In the case of the chiller, oil was the culprit. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has been warning that oil entrained in the refrigerant of a chiller significantly degrades performance, resulting in capacity loss - and higher utility bills.
In one ASHRAE research project (601-TRP), samples of refrigerant from 10 randomly selected operating chillers were analyzed for oil content. All of the chillers were found to contain excess oil in varying amounts. The three with the lowest amounts had been serviced and had their refrigerant recycled in the last six years, but the oil content in these three ranged from 3 to 7 percent. The oil content in the refrigerant of the remaining chillers ranged from 9 percent to more than 20 percent.
How much does excess oil in the evaporator degrade performance? Table 1 gives typical ranges for minor contamination levels.
Compared to moisture, which creates acids and leads to machine wear and catastrophic shutdowns, oil is a relatively benign contaminant. Most mechanical contractors routinely perform oil analysis to detect moisture, acids, and metal fragments. Refrigerant analysis, which reveals the presence of oil, costs five times as much to do.
Because oil usually accumulates gradually in refrigerant through migration, the attendant loss in efficiency is usually diagnosed to be some other cause. It isn't until performance has significantly degraded that oil is suspected.
So, the typical way of dealing with oil has been to wait until it becomes a serious performance problem, belatedly identify oil as the cause, and then decontaminate the refrigerant charge or install a fresh one. Unfortunately, this is an expensive solution both in the ramped-up power demands for the chiller and the cost of decontaminating or replacing the entire refrigerant charge.
School District Seeks SolutionMary Bryan Elementary School in Indianapolis had a performance problem with a 100-ton centrifugal chiller that had caused the school problems for more than two years.
"It was getting prohibitive to keep sending maintenance people over to Mary Bryan," said Norm Chastain, assistant director of Facilities Engineering for the MSD Perry Township School District. "We finally had to run the backup chiller to supplement the No. 1 system just to keep everybody cool."
Mike Hilterbrand is the service manager for Choice Mechanical, the mechanical contractor that has handled Perry Township's HVAC needs for more than a decade. "We started noticing the problem with this chiller about two years ago," he said. "Performance had started to drop."
"We noticed the problem, but had trouble identifying the solution," he added. "Nothing showed up in the oil analysis that we performed every year; so, since the problem seemed to be reduced heat transference, we figured the evaporator tubes were dirty and cleaned them during routine shutdown. That only created a minimal improvement."
After the second chiller was brought on line to make up for diminished capacity, the contractor decided to have a refrigerant analysis performed.
"We didn't routinely perform refrigerant analysis because it cost about $125, which is five times as much as a $25 oil analysis," said Hilterbrand. "We thought this gave us all the key information we needed on dangerous contaminants like moisture, acid, and metal fragments. What it didn't give us was information on excess oil in the refrigerant, and that's what showed up in the refrigerant analysis we did this spring."
The refrigerant in the chiller contained more than 20 percent oil.
"Oil contamination is something that takes place gradually by migration of tiny amounts over a period of time," explained Hilterbrand. "Unless an oil seal breaks and capacity drops dramatically, the loss of performance occurs slowly over a period of years and is often chalked up to normal wear and tear on the system. That's why ASHRAE has been warning us about excess oil and why we've been listening. We now make refrigerant analysis a standard feature of our annual service procedures."
Now that the problem was identified, the question was what to do about it.
Oil Removal"The standard solution," said Chastain, "would be to pull the charge, replace it with a clean charge, and send the contaminated refrigerant out for reclamation. But that is both expensive and it involved shutting the system down. Jim Vance asked us to look for a more cost-effective solution that would work over the long term."
Jim Vance is MSD Perry Township's energy manager. His duty: to minimize operating costs and maximize energy efficiency in the 22 buildings that compose the school district's facilities. He has been exceptionally effective during his tenure, according to Energy Education, an outside contractor that monitors the success of such programs. Vance's efforts have reduced costs by $7.6 million over the last seven years.
"Jim Vance and Norm Chastain came to us and asked if we had a better way of dealing with oil contamination," said Hilterbrand. "We told him we'd do some research. We thought with the recent emphasis on oil contamination there might be some new technology that could fill the bill."
Hilterbrand called Redi Controls. The manufacturer was in the process of bringing to market a new, patent-pending product named the OAM-Purger (short for oil, acid, and moisture purger), designed specifically to remove oil from the refrigerant charge and automatically return it to the chiller's oil sump. Redi Controls had retained an independent lab (Intertek Testing Services ETL Semko, an ARI- and ETL-approved lab) to perform efficiency testing, and the company was looking for a case study site. Hilterbrand's timing couldn't have been better.
The purger is designed to remove oil, acid, and moisture, but its primary purpose is to remove excess oil.
"We designed this system primarily to remove oil," said Mark Key, vice president of marketing for Redi Controls. "The acid and moisture removal are bonuses. Its advantages are that it connects easily to an operating chiller, operates passively and independently of the chiller whether it is operating or not, and has no effect on chiller operation other than increasing efficiency, regaining capacity, and decreasing energy usage."
