DPHX (dew point evaporative heat exchanger): System design and performance analysis

• The limitations of DP-IEC (dew point evaporative cooler) as an air handling unit are investigated.
• A new type of dew point evaporative cooler, the DPHX (dew point evaporative heat exchanger) is presented.
• The performance of the DPHX is analyzed through numerical analysis.
• System design process and energy performance of DP-IEC and DPHX with liquid-desiccant unit are presented.

The main purpose of this study is to propose a new type of DP-IEC (dew point evaporative cooler), a DPHX (dew point evaporative heat exchanger). A DP-IEC, known as regenerative evaporative cooler or M-cycle indirect evaporative cooler, has drawn great attention from researchers because it can theoretically cool the air to its dew point temperature, thereby overcoming the high SAT (supply air temperature) problem of IEC (indirect evaporative coolers). However, this study found that extracting air from dry channel leads to the two limitations of complex ventilation control and dehumidification energy waste. The DPHX, which introduces a portion of the return air to the wet channel, is proposed to overcome these two limitations. Using a finite difference model, the design process, cooling performance, and pressure drop are investigated. In addition, the systematic energy performance of DPHX with a LD (liquid-desiccant) unit (LD + DPHX) is evaluated in the summer design condition and compared to that of the VAV (variable-air-volume) system and DP-IEC with an LD unit (LD + DP-IEC). The simulation results show that the LD + DPHX can reduce source-weighted energy by 15% compared to the LD + DP-IEC by reducing the size of the LD unit and fans.

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