Design Contractors May See More Energy Recovery

March 20, 2001
ATLANTA, GA — It’s pretty well established that ASHRAE Standard 62, “IAQ for Acceptable Indoor Air Quality,” increases the outdoor air ventilation rate for commercial buildings. While this improves IAQ, it can also result in higher energy penalties. Do energy recovery ventilators (ERVs) really help improve system efficiency?

If so, then why aren’t they being used more often, especially in the United States?

Many ERVs have been proven to enhance energy recovery, was the premise of an ASHRAE Winter Meeting forum, “Energy Recovery Ventilators: Why or Why Not?” These systems include heat pipe heat exchangers, runaround loops, and similar technologies. However, “Maybe design engineers don’t know how to use them, especially for humidity control,” said a forum participant.

(Note: ASHRAE forums are intended to be open exchanges of information. Therefore, participants can only be identified in a very general sense, to help maintain their anonymity.)

A manufacturer’s rep for air-to-air ERVs stated that many engineers understand their benefits, but the project budget won’t support it. “What can we do to bring this to the table? Owners don’t believe the cost analysis.”

A consulting engineer asked why the systems still cost so much.

“You are absolutely correct,” replied a manufacturer. “The price has been high, but it’s dropping.”

An engineer said that he recently installed a new hvac system for a coffee shop. Smoking was allowed, and the owner wanted to get it out. “But why should I spend $3,000 in addition to $2,500 rooftop unit?” the owner asked.

The engineer sold the ERV design by asking in return, “What would it take to get the same results with standard equipment?”

The Climate Leveler

Contractors and other system designers may want to present systems that incorporate an ERV as a “weather compressor,” said another attendee. “You can move every mechanical system to San Diego,” he said. “You lose the peaks and valleys.”

Helping to close the ERV credibility gap is the fact that ARI now has a product section that gives certified ratings for ERV performance, said a participant.

Many engineers and owners seem afraid to take the energy credits they should be taking for these systems, another pointed out. Awareness of these savings needs to be raised.

Another consulting engineer said that, given the cost of natural gas rising, it’s “almost a given” that air-to-air heat exchanger designs would be approved, if they were offered.

Maintenance Issues

Getting the proper maintenance performed on ERVs or any system is another problem. Like any system, lack of proper maintenance can affect the system’s life-span.

Longevity is not a problem, a consulting engineer said, as long as the units are maintained properly. “We started working with energy recovery wheels in 1974. We installed one in a hospital; the media was just changed out after 20 years.”

A military engineer said that as far as maintenance goes, ERVs “are not maintainable when you try to get that extra 5% to 10% efficiency; the fins are too close together. We insist on coils that are full size,” and no more than six to eight. Therefore, a balance needs to be reached between efficiency and maintainability.

A consulting engineer said that in one Eastern European nation, at least, heat recovery is mandatory. And for his firm, there have been “no problems. We are using the wheels.”

One problem can result from pressure drop, he added, and the power of vent fans being too high. “But it’s not a question of whether or not to use [ERVs], but how to design them in with the least energy penalty.”

When it comes to pressure drop vs. overall cost, engineers need to balance drop against other savings, said an engineer. “But to ignore pressure drop could be fatal. Don’t size the system too small.”

“There is no free lunch,” pointed out another participant. “Physics reigns!”

Sizing, Climate

The sizing issue, said one participant, is a reason to use ERVs cautiously in humid, hot climates. “If you oversize, you’ll get a wet building. All of the moisture collected is condensed out and goes back out in building.”

A consulting engineer, however, responded that “I don’t remember the last time I haven’t used an ERV to keep the humidity level down. We keep coil temperature down around 54°F.”

A manufacturer recommended that system designers “Look at recent offerings from manufacturers. Things are changing.”

Publication date: 03/26/2001