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HVAC for less

June 4, 2009
Energy efficiency and HVAC

Energy prices remain volatile, carbon emission caps and trades seem inevitable and everybody wants to see more green, so energy efficiency continues to climb higher in our priorities. It’s clear that high energy efficiency is becoming a critical competitive advantage.

Even before the current economic meltdown, analysis by the American Council for an Energy Efficient Economy (ACEEE, www.aceee.org) found investments in energy efficiency to offer average annual returns of 25% at a risk of 8% — higher returns than any class of stocks with risks comparable to long-term bonds (Figure 1).

Figure 1. The American Council for an Energy Efficient Economy says investments in energy efficiency offer higher returns than stocks with risks comparable to long-term bonds.

There’s plenty we can do, especially in the area of space heating and cooling. Compared to the European Union, on average U.S transportation systems use 1.2 times as much energy per passenger-ton mile, and U.S. industries use 1.4 times as much per unit output. “But 39% of energy in the United States goes to buildings, and on the average, U.S. buildings use 2.5 times as much energy as in the European Union,” says Peter Garforth, principal, Garforth International, and Plant Services’ “Energy Expert” columnist. “That’s climate-adjusted, comfort-adjusted and per square foot. A huge opportunity.”

Know what’s going on

Compared to lighting, motors, process heating and even compressed air systems, HVAC energy consumption is complex. It’s also subject to outside influences (weather), internal whims (thermostats) and changes in production loading that make analysis difficult. Our experts described some low-hanging fruit that’s relatively easy to pick, but first it’s important to recognize that large, long-term gains depend on seeing and understanding your energy spend.

In the past, plant personnel never looked at energy costs. They were considered a fixed overhead, sometimes managed by general conservation strategies like thermostat setpoints.

Blowing hot and cold

Heating and cooling system experts gave us their favorite tips for increasing energy efficiency:

Erin Sperry, commercial heating product manager, Fulton (www.fulton.com):

  • Converting old steam heating systems to hot water with condensing boilers is a great way to save money. We have a 42 million BTU system in Mississippi where the bill went down so dramatically they thought there was something wrong with the meter.
  • If you have a hot water system, consider retrofitting a condensing boiler.
  • Decentralizing a boiler or steam system eliminates energy losses in transit, and smaller systems in each building can run only when needed. You can go from 50% or less to 93% efficiency.
  • Anything you can do to drive down the return water temperature will improve efficiency. Condensing boilers are best at a return temperature of 140°F or less, but don’t condense in a boiler that’s not designed for it.
  • Advanced burner designs, such as our pulse condensing boiler, are self-aspirating. There’s no blower on the burner, so it requires no electric power and saves several horsepower in electricity.

Ken Kolkebeck, president, Facility Diagnostics, Inc. (www.facilitydiagnostics.com):

  • One of the first places to look is the chilled water plant. The condenser water supply often is controlled at a fixed temperature, regardless of ambient conditions, but every degree you can drop that temperature trims 1% to 1.5% from operating cost. Set it based on the wet bulb temperature — instead of 80°F, 65°F. (For more on chillers, see the Web site of the Environmental Energy Technologies Division of Lawrence Livermore Laboratory at http://eetd.lbl.gov/eetd.html.
  • On cooling towers with variable-speed drives, modulate all the fans up and down together instead of turning the cells on and off.
  • Instead of using three-way valves to control chilled water at a constant volume through the air handlers regardless of load, use two-way valves and variable-speed drives on the pumps to vary the flow according to load. You have to maintain a minimum flow through cooling towers but chillers don’t need a constant-volume flow. In fact, they run most efficiently with about 10°F to 12°F delta-T. Varying the flow improves delta-T and efficiency.
  • Small temperature differentials and high pumping rates mean over-pumping or bypassing too much on pressure bypass.

“One of the biggest problems is visibility. Where are the energy dollars going?” says Ken Kolkebeck, president, Facility Diagnostics, Inc. (www.facilitydiagnostics.com). “The utility meter isn’t granular enough. You need weather information and measurements on individual systems like cooling towers, chillers and air handlers, on an hourly basis. That lets you see where the inefficiencies are and attack them.”

When energy costs are tracked to individual systems, it also becomes possible to detect deterioration. “About 20% of HVAC energy is lost because of incorrect maintenance,” says Rod Ellsworth, vice president, global asset sustainability, Infor (www.infor.com). A good monitoring system increases visibility of operating performance and energy consumption, and reveals efficiency deficiencies. Some can proactively alert so assets can be maintained to get them back into specification.

