Energy-saving renovation of hotels

Introduction and case analysis of comprehensive energy-saving technology in hotels

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. Vigorously promoting energy conservation and consumption reduction, alleviating the bottleneck of resources and realizing the sustainable development of energy, environment and economy and society are the core of energy use in China.

Energy is the basic power to ensure the operation of various electromechanical equipment in hotels. 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 has been decreasing year by year, compared with developed countries, there is still a big gap in the energy utilization efficiency of hotels in China. According to the characteristics of hotel electromechanical equipment, this paper briefly introduces the commonly used and verified energy-saving technologies. Analyze the basic theory of specific energy-saving projects and get technical support from the basic theory. Through the analysis of practical engineering cases, the energy-saving methods and matters needing attention in practical application are summarized. It aims to provide reference for everyone to carry out energy-saving work.

First, the basic situation of hotel energy consumption

At present, the energy consumption cost of hotel industry in China accounts for about 13% of hotel income on average.

The average proportion of hotel energy consumption is about:

Air conditioning 5 1%

Lighting 2 1%

Electromechanical 17%

Other 10%

Judging from the general proportion of hotel energy consumption, air conditioning accounts for more than half of hotel energy consumption, with the greatest energy-saving potential. Let's start with the basic theory of freezing. This paper analyzes the energy-saving ways of air conditioning, and demonstrates the corresponding energy-saving methods and practices.

Second, the hotel air conditioning energy-saving technology and methods

Brief introduction of (1) freezing basic theory

1, actual freezing period analysis:

Text expression of freezing cycle process;

Gaseous refrigerant coming out of the evaporator (4) in the state of 1(T 1, P 1); After adiabatic compression by the compressor, it becomes State 2(T2, P2). The compressed gas refrigerant is cooled in the condenser (2) and condensed at the same pressure, and becomes a liquid refrigerant in the state 4(T3, P2) through the state 3, and then expands to a low pressure (P 1) through the throttle valve (3) and becomes a state 5(T 1, P 1). Among them, the liquid refrigerant with low temperature (T 1) and low pressure (P 1) absorbs the heat of the cooled substance in the evaporator (4), and is gasified at P 1 to become the gaseous state of 1(T 1, P 1). 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 based on refrigeration theory (1)

(1) freezing coefficient ∑ = q1∕-w = q1∕ (-Q2)-q1.

Where q1-the heat absorbed by the refrigerant from the environment (cold object T 1) is positive;

Q2- The heat released by the refrigerant into the environment (hot object T2) is negative.

W- The work done by the compressor on the system (refrigerant) is negative.

Text expression: ∑ means that the coolant on a cold object can be removed by adding 1 unit of work.

Absorb energy. It is an important index to measure the efficiency of refrigeration cycle.

3. Analysis of energy-saving ways of air conditioning based on refrigeration theory (2)

(2) Ideal freezing cycle (reversible cycle)

Numerical expression: ∑ ke = q1∕ (-Q2)-q1= t1∕ T2-t1.

● Where: t1-the absolute temperature (evaporation temperature) of the cold object.

T2 —— Absolute temperature (condensation temperature) of hot objects.

● Description: For the ideal refrigeration cycle, because all parts are reversible, the efficiency of the ideal refrigeration cycle can be maximized. It is related to T 1 and T2, but has nothing to do with refrigerant.

● Analysis: When the evaporation temperature T 1 rises, the freezing coefficient increases; When T 1 decreases, the situation is just the opposite.

When the condensation temperature T2 decreases, the freezing coefficient increases. When T2 rises, the situation is just the opposite.

4, refrigeration theory analysis air conditioning energy-saving way (3)

(1) Calculate the freezing capacity on the T-S diagram

From the T-S diagram analysis of freezing cycle, we can get the following points:

● The standard freezing condition is (1-2-3-4-5- 1), and its cooling capacity integral area is q1;

When the condensation temperature drops to T2', the freezing condition is (1-2-3-4'-5'- 1), and the integrated area of cold capacity is q1+q1';

When the evaporation temperature rises to T 1', the freezing condition is (1-2-3-4-5'- 1', and the integrated area of refrigeration capacity is q 1+q 1'.

(2) Change the operating conditions and analyze the change of freezing quantity.

