Debugging of engineering systems after the building is put into operation.
The process of commissioning buildings and optimizing utility systems is developing together with communal information technologies.
This article presents a detailed analysis of the project carried out at the Research Center named after. David Skaggs Research Center in Boulder to identify operational problems, opportunities to improve utility system efficiency, and other improvements once a building is operational in the first year of construction.
It is assumed that the optimization carried out should pay for itself in less than a year. It improves the quality of utility services provided, allowing you to more reliably and efficiently meet the needs of customers in the building. Although the utility improvement process here was considered in the context of new construction, it can also be used for the renovation and recommissioning of existing utility systems, which have been shown to have a relatively quick payback. The findings also indicate that further developments in utility information technology will make these diagnostic techniques and their associated benefits more accessible to widespread use. This will fundamentally change the process of commissioning buildings and their subsequent use.
Project history
The US General Service Administration (GSA) created the David Skaggs Research Center for the needs of the Environmental Research Laboratory of the National Oceanic and Atmospheric Administration (NOAA), the National Weather Service and the National Geophysical Data Center and several other federal agencies. The complex, which houses the research center, has 720 offices with windows that open, 20 conference rooms, several computer centers and almost 100 wet and dry technology laboratories. The complex consists of three above-ground floors and one underground. The total area of the center is 34,500 sq. m.
To provide heating for the complex and a year-round supply of hot water, two gas boilers are used, the efficiency of which in stationary operation is 82%. The power of each of the boilers, installed at an altitude of 1646 m above sea level, is 1959 kW. Three centrifugal water-cooled chillers (with a full load efficiency of 0.63 kW/t with a capacity of 470 tons (1653 kW) each) supply cold water to cool the entire complex. Two small air coolers with piston pumps are used as backup for a centralized cooling system for computer rooms.
The five central air conditioning units are equipped with 100% economizers to control the outside air temperature, heating coils, cooling coils and two parallel 56 kW variable pitch axial fans. Two devices are equipped with heat recovery systems for air coming from laboratories.
All major equipment of the complex, including mechanical systems, central air conditioning elements, internal and external lighting systems of the complex, etc., are connected to the building automation system (BAS). Direct digital control (DDC) technology is used to control all devices connected to the BAS. This system includes more than 4,600 data points. To control it, the operator uses a graphical software interface on the main computer. In addition, the electrical distribution system is equipped with approximately 100 electrical energy consumption monitoring devices that detect faults in the electrical network, monitor voltage harmonic disturbances, and measure and record electrical energy consumption. Each device monitors at least 20 power system parameters, including momentary power consumption and total energy consumption. These devices are networked to a central operator terminal to monitor system status, generate alarms, and record load curves. And these two systems form what the authors call a “communal building information system.”
During the design of the complex building, the engineering team and commissioning agent allowed GSA to take significant initiative to reduce the cost of construction and operation of the complex through the implementation of a number of highly effective measures aimed at reducing the cost of water supply to the complex and the provision of electricity. One of these measures included a new approach to the commissioning of the building, taking into account the specifics of the construction work. Key activities included: pre-start-up inspection of installed equipment, equipment start-up, equipment testing, and set-up and operation checks, which were carried out for all major mechanical and electrical equipment, fire and safety systems, BAS controls, and sanitary facilities. equipped with water saving systems. In accordance with ASHRAE Guidelines 151996: The Commissioning Process for Heating, Ventilating, and Air Conditioning Systems, detailed personnel training and manuals for operating the system were developed during the commissioning process. After the completion of the construction phase, the focus shifted to carrying out commissioning work after the start of operation of the complex and optimizing the operation of the internal systems of the complex (POCx), which included:
— ensuring reliable uninterrupted operation of all main systems of the complex;
— identifying any problems or malfunctions and finding solutions to eliminate them;
— search and identification of opportunities to increase the efficiency of utility systems and generally improve the operation of equipment;
— development of the basis of documents regulating corrective actions during the operation of the system and actions aimed at improving its operation;
— creating standards for managing system operation in the future.
