1、 Current situation of elevators in China and elevators in tertiary hospitals
1. Current situation of China's elevator industry
As of the end of 2017, the total number of elevators in China had reached about 5.6 million, accounting for about 70% of the global total production. The annual production and ownership of elevators ranked first in the world, making China the world's largest elevator producer and exporter.
However, due to historical reasons such as technological limitations and lagging energy-saving standards for elevators, although China's elevator energy-saving technology has reached the international leading level in some aspects, brands such as Tongli, Mitsubishi, Thyssen, Xunda, Hitachi, etc. have successively launched more energy-efficient permanent magnet synchronous gearless small machine room and non machine room elevators in recent years. However, the penetration rate of energy-saving elevators in the market is still very low. The penetration rate of permanent magnet synchronous gearless elevators that save more than 30% of electricity is less than 10%, and the penetration rate of elevators with built-in energy feedback devices that have a regenerative energy recovery rate of 30% is less than 2%. There is a huge energy-saving space in the entire elevator industry in China, and there is a huge market space for energy-saving elevators.
Current situation of elevator operation in tertiary hospitals
As the main and only rail transportation tool for vertically transporting patients and medical staff on different floors of hospitals, elevators in tertiary hospitals have the following characteristics:
① The number of elevators transported is huge
According to statistics, as of 2017, the average annual outpatient volume of tertiary hospitals in China has reached over 2 million people. Taking Wuxi People's Hospital as an example, in 2015, the annual outpatient volume of Wuxi People's Hospital reached 3.09 million, with an actual opening of 2000 beds. Among them, more than 90% of patients and accompanying personnel need to take elevators to reach designated departments or ward floors. In addition, there are logistics service personnel such as doctors, nurses, administrative management personnel, cleaning and security maintenance personnel in the hospital, making the actual transportation volume of hospital elevators huge.
The following figure shows the daily average number of starts for elevators in hospitals of different levels according to relevant departments' statistics. Among them, the daily average number of starts for elevators in tertiary hospitals in the region has already exceeded 2000 times per day.
The effect of using energy-saving equipment in hospital elevators
▲ Figure 1 Statistics of daily average startup times of elevators in hospitals of different scales
② The elevator has been in use for a long time
Due to the specific needs and service groups of hospital elevators, most medical elevators require 24-hour operation. Taking Wuxi People's Hospital as an example, there are a total of 38 Guangzhou Hitachi brand vertical elevators in Wuxi People's Hospital. Among them, 16 medical elevators in the inpatient department are in a busy operation state 24 hours a day, 365 days a year, except for normal maintenance time. The daily start-up time for outpatient and emergency departments is also more than 12 hours.
③ Elevators have high energy consumption during use
According to statistical data, the average daily electricity consumption of each elevator in a tertiary hospital ranges from 60kW. h to 100kW. h, with an average of 80kW. h/day. In addition, the energy consumption of air conditioning or fans in the machine room specifically used for elevator cooling in summer can reach a comprehensive daily electricity consumption of 100 kW. h/day during peak hours. Taking a tertiary hospital with 40 elevators as an example, the daily electricity consumption of elevators during peak summer hours can reach 4000 kW. h, which is astonishing.
④ High temperature in elevator machine room
Currently, 90% of elevators on the market are VVVF (Variable Frequency Variable Speed Control) elevators, of which only about 2% have built-in energy feedback devices and are high-efficiency energy-saving elevators. The remaining 98% of elevators waste the electricity generated during light load up, heavy load down, and level braking through the use of braking resistors and electric thermal conversion. After a large amount of electricity is converted into heat energy, the temperature in the elevator machine room rises sharply. If forced cooling measures are not taken in a timely manner, the elevator will self protect due to high temperature, resulting in emergency shutdown accidents, seriously affecting the normal operation of the elevator and passenger satisfaction.
Therefore, the national quality and technical supervision and inspection department requires that all elevator machine rooms must be equipped with high-power cooling equipment such as air conditioning and fans, and explicitly stipulates that if the temperature in the elevator machine room exceeds 40 ℃, air conditioning must be turned on for cooling.
⑤ High failure rate of elevator usage
High temperature is one of the main causes of aging and failure of electronic components, and also one of the main reasons for "trapped accidents" caused by emergency shutdowns of elevators during operation. According to the Guizhou sample statistics of elevator big data, the failure rate of trapped people in hospital elevators ranks first among all types of elevators at 9.18%, far exceeding the residential elevator failure rate of 3.44%. Statistics also show that over 95% of "trapped accidents" in elevators occur during hot summer weather, with the vast majority of elevators being caused by excessive use and inadequate cooling measures.
2、 Elevator Regenerative Energy Utilization Technology - Introduction to Electric Energy Feedback Device
The elevator electric energy feedback device is a specialized energy-saving device used for energy consumption braking VVVF elevators. It recovers the direct current electric energy converted from mechanical kinetic energy and gravitational potential energy during light load up, heavy load down, and level braking operation of the elevator. After DC/AC inversion, rectification, and filtering, it is transmitted to the local power grid for use by surrounding electrical equipment of the elevator.
