fundamental question here: are servicing systems without a humidification function able to fulfil these criteria, providing the local weather conditions should in normal cases not lead to a RH above the Upper Recommended Humidity Limit?
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Roger Chang
Principal, Energy and Engineering LeaderDLR Group | Westlake Reed Leskosky
LEEDuser Expert
398 thumbs up
August 6, 2010 - 9:17 am
Previous versions of ASHRAE 55 required a minimum humidity. The latest version referenced by LEED eliminated this requirement. You may still want to consider humidification in very dry climates, especially if you're dealing with a museum, hospital, or data center.
Victoria Lockhart
Arup Associates125 thumbs up
August 9, 2010 - 11:29 am
really sorry, typed my original query too quickly. I wanted to ask about whether controlled DEhumidification is in all cases required or not.
If no dehumidification is foreseen, but it can be shown that in normal local weather conditions the humidity should not lie above the upper recommended limit, can this credit/ASHRAE 55 be fulfilled? I find the wording in the Standard: "Systems designed to control
humidity shall..." rather unclear - at any rate, it does not say that systems which don't control humidity are definitely ruled out.
Thanks in advance for any help!
Roger Chang
Principal, Energy and Engineering LeaderDLR Group | Westlake Reed Leskosky
LEEDuser Expert
398 thumbs up
August 11, 2010 - 8:31 pm
You can start by looking at hourly weather data / ASHRAE design data for your particular location to see whether the outdoor design dewpoint is above or below your interior target dewpoint. In many climate zones, use of a VAV system addresses dehumidification adequately, since air will be dried out to maintain a 55F supply air temerature.
In ASHRAE climate zones 1A-4A, I recommend that additional psychrometric analysis at design and part-load conditions be used to determine whether active dehumification is needed - it is usually helpful to include control sequences of operation to describe any actual dehumidification mode. I recommend coordinating with ASHRAE 62.1, which has a description of dehumification analysis, as well as 90.1, which has restrictions on simultaneous heating and cooling, which used to be common for dehumidification.