Choosing an Environmental Test Chamber
(Klímakamra kiválasztási szempontjai)
Humidity cabinets, controlled environment chambers, test chambers they are called many things, but all of them control temperature and/or humidity within a specific area. The laboratory manager’s job is to determine how many chambers of a specific size are sufficient for their current and future projects. While many systems meet the International Conference on Harmonization (ICH) guidelines, there are many different style chambers available today. All have an assortment of features that can be confusing. The following is a summary of what you will find when shopping for an environmental chamber. “Bench” style chambers can be up to 0.31 m3. While the name implies setting these units on a counter, they can weigh over 136 kg depending on the components. Another popular chamber size on the market today is an upright or “reach-in” chamber. These are available in a variety of sizes with 0,85 to 0,93 m3 being the most prevalent. There are also custom chambers that are made to your specifications. In addition to the variety of sizes on the market, there are also many choices for temperature and humidity control. Temperature control is accomplished by either adding heat or using refrig-eration for cooling. Most refrigeration systems on the market today are chlorofluorocarbon (CFC)–free or non-CFC, meaning that the manufacturer is complying with the US Clean Air Act to insure that the ozone-depleting refrigerants R11 and R12 are not being used in the system. Some refrigeration systems also include phenolic-coated evaporators. These are only required when corrosive material is being tested, and for most customers, this coating is not necessary. Humidity control is achieved by adding and removing humidity within the same chamber. The appropriate method for providing humidity is determined by the user’s temperature and hu-midity requirements. There are a variety of ways to increase humidity within a chamber, includ-ing spray nozzles, atomizers, and steam generators. For applications requiring high humidity levels, the cost of a chamber increases with higher requirements. Chambers with controlled humidity also require a source of purified water. As a general guideline, the feed water required for producing humidity within a chamber should have a specific resistance of 0,5 to 1 megohm. Some environmental chamber manufacturers include disposable cartridges to purify water, while others leave finding a suitable water supply up to the customer. Removing humidity from a chamber involves modifying refrigeration systems using compressed air or chemical dryers. Chamber costs for removing humidity increase as your relative humidity parameter is reduced. Adjustable vents are used to control fresh air exchange within the chamber on most models. Vents, in conjunction with mechanical airflow within the chamber (either horizontal or vertical), ensure optimum performance from your environmental chamber. To reduce condensation on the door from humidity, many manufacturers include a heated door as standard equipment. While temperature and humidity are two parameters that require specific components, there are also many accessories available for environmental chambers that may allow you to perform your tests more efficiently. Manufacturers vary greatly on what is considered an accessory compared to standard equipment. Common features and accessories include chart recorders, remote alarm contacts, RS-232 computer ports, programmable controllers, access ports, and internal electrical outlets. Which features are really needed can only be determined by the user’s specific requirements. Having a chamber that is larger than needed with wide temperature and humidity ranges is a common problem that can be avoided. The steps toward determining the most efficient chamber include defining the duration of the test, specific test protocols, and the size and quan-tity of the samples being tested. Defining the duration of a specific test is extremely important. While each laboratory is unique, many applications that require an environmental chamber run tests for an extended time period. Because of the longevity of these procedures, the most effi-cient chambers are designed for specific parameters. Using specific temperature and humidity parameters when choosing an environmental chamber will ensure your system operates under optimum conditions, thereby improving the overall life of the components. In addition, the chamber’s temperature and humidity performance is greatly improved over a chamber with a wide range of parameters. Finally, determine the size and quantity of samples for a specific test. In order to achieve tight uniformity and stability, airflow throughout the chamber must be consistent. The number of available shelves and their adjustment increments is also important. A general rule is that sam-ples require a minimum of 15-cm clearance on all sides to achieve good airflow within the chamber. By keeping this clearance consistent, the entire chamber will have good temperature and humidity uniformity. Taking the time to look at these three parameters will enable you to choose a chamber that meets your specific test protocols. In addition, you will have optimum temperature and humidity control in a space that fits your laboratory.
Kim Murdock-Timmerman Murdock