In hot summer, the demand for air-conditioning in cities increases with the rise in temperature, which naturally increases the burden of energy use.
The electricity consumed by air-conditioning has always accounted for a high proportion of the overall electricity consumption of a building. This is also true in a hospital that operates 24 hours a day. On average, the electricity involved in cooling accounts for 40-50% of the overall electricity consumption of a hospital facility. Among them, the efficiency of the cooling system It has a great impact on the effective energy saving.
The cooling system of an air conditioner is mainly divided into two types: "air cooling" and "water cooling". Due to various reasons such as technology and safety, hospitals have changed the cooling method from time to time in the past few decades. The Government has also built district cooling facilities in the development area to further reduce the energy consumption for cooling and cooling the whole area.
Written by: Yuan Bailiang, senior engineer and former president of the Institute of Engineers
The evolution of the dehumidification function of the hospital air-conditioning system was mentioned above. This time, I will discuss the evolution of different cooling systems. The original evolution has undergone several turns.
The heat dissipation effect of the air conditioner is closely related to the amount of energy used. The better the heat dissipation effect, the higher the mechanical and cooling efficiency. Traditional air conditioners mostly use condensate or refrigerant to absorb heat, which is a closed-loop system.
Its principle is similar to the operation of the refrigerant cycle in the refrigerator. This kind of condensate is originally in a low-pressure liquid state, and becomes a low-pressure gaseous state after absorbing heat indoors. , and continue to suck the indoor heat again.
The cooling system is mainly divided into "air cooling" and "water cooling". Air cooling uses air as the cooling medium, and the required area for the radiator is relatively large; as for water cooling, water with a lower temperature than the outdoor air is used as the cooling medium. Water, which has a specific heat capacity four times higher than air, will have a higher heat dissipation efficiency, and the heat will be dissipated through the cooling water tower.
In general, the air-conditioners of households mostly use air-cooling, and less use of water-cooling systems. The latter requires more complicated components such as water pumps and water treatment systems. If the household air-conditioners are used for fine cooling, it is not very cost-effective, while hospitals, etc. Large-scale building facilities are more in line with economic principles because of their large cooling capacity and large space.
The author and PolyU scholars have conducted relevant research, and the results have been published in international journals.
Hospitals built in the early years mostly used water cooling for heat dissipation. In the past, large hospitals were located close to the sea, and a one-time flow-away water cooling system would be installed, using seawater as the heat dissipation medium.
However, this move has location restrictions, the facility needs to be closer to the sea, and a seawater pumping station and connecting pipelines must be built to transport seawater.
Generally, the pipelines are located underground in public places, such as the road area. With the development of the city, the road surface work has become more and more frequent, and the problem of pipeline bursting caused by different conditions such as road excavation has become more and more serious. Cooling system to dissipate heat.
However, due to the limited area of the roof of the hospital, the installation of air-cooled units requires the use of fluid mechanics computer simulation analysis to select the installation location of the units to achieve the best heat dissipation effect. There are also many considerations for the installation. In addition, the air-cooled system uses large heat dissipation. The fan introduces airflow, which is noisy during operation, and the unit occupies a larger area. On the contrary, the water-cooled heat dissipation effect is better, so some hospitals later switched to fresh water for water-cooled heat dissipation.
However, after the construction of the hospital and the use of fresh water towers to dissipate heat, there is a chance of bacterial growth, which leads to the problem of Legionnaires' disease transmission.
Although the authorities later solved it through technology, such as setting up an automatic adding chemical solution system for sterilization, for safety reasons, they did not use fresh water for heat dissipation and switched to an air-cooled system.
Since 2000, due to the abundant water resources, the water cooling has been equipped with rigorous regular testing and dosing procedures to solve the problem of bacterial growth. The government has begun to vigorously promote the use of freshwater water cooling to help users improve the cooling efficiency of their air conditioners and reduce energy consumption.
In recent years, the Kai Tak Development Area has also installed a district cooling system that can further save energy. The cooling capacity of the central cooling source is transported and distributed to large commercial and public buildings in the area in the form of chilled water to meet the needs of their refrigeration and air conditioning. need.
Users only need to pay the chilled water fee to the system operator, including the shared infrastructure cost, and each user does not need to install an independent refrigeration unit and cooling system, which can make better use of the building area and reduce related maintenance costs and time. Compared with traditional air-cooled and water-cooled air-conditioning systems using cooling towers, district cooling systems can reduce electricity consumption by about 35% and 20%, respectively.
During the development of the district cooling system by the Hong Kong government, the author was also fortunate to join different professionals in Japan and Malaysia, which have experience in district cooling systems, to learn about the operation and practical difficulties of the local system, so as to make the operation of the system in Hong Kong smoother. .
In addition to Kai Tak, it is expected that in the future, new development areas in the north of Hong Kong will also have the potential to use such district cooling systems, which will bring more benefits to the overall social environmental protection emission reduction and the proposed carbon neutrality work.
"01 Medical Clinic" cooperates with senior engineer Yuan Bailiang to launch a column "Yuantu has you" every Monday to share the big and small matters of engineering and medical care.
Yuan Bailiang has always been committed to promoting the professional development of the engineering field, and has just stepped down as the President of the Institution of Engineers.
Decades of professional journey are really worth recalling, and I am convinced that later generations may be able to understand the key points of the engineering profession.
Yuantu has you, let everyone experience it together.
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