The evaporator takes heat from the air; fans run to move the air across its surface. Air flow is the volume of air these fans move per hour: 1,000–3,000 m³/h for a small cold room evaporator, 20,000–40,000 m³/h for a large warehouse evaporator. American catalogs use CFM (ft³/min); 1 CFM ≈ 1.7 m³/h. The unit converter has the m³/h–CFM conversion ready.
The ratio of air flow to room volume is the "air change rate". Storage rooms want 30–60 air changes per hour, a blast freezer more than 100; in blast freezing a high air velocity (3–5 m/s) is essential for the product to freeze quickly. In fruit and vegetable rooms and rooms with unpackaged meat, however, excessive air velocity dries the product; there the flow is chosen high enough to reach every point of the product but balanced enough not to dry it.
Along with air flow, air throw is checked: how many metres the evaporator can blow the air. In long rooms a single evaporator cannot reach the back wall; two evaporators or an air duct are needed. Air should travel over the top of the product stack and return underneath; the front of the evaporator must not be blocked with boxes. Our catalog gives air flow and air throw for every evaporator model.