(a) Refrigerators use ammonia as refrigerant. Standard operating conditions:

Evaporation temperature t 1 =- 15℃

Condensation temperature T2=30℃

Subcooling temperature T2' = 25℃

△ refrigerating capacity 100000KCal∕h

(b) After changing the operating conditions:

Evaporation temperature t 1 =- 10℃

Condensation temperature T2=25℃

Subcooling temperature T2' = 20℃

△ refrigerating capacity 135000KCal∕h

(5) Using the freezing theory to analyze the energy-saving ways of air conditioning (4)

☆ freezing theory and practice prove that

At a certain evaporation temperature:

The condensation temperature T2 increased by 65438 0℃, and the efficiency of air conditioning chiller decreased by about 4.2%.

The condensation temperature T2 decreased by 65438 0℃, and the efficiency of air conditioning chiller increased by about 4.0%.

At a certain condensation temperature:

Evaporation temperature T 1 drop 1℃, the efficiency of air conditioning chiller drops by about 4.2%.

The evaporation temperature T 1 is increased by 1℃, and the efficiency of air conditioning chiller is improved by about 4.0%.

(6) Using the freezing theory to analyze the energy-saving ways of air conditioning (5)

☆ Freezing theory supports the direction of energy saving.

A, the lower the condensation temperature, the greater the freezing 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 power consumption of the compressor.

C, the heat absorbed by the cooled object in the evaporation process and the heat generated by the compressor can be recycled.

According to the energy-saving mode of air conditioning supported by refrigeration theory, the corresponding energy-saving equipment, automatic control system and process pipeline are designed pertinently to realize the optimization of energy-saving transformation.

(2) Basic conditions and requirements for comprehensive energy-saving renovation of hotels.

1) Adjust measures to local conditions, and rationally adopt energy-saving technologies and methods suitable for hotel stores.

2) Familiar with the operation of the system and equipment.

3) The economic benefit of energy saving is obvious.

4) It will not affect the normal operation of facilities, systems and equipment and the quality of customer service.

5) Energy-saving facilities require simple operation, easy control and no potential safety hazard.

6) basically does not affect the surrounding environment.

7) Make decisions on energy-saving renovation projects through investigation and research and scientific demonstration.

(3) Introduce the energy-saving technology and method of hotel air conditioning and its application.

1, central air conditioning waste heat recovery technology and its application

Make full use of the principle of heat exchange, recover the waste heat (condensation heat) of air conditioning, and produce hot water at 50 ~ 60℃ 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 generated is zero energy consumption. At the same time, because part of the residual heat is recovered, the condensation temperature is reduced. The efficiency of central air-conditioning unit has been improved by 5- 10%. Because the load of the main engine is reduced after technical transformation, it not only saves the power consumption of the main engine, but also reduces the failure rate of the main engine and prolongs the service life of the main engine. It is an excellent energy-saving technology with multiple objectives.

(1) Schematic diagram of waste heat recovery technology of central air conditioning.

(2) Schematic diagram of air conditioning waste heat recovery process in holiday inn donghua shenzhen (case analysis)

Characteristics of air conditioning waste heat recovery system;

● A set of pipeline process flow of waste heat recovery system with two main engines as standby is realized, which further improves 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.

Widely used in piston and screw chillers.

The volume of hot water tank is suggested to be set at about 30% of the total water consumption.

The hot water boiler has a perfect standby system.

There is an automatic regulation system with constant hot water outlet temperature.

(4) area calculation of waste heat recovery device of key equipment

Heat transfer equation: q = KF △ TM

Physical meaning: heat transfer per unit area and temperature rise per degree in a certain heat transfer state.

Where: k-heat transfer coefficient kcal/m2.h.c

F- heat transfer area m2

△TM—— Logarithmic average temperature difference℃

Heat transfer coefficient k: describes the state of a heat transfer process, that is, the size of heat transfer capacity. There are three sources of K value: selecting production practice data; Experimental determination; Theoretical calculation.

It is recommended that the heat transfer coefficient k in the waste heat recovery area of air conditioning is 580 ~ 720 kcal/m2 h℃.

2, central air conditioning circulating water system frequency conversion energy-saving technology.

(1) Frequency conversion energy-saving technology for central air conditioning circulating water system

Analysis of cooling load of air conditioning operation;

At present, the rotating speed of freezing pump and cooling pump in the circulating water system of central air conditioning in most hotels is not adjustable. As long as the air conditioner runs, the refrigeration pump and cooling pump run at rated speed regardless of load and season, which is a serious waste of energy.

