Lubricants used outside their design working conditions can bite you in unexpectedly painful ways.
The morning of Monday, December 1, found Marnie Surfaceblow, vice president of Surfaceblow and Associates International, hiding deep within her winter coat in an effort to avoid the frigid air swirling around her airport departure gate. “Maya, I’m reminded of an old story. A man is freezing to death in the Alaskan wilderness, the numbness of death rapidly overtaking his body because he’s too cold to build a fire.”
Maya, Marnie’s lead field engineer, felt even colder than her boss, but replied, “Ma’am, I must advise that building a fire in the airport will result in certain arrest. Tasers may be deployed.”
“True,” Marnie replied, “but tasering warms you up from the muscle contractions, and then they’d put us in a snuggly warm jail!”
Maya turned and gave Marnie a stern look. “Ma’am, surely an engineer of your accomplishments and intelligence can find a better solution,” she responded.
Unable to craft a quick quip, Marnie thought, then suddenly looked around her, surveying the area. “Capital idea, Maya. We’re engineers, and I’m the Winston Wolf of engineering. I solve problems!” She rummaged through her voluminous Prada bag, muttering as she searched, until with an “A-ha!” she retrieved an infrared camera. She stood and held the camera up, scanning the terminal slowly in a circle.
A gate agent approached cautiously with a concerned expression. Maya caught her attention and said, “Do not worry ma’am; she is an engineer.” Apparently having encountered engineers in the wild before, the agent nodded and returned to the airline podium.
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1. A freezing cold Marnie performs some calculations on her laptop to gauge heating system performance at her airport boarding gate. Source: POWER |
After a few more scans toward the windows, floor, ceiling, and heating, ventilation, and air conditioning (HVAC) ductwork, Marnie sat and typed furiously into her laptop (Figure 1), asking Maya occasional questions such as: “What percentage of the walls have windows? What’s the albedo of that hideous ceiling? and How much would you say the passengers sitting next to us weigh?”
Half an hour later, Marnie stopped typing, then turned the screen to show Maya hundreds of lines of calculations, charts, and tables. “See? See? It’s –8F outside and 52F inside. This is the heat generated by the lighting and electronics. This is the insulation value of the structure. This is air circulation factor, convective and radiative heat losses, heat generated by the human bodies in here … and I only did a few hundred Monte Carlo simulations, but nonetheless … I conclude, the heating isn’t working at all!”
Maya frowned, scanning Marnie’s calculations. “Ma’am, very impressive. Respectfully, I disagree with some of your physical assumptions, but … hmmm … my results would be within your margin of error. How did you complete these calculations so rapidly?” Maya asked.
“Because I’m driven, Maya. Driven to be warm again. Let’s find out why this airport terminal has no heating!” Marnie snapped her laptop shut and picked up her phone to make a call, while Maya collected her bags and resignedly thought, “Just keep your boss from being tasered.”
Who’s in Charge?
The airport maintenance supervisor’s office was the cleanest such office Marnie or Maya had ever seen. Spartan in furnishings and containing no hint of anything related to operations and maintenance, the man sitting behind the desk could have been an accountant or insurance broker. Instead, Airport Facilities Director Nick Kramer was a man deeply troubled by the two women sitting across from him, who were accompanied by security officers, who stepped in after the older one was caught demanding to see “whoever’s in charge of this dreadful daft heating.”
Kramer turned Marnie’s creatively designed business card over and over in his hands, then asked, “So, Ms. Surfaceblow, Ms. Sharma, before I tell security to escort you both off the premises, why were you asking detailed questions about airport facilities?”
“Because I’m cold!” Marnie responded. Seeing Kramer was about to signal to security, Maya spoke up, “Sir, Ms. Surfaceblow is a well-known and established engineer, licensed in every state and many nations, who relishes solving complex engineering problems. Noting, as have I, that your heating system does not seem to be working, she wishes to offer her services for free to help solve your current problem.”
“I didn’t say ‘for free,’ ” Marnie muttered.
