Environmental Chambers are used for several purposes and different experiments, so it becomes important to choose the right one. As with any major purchase, several items must be considered before making the final decision. Many people are tempted to buy on price only. However, as we know, you get what you pay for. Quality, reliability, and service after the sale all add up to the value of your purchase. Over the life of the unit, that can become a costly mistake. Many different types of test chambers are available. Your application is primarily going to determine the type of chamber you need. The better you relay that information to your supplier, the better your chamber will match your needs.
The major distinction is the temperature range in which the chamber will operate. Most manufacturers have a standard high temperature range of 177°C to 190°C for reach-in chambers and welded walk-ins. To cool the chamber, several options are available. The two major categories are expendable refrigerant and mechanically cooled. The two most popular refrigerants are liquid nitrogen (LN2) and liquid carbon dioxide (CO2). Both of these gases are environmentally safe and can be vented to the atmosphere. One must be careful with the temperatures of the environmental chamber as a miscalculation can lead to severe damage.
Humidity is probably one of the most misunderstood topics when it comes to environmental test chambers because the relative humidity (RH) percentage is temperature specific. Since the amount of moisture varies at every temperature, the chamber manufacturers use dew point to describe the RH limitation. Inside the chamber, there is a refrigerated coil controlled at 5°C or slightly below. To achieve lower humidity levels, most manufacturers offer a low RH package.
Product in Chamber
This seems very basic: What is in the chamber and how much? If all the details are not given to the chamber manufacturer, the resulting selection may not be best for your application. For example, you are testing hydraulic valves under pressure and various temperatures. Rarely, if ever, does a fluid leak occur in the chamber. This does not concern you since the warmest temperature achieved in the chamber is well below the auto ignition point of the fluid. But, if a leak happens, the chamber will be at risk of an explosion because the standard nichrome wire heater used in most chambers can exceed 1,000°F surface temperature. For this type of application, a temperature-limited sheath heater must be used. There are many scenarios that could be used for examples, but the bottom line is to make sure you give your chamber manufacturer all the details of your tests.
Chamber construction is a critical area that needs to be evaluated when making a purchase. Most chambers have painted exteriors and stainless steel liners. It is easy to believe they are all built the same way. However, when you evaluate the details, you will see differences that can greatly affect the long-term reliability of the chamber. When leaks occur in the stainless steel liner, a path is opened for moisture to travel in and out of the chamber, especially when the chamber is used for temperature and humidity testing. Most chamber manufacturers use fiberglass insulation. A point of consideration should be the access ports. As the pressure in the chamber goes up and down during temperature transitions, the walls will deflect. Another area that can be compromised over time is where the refrigeration lines penetrate the stainless steel chamber. The refrigeration lines generally are copper tubing. If any sharp edges touch the tubing, a refrigerant leak will develop.
Air-Cooled or Water-Cooled Chamber
The refrigeration system removes heat from the product and the air that lowers the temperature in the chamber. There are primarily two choices when it comes to condensers: air cooled or water cooled. Most small chambers come standard as air cooled. The only utility connection required is power. This is very convenient for moving a chamber from one area to another. Some items, however, need to be considered with air-cooled units. First is the overall heat that is introduced into the room where the chamber is located since most chambers are in air-conditioned areas. Dirt is the second item to consider for an air-cooled system. Large volumes of air are passed through the condenser constantly. If your facility has process water pumped throughout the building and is routed to a cooling tower/dry cooler, a water-cooled chamber may be used. A water-cooled unit is easy to install and maintain.