Active Low Oxygen Display Cases
Active anoxic systems allow the use of a well-sealed case that has slight leakage, typically an air exchange rate of less than one air change every ten days. A stream of nitrogen is introduced into the showcase to displace any oxygen that might have leaked in. Active oxygen control generally includes an active control device for maintaining constant humidity.
Active systems are often unable to provide "true" anoxic conditions: Feed volumes from osmotic nitrogen generators are dramatically reduced as purity of the feed is increased. This usually limits the purity of the feed to 0.5% oxygen (or more), thus limiting the lower limit. Even with a nearly pure feed of nitrogen, a substantial flow rate of nitrogen is needed to counter leakage and maintain low oxygen levels. This limits showcase size, and increases energy costs with showcase volume.
An active system can be used on commonly available showcase designs. The nitrogen source can be hidden in the base of the showcase, but noise, heat and vibration considerations usually mitigate towards the location of the nitrogen source in a remote location. As purity of flow is directly related to higher pressures, energy costs may be substantial. As well, nitrogen generators all include high pressure compressors, and must be well maintained.