This study presents a scalable plate heat exchanger (PHE) model to assess thermal management and pump power consumption for a detailed proton exchange membrane (PEM) electrolyzer balance of plant (BoP) analysis and advanced process control. A PEM electrolyzer model, scaled from 46 kW to 1 MW using an IV-curve-based approach, is integrated with a PHE model developed via the ε-NTU method. The adapted PHE features 9 plates and achieves a cooling power of 340 kW at the PEM elelctrolyzers end of life (EoL). A step response from 100 kW to 1000 kW shows a settling time of 39.12 min within a 0.1 K error band, highlighting the sluggish thermal inertia for dynamic operation. Nevertheless, by controlling the cold water volume flow, the stack inlet and outlet temperatures maintain a safe temperature difference within 10 K, ensuring the mechanical integrity of the stack during the
most severe load changes considered in this study, namely a step response from 10 % to 100 % of the nominal load. Applying a wind turbine power profile demonstrates that, also under fluctuating load, the cold-water flow control stabilizes the stack temperature. The pump power consumption for cooling ranges between 1.1 % and 9.7 % of the total electrolyzer power. The feed water circuit is the main contributor to the pump power consumption. All findings of this work emphasize the significance of BoP components in PEM electrolyzer modeling and operation. Additionally, BoP must be considered if the electrolyzer is intended to perform grid-serving operations.