Controllable Heat Exchanger

Drain water heat recovery systems are heat exchangers, which use hot drain water to preheat cold water bound for the hot water tank. Current, passive drain water heat recovery systems have no control over the flow of the incoming cold water. That flow rate is entirely dependent on the depletion of the hot water tank. This team’s solution, RecoverE, actively manages the flow of cold water, by utilizing a control scheme dependent on the heat potential within incoming drain water and the current hot water tank volume. This allows for a better, more transparent system, which recovers heat from the previously uncaptured delayed-draining loads: clothes washer, dishwasher, and bath.

This project implemented a basic prototype consisting of simulated loads, temperature and flow meter sensors, and a controllable valve which was actuated according to the designed control logic.

It is estimated that, in the average residential setting, capturing these loads may improve drain water heat recovery system performance by as much as 28%. And, that system performance improvement may be larger in multiunit settings (hotels, apartments) and settings with a larger delayed-load constituent (laundromats, commercial kitchens). This performance improvement, and the appeal of a “smart” technology, may help spur customer adoption of drain water heat recovery – saving money, saving energy, and saving emissions.