Since February 2008, the collaborative team has used an iterative process to develop retrofit measures that maximize greenhouse gas and cost savings.

Project activities were divided into four phases: Inventory & Programming, Design Development, Design Documentation, and Final Documentation. Workshops, presentations to ownership, and deliverables helped to keep the team on track over the eight-month period. Daily activities included: building walk-throughs, meetings with the operations staff, collecting metered data, and pricing opportunities. The timeline below outlines key outputs from the project development process.

Sustainability Timeline

Lessons Learned

In the process of developing specific project recommendations, the team uncovered several key lessons for the retrofit of large multi-tenant commercial office buildings.

Five of the most important are described below – both to help others take on their own retrofit projects and to encourage further research.

  1. Developing robust solutions requires the coordination of several key stakeholders

    Developing robust solutions requires the coordination of several key stakeholders. Planning energy efficiency retrofits in large commercial office buildings must address a dynamic environment, which includes changing tenant profiles, varying vacancy rates, and planned building renovations. In the Empire State Building, the project team included engineers, property managers, energy modelers, energy efficiency experts, architects, and building management.

    Each of these stakeholders was needed to help build a robust energy model that addressed the building's changing tenant profile and helped the team model the impacts of its energy efficiency strategies. Coordination also included the tenants. Involving tenants and considering their perspective early on is critical because more than half of the energy efficiency measures that will be implemented at the Empire State Building involve working both with tenants and within their spaces.

  2. Maximizing Energy Savings Profitably Requires Planning and Coordination

    For an energy efficiency retrofit to be cost effective, the retrofit needs to align with the planned replacement or upgrades of multiple building systems and components. For instance, the Empire State Building had plans underway to replace its chillers, fix and reseal some of its windows, change corridor lighting, and install new tenant lighting with each new tenant.

    Since these upgrades were already going to be carried out, the team redesigned, eliminated and created projects that cost more than the initial budget but had significantly higher energy savings over a 15-year period. When these energy savings were accounted for along with the added upfront project costs, the net present value of the energy efficient retrofit projects was better than that of the initial retrofit projects. However, the energy savings are not substantial enough to offset the full capital cost. This means that doing energy efficiency projects well before major systems and components are ready for replacement will likely be cost prohibitive, with a poor net present value. The large volume of existing commercial buildings suggests that there is a tremendous opportunity to reduce energy consumption by existing buildings through energy efficiency; however, capturing these reductions in a profitable manner demands careful planning and coordination to ensure that energy efficiency retrofits align with building replacement cycles.

    For many buildings that are not in or approaching major replacements, there may still be a major opportunity to retro-commission the building. Retro-commissioning improves the operation of existing buildings, many of which are typically run to minimize complaints, rather than optimize energy performance and create comfortable working environments. Retro-commissioning can typically reduce energy use between 5 – 15 percent in most existing buildings. Developing a tool or set of tools that can quickly triage a building to determine if the building is a candidate for a whole building retrofit, retro-commissioning or no action until a few years more; will dramatically improve the effectiveness of funds and efforts directed towards energy efficiency retrofits of existing buildings.

  3. Finding the Winning Combination of Business Value and Reduced Energy Consumption

    In the Empire State Building, maximizing profitability from the energy efficiency retrofit leaves almost 50 percent of the energy reduction opportunity on the table. The building owner, while still selecting an optimal package of measures with a high net present value, sacrificed 30 percent of profit to deliver more energy reductions and improve the lighting and tenant comfort within the building. Changes in energy prices and/or the cost of energy efficiency technologies may help to better align profit maximization and energy reduction. However, as things stand currently, there is a gap between the socially desirable amount of energy reduction and the financially beneficial amount of energy reduction from a building owner's perspective.

  4. Creating a Replicable Process for a Whole Building Retrofit

    Developing the energy efficiency strategies that will be implemented in the Empire State Building took over nine months of intensive building audits, brainstorming charrettes, energy modeling, documentation, and financial analysis. Although the Empire State Building is a very unique building with unusual challenges, the process used to drive deep energy and carbon savings in the Empire State Building can be made much more efficient. Having completed the recommendations for the Empire State Building, the project team recognizes a number of opportunities for condensing the study period exist, these opportunities include: developing experienced teams, creating tools for rapidly diagnosing and categorizing a building (or a portfolio of buildings), quickly developing a “first-cut answer,” and developing and using tools to quickly iterate between financial and energy modeling to arrive at the optimal package of measures.

  5. Carbon Regulation Does Not Significantly Affect the Empire State Building Recommendation

    The financial decision-making tool helped the team to understand that the recommended package of energy efficiency measures would not significantly change even if there were carbon regulation that leads to higher energy prices over time. Carbon regulation that changed energy prices by less than two percent per year had little effect on the financial performance of the modeled packages. However, if energy prices rise by over 8 percent (associated with a carbon price of approximately $30/metric ton of CO2), a package with all of the energy efficiency measures that were analyzed (as opposed to those that were recommended), rises to NPV neutral instead of NPV negative.