(2) Technical feasibility of energy-saving transformation

Using AC inverter to control the operation of water pump is one of the effective ways to save energy in central air conditioning system at present. Figure 1 and Figure 2 show the pressure-flow (H-Q) relationship and power-flow (P-Q) relationship under the two working conditions of valve regulation and variable frequency governor control.

The curve (1) in figure 1 is the H-Q curve of the pump at rated speed, curve 2 is the H-Q curve of the 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 adjusting the valve opening under the condition of constant speed operation, the working point delay curve 1 moves from A to B; Under the condition of maximum valve opening, the pump speed is adjusted by frequency converter, 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 pump speed regulation.

In fig. 2, curve 5 is the P-Q curve in the variable frequency control water pump speed regulation operation mode, and curve 6 is the P-Q curve in the valve regulation mode. It can be seen that under the same flow rate, the inverter control mode consumes less energy than the valve adjustment mode, and the relationship between them can be expressed by the following formula:

△P=0.4+0.6Q/Qc-(Q/Qc)3Pc

Among them, Q is the actual load flow, Qc is the rated flow, Pc is the rated load power, and△ P is the power saving value. It is not difficult to calculate that when the load flow is reduced to 70% of its rated flow, the power saving rate will reach 48%.

(3) In addition to saving electricity, the application of frequency converter will also bring the following benefits to the operation of water chillers:

1) Adjust the water flow, control the inlet and return water temperature of the water chiller within a suitable 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 soft start of the motor is realized (the maximum starting current is less than the rated current), and there are protection measures such as undervoltage, overcurrent, lack of phase and leakage, which improve the operating conditions and reliability of the motor.

4) Smooth start, no impact load, greatly reducing equipment loss, prolonging equipment service life and reducing maintenance costs.

(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 in central air conditioning circulating water system:

1) is widely used in chilled water pumps, cooling water pumps and cooling towers. Large cold air coolers (air handlers) and other places with variable loads. General energy-saving space is about 20 ~ 50%.

2) The motor adopts frequency conversion closed-loop control, sets the temperature as required, and automatically adjusts the heat capacity reserved by the equipment system and the heat load changing with time and season through the rotating speed, so as to achieve maximum energy saving under the condition of meeting the normal use of the heat load.

3) It is necessary to conduct a comprehensive hydraulic calculation of the circulating water system.

Find out the total resistance of the pipeline

△ P = ∑hf=ho+hc+hj

n

=ho+(λ L/d+∑C)w2/2g [mH2O]

i= 1

● Where: ho- static head [mH2O]

HC-pipeline resistance head [mH2O]

HJ- Dynamic Head of Fluid [mH2O]

What is the pump head allowance of the system? So as to determine the energy-saving space.

4) Choose a suitable location, set minimum pressure difference protection and strengthen pipeline drag reduction management.

(5) Case analysis of frequency conversion energy-saving transformation of central air conditioning circulating water system.

A Case Study of Feng Dan Egret Hotel.

Control function of power supply circuit of circulating system:

1, the three pumps can run automatically and save energy 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 AC380V∕50Hz.

4. The parameters of the chilled water pump and the cooling water pump of the cooling tower are collected in closed loop and processed in the intelligent control substation, and instructions are issued to adjust the speed of the pump motor.

Since the energy-saving system has been put into operation, the energy-saving effect is obvious, and the average annual energy-saving rate is over 38%.

In the last issue of Hotel Comprehensive Energy-saving Technology Introduction and Case Analysis, the way of air-conditioning energy saving is analyzed by using refrigeration 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: waste heat recovery technology and application 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 conditioning:

First, VRV frequency conversion direct cooling air conditioning energy-saving technology and its application case

At present, most of the air conditioners in hotel rooms are central air conditioners and classic water circulation cooling systems. 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 variable frequency direct cooling air conditioning is one of the typical energy saving products. The following is the theoretical analysis and comparison between the water circulation cooling system air conditioner and the new VRV frequency conversion direct cooling air conditioner.

