Summary Essentials of water treatment for central air-conditioning chillers

Looking at the management of central air-conditioning throughout the country, it is found that very few are well managed, and all have problems of one kind or another to varying degrees. The main problems are described as follows:

1. Problems caused by the unreasonable design of the design department

Many central air conditioners in many units will have various problems during operation. After analysis, a considerable part of them are caused by unreasonable design or even design errors in the design department. Common unreasonable design problems are as follows:

1. In order to prevent scale, a magnetic water device is designed in the water treatment system

There are many types and names of magnetic water devices, some are called electronic water descalers, high-frequency water changers, etc. In short, they all magnetize (polarize) water molecules, and polarized water molecules have extremely strong electricity. Negative, attract calcium and magnesium ions, thereby delaying the scaling time and achieving the purpose of scale prevention. Water molecules with strong electronegativity can also degrade scale and rust. Therefore, some manufacturers say that the products have the functions of anti-scaling, anti-corrosion, descaling and rust removal. Indeed, magnetic water heaters have certain positive effects mentioned above. However, if the installation quantity and installation location of the magnetic water device are not designed properly, it will cause serious corrosion to the water system, and its negative effect is far greater than the positive effect. Cause serious harm to air conditioning equipment and water systems.

For example: For the fully imported central air conditioner of Shenzhen International Trade Building (50 storeys), the design department has designed and installed more than ten magnets in the water system, of which ten magnets are installed in the chilled water system alone. No other water treatment methods have been adopted. The equipment suffered severe corrosion after only one and a half years of operation. The water samples were tested, and the copper ions in the water were as high as 50 milligrams per liter, and the iron was as high as 200 milligrams per liter.

In order to solve the corrosion problem, when sampling from the side of the water inlet of the circulating water pump of the chilled water system, it was found that clumps of red rust gushed out with the water. There is about 8mm thick flocculent rust at the bottom of the 200ml conical flask. The corrosion of the water system is quite serious. I looked up and found that more than 10 magnets were working, and immediately turned off all the magnets of the chilled water system, and only one of the cooling water systems was left working (all magnets were turned off later). This is the source of serious corrosion in the system. It is recommended to use a series of water treatment agents for scale and corrosion prevention. Since the end of 1999, the central air-conditioning system of the building has adopted a series of water treatment chemicals to strengthen operation management. After injection, the equipment neither grows scale nor rust. Test water samples: copper content <0.02mg/L (not detectable), iron content <0.5mg/L.

Li Gong, the chief engineer of Lingdu, suggested that you don't install magnetic water heaters in the central air-conditioning system, and you should install magnetic water heaters on tea stoves and bath stoves.

2. A vertical decontamination device should be installed in the cooling water system

At present, the decontamination devices installed in the central air conditioners of chillers all over the country are all inverted Y-shaped, installed on the riser before the entrance of the air conditioning unit. This inverted Y-shaped decontamination device on the riser can only Capture construction waste in the early stage of equipment operation to prevent these waste from entering the condenser. However, this inverted Y-shaped decontamination device cannot capture fine scale and rust in daily operation, so it will cause condenser fouling, sludge and other impurities.

The correct method is to install a vertical decontamination device (same as the decontamination device in the hot water boiler system) before the water inlet of the condenser to trap various impurities in the cooling water system in the decontamination device.

3. Design a fast drain valve on the outlet side of the cooling water and chilled water of the air conditioner

At present, many units do not have quick drain valves installed at the cooling water end plates or chilled water end plates of central air conditioners, and some units also use seals to block these drain outlets. In fact, this approach is very wrong, and it is easy to cause internal accumulation of air conditioners. The accumulated impurities affect the heat exchange efficiency and also cause the condenser to be cleaned regularly every year.

The correct method is to discharge sewage from the outlet side of the condenser according to the "three-open and three-close method" for the cooling water system 2-3 times a week, and for the chilled water system to discharge sewage according to this method once a week.

4. Install a tap water meter on the make-up pipe of the cooling tower and the make-up pipe of the chilled water make-up tank.

