COLUMN ENGINEER'S NOTEBOOK the potential range of differential pressure FIGURE 2 Non-Decoupled CHW direct building connection. the building connection would encounter throughout the year. The most common Btu Meter VFD building connection in campus-type chilled T water systems is a direct connection since CHWS the same entity owns the central plant, distribution, and buildings. Direct connections DP are suitable in a system with low-rise buildings where the static head in the distribution T CHWR system can be kept low. FM Figure 2 shows a non-decoupled (series pumping) approach where the distribution system differential pressure at the building connection may not be adequate during FIGURE 3 Non-Decoupled CHW direct building connection with HRC. peak loads by adding a building booster Btu Meter VFD pump that is installed with a parallel bypass and check valve so the pump is only operT ated when it is required to increase differenCHWS tial pressure for the building. The primary purpose is for the HRC to HRC DP provide the building heating hot water while DP providing chilled water as the secondary benefit. The objective of the piping configuVFD T ration with the HRC example is to allow the FM CHWR HRC to provide chilled water to either the building load or the campus chilled water distribution system when the building heating load requires the HRC to operate. In the author's booster pumps from causing bypass flow through the experience, system operators always prefer simplicity HRC. over complexity to ensure more reliable operation. Figure 3 shows a simple means to connect the HRC into the pre- Concluding Remarks Heat recovery chiller performance and operation are vious diagram shown in Figure 1. a function of both good HRC selection and good system Figure 3 shows a dedicated variable speed CHW design and controls for both the chilled water and heatpump for the HRC to provide the required differential pressure setpoint across the HRC evaporator. The ing hot water system. Simplifying these piping diagrams while using variable speed pumps can simplify controls pump is required to be sized to overcome the highest to meet the project objectives. Hopefully, these tips can anticipated chilled water distribution system difhelp designers when faced with the challenge of interferential pressure at the building connection. Most large campus systems maintain minimal distribution facing remote heat recovery chillers (HRCs) in buildings that are connected to large campus chilled water differential pressure by including building booster systems. pumps to minimize pumping energy. In this piping configuration, the building will use the HRC chilled water and any additional chilled water will supply the References 1. California Senate. 2018. California SB-100, California campus chilled water distribution system. The autoRenewables Portfolio Standard Program: Emissions of Greenhouse matic isolation valve is required if the main distribuGases. tion pumps maintain neutral differential pressure 2. Peterson, K. 2014. "Improving performance of large chilled at the building connection to prevent the building water plants." ASHRAE Journal 56(1). N O V E M B E R 2 0 19 ashrae.org ASHRAE JOURNAL 71http://www.ashrae.org