There's no doubt that the Windy City faces its share of extreme weather - with temperatures prone to drop below zero in the winter and to reach over 100 degrees summer - so maintaining comfortable environments in the nation's third most populous city could be considered anything but a breeze. Mix in some stringent city codes, and HVAC designers have their hands full. With that in mind, here's a look at some unique projects in the city hosting this year's AHR Expo.
Providence-St. Mel School--Eighty years old and still kicking
Engineering firm Team Mechanical Inc. (TMI) is overcoming a host of challenges to cool a school more than 75 years old to ensure that students learn in a comfortable environment.Providence-St. Mel, a prestigious K-12 school located on Chicago's West Side, was built in the 1920s. The Archdiocese of Chicago closed the school's doors in 1978 due to the prohibitive cost of upkeep. Later that same year, principal Paul Adams reopened the school as an independent, private institution. Adams, who has the vision to offer a year-round curriculum at the school, recognized that the aging building's HVAC system would need to be updated. Adams engaged TMI to design and build a system that will create an air conditioned environment for the entire five-story, 65,000-sq-ft school.
Because Providence-St. Mel relies mainly on donations for its operating budget, the system upgrade must be done as economically as possible. TMI's relationship with Adams dates back 15 years, but because of budget constraints, TMI originally only provided advice and explained system functions to Adams, chief engineer Jack McGrath, and the maintenance crew.
Approximately 10 years ago, TMI began repairing and updating the antiquated heating system. Three years ago, TMI designed a plan to install the cooling system and upgrade the HVAC system, while leveraging from the school's existing configuration. Installation and upgrading began in October 2002 and the work is scheduled to be completed in 10 months - all while school remains in session.
"We've worked closely with Paul for a number of years on the school's HVAC needs while staying within budget," said Richard Bartuska, TMI president. "Now more donors are helping to keep this school alive and we're able to dramatically improve the building's systems."
"Classroom Cool"
To cool the classrooms, TMI considered, and rejected, the two most common approaches typically employed in retrofitting schools. With stone and concrete exterior walls more than two feet thick, the tactic of cutting holes and installing individual unit ventilators was quickly eliminated. Distributing cooled air from an AHU through ductwork run in the hallways was physically feasible, but not practical as installation would be too disruptive and unsafe for a school packed with 600 students.Instead, TMI worked with a manufacturer to develop a custom unit ventilator. The design involved a special fancoil to simultaneously bring in fresh air and discharge exhaust, and would utilize just one existing window in each classroom. TMI knew the design would work, would minimize installation disruptions, and would be economical.
While it was a handy solution, the single-window-unit design did not meet the city of Chicago's requirement for a 15-ft separation between fresh air and exhaust openings. Together, Providence-St. Mel; the unit manufacturer, Airedale; and TMI appealed to city code officials and, by allaying concerns about IAQ, were able to secure a one-time waiver of the requirement. TMI plans to install 48 custom unit ventilators in the school's classrooms in coming months.
TMI will save the school additional dollars by using the original heating system to cool the auditorium. By modifying the old system, which includes mushroom-style vents underneath rows of seats, TMI is reversing the airflow and using the existing configuration as the return for the cooling system. The supply comes from the ceiling, as insulated ductwork that serves the auditorium is installed in the attic.
Broken Records
Because of the building's long history and multiple owners, all building records have been unfortunately either lost or destroyed. Without records to guide it, TMI chipped away concrete walls to examine and gauge the strength of the steel beams in order to determine whether the roof could support the weight of a cooling tower. TMI had considered installing the cooling tower in an adjacent building on the school grounds, but after a thorough inspection of the beams, it ultimately decided the school's roof could support the cooling tower.From the cooling tower on the roof of the building, condenser piping is routed through a newly created shaft to the basement where pumps distribute cold water from the two newly installed water chillers, to vertical risers along the outside perimeter of the building. The bulk of TMI's project will be done during the winter; yet with all the cooling equipment, pumps, and distribution piping to be placed in the basement, the only disruption will be during the installation of individual units in each classroom. To avoid disturbing students and teachers while the risers and units are installed, classes are held in adjacent rooms.
"This project is proceeding while school is in session," said Bartuska. "We have to accommodate teachers and more than 600 students who are out of their regular classrooms for only a few days."
