with the sustained and rapid development of China's national economy, it has driven the long-term high-speed growth of energy consumption. At present, China's energy supply has shown a tense situation. It is the core of China's energy use work to vigorously promote energy conservation and consumption reduction, ease the bottleneck of resources and realize the sustainable development of energy environment and economy and society.
energy is the basic power to ensure the operation of various electromechanical equipment in the hotel. With the rapid development of modern hotels in China, although the energy management level of hotels has been greatly improved and the energy consumption of hotels is decreasing year by year, compared with developed countries, there is still a big gap in energy utilization efficiency of hotels in China. According to the characteristics of hotel electromechanical equipment, this paper briefly introduces the commonly used and proven energy-saving technologies. Analyze the basic theory of specific energy-saving projects and get the technical support of the basic theory. Based on the analysis of physical engineering cases, the energy-saving methods and points for attention in practical application are summarized. It aims to provide reference for everyone in carrying out energy-saving work.
first, the basic situation of hotel energy consumption
At present, the average energy consumption cost of hotel industry in China accounts for about 13% of hotel income.
the average proportion of hotel energy consumption is about:
air conditioning 51%
lighting 21%
electromechanical 17%
other 11%
from the general proportion of hotel energy consumption, air conditioning accounts for more than half of hotel energy consumption, which has the greatest energy saving potential. Let's start with the basic theory of freezing. This paper analyzes the ways of energy saving in air conditioning, and demonstrates the corresponding energy saving methods and practices.
2. Energy-saving technologies and methods of hotel air conditioning
(1) Brief introduction of basic freezing theory
1. Analysis of actual freezing cycle:
Text description of freezing cycle process:
Gaseous refrigerant coming out of evaporator (4) in the state of 1(T1,P1); After adiabatic compression by the compressor, it becomes state 2(T2,P2). The compressed gas refrigerant is cooled and condensed at the same pressure in the condenser (2), changed into liquid refrigerant in state 4(T3,P2) through state 3(T3,P2), and then expanded to low pressure (P1) through the throttle valve (3) to become a gas-liquid mixture in state 5(T1,P1). The liquid refrigerant at low temperature (T1) and low pressure (P1) absorbs the heat of the cooled substance in the evaporator (4), and gasifies at P1 to become the gaseous refrigerant in state 1(T1,P1). The gaseous refrigerant re-enters the compressor through the pipeline and starts a new cycle. These are the four processes of the freezing cycle.
2. Analysis of energy-saving ways of air conditioning by freezing theory (1)
(1) The freezing coefficient ∑ = Q1 ∕-W = Q1 ∕ (-Q2)-Q1
where the heat absorbed by Q1-refrigerant from the environment (cold object T1) is positive;
Q2-the heat released by the refrigerant to the environment (hot object T2) is negative.
w-the work done by the compressor on the system (refrigerant) is negative.
written expression: ∑ indicates that the refrigerant can
absorb energy from a cold object when 1 units of work are applied. It is an important index to measure the efficiency of refrigeration cycle.
3. Analysis of energy-saving ways of air conditioning by refrigeration theory (2)
(2) Ideal refrigeration cycle (reversible cycle)
Numerical expression: ∑ Ke = Q1 ∕ (-Q2)-Q1 = t1 ∕ T2-t1
● Where: t1-the absolute temperature of the cold object. But also related to T1 and T2, and has nothing to do with refrigerant.
● Analysis: When the evaporation temperature T1 increases, the freezing coefficient increases; When T1 decreases, the opposite is true.
when the condensation temperature T2 decreases, the freezing coefficient increases; When T2 rises, the opposite is true.
4. Analysis of energy-saving ways of air conditioning by refrigeration theory (3)
(1) Calculate the refrigeration capacity on the T-S diagram
From the analysis of the T-S diagram of the refrigeration cycle, we can get the following results:
● The standard refrigeration working condition is (1-2-3-4-5-1) and its refrigeration capacity integral area Q1;
● When the condensation temperature is reduced to T2', the freezing condition is (1-2-3-4'-5'-1), and the integrated area of refrigeration capacity is Q1+Q1';
● When the evaporation temperature rises to T1', the freezing condition is (1-2-3-4-5''-1), and the integrated area of refrigeration capacity is Q1+Q1''.
(2) Analysis of the change of refrigeration capacity by changing operating conditions
(a) The refrigerator uses ammonia as refrigerant. Standard operating conditions:
evaporation temperature t1 =-15℃
condensation temperature T2=31℃
supercooling temperature T2' = 25℃
△ refrigeration capacity 111111KCal∕h
(b) After changing operating conditions:
evaporation temperature t1 =-11℃.
(5) Analysis of energy-saving ways of air conditioning based on freezing theory (4)
☆ The freezing theory and practice prove that
under the condition of certain evaporation temperature:
When the condensation temperature T2 increases by 1℃, the efficiency of air conditioning chillers decreases by about 4.2%.
when the condensation temperature T2 is reduced by 1℃, the efficiency of air-conditioning chiller is increased by about 4.1%.
