Commissioning: Existing Buildings (Energy Engineering)

Abstract

Commissioning an existing building is referred to by various terms, including recommissioning, retrocommissioning, and continuous commissioning® (CC®). A comprehensive study of 182 existing buildings totaling over 22,000,000 ft2 in floor area reported average energy savings of 18% at an average cost of $0. 41/ft2 after they were commissioned, producing an average simple payback of 2.1 years. The commissioning process for an existing building involves steps that should include building screening, a commissioning assessment to estimate savings potential and cost, plan development and team formation, development of performance baselines, detailed measurements and commissioning measure development, implementation, and follow-up to maintain persistence. Existing building commissioning has been successfully used in energy management programs as a standalone measure, as a follow-up to the retrofit process, as a rapid payback Energy Conservation Measure (ECM) in a retrofit program, and as a means to ensure that a building meets or exceeds its energy performance goals. Very often, it is the most cost-effective single energy management option available in a large building.

INTRODUCTION

Commissioning an existing building has been shown to be a key energy management activity over the last decade, often resulting in energy savings of 10, 20 or sometimes 30% without significant capital investment. It generally provides an energy payback of less than three years. In addition, building comfort is improved, systems operate better, and maintenance cost is reduced. Commissioning measures typically require no capital investment, though the process often identifies maintenance that is required before the commissioning can be completed. Potential capital upgrades or retrofits are often identified during the commissioning activities, and knowledge gained during the process permits more accurate quantification of benefits than is possible with a typical audit. Involvement of facilities personnel in the process can also lead to improved staff technical skills.


This entry is intended to provide the reader with an overview of the costs, benefits, and process of commissioning an existing building. There is no single definition of commissioning for an existing building, so several widely used commissioning definitions are given. A short case study illustrates the changes made when an existing building is commissioned, along with its impact. This is followed by a short summary of published information on the range of costs and benefits. The major portion of the article describes the commissioning process used by the authors in existing buildings so the reader can determine whether and how to implement a commissioning program. Monitoring and verification (M&V) may be very important to a successful commissioning program. Some commissioning-specific M&V issues are discussed, particularly the role of M&V in identifying the need for follow-up commissioning activities.

COMMISSIONING DEFINITIONS

The commissioning of a navy ship is the order or process that makes it completely ready for active duty. Over the last two decades, the term has come to refer to the process that makes a building or some of its systems completely ready for use. In the case of existing buildings, it generally refers to a restoration or improvement in the operation or function of the building systems. A widely used short definition of new building commissioning is the process of ensuring systems are designed, installed, functionally tested, and operated in conformance with the design intent. Commissioning begins with planning and includes design, construction, start-up, acceptance, and training and can be applied throughout the life of the building. Furthermore, the commissioning process encompasses and coordinates the traditionally separate functions of systems documentation, equipment start-up, control system calibration, testing and balancing, and performance testing.[1]

Recommissioning

Recommissioning refers to commissioning a building that has already been commissioned at least once. After a building has been commissioned during the construction process, recommissioning ensures that the building continues to operate effectively and efficiently. Buildings, even if perfectly commissioned, will normally drift away from optimum performance over time, due to system degradation, usage changes, or failure to correctly diagnose the root cause of comfort complaints. Therefore, recommissioning normally reapplies the original commissioning procedures in order to keep the building operating according to design intent, or it may modify them for current operating needs.

Optimally, recommissioning becomes part of a facility’s continuing operations and maintenance (O&M) program. There is not a consensus on recommissioning frequency, but some consider that it should occur every 3-5 years. If there are frequent build-outs or changes in building use, recommissioning may need to be repeated more often.[2]

Retrocommissioning

Retrocommissioning is the first-time commissioning of an existing building. Many of the steps in the retrocommissioning process are similar to those for commissioning. Retrocommissioning, however, occurs after construction, as an independent process, and its focus is usually on energy-using equipment such as mechanical equipment and related controls. Retro-commissioning may or may not bring the building back to its original design intent, since the usage may have changed or the original design documentation may no longer exist.[2]

Pre-CC and post-CC heating water consumption at the Kleberg building vs daily average outdoor temperature.

Fig. 1 Pre-CC and post-CC heating water consumption at the Kleberg building vs daily average outdoor temperature.

Continuous Commissioning

Continuous Commissioning (CC®)[3] is an ongoing process to resolve operating problems, improve comfort, optimize energy use, and identify retrofits for existing commercial and institutional buildings and central plant facilities. Continuous commissioning focuses on improving overall system control and operations for the building as it is currently utilized, and on meeting existing facility needs. Continuous commissioning is much more than an O&M program. It is not intended to ensure that a building’s systems function as originally designed, but it ensures that the building and its systems operate optimally to meet the current uses of the building. As part of the CC process, a comprehensive engineering evaluation is conducted for both building functionality and system functions. Optimal operational parameters and schedules are developed based on actual building conditions and current occupancy requirements.

