എയർ കണ്ടിഷനിംഗിൽ ഉള്ള വി എ വി സിസ്റ്റം എന്നാൽ എന്ത്? വീഡിയോ കാണു
The primary goal of any heating, ventilation, and air conditioning (HVAC) system is to provide comfort to building occupants and maintain healthy and safe air quality and space temperatures. Variable air volume (VAV) systems enable energy-efficient HVAC system distribution by optimizing the amount and temperature of distributed air. Appropriate operations and maintenance (O&M) of VAV systems is necessary to optimize system performance and achieve high efficiency.The purpose of this equipment O&M Best Practice is to provide an overview of system components and maintenance activities to keep VAV systems operating safely and efficiently. Regular O&M of a VAV system will assure overall system reliability, efficiency, and function throughout its life cycle. Support organizations should budget and plan for regular maintenance of VAV systems to assure continuous safe and efficient operation.Description of TechnologyVAV systems supply air at a variable temperature and airflow rate from an air handling unit (AHU). Because VAV systems can meet varying heating and cooling needs of different building zones, these systems are found in many commercial buildings. Unlike most other air distribution systems, VAV systems use flow control to efficiently condition each building zone while maintaining required minimum flow rates.Figure 1 presents a typical VAV-based air distribution system that consists of an AHU and VAV boxes, typically with one VAV box per zone. Each VAV box can open or close an integral damper to modulate airflow to satisfy each zone’s temperature setpoints. In some cases, VAV boxes have auxiliary heat/reheat (electric or hot water) where the zone may require more heat, e.g., a perimeter zone with windows.Some features of a VAV system include the following:Distribution system provides conditioned air to spaces to meet varied zonal temperature and airflow requirements.Variable frequency drive-based air distribution system can reduce supply fan energy use.Supply-air temperature reset capability allows adjustment and reset of the primary delivery temperature with the potential for savings at the chiller or heating source.There are two major classifications of VAV boxes or terminals-pressure dependent and pressure independent.A VAV box is considered pressure dependent when the flow rate passing through the box varies with the inlet pressure in the supply duct. This form of control is less desirable because the damper in the box is controlled in response to temperature only and can lead to temperature swings and excessive noise.A pressure-independent VAV box uses a flow controller to maintain a constant flow rate regardless of variations in system inlet pressure. This type of box is more common and allows for more even and comfortable space conditioning. The balance of this guide will focus on pressure-independent VAV boxes.Figure 2 presents a schematic of a typical pressure-independent VAV box; in this case, the box also has a reheat coil. This VAV box has three modes of operation: a cooling mode with variable flow rates designed to meet a temperature setpoint; a dead-band mode whereby the setpoint is satisfied and flow is at a minimum value to meet ventilation requirements; and a reheating mode when the zone requires heat.There are several different types of VAV and terminal boxes. The most common include:Single duct terminal VAV box - the simplest and most common VAV box, shown in Figures 1 and 2, can be configured as cooling-only or with reheating.Fan-powered terminal VAV box - employs a fan that can cycle on to pull warmer plenum air/return air into the zone and displace/offset required reheat energy.Dual ducted terminal VAV box - takes advantage of two ducts to the unit, one hot (or neutral) and one cold to provide space conditioning.Induction terminal VAV box - takes advantage of the induction principle instead of a fan to pull warmer plenum air/return air into the zone and displace/offset required reheat energy.
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