Under the condition of a certain condensation temperature:
When the evaporation temperature T1 decreases by 1℃, the efficiency of air-conditioning chiller decreases by about 4.2%.
when the evaporation temperature T1 increases by 1℃, the efficiency of air conditioning chiller increases by about 4.1%.
(6) Analysis of energy-saving ways of air conditioning by refrigeration theory (5)
☆ The direction of energy-saving supported by refrigeration theory
A. The lower the condensation temperature, the greater the refrigeration coefficient, which can reduce the power consumption of the compressor.
B, the higher the evaporation temperature, the greater the freezing coefficient, which can reduce the electrical consumption of the compressor.
C, the heat of the cooled object absorbed in the evaporation process and the heat generated by the compressor's work can be recycled.
According to the energy-saving approach of air conditioning supported by refrigeration theory, we can design the corresponding energy-saving equipment, automatic control system and process pipeline with a clear aim, so as to achieve the optimization of energy-saving transformation.
(2) Basic conditions and requirements for comprehensive energy-saving renovation of hotels
1) According to local conditions, adopt energy-saving technologies and methods that are suitable for the hotel.
2) be familiar with the operating conditions of the system and equipment.
3) the economic benefit of energy saving is obvious.
4) It does not affect the normal operation of facilities, systems and equipment, and does not affect the quality of customer service.
5) Energy-saving facilities are required to be simple to operate, easy to control and free from potential safety hazards.
6) basically does not affect the surrounding environment.
7) after investigation and study, make a decision on energy-saving renovation project after scientific demonstration.
(III) Introduction of energy-saving technologies and methods of hotel air conditioning and their applications
1. Waste heat recovery technology of central air conditioning and its applications
Make full use of the heat exchange principle to recover the waste heat (condensation heat) of air conditioning and produce hot water at 51 ~ 61℃ for hotel rooms, saunas, staff bathrooms, etc. Because the recovered air conditioner is the residual heat of condensation heat. So the amount of hot water produced is zero energy consumption. At the same time, because part of the waste heat is recycled, the condensation temperature is reduced. And that efficiency of the central air condition unit is improved by 5-11%. As the load of the mainframe is reduced after the technical transformation, it not only saves the power consumption of the mainframe, but also reduces the failure rate of the mainframe and prolongs the service life of the mainframe. It is an excellent energy-saving technology with multiple goals.
(1) Schematic diagram of the principle flow of waste heat recovery technology for central air conditioning
(2) Schematic diagram of waste heat recovery flow of air conditioning in holiday inn donghua shenzhen (case study)
Features of air conditioning waste heat recovery system:
● The pipeline process flow of a set of waste heat recovery system with two hosts as backup is realized, thus further improving the waste heat recovery rate.
● The waste heat recovery hot water system is interconnected with the original hot water system to ensure the reliability of hot water supply.
(3) Application scope of waste heat recovery technology of central air conditioning
It is widely used in piston and screw chillers.
the volume of hot water tank is recommended to be set at about 31% of the total water consumption.
there is a complete standby system for hot water boilers.
there is an automatic regulation system with constant hot water outlet temperature.
(4) calculation of the area of the key equipment waste heat recovery device
heat transfer equation: q = KF △ TM
Physical meaning: the heat transferred per unit area and temperature rise per degree in a certain heat transfer state.
where: k-heat transfer coefficient kcal/m2.h.℃
f-heat transfer area m2
△ TM-logarithmic mean temperature difference℃
heat transfer coefficient k: describes the state of a heat transfer process, that is, the heat transfer capacity. There are three sources of K value: selecting production practice data; Experimental determination; Theoretical calculation.
it is recommended here that the heat transfer coefficient k of the waste heat recovery area of air conditioning is 581 ~ 721 kcal/m2.h℃
2. Frequency conversion energy-saving technology of central air conditioning circulating water system
(1) Frequency conversion energy-saving technology of central air conditioning circulating water system
Analysis of cooling load of air conditioning operation:
At present, the rotation speed of freezing pump and cooling pump of most central air conditioning circulating water systems in hotels is not available.
