Replacement of existing air-cooled chiller systems by water-cooled chiller systems in commercial buildings in hong kong Essay

Replacement of Existing Air-cooled Chiller Systems by Water-cooled Chiller Systems in Commercial Buildings in Hong Kong

Introduction

Harmonizing to F.W.H. Yik, J. Burnett & A ; I.Prescott, the air-cooled hair-raisers in Hong Kong are normally rated at an out-of-door temperature of 35 oC and COP of the air-cooled hair-raisers including the capacitor fan power is runing from 2.6 to 2.9. For a direct seawater-cooled hair-raiser works with saltwater come ining temperature of 27 oC, COP of the water-cooled hair-raiser works could accomplish 4 to 5. As the electricity ingestion for air-conditioning system in Hong Kong frequently accounts for a dominant part of the operating cost of the shopping composites, water-cooled air-conditioning systems are more preferred than air-cooled air-conditioning systems when infinite is sufficient for such installing and chilling H2O is available at low cost.

In the past old ages, portable H2O supply was chiefly imported from China and the dependability of this important H2O supply has been a major concern in Hong Kong. The usage of fresh H2O in air-conditioning system was banned by Waterworks Regulations in Hong Kong and this discouraged the usage of chilling towers in most commercial edifices including shopping composites. Hence, air-cooled air-conditioning systems were prevalently installed in Hong Kong in the old yearss. In order to conserve electricity and to cut down the emanation of nursery gases by electricity coevals, the Hong Kong Government has put attempt and accent on researching the feasibleness and viability of easing edifices to utilize water-cooled air-conditioning systems alternatively of air-cooled air-conditioning systems. Pilot Scheme for Wider Use of Fresh Water for Evaporative Cooling Towers was launched in June 2000 by the Hong Kong Government. The strategy aims to advance the energy efficient water-cooled air-conditioning systems and to measure the impacts on substructure, wellness and environmental effects with an ultimate purpose to ease territory-wide execution of water-cooled air conditioning systems in Hong Kong.

Technology of Water-cooled Chiller Systems in Commercial Buildings

The air-conditioning systems in edifices work on infrigidation rules by utilizing chilling medium to diminish the indoor air temperatures. In air-cooled air-conditioning systems, heat absorbed by the refrigerant is straight rejected to the ambient ; whereas in water-cooled air-conditioning systems, either fresh H2O or saltwater is used as a heat rejection medium. And heat absorbed by the refrigerant is rejected to the ambient by vaporization through chilling towers or by seawater dispatching into the sea. There are three major strategies in water-cooled air-conditioning systems, viz. , the chilling tower strategy, the cardinal sea H2O strategy, and the territory chilling strategy.

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In the chilling tower strategy, the air conditioning system uses evaporative chilling tower for heat rejection. Water in the chilling tower will be lost due to uninterrupted vaporization, bleed-off and air current impetus. The H2O lost would be replaced by H2O coming from the metropolis H2O brinies.

In cardinal sea H2O strategy, the air conditioning system uses saltwater for heat rejection. A dedicated cardinal sea H2O supply distributes seawater from the sea to the user edifice. The jilted warm jumper from the capacitor will be returned to the sea via dedicated pipe.

In territory chilling strategy, chilled H2O is produced by cardinal chilled H2O works. Individual user purchases chilled H2O for their edifice from the territory chilling strategy operator and do non necessitate to put in their ain hair-raiser workss. For this strategy, a cardinal hair-raiser works, a pump house and a cardinal distribution grapevine web would be required.

Water-cooled air conditioning system rejects heat depending on the ambient wet-bulb temperature instead than the dry-bulb temperature, so the refrigerant can be cooled to a lower temperature. This consequences in a better system coefficient of public presentation ( COP ) and therefore more energy efficient. The District Cooling Scheme and Cooling Tower Scheme are more efficient than conventional air-cooled system every bit much as 35 % and 20 % severally in conformity with a survey commissioned by the Electrical and Mechanical Services Department ( EMSD ) .

Professionals and Cons for Application of Water-cooled Chiller Systems

Equipped water-cooled hair-raisers and chilling tower with VSD and optimise their operation by mechanization control system could efficaciously pare down the peak demand charge, optimise the hair-raiser efficiency in off-design status, and lead to a more efficient operation of the overall water-cooled air-conditioning system.

Variable velocity thrust hair-raiser compressor can be considered as replacing of traditional hair-raiser in the hereafter, as its cost has been bit by bit reduced. The VSD hair-raiser compressor will let the compressor to run at lower velocity under part-load conditions, thereby giving a lower compressor kW/ton evaluation under such state of affairss than utilizing conventional centrifugal hair-raisers where part-load control is by commanding the recess usher vanes.

