Efficiency Centrifugal Chiller
Effect on Energy Savings and Reduction in CO 2 Emissions through Application of a HighEfficiency Centrifugal Chiller JUNNOSUKE NAKATANI*1 WATARU SEKI*2 MASAHIRO ISHII*2 FUTOSHI NISHIZAKI*2
Air-conditioning accounts for a large portion of the energy consumed by industrial and commercial facilities. More specifically, according to the Energy Conservation Center, Japan (ECCJ), air-conditioning amounts to approximately 40% of the energy consumed in commercial buildings such as shopping malls. Energy-efficient air-conditioning should therefore make an important contribution to the reduction in CO2 emissions. In response to such needs, Mitsubishi Heavy Industries, Ltd. (MHI) provides energy-saving solutions based on centrifugal chillers that produce an excellent level of efficiency. At the core of these solutions is the achievement of complete optimization by providing consistent heat source solution services commensurate with the life cycle of products and systems to promote more effective energy-savings. Here we introduce MHI’s involvement in this field.
open impellers that allow high-precision machining and eliminate the breakaway and stagnation of refrigerant gas flow. The compressor is designed with flow analysis including static channels, and it is more efficient than earlier models. An additional capacity control mechanism installed at the inlet of the second stage impellers has improved the efficiency in low-load operations. Furthermore, highcapacity machines, with inverter specifications, are also available so that the entire series of products successfully achieves the optimal rotational speed control and expands the zones of operation based on the operating conditions. As a result, the load tracking control remains efficient even if the cooling water inlet temperature falls to 12°C, contributing to dramatically improving the partial load performance (coefficient of performance, COP) as shown in Fig. 1.
1. Features of centrifugal chillers with exceptional levels of efficiency 1 The following section describes features of the latest cent r i f uga l chil ler models developed by M H I , which represent the key technology to energy-saving solutions. The refrigerant used in the chillers is HFC-134a, which does not destroy the ozone layer. Moreover, modifications and improvements to the compressors, heat exchangers, and other units achieve higher performance over the entire range of operation. The centrifugal compressor is equipped with two-stage
Major improvement in characteristics Cooling water inlet temperature
Comparison index (100 = value before the solution was implemented)
COP
Inverter machine (AART-I series) 22 20 18 16 14 12 10 8 6 4 2 0
: AART-I 12°C : AART-I 20°C : AART-I 25°C : AART-I 32°C : NART-I 13°C : NART-I 20°C : NART-I 25°C : NART-I 32°C
20
40 60 Load (%)
80 100
: Estimated reduction before the solution was implemented : Actual reduction after the solution was implemented
Reduction of about 70%
Running costs
Fig. 1 Partial load characteristics of the variable speed drive centrifugal chiller (chilled water outlet temperature: 7°C) The diagram shows a major improvement in the par tial load characteristics. The coefficient of performance (COP) can be expressed by the following equation. COP = output energy/input energy
Reduction of about 60%
Primary energy consumption
Reduction of about 65%
CO2 emissions
Fig. 2 Effects of reducing energy consumption and CO2 emissions The diagram shows that implementing the solution greatly reduces the yearly running costs and CO2 emissions.
*1 Takasago Research & Development Center, Technical Headquarters *2 Air-Conditioning & Refrigeration Systems Headquarters
73
Mitsubishi Heavy Industries, Ltd. Technical Review Vol. 45 No. 1 (Mar. 2008)
After introducing the solution Variable speed drive centrifugal chillers (360USRt × 2 units) - Introducing high-efficiency variable speed drive centrifugal chillers (major reduction in power consumption under partial load operation during intermediate seasons and winter) - Using the high-capacity cooling tower and cooling water pump of the absorption chiller (lowering cooling water temperatures and variable flow control of cooling water)
Steam
Steam-type absorption 6°C chiller 360USRt chilled water Steam
6°C Steam-type absorption chilled chiller 360USRt water
Chilled water reservoir tank
6°C chilled water
Electricity
Electricity
Variable speed drive centrifugal chillers 360USRt
6°C chilled water
6°C chilled water
Variable speed drive centrifugal chillers 360USRt
6°C chilled water
Load heat exchanger
Chilled water reservoir tank
Before introducing the solution Steam-type absorption chiller (360USRt × 2 units)
Load heat exchanger
Fig. 3 Example of an introduced solution An example in which the centrifugal chiller replaces the steam-type absorption chiller.
