Engineered Systems - August 2008 - (Page 60)

Q&A: Dehumidification 13. Question: Any comment on reliability and accuracy of CO2 and humidity sensors? Response: They are much better than they were 10 years ago, but our experience is that they will still require frequent recalibration. We try to limit the application of CO2 sensors to large spaces such as auditoriums, gymnasiums, and cafeterias so that their use is minimized and the maintenance burden (e.g., calibration) on the owner is kept to a minimum. Humidity sensors, when needed, are used to monitor several clustered areas with similar characteristics to minimize their use. Question: You mentioned having a summertime humidity analysis; what is included in this? Response: A thorough humidity analysis is needed when selecting equipment for dehumidification. Multiple temperature and humidity conditions for outside air should be considered in equipment selection. The equipment shall not just be evaluated at peak cooling (drybulb and wetbulb design) and heating loads, but also at part-load conditions with high humidity such as 70° and high humidity often found on rainy days with partial building occupancy. Question: Regarding DOAS, any thoughts on final discharge temperature, i.e., neutral-to-space usually requiring reheat or lower? Response: It depends upon the connection and arrangement of the DOAS system. If DOAS air is supplied directly to the space, we would likely make the DOAS temperature room neutral. However, if the DOAS air is supplied in conjunction with a terminal unit such as two-pipe system, we recommend it be supplied to deliver 15. warm air during cooling season and cool air during the heating season to address the concurrent heating and cooling demands of the space. Question: What about duty cycling the central air handler fans every 15 min for a peak shaving event? Would this wet and dry the cooling coil too much? Response: We do not advocate any strategies that would compromise IAQ, occupant comfort, or humidity control. However, if the realities of the situation are such that duty cycling is necessary, cycling the fan would compromise all three. Closing the OA damper would significantly reduce cooling load, but would only compromise IAQ. And if combined with CO2 monitoring, it might not even do that. Question: Is mold growth more a function of dewpoint or rh? Response: Mold growth is a function of rh. Question: What is the impact on the humidity levels when there is a significant breech in the building’s vapor barrier? Response: It would be impossible to predict the humidity impact, other than to say it would be unacceptable. The best strategy would be to repair the breech. Trying to make the HVAC system compensate would be an “iffy” solution and probably would significantly increase cooling cost. Question: Of the four systems — DOAS, reheat, VAV, and face and bypass — which is least expensive to install and operate over 20-yr duration for a central Missouri location? Response: In our opinion, the least expensive system to operate and install for most climate zones would be a two-pipe face and bypass system. All of our studies and experience show us that it is the least expensive to install and operate when properly designed and controlled. ES From left, Yamashita, Pruett, Durkin, Cecil, and Rooke, are with Durkin & Villalta Partners Engineering (Indianapolis, IN). 17. Question: In your opinion, what are the acceptable limits for temperature and humidity during unoccupied periods with the systems disabled? Response: We would start by looking at the dewpoint in lieu of using a specific temperature or humidity level. Any resulting temperature and relative humidity with a dewpoint temperature below 59° would be a good choice as long as the space temperature is above 72°. Refer to webinar slide 16 and stay in the “Safety Region.” 14. 16. 18. 19. ! NEW SECURE INSULATION IN A SNAP! INTRODUCING THE NEWLY-IMPROVED KLO-SHURE INSULATION COUPLING SYSTEM ® 20. Installs in seconds! One piece design No metal clamps Superior vapor barrier Supports tubing and secures insulation Eliminates insulation compression Improved finish – no tape, no glue Meets the 25/50 flame spread/smoke developed index Now, installing pipe insulation is a snap with Klo-Shure. Our new one piece design lets the installer insert the Klo-Shure Coupling into channel and lock the top – all in the snap of a ﬁnger. No glue, no tape and no separate parts. Visit www.klo-shure.com to see all of our systems and request a FREE catalog. Learn how Klo-Shure Insulation Couplings can improve your next project! 1-800-839-0891 www.klo-shure.com Input 75 at www.esmagazine.com/instantproductinfo ESM05084KLO-S.indd 1 60 En gi neer ed S y stem s August 2008 4/10/08 3:57:55 PM http://www.klo-shure.com http://www.klo-shure.com http://www.esmagazine.com/instantproductinfo

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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.