency and mean oxygen consumption depended on whether ventilation was apneic or non-apneic. When ventilation was non-apneic the relationship was positive and log-linear. When ventilation was apneic the relationship was log-log. Within the thermoneutral zone ventilation frequency was not significantly different from that predicted from allometric equations for a terrestrial mammal of equivalent body mass, but was significantly greater than that predicted for a bird. A reduction in the amount of oxygen consumed per breath occurred at ambient temperatures above the upper critical temperature (39 degrees C).

Regional lung ventilation in ankylosing spondylitis.

Patients with ankylosing spondylitis (AS) sometimes develop apical lung fibrosis and cavitation. It has been suggested that one causative factor is reduced apical ventilation due to rigidity of the thoracic cage. We measured regional ventilation in 27 patients with AS and 18 normal volunteers. Twelve patients (Group A) had chest expansion greater than 2 cm, twelve (Group B) had chest expansion of 2 cm or less and three (Group C) had apical lung lesions on chest radiographs; patients in Groups A and B had no radiographic lung lesions. Ventilation per unit volume (VE/VA min-1) was calculated from 81Krm washout curves. The ratio of upper zone to lower zone ventilation (VR) was calculated. VR in Group A (0.74 +/- 0.11) and group B (0.75 +/- 0.12) was not significantly different from VR in controls (0.76 +/- 0.08). There was no significant correlation between VR and FVC, FEV1 or maximal chest expansion. In patients with apical fibrosis only the radiographically abnormal areas had reduced ventilation. Patients with AS do not underventilate the upper zones of the lungs except in the presence of radiographically visible fibrosis.

Inspiratory flow rate and ventilation distribution in normal subjects and in patients with simple chronic bronchitis.

1. Seated subjects stopped ventilation briefly at end expiration while a 5 ml bolus of 133Xe was injected close to the mouth. They then inspired air at different flow rates and the distribution of radioactivity in the lungs was measured with a scanning technique during a period of breath-holding at maximal inspiration. 2. In five normal subjects the dependent zones received a greater fraction of the 133Xe bolus than the apex during slow inspirations, but apical distribution exceeded basal for fast inspirations. The volume history of the lungs before the bolus injection had no effect on the slow/fast difference in four out of five subjects. 3. In five patients with clinical bronchitis but normal forced expired volume, dependent zone ventilation was much reduced on a slow inspiration compared with normals, but at fast flow rates the distribution was normal. 4. Insofar as the bolus in the fast inspiration was distributed according to regional airway conductances, these results suggest that in normal subjects differences in airway resistance exist between the upper and lower zones of the upright lung. An early abnormality in bronchitis appears to be a reduction of compliance in the dependent zones, as judged from the decrease in basal ventilation on a slow inspiration.