How can we decrease the cooling load capacity without decreasing air flow (L/S) in hap 4.9 ?

decrease the on coil - Off coil temperature difference. you ll get relatively higher airflow for a particular cooling load.

tTop Answer: you can use ASHRAE Atrium. Calc. excel sheet and you will find a good description for the manual procedures  2.1.1 Convective Heat Release Rate The convective portion of the heat release rate (HRR) is Q c = XQ (1) where Q c = convective heat release rate, Btu/s (kW), Q = heat release rate, Btu/s (kW), X= convective fraction, dimensionless. The above equation is the same as the equation of NFPA 92 section 5.5.1.3. A convective fraction of 0.7 is commonly used for most design applications, but the value of X is much different for some fuels. 2.1.2 Axisymmetric Plume Design fires located in the large atrium space are usually analyzed as having an axisymmetric plume (Figure 1a). For z greater than or equal to z l (z >= z l ), the mass flow of this kind of plume is   m=(0.071 Qc ^1/3 Z^5/3) + (0.0018 Qc) For z less than z l (z z l ), the mass flow is  m = 0.032 Qc^3/5 Z where m = mass flow in the plume, lb/s (kg/s), Q c = convective heat release rate, Btu/s (kW), z = distance above the base of the fire, ft (m), z l = limiting elevation, ft (m).  For smoke temperature: Ts = To + (KsQc / m Cp) where: Ts = smoke layer temperature To = ambient or outdoor temperature Ks = 1 for steady smoke exhaust m = exhaust mass flow rate Cp = spacific heat for smoke for density of smoke: ps = Patm / (R(Ts+273)) where ps = smoke density kg/m3 Patm = atmospheric pressure Pa R = gas constant = 287 j/kg k Ts = smoke layer temperature