The general goals of the work and POCx included: a) increasing the comfort of conditions in the complex (temperature and air quality in its premises); b) reducing energy consumption and increasing environmental safety; c) reducing the number and cost of maintenance work; d) increasing the service life of equipment.
It was assumed that the ability to monitor the operation of the electrical distribution network would be useful for carrying out the planned work. Unfortunately, initially the control system worked only partially, which allowed it to be used only for some specific measurements. Subsequently, this system became fully operational, which allowed the complex employees to monitor the operation of electrical systems.
In the last decade, authors have used the term Post5Occupancy Commissioning (POCx) to distinguish work that occurs after a site is in use and to separate it from work that occurs while the site is under construction. Although the authors acknowledge and support the point of view that properly carried out commissioning work should include both work carried out during the design and construction stages, and work carried out after the start of operation of the relevant facilities. But many commissioning projects often end after acceptance of the entire project and do not include follow-up work.
These goals are consistent with those set forth in ASHRAE Guideline 151996: Heating System Commissioning Process. Ventilation and Air Conditioning» and the later «Model Commissioning Plan and Recommended Specifications, Ver. 2.05», developed by Portland
Energy Conservation, Inc. in cooperation with the Federal Energy Management Program. (When this material was written, ASHRAE’s Guideline 052005: Systems Commissioning Process had not yet been completed.)
Methods
The primary strategy for conducting POCx was to use pre-existing utility information systems to track, record, and analyze performance of the facility’s mechanical systems and then use this information to improve overall facility performance. The main tools used to complete this task were BAS and a spreadsheet program. A centralized system for monitoring electricity consumption would also be useful, but this only became fully operational after the completion of POCx.
Of the more than 4,600 data points to which the BAS was connected, approximately 200 were considered key — they were used to determine the operating parameters of the complex’s main mechanical systems. These key points were continuously collected and trend analyzed every 15 minutes. This data was automatically saved on the central operator’s terminal. Once a week, the data was downloaded over the network to the commissioning manufacturer for subsequent analysis. The major systems controlled included boilers, chillers and associated auxiliary equipment, five large central air handling units, and a number of other auxiliary systems.
The authors have developed several semi-automated programs to create spreadsheets based on trend analysis data imported from BAS, plot graphs based on combinations of this data, and create diagnostic tables summarizing the resulting data. These graphs and tables were then manually analyzed to check the system’s performance and to identify areas in need of improvement. Based on them, a permanent record of the system’s performance characteristics and its operating efficiency was kept. This made it possible to identify important events in the operation of the system, for example, failures of subsystems and individual equipment elements, which can be used in the future to create standards that determine the operating parameters of the system.
Any problems or equipment malfunctions were recorded in a special table throughout the entire process of putting the complex into operation. After taking actions to eliminate them, the results of these actions were monitored. On-site checks helped confirm that identified problems had been resolved before starting to analyze the following items in the compiled tables.
OAT — Outside temperature.
CH2 Amps — Current strength in the main cooler, A
СНЗ Amps — Current strength in the additional cooler, A
CHWST — Chilled water temperature leaving the chiller.
Lag Chiller Over-Cycling — Unnecessary frequent cycling of the after-chiller.
Fig. 1. Cooler operation schedule (June 9)
Results
The analysis identified more than twenty serious problems and opportunities for improvement of system performance, about 50% were related to system operation and management, 25% to system design, and another 25% were caused by hardware failures. Here is a detailed example of just one problem related to the operation of the system. But similar diagnostics and analysis were carried out and documented for all other identified problems.
Additional cooler mode switching too frequently.
