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Building systems and their controls have become very complex. A modern building automation system (BAS) can have thousands of data points, a network of controllers, and software with programming logic that is often inaccessible by the building personnel. If not regularly calibrated, maintained, and monitored, the complexity of the system can become more a liability than an asset.

This article is based on observations and lessons learned through field experience, as opposed to an in-depth discussion of controls theory or operations and maintenance methodologies. Based on experience from a multitude of retrocommissioning and energy efficiency projects, a pattern has emerged: existing buildings have a significant number of BAS defects which cause excessive energy consumption, reliability problems, and occupant comfort issues. Through case studies, this article illustrates the importance of implementing a process for uncovering control system defects and will discuss ongoing commissioning as a potential method for identifying and resolving BAS defects and achieving optimum building energy efficiency and system reliability.


Sophisticated control systems and strategies are looked upon as an opportunity to significantly reduce the building's annual energy consumption. Newly installed and commissioned systems have the potential to achieve anticipated energy savings while maintaining occupant comfort. A BAS is programmed to meet the operational requirements of the building when first installed; however, these requirements change over time, and equipment malfunctions. Defects can range from simple problems such as a dysfunctional sensor or misadjusted damper to more complex issues such as system integration and programming errors. Potential signs of inefficiencies such as comfort calls may be addressed without consideration of overall system performance. An ongoing commissioning process will enable continuous review of the building to identify these types of issues and assist with system optimization.

Retrocommissioning, decommissioning, and energy audits are excellent tools for finding energy reduction opportunities; however, each lasts for only a short duration and leaves many issues unaddressed for extended periods of time. Similarly, without ongoing review of the implemented measures, the savings may not persist. An aggressive, ongoing commissioning program can help establish a protocol for ongoing inspection of HVAC system components and BAS controls that will ensure issues are resolved in a timely manner and, once funds are invested to implement improvements, ensure that the resulting energy savings are actualized and persist.

Six case studies are presented to illustrate common issues identified when reviewing and monitoring building operations. The examples provided in each case study could have been discovered and resolved sooner with an ongoing commissioning plan.


Simultaneous Heating and Cooling due to Electric Heat Not Being Locked Out in Summer

Lack of a systems integration approach has been a key issue and a limiting factor in achieving energy efficiency in buildings. This case study focuses on a 4-story, 100,000-sq ft, all electric, multi-tenant office building located in northwest Chicago. One air-handling unit (AHU) and two electric, air-cooled, direct expansion (DX) chillers serve as the primary source of ventilation and cooling for the building. Chiller refrigerant passes through the AHU's DX cooling coils and cools the air supplied by the AHU to the spaces. The fan-powered boxes in the conditioned spaces are each equipped with electric reheat coils rated between 4kW and 12 kW. Individual thermostats in tenant spaces control space temperatures by modulating the amount of air flow through the fanpowered boxes (FPBs) and by activating and deactivating the electric reheat on the FPBs. The FPBs and thermostats are pneumatically controlled, whereas the AHU peripherals are controlled by direct digital control (DDC).

During a facility-wide retrocommissioning (RCx) study conducted in June 2011, the retrocommissioning engineering team installed data loggers to measure the discharge air temperature (DAT) from the AHU and to measure the electrical current draw on the electric reheat panel for sample floors. From the collected data, it was observed that the average DAT from the AHU was 53.2UF and that the chillers were operating.

It was also observed that the electric reheat on several of the FPBs was coming on to temper the supply air to the spaces. A majority of the thermostats were set between 72°F and 74°F. Typical DATs for summertime operation of office buildings are 55-58°F. The DAT setpoint for the building was set to 53°F and appeared low. There were few cold calls received from building occupants, as the electric reheat coils were tempering the discharge air from the AHU before delivering it to the spaces. Upon further investigation of the BAS and the electric reheat systems, the RCx team concluded that the reheat coils on the FPBs were activated for the entire year and are not locked out during the summer. The BAS had no control over the FPBs' operation. At the end of each heating season, the building engineer would lower the DAT setpoint on the AHU from 58-600F to 53°F. With no cold calls from the occupants, this issue of reheating the sub-cooled discharge air was not evident and, therefore, was overlooked. Analysis of the building monthly electric bills showed a nominal difference between the summer and winter energy consumption, confirming this inefficiency throughout the summer.

