Wednesday, March 30, 2011

LEED Calculations

We on the IE TAG of the USGBC, and members of ASHRAE SSPC 55 (Comfort) were recently tasked to assist some well meaning engineers in gaining the LEED 2009 point for designing for occupant comfort. As it turns out, there is a checklist now that requires the designer to predict/design the operative temperature, humidity, and air-speed in every type of space of their design. The question was asked, “Do we need to do calculations, or just a narrative?” A similar question has been asked about the proposed acoustical credits for New Construction posed in the draft of LEED 2012, which was out for public review in January.

While it would seem that there may be a future here for English Majors, especially those who specialized in creative writing, there are, in fact, many available tools to the engineer to do the necessary calculations.

The ASHRAE Comfort tool, which may be purchased from the ASHRAE bookstore, or even the Comfort Program available in the Krueger website, http://www.krueger-hvac.com/tools/comfort.asp, can provide the conditions which will meet the criteria, based on assumed metabolic rates and clothing.

Space conditions can be easily predicted using a number of load calculation tools. Radiant asymmetry is typically the most difficult to predict and very time consuming, but it is seldom an issue, unless one is using radiant panels, then many manufacturers have calculation programs available. Vertical temperature stratification will never be an issue with overhead air supply if one uses ADPI (maintaining a level >80%) to space and select air outlets. The Krueger K-Select program http://www.krueger-hvac.com/kselect/, has a robust ADPI calculation program that is able to graph ADPI as a function of air supply rate, which can be used (by the aforementioned English Major) to prove compliance to that part of the standard.

Acoustics for HVAC components is easily verified using the ASHRAE 885 Acoustical Application standard. The spreadsheet calculating those parameters is also available on the Krueger site (http://www.krueger-hvac.com/lit/xls/885_08_calc.xls).

Validating LEED requirements is likely a bit time consuming, but the resources are available to perform the necessary calculations to prove compliance.

Authored by: Dan Int-Hout, Chief Engineer Krueger