For your company focusing on green buildings and zero-energy building design and construction:

Your website address could be something like "greenbuildings.hk" or "zerocarbonconstruction.hk". This makes it easy for potential clients to understand the nature of your business at first glance.

As for how this ties into your other areas of expertise, here are some suggestions:

Intelligent Grid Operation & Maintenance:

An ideal domain name could be "smartgridmanagement.hk", clearly demonstrating your focus on intelligent grid operations and management.

Kitchen Appliances:

If your kitchen appliances cater specifically to the Hong Kong market, a domain such as "hk廚房電器.hk" (translated from Chinese to mean "Kitchen Appliances HK") would be suitable.

Public Relations:

In the case of public relations, consider using "prconsultancy.hk" or "hkpublicrelations.hk", reflecting your core service offering.

It's important to note that while these suggestions provide direction, the exact domain name you choose should be memorable, unique, and directly related to your brand or services offered.