chiller. This contributes to a major reduction in power consumpt ion dur ing pa r t ia l load operat ions in t he intermediate seasons and winter. (2) By effectively using the existing high-capacity cooling tower and the cooling water pump of the steam-type absor ption chiller, the resulting lower temperature cooling water and variable f low control of the cooling water help save more energy than was previously possible.
2. Case study of a solution for saving energy and reducing CO2 emissions T his sect ion int roduces a solut ion proposed to the Takasago plant of Suntory Ltd. Heating and cooling take place at various temperatures in this food and beverage factory, which requires a heat source capable of coping with loads that vary considerably. The proposed energysaving solution satisfied these requirements while achieving 6 0 % or more in energ y savings and reductions in CO 2 emissions (Fig. 2). Figure 3 provides a schematic of the proposal. The main points of the proposal are as follows. (1) A high- ef f iciency, variable speed drive centrif ugal chiller has replaced the existing steam-type absorption
3. Solution proposal scheme Figure 4 shows the schematic f low of events in the proposal in which the latest system technology improves the chiller, and its peripheral equipment and air conditioner reduce energy consumption. The flow of events is as follows.
Accurately interpret current conditions
2 1
3 CO2 DOWN
Assess client requirements
6
Measure and diagnose
Plan and study
Provide a complete solution to eliminate client concerns Reduce Energy Cost CO2 emissions savings reduction
Propose and implement a variety of solutions from the service menu, including remote monitoring service, operation, maintenance, and after-sales service
4
Total optimization
5 Propose solution plans Design and installation
Fig. 4 Energy-saving solution proposal scheme showing the event flow of the solution proposal commensurate with the life cycle of products and systems
Mitsubishi Heavy Industries, Ltd. Technical Review Vol. 45 No. 1 (Mar. 2008)
74
Remote monitoring system Client Monitoring center
• Periodical maintenance • Mobilization in an emergency
Internet or public phone line monitoring
• Monitoring operation data at monitoring center • In an emergency, the manufacturer’s service engineer diagnoses data to offer appropriate instructions to local service personnel
• Emergency measures and disposition report • Reporting periodical operation data • Recommending appropriate maintenance based on data Fig. 5 Outline of the remote monitoring service
Air conditioner
Chilled water 1360m /h 3
4747kW 1350RT 8°C
- t 3°C
User, air conditioner Supplier, heat source
5°C
Chilled water pump Cooling water pump Cooling tower Centrifugal chiller 1350RT 30kW 110kW 454m3/h Coping with a chilled water flow rate that exceeds the rated flow rate reduces the number of chillers in operation.
Excess operation
Chilled water pump Cooling water pump Cooling tower Centrifugal chiller 1350RT 30kW 110kW 454m3/h
Chilled water pump Cooling water pump Cooling tower Centrifugal chiller 1350RT 30kW 110kW 454m3/h Air conditioner
Chilled water 1360m3/h
4747kW 1350RT 8°C
User, air conditioner
- t 3°C
Supplier, heat source
5°C
Cooling water pump Cooling tower 30kW 110kW Group of chilled water pumps, pumping a maximum of 1360m3/h
Centrifugal chiller 1350RT
Fig. 6 Outline of the variable over water volume system (patented) Coping with a chilled water flow rate that exceeds the rated flow rate reduces the number of chillers in operation, which in turn reduces energy consumption.
