Free cooling is commonly used in data centers to reduce cooling system energy consumption using a water-side economizer (WSE). In this system, cooling mode is switched when wet bulb temperature (${\mathrm{T}}_{\mathrm{w}\mathrm{b}})$ reaches switchover temperature (${\mathrm{T}}_{\mathrm{s}\mathrm{w}}$), and the cooling tower fans are controlled to maintain a specified cooling water approach temperature (${\mathrm{T}}_{\mathrm{a}\mathrm{p}\mathrm{p}}$). Typically, both ${\mathrm{T}}_{\mathrm{s}\mathrm{w}}$ and ${\mathrm{T}}_{\mathrm{a}\mathrm{p}\mathrm{p}}$ values are fixed. However, under part load conditions, ${\mathrm{T}}_{\mathrm{s}\mathrm{w}}$ and ${\mathrm{T}}_{\mathrm{a}\mathrm{p}\mathrm{p}}$ can be optimized to maximize the system performance and save energy. Currently, there are few appropriate methods available to optimize ${\mathrm{T}}_{\mathrm{s}\mathrm{w}}$ and ${\mathrm{T}}_{\mathrm{a}\mathrm{p}\mathrm{p}}$ in partial-free cooling mode for data centers with WSE. Thus, this study presents a model based methodology to optimize ${\mathrm{T}}_{\mathrm{s}\mathrm{w}}$ and ${\mathrm{T}}_{\mathrm{a}\mathrm{p}\mathrm{p}}$ in different cooling modes. The proposed methodology is verified through a case study based on data of a real operating data center. Comparison between the calculated optimal ${\mathrm{T}}_{\mathrm{s}\mathrm{w}}$ and ${\mathrm{T}}_{\mathrm{a}\mathrm{p}\mathrm{p}}$ with that derived by simulation demonstrates the satisfactory accuracies of the proposed method. The case study illustrates that when ${\mathrm{T}}_{\mathrm{s}\mathrm{w}}$ and ${\mathrm{T}}_{\mathrm{a}\mathrm{p}\mathrm{p}}$ are optimized, the cooling system energy consumption can be saved by 10% when cooling load ratio is 0.6.

自然冷却常用于数据中心，以使用水侧节能器（WSE）来降低冷却系统的能耗。在该系统中，当湿球温度（${\mathrm{Ť}}_{\mathrm{w}\mathrm{b}}）$ 达到切换温度（${\mathrm{Ť}}_{\mathrm{s}\mathrm{w}}$），并控制冷却塔风扇以维持指定的冷却水接近温度（${\mathrm{Ť}}_{\mathrm{一种}\mathrm{p}\mathrm{p}}$）。通常，两者${\mathrm{Ť}}_{\mathrm{s}\mathrm{w}}$ 和 ${\mathrm{Ť}}_{\mathrm{一种}\mathrm{p}\mathrm{p}}$值是固定的。但是，在部分负载条件下，${\mathrm{Ť}}_{\mathrm{s}\mathrm{w}}$ 和 ${\mathrm{Ť}}_{\mathrm{一种}\mathrm{p}\mathrm{p}}$可以进行优化以最大化系统性能并节省能源。当前，很少有合适的方法可以优化${\mathrm{Ť}}_{\mathrm{s}\mathrm{w}}$ 和 ${\mathrm{Ť}}_{\mathrm{一种}\mathrm{p}\mathrm{p}}$采用WSE的数据中心采用部分自由冷却模式。因此，本研究提出了一种基于模型的方法来优化${\mathrm{Ť}}_{\mathrm{s}\mathrm{w}}$ 和 ${\mathrm{Ť}}_{\mathrm{一种}\mathrm{p}\mathrm{p}}$在不同的冷却模式下。通过基于实际运营数据中心数据的案例研究验证了所提出的方法。计算出的最优值之间的比较${\mathrm{Ť}}_{\mathrm{s}\mathrm{w}}$ 和 ${\mathrm{Ť}}_{\mathrm{一种}\mathrm{p}\mathrm{p}}$通过仿真得出的结果证明了该方法的令人满意的准确性。案例研究表明${\mathrm{Ť}}_{\mathrm{s}\mathrm{w}}$ 和 ${\mathrm{Ť}}_{\mathrm{一种}\mathrm{p}\mathrm{p}}$ 通过优化，当冷却负载比为0.6时，冷却系统的能耗可以节省10％。