CQM_Taikoo

Energy Saving Report for CQM Automatic Tube Cleaning System in Taikoo Place

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Energy Saving Report of

CQM Automatic Tube Cleaning System

in

Taikoo Place

by

Wallace Wu & Dave Chan


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Energy Saving Report of CQM Automatic Tube Cleaning System in Taikoo Place Project Background Taikoo Place is the commercial hub in Hong Kong Island east. It comprises of 9 buildings with over 4 million square feet office space. The buildings are using water-cooled air-conditioning with seawater cooling towers. In 2002, Swire installed one number of CQM Automatic Tube Cleaning System ( ATCS) in the 700 tons water-cooled chiller in Oxford House. After a few months of operation, it was found that CQM could improve the overall heat transfer efficiency of the condenser and save significant amount of energy.. Thereafter, in 2003, Swire decided to install CQM to the other 11 number of sea water-cooled chillers in the following buildings Dorset House : A 610,000 sq. ft. 39-storey office tower Oxford House : A 500,000 sq. ft. 40-storey Grade A office building with 183 car park spaces Lincoln House : A 342,000 sq. ft. 23-storey office tower overlooking the harbour with 164 car park spaces. Somerset House. : A 923,000 sq. ft. 22-floor Techno Centre with 80 car parking spaces ATAL Engineering Ltd. was appointed by Swire to carry out the contract work. Project Description The contract work includes the supply & installation of CQM to the following chillers :-

Oxford House Chiller : Chiller No.1 & 3 Tonnage of each chiller : 700 ton Model of CQM : CQM-10

Fig. 1

Lincoln House Chiller : Chiller No.1 ,2 & 3 Tonnage of each chiller : 400 ton Model of CQM : CQM-10 Fig. 2

Dorset House Chiller : Chiller No.1 ,2 & 3 Tonnage of each chiller : 1540 ton Model of CQM : CQM-18 Fig. 3


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Somerset House Chiller : Chiller No.1 ,2 & 3 Tonnage of each chiller : 780 ton Model of CQM : CQM-12 Fig. 4

CQM System Description In this project, two different types of systems were used. For Oxford & Dorset House, it used air injection system while Lincoln & Somerset House, it used water injection system.

This standard system for seawater uses air pressure to inject the sponge balls via the injector into the heat exchanger inlet pipe and through the check valve. The ball trap is installed on the main outlet of the heat exchanger. Both inline and angular ball traps are available. The balls return to the collector through the ball valve. The cycle is fully automatic and controlled by the PLC commander. The system consists of two automatic valves; one solenoid valve for air direction, and a 1 automatic ball valve that controls the drain

Air injection Configuration ( Oxford & Dorset House )

Fig. 5

The Water Injection and Drain System uses to its advantage the fact that the pressure in the heat exchanger main outlet is higher than that of the inlet, (circulation pump is installed after the heat exchanger). It is suitable for low and high-pressure systems. The sponge balls are injected by water pressure through the check valve into the main inlet of the heat exchanger. The balls return to the collector through the check valve. The cycle is fully automatic and controlled by the PLC commander. The system consists of two automatic valves, the first, a 1 ball valve that controls water injection, the second 1 ball valve that controls the drain.

Water injection Configuration ( Lincoln & Somerset House )

Compressor

Fig. 6


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Energy Saving from CQM System As the condenser is the important component in chiller, the operating condition of the condenser is the key factor that affects the efficiency of the unit. However, the condenser will be seriously deteriorated by the debris and foulants accumulated in the tubes of the condensers immediately after the unit comes into operating. When fouling and scaling in the condenser increase, the power consumption of chiller will increase too, as result the efficiency of chiller will decrease. Referring to the Condenser Fouling Factor Chart (Table 1) taken from the Carrier Handbook. This table shows that with an approximate 0.6mm scale thickness, an increase of 170% in heat transfer area is needed. Also, with the same thickness of scale formation, the Fouling Thermal Resistance is approximately 0.002, where it shows in the graph that an increase of 22% horsepower per ton is needed to obtain optimum performance.

Table 1 - Heat Transfer Surface Required to Offset Fouling

Fouling Thermal Resistance

(hr) (sq ft) (deg F temp diff) / t

Overall Transfer Coefficient

Btu/(hr) (sq ft) (deg F temp)*

Thickness Scale Approx.

(mm)

Increase in Heat Transfer Area Reqd.

(Approximate %)

Clean Tube 850 0 0

0.0005 595 0.15 45

0.001 460 0.3 85

0.002 315 0.6 170

0.003 240 0.9 250

Chart 1 - Effect of Scale on Energy Consumption of Chillers

Relative Horespower per Ton in Percent at 40F Suction

Source: Philip Kotz Clean system Approach to Air Conditioning Heating, Piping and Air Conditioning Journal

CQM automatic tube condenser cleaning system clean the condenser tubes and eliminate tubing fouling by removing debris from tube surfaces as often as they are deposited. This enables the condensers and heat exchanger to operate at 100% of rated capacity.

