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HVAC BALANCE Variable Air Volume Services - Call us at (800) 217-8437Example Balance Procedure: Operate all associated fans (supply, return and exhaust) at the appropriate speeds. We check to ensure that all deficiencies are repaired. We take pitot tube traverse of main supply ducts and obtain design CFM at fans. Here is a list of things that should be considered before balancing a constant volume unit: (1) Filters must be clean, (2) Check fan rotation, belt tension, and motor amp draw, (3) The grille design and unit airflow design should be the same, (4) Look for closed dampers in the return and supply duct, (5) Verify that all ductwork has been sealed, (6) If unit has outside air set the damper to an estimated position. Recheck fresh air amount after unit airflow has been balanced, (7) Condensate drain must be installed with vent in the correct location. The following guidelines are used in our water balance service: (1) Air balance should be completed before water balance begins, (2) Open all valves to full open position. Close coil bypass stop valves. Set mixing valve to full coil flow., (3) Verify that the responsible parties have removed and cleaned all strainers, (4) Examine water in system and determine if water has been treated and cleaned (5) Check pump rotation, (6) Check expansion tanks to determine they are not air bound and the system is completely full of water, (7) Check all vents at high points of water systems and determine all are operating freely, (8) Set all temperature controls so all coils are calling for full cooling. This should close all automatic bypass valves at coil and chiller. Same procedure when balancing hot water coils; set on call for full heating, (9) Check operation of automatic bypass valve, and (10) Check and set temperatures of boilers and chillers to design requirements. Zone requirements are direct indications of system load conditions and they are also used for supply air temperature reset. normally, the supply air temperature set point is set at the highest value that will keep the zone requiring the most cooling at its set points and zone humidity within acceptable limits. The drawback of this reset scheme is that it can potentially have one or two hot spots dictating the supply air temperature set point. This scheme can be seen as one variation of return air temperature based reset. The supply air temperature set point for a single-duct constant air volume air handling unit (AHU) is often reset based on either return air temperature or outside air temperature in order to reduce simultaneous cooling and heating energy consumption. Both reset strategies make engineering sense as long as the reset schedules are reasonable. Quite often the decision to use one over the other is made with the assumption that they will both achieve some sorts of energy savings. However, the impact of these two strategies on AHU energy consumption could be very different. A comparison of these two commonly used supply air temperature reset strategies for a single-duct constant air volume system is presented in this paper. It is shown that from either the building energy consumption or building comfort point of view, the reset strategy based on outside air temperature is inherently better than that based on return air temperature. Significant amount of heating energy savings can be achieved by switching from return air temperature based reset to outside air temperature based reset. In the early morning, for example, when the building does not require much cooling, the main fans will run more slowly, reducing the total air flow through the system. However, even at this time, a VAV terminal box supplying a room with many occupants can fully open its damper, providing needed cooling. As classrooms begin to fill up during the day and the sun rises, generally heating the building, the total air flow will increase as necessary. If some rooms remain unoccupied throughout a particular day however, the VAV terminal boxes for those rooms will remain closed. The use of high performance HVAC equipment can result in considerable energy, emissions, and cost savings (10%-40%). Whole building design coupled with an extended comfort zone can produce much greater savings (40%-70%). Extended comfort includes employing concepts such as providing warmer, but drier air using desiccant de-humidification in summer, or cooler air with warmer windows and warmer walls in winter. In addition, high-performance HVAC can provide increased user thermal comfort, and contribute to improved indoor environmental quality (IEQ). The term HVAC refers to the three disciplines of Heating, Ventilating, and Air-Conditioning. A fourth discipline, Controls, pervades the entire HVAC field. Controls determine how HVAC systems operate to meet the design goals of comfort, safety, and cost-effective operation. |
