Consulting-Specifying Engineer - September 2008 - (Page 64)

Equipment Lifecycles ing, and maintaining additional pumps, traps, valves, and controls. Steam-jacketed dispersion assemblies, when properly applied, do not waste condensate. The steam jacket is a closed loop of pressurized steam that travels from the steam boiler around the dispersion tube to the condensate return main and back to the boiler. Condensate generated within a steam-jacketed dispersion tube is revaporized by heat from the steam jacket. The heat given up to vaporize condensate from the dispersion tube causes condensate to form within the steam jacket. This condensate is sent to the condensate return main without using pumps, thus reducing water and boiler chemical waste. Short-absorption panels with tube insulation generate much less condensate than panels without tube insulation. However, because all condensate generated is nonpressurized, it is usually piped to a drain. The exception is a shortabsorption panel with a heat exchanger in the supply header (see Figure 2). Similar to a steam jacket, the heat exchanger is a closed loop of pressurized steam that travels from the steam boiler through the supply header and back to the boiler. In this type of system, dispersion-tube-generated condensate falls to the hot surface of the heat exchanger and is vaporized back into humidification steam and dispersed into the duct airstream. As with a steamjacketed system, the pressurized condensate is sent to the condensate return main without using pumps, thus eliminating water and boiler chemical waste, and the need for piping a condensate drain and tempering the condensate. Simultaneously achieving short-absorption distance, energy efficiency, and condensate return without pumps is possible by using an insulated short-absorption panel with a heat exchanger in the header. Regardless of the pressurized steam humidification system used, proper control is essential. Install a solenoid valve at the steam jacket or heat exchanger steam inlet, and install a temperature switch controlling the modulating humidification steam valve. This will ensure a warm startup (eliminating spitting) and the ability to shut off the jacket or heat exchanger steam when there is no call for humidity, thus saving additional energy. Managing condensate To lower operating costs, use dispersion tube insulation to reduce condensate production, and use pressurized return to capture condensate. If you need short absorption and want the energy- and water-saving benefits of tube insulation and pressurized return, use a shortabsorption panel with a heat exchanger in the supply header. If short absorption is not a concern, an insulated steam-jacketed system may be a good solution. Any one of these steam dispersion solutions will save considerable amounts of energy, water, and boiler chemicals. Using the short-absorption panel with the integral heat exchanger also may eliminate the need for installing and maintaining additional valves, traps, pumps, and controls for sending condensate to the condensate return main. These equipment choices will have a significant effect on your equipment lifecycle operating costs. Wasner is a freelance writer who has been writing about buildings and building products for more than 20 years. Lundgreen is a senior mechanical design engineer for DRI-STEEM Corp. with 14 years of professional mechanical design and development experience. Humidification steam exits tubelets, disperses in air stream Some steam condenses in dispersion tubes, falls to heat exchanger Humidification steam enters header Pressurized steam enters heat exchanger Heat exchanger vaporizes dispersion tube-generated condensate Pressurized steam and condensate exit heat exchanger Condensate Steam Pressurized condensate returns to boilers via condensate return main Figure 2 This illustration shows a short-absorption dispersion panel with dispersion tubes insulated with closed-cell foam and an integral heat exchanger in the panel header. Pressurized steam vaporizes condensate in the header via a heat exchanger. Source: DRI-STEEM Corp. 64 Consulting-Specifying Engineer • SEPTEMBER 2008

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Consulting-Specifying Engineer - September 2008 Contents Viewpoint Letters News M/E�Roundtable Selecting Appropriate Egress Strategies Commissioning On-Site Electrical Systems Mentoring Control Engineers and Technicians Casting Call for Cx Case Study New Products Equipment Lifecycles Advertiser Index Green Space

Consulting-Specifying Engineer - September 2008

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