Mechanical contractor works with engineer and general contractor to shift spec from 39 fixed-speed pumps to 19 ECM variable-speed models at Gallatin Field Airport Car Wash, cutting power consumption without undercutting longevity and performance.
Bozeman, Montana — Once the bids are submitted and the contracts awarded on a commercial project, it is not unusual for many of the specifications and perhaps even the mechanical-system designs themselves to undergo varying degrees of revision by one or more of the principals involved.
Sometimes a general contractor will poll his subs for “value-engineering” suggestions to help lower installation costs to stay within budget. Or perhaps the installing contractor has what he believes to be “a better way of doing things” and will convince the owner, the general, even the specifying engineer that building performance and longevity will be enhanced by his alternative approach — or at least not hindered.
The engineer may not exactly relish the experience of seeing his original designs and specifications tweaked, let alone given a radical makeover. Then again, if the client-owner is happy and his project well-served by the changes, he may not be inclined to argue.
All of the above scenarios came into play on a recent, successfully concluded project at the Gallatin Field Airport in Bozeman, Montana. The property owner and manager, the Gallatin Airport Authority (GAA), sought to replace an existing, five-building car-wash facility with a three-building, washing and detailing complex for use by four rental-car companies. The main unit, a 5,480 square-foot (sf) structure, would be devoted to vehicle washing, while the other two facilities — measuring 3,510 sf and 7,056 sf — would be used for vacuuming, windshield cleaning and other types of car-prep work.
Among the salient features of the project, which was finished in early May 2010:
- a radiant floor heating system inside the car wash facility; and
- snowmelt systems on the exterior slabs, front and back, of all three buildings
Zurn PEX (crosslinked polyethylene) tubing was used in all the radiant and snowmelt systems, while the manifolds and other components were furnished by Watts Radiant — all through local wholesaler-distributor MDM Supply Company and its Bozeman branch. The heat sources were eight high-efficiency, condensing boilers divided among the three buildings: Lochinvar Knight Heating Boilers with inputs from 210,000 BTU to 399,000 BTU.
Not surprisingly, given the rugged Montana winters, the build team regarded all four of these heating systems — one radiant and three snowmelt — as absolutely essential for a year-round car-wash operation of this magnitude. The Gallatin facility handles up to 200 vehicles daily, according to Pat McMullen, owner and president of PJ’s Plumbing & Heating (Belgrade, Mont.). PJ’s not only did the installation, but also — as we will see shortly — spearheaded significant changes in the way the radiant systems were built.
“In the cold-weather months,” McMullen continues, “with all that water dripping off the washed cars, the slabs would ice over, making safe driving impossible inside or outside. And with all the traffic in and out of the car-wash facility, the doors open and close constantly, too.”
Both of these factors made radiant the optimum choice for this application. Keeping the floors exterior pads warm would eliminate the hazardous ice for driving. Radiant would also keep the heat at employees’ feet rather than the ceiling, creating a reasonably comfortable working environment even on bitter-cold days with the facility doors wide open much of the time to accommodate vehicle movement.
Change in circulator strategy: PJ’s bid on — and won —the entire plumbing and mechanical portion of the Gallatin Car Wash job: trench drains, sand and oil separators, and bathrooms, as well as the slab heating inside and outside. But when general contractor Martel Construction approached its mechanical sub for ways to cut costs to bring the project more in line with budget projections, McMullen zeroed in on the radiant part of the job; specifically, the circulating pumps.
Created by the Bozeman office of Morrison-Maierle Inc., the original plans called for an injection-piping strategy in each building. Multiple boilers and a series of smaller circulators in a secondary loop would transfer warm fluid from a primary loop to the individual system loops: 1) low-temperature water for the radiant heating and snowmelt systems; 2) high-temperature water for the hot-water unit heaters warming the two “vacuum buildings,” and for an indirect water heater supplying the car-washing equipment. (The indirect unit was subsequently eliminated as unnecessary.) The number of circulators in all of these loops totaled 39, all fixed-speed models.
Even while bidding the project, McMullen pondered an alternative approach to the pumping. Upon winning the contract, he met with MDM sales representative Todd Sisson to revisit the pump strategy. The team thought they could shrink the circulator total to 19 by changing the piping layouts from primary-secondary to a direct supply-and-return. The new pumps would be somewhat larger and with more horsepower, but reducing the number of pumps from 39 to 19 and eliminating of all those electrical connections would cut costs substantially. (The final savings turned out to $12,368.)