The entire cooling system will be controlled from the facility engineer's office through a central automation and management system. The engineer can remotely adjust the temperatures in individual classrooms, floors, or other areas, and schedules can be created to help regulate cooling on a preset program. By regulating each room from a central control system, the school keeps cooling costs to a minimum.
Staying within budget and using existing systems add up to an HVAC system that will provide Providence-St. Mel the opportunity to offer year-round education for students.
Cermak Elementary & Teaching Academy--No Refrigerant Allowed in the Building? No Problem
The Chicago Board of Education's (CBOE) new 110,000-sq-ft Cermak Elementary & Teaching Academy includes an attached 45,000-sq-ft community center with a swimming pool - all designed by architect De Stefano & Partners, Ltd., Chicago. Ordinarily, specifying a DX-style dehumidifier would have been an easy task for the community center's 6,000-sq-ft recreational natatorium design; however, city codes prohibited the use of refrigerant-based equipment because the same building also hosts a daycare center.Although DX units dominate 95% of the swimming pool heat recovery dehumidifier market, the CBOE challenged Primera Engineers Ltd., to design a pool dehumidification system without refrigerant heat exchangers in the building or in the airstream.
"The city doesn't want refrigerant-based equipment around children under two years old because they're too young to vacate the building by themselves in the event of a refrigerant leak," explained Michael Belczak, senior associate/mechanical engineer, and one of 60 design professionals at Primera Engineers Ltd., Chicago.
Primera's design team found only two manufacturing candidates willing to build a custom heat recovery dehumidifier that would use a few dozen gal of 42 degrees F ethylene glycol instead of the customary hundreds of pounds of R-22 that's typically used in conventional dehumidifiers. The winning manufacturer, Dectron Internationale (Roswell, GA), built a custom dehumidification system to Primera's specifications via the manufacturer's representative Imbert Corp.
The system is split into a mechanical room air handler (Dry-O-Tron(r) Model DG-182) and a 60-ton rooftop chiller (manufactured by its RefPlus Division). While the chiller uses refrigerant, its remote rooftop location poses no threat because the refrigerant and the airstream of the air handler are separated by 30 ft of glycol piping installed by project mechanical contractor, Ortiz Mechanical.
The energy-conscious Primera specified a recycling dehumidification system that maintains a 50% rh by removing a capacity of 200 lb/moisture/hr while heating the pool water and heating or cooling the space to 83 degrees and 82 degrees temperature setpoints, respectively.
The challenge for RefPlus' in-house engineers was fulfilling Primera's project goals of designing a custom air cooled and water cooled chiller. The condenser loop hot water is used for pool water heating and air reheating. Once the pool water and space heating has been satisfied, the chiller rejects heat to the air cooled condenser.
In winter operation, heat generated from the chiller process is transferred to the pool area for space heating. In the event the dehumidification process can't totally supply pool water heating, a backup 715,000-Btu boiler is activated.
24-hour-a-day Dehumidification
Even though the school has a chilled water loop supplied by a main chiller plant - two 215-ton, air cooled chillers from Carrier Corp., which feed AHUs with 45 degrees chilled water throughout the school - Primera chose to keep the school and natatorium systems separate, mainly because of dissimilar schedules."Based on our experience of designing indoor pool spaces in the past, it seems to work out best when the pool system is separate from the rest of the building," Belczak said. "Plus, the school can maximize its energy savings this way because the dehumidification system runs 24 hours per day, while the rest of the school has downtimes during nighttime and vacation days."
In the same separation strategy, the pool area is monitored and controlled by the Dry-O-Tron's on-board microprocessor. However, the school/community center's Carrier DDC BAS also monitors the natatorium's vital statistics, while carrying the ability to enable and disable the dehumidification system.
Another concern in the design was outside air. Total air input in the pool room is 23,000 cfm, however, 4,250 cfm is outside air according to the city's requirement for pools, which is based on square footage. That amount is sufficient if the maximum occupancy of 150 people in the pool and 65 spectators is reached, according to Belczak.
