ASHRAE Journal - August 2011 - 10

letters
Solar House
Ty Newell and Ben Newell have done a wonderful job on the solar PV system. They wrote in June’s Solar NZEB Project column that the total energy collection from their laboratory solar PV system (3.2 kW) was more than 13,000 kWh since its start-up in August 2008. The system supplies approximately 30% of the 410 m2 (44,000 ft2) laboratories’ energy. Because the weather is different for other cities, I’m wondering if the authors could offer more detailed information. For example, what is the solar collector area of the 3.2 kW system, and what’s the measured solar panel average efficiency? Lei Wang, Associate Member ASHRAE, College Station, Texas

System Effect and Noise
I read with great interest, “System Effect: To Believe It Is to See It,” by Sutton G. Page, Member ASHRAE, in the June issue. As I read the article, I recalled the few instances where tight mechanical rooms required me to use multiple 90° elbows close to the supply outlet of the air handler, and noise was an issue. Based on the clear figures in the article, I suspect that system effect was the culprit causing the noise. As we all know, energy cannot be created or destroyed, so system effect must redirect the flow energy somewhere. Heat will be created by the collision of the air molecules, but as anyone who has dealt with excessive velocity with liquids knows, noise is also a by-product of velocity loss. Most system designers line ductwork to reduce noise. I reduce turns and other flow restrictions to reduce noise with excellent results and shy away from duct liners for air quality reasons. When removing ductwork from existing systems, I have noticed significant loss of duct liners at radical turns and fitting reductions, the very place Mr. Page shows turbulence. I would love to see research into noise and system effect. I am convinced they are significantly connected. Lloyd Hamilton, Associate Member ASHRAE, Rhinebeck, N.Y.

The Authors Respond
To compare solar system production dependency on location, PVWatts was run for Seattle and Phoenix with a 3.2 kW two-axis and an 8.2 kW stationary (30 degree tilt) to compare with our Central Illinois PVWatts results. Seattle produces 23% less for the two-axis tracker (4,140 kWh versus our prediction of 5,360 kWh per year) and 21% less for the stationary (8,130 kWh versus our 10,300 kWh). Phoenix produces 34% more for the two-axis tracker (7,180 kWh versus 5,360 kWh) and 26% more for the stationary (12,930 kWh versus 10,300 kWh). The higher percentage of clear sky days in Phoenix as opposed to Illinois and Seattle boosts the two-axis tracker as it favors clear sky conditions with more beam solar radiation. Assuming labor and other material costs are the same for the three locations (which they most likely are not), and using our assumed 12.5 cents per kWh Central Illinois installed cost, the harvested energy cost for Seattle would be 16.2 cents per kWh (two-axis tracker) and 15.8 cents per kWh (stationary). The harvested energy cost for Phoenix would be 9.3 cents per kWh (two-axis tracker) and 9.9 cents per kWh (stationary). Roughly, if installed costs are similar to Central Illinois, climatic variations would tend to be within ±3 cents per kWh of Central Illinois cost. As far as overall analysis for a residence, additional studies to optimize the house design for other locations are needed. For example, both Seattle and Phoenix have lower annual residential energy requirements because the climatic weather extremes are not as great as ours. Ty Newell, Member ASHRAE, and Ben Newell, Associate Member ASHRAE, Urbana, Ill.

The Author Responds
There is little doubt that some of the system effect losses are converted to heat, but we lack temperature instruments sensitive enough to measure that loss in an air-conditioned airstream at low temperatures. Regarding sound, these losses, if present, also will be very difficult to measure with any degree of certainty or repeatability. As to duct liners, the coefficient of roughness compared to smooth sheet metal is a likely culprit as well. The real problem with establishing a “model” for system effect is that there are an infinite number of possible duct connections that can result in an infinite number of losses, ranging from minor to major. This is noted in AMCA International’s Publication 201. The solution is to use radius fittings as large as space permits. Sutton G. Page, Member ASHRAE, Austin, Texas
10 ASHRAE Journal

System Effect and Noise
Sutton Page is to be commended for “System Effect: To Believe It Is to See It” in the June issue. Too often, as he noted, this is an unknown subject to many professionals in the field. This brings clearly into focus a problem that those of us in the noise control field have seen over the years: excessive low frequency noise. This is most often caused by turbulence related
ashrae.org August 2011

ASHRAE Journal - August 2011

Table of Contents for the Digital Edition of ASHRAE Journal - August 2011