In the conventional hair-raiser works mechanization control system, it controls the chilling tower to open the valves and get down the tower fan on one-to-one footing even in common heading system. When the condensation H2O temperature beads, the needed compressor caput will cut down. The efficiency of the water-cooled hair-raiser equipped with VSD will better by 4 to 5 % while the come ining condensation H2O temperature beads by 1 oC. It, hence, would be better to run the idle chilling towers in lower velocity in order to foster lower the condensing H2O temperature for the water-cooled hair-raisers so as to increase the efficiency of the hair-raisers. Lower entire fan power ingestion and lower condensation H2O temperature are resulted. As a consequence, optimisation of the hair-raiser and chilling tower operation with mechanization control system as above would foster increase efficiency of the water-cooled hair-raiser works.

The operating scheme of the multiple hair-raisers is besides important to accomplish efficient operation of the hair-raisers. For multiple hair-raisers runing at a part-load status, the 2nd hair-raiser should non be brought online until the first 1 is up to a pre-determined capacity. By and large, the least energy is used by one hair-raiser operating at 90 % capacity as compared with that used by two hair-raisers each operating at 45 % capacity. Retrofiting the bing air-cooled hair-raiser works with new water-cooled hair-raiser works could normally rectify the jobs of burden mismatching, low dependability of the bing hair-raiser works.

Extra benefit from the transition of air-cooled to water-cooled hair-raiser works would be the betterment of system dependability and minimisation of system downtime when all the water-cooled hair-raisers are furnished with variable velocity thrust as the starting motors. In instance of power loss, the restart clip of hair-raiser could be reduced from 30 proceedingss to 5 proceedingss when compared with the conventional and typical EM starting motor. Furthermore, after the transition of the water-cooled hair-raiser, less power would be consumed which means less CO2 emanation. This would cut down the green house consequence.

There are however some restrictions and possible hazards for replacing the bing air-cooled air-conditioning system with new water-cooled chilling tower system. Noise from chilling towers, dead H2O in dead legs of H2O pipe or in idle system, alimentary growing due to taint from environing countries and exposure to direct sunshine, hapless H2O quality such as Legionella count, lacks in chilling tower system, separation of the chilling towers and entree to bing building/residents, and occupational safety and wellness issues are all have to be dealt with carefully during the design phase, the installing phase every bit good as the operation and care phase. Appropriate chilling tower system design, regular and proper care including H2O intervention to the chilling tower system, and one-year audit are all necessary to minimise the possible hazards from the chilling tower system.

Besides, transition of the bing air-cooled hair-raiser works to water-cooled hair-raiser works takes up more infinites as the extra air-conditioning equipment including chilling towers, distilling H2O pumps, H2O armored combat vehicles, distilling H2O pipes, etc. shall be incorporated into the system and all of the equipment and the structural supporting frames for chilling towers and H2O armored combat vehicles require extra infinites. Like topographic points in Hong Kong where it is so dumbly populated and infinite is really limited with really high land monetary value, optimum use of edifice infinites is a really of import factor which the landlords would see.

Model to Access Efficiency Improvement – Execution of Load-based Speed Control for System Optimization in Water-cooled Chiller Systems

The system COP means the hair-raiser burden end product divided by the entire input power of the hair-raiser, capacitor H2O pump and chilling tower fan. For conventional operation of chilling towers, the fans are cycled on and off, or controlled at variable velocity to keep the temperature of chilling H2O go forthing the tower at its set point. The capacitor H2O pump is staged continuously to supply the hair-raiser runing with the rated flow of capacitor H2O for all loading conditions.

In conformity with the surveies performed by F. W. Yu and K. T. Chan, load-based control could be applied to heighten the energy public presentation of water-cooled hair-raiser systems. Thermodynamic-behavior hair-raiser and chilling tower theoretical accounts were developed to happen out how the energy usage varies for a hair-raiser system runing under assorted controls of capacitor H2O pumps and chilling tower fans. The optimal operation of the water-cooled hair-raiser systems could be obtained via the load-based velocity control which the velocity of the chilling tower fans and the capacitor H2O pumps is regulated as a additive map of the hair-raiser portion burden ratio. It resembles the typical sequencing of hair-raisers based on their burden conditions and without the demand of high quality humidness detectors to reset the chilling H2O temperature. The system COP under the optimum control could increase by 1.4 % to 16.1 % when compared with the tantamount system of fixed temperature and flow rate control for the chilling H2O go forthing the chilling towers.

Improvement in system public presentation could be achieved by using variable velocity control to the capacitor H2O pumps and the chilling tower fans. To optimise the system, the capacitor H2O flow rate would change in direct proportion to the hair-raiser burden. This consequences in the control algorithm of pump velocity ( Spump, op ) shown in Equation ( 1 ) , given that velocity is straight relative to flux rate in conformity with the pump Torahs. The minimal velocity is set at half of the full velocity ( Spump, full ) to guarantee the minimal capacitor H2O flow required when the hair-raiser burden in footings of portion burden ratio ( PLR ) drops to below 0.5.