Performance can be mapped to degree-days, temperature differentials and other operating conditions with direct and indirect measurements. “We measure every minute or five minutes, compare actual values to those predicted for the operating conditions,” says Ellsworth. “Whether it’s a rooftop unit, chiller or air handler, it doesn’t matter. We monitor the components — compressors, fans, economizers — for design versus actual consumption via submetering at the system or component level. When it goes out of spec, we notify knowledge workers so they can correct it.”

A combination of measures can reduce energy consumption at most industrial facilities as much as 40%, according to Dave Konye, area sales manager, Schneider Electric (www.schneider-electric.us). The first 2% to 5% comes from raising awareness through measuring and monitoring. Then 10% to 15% typically can be gained by more efficient devices such as motors, drives or lights. Active control of usage through scheduling and automation can gain 5% to 15%, and another 2% to 8% comes though continuous monitoring and improvements using the same measuring and monitoring system.

“It adds up to a potential 19% to 40% energy use reduction, with many energy efficiency funding sources available — state government, utility, federal government stimulus, etc.,” Konye says, adding as an aside that Schneider Electric Energy Solutions is beginning to provide a service to assist clients in proposing and submitting applications for such funding.

Funding help also is available on the private side, “Energy service companies will performance contract, for example, for a boiler replacement,” Konye says. “They’ll provide leasing options, power purchase agreements or a percentage of energy savings as payment.

“There's no excuse for not having an ample capital budget anymore. Energy expenditure is an operating budget item. You’re already spending on energy, therefore you have a budget to save this energy. You just have to get good with the numbers.”

Blowing hot and cold
  • Most facilities condition and use 100% outside air to make up for ventilation. Where I am in Pennsylvania, each cfm of conditioned air costs $3.50 to $4.00 per year on a 24-hour basis. Plants leave exhaust fans on all the time for operations or equipment that might be running only a few hours a day. Synchronize ventilation with operations.
  • On machines that generate a lot of heat, including mechanical equipment, understand where the heat is generated and deal with it near the source. Use spot exhausts instead of general exhaust and chilled plates to capture and remove radiated heat before it heats the surrounding area.

Ron Nordby, vice president, sales and marketing, John Henry Foster (www.jhfoster.com)

  • Nearly all industrial facilities use chillers, typically operating with an average water temperature of 45°F to 60°F. Simply by increasing the amount of water, many fluid cooling applications can operate successfully with cooling media temperatures of 70°F to 90°F. At this temperature, it’s possible to use other fluid cooling technologies, such as dry cooling or evaporative cooling, which reduces energy costs and can reduce or eliminate water consumption.

Question the status quo

Once you establish a baseline of energy consumption, you can question it. System designers tend to be very conservative. The installers sometimes do it their own way instead of strictly following the design. “You get a system that will hold temperature within half a degree, but heating and cooling are both running,” says Kolkebeck. “I do a lot of recommissioning work in existing facilities, fixing functional and efficiency problems from design and installation. I can’t tell you how many times I go in and the controls don’t work right. They’re not programmed right.”

Neither the designers nor the installers get to see the system operate on a day-to-day basis over time, or have the opportunity to modify the operating variables to suit actual running conditions. A plant’s insiders have a better understanding of its needs.

“Recommissioning is an extremely productive exercise,” Kolkebeck says. “You can do it yourself, but look at it not as the way it was designed, but for how it’s running now. The specifications were developed for its intended use. It’s common that by now, the whole scope of the building has changed. Go back in and zero-base it for what it is now, and for the future.”

For example, in 2007, Trane enacted a program to identify energy conservation opportunities in its Tyler, Texas production facility, the headquarters of Trane Residential Systems. “Our specification for chilled water temperature was 38°F leaving the plant. That was our measure of success: maintaining 38°F at the gauge,” says Paul Wheeler, national service engineer, Trane (www.trane.com). They did an analysis of actual requirements and found they could allow as much as 43°F during production and 47°F on weekends. “We changed our mindset to conditions in the building at the point of use rather than the point of delivery,” Wheeler says. “Point of use is what matters, so we modified the specification.”

For HVAC equipment, energy is generally the largest lifecycle cost, as much as 40% to 50% of an industrial facility’s energy costs. But most purchasers don’t factor energy into procurement decisions because they have no basis for doing so. When a facility has many units, which ones should be replaced when, with what? “We simplified that,” says Ellsworth. “We can capture OEM information like SEER and tons, and compare units to determine which can be replaced, which should be replaced, and when, based on energy and maintenance costs.”

Fan club

Ceiling fans can save energy by moving heated air down to floor level during the heating season, and by generating air motion to help cool personnel during the cooling season. Today’s highly engineered industrial fans move air more effectively with less energy than floor fans.

