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SINGLE-DUCT – Variable Air Volume

A VAV system, as shown in Figure 10, controls temperature in a space by varying the quantity of supply air rather than varying the supply air temperature. A VAV terminal unit at the zone varies the quantity of supply air … Continue reading

12. June 2019 by Jack
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SINGLE-DUCT – Constant Volume

While maintaining constant airflow, single-duct constant volume systems change the supply air temperature in response to the space load (Figure 9). Single-Zone Systems. The simplest all-air system is a supply unit serving a single-temperature control zone. The unit can be … Continue reading

12. June 2019 by Jack
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AHU – Equipment Isolation

Vibration and sound isolation equipment is required for most central fan installations. Standard mountings of fiberglass, ribbed rubber, neoprene mounts, and springs are available for most fans and prefabricated units. The designer must account for seismic restraint requirements for the … Continue reading

12. June 2019 by Jack
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AHU – Outside Air Requirements

common complaint regarding buildings is the lack of outside air. This problem is especially a concern in VAV systems where outside air quantities are established for peak loads and are then reduced in proportion to the air supplied during periods … Continue reading

12. June 2019 by Jack
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AHU – Supply Air Fan

Either axial flow, centrifugal, or plug fans may be chosen as supply air fans for straight-through flow applications. In factory-fabricated units, more than one centrifugal fan may be tied to the same shaft. If headroom permits, a single-inlet fan should … Continue reading

12. June 2019 by Jack
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AHU – Humidifiers

Humidifiers may be installed as part of the central station airhandling unit, or in terminals at the point of use, or both. Where close humidity control of selected spaces is required, the entire supply airstream may be humidified to a … Continue reading

12. June 2019 by Jack
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AHU – Reheat Coil

Reheat systems are strongly discouraged, unless recovered energy is used (see ASHRAE Standard 90.1). Reheating is limited to laboratory, health care, or similar applications where temperature and relative humidity must be controlled accurately. Heating coils located in the reheat position, … Continue reading

12. June 2019 by Jack
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AHU – Cooling Coil

In this section, sensible and latent heat are removed from the air. In all finned coils, some air passes through without contacting the fins or tubes. The amount of this bypass can vary from 30% for a four-row coil at … Continue reading

12. June 2019 by Jack
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AHU – Preheat Coil

The preheat coil should have wide fin spacing, be accessible for easy cleaning, and be protected by filters. If the preheat coil is located in the minimum outdoor airstream rather than in the mixed airstream as shown in Figure 1, … Continue reading

12. June 2019 by Jack
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AHU – Mixing Plenum

If the equipment is closely coupled to outdoor louvers in a wall, the minimum outdoor air damper should be located as close as possible to the return damper connection. An outside air damper sized for 7.5 m/s gives good control. … Continue reading

12. June 2019 by Jack
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