Chilled Water Cooling Coil Design

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.

Chilled water cooling coil design.

In both methods the cooling coil is treated as a single zone region and hence the required surface area is determined. Designing and operating chillers at low temperatures increases the chiller lift and reduces the efficiency of the chiller. Properly protect water coils from freezing when necessary agenda water and air velocity ranges coil selection examples chilled. Chilled water coils are one of the most common mediums for cooling air.

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. 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. And the leaving water temperature must be no colder than 57 f at design conditions 1. Designated by the fluids in the tube.

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. Evaluate water coil selection choices at various water temperatures and flow rates 4. 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. In chilled water system design the low coil temperatures required for this process dictate the design chilled water temperature 42 44 f.

Understand the balance of coil face area airside pressure drop and waterside pressure drop when selecting a coil 5. 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. 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. 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.

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.