Reducing the number of circulators by 20 would inevitably have lessened ongoing maintenance hours and costs, of course. But PJ’s believed their new approach could also shrink the airport authority’s monthly electric bills by a substantial percentage. “Just looking at the total wattage of the 20 circulators we were eliminating, we thought we could cut power consumption by half at least,” says McMullen.
“At least” is the key phrase here: PJ’s wanted not only to halve the number of pumps, but also to introduce a new, power-saving technology into the mix: ECM (electrically commutated motor) variable-speed circulators. As already noted, all the pumps in the original design for the car wash were constant-power — that is, “fully on no matter how much power is actually required,” explains Erik Chidester, a PJ’s field supervisor who oversaw the installation.
“We recommended a relatively new type of circulator that automatically adjusts its speed according to current demand, instead of maxing out every time it came on. We figured this variable-speed technology could cut power consumption by up to 70%.”
Alpha and Magna: The circulators that PJ’s ultimately recommended were the 115-volt Alpha and the 230-volt Magna, made by Grundfos Pumps USA and supplied by MDM. Both feature a permanent magnet motor design to cut power consumption dramatically. And both are equipped with proprietary logic circuitry — trade-named AUTOADAPT™ — that automatically varies circulator speed to match system demand.
- The Magna is the larger of the two circulators, with a flow range of up to 170 gallons per minute (GPM) and a head range up to 42 feet. Six of these units were ultimately installed to control the movement of warm water from the boilers to PEX loops in the snowmelt slabs outside the three buildings.
- Five of the smaller ALPHA circulators (22 GPM, 19 feet of max head) were subsequently used for the radiant slab heating system inside car wash facility: one for each of five zones, each with a different load.
- Rounding out the pump package at Gallatin are four Grundfos UP26-99 circulators (115-volt) and four Grundfos UPS26-150 circulators — all used at fixed speeds to manage boiler-loop circulation.
“Thanks to AUTOADAPT, we were able to use the same Alpha circulator in all five zones in the car wash building, despite their differing loads,” says Chidester.
“Variable speed pumps like the ones used on the Gallatin project eliminate the margin of error for friction calculations traditionally used to size pumps,” adds David Weiel, P.E. (pronounced “wheel”), the mechanical designer on the project.
“Reputable engineers use the best tools and techniques available to them to calculate friction losses. But not every situation is ideal, and piping layouts often change in the course of construction. As a result, projected head losses from calculated design parameters don’t always match what occurs in the real world once a system has been built.”
Other cost savings: The switch to variable-speed circulators enabled PJ’s to trim installation costs in two other important areas:
- No need for circuit setter balance valves: The original engineer drawings called for circuit setters to be installed with each of the 39 fixed-speed pumps. These devices are used to set the needed flow rate, but the AUTOADAPT function in the revised configuration made them unnecessary.
- Reduced need for testing and balancing: The experts who typically set the circuit setters are usually work for an independent testing and balancing company hired by the installing contractor. As the designation implies, the T&B mission is to set the various installed components in a heating system in line with the design parameters of the project before it is formally commissioned.
Balancing the flow rates of the various zones in a radiant or snowmelt system is “one of the trickier aspects of small and mid-sized commercial projects like the Gallatin Car Wash project,” says McMullen, echoing Weiel. “Engineering parameters don’t always coincide with the actual conditions a system must run under. The boiler and piping specifications may call for 50 GPM, but conditions may dictate only 10 GPM or 25 GPM.”
Balancing a system to handle flow rates that vary from 10 to 50 GPM requires additional components, such as secondary balance valves and pressure differential bypasses. These sophisticated technical components “tend not to stay in balance over the life of a system,” McMullen contends, “and must be regularly tweaked and adjusted. It’s a moving target.
“But this is where the AUTOADAPT function is so valuable for a builder owner as well as for an installer like myself. Once you install this type of pump and set it to the AUTOADAPT function, it will automatically adjust its speed after a short period. Put the pump on AA and walk away — it makes the installer’s job so much easier.”