COMMISSIONING CASE STUDY—KLEBERG BUILDING

The Kleberg Building is a teaching/research facility on the Texas A&M campus consisting of classrooms, offices, and laboratories, with a total floor area of approximately 165,030 ft2. A CC investigation was initiated in the summer of 1996 due to the extremely high level of simultaneous heating and cooling observed in the building.[4] Figs. 1 and 2 show daily heating and cooling consumption (expressed in average kBtu/h) as functions of daily average temperature. The pre-CC heating consumption data given in Fig. 1 show very little temperature dependence as indicated by the regression line derived from the data. Data values were typically between 5 and 6 MMBtu/h with occasional lower values. The cooling consumption is even higher (Fig. 2), though it shows more temperature dependence.

It was soon found that the preheat was operating continuously, heating the mixed air entering the cooling coil to approximately 105°F. The preheat was turned off, and heating and cooling consumption both dropped by about 2 MMBtu/h as shown by the middle clouds of data in Figs. 1 and 2. Subsequently, the building was thoroughly examined, and a comprehensive list of commissioning measures was developed and implemented. The principal measures implemented that led to reduced heating and cooling consumption were as follows:

• “Preheat to 105°F” was changed to “Preheat to 40°F.”

• The cold deck schedule was changed from “55°F fixed” to “Vary from 62 to 57°F as ambient temperature varies from 40 to 60°F.”

• The economizer was set to maintain mixed air at 57°F whenever the outside air was below 60°F.

• Static pressure control was reduced from 1.5 inH2O to 1.0 inH2O, and a nighttime set-back to 0.5 inH2O was implemented.

• A number of broken variable air volume terminal (VFD) boxes were replaced or repaired.

• Chilled water pump variable frequency drives (VFDs) were turned on.

These changes further reduced chilled water and heating hot water use as shown in Figs. 1 and 2 for a total annualized reduction of 63% in chilled-water use and 84% in hot-water use.

Pre-CC and post-CC chilled water consumption at the Kleberg building vs daily average outdoor temperature.

Fig. 2 Pre-CC and post-CC chilled water consumption at the Kleberg building vs daily average outdoor temperature.

COSTS AND BENEFITS OF COMMISSIONING EXISTING BUILDINGS

The most comprehensive study of the costs and benefits of commissioning existing buildings was conducted by Mills et al.[5'6] This study examined the impact of commissioning 182 existing buildings with over 22,000,000 ft2. The commissioning cost of these projects ranged from below $0.10/ft2-$3.86/ft2, but most were less than $0.50/ft2 with an average cost of $0.41/ft2. Savings ranged from essentially zero to 54% of total energy use, with an average of 18%. This range reflects not only differences among buildings in the potential for commissioning savings, but doubtless also includes differences in the level of commissioning applied and the skill of the commissioning providers. Simple payback times ranged from less than a month to over 20 years, with an average of 2.1 years. Fig. 3 illustrates the average payback as a function of building type and the precommissioning energy cost intensity. The sample sizes for office buildings and higher education are large enough that these averages for payback and energy savings may be representative, but the other sample sizes are so small that they may be significantly skewed by building specific and/or other factors.

Mills et al. concluded, “We find that commissioning is one of the most cost-effective means of improving energy efficiency in commercial buildings. While not a panacea, it can play a major and strategically important role in achieving national energy savings goals—with cost-effective savings potential of $18 billion per year or more in commercial buildings across the United States.”

Average simple payback time and percent energy savings from commissioning of existing buildings by building type.

Fig. 3 Average simple payback time and percent energy savings from commissioning of existing buildings by building type.

THE COMMISSIONING PROCESS IN EXISTING BUILDINGS

There are multiple terms that describe the commissioning process for existing buildings, as noted in the previous section. Likewise, there are many adaptations of the process itself. The same practitioner will implement the process differently in different buildings, based on the budget and the owner requirements. The process described here is the process used by the chapter authors when the owner wants a thorough commissioning job. The terminology used will refer to the CC process, but many of the steps are the same for retrocommissioning or recommissioning. The model described assumes that a commissioning provider is involved, since that is normally the case. Some (or all) of the steps may be implemented by the facility staff if they have the expertise and adequate staffing levels to take on the work.

