ABSTRACT
This chapter discusses the various components of heat losses and gains in buildings, which play a major role in steady-state load calculations. Loads refer to the thermal heat rates that must be supplied or removed by the HVAC equipment to maintain a space at the desired conditions. These can be broadly divided into three sources: from envelope-related flows, from internal heat sources, and from air infiltration (which was covered in Chapter 6). We start by addressing the prevalent engineering calculation procedures of estimating solar heat gains in buildings through walls, roof, and below-grade surfaces such as basement walls and floor and slab-on-grade floors (heat gains through windows have been treated in Chapter 5). For opaque surfaces on which solar radiation is incident, we introduce the concept of sol–air temperature. This is followed by a treatment of internal heat gains from occupants, lights, and equipment. We then discuss the notion of overall conductive heat loss coefficient and the concept of steady-state thermal balance of a building. How these concepts can be used to analyze unconditioned spaces is also presented. Finally, we address the need for thermal zoning of building spaces, i.e., the separate treatment of different spaces in a building where the loads are too dissimilar to be lumped together for satisfactory indoor thermal comfort.
