| Maintenance & Fan Life | Big Advantage. Fan & motor are at ground level in the cool, dry inlet air stream. Easier, safer access. Less corrosion and thermal stress on bearings/motor. | Fan & motor are in the hot, saturated exit air plume at the top. More corrosion, moisture ingress risk. Access requires climbing or rooftop work. | Forced Draft. Clear winner for serviceability and component longevity. |
| Thermal Efficiency & Performance | Slightly lower. Air travels horizontally; water falls vertically. This cross-flow is less thermally efficient than true counter-flow. Coil face may not be fully wetted. | Slightly higher. Air and spray water travel vertically opposite (counter-flow), maximizing the temperature difference (ΔT) and heat transfer across the entire coil. | Induced Draft. More efficient heat transfer in a given footprint. |
| Energy Efficiency (Fan Power) | Potential Advantage. Fan pushes dense, cool air. Motor runs cooler. System can use Plenum Fans (housed) which are efficient at static pressure. | Fan must pull/push moisture-laden, less dense air. Motor runs hotter. Often uses Propeller Fans which are efficient at moving high volumes against low pressure. | Contextual. For high-static applications, Forced Draft fans can be more efficient. For standard low-static, they are comparable. |
| Footprint & Space | Larger footprint for same capacity. Air enters from sides, requiring clear space. Design is often wider and shorter. | Smaller footprint. Air enters from bottom/sides and exits top. Can be more compact, especially in modular designs. | Induced Draft. Better for tight spaces. |
| Cold Climate Operation | Better for freeze protection. Fan is on the inlet. If the fan cycles off, cold air is not actively pulled through a wet coil, reducing the risk of the spray water freezing on the coil. | Higher freeze risk. When the top fan shuts off, natural convection can draw cold air up through the wet coil, leading to rapid ice formation. Requires careful controls. | Forced Draft. More forgiving in freezing conditions. |