“At our Tyler, Texas facility, the three main uses for chilled water are comfort — HVAC — and for the data center and the test lab,” says Paul Wheeler, national service engineer, Trane (www.trane.com). “We couldn’t do much with the second two, but we set standards for comfort at 78°F for cooling, 68°F for heating. Before, it was out of control. People turned the thermostats all the way down, and I estimate we had 1,000 kW in personal cooling fans. One fan doesn’t use a lot of power, but 1,000 do, and when people walk away, they don’t turn them off.”

Large and engineered fans also are more efficient than the multitudes of small ceiling fans often found in older facilities. "You can use one big fan for every 10 to 20 smaller fans,” says Christian Taber, Leed AP, applications engineer, Big Ass Fans (BAF, www.bigfans.com). “For destratification in the winter, the big fan will use about 100 W, where the smaller fans will each use more than 100 W.”

In the summer, you want air velocity — a breeze. Most industrial spaces are 20 ft. to 30 ft. high, and small fans don’t produce much air movement at floor level. “Small fans might make a breeze you can feel at one to two fan diameters from the center of the fan,” Taber says. “Air movement from a big fan is effective at six to eight diameters — a 20-ft. fan makes a 120-ft. diameter circle of cooling.”

Moving air at about 160 ft/min., which is where paper starts to flutter, gives the personnel cooling equivalent of a 4°F to 5°F lower ambient temperature. In winter, air speeds are typically kept at a maximum of 40 ft/min. to avoid the sensation of a draft.

Airius LLC is the offshoot of an injection-molding plant that developed engineered fans for its own facility. “Our gas consumption went down 42%,” says Scott Canby, project manager, Airius LLC (www.theairpear.com). “After installing the fans, we typically see 15% to 30% less run time on the HVAC equipment. That saves fuel, power and maintenance, and extends the life of the equipment.”

Fans improve air circulation and mixing, which can reduce venting requirements, compensate for marginal ductwork and help get conditioned air to the personnel who need it.

Recognize change

Are you adhering to outdated practices despite major changes in how your facility is operating? “My first ‘Aha!’ moment was realizing our plants were designed to run 24/7/365, but that’s not the way they’re operating today,” says Wheeler. With increased automation and productivity, the plant now runs one or two shifts, and almost never on weekends.

Wheeler’s second “Aha!” came when he saw that the plant systems — air conditioning, boiler, compressed air, lighting — were artifacts of previous processes. Advances in process technologies, automation and electronics have changed the way things are done.

For example, production used to steam-clean, so the boiler was twice the size that they needed. Spray-paint had given way to powder-coat, obsoleting the compressed air and ventilation system designs, and welding that was formerly done by hand is now being done by robots, which don’t need the same HVAC as people.

The energy management program team at Wheeler’s plant identified a phased investment plan, requesting and receiving a $2.1 million investment for Phase 1 implementation in anticipation of $1.1 million in recurring annual energy cost reduction, beginning in 2009. “It doesn’t involve any breakthrough technology, just a lot of opportunities for very good payback.” Wheeler says. “We have a long list of projects.”

The secret sauce

As in many other areas, increasing sophistication and falling prices for sensors and electronics are making them more cost-effective for saving energy in HVAC. Boilers, chillers, air handlers and dampers can be automated to run most efficiently for a given set of weather conditions, time of day and production activity.

“The most efficient boiler in the world won’t run efficiently if you don’t run it properly, and controls play a key role,” says Erin Sperry, commercial heating product manager, Fulton (www.fulton.com). Boilers are more efficient at low firing rates, so on a multiple-boiler system, use sequencing controls to bring them up evenly, for example, all at 20% instead of one at 100%, and modulate them together as a group. A sequencing controller also can monitor cycles and run hours for more efficient preventive maintenance, and rotate boilers to equalize wear and tear.

“Outdoor reset” is a feature that lets you vary settings based on outside temperature. “If it’s 0°F outside, use a 180°F loop temperature, but when it’s 60°F outside, set the loop temperature to 100°F,” Sperry says. “You don’t need a 180°F loop temperature when the weather is mild.”

Today’s automation systems also open the door to remote monitoring and control. For example, they allowed Trane’s Tyler plant to reduce building operations to two shifts from three shifts, to match production operations. “It’s a 50- or 60-year-old plant, and when we went to two production shifts, we still had maintenance on 24/7,” Wheeler says. “Now we remotely monitor plant temperatures and humidity [to prevent corrosion]. Controls automatically start equipment if needed, and if there’s a problem, we can dispatch maintenance.”

Fan club

“Ductwork in industrial spaces is typically at ceiling height,” says Taber. “Hot air rises, and when it’s 15°F or more above ambient, 20% of it never gets down to the occupants, it ends up back in the returns. A large fan stops this short-circuiting effect.”

