ASHRAE CONFERENCE | TECHNICAL HIGHLIGHTS GROWTH WARNING New humidity guidance on preventing mould was one of 350 presentations at the 2021 ASHRAE Virtual Winter Conference. Tim Dwyer reports on what it means for design, and listens in on sessions covering nuisance lift noise, insulation in lofts, and liquid desiccant Harriman cited places, such as Dubai, as having 80%+ of July hours above the limiting dew point; also Tangiers, with 40%+, and even northern European cities such as Amsterdam, with nearly 25%+. He concluded that there are many climates where there was a need to design for independent dehumidification equipment (and not cooling) particularly in unoccupied periods that should be used with appropriate dew-point controls. Benefits of liquid desiccant Over the past two decades, significant advances have been made in the use of liquid desiccants for simultaneous dehumidification and cooling. Modelling and proof-of-concept demonstrations have shown potential savings of 30-40% compared with other technologies. Peter Luttik, of Emerson, provided a useful overview on liquid-desiccant technologies, explaining that modern in-duct systems (see Figure 2) employ low-flow desiccant membrane technologies that have been March 2009 T he 2021 ASHRAE Virtual Winter Conference attracted 1,800 online delegates over three and a half days in February, when more than 350 presentations covered the increasingly wide range of topics that fall under the ASHRAE umbrella. A significant number were on areas associated with the pandemic and these are available on ASHRAEs Covid-19 resources page. Here, I have selected a small sample of the presentations to illustrate the diversity of subjects. New humidity guidance Lew Harriman, of Mason-Grant Consulting, has a long track record in measuring and predicting humidity in buildings. He is also coauthor, with the late CIBSE president Geoff Brundrett, of the seminal Humidity control design guide for commercial and institutional buildings. In his seminar, Harriman reported the change in the maximum humidity allowed in mechanically cooled buildings in the recently updated ASHRAE Standard 62.1-2019 Ventilation for acceptable air quality. It had previously been set at a maximum relative humidity (RH) of 65% and is now set to a maximum (absolute) dew-point temperature of 15C (or 65F). Harriman said this change reflects that surface temperatures near cold HVAC equipment and distribution systems raise the RH at the surface far higher than the RH as measured in the air. (Although RH governs absorption and desorption of excessive moisture in materials). With the old limit, systems designers assumed, incorrectly, that keeping the RH of the air below 65% meant that mould could not grow in the building (Figure 1). The new ASHRAE rules include occupied and unoccupied periods (although, when unoccupied for less than 12 hours, the limit reverts back to 65% RH). Figure 1: An example of an application where there was no effective moisture control (top) and, after with a maximum dew point of 15C (bottom) [Source: Lew Harriman] March 2016 Miller-Klein outlined the challenges of identifying the noise path by documenting all parts of the system even riding on top of the lift car 28 April 2021 www.cibsejournal.com CIBSE April 21 pp28-29 Ashrae technical conference.indd 28 26/03/2021 14:41