Spump, op = ( 1 )

Following the traditional control of chilling H2O temperature, the accountant for tower fan velocity transition has to measure the optimal set point ( Tctwl, op ) and operates the fan at the right velocity to run into that set point. Based on the analysis by F. W. Yu and K. T. Chan, it is possible to use load-based velocity control for chilling tower fans so as to accomplish optimal system operation. Figure 4 shows informations of the optimal fan velocity at which the upper limit system COP took topographic point for a set of operating conditions in footings of assorted combinations of PLRs from 0.2 to 1 at 0.1 intervals and wet-bulb temperatures from 16 to 28 DegC at 4 DegC intervals. Using arrested development analysis, a additive relationship between the optimal fan velocity ( Sfan, op ) and chiller PLR can be obtained as Equation ( 2 ) with the coefficient of finding ( R2 ) of 0.9215. Sfan, full denotes the full velocity of the tower fans and the changeless coefficients would be different for each specific design of the system.

Sfan, op = ( 0.7281PLR + 0.1776 ) Sfan, full ( 2 )

It is expected that the load-based velocity control is generic for all types of multiple-chiller systems with full or partial usage of variable velocity thrusts for the system constituents. The optimum control of the whole system could be extremely simplified in this manner as the sequencing of hair-raisers, pumps and tower fans and their single velocity controls can be based wholly on the hair-raiser burden conditions merely. The system COP under the optimum control could increase by 1.4 % to 16.1 % when compared with the tantamount system of fixed temperature and flow rate control for the chilling H2O go forthing the chilling towers.

Decision

Retrofiting the bing air-cooled hair-raiser works with new water-cooled hair-raiser works could normally rectify the jobs of burden mismatching and low dependability of the bing hair-raiser works. A better system coefficient of public presentation ( COP ) and therefore more energy efficient would be achieved. The application of water-cooled hair-raiser system is more efficient than the conventional air-cooled system for every bit much as 35 % . Execution of the load-based velocity control for the system could farther increase the system COP by every bit much as around 16 % .

Mentions:

1 ) F.W. Yu, K.T. Chan, Economic benefits of optimum control for water-cooled hair-raiser systems functioning hotels in a semitropical clime, Energy and Buildings ( 2009 ) 1-7.

2 ) F.W.H. Yik, J. Burnett, I. Prescott, A survey on the energy public presentation of three strategies for widening application of water-cooled air-conditioning systems in Hong Kong, Energy and Buildings 33 ( 2001 ) 167-182.

3 ) F.W. Yu, K.T. Chan, Energy signatures for measuring the energy public presentation of hair-raisers, Energy and Buildings 37 ( 2005 ) 739-746.

4 ) F.W. Yu, K.T. Chan, Optimization of water-cooled hair-raiser system with load-based velocity control, Applied Energy 85 ( 2008 ) 931-950.

5 ) Jerry Ackerman, What a Water-cooled HVAC System Can Make for Your Building, Buildings 102 ( 3 ) ( 2008 ) 72-76.

6 ) Jeff Strein, Air- or Water-cooled, ASHRAE Journal ( 7 ) ( 2009 ) 11-12.

7 ) Electrical & A ; Mechanical Services Department, Code of Practice for Water-cooled Air Conditioning Systems, Part 1: Design, Installation and Commissioning of Cooling Towers 2006 Edition ( 1 ) ( 2007 ) 1-37.

8 ) Electrical & A ; Mechanical Services Department, Energy Efficiency and Conservation for Buildings 1-40.

9 ) Electrical & A ; Mechanical Services Department, Code of Practice for Energy Efficiency of Air Conditioning Installations 2007 Edition 1-30.

10 ) Electrical & A ; Mechanical Services Department, Implementation Study for Water-cooled Air-Conditioning Systems at Wan Chai and Causeway Bay – Probe ( 7 ) ( 2005 ) 1-31.

11 ) Electrical & A ; Mechanical Services Department, Guidelines on Energy Efficiency of Air Conditioning Installations 1998 Edition 1-42.

12 ) Electrical & A ; Mechanical Services Department, Hong Kong Energy End-use Data 2008 ( 9 ) ( 2008 ) 1-39.

13 ) Ben Erpelding, Real Efficiency of Central Plants, Heating Piping Air Conditioning Engineering ( 5 ) ( 2007 )

14 ) Trane, Implications for Chilled-Water Plant Design, Engineers Newsletter Volume 28 No. 1 1-4.

15 ) W.L. Lee, Hua Chen, F.W.H. Yik, Modeling the public presentation features of water-cooled air-conditioners, Energy and Buildings 40 ( 2008 ) 1456-1465.

16 ) Electrical & A ; Mechanical Services Department, Territory-Wide Implementation Study for Water-cooled Air Conditioning Systems in Hong Kong ( 6 ) ( 2003 ) 1-28.

17 ) Ramez Naguib, Total Cost of Ownership for Air-Cooled and Water-cooled Chiller Systems, ASHRAE Journal ( 4 ) ( 2009 ) 42-48.

18 ) Trane, Promoting the Use of Water Cooled Air Conditioning System, Trane Newsletter 2 ( 9 ) ( 2005 ) 1-3.