1. Schematic diagram of water circulation cooling air conditioning system:

Schematic diagram of refrigeration process flow

2. Schematic diagram of 2.VRV variable frequency direct cooling air conditioning system

Schematic diagram of refrigeration process flow

3. Comparison between water circulation cooling air conditioning system and VRV frequency conversion 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. The main equipment includes chilled water pump, cooling water pump, cooling tower, power distribution cabinet, water circulation pipeline and valve fittings. The system is very complicated, occupying a lot of space in hotel rooms and consuming a lot of resources. VRV variable frequency direct cooling air conditioning system has no water circulation cooling system, and the refrigerant evaporates and absorbs heat directly in the fan coil. The heat of condensation is cooled by wind. The system is simple and the heat exchange efficiency is high. The heat transfer efficiency of direct refrigeration is about 8%~ 15% higher than that of indirect refrigeration. In other words, the refrigeration efficiency is improved by about 8%~ 15%.

Case analysis of VRV variable frequency direct cooling air conditioning in 4999 Feng Dan Egret Hotel:

(1) The total cooling load of the guest room is about 2330 kW/h.

(2) Energy consumption cost of 2)VRV variable frequency direct cooling air conditioner.

Analysis condition: the power consumption of air-conditioning compressor is not considered for the time being. Only consider the energy consumption and operation and maintenance cost of the condensing fan.

The actual data after running are as follows:

The annual power consumption of condensing fans is about 360,000 kWh (0.9 yuan/kWh).

The maintenance cost is about 25,000 yuan/year.

The total operating cost is 349,000 yuan/year.

(3) Energy consumption and cost of central air conditioning system with water circulation cooling.

Analysis conditions: The power consumption of air-conditioning compressor is not considered for the time being, only the energy consumption of water circulation equipment and operation and maintenance costs are considered.

According to the total cooling load of the guest room, the design selection and operation cost calculation data are as follows:

The annual power consumption of water recycling equipment is about 878,000 kWh (0.9 yuan/kWh).

The water consumption is 4600M3/ year (4.5 yuan /M3).

The water treatment cost is 20,000 yuan/year.

The maintenance cost is 25,000 yuan/year.

The total operating cost is 855,900 yuan/year.

(4) Comparison of energy-saving schemes

For the time being, it is considered that the compressed electric power of the two schemes is equal (the thermal efficiency of direct refrigeration heat exchange is 8%~ 15% higher than that of indirect refrigeration heat exchange, which is ignored for the time being).

Annual electricity saving: 5 18000KWH

Annual cost saving: 506,900 yuan

(5) payback period of investment

The equipment and installation cost of VRV direct cooling air conditioning system is 654.38+900,000 yuan more than that of traditional water circulation cooling central air conditioning system.

The payback period is about 3.7 years.

(6) Analysis results

Advantages: VRV direct cooling air conditioner not only saves electricity obviously, but also saves water resources without circulating water for refrigeration. At the same time, the environmental pollution caused by noise and water vapor of water cooling tower and chemical water pollution caused by water treatment are fundamentally solved. It has the advantages of low operating cost and high degree of automatic control.

Disadvantages: VRV direct cooling air conditioner used in hotel rooms needs several subsystems (outdoor host) and needs a large outdoor installation area. Due to the large number of refrigerant pipelines, once leakage occurs, it is difficult to find and maintain. At present, the length of refrigerant pipeline is limited to 90 ~120 m.

Second, air source heat pump triple supply technology and its application

At present, the common product manuals or technical introductions about various heat pumps are very mysterious. A simple question is complicated, perhaps because the more mysterious and complicated it is, the more scientific it is. The following is a popular introduction to various types of heat pumps.

Ground source heat pump, water source heat pump and air source heat pump are collectively called active heat pumps. No matter what kind of heat pump, its working principle is the same. The difference is that the name of the heat source is different.

Ground source heat pump technology uses shallow underground geothermal resources (including soil, groundwater and surface water), and takes the geothermal source as the cooling heat source of heat pump in summer and the low temperature heat source of heating in winter. Similarly, water source heat pump uses rivers, lakes, oceans and reservoirs near buildings as heat sources; At present, both practical technologies have realized the triple supply of building air conditioning, heating and domestic water; The air source heat pump absorbs heat from the air as a heat source, and the practical technology realizes the dual supply of building heating and domestic water. No matter what kind of heat pump, a large amount of heat energy can be obtained by inputting a small amount of electric energy, which can generally reach more than 1: 3.5.

To sum up, the advantages of ground source heat pump and water source heat pump are outstanding, but limited by the objective conditions, geological conditions and natural environment of buildings, they are often not suitable for application in many places. Especially for high-density buildings like Shenzhen, it is difficult to implement. Therefore, it is necessary to adapt to local conditions and adopt a product that is suitable for the south of China (subtropical climate) and is not affected by urban architecture and geological conditions. The new air source heat pump adds a set of evaporator on the basis of the original air source heat pump. It can still be achieved: air conditioning, refrigeration, heating and domestic hot water supply.

