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HVAC BALANCE - Call (800) 217-8437 for Locations & Availability
HVAC BALANCE Frequently Asked Questions (FAQ) - Call (800) 217-8437Our techniques in balancing VAV systems is based on balancing procedures outlined in the AABC National Standards. We check to verify that all start up is complete. We adjust all main supply and return air ducts to proper design CFM. In a rectangle duct traverse it is important to get an equal number of readings to cover the whole cross section of the duct. Drilling the correct number of holes and spacing the holes correctly is the most important part. The first step is finding the area of the duct in square feet. A dual duct system was popular in the early days of air conditioning. It had several advantages, but the disadvantages, like excessive energy consumption, led to its downfall after the energy crisis of 1973. The dual duct concept was fairly simple. A fan discharged air in a blow-thru arrangement that could either be directed through the cooling coil or the heating coil. What determined which path the air would take? Actually it was a device separate from either the fan or the coil, a device called the dual duct mixing box. Builders will soon need to get up to speed on duct testing, since recent code changes will require that all residential duct systems except those that are located entirely within a home thermal envelope will need to be tested for leakage. If some ducts are outside of the thermal envelope, the 2009 IRC will require duct tightness to be verified by either a rough-in test or a post-construction test. Either test requires all register boots to be taped or otherwise sealed during the test. The threshold for the rough-in test is total duct system leakage of 6 cfm per 100 square feet of conditioned floor area (when tested at 25 Pascals). If the air handler is not installed, the total leakage must be less than or equal to 4 cfm per 100 square feet of conditioned floor area. The threshold for the post-construction test is duct system leakage to outdoors of 8 cubic feet per minute (cfm) per 100 square feet of conditioned floor area when tested at 25 Pascals. Alternatively, total duct system leakage must be less than or equal to 12 cfm per 100 square feet of conditioned floor area. There are three types of VAV boxes: traditional, fan-powered and VAV with reheat. The traditional VAV box consists of VAV box with an integral damper and is controlled by thermostat. This is the most basic type of VAV box. The fan-powered VAV is built the same as the traditional, but it also contains a fan which is triggered when the area reaches optimal temperature or the damper is 50% closed. It provides additional air circulation when there is less demand for conditioned air. A VAV with reheat also is built the same as the traditional VAV, but it contains an electric coil designed to reheat the air when the damper reaches a predetermined position. This feature allows heating in the specific zone instead of having to heat the whole building. Mechanical ventilation is the use of mechanical air handling systems commonly referred to as heating, ventilation, and air conditioning (HVAC) systems to ventilate buildings. Most commercial buildings use mechanical ventilation, which is more controllable and responsive than natural ventilation in providing adequate indoor air quality. However, mechanical ventilation also can exacerbate infiltration and ex filtration, which can compromise indoor air quality. Energy Technologies offers a wide range of consulting services. Tap into our resources in the energy and environmental field, we can show you how to be energy wise and environmentally sound while saving money all at the same time! Heating can be accomplished by heating the air within a space (e.g. supply air systems, perimeter fin-tube radiators), or by heating the occupants directly by radiation (e.g. floor/ceiling/wall radiation or radiant panels). |