(1) C ol lec t i n for mat ion f rom t he cl ient on t he configuration of the facility and its operating conditions, energy consumption, and other details. (2) If necessary, measure the operat ion parameters of the facilit y and diagnose them to study the items requiring energy-saving.
(3) Based on the study results, use simulation or another method to calculate the energy-saving effect. (4) At a stage when the effect is confirmed, compile the study results into a solution proposal for submission to the client. (5) Discuss the proposal with the client. Upon securing the client’s Mitsubishi Heavy Industries, Ltd. Technical Review Vol. 45 No. 1 (Mar. 2008)
75
approval, begin detailed design and installation. (6) After installation, provide the client with solutions to the chiller operation, including support for energy-saving operations through remote monitoring and equipment diagnosis 24 hours a day, 365 days a year (Fig. 5) and 15-year operation support for functions, stable operation, and performance maintenance. Given this after-sales service menu, checking the operating conditions of the equipment and implementing appropriate maintenance enables the improvements to be evaluated and confirmed. This helps the client to better appreciate the major energy savings compared to a singleunit energy-saving proposal.
of the entire facility. To improve these situations, Mitsubishi Jisho Sekkei Inc. and MHI have codeveloped a Variable over water volume system. Figure 6 shows an outline of this system. To reduce the number of chillers in operation, the system can handle the flow rate of chilled water that exceeds the rated flow rate, enabling the system to reduce energy consumption. 4.2 Stealth Turbo ® system Facilities equipped with two or more absorption chillers to cope with peak loads in summer must operate fewer chillers under partial load during the intermediate seasons and winter when the load is generally reduced. In many cases like this, the entire facility is likely to operate at low efficiency. We suggest that clients in this situation install a smallcapacity centrifugal chiller, the Stealth Turbo ®, to realize energ y savings without investing money by increasing the contract power capacity. Mitsubishi Jisho Sekkei Inc., SANKI Engineering Co., LTD and MHI have codeveloped this system, which is outlined in Fig. 7.
4. System examples applying chillers The solution proposals involving the centrifugal chiller are divided into a variety of aspects covering the variable flow control of chilled water and cooling water, free cooling, and reuse of waste heat. The following sections introduce actual energy-saving proposals employing systems around chillers. 4.1 Variable over water volume system Genera lly, t her mal loads should be reduced in t he intermediate seasons and winter. However, depending on the control on the load circuit, the heat exchanger characteristics, and other factors, the reduction in the thermal loads may not be proportional to the reduction in the flow. This makes the temperature difference smaller between the supply water temperature and return water temperature, and is more likely to lead to nonreduction of the load flow. In facilities where the system controls two or more chillers, more than the necessary number of chillers are likely to operate in many cases, which lowers the efficiency
5. Conclusions Reducing energy consumption and CO2 emissions is one of the most critical issues facing the world. Given these circumstances, we have introduced MHI’s involvement in providing consistent heat source solutions from facility investment planning and installation to after-sales service. T hese solutions optimize the air conditioners and heat source facility to effectively reduce energy consumption and CO2 emissions. MHI’s home page at the URL below provides valuable information for clients. Air-Conditioning & Refrigeration Systems Headquarters URL: http://www.mhi.co.jp/en/aircon/index.html Reference
Cooling tower
Cooling tower
Absorption chiller
Absorption chiller
Absorption chiller
Small-capacity, high-efficiency centrifugal chiller
Stealth Turbo® system
Cooling tower
1. Seki, W. et al., New Model Turbo Chiller, AART Series, Contributes to the Reduction of Energ y Consumption under Year-Round Operation, Mitsubishi Heavy Industries Technical Review Vol.43 No.2 (2006) p.41
Junnosuke Nakatani
Wataru Seki
Masahiro Ishii
Chilled water header (return) Chilled water header (supply) Fig. 7 Outline of the Stealth Turbo® system (patent pending) A bypass circuit is hooked up to the existing chilled water and cooling water pipe lines to install a small-capacity, high-efficiency centrifugal chiller.
