Chilled Water Cooling Coil Design

So a chilled water coil is a fin and tube heat exchanger used for cooling air where the coolant is chilled water and the direct expansion coil is a fin and tube evaporator found in a vapour compression cycle.

Chilled water cooling coil design.

Chilled water coils are one of the most common mediums for cooling air. As warm air passes across the coil and comes in contact with the cold surface of the fins heat then transfers from the air to the water flowing through the tubes both cooling and dehumidifying the air. If the flow rate in the secondary side is low then some chilled water will flow into the secondary and some will recirculate back to the chillers. Beginning in its 2016 version ashrae standard 90 1 now requires chilled water cooling coils be designed for at least a 15 f temperature difference δt between the leaving and entering water.

There is really no difference between hot water coils and a chilled water coils in construction. The vast majority of chilled water coils are constructed from either 1 2 od tubes or 5 8 od tubes. The chilled water is generated and circulated in the primary side the secondary loops will pull chilled water out of the header to cool the building and then dump the warm return back into the header. Designated by the fluids in the tube.

Chilled water cooling coil selection example 4 chilled water coil worksheet example 5 chilled water coil worksheet 6 enthalpy of air table 1 7 air density correction at altitude table 2 7 air density correction at temperature table 3 7 log mean temperature difference table 4 8 basic capacity figure 1 8fpi 9 basic capacity figure 2 1ofpi 10. Evaluate water coil selection choices at various water temperatures and flow rates 4. Properly protect water coils from freezing when necessary agenda water and air velocity ranges coil selection examples chilled. Methods to design the cooling and dehumidifying coil either chilled water coil or dx evaporator coil are usually based on log mean enthalpy or log equivalent dry bulb temperature difference.

In both methods the cooling coil is treated as a single zone region and hence the required surface area is determined. Hot water coils are usually 1 or 2 rows and chilled water coils are usually 3 to 12 rows deep. The chilled water supply temperature usually has a fixed set point and the only variable that affects the output capacity of chiller is the return water temperature. Designing and operating chillers at low temperatures increases the chiller lift and reduces the efficiency of the chiller.

For a given design load the chiller is selected for fixed temperature range t and the associated chilled water pumps are selected for calculated flow rate.