therefore, wasting pump energy. Wireto-water overall efficiency in these small circulators is often in the range of 20%. The increased power required at each heat pump results in diminished system EER and COP. A one-pipe distribution system with constant circulation avoids the limitations of the subcentral GCHP systems. One-Pipe Advantages Reduced First Cost In a two-pipe network system, additional pipe and pipe fittings are required over the one-pipe arrangement. Multiple one-pipe installations in schools and office buildings have shown a piping installation cost savings of $0.50 to $1.50/ft2 ($5.38 to $16.15/m2). These systems are in the range of 50 to 200 tons (176 to 703 kW) and are located in Figure 3: Simple GCHP. Illinois. Cost savings are due to the installation efficiency associated with the coupled piping system and the design simplicity. Few piping size reductions are required. No flow control valves are needed, and there are low water Heat Pump Figure 4: Subcentral GCHP. Figure 5: One-pipe connection diagram. M Geo Heat Pump FCV Figure 6: Two-pipe variable flow heat pump connection diagram. balance requirements. The pipe insulation has reduced fitting and valve cover requirements. An additional, albeit less dramatic benefit, is the flexibility of locating the pumps anywhere within the system. Since the piping distribution is a single loop, pump location becomes irrelevant; locating pumps at the beginning of the piping network is no longer required. This offers flexible installation options that may be necessary in retrofit applications. Simplicity www.info.hotims.com/25209-4 In a one-pipe system (Figure 2), the main loop flow is provided by a pair of parallel flow pumps. These pumps are alternated October 2009 ASHRAE Journal