Futoshi Nishizaki
Mitsubishi Heavy Industries, Ltd. Technical Review Vol. 45 No. 1 (Mar. 2008)
76
Air-conditioning accounts for a large portion of the energy consumed by industrial and commercial facilities. More specifically, according to the Energy Conservation Center, Japan (ECCJ), air-conditioning amounts to approximately 40% of the energy consumed in commercial buildings such as shopping malls. Energy-efficient air-conditioning should therefore make an important contribution to the reduction in CO2 emissions. In response to such needs, Mitsubishi Heavy Industries, Ltd. (MHI) provides energy-saving solutions based on centrifugal chillers that produce an excellent level of efficiency. At the core of these solutions is the achievement of complete optimization by providing consistent heat source solution services commensurate with the life cycle of products and systems to promote more effective energy-savings. Here we introduce MHI’s involvement in this field.
open impellers that allow high-precision machining and eliminate the breakaway and stagnation of refrigerant gas flow. The compressor is designed with flow analysis including static channels, and it is more efficient than earlier models. An additional capacity control mechanism installed at the inlet of the second stage impellers has improved the efficiency in low-load operations. Furthermore, highcapacity machines, with inverter specifications, are also available so that the entire series of products successfully achieves the optimal rotational speed control and expands the zones of operation based on the operating conditions. As a result, the load tracking control remains efficient even if the cooling water inlet temperature falls to 12°C, contributing to dramatically improving the partial load performance (coefficient of performance, COP) as shown in Fig. 1.
1. Features of centrifugal chillers with exceptional levels of efficiency 1 The following section describes features of the latest cent r i f uga l chil ler models developed by M H I , which represent the key technology to energy-saving solutions. The refrigerant used in the chillers is HFC-134a, which does not destroy the ozone layer. Moreover, modifications and improvements to the compressors, heat exchangers, and other units achieve higher performance over the entire range of operation. The centrifugal compressor is equipped with two-stage
Major improvement in characteristics Cooling water inlet temperature
Comparison index (100 = value before the solution was implemented)
COP
Inverter machine (AART-I series) 22 20 18 16 14 12 10 8 6 4 2 0
: AART-I 12°C : AART-I 20°C : AART-I 25°C : AART-I 32°C : NART-I 13°C : NART-I 20°C : NART-I 25°C : NART-I 32°C
20
40 60 Load (%)
80 100
: Estimated reduction before the solution was implemented : Actual reduction after the solution was implemented
Reduction of about 70%
Running costs
Fig. 1 Partial load characteristics of the variable speed drive centrifugal chiller (chilled water outlet temperature: 7°C) The diagram shows a major improvement in the par tial load characteristics. The coefficient of performance (COP) can be expressed by the following equation. COP = output energy/input energy
Reduction of about 60%
Primary energy consumption
Reduction of about 65%
CO2 emissions
Fig. 2 Effects of reducing energy consumption and CO2 emissions The diagram shows that implementing the solution greatly reduces the yearly running costs and CO2 emissions.
*1 Takasago Research & Development Center, Technical Headquarters *2 Air-Conditioning & Refrigeration Systems Headquarters
73
Mitsubishi Heavy Industries, Ltd. Technical Review Vol. 45 No. 1 (Mar. 2008)
After introducing the solution Variable speed drive centrifugal chillers (360USRt × 2 units) - Introducing high-efficiency variable speed drive centrifugal chillers (major reduction in power consumption under partial load operation during intermediate seasons and winter) - Using the high-capacity cooling tower and cooling water pump of the absorption chiller (lowering cooling water temperatures and variable flow control of cooling water)
Steam
Steam-type absorption 6°C chiller 360USRt chilled water Steam
6°C Steam-type absorption chilled chiller 360USRt water
Chilled water reservoir tank
6°C chilled water
Electricity
Electricity
Variable speed drive centrifugal chillers 360USRt
6°C chilled water
6°C chilled water
Variable speed drive centrifugal chillers 360USRt
6°C chilled water
Load heat exchanger
Chilled water reservoir tank
Before introducing the solution Steam-type absorption chiller (360USRt × 2 units)
Load heat exchanger
Fig. 3 Example of an introduced solution An example in which the centrifugal chiller replaces the steam-type absorption chiller.
