Newer HVAC components spark retrofitting, dampen power bills.
By David Engle
You’re an Engineer? You’re Hired.”
So read a headline last year in US News and World Reports, telling of a booming profession with very low unemployment and steadily growing incomes.
Much of the credit goes to a resurgent and more innovative building industry. Despite years of weak new construction demand, vendors are offering new designs and products that make retrofits or upgrades easy to cost-justify.
Florida builder, Marc Rutenberg Homes in Palm Harbor near Tampa Bay, combines the concepts of onsite photovoltaic (PV) generation and extraordinary energy efficiency. Company president Marc Rutenberg touts this ultra-efficient design model as a potentially transformative “Zero Energy America” concept. By this he means that a resident can run on “net-zero-grid energy, leaving the homeowners without power bills,” he says.
Builder Rutenberg points out: “VRF [variable refrigerant flow] technology is now pervasive everywhere—except here in US.” He first began exploring VRF and other ductless systems in earnest about three years ago, and then made a design commitment based on the exceptional performance.
Previously, Rutenberg recalls that he had experienced “the success and failure of the last 20 years of zoning technology using Carrier and Trane.”
“Success” consisted of improved comfort. But there was also failure, in the sense that despite improvements via things like variable-speed fans, enhanced SEER (Seasonal Energy Efficiency Ratios), and better air filtration, he says, “you rarely had an opportunity to use traditional zoning where you can get any true reduction in the cost of operation.”
Lately, at a building show in 2013, Rutenberg was delighted to see that Lennox had taken on the challenge of introducing a duct-free, US-made HVAC system. But this smacks up against global HVAC tech dominance now enjoyed by Daikin, Mitsubishi, and LG.
At Rutenberg’s model, electric generation and consumption are now closely monitored. “Almost every day we generate more electricity than we use,” he says, and, as it happens, the excess can be sold back to the local utility Progress Energy, through net metering.
Rutenberg is also now breaking ground on the first Zero Energy Village prototype neighborhood, consisting of 20 1,600–2,400-square-foot homes built to similar “net-zero” standards.
HVAC system designers “have also altered their practices” as a result of VFDs’ continuous improvements since the technology “really does give them a bit of wiggle room now.”
As for why the US lags the world in HVAC efficiency innovations like VRF and duct-free systems (DFS), Rutenberg suggests that, from his perspective, US product development historically “was financed largely through natural gas distribution companies.” These benefitted from high fuel consumption.
Product development thus “did not come about through a consumer preference or awareness,” he adds, “but from an underlying … alliance that redirected builder specifications.” Now that times have changed, though, opportunities are again wide open.
Also on the theme of the surprisingly slow adoption here of VRF, an article in the architectural magazine AIA Journal suggests that US refrigeration engineers simply lack familiarity with this exotic design. To fix this, a half-dozen years ago, ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers) launched a documentation study group. Its work culminated in 2012 with the publication of a chapter in the new ASHRAE tech manual, devoted to VRF.
The above-named Big Three global manufacturers are also now funding schools for thousands of US engineers and technicians annually on VRF and ductless systems; Mitsubishi alone supports 1,100 US service locations.
As for applicability, VRF systems’ efficiencies come out best wherever loads vary, and buildings can be sectioned into many rooms that make natural control-zones: hotels, offices, schools, for example. Less ripe are sites with a single large open space, like auditoriums and gyms.
VRF brings with it at least a 20% higher first cost, but this is recouped with 10% or more in operational efficiency. Vendors’ product lines offer significant variations in capabilities, even as basic VRF principles remain similar.
For his 4,500-square-foot luxury model home in Palm Harbor, Rutenberg used LG’s VRF Single-Phase Multi V System. It provides independent zoning, with five ducted indoor units operating from a single outdoor unit. Saving on installation costs are achieved with certain ductless elements including specially designed heat exchangers and inverter technology.
Early in 2013 LG Electronics introduced an expanded line of VRF and DFS, new multi- and single-zone systems, air cleaning and filtration, control devices, an eight-zone duct-free split heat pump system, and the industry’s first duct-free product with a SEER approaching 28.
