Commissioning Tools For VRF And Chiller System: Now And Then

Commissioning Tools For VRF And Chiller System: Now And Then

In 1995, I was studying HVAC&R during my engineering days, we used to find refrigerant gas leaks with a soap solution and Halide Torches. Nowadays there are more than 10 technologies developed and have transformed the way refrigerant leaks are identified. Those days quality of commissioning use to depend on the time is taken for commissioning. Every step of commissioning was time-bound and a typical chiller commissioning would take 3 – 7 days. I clearly recall during my training days, once a commissioning engineer re-commissioned a chiller after a breakdown in 8 hours. His speedy work was really appreciated by customer and customer gave him an appreciation letter. When he came back to the office and showed this appreciation letter to director engineering, he was almost fired. Director was concerned about the shortcuts he might have taken to commission this chiller as if you follow the standard operating procedure (SOPs) you can’t complete the job in 8hours.

Do we now get time like 3 – 7 days for commissioning? If your answer is no then what has changed these days. Let’s take some example. Those days most of the chillers were built on-site as compared to today where we mostly get completely refrigerant charged chillers on-site. Even if we need to recommission them available tools have changed and equipped us to do it better and faster.

Pressure Testing: those days pressure testing will involve Nitrogen pressure to be held in the system for 24 hours and then we can proceed further. I exactly don’t know the reason of holding for 24 hours but as per my assumption, it must be the limitation of the technology. Say for example a good calibrated pressure gauge used for testing those days must be class 2 that means it can give an error of + - 2% of full-scale reading. If pressure test is performed at 350 PSIG, the gauge used must be 0 to 500 PSIG. This Gauge will give and error of -10PSIG to +10PSIG that means 20PSIG. In this case of 350 PSIG pressure hold, 20 PSIG can be gauge error for 6% of pressure drop can be due to measurement error. So, if you need to be certain that loss of nitrogen pressure is not due to leak you need to first overcome pressure gauge errors, and only way to that is wait for longer time. So, wait for 24 hours to 48 hours and then conclude if pressure test is ok or not. Now a day’s digital manifold gauges are equipped with programs that can make calculation and conclude in less than five minutes if the same system will be able to hold pressure in 24 hour or not. This is possible because of their least count of 0.1 PSIG which was not available in analogue gauges. Imagine if those days pressure test fails it was very difficult to find leaks as Nitrogen leaks that time can only be detected through soap solution. Soap solution was also made using shampoo or detergent. So same case if there is nitrogen test fail and we need to find leak we have following key options today:

• More accurate bubble based leak detectors like Leak Locator Plus which can detect minor leaks as bubbles don’t collapse easy and can last much longer. Since bubble are stable leaks make cloud formation around leak point.

Ultrasonic leak detectors are also available which detects specific noise of gas leaks irrespective of gas type. This have been very useful for commissioning engineers.

• Another option is to use 95% Nitrogen and 5% Hydrogen mixture instead of just Nitrogen for leak testing in this case only 5% Hydrogen does not make the mixture flammable but makes sniffing Hydrogen much easier with electronic leak detectors for Hydrogen.

Post Nitrogen Pressure Test comes vacuum and dehydrations. Two stage, high capacity, Vacuum pumps equipped with non-return valve and Gas Ballast valve and large diameter vacuum rated hoses and core removal tools makes vacuum much easier and faster. Also, same digital manifold are equipped with micron gauges and also built in programs to check for vacuum leak or moisture in system. Once vacuum level say 500microns is reached, system is kept on vacuum hold test similar to nitrogen pressure hold test. This vacuum hold test is not only for leak but also indicates if there is moisture in system. If during hold time vacuum level breaks and rises to nearly 5000 microns and then stabilizes then there is moisture in system. This is due to vaporization of water in vacuum till it reaches ambient temperature as boiling point. The vacuum rise graph plotted during hold test clearly indicated if there is leak or moisture or both in system. Only once system passed vacuum hold test, you are confident of good commissioning. This test also concludes in few minutes due to pre-programed algorithms; you save time and money.

Liquid charging by weight and charge optimization with liquid charging adapters like Blend Vaporizers make charging of blends and well as single refrigerants easy and quicker. Once charging is complete system is run and continuous monitoring of suction superheat and liquid subcooling with digital manifold ensures proper refrigerant charge. These digital manifolds come with temperature sensors for measuring accurate suction line and liquid line surface temperatures. These manifolds are programed with almost all refrigerants to enable calculation of superheat and subcooling on manifold itself. All this data is exported and recorded as authentic commissioning report. This helps future charge optimization and predictive maintenance.