But for making the selection procedure simpler, it is considered to be near-enough constant. It is not constant for different fluid conditions. Actual value of metal resistance for common air conditioning coils in the normal range of use is from about 0.005 to 0.03 (hr.sqft.F) per Btu, depending on the thickness and material of fins. With fins, most of the heat must pass through the small fin section. The metal resistance of bare pipe surface (no fins) is so small as to be of any significance compared to the normal values of other resistances to heat transfer in a coil. Metal resistance rm=0.025 (hr.sqft.F) per Btu.Outside to inside surface area ratio R = 18.3.Aluminum fins - 8 fpi, 1.3' wide per row.

Copper tube 5/8' OD, 22G thick, 1.5' triangular pitch, staggered from row to row.

The assumption can be reviewed based on the result of the initial selection (remember iteration?) The same value can be assumed for the initial selection. We generally assume bypass factor (BF) in air conditioning load calculations. The condition of air leaving the coil is the mixture condition of fully treated air at ADP and bypass air at the inlet condition.

Face velocity and depth of coil have a large influence on “bypass factor”. The coil inefficiency is expressed as a fraction of air bypassing the coil, or the “bypass factor”. But due to limitations in the coil construction and geometry, some air leaves the coil without getting fully cooled and dehumidified, as if a certain portion of air is bypassing the coil. Air passing over such a coil will leave the coil at a temperature equal to the ADP. In an ideal coil, we can expect 100 % heat transfer efficiency. Number of circuits (1 ton/ circuit for ' coil).Temperature of refrigerant in the evaporator coil.Chilled water entering and leaving temperature (EWT and LWT) for chilled water coil or.To start with, the following assumptions will have to be made Apparatus dew point ADP (F) (This denotes the average outside surface temperature of the coil.).Room DB temperature/Return air DB temperature (F).

Data requiredįor sizing the coil, the following data is required from the heat load calculations. Having understood the terms such as face area, face velocity and depth of coil, fallowing table can be used to estimate coil size.įinal Selection Procedure A. This value gives a very useful clue to quickly estimate the coil cost when one is making a sales proposal. Ft.) Initial Estimateįrom air conditioning load calculations, one can pick up some key values such as the dehumidified air flow (cfm), the total load (ton) and calculate dehumidified cfm/ton. Face Velocity (FPM) = Dehumidified Air Flow (CFM) / Face Area (Sq. Average air velocity across the face area is called coil face velocity or simply face velocity.

Dx coil selection software