This issue was resolved by adding an outside air temperature (OAT) based control sequence on the BAS to lock out the electric reheat in summer and raise the existing summertime DAT setpoint to +55"F. Addressing this issue resulted in 76,320 kWh in annual electric savings, which represent a 4.4% cost reduction, or $8,400 in saved annual energy costs at the facility.

The BAS at the facility was upgraded before the facility assessment to implement several energy efficiency best practices limited to DDC systems. The control capability of the BAS was expanded for the AHU operation only. Higher capital investments prohibited the conversion of the pneumatically controlled FPBs to DDC. Since there were no comfort issues identified at the building, it was assumed that building HVAC systems were well integrated and operating efficiently.

This case study highlights the importance of implementing a facility-wide, ongoing commissioning plan as opposed to a one-time retrocommissioning study of the major energy consuming systems in the building. A retrocommissioning approach conducted during the facility assessment led to the identification of this issue at the building. In this case, the issue was identified with retro, but ongoing would have identified it faster. Regular preventive maintenance (PM) of the electric reheat system control panels, as a subcomponent of an ongoing commissioning protocol, could have identified this issue sooner.

Simultaneous Heating and Cooling due to Leaking Coil Control Valves

Similar to the previous case study, this example focuses on simultaneous heating and cooling. In this case, simultaneous heating and cooling is caused from leaking coil control valves, which would have been discovered and repaired more quickly through the implementation of an ongoing commissioning program and by having funding readily available for system repairs.

This example of simultaneous heating and cooling was observed during a retrocommissioning project at a high-rise hotel in downtown Chicago. The facility has 55 stories, more than 770,000 sq ft, and 650 guest rooms. The hotel has both hydronic cooling and heating systems, with two-way valves controlling flow through AHU cooling and heating coils. The building's HVAC system is controlled using a BAS.

Facility staff knew that some of their AHU control valves were leaking, because they were causing comfort control issues. Since the valves were not capable of completely stopping flow though the AHU coils, the systems compensated either by opening the outside air dampers more than necessary or by using excessive terminal reheat. Figure 3 is a screen capture of an AHU taken from the BAS. It shows a hydronic heating coil control valve with a significant leak. The AHU's DAT setpoint was 60°F. The supply air was being overheated by 17°F. This was increasing the boiler's natural gas consumption as well as causing comfort issues in the building after being supplied with overheated air.

In addition, more water was being pumped through the hydronic system than necessary, resulting in increased pumping energy and also a low delta-T condition. (Hot water and chilled water pumps are controlled by variable frequency drives.) Figure 4 illustrates the hot water pump motor current, which remains effectively constant because the VFD remains at 60 hertz (full speed conditions) due to the leaking control valves.

The BAS and data loggers were used to collect trend data from the system, and it was determined that replacing leaking coil control valves was a good economic investment. Replacing the valves resulted in over 280,000 kWh of electric savings annually, with a two-year simple payback. The savings from this repair represent 2.5% of the building's annual electric consumption, or over $22,000 in annual electric cost.

This case study illustrates that, at times, facility staff are aware that the system has an issue but are unable to get approval for the funding to make repairs. An economic analysis, part of a retrocommissioning project, estimated the potential energy cost savings and cost associated with the replacement of the valves. With an attractive return on investment, funding for the project was approved immediately; however, the valves should have been replaced much earlier. The simple payback was only two years - and this considered only the energy wasted because of the leaking valves. Accounting for the amount of additional time that the building engineers spent responding to comfort calls due to the leaking valves would lower the simple payback period significantly.

Equipment Scheduling

Another problem frequently identified during energy audits and retrocommissioning projects is equipment scheduling that is not synched with the schedule of the spaces it is serving. An example of this was observed during the same retrocommissioning project described in the previous case study.

The hotel has multiple kitchen areas, and each kitchen has a dedicated exhaust system and make-up air unit (MAU).

Use of one kitchen space had changed significantly, from usage multiple times per week to only being used two to three times per month for special events. The exhaust fan was not controlled by the BAS and operated 24/7 throughout the year. Its MAU, also controlled by the BAS, operated from 4:30 a.m. to 8 p.m. daily throughout the year. A data logger and current transformer were installed on the exhaust fan motor to verify its operating hours and power consumption. The exhaust fan was operating continuously and drawing an almost constant electric current. The BAS was used to trend the status of the fan in the MAU to determine its scheduling. The MAU was scheduled on and off daily, but the fan operation was not properly aligned with the actual use of the space.

