Book - School of Science and Technology

Application 521Internal heat gain*This arises due to matters which occur within the room. In this case they are confined toheat gains from occupants and to lighting but might, in other circumstances, includecomputers, motors, or other sources of heat.From Figure 3.14, for persons at rest:sensible gain per occupantˆ 88 Wlatent gain per occupantˆ 30 WThus, sensible gain ˆ (500 88)ˆ 44:0kWand latent gain ˆ (500 30) ˆ 15:0kWFrom Basis of Design, sensible gain from lighting ˆ 20:0kWSupply air quantity to roomThis is calculated from the total of the individual sensible heat gains set out above. It willbe noted that no inclusion is made for the gain arising from the supply of outsideventilation air to the room for the benefit of the occupants. This latter is a load on theplant and thus does not affect that air quantity.Sensible heat gain in room:(23:9 ‡ 7:1 ‡ 44:0 ‡ 20:0) ˆ 95:0kWDesign criteria now assumed:air temperature rise, from supply to room ˆ 6Khence, supply air temperature ˆ (21 6) ˆ 15 CFrom Table 1.1, for dry air at 15 C:specific heat capacityˆ 1:02 kJ/kgKThus, total air supply mass required:95:0/(6 1:02) ˆ 15:52 kg/sVentilation airCriteria for the supply of outside air were set out in Table 1.9 (p. 17) and it is assumed thatsmoking is not allowed in this hall.From Basis of Design:number of occupants ˆ 500outside air quantity per personˆ 8 litre/sFrom Table 18.1, specific volume of dryair at room conditionˆ 0:83 m 3 /kgThus, mass flow of ventilation air:ˆ 4:82 kg/s(500 8)/(1000 0:83)* Sensible and latent heat gains arising from occupants assume here that they are seated at rest. In othercircumstances, the gain per occupant might be more but the number, equally, might be less.