Because the pool room has no windows and only one exterior wall, Primera felt money could be saved on the project by eliminating underdeck air distribution that is typically combined with overhead air to keep windows condensate-free. Instead, Primera designed a perimeter air distribution system approximately 25-ft high using 36-in.-dia, single-wall, painted, spiral, metal duct with registers every 10 ft.
The mechanical room housing the air handler and pool equipment is located conveniently in a second floor mezzanine. The supply duct entrance and return air grille are efficiently located on a wall that separates the mechanical room from the pool.
A Promising Future
Primera's selection of a separate system also saves the CBOE tens of thousands of dollars per year in energy savings. If the compressor heat of the rooftop chiller package isn't recovered by the dehumidification system to heat the pool water, all that energy would have been wasted according to Ref-Plus president, Michel Lecompte.The energy savings is important because the introduction of a secondary heat transfer fluid, such as the glycol loop, vs. its DX refrigerant counterpart results in a 10% efficiency loss, estimated Belczak. To compensate for the efficiency loss, the dehumidification coils are slightly larger than a conventional dehumidifier.
The CBOE's strategy of restricting refrigerant inside of buildings is an idea Dectron has been considering in light of the safety and rising cost issues of refrigerants, according to Lecompte. Safety is always an issue with any unit using hundreds of pounds of pressurized refrigerant in an occupied space. Plus, rising costs of R-22 due to a government-mandated phaseout and current high prices for HFC alternatives is interesting Dectron in glycol systems.
According to Dectron, glycol systems use 75% less refrigerant charge than is typically used in conventional dehumidification systems, plus it allows the refrigerant portion of the system to be located outside of the occupied space. With the success of the Cermak Elementary pool space concept and application, the CBOE and its project engineer, Primera, might be pioneers in what could become a future standard for natatoriums.
Niles North High School--Fabric duct benefits high school's seven gyms
Niles North High School is nearly 40 years old, but it has become a school of the future thanks to a multitude of leading-edge building products used in its school district's new, $110 million, three-phase remodeling project.The "new" Niles North, which is part of Niles Township High School District 219, now uses natural gas cogeneration and produces 95% of its own electricity. In the wake of nearby St. Charles High School's (St. Charles, IL) closure last year due to sick building syndrome, mold-resistant wall materials have been substituted for typical drywall. Even hand-driers in the Skokie, IL-based school's bathrooms have "green" classifications for energy savings.
So it's no surprise Keith Hammelman, project coordinator and mechanical engineer at KJWW Engineering Consultants, was encouraged by Matt Overeem, Niles Township High Schools' director of buildings, to use fabric duct instead of conventional metal duct.
The duct was put to use in seven gymnasiums totaling 40,000 sq ft, which were included in the HVAC retrofit portion of the three-phase project.
"With our ongoing retrofit program, we're always on the lookout for something innovative, green, or energy efficient that will help our engineers, architect [Legat Architects, Waukegan, IL], and HVAC contractors [Admiral Heating & Ventilating and Siemens Building Technologies 'think outside the box,'" said Overeem. "So it made perfect sense to reduce our roof's weight load with lightweight fabric duct instead using tons of steel. Fabric duct is easier to clean, it looks high tech, and it has better air distribution than round metal duct with widely-spaced registers."
Stifling the Stuffiness
Previously, the gyms - consisting of a dividable gymnastics room, a dividable wrestling room, and a main gym with two balconies that are regularly partitioned off-were hot and stuffy due to outdated air-handling systems that supplied and returned air from only single-wall grilles.Hammelman took Overeem's fabric duct suggestion and specified Comfort-Flow(tm) fabric duct manufactured by DuctSox(r). Comfort-Flow, combined with the aesthetic appearance of Sedona fabric is designed to allow 15% of the air to flow through its factory-engineered permeable fabric, which limits dust buildup. The other 85% of the airflow is dispersed evenly through two linear mesh vents that run the entire length of the duct at 4 o'clock and 8 o'clock positions.
The main gym's six indoor, packaged, McQuay International Vision Series AHUs totaling 80,000 cfm are installed in the joists and supplied by the school's existing hot water loop. The other four AHUs supplying the gymnastics and wrestling gyms are rooftop models.
Hammelman began designing the main gym's air distribution around the standard of six volumetric ach, which typically allows for a 10-degree breakpoint for noncooling situations.