Connecting the exhaust fan to the automation system and aligning the equipment schedule with space usage resulted in over 34,000 kWh of electric savings and 18,500 therms of natural gas savings per year, with less than a three-month simple payback. The repair represents a 2.3% reduction in the building's annual energy costs, or over $18,000.

This case study illustrates the importance of regularly verifying that equipment operation is aligned with current space usage. Using removable data loggers should be considered to sample equipment and ensure that it is operating as reported in the BAS. The simple payback period of less than three months highlights the need for ongoing cornmissioning of the building. By regularly evaluating equipment operation, the issue would have been resolved much earlier, with minimal financial investment.

Unoccupied Space Temperature Setback

This case study focuses on the need to monitor overall system performance and provides an example of how ongoing commissioning can identify hidden system integration issues.

A 44-story, one million-sq ft, 1980s Chicago high-rise office building was retrocommissioned. The majority of the building's HVAC system is controlled from a BAS, but the baseboard heaters are controlled by a dedicated control system that receives scheduling information from the BAS to set back space temperatures to 65°F during unoccupied hours. The master night setback setpoint was adjusted to 55CF and each zone's differential setpoint was adjusted to 100F, resulting in a setpoint temperature for the building of 65°F for all baseboard systems during unoccupied hours.

During a retrocommissioning project, space temperature and baseboard heater current were trended. Baseboards were observed to be operating during unoccupied hours, even though the space temperature was higher than the 65°F setpoint.

A second study was performed, which sampled space temperatures throughout the building using temporary data loggers while the building was in heating mode. The data indicated that space temperatures did not fall back to the 65°F setpoint during unoccupied hours. The building was maintained at an occupied setpoint temperature ranging from 700F to 75°F 24/7 during winter months.

Even though the BAS had a schedule for the baseboard heaters, and the baseboard heater control system had different setpoints for occupied and unoccupied space temperatures, further investigation determined that the two systems were not properly integrated. The BAS had been upgraded, and the updated system did not send a scheduling signal that the baseboard heater control system could recognize. The baseboard heater control system was updated and integrated into the BAS. After the situation was corrected, the project went through a measurement and verification (M&V) process, which verified over 1.7 million kWh of electricity savings annually. The savings from the repair of the heating control represents 10%, or more than $120,000, of the building's annual energy cost.

This scenario illustrates why regular monitoring of a building's major systems is necessary. Implementing an ongoing commissioning plan can facilitate this process. It is also important to take care when selecting the data collection method. Since terminal units in the facility were pneumatic and the baseboard heaters were controlled with a separate system, there were no trustworthy points that could be trended using the BAS. Temporary data loggers were installed to collect baseboard utilization factors, as well as to trend space temperatures. By adding sampling of space temperatures and baseboard heater amperages to the preventative maintenance program, this issue could have been identified and eliminated much sooner. Additionally, points could be added to the BAS to streamline the collection of this information or, alternatively, permanent data loggers could be installed.

Non-functioning Outside Air Dampers

Several of the outside air (OA) dampers on the AHUs serving a downtown Chicago hotel were discovered to be inoperable when the facility participated in a retrocommissioning project. The facility has 18 stories, over 430,000 sq ft, and 450 guest rooms. It has constant volume and variable air volume AHUs, which are controlled using a BAS. The inoperable OA dampers were discovered on two constant volume AHUs. The sequence of operation (SOO) for controlling the outside air dampers includes modulating the dampers to maintain a mixed air temperature (MAT) setpoint and to have a minimum position that ensures adequate ventilation; the AHUs did not have separate minimum outside air dampers.

During the retrocommissioning project, the AHUs were functionally tested. When outside air damper positions reported by the BAS were compared to the actual positions observed, discrepancies were discovered. A manual override was used in the BAS to set the outside air dampers to a specific position, and the behavior of the actual damper was observed. The dampers were overridden to adjust to 0%, 50%, and 100% open. It was determined that the dampers did not move, regardless of the BAS setting. Further investigation discovered that the damper actuators were nonfunctional and the AHU dampers remained fully closed throughout the year. The building was not able to take advantage of an economizing feature (use of OA for free-cooling) because of the failed OA dampers. Correcting these issues resulted in over 60,000 kWh of electric savings annually related to the use of free-cooling. This measure had a simple payback of less than one year.