chiller. This contributes to a major reduction in power consumpt ion dur ing pa r t ia l load operat ions in t he intermediate seasons and winter. (2) By effectively using the existing high-capacity cooling tower and the cooling water pump of the steam-type absor ption chiller, the resulting lower temperature cooling water and variable f low control of the cooling water help save more energy than was previously possible.
2. Case study of a solution for saving energy and reducing CO2 emissions T his sect ion int roduces a solut ion proposed to the Takasago plant of Suntory Ltd. Heating and cooling take place at various temperatures in this food and beverage factory, which requires a heat source capable of coping with loads that vary considerably. The proposed energysaving solution satisfied these requirements while achieving 6 0 % or more in energ y savings and reductions in CO 2 emissions (Fig. 2). Figure 3 provides a schematic of the proposal. The main points of the proposal are as follows. (1) A high- ef f iciency, variable speed drive centrif ugal chiller has replaced the existing steam-type absorption
3. Solution proposal scheme Figure 4 shows the schematic f low of events in the proposal in which the latest system technology improves the chiller, and its peripheral equipment and air conditioner reduce energy consumption. The flow of events is as follows.
Accurately interpret current conditions
2 1
3 CO2 DOWN
Assess client requirements
6
Measure and diagnose
Plan and study
Provide a complete solution to eliminate client concerns Reduce Energy Cost CO2 emissions savings reduction
Propose and implement a variety of solutions from the service menu, including remote monitoring service, operation, maintenance, and after-sales service
4
Total optimization
5 Propose solution plans Design and installation
Fig. 4 Energy-saving solution proposal scheme showing the event flow of the solution proposal commensurate with the life cycle of products and systems
Mitsubishi Heavy Industries, Ltd. Technical Review Vol. 45 No. 1 (Mar. 2008)
74
Remote monitoring system Client Monitoring center
• Periodical maintenance • Mobilization in an emergency
Internet or public phone line monitoring
• Monitoring operation data at monitoring center • In an emergency, the manufacturer’s service engineer diagnoses data to offer appropriate instructions to local service personnel
• Emergency measures and disposition report • Reporting periodical operation data • Recommending appropriate maintenance based on data Fig. 5 Outline of the remote monitoring service
Air conditioner
Chilled water 1360m /h 3
4747kW 1350RT 8°C
- t 3°C
User, air conditioner Supplier, heat source
5°C
Chilled water pump Cooling water pump Cooling tower Centrifugal chiller 1350RT 30kW 110kW 454m3/h Coping with a chilled water flow rate that exceeds the rated flow rate reduces the number of chillers in operation.
Excess operation
Chilled water pump Cooling water pump Cooling tower Centrifugal chiller 1350RT 30kW 110kW 454m3/h
Chilled water pump Cooling water pump Cooling tower Centrifugal chiller 1350RT 30kW 110kW 454m3/h Air conditioner
Chilled water 1360m3/h
4747kW 1350RT 8°C
User, air conditioner
- t 3°C
Supplier, heat source
5°C
Cooling water pump Cooling tower 30kW 110kW Group of chilled water pumps, pumping a maximum of 1360m3/h
Centrifugal chiller 1350RT
Fig. 6 Outline of the variable over water volume system (patented) Coping with a chilled water flow rate that exceeds the rated flow rate reduces the number of chillers in operation, which in turn reduces energy consumption.
(1) C ol lec t i n for mat ion f rom t he cl ient on t he configuration of the facility and its operating conditions, energy consumption, and other details. (2) If necessary, measure the operat ion parameters of the facilit y and diagnose them to study the items requiring energy-saving.
