COIL DESIGN BASICS ( HVAC )

 

COIL DESIGN BASICS

Ø  FACE VELOCITY FOR LARGE FLOOR MOUNTED AHU's SHOULD BE LIMITED TO MAXIMUN 550 FPM, FOR DX & CHILLED WATER COILS TO AVOID MOISTURE CARRY OVER

Ø  FOR TERMINAL UNITS LIKE FCU's IT CAN BE 300 FPM FOR LOW AIR SIDE PRESSURE DROP.

Ø  WATER VELOCITY SHOULD BE PRFERABLY KEPT BELOW 6 FPS AND MORE THAN 2 FPS

Ø  HIGHER WATER PRESSURE DROP WILL CONSUME MORE PUMPING ENERGY. HIGHER AIR PRESSURE DROP WILL MEAN MORE FAN POWER

Ø  FOR HOT WATER COILS, WHERE THERE IS NO CONDENSATE, FACE VELOCITY CAN BE KEPT UPTO 750 FPM.

Ø  HOWEVER IF HEATING COIL IS PLACED IMMEDIATELY AFTER COOLING COIL IT SHOULD HAVE SAME VELOCITY AS COOLING COIL. AIR PRESSURE DROP FOR HOT WATER COIL IS LOW, SINCE COIL IS DRY.

Ø  FOR DX - COILS, REFRIGERANT PRESSURE DROP SHOULD BE KEPT TO MINIMUM.

Ø  DIRECT EXPANSION COILS ARE ONE IN WHICH REFRIGERANT IS INTRODUCED DIRECTLY. THE REFRIGERANT LIQUID UNDERGOES A PHASE CHANGE. A DISTRIBUTOR SHOULD BE USED WITH EXPANSION VALVE TO DISTRIBUTE

REFRIGERANT UNIFORMALLY IN ALL THE CIRCUITS.

HVAC coil design involves several key considerations to ensure optimal performance and efficiency. Here are some basic factors to consider in HVAC coil design:

1. Heat transfer surface: The coil design should maximize the surface area available for heat transfer. This is typically achieved by using a serpentine or zigzag pattern of tubes or fins. Increasing the surface area enhances the efficiency of heat exchange between the coil and the air or refrigerant.

2. Tube and fin configuration: The selection of tube and fin materials, size, and spacing is crucial in coil design. Copper, aluminum, or other materials with good thermal conductivity are commonly used for tubes and fins. The size and spacing of tubes and fins affect the heat transfer characteristics and airflow resistance. A balance must be struck to achieve efficient heat transfer while minimizing pressure drop.

3. Fluid flow: Proper fluid flow through the coil is essential. In chilled water coils, the design should ensure adequate water velocity and distribution across the coil to achieve uniform cooling. In DX coils, the refrigerant flow rate and pressure drop must be considered to maintain efficient heat exchange.

4. Airflow: The coil design should accommodate the required airflow rates to achieve effective heat transfer. Proper consideration should be given to the air-side pressure drop and resistance, which can impact the overall system performance and energy consumption. This may involve selecting the appropriate coil depth, fin density, and fin spacing.

5. Coil sizing: The coil size should be determined based on the specific cooling load requirements of the space or system. This involves considering factors such as the heat load, desired temperature differential, airflow rates, and available space for installation.

6. Coil cleanliness and maintenance: Coil design should also consider ease of cleaning and maintenance. Coils can accumulate dirt, debris, and contaminants over time, which can reduce efficiency. Accessible coil designs with proper drain pans and serviceability features make maintenance tasks more manageable.

It's important to note that HVAC coil design can vary depending on the specific application and system requirements. Consulting with a professional HVAC engineer or designer is recommended to ensure the coil design meets the specific needs of the project and complies with applicable standards and regulations.