analysis and practice of refrigeration and air
TRANSCRIPT
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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 [email protected]
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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