Comfort ventilation

A young scientist said, I have never seen a complex scientific area such as industrial ventilation, where so little scientific research and brain power has been applied. This is one of the major reasons activities in the industrial ventilation field at the global level were started. The young scientist was right. The challenges faced by designers and practitioners in the industrial ventilation field, compared to comfort ventilation, are much more complex. In industrial ventilation, it is essential to have an in-depth knowledge of modern computational fluid dynamics (CFD), three-dimensional heat flow, complex fluid flows, steady state and transient conditions, operator issues, contaminants inside and outside the facility, etc. 

When we compare industrial air technology (lAT) with comfort ventilation, we can see that technologically our task is very challenging. To fulfill all the needs of the end user is often impossible. If the lAQ is fulfilled, the amount of air may be so large that draftiness is too high. We must also have the courage to say what is possible and what is not. We also have to cteate tools to validate this. 

This section shows some examples of the use of model experiments. The examples cover the range from natural ventilation of buildings, comfort ventilation of an exhibition hall, to local ventilation in industrial areas. 

Comfort ventilation The minimum amount of air that must be provided to a worker to ensure... 

One will recall from Equations 18-2and 18-4 that air velocity is one of the key physical parameters contributing to control of heat stress. Air velocity strongly influences convective and evaporative cooling. When it is warm indoors and cool outdoors, we may open a window in a building to let in clean air. Not only is there a temperature difference, but there is air movement. We turn on a fan or set a fan in a window to increase air velocity. Most often we use thermal comfort ventilation to provide cooling. However, if the conditions are right, ventilation can warm a space and its occupants. 

Although it is not effective in removing potentially toxic contaminants, general ventilation is often acceptable in providing comfort ventilation to control humidity, ternperamre, odors and carbon dioxide build-up and to remove dusts and biological agents from the air supply. 

Heat control ventilation (sometimes called comfort ventilation) is used to control indoor atmospheric conditions associated with hot industrial environments such as those found in laundries, foundries, bakeries, and so on, for the purpose of preventing worker discomfort. In many laboratories, there are significant heat sources that can cause an elevation of the workplace temperature. Obviously, this is not a good or comfortable situation for the workers. Thus, exhaust ventilation is provided to control the heat and humidity to provide comfort. 

The elements of a PM plan include periodic inspection, cleaning, and service as warranted, adjustment and calibration of control system components, maintenance equipment and replacement parts that are of good quality and properly selected for the intended function. Critical HVAC system components that require PM in order to maintain comfort and deliver adequate ventilation air include a outdoor air intake opening, damper controls, air filters, drip pans, cooling and heating coils, fan belts, humidification equipment and controls, distribution systems, exhaust fans. 

Systematic studies have been carried out for the purpose of studying how low-frequency tones, broad-band components, and/or time fluctuations in ventilation noise interfere w ith disturbance reactions, In one of these studies, the respondents were exposed to ventilation noise that is representative of the noise encountered in office premises. The respondents were asked to use a rotating potentiometer to set the most acceptable noise level and the least acceptable noise level for each noise, taking account of comfort, disturbance, and performance, w hile performing their work at the same time. The noise level was maintained at a constant level of 40 d.B(A). 

Ventil u u m Corrosion Materials Pressure difterence (.iorrosinn Lhermal conditions Materials Openings lightness Comfort lAQ Corrosion Materials Irinissions limnissiofis... 

Fissore, A. A., and G.. A. Lieheck. 1991. A simple empirical model for predicting velocity distri butions and comfort in a large slot ventilated space. ASHRAE Transactions, vol. 97, no. 2. 

Li, Z. H. 1994. Fundamental studies on ventilation for improving thermal comfort and I.AQ. Ph.D. thesis. University of Illinois. 

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. 

If the flow is isothermal, there is no need to solve for the temperature equation (Eq. (11.6)). In this case the last term in Eq. (11.5) is also dropped. If, however, the thermal comfort is simulated, then the temperature equation must be solved. In ventilation the temperature variations are normally small, which means that it is sufficient to account for density variation only in the gravitation term (the last term in Eq. (11.5)). The gravitation term acts in the vertical direction, and in Eq. (11.5) it is assumed that the xj coordinate is directed vertically upward. denotes a reference temperature, which should be constant. It does not influence the predicted results, except that the pressure level is changed. It could, however, affect convergence rate (i.e., increase the number of required iterations required to reach a converged solution), and it should be chosen to a reasonable value, such as the inlet temperature. 

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. 

Thermal comfort analysis in naturally ventilated buildings... 

Nighttime ventilation is necessary under summer conditions to keep temperatures in the comfort range. The ventilation openings should be closed if... 

In industrial ventilation the majority of air velocity measurements are related to different means of controlling indoor conditions, like prediction of thermal comfort contaminant dispersion analysis adjustment of supply airflow patterns, and testing of local exhausts, air curtains, and other devices. In all these applications the nature of the flow is highly turbulent and the velocity has a wide range, from O.l m in the occupied zone to 5-15 m s" in supply jets and up to 30-40 m s in air curtain devices. Furthermore, the flow velocity and direction as well as air temperature often have significant variations in time, which make measurement difficult. 

In recent years, many closed buildings have again been built in order to meet new noise regulations. The buildings are usually provided with forced ventilation, but this is much less effective than natural ventilation and is usually designed for the comfort of the operators rather than the dispersion of leaks. 

Research done by experts in the field as well as in laboratories has helped them understand the relationship between lAQ, ventilation, and energy. More research is needed to link specific health symptoms with exposure to specific or a group of pollutants. The policy challenge will be to raise awareness of indoor air quality so that healthy, comfortable environments can be provided by energy efficient technology. 

Building comfort is one of the key elements of a successful commercial building. The thermal comfort of a building is often as compelling as the aesthetics of the design. Modern building mechanical systems have two primary functions maintain spaces within a predefined comfort range and deliver outdoor air to each space to assure proper ventilation. They have to do this in a qniet and efficient manner. 

Drafts, condensation on windows, ice damming, excessive noise from outdoors or equipment operation, and rooms that are cold in winter and hot in summer will diminish comfort in a home. Air-sealed construction, improved insulation, high-performance windows, right-sized, efficient hcating/cooling distribution systems, and mechanical ventilation commonly found in energy-efficient homes all work together to effectively eliminate these problems. 

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