Mitsubishi markets a 100% inverter-driven VRF technology in which the compressor varies its speed to match cooling or heating demand; it only consumes the minimally required energy. The company’s City Multi VRF systems, available in 208-V/230-V/460-V capabilities, can be designed for up to 50 zones per system. Smaller single-phase systems can be configured for up to eight zones. A total of 11 indoor unit styles, ducted and ductless, are offered. By being integrated with Mitsubishi control software, up to 2,000 zones can be managed from a single-networked PC.
On Lake Sammamish near Seattle, WA, the 16-unit luxury condos at Bella Mira are sized up to 3,100 square feet. The high-rise buildings lacked space for a rooftop cooling tower, and there was no place for interior air handling units either. “We would have had to put them in valuable closet space,” recalls contractor Doug Happe, of Emerald Aire Inc., in Auburn, WA.
Happe selected Mitsubishi’s City Multi VRF zoning system. Its inverter technology varies compressor speeds of the outdoor unit to match the variable indoor zone loads. Each zone has its own indoor unit or group of indoor units. Equipment is sited in a small mechanical well on the garage rooftops to hide them.
Five outdoor units maintain the 16 indoor air-handling units, for simultaneous cooling and/or heating as needed. The outdoor units are engaged only when called upon. Indoor air-handling fan coils precisely manage indoor temperatures “with just a whisper of sound,” says Happe. His first Mira Bella service call came from a tenant who complained the system wasn’t working, when, in fact, it was running so quietly that the resident couldn’t hear it, Happe says.
Tenant billing is also facilitated. Integrated software enables control of up to 40 centralized controllers with a maximum of 2,000 air handlers on multiple outdoor units. All this occurs on a single PC. Tracking of energy usage is precise, making it easy to apportion charges on the monthly Puget Sound Energy bill.
VFD: The “Revolution” Continues
First introduced about two decades ago, this epoch-making acronym for variable frequency drives has now triumphed completely as the ultimate HVAC efficiency retrofit boom-maker. Energy improvements with VFDs compared with wasteful one-speed motor predecessors range from 35% to 50%, and can go as high as 95%. VFDs accomplish this because their variable RPMs are able to match momentary system demands precisely, rather than running full tilt for every task. Throttling back with just a modest speed reduction translates into disproportionately great power savings. Example: running 63% slower, a motor needs only 25% of its full-speed power; slowing by 50% saves 90%. Efficiencies are especially impressive in variable-torque fan and pump applications. Both abound in HVAC systems.
VFDs on even a small electrical motor can reduce energy use.
Colin Moar, a specialist in building commissioning, has probably observed hundreds of VFD-equipped HVAC systems in all stages of development over the past 20 years. “VFDs are now so widely available that manufacturers are gearing-up the drives to be much more user-friendly and more easily retrofitted onto old motors,” he says. “That’s the major breakthrough I’ve seen over the last three or four years.
“Five or six good vendors out there are producing VFD from three-kilowatt size and above. You can put a VFD on even a very small electrical motor, and over time it will save you money,” adds Moar, who is West Region Commissioning Director and a vice president of Heery, a national design, engineering, commissioning, and construction management firm with about two-dozen US regional offices.
Meanwhile, Moar continues, even as capabilities are blossoming, “The cost of VFD has come down tremendously since they first came out and were utilized for commercial sites.”
Product literature from VFD-makers describes a growing list of innovations including: the built-in capability to display performance info continually on networked monitors; controls that offer extensive parameter selection; closed-loop controls; industry-standard manual/off/auto functionality; internal programmability; sleep functions; and embedded BACnet Communications (and other) protocols. HVAC VFD sizes seem to range from as little as one-half horsepower upwards to several hundred.
Moar says HVAC system designers “have also altered their practices” as a result of VFDs’ continuous improvements since the technology “really does give them a bit of wiggle room now. Designing doesn’t have to be as exact as 10 years ago. . . . You can go from 30-hertz, to 75-hertz, or 80-hertz if you need to . . . up and down the curve.”
Flexibility proves invaluable when retrofitting older buildings. “What was designed 15 or 20 years ago may have changed dramatically since then,” he notes. Tweaking an HVAC system simply by changing out fixed-speed with VFD becomes a relatively inexpensive and easy route to go.
