Engineered Systems - October 2008 - (Page 55)

valve modulation or pump flows, or closing ancillary dampers to provide a tighter close-off against cold outdoor air. Cold climates offer challenges as well as opportunities for building designers. Large expanses of finished space above a slab-on-grade are one challenge. These spaces can quickly exceed the effectiveness of perimeter radiation heating elements. Auditoriums are one common example of this type of space. Although the air temperature is appropriate four feet off the slab, the temperature of the air at ankle level can be cold. People who are sitting for long periods in this type of construction can complain of uncomfortable ankles and feet. This design challenge can be met with better insulation under the slab, and/or a radiant heating system within the slab. Control of this heating is critical, as it is possible to overheat the space with such a large slab. AIRSIDE ECONOMIZERS Airside economizers are a natural opportunity in cold climates. With increases in internal loading from computers and other equipment, the balance temperature for occupied buildings is continuously decreasing. (The balance temperature is the exterior temperature at which a building’s operational dynamic requires mechanical cooling for proper temperature control.) The outdoor air in cold climates can offer ‘free cooling’ for much of the year. However, overuse of this opportunity can result in improper moisture levels within the building. For example, cool exterior temperatures along the coast also typically come with high moisture levels. Overuse of an economizer in this situation can allow excessive water to enter the building without noticeable discomfort. However, when warmer temperatures arrive later in the day, the cooling equipment is faced with the task of removing not just the sensible heat but also the excess moisture that was allowed to enter the building during the morning economizer operation. This is a common situation where enthalpy-based changeovers should be used instead of db temperature-based changeovers. Special care needs to be given to protecting the building utilities such as water, sanitary, gas, storm water, electric, etc., as they run into the building. Typically, frost in unprotected (non-snow covered) areas of the site drive down several feet below the finished grade. Building utilities are typically designed to be installed below these frost lines. Obvious risk of freezing and/or unwanted movement would be present if these special precautions were not incorporated. BUILDING PRESSURIZATION Building pressurization in typical commercial construction is an important way to control unwanted infiltration. In most cases, uncontrolled infiltration is a building’s enemy. Uncontrolled infiltration caused by negative building pressures has consequences in both increased building energy consumption and ultimate operating costs. Positive building pressure can be accomplished mechanically through synchronizing outside air quantities introduced into the building and return or relief fans. Building pressure can also be pas- • Uniform Air Dispersion within the UFAD Plenum provides consistent temperature • Less Thermal Decay in high heat load zones • Flexible Fabric allows for smoother installation and accessibility • Simple, low cost for new and retrofit applications For more information, please conatct: Dispersion Better Air Underfloor Plenums for 4343 Chavenelle Rd • 866-382-8769 Dubuque, IA • 52002-2654 w w w. d u c t s ox . c o m Input 195 at www.esmagazine.com/instantproductinfo ESM10084Ductsox.indd 1 w w w. esmag a zin e. c o m 9/23/08 2:35:02 PM 55 http://www.ductsox.com http://www.ductsox.com http://www.esmagazine.com/instantproductinfo http://www.esmagazine.com

Table of Contents Feed for the Digital Edition of Engineered Systems - October 2008

Engineered Systems - October 2008 Contents Editor’s Note Letters Back2Basics HVAC Challenge Case in Point Commissioning Building Automation HydroTech HVACR Designer Tips Special Insert: Engineer's Technical Library Fall 2008 Living Wild! Chilled Beams in Chicago Phoenix Convention Center: On The Rise Cold-Climate HVAC Challenges Humidification Strategies For Data Centers & Network Rooms Special Advertising Supplement: Tabb Talk Computers & Software Issues & Events Products Literature & Catalogs Glossary Classifieds Advertiser Index Tomorrow’s Environment

Engineered Systems - October 2008

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