Experimental assessment of thermal effectiveness of a regenerative indirect evaporative cooler

Heating, ventilation and air-conditioning, HVAC, systems represent a significant energy use in Europe, around 50% of total energy use in buildings. Conventional HVAC systems are mainly based on direct expansion units, whose use of 100% outdoor air leads to high energy use. Then, different innovative and efficient air-cooling systems could be an interesting alternative to approach Nearly Zero Energy Buildings, nZEB. One of these efficient solutions is the technology of indirect evaporative cooling. This work was based on the experimental evaluation of a regenerative indirect evaporative cooler, RIEC. Several empirical tests were carried out under different inlet conditions: inlet air temperature values between 29 °C and 43 °C, <em>T_OA</em>, and inlet air humidity ratio values between 9 g/kg and 13 g/kg, 𝜔<em>_OA</em>, were considered. A constant inlet air stream, V<em>_0A</em>, and a constant supply air stream, <em>_SA</em>, were adjusted during these tests for a steady-state period of thirty minutes each. The response variables which evaluated the thermal behaviour of this RIEC system were: (i) dew point effectiveness, <em>ε_dp</em>; (ii) wet bulb effectiveness, <em>ε_wb</em>. High values of <em>ε_dp</em> and <em>ε_wb</em>were reached when the inlet air humidity ratio was 9 g/kg, around 0.87 and 0.92, respectively. However, low values of dew point effectiveness, 0.71, and wet bulb effectiveness, 0.78, were showed when the inlet air temperature was 29 °C and the inlet air humidity ratio was 13 g/kg. According to the results that this study showed, the RIEC system could be an interesting alternative in spaces where improved indoor air quality is required by using 100% outdoor air. This type of systems could achieve high values of thermal performance, specially under hot-dry climatic conditions.供暖、通风与空调（Heating, ventilation and air-conditioning, HVAC）系统在欧洲的能源消耗中占比可观，约占建筑总能耗的50%。传统HVAC系统主要以直接蒸发式机组为主，其100%使用室外新风的运行模式会导致较高的能源消耗。为此，各类创新性高效空气冷却系统可作为实现近零能耗建筑（Nearly Zero Energy Buildings, nZEB）的可行备选方案之一，其中间接蒸发冷却技术便是这类高效解决方案中的典型代表。本研究针对一款蓄热式间接蒸发冷却器（regenerative indirect evaporative cooler, RIEC）开展了实验评估。实验在多种进气工况下进行：设置室外新风进气温度（T_OA）介于29 ℃至43 ℃之间，室外新风进气含湿量（ω_OA）介于9 g/kg至13 g/kg之间。实验过程中，将新风进气流量（V_0A）与送风流量（V_SA）均调整为恒定值，每个稳态测试阶段持续30分钟。本研究用于表征该RIEC系统热行为的响应变量包括：（i）露点效率（ε_dp）；（ii）湿球效率（ε_wb）。实验结果显示，当室外新风进气含湿量为9 g/kg时，该系统可获得较高的露点效率与湿球效率，分别约为0.87和0.92。然而，当室外新风进气温度为29 ℃、进气含湿量为13 g/kg时，其露点效率仅为0.71，湿球效率仅为0.78，性能表现较低。基于本研究的实验结果，RIEC系统可作为需采用100%室外新风以提升室内空气质量的场景的备选方案。这类系统可实现优异的热性能，尤其在炎热干燥的气候条件下表现更为突出。