Thursday, June 7, 2012

LEED 2012 Delayed

We received a notice from the head of the USGBC that the release of the next edition of the LEED Rating System has been delayed. It was decided to give folks more time to respond to the next edition of the LEED rating system, to fully reply to those concerns and to better prepare the resource documentation for the many points that can be gained. The next edition of the LEED rating system will now be referred to as V4.0, rather than LEED 2012, and will be delayed until mid-year 2013.

This delay reflects a number of issues. LEED, like ASHRAE, is driven primarily by volunteers who also have to manage a professional career. In addition, there are several issues regarding new credits that apparently are still unresolved. While there are some issues that are still open for discussion, the ones affecting air distribution are not. I feel that the most important ones affecting our industry are as follows.

1.) ASHRAE 62.1 Ventilation Rate Procedure is a pre-requisite. There are a couple ‘zingers’ in here that are often overlooked:

-- Minimum Ventilation Rates in table 6.1 are adjusted by the air change effectiveness of table 6.2. For overhead cooling, this value is 1, but for heating from overhead, if the discharge is more than 15F above the thermostat set point, or the throw from the ceiling air outlet doesn’t come half way down the window, the minimum ventilation rate is increased by 25%. Displacement and short throw Underfloor Air Distribution (UFAD) outlets get a 25% reduction.

-- Charcoal Filters with 30% effective removal for ozone are required on outside air outlets in “EPA non-attainment zones”. At present, that is Los Angeles and Houston, but the EPA is petitioning to reduce the allowable concentration, which would greatly increase the covered areas.

-- Outside air quantities need to be measured. This will have a great effect on operation of VAV systems, which with the reduced interior loads we are seeing, will likely result in many VAV systems operating at or near 100% outside air. The good news is that in this condition, in the summer, most of the heat of the lights is discarded. The bad news is that many systems can’t actually handle the latent load at design ventilation rates. Measuring ventilation rates at each zone has the potential for significant reduction in required total ventilation rates.

2.) HVAC system acoustics has been defined as a separate item (as opposed to general room noise levels, which could include many uncontrolled noise sources). HVAC noise generation will be addressed through either the ASHRAE handbook (which is not sufficiently complete to do all the necessary sound path calculations) or more importantly, through AHRI 885, which has a spreadsheet to perform necessary calculations. This means the design engineer doesn’t have to hire an acoustical consultant for an “estimate” of the sound generation. LEED for Schools will have a 40dBA maximum requirement as a pre-requisite. Other types of spaces will have a credit available based on recommended maximum sound levels, often expressed in NC ratings.

3.) Thermal Comfort, as defined in Standard 55, will require a form be filled out which includes design clothing levels and metabolic rates of occupants. Discharging ceiling supplied, heated air that is more than 15F above room setpoint will negate the comfort credit. Room air speeds will need to be addressed, as well as vertical temperature stratification within the “occupied zone”. The use of ADPI can assist meeting this requirement for overhead air systems. Meeting the requirement for UFAD and Displacement Ventilation (DV) systems is problematic and will likely result in ‘creative’ inputs from designers that want to achieve this credit.

Authored by: Dan Int-Hout, Chief Engineer Krueger