“Retrofitting with a variable-volume system, with good control, you may not have to touch much of the infrastructure at all,” says Moar. Thus, you’re generally assured of a relatively quick payback or ROI.
One example, reported in the ASHRAE Journal of December 2012 by Geneviève Lussier et al., tells of overhauling a 30-year-old condo, Les Verrières sur le Fleuve near Montreal, Canada. Two 18-story towers there house 120 apartments each, as well as an indoor pool, heated interior parking, and multi-use rooms.
Les Verrieres’ owners wanted to cut their big electric bills. Retrofit VFDs harnessed a 10-hp domestic water booster pump (50% power saving), as well as the exhaust and makeup air ventilation systems, the cooling towers (four 20-hp pumps and two 25-hp fans), the pool ventilation and outdoor pool water heating/ventilation system. On each tower, occupant exhaust fans were “VFD’d,” as were two 6-ton geothermal heat pumps. VFD fans were put on essentially all motor for exhaust and fresh air. Cumulative efficiency savings came to 43%.
The world’s largest VFD maker, Yaskawa, touts scores of VFD designs and products specialized for HVAC air handlers, cooling towers and pumps. Steve Acheson, a Yaskawa America Inc. applications engineer in the HVAC VFD group, reports having seen in recent years “some unbelievable rebates available for installing drives and retrofitting in buildings.” A few do-it-yourselfer saw paybacks come within one week, he adds. More routinely, cost-recovery usually takes less than three years and not uncommonly less than one. For info on what’s offered, see the Database of State Incentives for Renewable & Efficiency.
Now: Wireless HVAC Thermostats
So much for rewiring HVAC with VRFs, DFS, and VFDs. Also embracing efficiency needs from a rather different tack are new control systems.
Here, the explosive growth of wireless networking is now transforming building management from end to end. Wi-Fi can be applied for this at even a basic level for a single HVAC thermostat, then integrated with other Wi-Fi-enabled controls to handle lighting, plug loads, and metering. Still more automation can be gained with wireless occupancy sensors.
What wireless mesh networking gives to this assemblage, chiefly, is low cost and ease of use. Eliminating wires will slash the high expense associated with previous-generation building management systems. Wireless nets create “mini” BMS systems practical for millions of small-and mid-size sites, which, with only modest investment, can cut utility bills dramatically. And here again, retrofits may qualify for federal-state-local incentives.
Walt Dowling is a spokesman for one Wi-Fi mesh developer, Autani, which introduced its latest-generation Stat Center product for wirelessly networked thermostats—part of its Energy Center product suite—in 2012. Having shipped the latter for about 18 months now, Dowling reports the product is already now operating in just less than 1,000 buildings.
In a typical installation, a site simply replaces its existing thermostats with wireless networking ones, perhaps adding appropriate occupancy detectors and other sensors. What this will accomplish, for example, in a school gymnasium, will be the ability to turn off the HVAC automatically if sensors detect windows open or doors ajar—common events throughout the school week, notes Dowling. “Occupancy sensors and thermostats all talk to each other on integrated wireless mesh network and talk back to our management appliance, which is the heart of wireless network,” he explains.
Here, a Web dashboard enables extensive HVAC (or other system) control, efficiency feedback, and energy-saving management. For example, regular on/off events can be scheduled, and thermostat temperature ranges can be individualized and fine-tuned. If, say, a large church has 20 thermostats, but lacks central control, a wireless network would enable managing devices centrally (even offsite remotely), and vary the resource activity according to room use and individual zone needs.
Ripest buildings for retrofits are offices and factories where peak demand billing occurs, and buildings aren’t continuously occupied. Payback from efficient management generally happens “inside of three years,” says Dowling. “Typically, you are going to reduce energy consumption by 25% to 50%, with payback anywhere from 12 to 36 months.”
For a final caveat or two, Moar points out some of difficulties to be considered with today’s HVAC drive retrofits, driven mainly by overly high expectations.
First, he notes, there’s often a bit of a gap between the high-end development work being achieved by technology vendors, and the skills at line level. “Even as the technology has moved ahead so quickly, some of the building operatives haven’t,” he says.
For example, Moar recalls commissioning “a very sophisticated energy recovery and control scheme” for a small school district. “It was a little bit too complex and over complicated,” he says. “We were getting a Rolls Royce control sequence and only needed a Chevy.”
