Smart Buildings Systems for Architects, Owners and Builders

are composed of tubes housing flowing water surrounded by combustion gases
that transfer heat to the water in the tubes. Water-tube boilers are capable of
achieving higher capacities than fire-tube boilers because water or steam pres-
sure can be contained within the tubes. Combined heat and power (CHP) sys-
tems are boilers that provide electricity while also providing heat for a
building, but can be costly to install.

Chillers

Chillers, or air conditioners, utilize heat exchangesand circulate fluid or gas
to cool the air that is passed through the unit. Chillers are often located in a
mechanical area at ground level, or ina central plant in a campus environ-
ment. Chillers cool air by removing heat using the refrigeration or vapor-
compression cycle (also known as the reverse-Rankine cycle), which consists
of compression, condensation, expansion, and evaporation (Fig. 3.2).
A refrigerant in vapor form is initially compressed in a compressor, reduc-
ing its volume and increasing its temperature. It is then pumped to a condens-
ing unit, where the refrigerant is cooled and condensed into a liquid. This
liquid is then pumped to the indoor evaporator unit, where it is passed through

Fan

Evaporator

Vapor Vapor

Condenser

Note: Condenser may

be water-cooled or

air-cooled

Compressor

Liquid and Vapor Liquid

Valve

Warm

Air

Cold

Air

Figure 3.2 Vapor compression cycle.

34 Smart Building Systems for Architects, Owners, and Builders