"With these high airflows, what you have to watch out for in large gyms is the fact that spectators and athletes get drafty blasts of air if they're under registers on spiral or fiberglass duct, both of which we've used in previous applications," said Hammelman.
"With registers placed every 10 to 15 ft or so, some people get a draft and some people won't. With the ability of fabric duct manufacturers to sew in linear diffusers along the duct - at a lower installed cost than installing linear diffusers on round metal duct - this problem is eliminated. It's much easier to sew in a linear diffuser, and the aesthetics are better."
Maintaining Space for Airballs and Pop-ups
Hammelman began sizing the project's 1,500 linear feet of duct similar to its alternative, single-wall spiral duct's requirements. With the cfm's sized and six ach's specified [VGC8], the linear ft of duct was dependent on even distribution, linear vent air throws, and what diameter would fit inside each gym's existing open ceiling steel truss network while avoiding electrical and utility lines. Fitting the duct above the bottom chord of each steel truss was vital for keeping ceiling space as free as possible for basketball shots and gymnastics equipment, some of which is hung from the ceiling.Hammelman also notes that metal duct surfaces would be susceptible to dents from errant baseballs, basketballs, and other flying objects during indoor practices, while fabric duct doesn't sustain dents.
Installation of all the gym ducts was performed in less than a week with a six-man crew, which helped keep the two-month summer time allotment for the gyms' retrofits on a fast track, according to Admiral's Sam Gattuso, project manager. "I like the fact that we didn't have to paint it, and it required a short learning curve to install it," said Gattuso.
An H-track system, which holds the duct at the 10 o'clock and 2 o'clock positions to eliminate sagging during off times, is often recommended for ceiling truss hanging. However, to accommodate the existing Niles North ceilings, engineers recommended a double-row cable suspension system that was easier to mount through ceiling joists. Preventing the fabric from any accidental contact with the bottom of the joists eliminates premature material wear from vibration.
Typically, each air handler connects to straight duct trunk runs ranging from 22- to 34-in./dia. DuctSox's DuctBuckle(tm) strap fastener connects the fabric to a round metal collar that Admiral fabricated for the transition. A fabric sleeve covers the connection to simulate a seamless joining. Although metal elbows were sometimes used on the air handler side of the transition to avoid obstructions, generally Hammelman kept trunk lines straight.
Accommodating Speakers and Screamers
While metal duct would have required balancing, fabric duct needs only the assurance that the airflow through the air handler is within guidelines, which greatly reduces system-balancing time. Fabric duct also has sound attenuation qualities as well, which is important since the gyms have the dual use for athletic and speaking events. Air noise is lessened because of the decreased reverberation fabric offers vs. metal. Additionally, linear vents can produce the same cfm but at a quieter velocity than metal ducts' registers."You can always attenuate sound with insulated metal duct, but with today's IAQ concerns, insulation-lined duct can be a dust collector, costly, and difficult to clean. If fabric duct becomes dirty, the facility's in-house maintenance staff can take it down, machine wash it, and just rehang it," Hammelman added.
Other equipment installed for the retrofit included three 450-hp flexible watertube boilers by Bryan Steam LLC. The former pneumatic control system was replaced with a DDC BAS under a performance contract with Siemens Building Technologies. All AHUs are equipped with full economizer modes. Loren Cook Co., exhaust fans combined with Siemens VSDs are activated depending on the pressure in each spaces.
Also part of the retrofit was the replacement of two 300-ton chillers with two 550-ton McQuay chillers that supply a chilled water loop - that when combined with another future chiller - will someday be connected to four of the main gym's AHUs that are equipped with A/C coils.
Since activities in the spaces can vary from just a few athletes at practice to a full spectator event with hundreds of occupants, outside air and return air ratios are monitored and controlled according to CO2 levels. An additional four 10,000-cfm AHUs serve both the wrestling and gymnastics rooms. When the rooms are divided in two, each newly created space can be heated and controlled with its own separate AHUs.
The next phase of the district's remodeling plans include sister school, Niles West, which will also get an HVAC retrofit featuring much of the same equipment and fabric air dispersion. "Probably the biggest savings is the lower installation costs associated with fabric duct," Overeem added. ES