The contractors had completed their work and left the area, but the training of the client’s operators “was sketchy at best,” and management oversight was all done in-house. “Only because they didn’t know how the whole system operated,” he says, “all of the VFDs were running continuously at 60 hertz” instead of optimized as designed. “It was all too complex.”
Moar’s team was summoned to do a retrocommissioning. “We actually put it back to its design parameters and then sat with them basically for two weeks and helped them understand interactive operation and what they should be looking for. We walked them through it, hand holding. Their energy bill has finally dropped about 30% this winter, and I think it’s going to be dropping a bit more in the summer.
“The good news is,” he continues, “VFDs are easily brought back under control. You just need to have people to be fully trained to use them effectively—not just the VFD but the associated control system.”
Regarding the wireless HVAC control systems that are now proliferating, he says, “There are lots of them that are very good. But whether it’s a small, less sophisticated one, or very complex . . . the way the operation interacts with the equipment has got to be, in my opinion, the very best that you can afford to get. Because it’s the engineering of planning, more than technology, that matters. The controllers are just commodities. It’s the programing—tantamount to making them work and then keeping them operational—where they pay their dividends.”
Moar recently commissioned a hospital data center in California using wireless temperature and occupancy detectors. This latter job illustrates the current Wi-Fi mentality well. He notes: “No one wanted to run wires and cable-conduit through a live data center, so they put transmitters and sensors on columns. So HVAC drives and pumps and fans and controllers were still hard wired in the back of house plant rooms but out of the way.” Data is measured, transmitted, and sent wirelessly to receivers connected to programmable controllers, then controlled via hardwired connections to equipment and communications cables for display and monitoring.
The proliferation of more than a dozen BMS networking system vendors, and many communications protocols and dozens of variants, is also somewhat chaotic. Again, says Moar, the underlying engineering concept and system operation surpasses in importance the control and communications; vendors’ priorities on this score are too often reversed, Moar suggests.
In discussing HVAC vendors’ roles when validating building systems performance and commissioning, Moar alludes several times to a “fox in the henhouse” conflict-of-interest. In this scenario, vendors often sign-off on their own work for an owner. “If a building owner shops for lowest bidders, then designers and contractors undertake and carry out the contract,” he notes. “But there’s often no one engaged in actually proving, verifying, and testing that it actually works through the full range, in accordance with the owner’s requirement and designer’s intent, and what they purchased from the specialist contractors.”
Another issue to consider with high-expectation HVAC designs is long-term performance. Moar offers the concept of continuous commissioning as a solution “to validate that the owner’s payback continues over 15 or 20 years.” This is similar to scheduled automobile servicing throughout one’s ownership. Similarly, energy-wise recommissioning should become routine thinking, he says. Every major change in use or operation in a building should spark the question of whether HVAC recommissioning is needed, he adds. There should also be periodic review of the utility bills and sub-meters to see where the energy use is occurring and determine if it could be reduced without losing the building’s environmental criteria. In the UK (Moar’s native country), high-profile, high-efficiency buildings are regularly recommissioned, and occasionally even for each change of season.
Moreover, whenever contractors guarantee energy savings, these, too, “can be difficult to verify,” he suggests, especially if system operation results are not regularly measured and validated independently. A vendor’s manner of interpreting what is proper performance becomes easily skewed and self-serving to prove the energy conceptual model. Certain innocent-sounding assumptions are nearly impossible to enforce, such as HVAC systems that claim to factor-in weather forecasting.
In sum, contractual terms for validation must be strongly credible, he says; “otherwise, they can be just marketing claims and non-provable numbers in a formula sheet.”
If savings are not indeed happening, then the assessment process must also be skillful enough to determine why, and what might fix it, he adds. “The validation exercise needs to be a little harder. It’s doesn’t necessarily have to be limited to once, at commissioning-time only. It could be, and should be, done at any time.”
“It’s not that they’re not meeting their intentions,” he says. “It’s just that their contract language allows them a lot of latitude, in legal terms, if the owner makes any changes. Energy performance contracting has its place in the industry. But you need somebody competent to verify it independently.”
Author’s Bio: Writer David Engle specializes in energy-related topics.