Indirect bottleneck

The Glitch:

An installer is asked to provide a 4-ton-rated (48,000 Btu/h) geothermal heat pump system that can provide space heating and domestic hot water. The client doesn’t want cooling for the initial installation but would like the possibility of adding it in the future. The installer selects an indirect water heater with a coil rated to deliver 60,000 Btu/h to the tank when supplied with 180° F water from a boiler. He also includes a buffer tank in the system to protect the heat pump against short cycling when supplying a zoned distribution system. A motorized diverter valve is used to route the heated water from the heat pump to either the indirect water heater or the buffer tank. A schematic for the installation is shown in Figure 1. Can you describe what issues might arise with this approach? What would be a simpler design?

Are you an ace troubleshooter?

Within the pages of this magazine, PM’s Hydronics Editor John Siegenthaler, P.E., will pose a question to you, our readers, to review a system’s schematic layout and discover its faults, flaws and defects. Discover archived “The Glitch & The Fix” exercises at its radiant-focused website, www.radiantandhydronics.com. Good luck!