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It is defined as the ratio of the effective room sensible heat to the effective room total heat where ERSH = Effective room sensible heat = RSH + OASH × BPF = RSH + 0.0204 V̇1(td1 − td2) × BPT Figure 20.32 Effective room sensible heat factor ERLH = Effective room latent heat = RLH + OALH × BPF =…

It is defined as the ratio of total sensible heat to the grand total heat which the cooling coil or conditioning apparatus is required to handle (Fig. 20.31). where TSH = total sensible heat = RSH + OASH TLH = total latent heat = RLH + OALH GTH = grand total heat = TSH +…

It is defined as the ratio of room sensible heat to the total heat (Fig. 20.29). where RSH, RLH, RTH = room sensible, latent and total heats respectively. Figure 20.29 Room and supply air conditions and ADP Figure 20.30 Grand sensible heat factor 1 Estimation of Supply Air Conditions When the supply air conditions are not known, then the…

An estimate of the heating load is made on the basis of maximum probable heat loss of the conditioned heated space. The heating loads are:

The components of a cooling load are: 1 Heat Transfer Through Walls and Roofs The heat transferred through a plane wall by conduction is given by Fourier law. For a single wall shown in Fig. 20.28(a), we have where   k = thermal conductivity of wall, W/(m. °C) Ac = area of wall cross-section, m2 Δt = temperature difference on…

1 Selection of Inside Design Conditions The inside design conditions depend on the particular air-conditioning system. The important air-conditioning systems are: 1. Cold storage, 2. Industrial air-conditioning, 3. Comfort air conditioning   Table 20.1 Storage conditions and properties of food products 2 Selection of Outside Design Conditions For the outside design conditions in summer, it is…

Effective temperature (ET) is defined as the temperature of saturated air (RH = 100%) at which the human beings would experience the same feeling of comfort as experienced in the actual unsaturated environment. It may also be defined as that index which correlates the combined effects of air temperature, relative humidity and air velocity on…

The rate at which body produces heat is called the metabolic rate. The heat produced by a normal healthy person while sleeping is called the basal metabolic rate, which is of the order of 60 W. The maximum value may be 10 times as much as this for a person engaged in sustained hard work. Human comfort is…

Consider two air streams 1 and 2 mixing adiabatically, as shown in Fig. 20.19(a) Let   ma1, h1, w1 = mass, enthalpy and specific humidity of entering air at 1. ma2, h2, w2 = corresponding values of entering air at 2. ma3, h3, w3 = corresponding values of leaving air at 3. The mixing process on psychrometic chart is shown in Fig. 20.19(b). For the mass balance,…

The psychrometric processes by which the state of moist air can be altered are shown in Fig. 20.7. These processes are: Figure 20.7 Basic psychrometric processes 1 Sensible Heating or Cooling Process The heating/cooling of air without any change in its specific humidity is known as sensible heating/cooling. The process of sensible heating (line 1-2) or cooling…