The first step is to explore those variables in a building that you do have immediate control over: operating efficiency of heating plant and domestic hot water system, common area and exterior lighting and choice of heating fuels. Heating fuel: #6, #4 or #2? Availability of adequate gas to effect a conversion? Duel fuel or single fuel burner? Have you capitalized on the rebate/incentive programs for the updating of both interior and exterior lighting? If your building has a large number of thru-wall ac units is the perimeter insulated? Going Green isnt always about adding new technologies, its also about ensuring existing technologies are operating at their optimal level.