Ventilation evaluation

This case illustrates the importance of serial night studies in identifying the need for ventilation, evaluating its effectiveness and providing objective evidence for the consideration of alternate options for ventilatory support. 

The significant differences in disturbance, when evaluated with regard to the average noise levels, shows that the noise level is a decisive factor with regard to disturbance. Measures to limit the disturbance reaction due to ventilation noise should, therefore, naturally be directed in the first instance at lowering the noise level. 

Today occupants, building owners, and other end users of ventilation systems are more interested in the level of air quality and thermal climate than in the techniques by which that level is achieved. This is supported by the fact that industrial ventilation system.s in modern premises are more complicated and tightly integrated with the process and building automation. It is therefore difficult for end users or nonprofessionals to evaluate whether a ventilation system is functioning correctly. 

The latter information is important in evaluating the size of the rxrcupied zone that can be effectively ventilated by inclined jets. It was proposed that the occupied zone of rooms is well ventilated by inclined jets (particularly in industrial rooms with contaminant release) if air velocity in the occupied zone exceeds 0.1 m/s. 

Natural ventilation design allows one to size the inlets, and outlets, / p based on their pressure loss characteristics, Cp, and on the airflow rate, G , required to maintain the occupied zone within desired limits. The reverse design procedure is commonly used to evaluate the airflow rate through the building given the sizes, characteristics, and locations of inlets and outlets and the heat load and characteristics of heat sources. 

Another factor influencing contaminant and heat transfer from dirty to clean zones against the stable airflow is a turbulent exchange between these zones. This process should be considered in the design of displacement or natural ventilation systems and evaluation of the emission rate of contaminants from the encapsulated process equipment (Fig. 7.111a). 

When detailed information on heat and contaminant sources is available, assessment of design is improved by evaluating the effectiveness of contaminant removal achieved by space ventilation. The set of contaminant removal effectiveness indices in Table 8.5 is given in accordance with contemporary use of indices. 

Application of the age of air concept can be justified by the fact that the content of contaminants found in the exhaust air normally rises from the value found in supply air entering the room. On its voyage through the room, the air is likely to pick up more contaminants the longer it stays in the room. This is a very simple assumption. It can be argued, however, that using the age of air concept is the best way to evaluate ventilation design for scenarios where little or no information is available on use of the room and locations and emission rates for heat and contaminant sources. 

Evaluation procedures for local ventilation are described in Section 10.5. The actual evaluation procedure for a specific system is mostly described in connection with the different parameters that influence the function of the system. Many of the evaluation procedures for general ventilation systems described in Chapter 12 could be used also for local ventilation. 

LVHV nozzles can create problems that may be sufficiently severe as to prevent their use, usually in the form of ergonomic encumbrances and excessive noise. These problems can be dealt with, to limited extents, and LVHV applications can be effective. It must also be understood that dust control by 1..VHV systems is ultimately limited. No ventilation control measure can ensure sufficient worker protection down to extraordinatily low acceptable dust levels. Worker protection must always be confirmed by industrial hygiene monitoring and evaluation, and administrative control measures such as respiratory protection may be necessary. 

For supply inlets in rooms some performance measurements exist, such as air exchange and ventilation efficiencies (see Chapter 8). It is usually not possible to use these for local ventilation supply inlets, and for the moment there are no specific measurements to evaluate the influence of an inlet on contaminants. Some trials with comparison indices, which compare inhaled concentrations (or exposures) with and without a supply inlet, have been done. 

TTie ability of the ventilation system to protect the worker efficiently can readily be determined by personal samples. The PIMEX method (see Chapter 12) can be used to determine the worker s exposure during various work phases. The capture efficiency as well as the supply air fraction can be measured using tracer gas techniques. Simple evaluation is carried out visually with smoke tube or pellet tests. Daily system evaluation is recommended using airflow or static pressure measurements at appropriate parts of the system. The air velocities, turbulence intensities, air temperature, mean radiant temperature, and air humidity should also be measured to provide an assessment ol thermal comfort. 

A visual evaluation of ventilation system performance can be performed by injecting smoke into the jet. No quantitative evaluation methods for these systems have been reported, but it should be possible to measure the containment of a hood with side walls (partial enclosure) using one of the containment indices (see Sections 10.2.1 and 10..5). Additional information may be obtained by measuring capture efficiency. 

Different available measurement instruments and evaluation methods are described in Chapter 12. Some specific methods to evaluate local ventilation systems are described in this section. All local ventilation systems should be evaluated regularly. The evaluation procedures can be divided into detailed and simple, as well as direct and indirect, procedures. The detailed procedures need special instruments and competence, whereas it should be possible to use the simple procedures every day. Since the simple procedures do not measure directly the performance of the exhaust, it is usually necessary to calibrate a simple procedure by using a detailed procedure. ... 

Combined thermal and multizone airflow models are needed for problems such as thermal comfort analysis in naturally ventilated buildings, determination of heat-removal capacity by natural ventilation, design and evaluation of passive cooling by nighttime ventilation. This is outlined in more detail in Section 11.5. 

This example considers the thermal summer condition evaluation of a large, naturally ventilated test laboratory hall at EMPA (Fig. 11.50). 

Several tools can be used to evaluate the environmental consequences of an industrial ventilation project. Some of the most common methods used are covered in this chapter. The life cycle assessment tool is considered in detail, as it is a comprehensive and product-oriented approach that is covered by international standardization. Other tools, such as risk assessment, cost-benefit... 

Using formalized risk assessment techniques for industrial ventilation projects may complicate the issue more than necessary. The work environment and its exposure conditions are the focus. However, when evaluating new technology, including waste management, the risk assessment approach may be valuable. 

The CBA technique is frequently used in the United States. It is relevant for evaluating industtial ventilation projects, but is possibly not feasible for... 

Some elements of the EIA process may be relevant for evaluating industrial ventilation projects. Of particular interest are the requirements for industrial ventilation put forth by EIAs. 

Buildings erected must be adequate witli respect to explosion venting and ventilation, firewalls, exits, drainage, and electrical wiring. The safety of the equipment and the structures is often a function of tlieir age. Tlie degree of "adequacy" must be evaluated based on tliis as well as the factors above. 

In a cosmetic laboratory, a recirculating system would have been adequate except for one very special condition. The noses had to perform their fragrance evaluations in a clean atmosphere. This called for once-through ventilation and included placing drying ovens under a simple hood extending part way down from the ceiling. The result was excellent. 

The laboratory area had no ventilation, and the system used elsewhere in the building was unable to handle the extra load. As a result, a separate system had to be installed. At the laboratory operator s insistence, this was to be a system -with no recirculation of ah . There was considerable resistance from management due to the higher cost for both installation and operation. To make matters more difficult, the heating engineer had never seen a need for such a system on previous jobs. One argument finally settled the situation. It was pointed out that fragrance evaluations would often have to be performed as part of product evaluation. This would be difficult if much of the air were recirculated. 

The patient has been transferred from the CT scanner to the surgical intensive care unit for mechanical ventilation, blood pressure support, and surgical evaluation. A diagnosis of acute pancreatitis with pancreatic necrosis is made. 

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