Additionally, with the OA dampers fully closed, the space may not have been ventilated properly. The air handlers serve a large atrium area, and CO2 levels were monitored and determined to be significantly under code requirements, even with the OA dampers fully closed.

With the OA damper operation repaired on the two AHUs, a solid foundation was built for more sophisticated control strategies to be implemented. In this case, demand control ventilation (DCV) was also installed on other AHUs bringing in excessive OA. Installation of a DCV control on the remainder of the AHUs resulted in over 15,000 therms of natural gas reduction annually, with less than one year of simple payback. The combined energy savings from the repair of the outdoor air damper control and the addition of the DCV represents 2% of the building's annual energy consumption and cost savings of more than $16,500 in annual energy expenses. The energy reduction achieved from installing demand control ventilation also illustrates how significant the impact of a failed outside air damper can be.

This case study illustrates the importance of regular functional testing of a building's major energy consuming systems. Many times there are red flags that can be spotted in the BAS; in this case, the MATs were not realistic based on the return air temperatures (RATs) and outside air temperature (OAT). It was impossible for the outside air dampers to be positioned as stated while maintaining the reported MAT.

If an ongoing commissioning plan had been in place which either functionally tested equipment or compared variables in the BAS to expected sequences of operation, the inoperable OA damper failure would have been discovered more quickly. This practice can also develop confidence in the automation system and its data, which is critical for optimal building system performance and for implementing more advanced control strategies.

Partially Commissioned BAS

The focus of this case study is a 50,000-sq ft suburban Chicago office and warehouse building built in 1995. Approximately 60% of the total building area is office space, and the remainder is warehouse space. The office spaces are heated and air-conditioned via three packaged rooftop units (RTUs); the warehouse space receives heat from several overhead natural gas-fired furnaces. Observations presented in this case study are limited to HVAC systems and controls in the office space. There were three identical RTUs, each equipped with a natural gasfired furnace for heating and electric scroll compressors, providing a direct expansion (DX) method of cooling. The office layout is an open seating arrangement and features supply air diffusers receiving conditioned air from all three RTUs. Within this open area are multiple zones receiving conditioned air from each RTU; a temperature sensor for each zone reports the space conditions to the BAS.

During an ASHRAE Level II energy audit conducted in the winter of 2010, data were collected on the space temperatures and DATs from the three RTUs. RTU fan and compressor electrical data were also recorded using data loggers. Preliminary analysis of the collected temperature data revealed signs of heating and cooling systems operating simultaneously. Further investigation of the HVAC systems and controls confirmed that the BAS was directing the RTUs to operate in two different modes, heating and cooling. Upon sensing a space temperature lower than the setpoint in given space, the BAS would command an RTU to operate in heating mode. This resulted in a supply of very hot air (approximately 95 0F) from a select few diffusers to the space. The temperature sensors would then record an instantaneous increase in space temperature, causing the BAS to shut off the furnaces and immediately start the scroll compressors on the RTUs to cool the spaces. The heating and cooling systems were continuously cycling on and off and failing to maintain the space temperature setpoint.

To solve this issue, the temperature sensors were checked for calibration and found to be properly calibrated. Then, personnel from the HVAC controls company were involved to verify the heating and cooling SOO of the RTUs. The existing SOO on the BAS would command both stages of heating to come on at once and increase the supply air temperature to uncomfortably high levels. Also, the compressors were not locked out in winter. The SOO was reprogrammed to lock out the cooling compressors based on outside air temperature, and the heating SOO was updated to start one stage of heating at a time. Addressing this issue resulted in 53,000 kWh of annual electric savings and a 5,500-therm reduction in annual natural gas consumption at the facility. The cost savings represent a 14% reduction, equal to $8,500 in annual energy costs at the facility.

It was learned that after the current owner purchased the building four years ago, new space temperature sensors were put in place and connected to the BAS. At that time, RTUs were inspected for their basic operation and new data points were added on the BAS. However, the BAS SOO was not updated to ensure proper operation of the overall HVAC systems.

This case study emphasizes the importance of having an overall systems integration approach in place. This ensures that the HVAC systems and controls are operating efficiently by taking into account all possible interactions between the two. Ongoing commissioning of the HVAC systems involves functional testing of the HVAC and associated controls systems. A step-wise approach practiced in the ongoing commissioning process would have identified this issue well in advance.


