Floral coolers are specially designed refrigeration units. They differ from other types of coolers in that they have humidifier units to provide a high level of relative humidity. Floral authorities believe that the proper level of relative humidity is just as important as the proper temperature. Coolers without humidifiers can actually dehydrate flowers and thereby shorten their lifespan. A cooler that simply provides a certain temperature range, such as a beverage cooler, is not suitable for flowers.
There are essentially two types of floral refrigerators: storage and display. In those two categories there is a wide selection available, but each should provide a temperature of 34 to 36oF (40oF maximum) and a relative humidity of 90 to 95% (80% is the minimum acceptable according to floral industry standards).
To achieve the lower temperature range, a more expensive cooling coil is needed, but this is considered to be well worth the investment. Cooler temperatures prolong flower life. Flowers stored at 41oF deteriorate three times faster than those stored at 30oF. Most flowers do not freeze at 32oF; generally the temperature must dip below 30oF (as low as 28oF) to freeze flowers.
The relative humidity in floral coolers should be no lower than 80%, and ideally should be 90 to 95%. Humidity is important because it reduces the rate at which a cut flower or green gives off moisture to the air. At a low relative humidity, cut flowers must replace more lost water and can dry out and wilt prematurely. At low temperatures and high relative humidity, a cut flower takes up less water from the container because it is losing less water to the surrounding air.
High humidity does not mean that a cooler should have any standing water in it. If any amount of water accumulates in a cooler, it is not working properly. Condensation on any glass panels can be controlled by purchasing a unit that has heating elements in the glass that will gently defrost the windows without creating heat that will affect nearby flowers or the cooler operation.