You can change. However, don’t think about specific area like big data, ai, ux, etc. It is like me saying I want to get into construction and should I start in electrical, plumbing or roofing etc.

Start with learning fundamentals of Computer Science.

Are there any transferable skills? Can you think about some problems you face/faced as a smart buildings engineer. This is your advantage- so to speak - since you are already familiar with another area and can look into practical applications and problem solving.

Let me know if you want to brainstorm or if you want a primer on CS fundamentals and such.

This is a good perspective to think about, I didn't see it like that. It makes sense.

Computer Science is something that always pops up, is it expensive to go down this path, are there any "open learning" courses you can advise on?

There might be a few transferable skills, smart building involves writing your own software (albeit function block style), networking, and graphic design for the interfaces. We also have to use many protocols to interface various bits of kit together to get things chatting, and sharing the data.

I'd love to know more about going down a CS path, thank you.

Some of the resources you can try are:

Path to a free self-taught education in Computer Science! https://github.com/ossu/computer-science

Foundations of Computer Science http://i.stanford.edu/~ullman/focs.html

MIT OpenCourseWare https://ocw.mit.edu/search/?d=Electrical%20Engineering%20and...

and so on.

Try to stay clear of coding schools, dojos etc.

However, it would work best if you have a project idea in mind. Abstraction is your friend. You don't need to be an engineer, but an engineering / problem-solving mindset is very important. There are quite a few well known programmers who don't have the traditional CS background, including yours truly. I self-taught myself and keep learning and writing programs. Feel free to reach out to me (my encoded email is in my profile)