Letters to the Editor
School HVAC debate revisited and questionedI would like to compliment CSE for publishing the exchange of letters between Mark Lentz and Fred Schultz (CSE, September 2001). Mr Lentz' letter raised numerous valid issues, and this type of exchange is good for our industry—and badly needed.
School HVAC debate revisited and questioned
I would like to compliment CSE for publishing the exchange of letters between Mark Lentz and Fred Schultz ( CSE , September 2001). Mr Lentz' letter raised numerous valid issues, and this type of exchange is good for our industry—and badly needed. On the other hand, elements of Mr. Schultz' original article (June 2001) and response were very disturbing, especially given that Mr. Schultz is a consulting editor.
Specifically, Mr. Schultz failed to cite any relevant peer-reviewed studies or consensus industry standards, inferring that his more than 50 years of practice alone somehow made his arguments legitimate. For example, Mr. Schultz states that 7.5 cfm of outside air per occupant at design winter conditions is more than adequate to satisfy any environmental requirement. But that conflicts with ASHRAE Standard 62-1999 and most building codes that are based on it.
Furthermore, the ventilation rates Mr. Schultz espoused in his June article would only be code legal in Wisconsin, and even there, they fall below the standard of care. For example, in Call vs. Prudential , one of the most famous sick-building lawsuits, the defending mechanical engineer designed a building with an outdoor ventilation rate less than what is called for by ASHRAE 62-1989 (15 cfm). Even though the engineer claimed he did meet the local code, which required less than 15 cfm, the trial judge ruled the ASHRAE standard constituted the "professional standard of care." The ruling resulted in an out-of-court settlement rumored to be in the seven figures.
That case, and Mr. Schultz' stance, begs the question: Why are you permitting a consulting editor to advise your readership to violate national standards of care and thus exposing them to serious IAQ liability?
Michael S. Sheber, P.E., Sherber Assocs., Avon, Conn.
After reviewing Fred Schultz's response to my comments addressing specific technical issues and the underlying assumptions behind them in regard to school HVAC system design, Mr. Schultz failed to challenge even one of those specific comments. Instead, he resorted to personal attack and was arrogantly dismissive.
Worse yet, the tone of Mr. Schultz's response is a clear example of one of the biggest problems in the HVAC industry. ASHRAE is an association of professionals dedicated to the collection and dissemination of information, and the generation of engineering standards. While ASHRAE does perform research, the technical leadership role properly falls to the consulting engineering community, which has consistently failed to accept it.
In fact, the HVAC design field, in my opinion, quickly beats any technological initiative out of young engineers. Even when "advances" are generated, many engineers refuse to accept them because they do not know how to employ them properly, and because adoption of new strategies may be disruptive to low cost, "cookie-cutter" practices. And we wonder why the consulting engineering profession has fallen into disrepute?
The fact is that there is more room for improvement in the HVAC industry than in most others. We currently have available to us all of the technologies necessary to simultaneously eliminate air quality problems and dramatically reduce energy use, and it can be done cost effectively.
Do I take offense at Mr. Schultz' response? Of course, as I am sure he did with regard to my comments. Over the 25 years I have been in this business, I have maintained a personal policy of trying to improve every project I design over the last one. To do so, one must research, understand and apply alternative solutions, and one has to develop a rather iconoclastic attitude.
I can back up my comments with ASHRAE-published materials and other documentation. I can also back them up with successful project work. However, as long as Fred Schultz is a consulting editor, I think Consulting-Specifying Engineer's credibility is on the line.
Mark S. Lentz, P.E., President, Lentz Engineering Associates
On the subject of improving system efficiencies in conjunction with motor improvements (Specifier's Notebook, August 2001), specifically pumps, most pump design concepts teach that the maximum efficiency of the centrifugal pump is a function of size, gallons per minute and pressure. These factors, plus the speed of the pump, are the major contributors to hydraulic efficiency.
A chart, published years ago, uses the parameter-specific speed, which defines impeller shape, to compare the average efficiencies with size. For instance, below 100 gpm, 40% to 60% effciency; at 500 to 1,000 gpm, 50% to 70%; and about 80% at 1,000 to 3,000 gpm. Larger pumps can be expected to operate at 90%, but the efficiency drops when the pump is operated other than its design at flow or pressure. That's where the system design engineer enters the picture. A pump and driver are part of a system. There are two basic systems: transfer and closed. In each case, liquid is taken from a source into a pump that supplies the energy to move it. The major error source in pump application is the calculation of system losses. The pipe, valve and other component friction
losses vary with the flow and comprise, with the fixed system static or elevation head differences.
Pipe friction varies with pipe age for a given type. The problem magnifies. The system designer can select the optimum condition and use tools like variable-speed drives,valve control, multiple pump sizes, etc., and then look for the best pump or pumps to meet the need.
J. Robert Krebs, P.E., Krebs Consulting Service
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