ASHRAE Journal - May 2009 - 62

ASHRAE 19 Wall and Roof Insulation 2-4 in. 2 in. Ceiling, None Wall 1-2 in. since 1946, None prior to 1946 2 in. Floor/Floor (Roof) Height 12 ft 12 ft Floor/ Ceiling Height 10 ft 10 ft 50 59–2009 Utility Location Ceiling or Part Tunnel Ceiling and Tunnel Some Ceiling, Mostly Tunnel and Basement and Vertical Exposed Ceiling and Buried in Slab YE A R S JOURNAL Type of Building Compact Finger-Type Percent Glass None to 10% 50 to 80% Basement Provided (or Tunnel) None or Minimum None or Minimum Tunnel Since 1946 Basement Prior to 1946 None Accessory Ceiling Yes Yes Yes Since 1946, Basement Prior to 1946 Yes U Factor Ceiling 0.10 0.15 U Factor Wall 0.15 0.25 Lights Watts/Sq Ft 2.5 to 3.5 2.0 to 3.0 Multi-story Rectangle 50 to 75% 13 to 14 ft 10 to 12 ft 0.15 (1946 +) 0.25 (1946 –) 0.25 2.0 to 3.0 (1946 +) 1.0 to 2.0 (1946 –) Mobile 25% Pitched Roof 10 ft Maximum 0.15 0.20 1.5 to 2.5 Table 1 Description of school buildings. construction are similar to those of the finger-type building design. The multi-story rectangle building built prior to 1946 is characterized by high ceilings, large glass areas on the perimeter, about 50 to 75%, and a high percentage of movable sash, with a corresponding amount of infiltration. The heating system is probably cast iron or convectors supplied with either steam or hot water, with all utility headers in the basement and vertical risers up through the building, supplying individual rooms. In all probability, this school building has no supplementary positive ventilation system. However, on some of these buildings, a gravity ventilation exhaust system is utilized. The loading characteristics, fluctuations and demands, as noted for the multi-story building built since 1946, are the same for this building also. In addition, the infiltration rate is much higher for this building and must be taken into account. Another item to be considered is that the light intensities in this type of building are probably 20 to 35% less than those for the previous buildings discussed. However, in the design of any air-conditioning 62 ASHRAE Journal system for these buildings, one should take into consideration the fact that these, in all probability, would be upgraded with regard to the lighting system. Mobile-Type Building The mobile-type classroom building is an upgraded model of what was commonly referred to as the annex type building utilized on university campuses immediately after World War II. The proponents of this building point out that they can be moved at any time to another location should a new school be built in that immediate area. These buildings generally consist of five or six classrooms, with a minimum administration area to support them. They are usually built of prefabricated steel design with prefabricated interior wall surfaces and partitions. The length to width ratio of these buildings is about two and one-half to one. The glass area is approximately 25% of the gross wall area. These buildings utilize a pitched roof and are primarily of one-story design only. The walls usually have about 1 in. of insulation and the ceiling about 2 in. a s h r a e. o rg These buildings are generally heated with a gas-fired furnace or small residential-type boiler with hot water radiation. In some localities where the rate is low enough, they might utilize electric heat. The life expectancy of these buildings is about ten years. The light loading in this mobile-type building is approximately 11/2 to 21/2 watt/sq ft. The air-conditioning loads characterized by this building are such that the outside temperature will have a significant effect upon these buildings, due to the short time lag. The effect of the sun on this type of building would tend to make the loading characteristics fall between the compact building and the finger-type building, as shown in Fig. 2. TYPES OF AIR-CONDITIONING SYSTEMS Some of the systems that could serve these buildings and respond to the variances in loads as they occur will be described. All-Air Systems All-air systems are dual-duct, lowvelocity; dual-duct, high-velocity; single-duct, variable-volume variableMay 2009

ASHRAE Journal - May 2009

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