Air handling units

Figure 20-87 shows a typical production-size batch fluid-bed granulator. The air-handling unit dehumidifies and heats the inlet air. Heated fluidization air enters the processing zone through a distribu-... 

Air-handling units equipped with heat recovery and sophisticated control of the key parameters of HVAC systems, such as temperature, airflow rate, and pressure difference... 

Normally there is some connection between the airflow rate and noise and vibration generation. This could modify the building construction either to prevent spreading or to diminish the levels of noise and vibrations from the air-handling units. This naturally includes all parts of these units, i.e., fans, pumps, and valves (see Chapters 5 and 9). The demands on noise insulation also include the noise and vibrations from the process equipment, which often has a higher level of noise and vibration than the ventilation system. 

Criteria for Acceptable Air-Handling Units and HVAC Sjrstem Noise Levels 800... 

The basic topic of this chapter is theoretical aspects of air handling units, ductwork design, and the optimization of building energy systems. 

In work areas, the noise is usually generated by different sources, such as air-handling units, refrigerating plants, etc. (especially extract and supply air fans). 

Concerning the sound pressure level, when a noise generated by an HVAC system or an air-handling unit increases the ambient background noise by a dB, the noise increase is just perceptible. On the contrary, an increase oi 5 dB or more is clearly perceptible. 

Dampers in air handling units and air distribution systems Attention has to be paid to reducing the leakages, in accordance with EN 1751. Dampers used in mixing sections of air-handling units must fulfill additional requirements, in accordance with prEN 13053. 

Mixing in air-handling units and air distribution systems Some main principles are presented in Section 9.4. However, air mixing is a complicated process under srrong development. Also, the need for major improvements in the equipment has been identified very recently in connection with the standardization work in CEN (prEN 13053). 

Air handling unit A self-contained unit for the introduction or removal of air from a space. It consists of one or more of the following plant items heating or cooling coils, filters, fans, damper provision for mixing and recirculation, humidification controls, and acoustic treatment. 

Blow-through unit An air-handling unit downstream of the supply fan. 

External fan pressure difference The difference between the total gauge pressure at the outlet of an air handling unit and the total gauge pressure at the inlet. 

Fan section of air handling unit A unit in which one or more fans are housed. 

Filter section of an AHU The section of an air-handling unit that contains a filter. 

Pressure burst A failure in a filter, duct work, or an air handling unit due to high differential pressure. 

Straighteners Vanes fitted in ductwork or air handling units before or after a change in section to produce a reduction in pressure drop. 

An example would be where the consultant had already invited competitive quotations for supplying air-handling units so that he could design a particular make into the system and ensure that his client received the best value for money. The bidder would include in his bid, either separately shown or in the body of his figures, a sum to cover profit and on-cost in handling the equipment. The contractor appointed would be responsible for organizing delivery and would give a warranty on the equipment, in accordance with the contract. This aspect is amplified in Section 8.20. 

Air-handling unit A self-contained package incorporating all equipment needed to move and treat air, requiring only connection to ductwork and services to provide a complete ventilation system. 

Larger ducted ventilation systems, as used in offices and commercial premises using a central air-handling unit and fabricated distribution ductwork, are akin to air-conditioning systems but with less treatment to the air at the AHU (see Chapter 29). 

Direct expansion cooling Temperature difference Air changes (room volumes) per hour Air-handling unit Static water gauge... 

While the air distribution must match the heat distribution, the position of extracts is not important. Direct return to air-handling units mounted around the room in numbers necessary for reliability is common practice. In the event of loss of one or more cooling modules a well-designed ventilated ceiling adds to reliability by distributing the reduced amount of air in the same proportions throughout the room. 

Large fans are required for boiler plant, furnaces and large air-handling units. These fans can now be fitted with variable-speed motors to reduce electricity consumption and maximum power, albeit at additional cost. 

Chilled water air-handling unit taking chilled water from a package or the central plantroom... 

This is a conventional water loop heat pump system using a boiler and cooling tower to maintain the water loop temperature (see Measures S15-S17 in Section 6.2). Since outside air handling unit and other terminal devices like unit heaters, wall fin convectors, etc which are often used with this water loop heat pump system need a different operating water temperature than that of the water loop, a plate heat exchanger is used between the primary heating circuit... 

Humidification can be done at the system level by having humidifier section at the air-handling unit supplying fresh air. The humidifier can be electric or gas type. Another method is to use evaporative pads such as GLASdek from Munters. This eliminates the use of gas or electricity for humidification. 

Outdoor air is treated and supphed by a central air-handling unit. The required amount of air is delivered into the return air plenum of the fan coil units. The air-handling unit is provided with a hot water coil and chilled water coil. Both the coils are served by central reversing heat pump. A total enthalpy wheel can reduce the energy consumed for treating outdoor air. 

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