Dramatic ResultsVance, Chastain, and Hilterbrand were hesitant at first; the performance literature on the purger seemed to be too good to be true, but the benefits outweighed the risks. Besides, the OAM-Purger worked without taking the chiller off line, so student comfort wouldn't be sacrificed.
Michael Shows, representing Intertek ETL Semko (ITS), oversaw the test at Mary Bryan Elementary School. First he needed to establish the current state of the chiller.
"It was not possible to achieve and maintain the standard rating condition of 55 degrees F entering and 45 degrees leaving water temperatures," he reported. "During the initial test on May 7, 2003, the chiller was found incapable of achieving the standard condition without assistance from a second chiller at the facility."
The reason cited was excess oil in the first chiller. The conclusion of the test was scheduled for June 20, 2003, but some interesting events happened shortly after the testing began.
"On the Friday following ITS' initial work, we installed the OAM-Purger," said Hilterbrand. "Since there was so much oil mixed with the refrigerant, we installed a 30-gallon cylinder to collect the excess oil. After approximately two to three weeks from installation, about 125 pounds of excess oil was removed from the system. The chiller was brought into equilibrium with the correct amount of oil and refrigerant, and the purger and the chiller have been operating efficiently and effectively."
Verified By TestingShows reported that the unit's performance increased significantly between May 7, 2003, and June 20, 2003. "On the evaporator side of the unit, the measured tonnage increased from 75.2 tons to 92.8 tons. This was a measured increase of over 17 tons, which is a 19 percent increase in capacity.
"By taking this measure in concert with power usage, the kilowatts per ton [kW/ton] was calculated for both tests. There was a significant increase in kW/ton produced by the unit. The rate per ton of cooling decreased 19 percent (nearly a 20 percent de-crease in energy usage). This does not take into account the amount of additional cost savings associated with the decrease in operation of the second chiller, as the first chiller now obtains efficient cooling capacity alone."
Succeeding independent tests showed trace amounts of oil - 1.35 percent on July 28, 2003, and 0.88 percent on August 21, 2003.
Those results decided things for Vance. "We have asked Redi Controls and Choice Mechanical for bids on installing these purger systems in our two high schools," said Vance. "That's five chillers in total. If they work as well as they did at Mary Bryan Elementary School, we'll look at putting them in our other facilities as well."
Classroom ComfortMeanwhile, in Raytown, Mo., Michael Richardson had a problem that was driving him and everyone else in the Raytown School District maintenance department crazy.
"It was the science wing of one of the high schools," said Richardson, the district's director of Buildings and Grounds. "There are 10 classrooms in that wing, and we were getting six or seven calls a day complaining that it was too hot or too cold." Such problems frequently indicate an underlying control problem. Such a problem can add to the building's energy consumption, even though that may not be the most obvious symptom.
Raytown is a suburb of Kansas City that supports 18 schools. The building wing in question was fairly new, built in 1992, but the zone control system that had been installed had never worked correctly.
"It operated on pneumatics, opening and closing the vents to the individual rooms on demand," said Steve Atkin, head HVAC technician. "But the contractor had never gotten it to work right. So we were always sending maintenance guys to the rooms.
"If it was too hot, all they could do was turn off the heat. Then they'd have to return two or three hours later to turn the heat back on. It was the same with air conditioning. In the spring and fall we were averaging six to seven calls a day. We had one rooftop unit for every two classrooms. We looked into replacing them, but the cost was prohibitive."
Network ThermostatsThe school board approved a three-year plan to replace old systems with heat pumps in 15 buildings over three years and the science wing became priority one.
"We checked out several alternatives," said Richardson. "Everything we found cost between $35,000 and $40,000. It was just too much money to spend on a relatively new system. Then we asked our HVACR distributor for his opinion, and he recommended network thermostats."
Fred Schoen is the branch manager for Geo Enterprises in Buffalo, Mo., a large distributor of HVACR products.
"Raytown schools didn't need to replace their rooftop units in that wing," he said. "They just needed to be able to control them. I suggested instead of controlling the vents, why not control the heating and air conditioning systems themselves? I had been carrying a line of network thermostats from XCI Corp. for the last several years and had supplied them to another school district in Cameron. They had used them successfully to remotely manage geo exchange systems in two buildings, one existing and one new."
"It looked like the ideal solution to our immediate problem in the science wing," said Richardson. "Fred explained that we could install them ourselves and the price for thermostats, sensors, and controllers was only $4,500. That was a significant savings over the other options. We decided to treat the science wing as a beta site for the rest of the project and went ahead with the XCI thermostats to determine how well they worked."
Designed To Fill A NeedThe idea of network thermostats is relatively new. XCI introduced their first product in 1995.
"We were the first to exhibit network thermostats at a trade show," said Jerry Drew, founder and CEO of XCI, "and we've been increasing our product line ever since." The company currently offers four lines of network thermostats, a variety of remote sensors, and three network controllers for any size installation. They have recently added Internet and LAN access to their systems.
"It all started when I was working as an engineering manager at Texas Instruments in weapons systems development and doing consulting work on the side on automation systems for high-end residences," said Drew. "I realized that there was a serious need for something that could fill the void between individual thermostats and expensive building automation systems.