“For free,” emphasized Maya, with a side-eye toward her boss.
Kramer thought for a bit, and said, “We have professional contractors on this job. We don’t need anyone’s help.”
Marnie shook her head. “You sure about that?” she asked. “I spoke to airport staff, and they said this problem started four days ago when this cold weather rolled in. This is a new airport terminal, presumably with a modern HVAC system. It shouldn’t be failing so soon, and at a minimum, should be easily fixable—unless the problem is a challenge. Well, I adore challenges. Moreover, I’m cold. Your passengers are cold. Your staff are cold. Everyone is cold. Pretty please, with sugar on it, let us look at your system.”
Dumbfounded, Kramer stared at the women, then exasperatedly said, “No. No I will not. Do you know how many security clearances you’d need for me to let some strangers just get access to our …” Kramer stopped as his desk phone rang loudly. Marnie raised an eyebrow, then said confidently, “It’s for you. You should answer that.”
Kramer glared at Marnie, then waited obstinately until his phone reached the seventh ring. Snatching the handset up, he said, “Yes? What?” There was a pause, then he said, “Yes, they’re here, and … what? … who? … Oh, yes sir. Yes sir. Yes sir. No, not at all, thank you sir.”
Slowly hanging up the phone, Kramer turned and glared at Marnie, who sat smugly beaming a smile toward the harried facilities director. Standing and opening his door, Kramer simply said, “Come with me, please.”
Winter Arrives Early
Nick had his team meet the duo in the concourse maintenance room. It was comfortably filled with electric space heaters, which Marnie highly appreciated while she comfortably filled herself with fresh coffee.
Facilities Engineer Mike Burns outlined the problem. “Each concourse has its own heat pump system. Winter comes late around here, so we have an outage to switch from cooling to heating mode the second Saturday in December,” he explained. “Well, one minute we were in the mid-50s, then this polar vortex hit and looked like it was bound to stay a while, so management decided to turn the heat on early. Ain’t that right, Nick?” Kramer, still sulking after receiving the mysterious phone call, just nodded.
“We didn’t have time for our usual winter outage,” added Lead Maintenance Engineer Wendy Brooks, “but the system’s been performing OK all year, so we just did it.”
Mike continued, “It worked for about a day, then four days ago we started hearing a vibration in the piping. We checked the system and the only thing we saw was low pressure at the compressor inlet, and the compressor was running hot.”
“I checked the pipe mounts to see if the cold weather had caused the pipe mounts to loosen,” Wendy added, “but they were all tight. I did find some leakage from the filter-dryer bypass, which I’ve never seen before, so I’m thinking maybe air got into the system.”
“How did your high- and low-side pressures look?” asked Marnie.
“The high side was high, and the low side was low, but we figured that was OK,” Mike replied. “I mean, we looked online and lots of folks said that was a feature of high-efficiency heat pumps.”
“Oooooo … kay,” Marnie replied, trapped between the Scylla of yelling at the hapless facilities engineer or the Charybdis of laughing at him. She was saved from making that agonizing choice as Maya, understanding what was about to happen, paused taking notes and jumped in to ask a question. “Excuse me sir, but what type of refrigerant do you employ? R32, I suspect,” she said.
“We use R454B,” Mike answered. “I’m told it doesn’t perform as good as R32, but it’s less flammable. We have jets being fueled just 20 feet from the concourse, so it’s required.”
Having recovered some of her composure, Marnie said through gritted teeth, “Let’s go take a look at the system.”
Online Advice
With a clear reluctance to go back out in the cold, Mike led the group out of the warm maintenance room and into the unheated mechanical systems area under the concourse. The heart of the heat pump system was nicely contained on a large compressor skid resting on the ground floor concrete (Figure 2). While shielded from the rain and snow, it was directly exposed to howling wind that made Marnie think of the frozen Niflheim of Norse legend. Through an open doorway she saw a rime-coated Boeing 737, sitting abandoned in the cold like a frozen white dragon.
