Improve The Efficiency Of The Heating And Cooling Distribution System
November 13, 2013
Today's tip from Building Operating Management
comes from Daniel H. Nall of Flack + Kurtz. After available environmental resources have been fully exploited to reduce heating and cooling requirements, the next strategy is to improve the efficiency of the heating and cooling distribution system for the building.
One approach to reduced transport energy is to utilize water, to as great an extent possible, as the heat transport fluid for the building. Transport of heat by water is 4 to 10 times as energy efficient as transport by air. The trade-off for reduced transport energy, however, is the decreased effectiveness of free-cooling strategies in water based distribution systems. All water distribution systems, therefore, will be most effective in extreme climates, those that are too hot and humid to provide free cooling, or so cold that waterside free cooling is frequently effective. For these climates, a dedicated outdoor air system with heat recovery, for ventilation and dehumidification, along with a primarily hydronic sensible heating and cooling distribution system, such as fan coils, chilled beams, or radiant panels is likely the most energy efficient system selection.
For peak load operation, the efficiency of distribution systems can be significantly improved by minimizing the pressure drop against which the system must operate. For hydronic systems, pipe sizing and selection of valves is critical for minimizing flow pressure drop. Similarly, for air distribution systems, duct sizing, selection of aerodynamic flow accessories — such as turning vanes — and optimal sizing and selection of dampers are critical to minimizing pressure drop. Coils and other heat exchangers should be selected for reduced pressure drop on both the primary and secondary sides of the exchanger. Minimized approach temperature should also be considered in the selection of coils and heat exchangers. The ideal distribution system, whether air or water, should feature reduced pressure drop along with maximized temperature differential across the system.
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