140%

130%

120%

110%

100% 0 0.3 0.6 0.9 1.2 Scale Thickness (mm)


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Objectives of the report

The objective of this report is to calculate the energy saving of using CQM - Automatic Tube Clearing System for the sea water-cooled chillers. The data on chiller operation were collected before and after the CQM installation which enable the study of effectiveness of the system in improving the working condition and in reducing energy used. Analysis Approaches and Basic Theory Swire kept log of all the working parameters of the chiller plant operation on hourly basis everyday. The approach is to analyze the data before and after the installation with period as follows :- Before CQM installation : July December 2002 After CQM installation : July December 2003 The first analysis approach is to compare the improvement in heat transfer efficiency in the condenser tube by comparing the improvement in fouling factor of the condenser ( Rf ) which is proportional to the temperature difference between the condensing refrigerant and the condensing water outlet.

T = Tc Tco...(1) In addition, the energy saving of the system is calculated by measuring the improvement in Coefficient of Performance (COP) before and after installation.. Where, Qe =Refrigeration Effect of Chiller 1 (kW)

Me = Mass flow rate of chilled water (kg/s) Cp = Specific heat capacity of water (kJ/kg) te = Entering chilled water temperature (oC) tl = Leaving chilled water temperature (oC) WD = Power Consumption of Chiller 1 (kW) V = Voltage (V) I = Current (A) p.f. = Power factor COP = Coefficient of Performance Tc = Condensing refrigeration temperature Tco = Condensing water outlet temperature T = Condenser Approach

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%Saven= Percentage of Energy Saving in particular load range (%) COPn = Coefficient of Performance of after CQM Installation COPo = Coefficient of Performance of before CQM Installation On = Occurrence in particular load (%) %Save = Average Energy Saving at particular condensing temperature (oC) Result and Analysis T between condensing refrigerant & condensing water outlet temperature By comparing the T in each condensing water inlet temperature conditions, the changes of fouling factor of condenser during the data-recording period are shown in the following figures. As can be seen in the figure, the performance of chiller was improved when the Automatic Tube Clearing System was installed. Oxford House

Condensing Water Inlet Temperature between 27 and 28

0

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0 100 200 300 400 500 600

electrical power input (kW)

T

betw

een c

onde

nsing

refri

geran

tan

d con

dens

ing w

ater o

utlet

()

before install CQM after install CQM linear (before install CQM) linear (after install CQM)Figure 7.1 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Oxford House with condensing water inlet temperature between 27 and 28


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T

betw

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nsing

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ater o

utlet

()

before instal CQM after install CQM linear (before install CQM) linear (after install CQM)

Figure 7.2 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Oxford House with condensing water inlet temperature between 28 and 29


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T

betw

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ensin

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frig

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cond

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g w

ater

out

let (

)

before install CQM after install CQM linear (before install CQM) linear (after install CQM)

Figure 7.3 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Oxford House with condensing water inlet temperature between 29 and 30 After the installing CQM in Oxford House, the fouling factor has been improved by 181% with average T decreased by 2.77.


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Lincoln House


0

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0 50 100 150 200 250 300 350


T

betw

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water

outle

t (

)


Figure 8.1 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Lincoln House with condensing water inlet temperature between 27 and 28


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0 50 100 150 200 250 300 350electrical power input (kW)

T

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t an d

cond

ensi

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ater

out

let (

)


Figure 8.2 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Lincoln House with condensing water inlet temperature between 28 and 29


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0

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electrica power input (kW)

T

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ater

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let (

)


Figure 8.3 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Lincoln House with condensing water inlet temperature between 29 and 30 In Lincoln House, the fouling factor has been improved by 77% with average T greatly reduced from 6.39 to 1.42 (i.e. 4.97 improvement). Dorset House


0.0

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T

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and c

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wate

rou

tlet

()


Figure 9.1 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Dorset House with condensing water inlet temperature between 27 and 28


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0.01.02.03.04.05.06.07.08.09.0

10.0


T

betw

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ensi

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frig

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d co

nden

sing

wat

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t ()


Figure 9.2 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Dorset House with condensing water inlet temperature between 28 and 29 Condensing Water Inlet Temperature between 29 and 30

0.0

1.0

2.0

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T

betw

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before install CQM after install CQM linear (before install CQM) linear (after install CQM)Figure 9.3 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Dorset House with condensing water inlet temperature between 29 and 30 In Dorset House, the average T is reduced from 6.72 to 4.84 and the fouling factor has reduced by 28.%.


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Somerest House


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Electrical PowerInput (kW)

T

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t an d

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ensi

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ater

out

let (

)

before install CQM after install CQM lineatr (before install CQM) linear (after install CQM)

Figure 10.1 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Somerest House with condensing water inlet temperature between 27 and 28


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0 100 200 300 400 500 600


T

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g wate

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et (

)

before install CQM after install CQM linear (before install CQM) linear (after install CQM)Figure 10.2 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Somerest House with condensing water inlet temperature between 28 and 29


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0 100 200 300 400 500 600electrical power input (kW)

T

betw

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frig

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d co

nden

sing

wat

er o

utle

t ()


Figure 10.3 the temperature difference between the condensing refrigerant and condensing water outlet against electrical power input in Somerest House with condensing water inlet temperature between 29 and 30 In Somerset House, the average T is reduced by 1.35 and the average improvement on fouling factor is 26%.


