Wednesday, February 6, 2013

ASHRAE Review

Well, another ASHRAE meeting is now behind us. This last meeting was here in Dallas. As usual, I was fully committed to a number of technical meetings. I won’t bore you all with the machinery of managing Technical Committees (I am a new member of the Technical Activities Committee, TAC). There were a couple of interesting things that happened at the meeting that I can report on, however.

The committee to rewrite the Underfloor Design Manual finally finished its work and voted a document out for publication. While not pleasing everyone (naturally), it contains a great deal of what we have learned in the several years since the first Design Guide was published. This document is the first time a committee has ever attempted to write a design guide. In the past, design guides are commissioned by a TC and ASHRAE pays a contractor to prepare it. This one was different, as the GSA had complained they had a number of buildings with UFAD systems which are “underperforming”. We have learned this means high energy use and difficult maintenance. Many of the problems stem from a number of buildings being built by first-time contractors without experience in some of the unique construction details required to maintain pressurization in the plenum. Other problems involve the need to manage infiltration when the system is shut down at night and condensation occurs. The guide also describes the issue of heat gain, or “thermal decay” and recommends several ways to minimize this effect. Sadly, there is still little data on actual energy consumption, and claims of energy savings with this technology are still mostly anecdotal and unproven.

The Thermal Comfort Standard (ASHRAE Standard 55) is proceeding towards a revision with most of the informative stuff moved into an informative appendix, leaving only mandatory requirements in the main body. The issue of compliance to a 40 fpm allowed maximum “average air speed” (30fpm when the setpoint is below 72.5) is still an open issue.  

A committee representing the VRF (Variable Refrigerant Flow) suppliers requested to be exempted from meeting the Standard 62.1’s requirement for a MERV 6 filter (ASHRAE 189 is requiring a MERV8) upstream from “:any wetted surface”, which means their condensing coils. This is actually a code requirement wherever ASHRAE 62.1 is included in code (like the 2009 International Mechanical Code). If granted, I see a lot of other devices wanting to be included as well. Frankly, I don’t see the justification. 

The final report from the research project at the Yahoo campus was presented. Interior loads were reported to be less than 6 btuh/sf (vs. the typical design of 22 at 1cfm/sf). This is essentially the ventilation load. At the same time, 62.1 is discussing variable ventilation rates for occupied, temporarily unoccupied, and truly unoccupied spaces. I predict that this will require pressure independent ventilation supply systems for any type of equipment, be it fan coil, VRV, WSHP or even Chilled Beam. It makes one wonder why someone doesn’t just install a VAV system, doesn’t it?

Authored by: Dan Int-Hout, Chief Engineer Krueger