2017 3rd International Symposium on Mechatronics and Industrial Informatics (ISMII 2017) ISBN: 978-1-60595-501-8

Analysis and Practice of Refrigeration and Air Conditioning System Energy Saving Opportunity in Cigarette Factory

Shu Xina, Xia Yaoguangb, Xia Yunfeic and Wang Hud

China Tobacco Zhejiang Industrial Co., Ltd, Hangzhou, China ashuxin@zjtobacco.com

Keywords: refrigeration unit; Air conditioning unit; Energy saving opportunities; Energy saving effect

Abstract. The national tobacco industry put forward the enterprise management policy of lean

management and efficiency management. Industry enterprises attach great importance to the

energy-saving work will be raised to a strategic height to be implemented. This paper from

refrigeration unit and air conditioning unit two aspects do key energy-saving technology analysis, and

achieved significant energy saving results, which provides a reference for Industry enterprises to

reference.

1. Introduction

According to Hangzhou cigarette factory energy consumption statistics, the annual energy

consumption of central air conditioning system accounts for more than 50% of the plant energy

consumption, refrigerators, pumps and other equipment, energy consumption accounted for more

than 40% of air conditioning energy consumption; air conditioning energy consumption account for

more than 60%, there is a huge energy-saving space.

2. Refrigeration air-conditioning system

Refrigeration and air conditioning system consists of cold source system and air conditioning system.

The cold source system is composed of centrifugal chillers, chilled water pumps, cooling water

pumps, cooling towers and other auxiliary equipment for the application of air conditioning

equipment, which provide chilled water to refrigeration or dehumidification for air conditioning

equipment. as shown in Fig1.

Figure 1. Central air conditioning system for cigarette factory production.

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The air conditioning system is composed by air conditioning cabinet, filter, surface cooler, heater,

humidifier, return wind turbine fan and pipeline valve control system. It enables precision control of

environment temperature and humidity, as shown in Fig2.

Figure 2. Air conditioning system.

3. Cold source system-refrigeration unit energy saving opportunities

3.1 Improve the temperature of the refrigerator water supply

Air condition system is generally designed to 7 ℃ / 12 ℃ as chilled water supply back water

temperature, The temperature of the chiller is also set at 7 ° C. However, in the actual operation of the

air conditioning system, because of the weather conditions and other factors, The real-time load of the

air conditioning system is less than the design load. Therefore, according to the air conditioning

system load changes in a year, adjusting the operating parameters of the chiller in the partial load

period will lead to energy saving opportunities.

The water supply temperature of centrifugal chiller increase each 1℃, can save about 3% to 4%

energy consumption, as shown in Figure 3. In theory, the temperature of cold water is directly related

to the evaporative temperature of the unit. When the other conditions are the same, the lower the

cooling water temperature, the unit's energy consumption will increase, the cooling capacity will be

reduced.

Figure 3. Characteristic curve of centrifugal chiller.

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In the transition season, the temperature and humidity control is easy so we can switch to a higher

cold water outlet temperature，which can get significant energy saving effect, but also to eliminate

the transition dehumidification, dehumidification and then humidification, hot and cold offset and

other energy consumption waste phenomenon.

At the transitional season from May to June, we will set the original temperature of the refrigerator

7 ℃ to 9 ℃ or 10 ℃, according to industrial electricity 0.8 yuan / KWH calculation, the energy saving

effect as follows Table 2-1:

Table 2-1. The statistics of refrigeration water temperature setting 9 ℃ Energy saving from May to June 2015.

Time

Actual power

consumption after

improved (KWH)

COP before

the upgrade

COP after

the upgrade

If not to improve the

theoretical power

consumption (KWH)

Saving electricity

(KWH)

income

(￥)

May-Jun 1535075 4.15 4.25 1572065 36990 30331.8

It can be seen from Table 1 that the energy efficiency of the unit is significantly improved when the

temperature of the chilled water is increased. Unit energy efficiency COP (COP = cooling capacity /

unit power) increased from 4.15 to 4.25. only 2 months energy saving income reached 3 million yuan.

3.2 Water pump of cooling system motor frequency control energy saving The cooling water pump and chilled water pump which in cooling system is generally fixed frequency

motor, constant speed, the unit equipment is basically selected according to the needs of the

maximum cooling load, and leave sufficient margin. No matter how the load changes, the chilled

water pump or cooling water pump motor is fixed in the rated flow mode for a long time, Although it

can meet the maximum heat load, but does not have the function of automatic adjustment with the

load, while the load is low when the long run, which resulted in a lot of energy waste.