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Coefficient of Performance The comparisons between the COP before and after CQM installation at different condensing temperature are shown in the following figures. All the COP have been greatly improved except the chillers at Oxford Housing where the chiller water set point has been changed during the data recording period. Lincoln House


0

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COP


Figure 11.1 the coefficient of performance before and after CQM installation in Lincoln House with condensing water inlet temperature between 27 and 28

The average COP is increased by 24.35%


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COP

before install CQM after install CQM linear (before instaall CQM) linear (after install CQM)

Figure 11.2 the coefficient of performance before and after CQM installation in Lincoln House with condensing water inlet temperature between 28and 29 Condensor Water Inlet Temperature between 29 and 30

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COP


Figure 11.3 the coefficient of performance before and after CQM installation in Lincoln House with condensing water inlet temperature between 29 and 30 In Lincoln House, the average COP improvement under the condensing temperature range between 27 and 30 is 21.2%.




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Dorset House


0.0

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COP

before install CQM after install CQM linear (before install CQM) linear (after install CQM Figure 12.1 the coefficient of performance before and after CQM installation in Dorset House with condensing water inlet temperature between 27 and 28


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COP


Figure 12.2 the coefficient of performance before and after CQM installation in Dorset House with condensing water inlet temperature between 28 and 29




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Condensor Water Inlet Temperwture between 29 and 30

0.0

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COP

before install CQM after install CQM linear (after install CQM) Linear (before install CQM)

Figure 12.3 the coefficient of performance before and after CQM installation in Dorset House with condensing water inlet temperature between 29 and 30 The average COP of the chiller in Dorset House has improved by 9.88%. Somerest Hosue

Condensor Water Inlet Temperature between 27 and 28

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COP


Figure 13.1 the coefficient of performance before and after CQM installation in Somerset House with condensing water inlet temperature between 27 and 28




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Condensor Water Inlet Temperature between 28 and 29

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COP


Figure 13.2 the coefficient of performance before and after CQM installation in Somerest Housing with condensing water inlet temperature 28 and 29


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COP


Figure 12.3 the coefficient of performance before and after CQM installation in Somerest Housing with condensing water inlet temperature between 29 and 30 In Somerset House, the average saving on COP is up to 13.1%.




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Oxford House


0

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COP


Figure 13.1 the coefficient of performance before and after CQM installation in Oxford House with condensing water inlet temperature between 27 and 28


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COP

before install CQM after install CQM linear (before install CQM) linear (after install CQM)Figure 13.2 the coefficient of performance before and after CQM installation in Oxford House with condensing water inlet temperature between 28 and 29




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COP


Figure 13.3 the coefficient of performance before and after CQM installation in Oxford House with condensing water inlet temperature between 29 and 30 In Oxford House, the average COP is only improved by 0.03%. However, we find that the chiller supply set point in 2002 was 8 while the set point in 2003 was reduced to 7.4. As we do not have a exact figures from Carrier, we would estimate that the 0.6 decreased in chiller supply temperature set point had imposed more than 10% burden on COP of the chiller. From the improvement on condenser T ( 2.77 ), we would project the saving by interrelating it with Lincoln , i.e. Improvement in COP in Oxford = 2.77 / 4.97 * 21.2% = 11.8%. Therefore, in Oxford House, we estimate the improvement on COP is around 11.8% Payback Analysis From the above analysis, we can see that CQM provide a significant improvement on COP. The projected energy saving can be estimated by the following formula Annual Energy Saving = Rated Power Input * working hour per day * working days per year *

diversity factor * Electricity charge * % saving on COP Assumption : Working hour per day = 12 hours Working days per year = 5 1/2 days * 52 weeks = 286 Diversity Factor = 0.5 Electricity charge = HK$ 0.94 per kwh Simple Payback Period = Cost of CQM / (Annual energy saving annual maintenance )

The average COP is reduced by 0.01%


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Payback results :-

Building Name

Power Input (kw)

Saving ( % )

Annual Energy saving

( HK$)

Cost of CQM

( HK$ )

Annual Maintenance

( HK$ )

Simple Payback Period

Lincoln House 300 21.2% $ 102,589 $ 160,000 $ 10,000 1.72 year Oxford House 509 11.8% $ 96,882 $ 145,000 $ 10,000 1.66 year Dorset House 1080 9.88% $ 172,117 $ 290,000 $ 12,000 1.81 year Somerset House 553 13.1% $ 116,853 $ 200,000 $ 12,000 1.91 year Summary From the above analysis, it proves that CQM Automatic Tube Cleaning System can greatly improve the heat transfer efficiency of the condenser tube and save significant amount of energy in water-cooled chiller. Besides, from the economic analysis, it shows that the payback is less than 2 years.

CQM_Taikoo

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