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HVAC DESIGN

This section provides useful guidelines for designing an HVAC system. Here you will find a brief description of the basic design process and various type of systems, tools for doing calculations, and links to sites that provide useful design information such as industry standards, and design tips.

Design Process -

The basic design process involves various steps as follows -

• Determine the design parameters of the conditioned space - temperature, humidity, air quality, etc.

• Calculate the cooling loads, heating loads, and air flow requirements based on the above design parameters.

[Go to "HVAC Software" link given above for the available software for doing cooling & heating load calculations].

• Establish conceptual design and duct layout.

[See the description of various types of systems given below].

• Calculate fan pressure drop.

[Go to "HVAC Software" link given above for the available software for doing fan pressure drop calculations].

• Equipment selection and specification.

[See the description of various types of equipment (Chillers & DX units, Dampers, Fans) on their respective links on this website].

• Depending on the system type, other design steps may involve chilled water pump pressure drop calculation, refrigerant pipe sizing calculation, etc.

[Go to "HVAC Software" link given above for the available software for refrigerant pipe sizing calculation].

Types of Cooling Systems -

There are various types of cooling systems depending on the application requirements. The three main categories of cooling systems are as follows -

• Air Conditioning System, which uses a refrigerant system for cooling air. This has a broad range of applications ranging from comfort cooling to industrial process cooling.
• Evaporative cooling System, which uses 100% outside air and water evaporation for cooling. This is used mainly in dry locations, where temperature requirements are not very low and humidity is not a concern. This may be used for comfort cooling or industrial applications. It is used for comfort cooling only in dry areas and where the space temperature/ humidity requirements are not stringent.
• Ventilation System, which uses 100% outside air for cooling the space. This is used mainly where temperature requirements are relatively high, and/or where constant fresh air is required. It is mostly used for industrial/ warehouse applications.

Air Conditioning Systems can be either chilled water or direct expansion. Chilled water systems involve water being cooled by a refrigerant system, and this chilled water is then used in the air cooling coils. Direct expansion or DX systems involve the liquid refrigerant being supplied directly to the air cooling coils, where it expands and provides the air cooling. There are various reasons for using one or the other. Normally chilled water systems are used for medium to large systems, and direct expansion systems are used for small to medium systems. The chilled water system normally has a package chiller unit with pump and piping system to supply chilled water to various air cooling coils. The DX system can be a package unit with the compressor and cooling coil all on the same skid, or a split system with the compressor or condensing unit located separate from the cooling coil. The refrigerant piping for packaged chiller & DX units is designed by the equipment manufacturer. The refrigerant piping for a split DX system has to be designed by the HVAC Engineer, and extra caution should be used since it is for a two phase flow and it is critical for reliable operation of the system. The refrigerant piping design guidelines are given in the ASHRAE and Carrier Handbooks. The various type of Chiller & DX units and other details are given under the link for "Chiller & DX" on this website.

Evaporative Cooling Systems are basically of two types. One uses water sprays, while the other uses wet media. The spray systems result in higher moisture, and are used only for large industrial systems. The media type systems provide a better control on moisture content depending on the type of media, and are used for relatively smaller systems. Both systems are sensitive to the hardness of water used, since hard water deposits tend to block the media or spray nozzles.

Ventilation Systems are basically a combination of fans, duct and dampers. The various types of fans used are described under the link for "Fans" on this website.

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Last modified:11/08/2008