(3) Based on the study results, use simulation or another method to calculate the energy-saving effect. (4) At a stage when the effect is confirmed, compile the study results into a solution proposal for submission to the client. (5) Discuss the proposal with the client. Upon securing the client’s Mitsubishi Heavy Industries, Ltd. Technical Review Vol. 45 No. 1 (Mar. 2008)
75
approval, begin detailed design and installation. (6) After installation, provide the client with solutions to the chiller operation, including support for energy-saving operations through remote monitoring and equipment diagnosis 24 hours a day, 365 days a year (Fig. 5) and 15-year operation support for functions, stable operation, and performance maintenance. Given this after-sales service menu, checking the operating conditions of the equipment and implementing appropriate maintenance enables the improvements to be evaluated and confirmed. This helps the client to better appreciate the major energy savings compared to a singleunit energy-saving proposal.
of the entire facility. To improve these situations, Mitsubishi Jisho Sekkei Inc. and MHI have codeveloped a Variable over water volume system. Figure 6 shows an outline of this system. To reduce the number of chillers in operation, the system can handle the flow rate of chilled water that exceeds the rated flow rate, enabling the system to reduce energy consumption. 4.2 Stealth Turbo ® system Facilities equipped with two or more absorption chillers to cope with peak loads in summer must operate fewer chillers under partial load during the intermediate seasons and winter when the load is generally reduced. In many cases like this, the entire facility is likely to operate at low efficiency. We suggest that clients in this situation install a smallcapacity centrifugal chiller, the Stealth Turbo ®, to realize energ y savings without investing money by increasing the contract power capacity. Mitsubishi Jisho Sekkei Inc., SANKI Engineering Co., LTD and MHI have codeveloped this system, which is outlined in Fig. 7.
4. System examples applying chillers The solution proposals involving the centrifugal chiller are divided into a variety of aspects covering the variable flow control of chilled water and cooling water, free cooling, and reuse of waste heat. The following sections introduce actual energy-saving proposals employing systems around chillers. 4.1 Variable over water volume system Genera lly, t her mal loads should be reduced in t he intermediate seasons and winter. However, depending on the control on the load circuit, the heat exchanger characteristics, and other factors, the reduction in the thermal loads may not be proportional to the reduction in the flow. This makes the temperature difference smaller between the supply water temperature and return water temperature, and is more likely to lead to nonreduction of the load flow. In facilities where the system controls two or more chillers, more than the necessary number of chillers are likely to operate in many cases, which lowers the efficiency
5. Conclusions Reducing energy consumption and CO2 emissions is one of the most critical issues facing the world. Given these circumstances, we have introduced MHI’s involvement in providing consistent heat source solutions from facility investment planning and installation to after-sales service. T hese solutions optimize the air conditioners and heat source facility to effectively reduce energy consumption and CO2 emissions. MHI’s home page at the URL below provides valuable information for clients. Air-Conditioning & Refrigeration Systems Headquarters URL: http://www.mhi.co.jp/en/aircon/index.html Reference
Cooling tower
Cooling tower
Absorption chiller
Absorption chiller
Absorption chiller
Small-capacity, high-efficiency centrifugal chiller
Stealth Turbo® system
Cooling tower
1. Seki, W. et al., New Model Turbo Chiller, AART Series, Contributes to the Reduction of Energ y Consumption under Year-Round Operation, Mitsubishi Heavy Industries Technical Review Vol.43 No.2 (2006) p.41
Junnosuke Nakatani
Wataru Seki
Masahiro Ishii
Chilled water header (return) Chilled water header (supply) Fig. 7 Outline of the Stealth Turbo® system (patent pending) A bypass circuit is hooked up to the existing chilled water and cooling water pipe lines to install a small-capacity, high-efficiency centrifugal chiller.
Futoshi Nishizaki
Mitsubishi Heavy Industries, Ltd. Technical Review Vol. 45 No. 1 (Mar. 2008)
76