At present, there is no tap water meter installed on the cooling water and chilled water supply pipes of a considerable part of central air conditioners, so that users do not know how much water there is in the system or how many tons of water are added per day, which brings a lot of trouble to operation and management. Because central air-conditioning water treatment generally uses chemical treatment, it must be dosed according to the amount of water supplemented and the amount of system water, so these two water meters are indispensable in design.

5. It is best not to use softened water as the central air-conditioning water supplement

Li Gong, chief engineer of Lingdu, discovered in 2002 that sodium ion exchange regeneration waste liquid caused permanent pollution to groundwater. In Guangzhou, 2 to 5 kilograms of salt are discharged underground for every ton of softened water produced. Due to the requirements of the low-pressure boiler water quality standard (now called the "industrial boiler water quality standard") GB1576, almost all industrial boilers (boilers with pressure ≤ 2.5Mpa) use softened water as boiler feed water. There are more than 9,000 boiler rooms in Guangzhou. Among them, there are more than 2,800 large-scale boiler houses, and hundreds of thousands of tons of salt are discharged underground every year, causing permanent pollution of groundwater, leading to increased risk of humans suffering from high blood pressure, heart disease, and cancer. The consequences are terrible. The United States has restricted the use of sodium ion exchangers.

As mentioned above, it can be seen that the use of softened water is very harmful, so it is recommended that the design department never use softened water as makeup water when designing central air-conditioning. One is to reduce the pollution of groundwater, and the other is to ensure the safe and reasonable operation of the central air conditioner itself. Because softened water is only scale-proof and not anti-corrosive, it is more corrosive than tap water. Using softened water as a water source will cause corrosion of the air-conditioning water system, and it will eventually require anti-corrosion. The general water treatment chemicals should be both anti-scaling and anti-corrosion. In this way, choosing softened water for hydrating is not a good way.

2. Several issues that should be paid attention to in operation control

As the saying goes, "three points for medicine, seven points for management", it can be seen that it is also very important to formulate indicators and methods for central air-conditioning operation and management. Doing a good job in the water treatment operation management of central air conditioning is nothing more than anti-scaling, anti-corrosion, sterilization, and algae killing, and to extend the service life of equipment.

1. Anti-scaling, anti-corrosion

For anti-scaling and anti-corrosion, advanced water treatment chemicals should be selected to ensure that the equipment is free of scale and corrosion.

2. Sterilization and algae killing

The refrigeration system of central air-conditioning generally runs in the hot summer, not only the cooling tower tray is prone to bacteria and algae. Therefore, most units in the south are adding fungicides and algaecides on a regular basis. At present, the commonly used bactericidal and algicides on the market are all oxidizing (and there are non-oxidizing ones), so they have corrosive effects on the iron system. Long-term addition will cause corrosion to the system. Users should pay attention when choosing a bactericidal and algicide.

Sterilization and algae killing is a passive approach. If we choose antiseptic and scale inhibitors and choose agents that can inhibit the growth of bacteria and algae, it will serve the purpose of multiple functions, so that we can avoid or use less bactericidal and algicide. The water system is free of scale, corrosion, bacteria and algae, and the entire water system is free of any impurities, saving more than 20% of electricity during operation.

3. Adjust and control the PH value of the air conditioning water system

There are both copper and iron in the air-conditioning water system, so that both metals are protected. This should control the PH value of the system water between 9 and 9.9, because the passivation zone of iron is at a pH value of 9 to 13. Iron likes alkaline medium, while copper is afraid of alkali. When the pH value reaches 10, copper begins to be corroded. Therefore, in a water system where copper and iron coexist, the pH value should be strictly controlled at 9-9.9 (preferably 9.0-9.9) ).

This also helps to inhibit the growth of bacteria and algae.

It is not difficult to do a good job in the water treatment of central air conditioning. As long as the design and installation are reasonable, the selection of advanced chemicals, and the operation control are reasonable, the water treatment of the central air conditioning can be successfully completed.