The system shown was installed to provide domestic hot water to a high-end home with six bathrooms. The installer selected the largest 119-gallon indirect water heater available from his local supplier. The tank’s internal heat exchanger was rated to transfer 250,000 Btu/hr when supplied with 180º F water from the boiler.
The installer piped it in with 1-in. copper tubing because that was the size of the piping connections on the tank. He used three identical “zone” circulators, one for each boiler and one for the indirect tank. He used a larger circulator for flow to the space-heating portion of the system.
Being concerned about a potential complaint over not enough hot water, the contractor convinced the owner to double-up on boiler capacity, and thus installed two boilers, each rated at 250,000 Btu/hr. He also set the internal high-temperature limits on each boiler for 200º during a call for domestic water heating (because that’s as high as the control would allow). He figured that 200º will significantly increase the heat transfer through the tank’s coil heat exchanger.
When put in operation, the system experienced serious problems. The 15-gpm “tropical downpour showering experience” in the master bathroom was only comfortable for about five minutes, followed by a rapid drop in water temperature. The boilers also short-cycled and emitted knocking sounds during the DWH mode. Even worse, the house quickly overheated each time there was a call for domestic water heating.
Can you spot at least five details in the Glitch drawing that are incorrect and also recommend how to fix this situation?