How do large hotels?
It is a tremendous cost, and for franchises/chains like you're talking about, it's significant enough to typically warrant a full-time person or small department to manage the issue. Pick a company on LinkedIN and look for someone with "Energy Manager" in their title or with a "CEM" qualification (Certified Energy Manager). These are the individuals that deal with utilities, but electricity, natural gas, fuel oil, etc., and who typically drive projects based on energy savings. The methods they employ, are as varied as the individuals, and depend largely on the needs and or interests of the business.