Engineered Systems - August 2008 - (Page 58)

Q&A: Dehumidification because mold occurs with protracted exposure to high rh. We recommend staying well below the marginal area on the chart. study, and only this area currently is showing mold. I have two proposals on the table — hot gas bypass and a DOAS for this plus five other RTUs. I am wondering if it is an equipment issue or a building issue and how to proceed. I’m planning a summertime study of humidity with dataloggers. Response: We would check the unit to ensure that no air is bypassing the filters since dirt in the airstream will be a source of food for mold spores. However, there may potentially be other sources of high latent air causing this problem. High outside air concentrations could be coming in via an adjacent vestibule introducing outside air near this diffuser, or via envelope leakage, resulting in the condensation and subsequent mold. We would not rule out other issues outside of the ductwork and rooftop unit. 7. Question: My building only has a mold issue at the first register out of a rooftop unit. It is an office building. Would this suggest that it is most likely a condensate carryover issue? What might be some likely causes? I’m thinking improper cleaning, but what may be others? We have done a mold 8. N N W et C LA on Question: Do you design reheat systems for school A/C systems? Response: If there is adequate justification for it. However, if we elect to use reheat for humidity control, we advocate the use of a heat recovery chiller so that we reheat without “new” energy. Question: What are your thoughts on the use of heat pipes and runaround coils? Response: It depends upon the application. Heat recovered from a heat pipe to be used at an AHU may make sense in some applications. However, it is impractical to use the recovered heat at terminal units. Runaround coils are typically inefficient and require exacting economic analysis to verify their cost-effectiveness. A large disadvantage of both of these applications is that the greatest need for reheat often occurs at low load, when there isn’t much energy available for them to recover. Question: With today’s energy costs, who will design a 24-hr ne N ct iv ity EW /L A Et h 9. er n What happened 17 weeks ago on Tuesday at 12:36 PM? Vaisala HUMICAP® Humidity Transmitter will tell you. 10. operation? Response: It’s not a question of who will design it, but if it inadvertently happens. If the building HVAC occupancy is not correctly scheduled, or if someone thinks that humidity problems will be better helped by allowing the equipment to run constantly, there will most likely be humidity problems as a result. Question: What manufacturers have you found to be most effective for DHRC applications? Response: The right DHRC equipment is any water cooled chiller that can make 130° condenser water and has the control capability to seamlessly switch between evaporator and condenser control. Question: For museum applications that require tight temperature and humidity control, what is the best system? Response: It is best to follow the guidelines outlined in the ASHRAE Handbook — Applications. However, we recommend that any reheat required comes from recovered heat. 11. Vaisala HUMICAP® Humidity and Temperature Transmitter Series HMT330 Call our experts or visit: www.vaisala.com/HMT330 Visit Vaisala www.vaisala.com Vaisala Inc. Tel. 1-888-VAISALA (824-7252) Fax 781-933-8029 instruments@vaisala.com 12. Input 20 at www.esmagazine.com/instantproductinfo 58 En gi neer ed S y stem s August 2008 7/18/08 10:42:24 AM ESM08084Vaisala.indd 1 http://www.vaisala.com/HMT330 http://www.vaisala.com http://www.vaisala.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

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