From the working principle of the pump can be seen:

Flow rate proportional law：Q1/Q2=n1/n2（1）

Law of head and speed proportional：H1/H2=(n1/n2)²（2）

Basic formula of pump shaft power： P=Q·H·g·ρ/η（3）

Law of shaft power and speed proportional：P1/P2=（n1/n2）³（4）

Basic formula of motor speed： n=60f/p （5）

Law of frequency proportional：P1/P2=（f1/f2）³（6）

Where q is the pump flow rate, H is the head, P is the motor shaft power, n is the motor

synchronous speed, g is the gravitational acceleration, ρ is the density of the pump delivery medium, η

is the pump efficiency, f is the supply frequency, p is the motor Pole pairs.

By the above formula can be introduced by the pump shaft power and power supply frequency is

proportional to the third power, then change the frequency of the pump can change the pump power. If

the average pump frequency is reduced from 50HZ to 45HZ, then P45 / P50 = (45/50) ³ = 0.729, or

P45 = 0.729 P50, that is, energy consumption can be reduced by 27.1%.

I plant refrigeration unit chilled water pump and cooling water pump through the frequency control

transformation, such as the cost of industrial electricity by 0.8 yuan / kWh basis, the 2015 energy

efficiency as follows Table 2-2:

Table 2-2. Energy consumption statistics of pump frequency conversion for 2015 refrigeration units.

Total run

time in

2015

(hour)

Rated

power

(KW)

Rated annual

consumption（KWH）

Rated total

electricity

consumption（KWH）

Actual total

electricity

consumption（KWH）

Saving power（KWH）

Income （￥）

Cooling 10712 132 1413984 3200864 2629692 571172 456937.6

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water pump

Chilled

water pump 11168 160 1786880

Can be seen from Table 2-2, after the pump through the frequency transformation, energy-saving

effect is obvious, saving 45 million yuan in 2015.

3.3 The saving point of cooling tower cooling system energy

Cooling tower cooling can be divided into cooling tower direct cooling system and cooling tower

indirect cooling system. Direct cooling system, no intermediate heat transfer process, water flow and

outdoor air contact heat transfer, easy to be polluted, resulting in the system of pipeline corrosion,

scaling and blocking, affecting the stability of the system operation. Cooling tower indirect cooling

system is the installation of a plate heat exchanger, the cooling water ring and cold water loop

separated, so that independent of each other, not direct contact, energy transfer depends on the plate

heat exchanger to carry out. The characteristic of this way is the cold water will not pollution by

cooling water. there is an intermediate heat loss, the efficiency will be low. However, its impact on the

entire air-conditioning water system is small, so the transformation is relatively low difficulty. As

shown in Figure 4 below.

Figure 4. Cooling tower cooling system diagram.

When the outdoor air wet bulb temperature is below a certain value, close the chiller to cool the

cooling water flowing through the cooling tower to the air conditioning end system to reduce the high

energy consumption of the cooling unit running time.

After the technological transformation, the energy consumption is shown in Table 2-3.

Table 2-.3 Cooling tower cooling operation mode energy saving effect statistics.

Time

The actual

power

consumption

after improve（KWH）

COP before the

upgrade

(Rated)

COP after the

upgrade

(actual)

If not to improve the

theoretical power

consumption (KWH)

Saving electricity

(KWH) income

2015.12 177892 4.37 6.16 250759 72867 58293.6

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2016.1 162482 4.37 7.67 285180 122698 98158.4

2016.2 135802 4.37 6.72 208831 73029 58423.2

2016.3 250791 4.37 6.98 400577 149786 119828.8

total 726967 — — 1145347 418380 334704.0

From Table 2-3 we can see that only use the cooling tower cooling mode for 4 months, the COP

increased to 6, 4 months total savings of 33.4 million yuan.

4. Conclusion

According to the above refrigeration and air conditioning system energy-saving opportunities

analysis, and the implementation of the corresponding transformation have achieved remarkable

results. This article is summarized as follows:

1) We should properly improve the chilled water temperature according to the need of air

conditioning unit and dehumidification.

2) Variable Frequency Flow Control of cooling water pump motor should be controlled by the

difference of return and supply water, Variable Frequency Flow Control of Chilled Water Pump

Motor should be controlled by the pressure between Water collector and water separator

3) Cooling tower indirect cooling technology is suitable for the occasions of transition season or

outdoor air wet bulb temperature is low in winter.

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