Examples of building controls issues, including simultaneous heating and cooling, equipment scheduling, non-functioning outside air dampers, and a heating system not setting back during unoccupied hours have been provided to illustrate the need for implementing an ongoing commissioning plan. These examples are part of a much longer list of potential issues that may be discovered and resolved. Other defects may include improperly operating variable frequency drives, overly conservative equipment start times, suboptimal startup SOOs, suboptimal equipment sequencing, and many others.

These case studies provide evidence of the need to establish a process to identify and resolve defects in the BAS and building operation and maintenance issues quickly to achieve optimum building energy efficiency and system reliability. The information gathered from the process can also be used to implement enhanced control strategies that were not part of the building's original design, such as demand control ventilation. It can also be used to assist with measurement and verification of projects as well as to ensure the persistence of energy reduction measures.

Ongoing commissioning is not a novel concept. It has been discussed in several previous articles and papers. A good example of this is The Continuous Commissioning® Guidebook for Federal Energy Managers, published almost ten years ago. The guide describes the benefits of continuous commissioning®, or ongoing commissioning, as well as methods for implementing the process. Yet, based on the authors' experience, the process has not been widely adopted by the industry.

One question likely to be raised is whether an additional process is necessary if the facility has an automation system service agreement with a controls contractor. Several automation system maintenance contracts were reviewed during research for this article, and at first glance they appear to suffice. They include provisions for reviewing control loop operation,, verification of the accuracy of control points, and functional testing of dampers and control valves. The fact is that each case study discussed in this article had a service agreement, and significant energy reductions were achieved by making adjustments and repairs to the automation systems. The service agreement may be beneficial, but it needs to be paired with a regularly occurring, systems-wide process to identify malfunctioning components.

An ongoing commissioning plan requires a time commitment to develop and to implement. Is the additional cost associated with the effort offset by the benefits of the process? Each facility operates at a different level of performance; therefore, it is good practice to benchmark the facility's energy consumption relative to its peers. The benchmarking results should help evaluate the potential for additional energy cost savings at a given facility. In general, it has been determined that implementing an ongoing commissioning plan is a cost effective process. A study published by Lawrence Berkley National Laboratory concluded that monitoring-based commissioning projects resulted in a median simple payback of 2.5 years*. The case studies presented in this article support this finding, especially when you consider that the findings presented are merely provided as examples and that every project used as an example had multiple energy reduction measures presented, not just one recommendation. Implementation of all of the recommendations further justifies the implementation cost of an ongoing commissioning process.

Another potential question may be whether a facility's current preventive maintenance (PM) plan is sufficient to keep the BAS operating efficiently. One common resource for developing a PM plan is the ASHRAE /ACCA Standard Practice for Inspection and Maintenance of Commercial Building HVAC Systems. Although a PM plan is important for maintaining a building, it does not appear to be sufficient for keeping the BAS operating efficiently (assuming it was operating efficiently at the time of installation). The standard does state that, for AHUs, it is recommended that the control system be checked for "evidence of improper operation." Each facility presented in the case studies had preventative maintenance plans, and controls issues were still discovered. PM plans typically do not have an in-depth description of trending or functional testing required to continuously check the control system for optimal performance. The U.S. Green Building Council's (USGBCs) LEED Reference Guide for Green Building Operations and Maintenance states that "ongoing commissioning is distinct from preventive maintenance" and goes on to say that "ongoing commissioning emphasizes a systemswide approach" in the description of EA Credit 2.3. Although PM is a best practice, ongoing commissioning is needed to ensure facility-wide system performance.

Retrocommissioning, recommissioning, and energy auditing are excellent processes for evaluating a building, but these projects all occur over a discrete period of time. Completing one such project will benefit building operations and produce energy savings; however, to ensure persistence of the changes made during retrocommissioning, recommissioning, or the energy audit project - and to manage ongoing control system maintenance and changes in facility operations - an ongoing process should also be developed and put in place.

