I have this same shed, I was concerned at first about heat buildup and wondered if I would need to put vents in, or even a vent with a fan. But the temp in shed actually stays down with the pump running(VS pump at 1200 rpm), probably because water flowing through the pipes and filter help pull heat out of the shed. If the pump is off with the sun shining on the shed, then it gets hot inside.
The lid on the shed doesn't seal down on the top and has a gap to let hotter air out too.