Mixing also increases the effectiveness of ventilation, because it ensures that contaminants get to the ventilation system. “You might be able to reduce the amount of ventilation slightly,” Taber adds. “For example, ASHRAE specifies 1,250 cfm for 1,000 sq.ft. at a zone air distribution effectiveness of 0.8. With better mixing, 1,000 cfm may be enough.”

Air quality and thermal comfort are important, even in places where they’re often ignored, such as warehouses and industrial spaces. And especially where energy is expensive, air conditioning would cost too much, more even temperature distribution is vital (such as storage of temperature-sensitive materials like pharmaceuticals or food).

Where large doors are opened or large items are brought in, fans also can reduce the time it takes to bring the space back to temperature – the rebound time – by half. They can also minimize problems like condensation when cold steel is brought into a warmed environment.

Running the plant according to production needs saved significant amounts of energy on off shifts (Figure 2).

The information sensors and software collect can be used to evaluate and optimize control strategies. “We had three identical facilities, each with two chillers,” says Ellsworth. “One cycled between units, one kept both running, the third had one running all the time and the other in standby. In this case, the best strategy — cycling between units — saves $20,000 per month over the worst.”

It’s not necessary to keep spaces at 72°F when nobody’s there. Use energy-saving settings for unoccupied versus occupied, and to follow the scheduling of production operations. “People can be comfortable and happy with systems that are running very efficiently, or very inefficiently,” says Kolkebeck. “Controls are the secret sauce.”

Kolkebeck recently recommissioned a high-density laboratory facility at Penn State. “It was built in 2004, so it’s a completely modern building, but it was using $1.2 million per year for energy,” he says. “We have it down to $600,000.

“It doesn’t take a lot of capital dollars, it takes flowmeters, power measurements, kilowatts from variable-speed drives — controls can gather all that data. Then apply common sense. People see drives running at one-third speed and they love the drives, when in fact the whole pumping loop might not be necessary.”

Drives to succeed

Figure 2. At Trane’s Tyler, Texas facility, controlling the physical plant according to production scheduling saves significant amounts of energy on off shifts.

Like automation systems, variable-speed drive (VSD) costs are becoming more attractive, increasing their range of potentially cost-effective applications. “Overall energy costs are up 10%, utility charges are up 19%, and drive costs are coming down,” says Mike Mattingly, senior drives specialist, Schneider Electric (www.schneider-electric.us). “Consider drives for motors as small as 3 hp, sometimes smaller.” Drives let you move only the amount of air or fluid needed, with valves or dampers left open for minimum restriction.

Pumps and fans typically are designed for the worst-case scenario, for example, a 90°F day. If you can reduce the speed, you can save a significant amount of energy, as shown by the affinity laws (flow is proportional to speed, but energy is proportional to the speed cubed). Reducing the flow to 90% takes 73% of the power, and 50% flow takes 12% power.

“If you have a 20-hp fan running full speed all the time, and you can put it on a VSD and run it full speed 25% of the time, 80% speed for half the time and 50% for 25% of the time, at $0.09/kWh, you’ll save $1,939 per year,” Mattingly says. “The installed cost of the drive is $2,709, so the payback is less than 18 months. With incentives, it can be less than a year.” (See more energy-savings estimating tools at www.squaredleantools.com, www.gates.com/ptsavings and www.cee1.org.)

Any fan or pump under consideration for a VSD also can be evaluated for the efficiency and integrity of its drive system. Converting from V-belt to synchronous drives typically saves 5%. “But study the system,” says Brent Oman, manager, power transmission product application, Gates (www.gates.com). “Maybe they don’t have to run as fast. Then design for synchronous drive — no slip, and low maintenance.”

VSD savings come from running at lower rpm, and this also can be done with ratio changes. When considering a change, bear in mind that designers often build in extra capacity because V-belts slip over time. “There aren’t enough maintenance people to keep all the belts tensioned, so they slip and slow down,” Oman says. “Designers might have accommodated this in the design, and certainly you haven’t been getting full speed all the time.”

A VSD provides soft starts so motors and belts might last longer with less maintenance and downtime. They also might reduce peak demand, and provide real-time power and condition information for monitoring and control.

Pay attention to the physical condition of equipment. “If your machine is battling misalignment or bad bearings, it’s fighting to do its job,” says Joe Van Dyke, president, Government Services Division, Azima DLI (www.azimadli.com). “It’s not a major cause of energy consumption, but detecting and correcting these problems not only increases efficiency, it can prevent a costly downtime incident.”

Standard practice is periodic checks of air handlers, compressors and cooling towers. “It’s especially important to check them before they go into seasons of high loads,” Van Dyke says. Online systems harvest data around the clock, and are increasingly being specified on critical equipment such as compressors.

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