Experimental and analytical investigation of hydronic system retrofits in an urban high-rise mixed use building

As the size of buildings and demands on large centralized heating and cooling systems increases concurrent with rapid worldwide urbanization, the energy impact of hydronic distribution systems will become increasingly important in reducing greenhouse gas emissions. Further, in the U.S., the growth in multi-family buildings and the share of residential units in large multifamily buildings is far outpacing single-family construction. This paper describes a study of the pumping energy requirements of an urban 23-story mixed-use, primarily multifamily residential building before and after a suite of energy conservation measures. The retrofit focused on waterside technologies: Variable frequency drives (VFDs), constant and variable speed pumps, and pressure-independent control valves. In the original building, the central pumping equipment was found to be responsible for 55% of total annual owner-metered electricity usage and 29% of all annual owner-paid utility bills. Using extensive in-situ monitoring and analytical models developed for this effort, the full retrofit was computed to achieve a 41% reduction in annual central pumping electricity, representing an annual savings of 12% of all owner-paid energy bills. The most significant energy impact is attributable to the VFDs, and it can be inferred that additional savings could be achieved by installing VFDs on constant speed pumps.