PM Engineer is proud to announce that one winner and an honorable mention have been chosen to receive PME Excellence in Design Awards for 2007. Congratulations to Durkin & Villalta Partners Engineering of Indianapolis, IN, for its innovative upgrade of an HVAC system at George Washington Carver Elementary School; and to Peter Basso Associates, Inc., Troy, MI, for its LEED® Silver-winning design of an HVAC system for new Whitmore Lake High School in Whitmore Lake, MI. (See page 89.)
These designs were judged by our panel of editors and engineers based on the following criteria: innovation in design, customer satisfaction, ability to meet schedules, cost-efficient strategies and community improvement. The winners were selected from several outstanding submittals; in fact, many judges feel it was the best group of submittals ever received. Nominated designs could be submitted by consulting, specifying or design engineering firms.
The Winner: Durkin & Villalta Partners EngineeringWhen George Washington Carver Elementary School (GWCES) in Indianapolis, IN, was built in 1935, an underground spring that flows continuously was inadvertently intercepted by excavators during construction of the boiler room. For the next 70 years, the groundwater there was seen as a significant liability-with sump pumps having to run continuously to remove approximately 150 gallons of groundwater per minute from the school’s basement.
In fact, there had been several occasions when a power outage disabled the sump pumps and resulted in flooding of the boiler room to a depth of six feet. Then in 2006, the Indianapolis School Board selected GWCES (Indianapolis Public School #87) to be a year-round, inner city magnet school, requiring the addition of air conditioning.
According to Steve Young, Indianapolis Public Schools (IPS) Facilities Management Division Chief, IPS is five years into a capital improvement project to update and modernize all of their facilities. “IPS consultants have designed virtually every conceivable type of school HVAC system, having been encouraged by the owner to seek ways to improve energy efficiency and reduce maintenance as schools are renovated or rebuilt.”
Many systems have been used, including geo-thermal using well water in a heat exchanger arrangement, notes Young. “Experience with those systems led our maintenance personnel to wonder if the groundwater coming into GWCES could be used to heat and cool the building, turning a significant liability into an asset.”
IPS then sought out a consultant who had the technical expertise to make IPS’s vision a reality. That consultant was Tom Durkin, P.E., vice president and COO of Durkin & Villalta Partners Engineering (DVPE) Indianapolis, IN [http://dvpe.net/]. The engineers of DVPE accomplished this by using the groundwater as both the heating-source and cooling-sink for the A/C system (i.e., as a central reversing chiller).
As a result, the new system is now cooling for less than half the cost of conventional equipment, and heating for about one quarter the cost of the old system. “Total utility bills with A/C are 83% of the previous bills without cooling,” says Durkin. In addition, IPS will make study of the system part of the science curriculum at this school. According to Young, total project installation cost showed no premium versus other HVAC renovation projects.
A Synthesis HVAC SystemDurkin describes the new system (completed in July 2006) as a synthesis of three technologies that, separately, have proven to be very effective:
“From two-pipe HVAC comes economy and simplicity for school designs, and the proven ability to heat large buildings with low temperature water,” says Durkin. “From dedicated heat recovery chillers comes a proven machine that can be programmed to produce 44°F cooling water and 130°F heating water. And from geothermal comes a very efficient heating and cooling source.”
Unlike conventional geothermal heat pumps - which have multiple distributed compressorized units throughout a building - this system has a single unit located in a central mechanical room. The heart of the system is a geothermal heater/chiller (or GEO-H/C), which is a single unit (multiple refrigeration circuits provide redundancy) that heats the building in the winter and cools it in the summer.
Although GWCES is the only IPS school using GEO-H/C, IPS does have six other two-pipe buildings operating with conventional heating and cooling sources. According to Young, “We prefer this particular two-pipe design because we get fewer hot/cold calls and fewer maintenance orders than any of our other buildings. We would gladly pay more for this improved reliability, but we actually pay less.”
System BasicsThe GEO-H/C is connected to a two-pipe building system, and the airside equipment includes standard air handlers (AHUs), unit ventilators and fan coils. “This configuration can operate airside economizers and use the groundwater to cool the building directly when the water temperature and indoor humidity allow, thus giving two sources of free cooling,” notes Durkin.
According to Durkin, when outside temperatures are cool, air side economizers on AHUs and unit ventilators provide cooling without any compressors running; and when the well return temperature is cool enough, the sensible cooling mode provides air conditioning - again, without compressors operating. “Economizer availability in this scheme is a significant efficiency benefit. The ability to run the sensible cooling mode (using the cool tank water through the heat exchangers directly into the building loop) is also an energy-free way of cooling the building loop and all the coils when the two-pipe system changes over from heating to cooling.”
