Never been to Pennhurst myself, being over in Pendle, but this sort of thing catches my attention because I've had similar experiences near old abandoned buildings up here and the feeling is hard to describe to people who haven't felt it.
What exactly did you experience? Was it more of a pressure sensation or something more like your thoughts going strange on you? I ask because there does seem to be a pattern across different locations where caretaker buildings specifically produce these reports more than the main structures, which I find genuinely interesting. Could be related to the amount of time one person spent in that small space over many years, if you believe that kind of emotional residue is a real thing.
There's a gamekeeper's cottage not far from me that gives me the same feeling every time I walk past it on an evening. Been meaning to take a proper reading over there with a meter but haven't got round to it yet. Would be good to hear from others who've visited Pennhurst and compare notes properly.