In construction projects in which water-cooled chillers are used, the possibility of condenser clogging is higher due to the need to cool the condenser of the chiller, which is done using a cooling tower. Because cooling towers consume a high amount of compensation water. and sometimes this water enters the circuit without hardening and finally causes clogging and accumulation of sediment in the condenser of the chiller. The term is called Chemical Cleaning and in the common air conditioning literature it is called acid washing.

In cases where the water in the cooling circuit, which is a closed circuit, is not filled with hardened water or the system is not properly flushed before the work is done, the need for acid washing of the chiller evaporator has also been observed. It should be noted that when various sediments accumulate in the heat exchanger, it causes the heat transfer level to decrease and as a result, this heat exchanger has lower efficiency and efficiency. Heat exchangers are used in all types of absorption chillers, centrifugal chillers, water-cooled or air-cooled compression chillers, mini chillers, or even fan coils and ventilators.

Types of chiller acid washing

Acid washing before the initial start-up of the device

Acid washing for repairs and maintenance and fixing the defects of the device

Acid washing before the initial start-up of the device

Before the initial start-up of the system, the circuit of the system can be acid washed. Sometimes you can see oil, grease, metal chips, decay or rust in the cooling or heating circuit, and it is better to use an acid washing solution before starting to prevent damage to the device’s converters and circuit control valves. Used the device first.

Another method that is used is mechanical cleaning of converters, which I will discuss more in future articles.

Acid washing of the chiller (for repairs and maintenance and to eliminate the defects of the device)

This type of chiller acid washing is called Remedial Cleaning, which can be used to remove deposits, corrosion and rust or microbiological biomass. To do the work, cleaning materials – which include acid, neutralizing materials and specialized cleaning materials – are used.

Safety and environment in chiller acid washing

It should be noted that this should be done by an experienced and experienced specialist, in addition to the need to comply with safety requirements, including proper equipment, working with acid also requires mechanical ventilation of the space. And finally, measures should be taken so that the output acid does not enter the underground water table as much as possible. This is not observed in Iran, but it is a responsibility that weighs heavily on all of us, and we know that the future and engineering standards are built with the decisions of the present time.

Choosing an acid to wash the chiller

Hydrochloric acid and sulfamic acid solutions can be used for acid washing.

5 to 20% hydrochloric acid is suitable for removing iron oxide, calcium deposits, carbonate deposits, phosphates, silicates and sulfates. Below I describe the correct way to make a 10% solution with an example from the American Society for Testing and Materials ASTM. You must prepare and mix the following ingredients. In the American version, these instructions are written to prepare 1000 gallons of solution, and I have converted the units to liters.

1079 liters of 36% hydrochloric acid

2271 liters of water

Inhibitor in the necessary amount – MIL-I-17433

In a separate tank, add 39 kg of copper metal corrosion inhibitor. Diethylthiourea can be used.

Add 55 kg of bifluoride and 3.79 liters of wetting agent MIL-D-16791.

Finally, mix both tanks together to obtain 3,785 liters or 1,000 gallons of solution.

How to acid wash the chiller
Close the inlet and outlet valves of the chiller and isolate the device.
Install the ball valve or ball valve at the lowest point of the chiller. You can prevent backflow by closing this valve.
Connect the circuit rotation housing connections. Currently you pump from the bottom of the chiller and the fluid circulates from the top of the chiller.
The housing should be installed in the highest part of the chiller. If the output of the converter pipes is lower, install the housing higher.
Fill the chiller with water and perform the hydrostatic test. By doing this, we make sure that the circuit works properly and without leakage.
As the sediments come out, you need more water and you have to add it to the circuit.
During the operation, you must check that the inlet and outlet valves of the chiller are completely closed.
Add acid to the circuit. And according to the relevant tables, give it time to dissolve the deposits.
It is very important to control the pH of the circuit during the process.
Turn off the pump, disconnect the connections and connect the drain and flush the system.
Add water to the circuit and continue circulation for 10 to 15 minutes.
Turn off the pump and disconnect its connections and return the chiller to the main circuit and connect the valves.

After the publication of the text, Engineer Charakh, who is an expert in the construction and maintenance of all types of chillers, added two practical points:

During acid washing of absorption chillers, nitrogen must be injected and the vacuum of the device must be broken. This operation is done because if the tubes are leaking due to corrosion, the acid will not enter the lithium bromide. And another thing is that neutralizing materials must be used before dewatering and starting the chiller so that the effects of the acid are completely eliminated