All sump pumps, storage tank, transfer pump and heat exchanger are backed up with 100% redundant spares. The groundwater is pumped into a 10,000-gallon stainless steel storage tank that overflows to the building sewer, just as it has for 70 years. Transfer pumps route the groundwater through a set of 100%-redundant heat exchangers that allow building circulating water to be segregated from the groundwater. The tank is designed so that the transfer pumps provide the most efficient water temperature in both the heating and cooling modes. It features both inlet and outlet diffusion headers that allow the tank to stratify the cooler water at the bottom. As an added precaution, the sump pumps are on an emergency generator, since power failure would flood the boiler room in about a half hour. Each sump has multiple high-level alarms.
There are three water-flow arrangements for the building system, says Durkin. Each arrangement features two-position three-way valves to reverse the water flow from heating to cooling; and two-way, two-position valves that open for water side economizer (sensible cooling) operation. Because the groundwater temperature is a relatively constant 55°F to 58°F, sensible cooling is possible during those times of the year when the outside air dew point is low enough to avoid elevated space relative humidity.
“Since a GEO-H/C outage could leave the building without heat, and since the concept had never been tried before, IPS asked that emergency heating boilers be provided in the design,” Durkin says. During the winter of 2006-07, this proved to be a wise decision, he notes, because the boilers did run on several occasions until the GEO-H/C control sequences were refined. “It is hoped (expected) that future winters will not require boiler operation. The boilers are piped so that they can supplement the GEO-H/C output or operate independently.”
Sensible InnovationThe innovative aspects of this system begin with using GEO-H/C and conventional air side equipment rather than heat pumps to avoid the additional expense of a decoupled make-up air system required with a GSHP design. This setup is only possible because the GEO-H/C is combined with an air side system that is designed to utilize low-temp (130°F max.) heating water. “The two-pipe building system utilizes face and bypass unit controls in lieu of control valves to guarantee freeze protection and humidity control. Control sequences utilize single zone variable-air volume, fan speed modulation and outside air management techniques to improve both energy management and summer humidity control,” says Durkin.
GEO-H/C control sequences are a critical aspect of the operation. In cooling mode, there is a fixed chilled water set point, compressors stage off and on as required to meet the load and the transfer pumps run at a slow speed to ensure that the GEO-H/C condenser cooling water isn’t too cool.
“In heating mode, things are much more complicated,” says Durkin. The building supply water temperature is on a reset schedule versus outside air temperature (OAT), such that at 60°F OAT the hot water supply (HWS) temperature is 90°F. The HWS is reset up to 130°F HWS at 10°F OAT or colder. The initial GEO-H/C heating set point would occur under the following parameters: the building pumps are connected to the condenser side of the GEO-H/C running at a constant speed; there is normal evaporator set point (44°F); and the speed of the tank transfer pumps are varied to create enough load to raise the condenser temperature to the desired level.
“As the outside air temperature goes down and the hot water supply set point increases, the transfer pumps speed up to create more evaporator load. And since the building pumps (connected to the condenser) are at a constant speed, increasing evaporator load results in increased condenser temperature,” Durkin explains.
Once the transfer pumps are at 100% speed, further increases in HWS temperature are done by lowering the GEO-H/C evaporator set point. Doing this once again increases chiller load at a fixed condenser flow rate, resulting in increased HWS to meet the reset schedule. The building loop contains an engineered heat transfer solution that allows for evaporator operation down to 34°F.
Additional BenefitsDurkin touched on several other benefits this new HVAC system has provided the elementary school.
Heating: Initially, GWCES was heated by coal-fired, low-pressure steam boilers serving classroom unit ventilators and fan coils. At some point in the intervening years, the boilers were replaced with 80% efficient gas-fired units. Another upgrade converted classroom terminal heating equipment to 180°F hot water, and the boiler room was retrofitted with a steam-to-hot-water heat exchanger. Although no definitive measurements were made, it is estimated that the Annual Fuel Utilization Efficiency of the old system was in the 50% range, or a coefficient of performance (COP) of 0.5 (gas).
The new system operates in heating at an average COP of 4.2 (electric). “When corrected for the price of the two energy sources, the new system operates in heating for one quarter the annual cost of the old system,” says Durkin. The back-up boilers are high-efficiency condensing style (the IPS standard), and the entire building heating loop is designed for significantly lower heating water temperatures (130°F max) than what had been used here and the “industry average” of 180°F, resulting in significantly lower parasitic losses from piping, etc.