1, air source heat pump triple supply technology.

The average annual temperature in South China (Shenzhen, Hainan and southern Guangdong) is above 20℃. The average climate in winter is 9~ 16℃, and the extreme temperature is not lower than 3℃. Superior climatic conditions have opened up a good prospect for air-source heat pumps.

2. Schematic diagram of process flow of air source heat pump triple supply technology

According to the schematic diagram of the process flow, the heat source of the heat pump comes from the air conditioning load in the air conditioning season in spring, summer and autumn, and the heat source comes from the outdoor air in the non-air conditioning season in winter. The compressor does work, compressing the gaseous endothermic refrigerant after endothermic evaporation into gaseous refrigerant with high temperature and high pressure, and releasing heat in the condenser to heat domestic hot water (or heating hot water). The gaseous refrigerant is cooled and condensed into liquid refrigerant, and after throttling, it expands to the evaporator to evaporate and absorb heat, completing a thermodynamic cycle.

3. Features of the equipment:

There are two sets of evaporator systems, one set (i.e. refrigeration terminal equipment) is used in air conditioning season in spring, summer and autumn, and the other set is used in non-air conditioning season in winter, that is, it operates in two working conditions.

4, air source heat pump technical indicators

The average temperature of gas source energy is 9~26℃

Refrigeration temperature: 7~9℃

Heating temperature: 55℃ (hot water)

Refrigerant medium: 134a

Refrigeration heating efficiency: > 3.2 ~ 3.5

5, technical characteristics

Air-source heat pump technology is especially suitable for areas in southern China where the extreme temperature exceeds 3℃ in winter, and it can save energy costs by about 40% in the whole year.

Taking air as the heat source of heat pump is inexhaustible. The cost of heat source is equal to zero, there is no need to drill wells and bury pipes, the one-time investment cost is low, and it is not affected by geological conditions and buildings.

The maintenance is convenient, and the operating cost is lower than that of ground source water source heat pump.

The specifications of air source heat pump produced in China are relatively small, and there is no large equipment for the time being. As a large hotel heating, it needs to be developed. At present, air source heat pump is mainly used to produce domestic hot water and is widely used as a by-product of air conditioning and refrigeration.

6. Application of air source heat pump in hotels.

It is suggested to prepare air conditioning host+air source heat pump, and the choice of heat pump can be considered according to the total consumption of domestic hot water in the hotel.

In winter (non-air conditioning season), some hotels still use air source heat pump refrigeration for hotel air dehumidification, and achieved good results.

Three. Introduction of new technology for controlling fresh air volume by CO2 concentration.

The air conditioning load in public areas such as banquet hall, multi-function hall and restaurant is heavy. When not eating, or not holding banquets, or holding various celebration meetings and activities, the indoor air conditioning load is very low. But once it starts, the number of people often increases greatly, and the guests are full and packed, sometimes even exceeding 20%. Therefore, when designing and calculating the air-conditioning cooling load of banquet hall, multi-function hall and restaurant, the cooling load margin of full staff and overcrowding should be fully considered, so the design cooling load is very large.

This kind of air conditioning mostly adopts combined large-capacity air conditioning units with brand-new air and low wind speed for refrigeration. There are two common ways to return air:

A) only for the wind, not return air;

B) There are air supply and return modes; Either way, the percentage of fresh air in the system is very large. The refrigeration capacity of general air conditioners is more than double that of circulating refrigeration.

How to reasonably adjust the fresh air volume according to the actual load change of air conditioning to achieve the purpose of energy saving is the central content of this technical introduction. Adjust the fresh air volume with CO2 concentration to save energy, as shown in the figure:

Schematic diagram of fresh air energy saving scheme for banquet hall and public places

The energy-saving technology of adjusting the fresh air volume of air conditioning by CO2 concentration is adopted in public areas such as hotel banquet hall, multi-function hall and restaurant. The CO2 probe is mainly used to collect the CO2 concentration in the space, and the sensor sends instructions to the intelligent analysis controller, so as to control the electric differential regulating air valve. So as to regulate the fresh air volume and keep it in the best energy-saving operation state. This technology is suitable for occasions with air conditioning mode of return air. The average energy saving value can reach more than 20~35%.