Because of this automatically self-adjusting, variable-speed technology, PJ’s did not use its customary T&B partner quite so extensively at Gallatin. “Our testing and balancing guy is very skilled, but we can foresee the day when testing and balancing will not be necessary on the wet side of a radiant and snowmelt system. The intelligence of the variable-speed pump will take care of the balancing for us.”
It is also interesting to note that the versatile ECM circulators also offer fixed-speed options that McMullen and his team find highly practical: “That feature is handy for air-elimination and purging a heating system. After an initial purge with a glycol-ionized water solution, for which we do not use the circulators, we just ramp the circulator up to Constant Speed 2 to get the air out more quickly, removing the micro-bubbles from the glycol solution. Once the system is ready to go ‘live,’ we switch to AUTOADAPT.”
True believer: The ultimate impact of the switch to variable-speed pumping technology at Gallatin Field will not be fully understood until the performance results through the 2010-2011 winter are recorded and analyzed. But the owner of PJ’s Plumbing & Heating is fully confident his recommendations to the general contractor were on the mark.
McMullen first encountered — and became a true believer in — ECM variable-speed technology in 2008, as one of roughly 200 beta-testers of the Alpha circulator in the United States. He replaced two 85-Watt circulators in his own home right before the 2008-2009 heating season. Over the next two years, the replacement pair operated consistently at an average of nine watts, he reports, even on days when the mercury nosedived seriously below 0°F, as it will often do during Montana’s brutal winters.
“Over the past 35 years, PJ’s has installed up to 1,000 hydronic and radiant heating systems, with all kinds of boilers in all types of system configurations,” says McMullen, who estimates he used Alpha circulators in up to 15 projects over the past year and a half. “We have a fair amount of heating experience, but I have never come across a circulator that works so easily and efficiently with so little power.”
What’s best for the client? Which brings our story back to the specifying engineering firm that developed the original plans and specifications. As McMullen graciously notes, “Morrison-Maierle was very progressive and very open to our alternative ideas. We understood that we not only had to save the project money, but also to make sure it performed to the level that the engineer, the general contractor and the owner all expected.”
Mark Maierle of Morrison-Maierle characterizes the mechanical aspects of the Gallatin job as unusual, if only because “it’s not that often that our firm will redesign a project at the installer’s request.” On the other hand, Maierle is savvy enough to acknowledge the downside of compelling experienced professional installers like McMullen and his team in a direction they don’t really want to go.
“There are many different ways to skin a cat, so we were responsive to Pat’s comments and suggestions,” Maierle continues. “We believed — and still believe —our original primary-secondary loop system would have served the airport authority well for many years. But the airport now has a system that will work equally well, and, in the end, that’s the most important consideration.”
Morrison-Maierle’s Weiel has serious reservations about the projected energy savings from the 11 variable-speed circulators, at least when comparing them to the pumps they replaced from the original piping design. He comments:
“We chose the injection piping scheme for several reasons, including greater boiler redundancy — so the system could function close to its intended capacity with one boiler completely out of service — and to handle multiple water temperatures on the same system. Each loop had two circulators, which is why the reconfigured system was able to reduce the number of pumps by half. But in our injection-piping scheme, only one circulator would’ve run the majority of the time, because the injection pump operates only when the system demands additional heating.”
Weiel does not doubt the ability of AUTOADAPT to cut power costs from the injection-piping scenario: “But by 50% or more? That does not seem feasible to me, given the thorough consideration we gave to energy conservation with the original design.
“In addition, the original pumps were not greatly oversized,” Weiel continues. “In fact, they were closely tailored to the head losses calculated for the loops they served. That is why a wide number of different model number circulators were originally specified.”
Nonetheless, Maierle and Weiel could readily see — and appreciate —the strong convictions that McMullen and this crew had for their alternative, variable-speed pumping solution. Weiel notes that Morrison-Maierle came to regard this alternative and the design changes it necessitated as net positives for the project.
“When the contractor is more familiar with the design — as was the case here with PJ’s and the variable-speed circulators they recommended — he is usually more comfortable doing the installation as well as any servicing that may follow the commissioning,” he comments. “A contractor taking ownership for what he is installing becomes a win-win situation for everyone —most especially the owner. As long as the alternative approach does not compromise the quality, performance or longevity of the project, we are willing to work with the contractor on pursuing that alternative.
“In the end, we’re all here to help our clients achieve the best possible finished product.”