Engineered Systems - November 2008 - (Page 34)

The IAQ TOP 1O air. Oftentimes, a space that was designed with air conditioning but no outdoor air intake, such as a system for a server room, is converted to an occupied space (e.g. a conference room, office space, or classroom) without modifying the system to bring in the required outdoor air. Secondly, the control system needs to operate the system when the space is occupied. In many light commercial buildings, thermostats control the small rooftop ventilation systems. These thermostats, like residential thermostats, are equipped with fan switches. The fan switch has both “on” and “auto” operational positions. If the system is allowed to operate with the fan switch in the “auto” position, the fan cycles on and off to control the thermal loads, and does not provide outdoor air ventilation to the space continuously. When the fan switch is in the “on” position, the ventilation system provides outdoor air to the space continuously. Most building codes require that for spaces without operable windows, a mechanical ventilation system must be installed that has the capability to provide the required outdoor air ventilation. These building codes do not require that the system be actually operated, just capable of operating. In California, the State Labor Code Section 5142 requires that the ventilation system be operated continuously during the hours the building is occupied. In addition, I recommend that buildings be provided with between one and three air changes of outdoor air prior to building occupancy to remove contaminants and odors that have built up during the night when the building ventilation system is turned off. The exact amount of outdoor air required to purge the building to an acceptable concentration of contaminants will depend upon the specific sources in the building and can be determined on a trial basis using building odor as a criteria. In hot humid climates, it is important to provide adequate dehumidification of the humid outside air being brought into the building, or moisture problems and mold growth can occur. One way to ensure that proper dehumidification of the outdoor air in hot/humid climates occurs is to have a separate 100% outdoor air ventilation system to provide dehumidified dry outdoor air to the space with separate recirculating ventilation systems to control that actual space temperatures. The minimum outdoor air ventilation rates that should be delivered are those in ASHRAE 62.2, although providing higher outdoor air ventilation rates, will provide indoor air with a higher perceived air quality. I recommend a minimum of 15 cfm/occupant or 1.0 ach, whichever is greater. Remember to “build it tight, but ventilate it right.” Commercial Replacement Coils Tel: 800-225-4328 Fax 662-229-4212 OEM Coils Tel: 662-229-2000 Fax 662-229-2297 Aluminum Coils Tel: 662-229-2587 Fax 662-229-2571 ● ● ● ● ● ● ● Quality Lead-time Reliability Factory Trained Representation Selection/Rating Software ARI & UL Certification UL Qualified Client Test Data Program coils@luvata.com www.luvata.com/heatcraft Input 208 at www.esmagazine.com/instantproductinfo 4 5/21/08 11:40:41 AM OUTDOOR AIR INLET If the ventilation system represents the lungs of the building, the outdoor air inlet represents the nose of the building. It is important that the outdoor air intake is located away from stinky things such as sewer vents, kitchen, and bathroom exhausts, loading docks, garbage dumpsters, etc. It is often difficult to relocate an outdoor air inlet after 34 En gi neer ed S y stem s November 2008 ESM06084LUVATAGR.indd 1 http://www.luvata.com/heatcraft http://www.luvata.com/heatcraft http://www.esmagazine.com/instantproductinfo

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

Engineered Systems - November 2008 Contents Editor’s Note HVAC Challenge Back2Basics Case In Point Commissioning Building Automation HVACR Designer Tips Show Me The Motor Money The IAQ Top 10 Putting A Damper on Tragedy Special: Lighting Controls Computers & Software Products Glossary Classifieds Advertiser Index Tomorrow’s Environment

Engineered Systems - November 2008

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