“It can go straight into building code, without someone having to take the time to rewrite it in enforceable language,” said Ron Jarnagin, staff scientist at Pacific Northwest National Laboratory and chairman of the 90.1 committee, when the standard was approved in 1999.
Now, however, that same simplicity may be at odds with newer technologies. As the standard was originally written, it mandates that motor efficiencies be gauged according to their horsepower ratings; this negatively affects variable-speed motor applications, according to a forum held at the society’s Summer Meeting here.
You see, these high-efficiency motors don’t reach their nameplate rating often, if at all.
One manufacturer pointed out that such motors then need to be installed at a higher amp draw to match the nameplate. This also entails the use of a bigger breaker and larger gauge wire. “I honestly don’t know how that affects efficiency,” he said.
Compare a permanent-split capacitor (PSC) to an electronically commutated motor (ECM), he continued. The PSC could be used with a 400-watt (W) transformer, while the ECM would need a 700-W transformer. “The losses [for the ECM] could be less,” he said.
It was a challenge to the 90.1 committee, said a forum participant, “to figure out how to dumb it down for building inspectors. All they had was nameplate data.”
One consulting engineer suggested that, to maintain the standard’s simplicity while allowing for variable-speed motor efficiency, “If the motor is variable-speed drive, you can deduct three-quarters of the nameplate rating. You can reduce the nameplate rating by, say, 75%.” In such a case, the committee would need to work with manufacturers to determine what an acceptable figure would be.
A participant from academia stated that “It’s essentially an issue of motor efficiency. There are some PSCs with more copper that run at high efficiency on full load.” He suggested that the standard use a watts-per-square-foot (W/sq ft) equation on fans to credit PSCs as well as ECMs.
“Don’t differentiate between motors,” he said. “Use the application data with reasonable static pressure.”
An engineer pointed out that “We’re trying to handle separate issues. The biggest energy user is unitary equipment. There is a bias against variable speed. There are significantly easier ways to reduce peak demand — easier than to ask people to shut their air conditioning at peak times.”
Another engineer suggested, “If there’s a discrepancy with the nameplate, why don’t we turn it over to the manufacturers? We may need a curve with an x and a y rather than a single point.”
Still another pointed out the necessity of keeping it usable for code officials. “You’ve got to give them something they’ll understand. Pick a number.”
A manufacturer said the market “will move the industry toward using more efficient combinations.”
An equipment manufacturer added that “The process of getting data available, getting ARI to change, then test in the lab, takes years. There’s probably a three-year window if something is agreed upon now.”
Publication date: 07/23/2001