As shown in Fig. 1, from the average graph of cooler operating parameters (created on the basis of automatically collected data) it can be seen that the additional cooler was often turned on and off — sometimes up to 4 times per hour and up to 20 times per day. Switching the cooler operating modes too frequently leads to its rapid wear, increases energy consumption, increases the cost of equipment maintenance and can quickly lead to cooler failure. Based on the analysis of the obtained graphs, it was revealed that the additional cooler was turned off when the current strength in both coolers (CH2, CH3) dropped below
50% of the value corresponding to the operation of coolers at maximum load. This operating parameter setting value corresponded to that specified in the design documentation created by the control system developer. Probably, the developer assumed that the base value would be adjusted during commissioning, but this was not done. Since the system load was usually slightly greater than the capacity of the main cooler, when the after-cooler was turned off, the water temperature (CHWST) increased and the after-cooler was turned on again. The problem was solved simply: the current threshold for turning off the additional cooler was reduced from 50 to 45% of the maximum load current.
OAT — Outside temperature.
CH2 Amps — Main cooler current, A
CH2 Amps — Additional cooler current, A
CHWST — Chilled water temperature leaving the cooler.
Lag Chiller Comes On When Secondary CHW Supply Temp. Rises — The after-chiller turns on when
the temperature of the chilled water leaving the chiller rises.
Lag Chiller Goes Off When One chiller Can Handle the Load — The after-chiller turns off when with
the load, running alone, the main cooler can handle it.
Lag Chiller Comes Back On, But With a Single On/Off Cycle — The additional cooler turns on again after
one unnecessary on-off cycle.
Fig. 2. Cooler operating schedule (June 17-18)
In Fig. Figure 2 shows the results obtained with this change. If the load exceeds the capacity of the main cooler, the water temperature rises and the additional cooler is switched on. If the current in both coolers drops to 45% of the maximum load current, the second cooler is turned off and remains turned off until the cooling capacity of the main cooler is exceeded again. As can be seen from Fig. On June 2, 18, there was only one unnecessary shutdown of the additional cooler, the cause of which cannot be determined without analyzing additional information. That is, it is necessary to continue to monitor the operating mode of the coolers (and, possibly, with more frequent measurements) to identify possible additional problems that require solutions.
Review of the program code that controlled the chillers also revealed several timers and other variables related to chiller control that were not directly controlled by the BAS operators. In the interests of managing the operation of the complex’s utility systems, it was necessary to develop a simpler and more intuitive interface for monitoring and controlling the operation of the cooler. The company that created BAS subsequently redesigned the graphical interface for controlling the operation of the cooling water system from the BAS central computer, including the display of all the variables necessary to control the operation of the cooling system, as well as the ability to control these variables. This has significantly increased the ability of operators to control the operation of the central cooling system.
Analysis methods similar to the above have been developed for all other major mechanical systems.
Let us give two more examples.
Frequent shutdowns of central air conditioning system ventilation units due to the accumulation of static pressure. The supply fans of central air conditioning units frequently shut down due to low static pressure on the supply side of the axial fans. The fans remained off until technicians manually reset the system’s sensors. This could disrupt the required level of comfort in the premises of the complex and cause an imbalance in the operation of the ventilation system. After identifying the cause of the fans turning off, a temporary solution to the problem was found. The air valve control was set to economizer mode (100% use of outside air) by directly changing the settings on the BAS central computer. A completely logical temporary solution for spring and autumn, it led to excess energy consumption and increased the load on the cooling system on warm days. But in the absence of another solution, this could lead to the inability to provide the necessary air cooling in the summer heat.
Using BAS graphs and observational data, the cause of the problem was identified. It consisted of an air flow control algorithm, due to which, when the economizer mode was turned off (main outside air valves closed, auxiliary valves open), the recirculated air valves were closed to maintain a minimum flow of outside air intake through the auxiliary valve. This was expected to close the supply fan inlet to increase the negative static pressure and
increase the minimum outside air flow. However, the required negative static pressure was well below the trigger point of the safety system sensors, causing the fans to shut down (the minimum outside air intake valve inlet size was relatively small and likely too small for the system to operate properly).