Cooling: Prior to this retrofit, the only parts of GWCES that were cooled were the principal’s office, the cafeteria and the parents’ room. Indianapolis Public School policy calls for adding cooling to all buildings as renovation budgets allow. According to Durkin, the IPS standard for elementary buildings is the air-cooled chiller with an ARI rating of 1.25 kW/Ton. The new system utilizing the GEO-H/C operates at a worst-case efficiency of 0.65 kW/Ton and an average of 0.55 kW/Ton. The GEO-H/C system requires an additional pump that a conventional primary/secondary system would not have, increasing the GEO-H/C kilowatt per ton by 0.07.
Based on data accumulated over its first year of use, the system has reduced gas consumption from 25,370 therms ($28,501) to 796 therms ($1,098), a 97% savings. At the same time, electric consumption has increased, from $22,770 to $41,574.
However, Durkin says that the total utility cost has dropped from $51,271 (before the renovation, with no A/C) to $42,672 after the renovation with the entire building cooled - a 17% reduction (see Table 1). In addition, GWCES now operates a year-round schedule, and months when kids were previously on vacation now see the building occupied.
[Editor’s Note: The After Renovation figures represent the 12 months from Aug. 2006 through July 2007; Before Renovation figures represent the 12 months from Aug. 2005 to July 2006.]
“Through two cooling seasons and one heating season, the GEO-H/C system has operated with almost no maintenance problems. The only outage was caused by reduced water flow due to a blocked strainer from the sump pumps to the tank,” says Young. That situation was remedied by a change in filter mesh and the addition of an automatic blow-down sequence. Thus far, the system has met all room temperatures in both summer and winter.
The scaling potential of the groundwater is a maintenance concern since Indianapolis water is notoriously hard. The heat exchanger condition is continuously monitored via differential pressure, and no changes have been seen to date. Durkin anticipates that scaling, while a concern, will not become an issue due to the relatively small changes in temperature through the system.
Community Environmental Impact
“The groundwater used as the heat source/heat sink is seen as a zero impact environmentally,” says Durkin. As for air pollutants produced by the new system, Table 2 lists their respective pounds through 12 months [Before for Aug. 2005 through July 2006; After for Aug. 2006 through July 2007] “They show a modest net increase, but we did add air conditioning and go to a 12-month calendar.”
The average temperature change of the groundwater is less than 15°F in either summer or winter, and the receiving sewer is of such a size and capacity that no temperature changes have been seen at the treatment facility. Durkin notes that the local water/sewer utility does not require monitoring of the water quality.
The heat exchangers are 125-pound rated but operate at a maximum pressure of about 15 psi on the building side and a differential of 10 psi, with the building side being higher. Also, there is an automatic make-up on the building side that will register a “critical alarm” if the system is making up water.
“Other IPS projects have faced occasional complaints from neighbors due to the noise of air-cooled chillers operating in residential settings. This is obviously not a concern at GWCES.”
Keys to Success and SatisfactionMeeting the project budget was, in one way, very easy, and in another way, very difficult for DVPE. “This was the 170th two-pipe-design we had done, so that part of the project cost was easily predicted,” says Durkin. “The boiler room was a different story, though. Limited access dictated the shape and construction of the tank, which had to be completely fabricated onsite. And given the complexity and uniqueness of the control sequences, we spent quite a bit of time working with the temp control contractor (Johnson Control, Indianapolis) to make sure their people knew what we wanted.”
Durkin says several key aspects contributed to this project being completed on time:
“The project to air condition this school had an extremely tight schedule because of the school’s starting and ending class dates,” explains Steve Young. “The School Board made a decision to create a new magnet school and place it on the ‘Alternative Calendar,’ which begins in mid-July instead of mid-August.”
As a result, school ended the first of June and would resume the middle of July, leaving only six weeks for construction without students in the building. According to Young, DVPE developed a construction schedule that allowed work to begin in April in selected parts of the building. “Their understanding of a very complex project and ability to structure a work schedule that allowed work to proceed while classes were in session resulted in a very successful project, which was completed by the start of school in July. DVPE was instrumental in the development and execution of a truly innovative approach to providing an excellent educational environment in an inner-city school.”
Young says IPS did HVAC renovation at one other building during the same summer that GWCES was renovated, but notes that that building was designed around a conventional four-pipe system utilizing boilers and an air-cooled chiller. Nonetheless, on a per-square-foot basis, the two projects were very comparable cost-wise. The reason? “The additional boiler room equipment at GWCES (tank, heat exchangers, pumps, etc.) was covered by the cost savings of the two-pipe distribution system versus the four-pipe at the other building,” says Young.
“The design at GWCES is now cooling and heating the building for less than the heating alone cost prior to the conversion. The groundwater is now a significant asset, and the creative legacy of George Washington Carver continues at his namesake school.”
[sidebar] Project ProfileSummary: Elementary school HVAC upgrade using sump pump discharge water as a geothermal source.
Project Cost and Duration: $1.6 million (64,000 sq. ft.); project started in April 2006 and was completed in July 2006 (3-1/2 months).
On Winning the Award: “Everyone involved (contractors, equipment suppliers, control technicians and commissioning people) bought into the uniqueness of this project, and I would like to share this honor with them. Steve Young and Steve Johnson from Indianapolis Public Schools were especially supportive. They recognized the energy-saving potential as being more important than the risk of building something that had never been tried before. I appreciate their confidence in my firm. The ‘Excellence in Design Award’ will be proudly displayed in our lobby as an inspiration to our staff to continue to work for energy efficiency and environmental awareness.”
-Thomas H. (Tom) Durkin, PE, Senior Partner, Durkin & Villalta Partners Engineering
Honorable Mention: Peter Basso Associates, Inc.Whitmore Lake (MI) High School
Opened in Aug. 2006, the new Whitmore Lake High School in Whitmore Lake, MI, showcases the school district’s strong commitment to sustainability - as well as the design firm’s innovation and construction team’s successful delivery of the project.
“District personnel and school board members had an intimate involvement with the design team, which provided a reassuring presence and kept the team’s actions in line with their guiding vision,” says Robert N. Roop, CPD, Vice President, Peter Basso Associates, Inc.
As part of the district’s commitment to sustainable design, LEED certification was determined early on as a project requirement. Through a cooperative effort of all design and construction team members, the US Green Building Council announced in Aug. 2007 that the project attained LEED Silver status, surpassing the basic requirements of a certified building.
“An internal peer review process was utilized throughout the design process to minimize construction coordination issues, and a third-party commissioning process oversaw the installation and functional testing phases,” notes Roop. In addition, a thorough value engineering process - involving all design team members, owner’s representatives and trade contractors - helped bring the project in within the established construction budget.
The project cost just over $30.5 million. Construction began in July 2004 and was completed in Aug. 2006. The architects for the project were Mitchell and Mouat, partnered with TMP Associates.
“At Peter Basso Associates, we work hard to find innovative yet practical solutions for our clients,” says Roop. “It is an honor to be recognized for that effort with this Excellence in Design award, and a testament to the teamwork that made it possible.”
System DesignThe building’s heating and cooling needs are served completely by a geothermal water source heat pump system consisting of nearly 47 miles of piping, approximately one third of which is located in a pond. Roop says that each space in the building is provided with a measured quantity of outside air, which is pretreated by dedicated energy recovery units to minimize the impact of the outside air load on the space-tempering equipment.
Every classroom has independent temperature control through a water source heat pump, which operates in conjunction with space temperature and CO2 sensors to maintain a properly ventilated space within the design temperature range. According to Roop, calculations have shown an estimated annual energy savings of more than $80,000 per year in operating costs when compared to conventional systems for this building.
District maintenance personnel also had input to the locations of mechanical system components. “For ease of maintainability nearly all equipment is located in indoor spaces. Care was taken in placing these mechanical spaces relative to the proximity of those spaces they serve in an effort to reduce delivery cost by reducing required fan energy and ductwork. Additionally, all ceiling spaces are return air plenums, which eliminated the need to insulate the ductwork, further reducing first cost.”
Because the facility was constructed in a former farm field in a rural area, there was a need for on-site storm water retention and a water supply for the fire protection system. Roop says these two needs were combined and met through the creation of a pond, which let designers use the water as a portion of the heat sink/source for the geothermal field. In addition, an area was created along the pond shore for an outdoor education area for student use and observation.
Along with the district’s commitment to a sustainable facility, they also wanted a state-of-the-art building to serve not only their educational needs but also the needs of a growing community. “A 600-seat auditorium was provided for the school and community, and a separately funded natatorium, provided by a community-approved recreation millage, also has been a great addition to the learning environment and the community,” Roop concluded.