Forced Draft Evaporative Condenser
A Forced Draft Evaporative Condenser is a specific type of heat rejection system that uses the evaporation of water to condense refrigerant gas within a closed coil. The “Forced Draft” part refers to how the air is moved through the unit.
How It Works: The Three-Step Process
Imagine an air conditioner or refrigeration system. The compressor pumps out hot, high-pressure refrigerant gas. This gas needs to condense to release its heat and turn back into a liquid. Here’s how the forced draft evaporative condenser handles this:
1. Heat Absorption:
- The hot, high-pressure refrigerant gas from the compressor is pumped into a coil (often called a condenser coil), which is housed inside the unit.
2. The Evaporative Cooling Process:
- A water pump draws water from a basin at the bottom of the unit and sprays it directly onto the outside of the hot refrigerant coil.
- Simultaneously, one or more powerful fans (forced draft fans) are mounted on the side or bottom of the unit. They force ambient air into the unit and through the spray-soaked coil.
- As the air is forced through the water spray and over the coil, a small portion of the water evaporates.
3. Heat Rejection:
- The energy (latent heat) required for this evaporation is drawn directly from the refrigerant coil.
- This rapid removal of heat causes the refrigerant gas inside the coil to condense back into a liquid.
- The now-cooled liquid refrigerant is then sent to the expansion device and evaporator to complete the cycle.
The warm, moist air created by this process is then discharged out the top of the unit. A bleed-off (blowdown) system and a make-up water float valve manage water quality and level, just like in a fluid cooler.
Key Feature: “Forced Draft” Explained
The “Forced Draft” design is a crucial characteristic with specific advantages and disadvantages:
- How it works: The fan(s) are located at the air inlet side (usually on the bottom or lower sides of the unit). They push ambient air into the unit and through the water spray and coil.
- Advantages:
- Easier Maintenance: The fans and motors are located at ground level or on an accessible platform, making them much easier to service and maintain.
- Stable Operation: The coil operates under positive pressure, which can help ensure more even air distribution.
- Better in Dirty Environments: Since the fan is pushing air, the motor and drive are exposed to the cooler, cleaner ambient air rather than the hot, saturated exhaust air