Engineered Systems - August 2008 - (Page 56)

In April, Tom Durkin hosted an extremely popular ES webinar tackling humidity in schools. We ran out of time and had a slew of leftover questions, so here, his engineering team joins him in addressing them. Caveat: The questions often solicit professional opinions based on experience, but that candid exchange is part of the beauty of the webinar, right? BY THOMAS H. DURKIN, P.E., KEITH CECIL, P.E., JOHN PRUETT, P.E., STEVE ROOKE, P.E., AND CAMERON YAMASHITA 1. Question: You started by saying that high summer humidity was the number one IAQ issue. What about lack of fresh air? Response: As a firm, we have investigated over 50 IAQ problems in buildings. We have found all calls to be a result of high indoor humidity levels, not due to a lack of fresh air. Invariably, once we were on site doing our IAQ testing, we also often found elevated CO2 levels indicating low ventilation rates. While lack of fresh air is a significant IAQ issue, it does not seem, to us, to be what generates the initial complaint. Question: Are parts of the country more prone to humidity problems than others? Response: Any area east of the Rockies and the Pacific Northwest is most likely to be susceptible to high humidity problems. Question: How do you balance humidity control and energy efficiency? Response: This is the single biggest issue facing the engineer trying to control humidity. The prerequisites for acceptable design are IAQ, humidity control, and occupant comfort. Only after those items are thoroughly addressed, should energy efficiency be considered. Question: What’s your opinion on varying chilled water supply temp to aid humidity control? Response: The lowest chilled water temperature is needed when the building has the greatest demand for dehumidification. If your motivation for varying chilled water supply temperature is to save energy by delivering higher chilled water temperature, it’s important to remember not to compromise humidity control for the sake of operating costs. If More Where These Came From We answered many more questions from viewers during the actual “Humidity Control in School Buildings” webinar, sponsored by Munters and Nortec. To watch a recording of the entire one-hour event, including the main presentation and subsequent Q&A, go to http://webinars.esmagazine.com, complete the free registration, and enjoy. the question concenrs improving dehumidification by lowering CHW temperature, we don’t think that would help much, unless the air-handling equipment cannot get to design leaving air temperature. 2. 3. 4. 5. Question: If the weather conditions permit, why not use the HVAC system in full economizer to dry the carpet in lieu of dehumidifiers? Response: If weather conditions permit (outdoor air dewpoint under 52°F), this might be an acceptable strategy. However, during the summer, when most school carpeting gets cleaned, the outside air conditions would probably not be conducive to air drying. Question: We are looking to do demand shaving by resetting the send-out central chiller plant for an event that may occur for 6 hrs, 10 times during the cooling season. Any thoughts on mold control? Response: Refer to the chart on slide 16 of the webinar (2007 AHSRAE Handbook – Applications, page 21-3). The chart shows that as long as the duration of high humidity is not significant, mold growth is less likely 6. 56 En gi neer ed S y stem s August 2008 http://webinars.esmagazine.com

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

Engineered Systems - August 2008 Contents Editor's Note Back2Basics HVAC Challenge Case In Point Commissioning Building Automation Efficiency Incentives HVACR Designer Tips Glass Box to Grand Casino Looking Radiant In Green Mechanical Products Sourcebook Q&A: Dehumidification In Schools Building Oversight Management: M&V And More Products Classifieds Advertiser Index Tomorrow's Environment

Engineered Systems - August 2008

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