"I reasoned that there had to be a market out there in high-end residential and light commercial, like schools, banks, retail, churches, and so forth - areas where the cost of BAS [building automation systems] could not be justified. I came up with the idea of networking thermostats and controlling them through a personal computer.
"I put my years of high-reliability engineering experience to work and before I knew it I was in business. We introduced our first network thermostat product at the Home Automation Association Show (now the CEDIA Show) in 1995.
"I also designed it to be so easy to use that anyone could install it, even a homeowner. Judging by the comments of my customers, I succeeded. In fact, many of our applications have been as replacements for systems that didn't do the job."
Today, XCI thermostats control the temperature in thousands of homes and light commercial establishments, including names such as MacDonald's, Pier 1, and Crate & Barrel.
Easy InstallationAccording to Atkin, "It took two technicians two days to install 10 sensors, six thermostats, and the controller that connected to our LAN system. Now that we have done a few, it won't take nearly that long in the future.
"All the wiring we had to do was pull one wire to each thermostat, a CAT 5 communications wire. We installed the controller in a utility closet and ran the communications wires from it to each room. A LAN adaptor connected the controller to our Ethernet system which connects to our computer in the maintenance offices. The thermostat wires were already in the walls. To hook up the stats and the sensors was just a matter of connecting two wires."
In this installation, where two classrooms shared one rooftop unit, one room had a thermostat installed and the other a sensor. "It's a master/slave arrangement," said Schoen. "The system averages the readings from both rooms and turns on the heat or chilled air as needed and supplies both rooms."
What about the programming? Said Atkin, "It's very user friendly. It works on Windows and is al-most entirely point-and-click. You can monitor any thermostat from your computer and change the settings at will. The screen displays the image of the thermostat, and all you need to do is use the mouse to make the settings just as you would on a programmable thermostat. It's so easy you don't need any computer experience at all to do the setpoints."
Schoen agrees. "You can program in an almost infinite number of settings for temperature, high and low ranges, settings for when the room is in use and lower settings for when it is not," he said. "One of the benefits I like about these thermostats is that you can allow a teacher to change settings for the thermostat in his or her room, but only within a range set by the maintenance department for their computer.
"People like to have control over their environment, but many believe that if you turn a thermostat up to 90 degrees it will warm the room faster when, in reality, all it does is wear the system out faster. With these thermostats, if the maximum setting programmed by maintenance is 75 degrees, that's as high as it will go no matter where the thermostat is set. The same is true for the lowest programmed setting."
"The programming flexibility is particularly useful for schools," said Richardson, "where there are so many after-hours events for so many different parts of the facilities: basketball games, parent/teacher meetings, PTA, dances, and so on. If there's a basketball game, maintenance can pre-program the thermostats in the gym, lockers, and appropriate restrooms to normal comfort levels from 5 to 8 p.m. and then change them to lower settings after that."
Control Improves Efficiency"All of that flexibility results in energy savings," confirms Schoen. "It's a regular energy management program, a mini building automation system. By controlling all of those settings from a central point, you have significantly better control over how energy is used in all of the facilities, and that means greater energy efficiency, which translates into savings. People who have retrofitted these network thermostats to replace outmoded systems typically experience a savings in the 10 to 20 percent range. There's also savings to be made by using two-stage systems, which these thermostats can also control."
A single-stage system operates at full power whenever it is on and uses more energy. A two-stage system saves fuel by operating on half the energy on the first stage for low to moderate demand times and then on full power when demand is high.
"That's particularly useful in Missouri with our hot and humid weather," said Schoen. "If an air conditioning system could only run on one stage, it would be running at full power and with too many off cycles in the spring and early fall. But with the network thermostat keeping it running longer in its first stage, you get a more stable temperature and energy savings. But equally important, you more efficiently remove humidity from the air because an air conditioner only dehumidifies when it is operating."
Installation And OperationThe new system has worked particularly well for the Raytown School District since its installation in the science wing eight months ago.
"After what we'd been through with the old system, I expected some glitches," said Richardson. "But we only had one problem, and Jerry Drew handled that for us very efficiently."
"Jerry came to Raytown for a day to walk us through how to hook up to our network," said Atkin. "We had trouble connecting with the host and thought the trouble might be with the XCI equipment, but Jerry found that we had fire wall problems connecting with our LAN adaptor. Our Windows hyper terminal wasn't setup right. Jerry helped us through the set up and everything ran smooth from there on. After getting half a dozen calls a day, we have only had one complaint in eight months, and that only involved readjusting a vent."
In fact, the system has worked so well that the school board agreed to add the network thermostats to the three-year program for the retrofit on the other four buildings over the next three years. Raytown School District has ordered an additional 395 XCI thermostats to complement its HVAC upgrade.
Sidebar: You Should Look Into Network Thermostats If ...You have been under pressure to reduce energy use.
Your system relies on locked manual thermostats.
Your system consists of labor-intensive programmable thermostats.
You want remote control of all individual rooms in your school system.
Your current control system requires extensive computer skills and can only be operated by a few people on staff.
You have rejected a building automation system because it is too costly.
Source: XCI Corp.
Publication date: 01/19/2004