with an extra 198 cfm [93 L/s] of relief air at room conditions when the room is occupied. This yields the same room relative humidity with a satisfactory volume of total air movement. 5. Room 5 at 80% lighting and 100% occupancy loads. This room needs 188 cfm [89 L/s] or 0.59 cfm/ft 2 [3.0 L/s m 2 ]. The intense solar effect at design condition places too much of a throt- tling demand on a west perimeter zone during sunless periods, with a similar but less intense situation for the east exposure. During weather below 76°F [24.4°C], this can be taken care of with separate zoning of east and west radiation and selective reset of the radiation schedule for excess radiation, when appropriate, to maintain the minimum airflow in the shaded rooms. Thus, Room 5 would need only 400 Btu/h [117 W] excess radiation to maintain 0.65 cfm/ft 2 [3.30 L/s m 2 ]. If moving shadows result in simultaneous sunlit and shaded rooms on the same exposure, with the shaded room set for radiation to maintain
324 ⏐ A PPENDIX C 0.65 cfm/ft 2 [3.30 L/s m 2 ], the sunlit room will have excess cooling available to neutralize the solar radiation effect in each module (16 ft deep, 1 ft wide [4.9 by 0.3 m]) in a west exposure of (1.1) (2.34 – 0.65 cfm/ft 2 ) (76 – 58.1) = 33.3 Btu/h ft 2 [(1.2) (11.89 – 3.30 L/s m 2 ) (24.4 – 14.5) = 102 kW/m 2 ], which is more than required to neutralize the excess radiation and the sun effect in a sunlit room. During weather above 76°F [24.4°C], the problem is nonexistent because the additional conduction load brings the sensible load and the room air rate within the criteria limits. Since room types 2, 3, and 5 constitute practically the entire building and can be maintained at 45.5% relative humidity or less with a supply temperature of 58.1°F [14.5°C], the designer should explore raising this temperature and even lowering the room tem- perature somewhat below 76°F [24.4°C] in order to raise the room airflow rate. In the illustration given, there is no doubt that the west- and east-side exposures could be brought up to 0.65 cfm/ft 2 [3.30 L/s m 2 ] with supply air scheduling alone, leaving radiation sequence reset only for more stringent requirements. The tabulation is shown with excess radiation. With effective distribution, 0.65 cfm/ft 2 [3.30 L/s m 2 ] can pro- duce in excess of 10 fpm [0.05 m/s] air motion in the occupied zone. Simple VAV systems under certain part-load conditions can operate satisfactorily with considerably less than that value, although occupant complaints have been encountered. The designer must use judgment in appraising these results, and the effect of air quality control and code restrictions during part-load operation, upon the design. Diffusers with a high induction ratio may be help- ful in avoiding potential low-circulation problems. C.4 COOLING CALCULATIONS FOR WINTER PEAK LOAD This analysis assumes outdoor conditions of 0°F [–17.8°C] and relates to Figure C-1(B).
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- ASHRAE, air-conditioning system design