The valve operation control algorithm was changed — it included a minimum time interval for the main valve supplying outside air. This eliminated unnecessary triggering of safety sensors and also allowed minimum ventilation requirements to be met while reducing fan power consumption.
The static pressure in the ducts is too high. At the beginning of the complex’s operation, the angle at which the fan blades were located, forcing air into the central air conditioning system, was adjusted so that the static pressure in the air ducts was maintained in the region of 1.5 inches of water column (373.2 Pa). In our experience, this is the starting point from which subsequent pressure adjustment begins.
Since static pressure variable air volume (VAV) terminals are nominally designed to operate in ducts of 0.5 inH2O (124.4 Pa) or lower, an experiment was conducted to measure how much energy could be saved , reducing the static pressure in the air ducts, and check whether the comfort of people in the complex will be impaired. At the time of this experiment, the electrical control system had not yet been put into operation and portable power current meters were installed on two central air conditioning units. The experiment, which lasted several weeks, recorded fan power consumption, duct static pressure, outside temperature, and wind speed, but first for a nominal duct static pressure of 1.5 inches of water (373.2 Pa), and then for a nominal pressure of 1.0 inH2O (248.8 Pa).
The results showed that the expected savings from reducing fan power consumption would be about 10% per year (i.e. $3,600), but there was no disruption to the operation of the VAV air conditioning system terminals (e.g., with maximum air flow under standard operating conditions of the terminals) or disruption of the comfort of people staying in the complex. As a result of this experiment, the base static duct pressure was reduced to 1 inch of water (248.8 Pa) for all five central air conditioning installations (and may be further reduced in the future).
Other Results received during POCx included:
– detection and correction of excessive auxiliary boiler switching, inaccurate chilled water temperature (superheat) control, faulty air temperature control system in central air conditioning units, incorrect air flow measurement system calibration values, loose valve and inaccurate or faulty sensors and actuators BAS mechanisms;
– development of recommendations for improving system control algorithms, including static pressure accumulation, economizer mode switching, heat recovery system operation, and cooling tower bypass valve operation.
After completion of POCx, several organizations conducted energy use reviews in accordance with US federal laws.
Prior to the start of the audit, a centralized energy monitoring system was put in place with sufficient resolution to measure actual grid load patterns, peak energy consumption and electricity consumption of various major end-user categories. In Fig. Figure 3 shows the summary results of three days of testing. These data, together with others, can be used to develop standards with which the system’s operating parameters will be constantly compared under different weather and different conditions in general, with the correct configuration of information systems and their introduction
into the routine practice of managing the operation of the utility systems of the complex.
Fig. 3 Shares of various categories of end consumers in daily consumption
of electricity (averaged data for August 24 — 26).
Computers, Lab Equipment, and Misc. Plug Loads – Computers, laboratory equipment and various systems
connected to electrical outlets. Cooling — Cooling. Lighting — Lighting.
HVAC Fans and Pumps — System fans and pumps
ventilation, heating and air conditioning.
Average outside temperatures for the three-day period covered:
Max: 90.5o F (32.5o C)
Min: 63.2o F (17. 3o C)
Avg: 76.2o F (24.55o C)
Average Daily Energy Consumption = 29,782 kWh/day
Average Peak Power Consumption = 1537 kW
Discussion
The POCx carried out at the Research Center made it possible to increase the efficiency of its utility systems, simplify their maintenance, and increase the service life of equipment. Some consequences are very difficult
to quantify. And taking into account the above facts, it is possible to make a number of reasonable assessments of the economic efficiency of the work performed. In some cases, these estimates can be quite accurate. However, many of the benefits achieved cannot be directly quantified.
They can be described qualitatively or in the context of their potential impact on the cost of operating the utility system.