Continuous commissioning focuses on improving overall system control and operations for the building as it is currently utilized, and on meeting existing facility needs. It does not ensure that the systems function as originally designed, but ensures that the building and systems operate optimally to meet the current requirements. During the CC process, a comprehensive engineering evaluation is conducted for both building functionality and system functions. The optimal operational parameters and schedules are developed based on actual building conditions and current occupancy requirements. An integrated approach is used to implement these optimal schedules to ensure practical local and global system optimization and persistence of the improved operation schedules.

Outline of phase II of the CC process: implementation and verification.

Fig. 4 Outline of phase II of the CC process: implementation and verification.

Commissioning Team

The CC team consists of a project manager, one or more CC engineers and CC technicians, and one or more designated members of the facility operating team. The primary responsibilities of the team members are shown in Table 1. The project manager can be an owner representative or a CC provider representative. It is essential that the engineers have the qualifications and experience to perform the work specified in the table. The designated facility team members generally include at least one lead heating, ventilating and air conditioning (HVAC) technician and an energy management control system (EMCS) operator or engineer. It is essential that the designated members of the facility operating team actively participate in the process and be convinced of the value of the measures proposed and implemented, or operation will rapidly revert to old practices.

Continuous Commissioning Process

The CC process consists of two phases. The first phase is the project development phase that identifies the buildings to be included in the project and develops the project scope. At the end of this phase, the CC scope is clearly defined and a CC contract is signed, as described in “Phase 1: Project Development.” The second phase implements CC and verifies project performance through the six steps outlined in Fig. 4 and described in “Phase 2: CC Implementation and Verification.”

Phase 1: Project Development

Step 1: Identify Candidate Buildings. Buildings are screened to identify those that will receive a CC assessment. Buildings that provide poor thermal comfort, consume excessive energy, or have design features of the HVAC systems that are not fully used are typically good candidates for a CC assessment. Continuous commissioning can be effectively implemented in buildings that have received energy efficiency retrofits, in newer buildings, and in existing buildings that have not received energy efficiency upgrades. In other words, virtually any building can be a potential CC candidate. The CC provider should perform a preliminary analysis to check the feasibility of using the CC process on candidate facilities before performing a CC assessment.

The following information is needed for the preliminary assessment:

• Monthly utility bills for at least 12 months.

• General building information—size, function, major equipment, and occupancy schedules.

Table 1 Commissioning team members and their primary responsibilities

Team member(s) Primary responsibilities
Project manager 1. Coordinate the activities of building personnel and the commissioning team

2. Schedule project activities

Continuous commissioning (CC) engineer(s) 1. Develop metering and field measurement plans

2. Develop improved operational and control schedules

3. Work with building staff to develop mutually acceptable implementation plans

4. Make necessary programming changes to the building automation system

5. Supervise technicians implementing mechanical systems changes

6. Project potential performance changes and energy savings

7. Conduct an engineering analysis of the system changes

8. Write the project report

Designated facility staff 1. Participate in the initial facility survey

2. Provide information about problems with facility operation

3. Suggest commissioning measures for evaluation

4. Approve all CC measures before implementation

5. Actively participate in the implementation process

CC Technicians 1. Conduct field measurements

2. Implement mechanical, electrical, and control system program modifications and changes, under the direction of the project engineer

• O&M records, if available.

• Description of any problems in the building, such as thermal comfort, indoor air quality, moisture, or mildew.

An experienced engineer should review this information and determine the potential of the CC process to improve comfort and reduce energy cost. If the CC potential is good, a CC assessment should be performed.

Step 2: Perform CC Assessment and Develop Project Scope. The CC assessment involves a site visit by an experienced commissioning engineer who examines EMCS screens, conducts spot measurements throughout the building systems, and identifies major CC measures suitable for the building. The CC assessment report lists and describes the preliminary CC measures identified, the estimated energy savings from implementation, and the cost of carrying out the CC process on the building(s) evaluated in the assessment. Once a commissioning contract is signed, the process moves to Phase 2.

Phase 2: CC Implementation and Verification

Step 1: Develop CC Plan and Form the Project Team. The CC project manager and project engineer develop a detailed work plan for the project that includes major tasks, their sequence, time requirements, and technical requirements. The work plan is then presented to the building owner or representative(s) at a meeting attended by any additional CC engineers and technicians on the project team. Owner contact personnel and in-house technicians who will work on the project are identified.

Step 2: Develop Performance Baselines. This step should document all known comfort problems in individual rooms resulting from too much heating, cooling, noise, humidity, or odors (especially from mold or mildew), or lack of outside air. Also, identify and document any HVAC system problems.

Baseline energy models of building performance are necessary to document the energy savings after commissioning. The baseline energy models can be developed using one or more of the following types of data:

• Short-term measured data obtained from data loggers or the EMCS system.

