Development of a Laboratory Data-Based Algorithm for Horizontal Drain Water Heat Recovery Devices, and Predictions of In-Field Performance

Horizontal drain water heat recovery (H-DWHR) devices are products designed to recover heat from heated drain water and transfer it to potable cold water entering a building. They are counter-flow heat exchangers, similar to previously studied vertical drain water heat recovery (V-DWHR) devices, with the fundamental difference being that they are intended to be installed nearly horizontally instead of vertically. These H-DWHR devices are heat exchangers featuring a flat plate for the hot drain water to flow across, and tubes below the plate for the fresh cold water to pass through. Unlike V-DWHR devices, they employ turbulators in the cold water pipes to increase heat transfer and the resulting temperature rise in the cold water entering the building. This project evaluated H-DWHR performance and practical issues through laboratory testing of three HDWHR devices, algorithm development, and simulation studies. The three units were selected for their different lengths, representing available H-DWHR units. One was chosen because it is designed for installation in commercial kitchen dishwashers. Laboratory testing results were used to develop regressions predicting the effectiveness and energy recovery of horizontal drain water heat recovery devices as a function of flow rate through the unit. Algorithms for both V-DWHR and H-DWHR are currently being added to California Title 24, Part 6.