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2. Marnie troubleshoots heat pump issues at the airport. Source: POWER |
So lost was she in thinking about mythological ice creatures that Marnie missed the first part of Mike’s description of the compressor station. “… it kept running so hot it tripped the alarms, but not the system. At first, we thought the compressor oil was too thick, or maybe it was degraded or contaminated. I don’t think it’s been changed since the system first started, and it runs 24/7 so it’s definitely overdue.”
Through clenched teeth, Marnie asked sarcastically, “Did you ask about it online?”
“They did!” Kramer replied. “And they convinced me to sign off on changing the compressor oil to a lower-viscosity type.”
“I’m guessing that didn’t help things very much,” Marnie supposed.
Mike and Wendy, sensing Marnie’s disapproval of online advice, paused in their response, so Kramer replied, “No, no it didn’t. It also cost more money than we had budgeted.”
Wanting to change the subject, Wendy jumped in. “We wondered if the coils were frozen—we can’t really see them because they’re on the roof. When the temperatures crashed, we had some light snow, so maybe there was enough to melt and re-freeze onto the coils,” she suggested. “So, we shut the system down early this morning and changed it to defrost mode, but nothing happened. The compressor runs, but it runs too easily, like there’s no refrigerant in it. We’ve been trying all day to put it back into heating mode, but it just won’t work.”
Marnie sighed. “OK, I know how to fix that for you,” she said. “I need a heat blanket or heating pad, and a hundred-foot extension cord. Nick, I saw a heating pad on your office chair, bring that please.” Kramer, looking nonplussed at the loss of the only source of heat in his office, trudged off.
“Ma’am, I would like to look at the system specifications, especially the refrigerant,” added Maya. “Mr. Burns, can you guide me to your manuals and records please?”
Marnie nodded agreement with Maya, then turned to Wendy and said, “Take me to your reversing valve, and when Nick brings that heat pad, let’s find some way to plug it in.”
Bringing the Heat
It took almost half an hour for Kramer to return with his precious heating pad. His fears for its future were realized as Marnie plugged it in, then wrapped it around an oily valve block connected to four pipes and an electrical solenoid linear actuator.
“My heating pad,” Kramer said dejectedly.
“Ach, don’t worry there. I’m certain St. Nick—is he related?—will bring you a new one,” quipped Marnie. “Now, my guess is your reversing valve is a cheaper design that can get stuck in bi-flow mode. Normally this happens only under extreme circumstances, like when your ambient temperature is 60F colder than normal. In bi-flow mode, the system doesn’t send refrigerant to one side or the other, it sends it to both, meaning your compressor can’t really pump it effectively.”
Shaking her head in surprise, Wendy asked, “But why is it sticking? Is the cold causing the valve solenoid to stick?”
“The cold is the cause, but I don’t think it’s for the obvious reasons,” replied Marnie. Let’s let this blanket sit on here for an hour or two, and then try switching modes again. I’ll bet you a Scotch coffee the valve frees up nicely.”
Lubricants Matter
While Marnie was returning and regaling Wendy and Nick with specialty holiday coffee recipes, Maya was going through the system specifications with Mike. After reviewing the equipment manuals, Maya asked, “Sir, I notice along with the R454B refrigerant you employ, you chose a polyolester oil lubricant rated ISO-150. That is rather viscous, yes?”
“Well, it mixes great with the refrigerant, and it gets pretty hot here in the summer, so we chose a hot-weather oil. I ran a refrigeration facility once where they used an oil that was too thin, and it migrated out from the refrigerant and contaminated the compressor oil,” Mike explained. “Not only that, losing lubricating oil from the refrigerant meant we had to completely drain, evacuate, and refill the system. That was expensive.”
“I’m certain that it was,” Maya agreed, “but perhaps a better choice would have been ISO-68, which is recommended for the summer.”
Mike shrugged. “Does it make that much difference?” he asked. “I mean look at this chart showing viscosity.” Mike pointed at a graphic in the heat pump system operations manual and said, “At 50F, ISO-68 is about half of ISO-150, right?”