• Long-term hourly or 15-min whole building energy data, such as whole-building electricity, cooling, and heating consumption.

• Utility bills for electricity, gas, or chilled or hot water.

The baselines developed should be consistent with the International Performance Measurement and Verification Protocol,[7] with ASHRAE Guideline 14, or with both.[8]

Step 3: Conduct System Measurements and Develop Proposed CC Measures. The CC team uses EMCS trend data complemented by site measurements to identify current operational schedules and problems. The CC engineer conducts an engineering analysis to develop solutions for the existing problems; establishing improved operation and control schedules and set points for terminal boxes, air handling units (AHUs), exhaust systems, water and steam distribution systems, heat exchangers, chillers, boilers, and other components or systems as appropriate. Cost-effective energy retrofit measures can also be identified and documented during this step, if desired by the building owner.

Step 4: Implement CC measures. The CC project manager and/or project engineer presents the engineering solutions to existing problems and the improved operational and control schedules to the designated operating staff members and the building owner’s representative to get “buy-in” and approval. Measures may be approved, modified, or rejected. A detailed implementation schedule is then developed by the CC engineer in consultation with the operating staff.

Continuous commissioning implementation normally starts by solving existing problems. Implementation of the improved operation and control schedules starts at the end of the comfort delivery system, such as at the terminal boxes, and ends with the central plant. The CC engineer closely supervises the implementation and refines the operational and control schedules as necessary. Following implementation, the new operation and control sequences are documented in a way that helps the building staff understand why they were implemented.

Step 5: Document Comfort Improvements and Preliminary Energy Savings. The comfort measurements taken in Step 2 (Phase 2) should be repeated at the same locations under comparable conditions and compared with the earlier measurements. The M&V procedures adopted in Step 2 should be used to determine the early post-CC energy performance and weather normalized to provide a preliminary evaluation of savings.

Step 6: Keep the Commissioning Continuous. The CC engineer should review the system operation after 6-12 months to identify any operating problems and make any adjustments needed. One year after CC implementation is complete, the CC engineer should write a project follow-up report that documents the first-year savings, recommendations or changes resulting from any consultation or site visits provided, and any recommendations to further improve building operations. Subsequently, the consumption should be tracked and compared with the first-year post-CC consumption during this period. Any significant and persistent increases in consumption should be investigated by the staff and/or CC engineer.

USES OF COMMISSIONING IN THE ENERGY MANAGEMENT PROCESS

Commissioning can be used as a part of the energy management program in several different ways:

• As a standalone measure. Commissioning is probably most often implemented in existing buildings because it is the most cost-effective step the owner can take to increase the energy efficiency of the building, generally offering a payback under three years, and often 1-2 years.

• As a follow-up to the retrofit process. Continuous commissioning has often been used to provide additional savings after a successful retrofit and has also been used numerous times to make an under-performing retrofit meet or exceed the original expectations.

• As an ECM in a retrofit program. The rapid payback that generally results from CC may be used to lower the payback of a package of measures to enable inclusion of a desired equipment replacement that has a longer payback in a retrofit package. This is illustrated by a case study in the next section. In this approach, the CC engineers conduct the CC audit in parallel with the retrofit audit conducted by the design engineering firm. Because the two approaches are different and look at different opportunities, it is very important to closely coordinate these two audits.

• To ensure that a new building meets or exceeds its energy performance goals. It may be used to significantly improve the efficiency of a new building by optimizing operation to meet its actual loads and uses instead of working to design assumptions.

CASE STUDY WITH CC AS AN ECM

Prairie View A&M University is a 1.7-million square foot campus, with most buildings served by a central thermal plant. Electricity is purchased from a local electric co-op.

University staff identified the need for major plant equipment replacements on campus. They wished to finance the upgrades through the Texas LoanSTAR program, which requires that the aggregate energy payback of all ECMs financed be ten years or less. Replacement of items such as chillers, cooling towers, and building automation systems typically have paybacks of considerably more than ten years. Hence, they can only be included in a loan if packaged with low payback measures that bring the aggregate payback below ten [9] years.

The university administration wanted to maximize the loan amount to get as much equipment replacement as possible. They also wanted to ensure that the retrofits worked properly after they are installed. To maximize their loan dollars, they chose to include CC as an ECM.

The LoanSTAR Program provides a brief walkthrough audit of the candidate buildings and plants. This audit is performed to determine whether there is sufficient retrofit potential to justify a more thorough investment grade audit.

