HVAC Systems

Heating Ventilation and Air Conditioning

 

 

 

 

 

Design Considerations

Minimize the number of fittings.—Fittings are expensive and cause significant increases in pressure loss compared to straight duct.

Use semi-extended plenums.—Plenums reduce the number of transition fittings and facilitate balancing. use of the extended plenum concept can reduce the number of fittings and simplify a duct design.

Seal ductwork.—Standard duct sealing requirements

Kruger ventilation products

Ducting designing and implementation

Inhouse Manufacturing And Assembling Unit

Desigining for Heating, Ventilating, and Air Conditioning Systems

DESIGN CONSIDERATIONS

  • Load Calculations and Weather Conditions.
  • Plant Design and Construction
  • Special Environmental Conditions
  • Redundant Systems or Equipment.
  • Basic HVAC Scheme for Plants
    • Location of Air Intakes and Exhaust Openings
    • Airflow
    • Substructure Heating, Cooling, and Ventilation
    • Superstructure Heating, Cooling, and Ventilation
  • Ductwork

Selection of HVAC Equipment

  • In most parts of the country, climatic conditions require that outdoor air must be heated and cooled to provide acceptable thermal comfort for building occupants, requiring the addition of HVAC systems. The selection of equipment for heating, cooling and ventilating the school building is a complex design decision that must balance a great many factors, including:
  • heating and cooling needs
  • energy efficiency
  • humidity control
  • potential for natural ventilation
  • adherence to codes and standards
  • outdoor air quantity and quality
  • indoor air quality
  • cost

Consider specifying energy recovery ventilation equipment.

Indoor air can be 2 to 5 times more polluted than outdoor air; therefore, most HVAC system designers understand that increased amounts of outdoor air supply is generally better for IAQ. Yet there are concerns over the implications that this added amount of outdoor air supply has on the first cost and operating cost of the HVAC system, as well as moisture control

GI Ducting

 

Galvanized Duct.—Galvanized duct is commonly used and is the preferred material for Reclamation applications.

(1) Pressure class.—Specify and use the lowest pressure class.

The default value may or may not be adequate for the intended application. The pressure class has significant effects on the metal gauge thickness and reinforcement requirements for the duct.

(2) Galvanized coating.—Sheet steel should be G-60 (for dry or low humidity) or G-90 (for damp or wet areas) coated galvanized steel of lock forming grade conforming to American Society for Testing and Materials (ASTM) A653 and A924 standards.

(3) Reinforcement.—Depending on the pressure class, duct dimensions, and metal gauge, duct may or may not require reinforcement. SMACNA Duct Construction Standards – Metal and Flexible, dictates when and what type of reinforcement is required. Therefore, designers may select the pressure class, metal gauge thickness and reinforcement requirements or choose to specify the pressure class requirements and leave the details to the contractor. The latter has been the more common approach on Reclamation jobs.

(4) Leakage class.—All duct constructed for 2 and 1-inch pressure classes should be sealed to Class C requirements. Standard sealants are not intended for extreme applications such as weatherproof, waterproof, or ultra-violet resistant; temperatures above 120 ºF; submerged below water; or

totally leak free. Where any of these conditions are to be encountered, special sealants should be specified.

(5) Leakage testing.—Unless the application is critical, leakage testing of systems below 3-inch pressure class is not recommended due to the expense.  Ductwork rated above 3-inch pressure class should be leak tested only if the expense can be justified.

Location of Outdoor Air Intakes and Exhaust

  • Sloped Intake Plenum and Accessible Intake Screen
  • Proper location of outdoor air intakes can minimize the blockage of airflow and intake of contaminated air.
  • Intakes should not be placed within 25 feet of any potential sources of air contaminants, including sewer vents, exhaust air from the site, loading docks, bus loading areas, garbage receptacles, boiler or generator exhausts and mist from cooling towers.
  • Grilles protecting air intakes should be bird- and rodent-proofed to prevent perching, roosting and nesting. .
  • Intake Screens must be accessible for inspection and cleaning.
  • Consider adding a section of sloped intake plenum that causes moisture to flow to the outside or to a drain if intake grilles are not designed to completely eliminate the intake of rain or snow.

Ductwork

Ductwork.—Ductwork should be designed in accordance with the provisions of  the Sheet Metal and Air Condition Contractor’s National Association

  1. Design Considerations

(1) Minimize the number of fittings.—Fittings are expensive and cause significant increases in pressure loss compared to straight duct.

(2) Use semi-extended plenums.—Plenums reduce the number of transition fittings and facilitate balancing by using of the extended plenum concept can reduce the number of fittings and simplify a duct design.

(3) Seal ductwork.—Standard duct sealing requirements air leakage from the longitudinal seams of unsealed ductwork. The Longitudinal seam leakage for metal duct is approximately 10 to 15 percent of the total duct leakage.

Air Distribution and Duct Insulation

  • Dirt and moisture should not be present in duct systems and must be controlled to prevent mold growth. However, it is not always possible to assure that ducts remain dirt and moisture free. In many existing locations, sheet metal ducts, as well as those constructed of or lined with insulation products, are often contaminated with mold because dirt and moisture found their way into the system.
  • Duct board and duct liner are widely used in duct systems because of their excellent acoustic, thermal and condensation control properties. If the HVAC system is properly designed, fabricated, installed, operated and maintained, these duct systems pose no greater risk of mold growth than duct systems made of sheet metal or any other materials.
  • However, the very properties that make duct board and duct liner superior insulators (e.g., a fibrous structure with large surface area that creates insulating air pockets), also makes them capable of trapping and retaining moisture if they do get wet (though the fibers themselves do not absorb moisture).
  • While there is an ongoing debate about the wisdom of using insulation materials in duct systems that might retain moisture longer, all sides agree that extraordinary attention to preventing moisture contamination of the duct work should be the primary strategy for preventing mold growth..
  • As a secondary strategy, designers should consider methods of reducing the potential for future problems to occur due to unforeseen moisture contamination by investigating insulation products now on the market that minimize the potential for moisture to penetrate the insulation material. These include foil vapor retarders, tightly bonded non-woven vapor retarders, butt or shiplap edges and other techniques that have been developed by insulation manufacturers to address concerns about moisture.
    • Pay special attention to preventing moisture from entering duct work.
    • If specifying duct board or internal duct lining for thermal and/or acoustical control, be sure to consider the potential for uncontrolled moisture to enter the duct over the life of the system.
    • Degrease sheet metal air ducts. Seal air ducts to prevent HVAC system air leakage.

Art Of Precision Ducting

Guidelines for centrifugal fan installations.

Guidelines for unducted axial flow fan installations

Guidelines for sound trap placement near fans and duct fittings.

Energy Recovery Ventilators (ERV’s)