The importance of an ongoing commissioning process is substantiated by several industry standards or best practices. The USGBCs LEED EB O&M includes EA Credit 2.3 - Existing Building Commissioning - Ongoing Commissioning; EA Credit 3.1 - Performance Measurement - Building Automation System; and EA Credit 3.2 - Performance Measurement - System-level Metering. The U.S. Department of Energy's Energy Efficiency and Renewable Energy (EERE) publishes a document titled Operations & Maintenance Best Practices that includes discussion of Continuous Commissioning(TM). Generally, an ongoing process of reviewing BAS performance is considered a best practice. The tools and methodology may range from a plan executed entirely by internal staff to monitoring-based commissioning performed by an outside contractor. This depends on facility size and type, but the key is that an ongoing, systems-wide process should be put into place. An excellent guide for implementing such a process is The Continuous Commissioning® Guidebook for Federal Energy Managers.

When developing an ongoing commissioning plan, it is important to document the SOO of each major piece of energy-consuming equipment. The SOOs should reflect current operational needs as opposed to the building's original design intent. Variations in operation throughout the year should also be documented since system operation may vary significantly depending on the season. Once this documentation is complete, the plan needs to be converted into practical checks and functional testing that can be performed by facilities staff. One excellent resource for developing functional testing plans is Portland Energy Conservation, Inc.'s (PECI) website. The Control System Functional Testing Guide, specifically, may be particularly useful. The California Commissioning Collaborative also provides samples and templates for an ongoing commissioning plan on its website.

Another option for implementing an ongoing commissioning process is to implement monitoring-based commissioning. Monitoring is typically performed using spreadsheets or custom software that analyzes BAS trend data to compare actual systems operation to an optimal SOO. The building data is monitored constantly for potential modifications that can be made to optimize building system performance.

Another key component to putting a process in place is ensuring that funding is available for identified repairs. The need for this was illustrated in Case Study #2. Many control system repairs have very short payback periods, often a matter of months. Spending several months, or even years, waiting for funding to make BAS repairs with this short of a return is not financially sound. Many controls issues also increase the amount of time that building engineers need to spend making adjustments to the BAS and responding to hot or cold calls, which also support the economic importance of making BAS repairs quickly.

Ongoing commissioning can go beyond quickly identifying malfunctioning or misadjusted equipment. It is highly likely that a building is not operating at its highest possible efficiency, even after just being constructed. Case study number 5 provides a good example of this, with demand control ventilation being installed after it was discovered that the C02 levels in the space were significantly lower than required by code.

Most facilities are in a perpetual state of modification, be it replacing or upgrading equipment, changing space use, or making additions or modifications. An ongoing commissioning process allows facilities staff to continuously work towards optimizing the building and its operations. When modifications occur, the process will provide a mechanism for identifying changes that need to be made to realign operations.

An ongoing commissioning process is a proven means of identifying deficiencies in a facility's energy-consuming systems on a continued basis. Implementing ongoing commissioning at a facility ensures that a continuous process is in place that is focused on optimizing operating efficiency and occupant comfort while reducing energy usage and costs.

*Monitoring-based commissioning is defined in LBL's report as a process that "combines ongoing building energy system monitoring with standard retrocommissioning (RCx) practices."



U.S. Green Building Council's (USGBC) LEED 2009 for Existing Buildings Operations and Maintenance

Portland Energy Conservation, Inc.'s (PECI) Functional Testing Guide: http: / / www. peci org / large-commercial / tools-guides-research / tools-guides.html

California Commissioning Collaborative:

Existing Building Commissioning Toolkit

Templates and Sample Documents

http: / / / resources/ rcxtools / templates_samples.html

U.S. Department of Energy

Energy Efficiency and Renewable Energy:

Continuous CommissioningSM Guidebook

Maximizing Building Energy Efficiency and Comfort

http: / / wwwl / femp / pdfs / ccg02_introductory.pdf

Lawrence Berkley National Lab:

Building Commissioning

A Golden Opportunity for Reducing Energy Costs and Greenhouse-Gas Emissions

http: / / ex. Ibi .gov / cost-benefit.html

Philip L. Keuhn, CEM, LEED AP

Yogesh M. Mardikar, PhD, CEM, LEED AP


Philip Keuhn and Yogesh Mardikar are Senior Energy Engineers with Sieben Energy Associates located in Chicago, Illinois.

Sieben Energy Associates I Energy & Sustainability Solutions

333 N. Michigan Avenue, Suite 2100 I Chicago, Illinois 60601 I P: 312-899-1000 I F: 312-899-4540


Copyright Fairmont Press, Incorporated 2013

This article was written by Philip L Keuhn and Yogesh M Mardikar from Energy Engineering and was legally licensed through the NewsCred publisher network.