The CC assessment is conducted in parallel with the retrofit audit conducted by the engineering design firm, when CC is to be included as an ECM. The two approaches look at different opportunities, but there can be some overlap, so it is very important to closely coordinate both audits. It is particularly important that the savings estimated by the audit team are not “double counted.” The area of greatest overlap in this case was the building automation system. Considerable care was taken not to mix improved EMCS operation with operational improvements determined by the CC engineer, so both measures received proper credit.

The CC measures identified included the following:

• Hot and cold deck temperature resets.

• Extensive EMCS programming to avoid simultaneous

heating and cooling.

• Air and water balancing.

• Duct static pressure resets.

• Sensor calibration and repair.

• Improved start, stop, warm-up, and shutdown schedules.

The CC engineers took the measurements required and collected adequate data on building operation during the CC assessment to perform a calibrated simulation on the major buildings. Available metered data and building EMCS data were also used. The CC energy savings were then written as an ECM and discussed with the design engineer. Any potential overlaps were removed. The combined ECMs were then listed and the total savings determined.

Table 2 summarizes the ECMs identified from the two audits:

The CC savings were calculated to be $204,563, as determined by conducting calibrated simulation of 16 campus buildings and by engineering calculations of savings from improved loop pumping. No CC savings were claimed for central plant optimization. Those savings were all applied to ECM #7, although it seems likely that additional CC savings will accrue from this measure. The simple payback from CC is slightly under three years, making it by far the most cost effective of the ECMs to be implemented. The CC savings represent nearly 30% of the total project savings.

Perhaps more importantly, CC accounted for two-thirds of the “surplus” savings dollars available to buy down the payback of the chillers and EMCS upgrade. Without CC as an ECM, the University would have had to delete one chiller and the EMCS upgrades, or some combination of chillers and a portion of the building EMCS upgrades from the project to meet the ten-year payback criteria—one chiller and the EMCS upgrades, or some combination of chillers and limited building EMCS upgrades. With CC, however, the university was able to include all these hardware items, and still meet the ten-year payback.

Lable 2 Summary of energy cost measures (ECMs)

Annual savings
Electric demand
ECM # ECM Electric kWh/yr kW/yr Gas MCF/yr Cost savings Cost to implement Simple payback
#1 Lighting 1,565,342 5221 (820) $94,669 $561,301 6.0
#2 Replace chiller #3 596,891 1250 -0- $33,707 $668,549 19.8
#3 Repair steam system -0- -0- 13,251 $58,616 $422,693 7.2
#4 Install motion sensors 81,616 -0- (44.6) $3567 $26,087 7.3
#5 Add 2 bldgs. to CW loop 557,676 7050 -0- $60,903 $508,565 8.4
#6 Add chiller #4 599,891 1250 -0- $33,707 $668,549 19.8
#7 Primary/

secondary

pumping

1,070,207 -0- -0- $49,230 $441,880 9.0
#8 Replace DX systems 38,237 233 -0- $2923 $37,929 13.0
#9 Replace DDC/ EMCS 2,969,962 670 2736 $151,488 $2,071,932 13.7
#10 Continuous commissioning

Assessment reports

Metering

M&V

2,129,855 -0- 25,318 $204,563 $ 605,000

$102,775

$157,700 $197,500

3.0
9,606,677 15,674 40,440 $693,373 $6,470,460 9.3

SUMMARY

Commissioning of existing buildings is emerging as one of the most cost-effective ways for an energy manager to lower operating costs, and typically does so with no capital investment, or with a very minimal amount. It has been successfully implemented in several hundred buildings and provides typical paybacks of one to three years.

It is much more than the typical O&M program. It does not ensure that the systems function as originally designed, but focuses on improving overall system control and operations for the building as it is currently utilized and on meeting existing facility needs. During the CC process, a comprehensive engineering evaluation is conducted for both building functionality and system functions. The optimal operational parameters and schedules are developed based on actual building conditions. An integrated approach is used to implement these optimal schedules to ensure practical local and global system optimization and to ensure persistence of the improved operational schedules.

The approach presented in this chapter begins by conducting a thorough examination of all problem areas or operating problems in the building, diagnoses these problems, and develops solutions that solve these problems while almost always reducing operating costs at the same time. Equipment upgrades or retrofits may be implemented as well, but have not been a factor in the case studies presented, except where the commissioning was used to finance equipment upgrades. This is in sharp contrast to the more usual approach to improving the efficiency of HVAC systems and cutting operating costs, which primarily emphasizes system upgrades or retrofits to improve efficiency.

Commissioning of new buildings is also an important option for the energy manager, offering an opportunity to help ensure that new buildings have the energy efficiency and operational features that are most needed.

Next post:

Previous post: