1、492 2009 ASHRAEABSTRACTThe Continuous Commissioning Leading Project (CCLEP) process is an ongoing process to apply system opti-mization theory and advanced technologies in commercial retrofit projects. The CCLEP process was applied to a luxury shopping mall and office building. The case study buildi
2、ng has ten single fan dual-duct VAV AHUs, 123 dual-duct pneumatic controlled pressure independent terminal boxes, and a central heating and cooling plant. Major retrofit efforts include upgrading pneumatic to DDC controls for all AHUs, installing main hot deck dampers, replacing the boiler, installi
3、ng VFD on fans and pumps, and installing Fan Airflow Stations (FAS) and Pump Waterflow Stations (PWS). This paper presents the opti-mal control strategies, which include main hot deck damper control, supply fan control integrated with FAS, return fan control, optimal control for terminal boxes, chil
4、led water temperature and chilled water pump speed control, hot water temperature and hot water pump speed control. Boiler size was optimized at the time of replacement while the performance was measured and verified. The measured hourly utility data after CCLEP show that annual HVAC electricity con
5、sumption is reduced by 56% and gas use is reduced by 36%. INTRODUCTIONThe Continuous Commissioning Leading Project (CCLEP) process is an ongoing process to apply system opti-mization theory and advanced technologies to commercial retrofit projects. It was developed by Liu et al (2006) through a U.S.
6、 Department of Energy grant to the University of Nebraska and the Omaha Public Power District (OPPD) for continuous commissioning applications in commercial retro-fit projects. The CCLEP process, procedures and seven case study results have already been presented (Liu et al 2006).CCLEP was applied t
7、o a luxury shopping mall and office building. The case study building has ten single fan dual-duct VAV AHUs, 123 dual-duct pneumatic controller pressure independent terminal boxes, and a central heating and cooling plant. Major retrofit efforts include upgrading pneumatic to DDC controls for all AHU
8、s, installing main hot deck dampers, replacing the boiler, installing VFD on fans and pumps, and installing Fan Airflow Stations (FAS) and Pump Waterflow Stations (PWS). This paper presents the optimal control strat-egies, which include main hot deck damper control, supply fan control integrated wit
9、h FAS, return fan control, optimal control for terminal boxes, chilled water temperature and chilled water pump speed control, hot water temperature and hot water pump control. The measured hourly utility data after CCLEP show that annual HVAC electricity consumption is reduced by 56% and gas use is
10、 reduced by 36%. This paper demonstrates the energy savings and system performance improvement through retrofits and optimal system control. This paper will present the case study building information, CCLEP major retrofits, CCLEP optimal control strategies, CCLEP results and conclusions. BUILDING I
11、NFORMATIONThe case study building is located in Omaha, NE. The two-story shopping mall and office building was built in 1975 with a total floor area of 231,000 ft2(21,461 m2). There are multiple stores owned by different owners. The building is occupied from Monday to Sunday each week while the occu
12、-pancy schedule is different from store to store. CCLEP Reduces Energy Consumption by More than 50% for a Luxury Shopping MallL. Wu M. Liu, PhD, PE X. Pang G. Wang, PhD, PEStudent Member ASHRAE Member ASHRAE Student Member ASHRAE Member ASHRAEJ. Wang, PE T.G. LewisMember ASHRAE Member ASHRAEL. Wu an
13、d X. Pang are doctoral students and research assistants, G. Wang is a research associate professor, and M. Liu is a professor and chair of the graduate committee in the Department of Architectural Engineering, University of NebraskaLincoln, Linclon, NE. J. Wang is the manager and T.G. Lewis is a sen
14、ior technical analysis engineer of Commercial & Industrial Solutions at Omaha Public Power District, Omaha, NE.LO-09-046 2009, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2009, vol. 115, part 2. For personal use o
15、nly. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.ASHRAE Transactions 493A total of 123 dual-duct CAV and VAV pressure indepen-dent terminal boxes serve the conditioned area. The VAV box dampers are c
16、ontrolled by pneumatic controllers with inputs from the pneumatic thermostats.There are ten single fan dual-duct variable air volume (VAV) AHUs with inlet guide vanes. The design airflow is 45,000 CFM (76,451 m3/h) for both supply fan and return fan. For each AHU, the inlet guide vane was locked at
17、a fixed posi-tion due to lack of control. Thus, the air handling units were operated as constant air volume systems. These AHUs supply conditioned air to the entire building. Each AHU has a differ-ent operation schedule based on the occupied hours of the serving area. The AHU and central plants are
18、shut down when the building is unoccupied. The control valves for cooling coils and heating coils of AHUs are all three-way valves.The central plant consists of chilled water and hot water systems. The chilled water system includes two water cooled centrifugal chillers, 770 ton (2,462 kW) for each,
19、three constant speed primary chilled water pumps, four secondary chilled water pumps, one cooling tower with two constant speed fans, and three constant speed condensing water pumps. The chilled waterside has two parallel circuits with two secondary pumps for each circuit. Circuit 1 serves the cooli
20、ng coils of AHU1 to AHU4, and Circuit 2 serves the cooling coils of AHU5 to AHU10. Each circuit has two secondary pumps in parallel. The hot water system included three gas-fired steam boilers, 13.4 MMBtu/h (3.9 MW) for each, three constant speed circulation pumps and three constant speed secondary
21、pumps. The footprint of the hot water system was 5,000 ft2(464 m2). The central plant was not only serving this building but also an adjacent building for which the service was cut off years ago before the CCLEP. There was an Energy Management Computer System (EMCS) for the central plant only. The p
22、neumatic control of AHUs limited the capability of implementing advanced control.CCLEP MAJOR EVALUATION RESULTS The typical CCLEP process consists of four phases: a walk-through phase (Phase I), a detailed energy audit phase (Phase II), an implementation phase (Phase III) and a follow-up phase (Phas
23、e IV). In Phase I and II evaluation process, the building and facility performance are audited, the comfort and energy consumption issues are identified and advanced tech-nologies are developed as solutions based on comprehensive measurement and evaluation. The work scope is clearly defined. In Phas
24、e III and IV, the implementation and verifica-tion phase, mechanical design requirement and control upgrade specifications are developed. After defining the performance baselines, optimal control strategies are devel-oped and implemented. Comfort improvements and energy savings are identified, docum
25、ented and verified. Trouble-shooting and follow-up maintenance are provided to keep the commissioning persistent.Through the continuous commissioning Phase I and II evaluation process, the evaluation results and major findings for the existing system are summarized as the following: 1. The constant
26、air volume boxes were associated the constant air-volume operated air 1 handling units. Under partial load conditions, the excessive airflow can result in higher fan power and higher thermal energy consump-tion. Also malfunctions on the terminal box dampers, controllers and actuators were identified
27、.2. Due to lack of control, the inlet guide vanes were only used to choke down the airflow of the air handling units without any modulation. With such kind of configuration, the system was operated as constant air volume one. Significant fan power is wasted under partial load condi-tions.3. The chil
28、led water system was configured as a primary-secondary constant water flow system. It was verified and proved through on-site test that the secondary pumps were capable to satisfy the water flow and pressure requirement. The system can be simplified to a single-loop chilled water system.4. All chill
29、ed water and cooling tower pumps are running at constant speed. This will result in high pump power under partial load condition. Moreover, the constant water flow system can the constant speed pumps will add extra cool-ing load on the chillers, and degrade the chiller efficiency due to decreased ch
30、illed water return temperature. CC optimal pump control and pump flow station technology can significantly reduce the energy consumption and improve system efficiency.5. With the constant speed pump in operation, the hot water pump power is wasted under partial load condition. The boiler efficiency
31、is also degrades with the high return hot water temperature. CC optimal pump control and parallel pump control technology can significantly reduce the pump power and improve system efficiency.6. For the hot water system, only one boiler was in operation at one time for the old hot water system. Anot
32、her one was standing by for rotation purpose. The third one was not in use for 15 years since the service was cut-off for the adja-cent building, which had its own heating plant added later. The city code requires a certified engineer 24/7 attention during boiler operation if the heating surface of
33、the boilers exceed 1,000 ft2(93 m2). This plant has 4,000 ft2(372 m2) heating surface so it is too large to exempt the engineer requirement. There was high operation and maintenance cost due to the oversized boiler and city code. During audition, when outside air temperature was 45F (7C), it was obs
34、erved that the temperature differ-ence between supply and return hot water was only 4.4F (-15.3C) while the total power of the associated pumps was measured as 49.6 kW. This indicates significant pump energy was wasted due to constant speed pumps. Figure 1 shows the correlation between the measured
35、494 ASHRAE Transactionsheating energy and outside air temperature. The peak heating load at design condition was identified as 11 MMBtu/h (3 MW) without any retrofits. 7. There was no Energy Management Control System (EMCS). The HVAC system used old pneumatic control. The existing control system has
36、 high risk of control fail-ure, which may cause comfort issues, increase mainte-nance work and is hard for operation. Upgrading all pneumatic controlled valves and actuators to DDC control could improve system control and operation reliability. Based on the evaluation results, the CCLEP process real
37、-ized a series of retrofits, energy conservation control measures and energy savings as presented in the following sections.CCLEP MAJOR RETROFITS To realize the optimal control and better building energy operation and energy performance, a series retrofits are done through the CCLEP process as descr
38、ibed below. For the existing CAV boxes, some interiors CAV boxes are converted into cooling only boxes while the rest are sched-uled to be replaced by VAV boxes. For VAV boxes, the malfunction parts, such as actuator, damper linkage and controller, are identified and replaced or fixed accordingly. I
39、nlet guide vanes (IGV) at the AHUs are adjusted and locked at full open positions. This action eliminate the cost of demolishment of the IGVs and interruption of the system operation. The open IGVs reduced the pressure loss across the vanes and ultimately reduce the fan head. VFDs are installed on b
40、oth the supply fans and return fans for all AHUs. Fan airflow stations are installed for all ten AHUs to improve building pressure control and integrated with static pressure control. Main hot deck dampers are installed for all AHUs for hot deck air control. The outside air intake is determined base
41、d on ASHRAE standard 62.1. In addition, CO2sensors are installed in the return air duct for all AHUs for monitoring purposes. The AHU system shares five newly installed outside air temperature and relative humidity sensors. The economizer dampers are upgraded from pneumatic to DDC control for all AH
42、Us. The three-way control valves for the coils are all converted to two-way valves. Three constant speed primary chilled water pumps are taken out in the central plant to turn the system into a single loop system. VFDs are installed for the secondary chilled water pumps. Pump Flow Stations are insta
43、lled for all chilled water pumps to improve pump speed control and ensure the evaporator minimum water flow requirement. With the Pump Flow Stations, the spontaneous working point of the pump can be tracked with pump head, pump water flow rate, pump speed and pump power provided. Boilers are typical
44、ly designed to be oversized, with redundant safety factors and without consideration of building internal heat gains. Hot water systems, including boilers and hot water pumps, should be sized optimally to meet the maxi-mum demand required by the facility through the heating season. In addition, most
45、 boilers are designed to operate at maximum efficiency when they generate the design output. Significant energy savings can be achieved by optimizing the selection of commercial boiler systems and utilizing proper operation and optimal controls. After a through evaluation and analysis, three old boi
46、lers with a total capacity of 13.4 MMBtu/h (3.9 MW) are replaced by three new boilers with a total capacity of 5.1 MMBtu/h (1.5 MW) after CCLEP. The peak heating load is reduced from 11 MMBtu/h (3.2 MW) to 5 MMBtu/h (1.5 MW). The total heating surface is reduced from 4,000 ft2(372 m2) to 600 ft2(56
47、m2) which exempts the city code of 24/7 attention. Three old hot water pumps are replaced by two new pumps with VFDs installed. One loop differential pressure sensor is installed between the supply and return how water pipes. The boiler house of 5,000 ft2(464 m2) was converted to commercial use, whi
48、ch increased the prop-erty value significantly by $5,000,000 for the building owner. Figure 1 Correlation between the heating energy consumption and the outside air temperature.ASHRAE Transactions 495The new boilers and pumps with a footprint of 800 ft2 (74 m2)were moved to the basement with central
49、 chiller plant. The EMCS is completed to include air handling units control as well as central plant control. The whole control system is upgraded to DDC control.CCLEP OPTIMAL CONTROL STRATEGIESThe optimal control strategies, which include main hot deck damper control, supply fan control integrated with FAS, return fan control, optimal control for terminal boxes, chilled water temperature and chilled water pump speed control, hot water temperature and hot water pump control. Terminal Boxes Since the CAV boxes are retrofitted to VAV boxes, this section is only about the optimal co