Future Research

After nine months of extensively studying and evaluating the Empire State Building, the project team has discovered several research topics that could help accelerate greater carbon savings across the U.S. and global existing commercial building stock.

The project team realizes many other groups and projects are attempting to address similar issues. To comment on your work in these areas, please email, and we will update the research site accordingly.

Capturing Tenant Energy Savings

In existing commercial buildings, capturing many profitable energy efficiency opportunities requires engaging with tenants. In the Empire State Building retrofit, over 50 percent of the opportunities required some level of tenant engagement. Often energy efficiency opportunities that require tenant engagement are not implemented because of numerous real or perceived barriers including split incentives, business interruption, etc.

Research is needed to collect case studies demonstrating the business case for engaging tenants in building retrofits. In addition, best practices and recommendations for engaging tenants could help spur building owners to pursue tenant energy savings potential. In the team's experience, recommendations could include a set of actionable items such as sub-metering, creating green lease rider templates, creating programs to incentivize and engage tenants, etc. that will help owners and operators overcome real and perceived barriers to engaging tenants in energy efficiency projects.

Energy Efficiency Retrofit Measures: Why do some typically make the cut and others don't and what can be done to increase the pool of opportunities?

In a typical energy efficiency retrofit project led by an ESCO, the ESCO focuses on upgrading lighting systems and HVAC controls (1,2).

This focus can usually generates 15-20 percent reduction in a building's utility bills. In the Empire State Building retrofit, the team initially conjured up more than 50 potential energy efficiency retrofit measures. Rigorous energy and financial analyses whittled the list down to only eight measures that will generate approximately 38 percent reduction in the Empire State Building's utility bills. Why did the other 42 not make the cut? Why do most retrofit projects fail to incorporate measures beyond lighting systems and HVAC controls?

Research and case studies are needed to help identify broader sets of measures with commercially viable financial returns and to determine the conditions that will make other measures technologically and commercially viable in a typical building retrofit.

Retrofit Diagnostic Tool

Evidence from the Empire State Building retrofit suggests that without proper planning it will be difficult to realize energy and carbon reductions that pay back initial investments in a timely manner (i.e., NPV positive). For energy savings to adequately compensate for initial capital investments, a retrofit must typically be preformed during the time when the building would replace major systems and components like windows, lighting, and HVAC. Aligning a building's replacement cycle and an energy efficiency retrofit requires planning, particularly if a large amount of the 75 billion square feet of commercial buildings in the U.S. are to receive energy efficiency retrofits in the future.

A diagnostic tool that could determine when a building is “ripe for retrofit” or ready for other types of energy efficiency improvements like retro-commissioning or tune-ups would improve the industry's ability and effectiveness in planning retrofits across the building stock. Such a tool could help the government and many other large building owners determine how to allocate billions of dollars of capital devoted to energy efficiency retrofits—identifying when and where money should be allocated to bring about the greatest financial returns and cheapest carbon reductions.

Optimizing the Empire State Building Retrofit Process

The process of identifying, evaluating and choosing energy efficiency measures for the Empire State Building took over nine months; typical energy efficiency retrofit recommendations take 2-3 months. Many unique project elements contributed to the length of time needed to finalize a set of energy efficiency measures for the Empire State Building. These unique elements included:

  • Size of the building and diverse tenant profile;
  • Documentation of process to help other owners and ESCOs produce similar retrofits;
  • Collaboration and coordination among a project team took that included the building owner, the property management firm, the ESCO, the sustainability advisor, and select tenants;
  • Modeling of the energy use of the building and the reduction potential of energy efficiency measures using eQUEST; and
  • Evaluation of efficiency measures to reduce energy use in tenant space, and not just in the base building.

Many of these elements contributed to the project's ability to achieve savings that are more than twice that of typical commercial building energy efficiency retrofits. However, to make the Empire State Building process replicable, the process needs to be streamlined. The development of a streamlined process complemented by a set of tools to more quickly identify and evaluate efficiency measures would improve the likelihood that other energy efficiency retrofits could replicate the savings that were identified in the Empire State Building.

What Do You Think…

This list of research topics is a work in progress, and we are interested in hearing input on research and projects that are addressing these topics or other topics that are critical to energy efficiency retrofits in existing buildings. Please send your comments on these issues to As we receive comments on these and other relevant research topics, we will update this site.


1. Hopper, Nicole, Charles Goldman, Jennifer McWilliams, Dave Birr and Kate McMordie Stoughton, 2005. “Public and Institutional Markets for ESCO Services: Comparing Programs, Practices and Performance” Lawrence Berkeley National Laboratory: LBNL-55002, Berkeley, CA, March.

2. Goldman, C., J. Osborn, N. Hopper, and T. Singer, 2002. “Market Trends in the U.S. ESCO Industry: Results from the NAESCO Database Project” Lawrence Berkeley National Laboratory: LBNL-49601, Berkeley, CA, May.