ASHRAE Journal - June 2009 - 10

Purifying Air To Reduce OA Regarding April’s column, “Air Purification to Reduce OA,” by John Dieckmann, Kurtis McKenney, and James Brodrick, Ph.D., I have to ask: if someone can come up with this magic wand of controlling outdoor air (OA) by reading every contaminant in nature referenced in the 2005 ASHRAE Handbook— Fundamentals, Chapters 12 and 13, then can we have a super-duper demandcontrolled ventilation (DCV) system? Meanwhile, I will be using the Ventilation Rate Procedure and separating OA from the system using dedicated OA where I can. Here in the North, energy recovery ventilators (ERV) are commonplace because many buildings are not heated with air. ERVs provide all the attributes of supply and exhaust with energy savings, probably beyond what is saved by DCV . Perhaps a study should compare ERVs using reduced OA and DCV with air purification methods. In my opinion, the most important part of this article is the statement that “Field experience indicates that actual occupancy levels are often 25% to 30% lower, and as much as 60% to 75% lower in some buildings, than design levels.” I find this to be true in just about every building I visit. So why are we designing the ventilation systems to these design levels? ASHRAE design levels for occupancy are ridiculous and overburdening the systems and producing excessive energy use. Why not use realistic numbers for occupancy? Has anyone tested IAQ with realistic occupancies and compared energy use, costs, and air quality to see the difference? Worst-case loads are intermittent. We all know that. Why are we not allowing for more occupancy relief in the standards? We keep inventing more complicated controls and systems and emerging technologies to deal with ways to reduce the numbers. I have to ask, isn’t there an easier way? Robert P. Sutton, P.E., Member ASHRAE, Damariscotta, Maine 10 ASHRAE Journal Re: Duct Sizing May’s “Equal Friction Solution for Duct Sizing” by Fred W. Dougherty, P.E., was greatly appreciated by me and others practicing in design. This is the second or third article I’ve seen in the Journal that included a link to an Excel design tool developed by the author. I hope the Journal will continue to publish similar such “extended content.” Tom Phelps, P.E., Member ASHRAE, Raleigh, N.C. Re: Portable Classrooms In May’s “Lessons Learned in Portable Classrooms” by Stephanie Thomas-Rees, Danny Parker and John Sherwin, these studies are fantastic, not only because they show how to improve energy efficiency and improve the learning environment for our children, but also because these lessons can be applicable to the massive mobile parks in the U.S. The energy savings that these studies show will make up a huge savings for people in this type of housing in comparison to their income. These are usually the people greatest affected by fluctuations in our economy, fuel and energy prices. Carmen Baez Yellen, Associate Member ASHRAE, Cary, N.C IAQ, with more or less outdoor makeup air and with and without air purification measures, must still be addressed. Relative to design occupancy levels versus actual real-time occupancy, we have two observations. First, the occupancy densities for the VRP that are given in Table 6-1 of Standard 62.1-2007 are default values. Second, since ventilation is removing other indoor pollutants besides exhaled CO2 and bioeffluents, reduced real-time occupancy is not necessarily a sufficient reason to reduce ventilation airflow rates. John Dieckmann, Member ASHRAE; Kurtis McKenney; James Brodrick, Ph.D., Member ASHRAE June 2009 The Authors Respond We can offer a few comments/clarifications relative to Mr. Sutton’s observations. Regarding the challenge of applying ASHRAE Standard 62.1’s Indoor Air Quality (IAQ) Procedure, while we don’t think the column overstates the challenge and professional responsibility assumed in applying this procedure, we are sure there are practitioners in the field who apply the IAQ Procedure based on confidence that they have a pretty good handle on the kinds and amounts of contaminants that must be addressed within a class of buildings. However, we do not have a sense of how many are regularly designing ventilation in accordance with the IAQ Procedure and, in the process, specifying significant reductions in outdoor ventilation makeup air compared to levels required by the VRP. We would guess that a large majority of HVAC design engineers stick with the VRP. We agree that a study of energy saved with, and cost effectiveness of, energy recovery ventilators (ERVs) compared to reduced OA with DCV air purification, or , other methods would be useful. Of course, ERVs also save energy when used in conjunction with reduced OA, so the combination of ERV and reduced OA should also be included in such a study. The more complicated question of whether there is a meaningful difference in the resulting ashrae.org

ASHRAE Journal - June 2009

Table of Contents for the Digital Edition of ASHRAE Journal - June 2009