The David Skaggs Research Center assumed that annual utility costs, including electricity, natural gas and water, would be $19.16/m2. This figure was based on a computer model of the complex under construction, taking into account utility costs for the first three months after the start of operation. The center’s projected annual budget for equipment operation and repair is $12.16/m2. Funds for major equipment repairs and replacements are allocated as a separate line item in the GSA budget. And the total cost that can be impacted by POCx (excluding major repairs and equipment replacement) is $31.32/m2 per year. If the expected cost reduction is between 5 and 10% (which is a fairly conservative estimate based on the literature data, and is further supported by the quantified cost reduction results for the package in question), the estimated cost savings would be between $1.40 and $2.90. /m2.
An example of benefits that cannot be quantified is the elimination of excessive switching of operating modes for the auxiliary boiler and auxiliary chiller described above. It is difficult to accurately quantify the excess wear and tear of equipment, the associated additional costs for its maintenance and the inconvenience experienced by people in the complex caused by frequent switching of equipment operating modes. It can be assumed that this problem developed over time
would have been identified and corrected during normal equipment operation and maintenance, but the main advantage of POCx is that this problem was identified and corrected much earlier.
The cost to conduct POCx at the David Skaggs Research Center over six months was approximately $1.08/m2, i.e. approximately 12% of the cost of all commissioning works carried out during construction. These costs included only the cost of obtaining consulting services from third-party companies before the start of the planned work, the cost of weekly analysis of the data received, visiting the work site if necessary, and interacting with the center’s technical staff and the work contractors to eliminate identified problems. Given the expected savings discussed above, this work can be considered to pay for itself in less than one year of direct cost savings alone.
The Future of Utility Information Systems
After six months of POCx, this work was discontinued because there was no easy way to integrate it into the day-to-day operation of the complex — requiring several hours of technical staff time per week. Technological advances needed to enable wider use of such diagnostic techniques include:
– systems for automatic data collection and analysis, capable of integrating information from various independent control and measurement systems and then subjecting it to further analysis;
– the ability to create interactive graphs and reports that allow you to quickly visualize key information about the operation of utility systems, such as peak graphs and daily energy consumption, etc.;
– An easy-to-use POCx interface that allows technicians to easily create and use new diagnostic functions, graphs and reports as existing utility systems change and as the information requirements needed to manage those systems change.
These and other capabilities are gradually being offered by public, private organizations, government agencies, traditional automation system manufacturers, and new high-tech companies. The question is not whether new technologies will become more accessible and more widely used, but how quickly this will happen. Since investments are carried out on an experimental basis, and the importance of the necessary information in comparison with the costs of obtaining and analyzing it becomes more and more obvious, new technologies, more economically profitable, are one of the main drivers of the development of this market .
As the adoption and use of utility information systems increases, the costs of building and operating them should drop markedly. Over time, the use of such systems for the construction, commissioning and commissioning of buildings will become the rule rather than the exception.
Even in properly constructed buildings there is an opportunity to continuously improve the performance of utility systems. Utility information systems promise to help cost-effective maintenance in the future, helping to increase the efficiency of the created comfort when upgrading these systems as they age and when replacing the equipment included in them.
Credits: Engineer Mark Bowman, formerly lead designer at E-Cube, now chief engineer at Bowman Consulting in Seattle. Jack S. Wolpert, president of E-Cube in Boulder, Colorado, Ph.D. Participated in the development of ASHRAE Guidelines 1-1996: Commissioning Process for Heating, Ventilating and Air Conditioning Systems. Member of GPC 14P, Measuring Energy Demand and Consumption Reductions.
Translated with permission from ASHRAE Journal, June 2006
(c). American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc. All rights reserved. Translated with abbreviations and distributed by the BIG_RU Association. ASHRAE is not responsible for the accuracy of the translation. To obtain the original version of this article, contact ASHRAE: 1791 Tullie Circle, NE, Atlanta, GA 30329_2305, USA,ashrae.org