Maya closed her eyes briefly and pinched the bridge of her nose. “Sir, respectfully, the chart is on a logarithmic scale, and the viscosity is closer to a 3.5 to 1 difference,” she said.
“Oh,” replied Mike. “It’s still close. Right?”
In the Thick of It
Meeting again in the comfortably warm maintenance room, Marnie began laying out the problem and solution. “The root cause of the problem is the lubricant in your refrigerant. R454B uses polyolester oil lubricant, and it’s known for having a steeper temperature-viscosity curve than other lubricants. Maya did some research and found dropping the temperature from 55F to 0F raises the viscosity by 10 times. Moreover, your baseline lubricant viscosity is too thick. ISO-150 is about 3.5 times as thick as the recommended ISO-68. By the way, good find on those points, Maya. Would you like to continue?”
Pleased at the praise from her boss, Maya accepted the challenge. “As you encountered the unusual cold weather, the oil entrained in your refrigerant thickened significantly, until your compressor inlet pressure fell below specifications,” she said. “Under this condition, cavitation began, resulting in the vibration and noise from the pipes.”
As the maintenance team nodded agreement, Maya continued her analysis. “Next, the filter-dryer system must never operate in bypass mode, as that places the system at risk. Indeed, the fact this occurred should have caused serious concern!” she noted emphatically. “This occurred as the increased viscosity of refrigerant lubricating oil restricted flow through the filter-dryer.”
“And then we come to the compressor,” Marnie added. “Even with the filter-dryer bypassed the refrigerant was hard to pump, causing your compressor motor to draw a lot more amps than normal, and generating a lot of heat. I can understand trying to run the system in defrost mode to see if you could clear some icing, but you really should just check first to see if you have icing in the first place. And in this case, when you tried reversing the system to run in defrost mode, the reversing valve stuck. Worst of all, it didn’t stick one way or the other, it stuck in the middle due to the thickened oil. This meant refrigerant flowed through both outlet pipes, meaning the compressor was doing a lot of work for nothing.”
“Something I’m well acquainted with,” Marnie thought to herself.
Kramer stepped forward, looking very guardedly optimistic. “A nice story, Ms. Surfaceblow, but what’s your recommendation? After all, General Dannenberg himself vouched for you.”
“Oh, was that Larry on the phone? I’ll have to thank him,” Marnie irreverently replied. “My recommendations are legion. First, wait until your heating pad thaws out the reversing valve enough to make it cycle properly—and that valve needs gentle heat, don’t believe that crap online about using a torch or banging on it with a hammer. Start up in heating mode and turn the heat exchanger fan down to the lowest setting in the concourse, so you retain some heat in the system. It’s going to run a lot less efficiently, but at least you’ll get some heat and keep the refrigerant oil flowing. Insulate that reversing valve to keep it from freezing up again, and it wouldn’t hurt to get some moveable doors to shield the compressor from these Arctic gales.”
“And as soon as feasible,” Maya added, “kindly replace your refrigerant with a new mixture using ISO-68 grade oil.”
Some final details were worked out, then Kramer led Marnie and Maya back to the main concourse. A short farewell was said before the two women returned to their same seats at the same gate, noting with surprise that they hadn’t missed their outbound flight, but it was boarding in 15 minutes. As they took their place in line, Maya asked her boss, “Ma’am, in Mr. Kramer’s office, how did you know that phone call was for him? You made it seem so dramatic!”
Marnie smiled broadly, laughed, and said, “Well, it was his office after all, so any call was almost certainly meant for him! And that was the number I gave our intern, Eric, the one who does those great impersonations …”
Afterword
On December 24, a package from Ms. M.O. Surfaceblow was delivered to Nick Kramer. It contained one extra-large designer heating pad with a message saying, “Merry Christmas! Ho, ho, ho!” Nick was pleasantly surprised.
—Una Nowling, PE is an international power and energy operations consultant.