Before the implementation of energy-saving renovation, the characteristic of VVVF elevators using energy consumption braking was not that they consumed a lot of energy, but that they generated a large amount of electricity but were not recycled. On the contrary, the available electrical energy was converted into heat energy and burned away in vain. The secondary problem caused by this was a sudden rise in temperature in the elevator machine room, which required the installation of specialized cooling equipment (air conditioning fans), otherwise it would affect the normal operation of the elevator. The operating energy consumption of cooling equipment itself is also an energy consumption. In elevator machine rooms with poor heat dissipation in summer, the operating energy consumption of elevator air conditioning can even exceed the operating energy consumption of the elevator itself, so energy waste is very serious.
The energy-saving transformation is carried out by using an elevator electric energy feedback device, without changing the original structure of the elevator. Only an energy recovery device is physically connected in parallel. The working voltage of the feedback device is lower than that of the elevator braking resistor, so the feedback device takes priority over the braking resistor and feeds back the electric energy to the grid for recycling in advance. Once the feedback device malfunctions, the DC bus voltage of the elevator will continue to rise, the elevator braking resistor will restart, and the elevator will automatically switch to the original non energy saving working state, but it will not affect the normal use of the elevator. Therefore, the elevator electric energy feedback device is safe. Mitsubishi's GPM-M series and OTIS's REGEN series elevators both come with energy feedback devices.
The effect of using energy-saving equipment in hospital elevators
▲ Figure 2 Working principle diagram of elevator electric energy feedback device
The energy conversion rate of the elevator energy feedback device can reach 97%, with a direct energy-saving rate between 15% and 45%, and an average energy-saving rate of 30%. The highest energy-saving rate measured in hospital energy-saving projects is 51%.
After adopting the elevator energy feedback device, all the electrical energy converted from mechanical energy and potential energy is recycled. The main heat source braking resistor in the elevator machine room stops working and no longer generates heat. Therefore, the temperature in the elevator machine room can be greatly reduced. The air conditioner that originally needed to be continuously turned on to cool the elevator can now be turned on or off less, achieving secondary energy saving by saving air conditioner electricity and electricity costs.
In addition, due to the main heat source braking resistor in the elevator machine room stopping working, the temperature in the machine room has significantly decreased, and the working environment of the elevator has been improved. The elevator can avoid accidents caused by emergency shutdown due to high temperature self-protection. After the improvement of the elevator machine room environment, the aging rate of electronic components on the elevator circuit board will slow down, the elevator failure rate will significantly decrease, and the maintenance cost of the elevator will correspondingly decrease; At the same time, the actual service life of the elevator will also be correspondingly extended.
3、 Benefit analysis after adopting elevator regenerative energy utilization technology
Based on the investigation of successful energy-saving cases of elevators in hospitals of the same level, and combined with the obvious energy-saving effects of on-site testing of elevators at Wuxi People's Hospital, Wuxi People's Hospital carried out energy-saving renovations on 33 VVVF medical elevators that meet the conditions for energy-saving renovation using renewable energy utilization technology and have investment value in two batches. Elevator energy feedback devices were installed, and the energy-saving effects were significant. The results are as follows:
① Energy saving effect
The test results after energy-saving renovation show that the use of renewable energy utilization technology for energy-saving renovation has a significant energy-saving effect on elevators, with a sampling test energy-saving rate of 34.33% and an average energy-saving rate of 30%; At the same time, the temperature in the elevator machine room decreased significantly, and the temperature of the braking resistor dropped from 191.6 ℃ to 27.0 ℃. The failure rate of elevator operation also showed a clear downward trend, and the overall project achieved the goal of achieving high efficiency and energy saving while ensuring smooth and safe operation of the elevator.
Table 1: On site records of energy-saving rate effect testing for the project
The effect of using energy-saving equipment in hospital elevators
② Investment income
This energy-saving project can recover all energy-saving investment in about 2 years. The designed service life of the equipment is 15 years, and the remaining 13 years of energy-saving benefits are the hospital's net income.
③ Environmental benefits
After the implementation of this energy-saving project, it can save about 1980 tons of raw coal for the country, reduce carbon dioxide emissions by about 5.1876 million kilograms, reduce sulfur dioxide emissions by about 16830 kilograms, and reduce nitrogen oxide emissions by about 14652 kilograms.
Table 2 Calculation of Environmental Benefits of the Project
The effect of using energy-saving equipment in hospital elevators
4、 Conclusion
As an important rail transportation tool in hospitals, the safe and smooth operation of medical elevators is related to the efficiency and image of hospital operations, as well as the speed of saving lives. Therefore, ensuring safe and smooth operation of medical elevators in a good working environment is of great significance.
Due to historical reasons such as energy-saving requirements, industry standards, and technical limitations, the proportion of public institutions such as tertiary hospitals using elevators with energy-saving technologies such as energy regeneration technology and permanent magnet synchronous gearless technology is relatively low. Most tertiary hospital elevators have the characteristics of high working environment temperature, high energy consumption during elevator operation, and high failure rate during elevator operation.
Based on the experience of Wuxi People's Hospital in implementing energy-saving renovation of elevators using renewable energy utilization technology for a period of time, it is recommended that colleagues choose high-efficiency elevators with renewable energy utilization technology and permanent magnet synchronous gearless technology as much as possible in the process of hospital construction, expansion, and renovation. For existing buildings in hospitals, it is recommended that hospitals choose energy-saving service companies with renovation experience and qualifications, and scientifically renovate elevators by installing electric energy feedback devices on the basis of ensuring safety, in order to save elevator operating energy consumption, reduce hospital operating costs, and create a green hospital.