Duct shape oRectangular ducts - As fan coil units (FCU) typically have rectangular connections with the main duct, rectangular ducts fit better and have good height clearance. While most designers consider flat oval and circular ducts to be similar, they have different air flow properties. Higher air velocity rates require larger ducts to avoid restriction of air flow.Equipment Selection Choosing the right type and size of equipment is essential in ensuring that heating and cooling is provided efficiently. In cases where a sudden change in direction cannot be avoided, turning vanes should be used to reduce the loss of pressure. While designing ducts for air distribution systems, heat load calculations must be completed accurately to determine the required air flow rates. A detailed account of inputs required is described in a previous article titled, &39;Decoding the Ductwork Design Process, Methods and Standards&39;. External considerations - There are also external considerations in the duct design process such as budgetary constraints and adherence to standards and guidelines based on which calculations should be done and duct sizes and layout must be designed. oFlat oval ducts - Flat oval ducts not only provide the same efficiency as circular ducts, they also have more clearance than that which circular ducts offer.

There are various design aspects from duct layout, shape, material to air velocity that have an impact on the performance of a ducting system. Duct material must be selected based on the cost, ease of installation, performance capability to reduce friction loss and conserve fan energy, acoustic properties to reduce noise transmission and insulation or thermal properties to prevent heat loss or gain. Here are some general rules of duct design that must be considered: a. Recommendations for Ductwork Design HVAC design and sizing vary depending on energy consumption, the number of occupants in the building, material and orientation of the building and preferences of temperature levels. • Adherence to standards and guidelines - Incorrect calculations of heat load and duct sizes lead to poor ductwork designs resulting in lower comfort, higher operating costs for maintaining equipment and an increase in energy costs. In an ideal air distribution system, ductwork must be designed to provide the right amount air flow at the right speed to the right conditioned space while improving energy efficiency, maintaining air quality and providing comfort. HVAC designers must refer to HVAC industry standards and handbooks when making calculations, selecting equipment and choosing duct design and size.

The challenge in duct design is to design a layout, use a method and select the material and equipment that will be energy efficient and reduce overall energy and operating costs. oCircular ducts - To convey air using less fan horsepower, with low pressure at lower installation costs, circular ducts are sometimes preferred. The cost incurred due to air leaks has a high impact on overall energy costs as it pressurises system performance. Insulating ducts and pipes could also help in reducing noise transmission and maintaining acoustics. While many parameters must be considered when selecting duct designs, sizes and layout and method, there are common guidelines that duct designers could consider when designing to achieve energy efficiency, cost effectiveness and comfort. Air velocities - To reduce vibration, noise, friction loss and unnecessary energy consumption, the air velocity rate must be regulated. The combination of different duct shapes used for conveying air and the fittings used for transitioning must be carefully considered as they affect air flow efficiency. This manual is used to measure heating and cooling load calculation and provide accurate air flow rates so that every conditioned space gets the exact amount of air flow required. Duct layout - Sudden changes in direction in a duct layout must be avoided as it results in pressure loss. As industry demands increase, duct design must evolve to achieve higher energy efficiency, cost effectiveness and greater overall comfort. General Rules of Duct Design The basic principle of duct design is to distribute air as direct as possible through the most feasible way while saving energy and reducing operating costs. The shape and size of ducts need to be determined based on the heating and cooling load requirements of the conditioned space.

Air flow must be kept at a low or medium velocity based on the activity, the number of people and application, to minimise vibration and noise levels. Before starting the ductwork design process all information must be provided such as the type of application, the number of people using the conditioned space, the activity or operations that will be conducted, building orientation and technical specifications such as the method of duct design and type of equipment and material. If rectangular ducts are used, it is recommended to make them as square shaped as possible to reduce the minimum duct surface and cost involved in carrying the same capacity of air. • Noise, vibration control and acoustics - Some designers use high air velocity in ducts to reduce initial costs. • Leakage/air tightness - Faulty duct design invariably results in air leakage from ducts, accessories and equipment such as air handling units (AHUs) and variable air volume (VAV) boxes. In any given air distribution system, only one set of combinations is ideal for distributing the required amount of air flow. Design parameters must be identified to determine the best combination and optimal design. An ideal duct system design must take into consideration industry standards and manuals, duct layout, size, shape, material and air velocity required to improve performance and reduce costs. Making the right calculations, selecting the right equipment and developing designs that are cost effective, energy efficient and per industry standards is one way of keeping controlling costs. To prevent such faults due to miscalculations, this manual provides details on how to select wholesale refrigerators and size supply air diffusers, return grilles and registers.