(2) Technical feasibility of energy-saving transformation
It is one of the effective ways to save energy in central air-conditioning system to control the operation of water pump with AC inverter. Figures 1 and 2 show the pressure-flow (H-Q) relationship and the power-flow (P-Q) relationship in the two operating states of valve regulation and frequency conversion governor control.
curve (1) in figure 1 is a water pump. curve 1 in figure 1 is the H-Q curve of the water pump at rated speed, curve 2 is the H-Q curve of the water pump at a certain low speed, curve 3 is the H-Q curve of the pipeline at the maximum valve opening, and curve 4 is the H-Q curve of the pipeline at a certain small valve opening. When the valve opening is adjusted under the condition of constant speed operation, the working condition point delay curve 1 moves from A to B; Under the condition of the maximum valve opening, the frequency converter is used to adjust the pump speed, so the working point moves from A to C along curve 3. Obviously, the flow at point B is the same as that at point C, but the pressure at point B is much higher than that at point C, that is to say, the energy-saving effect is remarkable under the condition of variable frequency control of water pump speed regulation operation.
in figure 2, curve 5 is the P-Q curve under the pump speed regulation mode controlled by frequency converter, and curve 6 is the P-Q curve under the valve regulation mode. It can be seen that under the same flow rate, the frequency conversion control mode consumes less energy than the valve regulation mode, and the relationship between them can be expressed by the following formula:
△P = 1.4+1.6q/Qc-(q/QC) 3pc
. It is not difficult to calculate that when the load flow drops to 71% of its rated flow, the power saving rate will reach 48%.
(3) In addition to saving electric energy, the application of frequency converter will also bring the following advantages to the operation of water chillers:
1) Adjust the water flow, control the inlet and return water temperatures of water chillers within a proper range, ensure the heat exchange rate of the main engine, and save the energy consumption of the main engine.
2) The pipeline valve is opened to the maximum, which eliminates the local loss of throttling on the valve and saves electricity.
3) The motor is soft-started (the maximum starting current is less than the rated current), and there are protection measures such as undervoltage, overcurrent, phase loss and leakage, which improves the motor operating conditions and improves the reliability of operation.
4) It starts smoothly and has no impact load, which greatly reduces the equipment loss, prolongs the service life of the equipment and reduces the maintenance cost.
(4) Frequency conversion energy-saving control of central air-conditioning circulating water system
(5) Basic conditions for practical application of frequency conversion energy-saving technology of central air-conditioning circulating water system:
1) Widely used in chilled water pumps, cooling water pumps and cooling towers. Large cold air cooler (air handler) and other places with variable load. General energy-saving space is about 21 ~ 51%.
2) The motor is controlled by frequency conversion closed loop, and the temperature is set as required, so that the heat capacity reserved by the equipment system and the heat load changing with time and season can be automatically adjusted through the rotating speed, and the maximum energy saving can be achieved under the condition that the heat load is normally used.
3) it is necessary to make a comprehensive hydraulic calculation of the circulating water system
to get the total pipeline resistance
△ p = ∑ HF = HO+HC+HJ
n
= HO+(λ L/D+∑ C) W2/2g [mH2O]
I = 1. Thereby confirming the energy-saving space.
4) Choose a suitable location, set minimum pressure difference protection, and strengthen pipeline resistance reduction management.
(5) Case analysis of frequency conversion energy-saving transformation of circulating water system of central air conditioner
1) Case analysis of Shenzhen Danfeng Bailu Hotel
Control function of power loop of circulating system:
1. Three pumps can automatically run energy-saving under frequency conversion regulation.
2. The frequency converter directly controls two pumps and indirectly controls one pump.
3. after the frequency conversion part fails, it can run under the condition of power frequency AC381V∕51Hz.
4. Closed-loop collection of parameters of water cooling tower of freezing pump and cooling pump is sent to the intelligent control substation for processing, and instructions are issued to adjust the speed of water pump motor.
since the energy-saving system was put into operation, the energy-saving effect is obvious, and the annual average energy-saving rate is over 38%.
in one of the introduction and case analysis of comprehensive energy-saving technology in hotels in the last issue, the way of air-conditioning energy-saving is analyzed by using freezing theory, and the way and direction of air-conditioning energy-saving are pointed out; This paper introduces the energy-saving technology and method of hotel air conditioning and its application: the technology and application of waste heat recovery of central air conditioning; Frequency conversion energy saving technology of central air conditioning water circulation system. This chapter continues to introduce energy-saving technologies, methods and applications of air conditioners:
1. Energy-saving technologies of VRV variable frequency direct cooling air conditioners and their application cases
At present, most air conditioners in hotel rooms are central air conditioners with classic water circulation cooling system. The air conditioning system is mature and reliable, with a long history, and is widely used in various occasions. With the further enhancement of people's awareness of energy saving, many new generation air conditioning systems with energy saving, environmental protection and practicality have been developed, and VRV frequency conversion direct cooling air conditioning is one of the typical energy saving products. The following is a theoretical analysis and comparison between the water circulation cooling system air conditioner and the new VRV variable frequency direct cooling air conditioner.
1. Schematic diagram of water circulation cooling air-conditioning system:
Schematic diagram of refrigeration process
2. Schematic diagram of VRV variable frequency direct cooling air-conditioning system
3. Comparison between water circulation cooling air-conditioning system and VRV variable frequency direct cooling air-conditioning system
According to the analysis of the above two refrigeration process flow charts, it is not difficult to see that the water circulation cooling air-conditioning system has a chilled water circulation system and a cooling water circulation system.