Return grill

Figure 27.14 Discharge and return grilles on same wall (plan view)...

Engine components. Parts fabricated from injection-molded fiber-reinforced polyamide-imides provide a lower-cost solution to previously machined metal pieces and maintain, due to low shrinkage, very tight tolerances which are required in these applications. Polyamide-imide compounds have replaced expensive titanium in air return grills for commercial aircraft engines (Fig. 12.13). The shroud on the interior of the aircraft engine, responsible for directing airflow, consists of an assembly of multiple polyamide-imide injection-molded pieces (Fig. 12.14). 

Identification of the pollutant source and installation of the local exhaust is critically important. For example, an improperly designed local exhaust can draw other contaminants through the occupied space and make the problem worse. The physical layout of grilles and diffusers relative to room occupants and pollutant sources can be important. If supply diffusers are all at one end of a room and returns are all at the other end, the people located near the supplies may be provided with relatively clean air while those located near the returns breathe air that has already picked up contaminants from all the sources in the room that are not served by local exhaust. 

Air-conditioning, having the air cooling coil with drip tray under, expansion valve, fan and motor, air filters, inlet and outlet grilles. They may also include dampers and duct connections for return and fresh air, heaters, humidifiers and various controls. 

Low-level return or exhaust air grilles are usually preferred. However, where this is not possible, a higher air change rate may be needed to achieve a specified clean area classification, e.g. where ceiling return air grilles are used. 

Airflow volume (To verify air change rates) All classes 12 months Airflow readings for supply air and return air grilles to be measured and air change rates to be calculated. In accordance with ISO 14644-3 Annex BI3 ... 

Cold air return- The ductwork (and related grills) that carries room air back to the furnace for re-heating. 

Register- A grill placed over a heating duct or cold air return. 

A common renovation problem arises when additional personnel need to be accommodated in a space. Office or instructional areas are often partitioned and additional furniture and equipment is installed. Anticipate the need to modify the air distribution in these situations. Conversely, when partitions are removed, creating new spaces, the ventilation distribution and balance must be revised. Care must be taken to ensure that, in the final layout, air-supply grilles are located far enough away from the returns so that complete air balance and mixing does occur. Otherwise, stagnant areas wiU develop. 

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