The numbers are in: how do LEED-NC buildings compare to LEED-EB:O&M

There has long been a debate about whether today’s green buildings really save energy, particularly when compared with their existing building counterparts. Enermodal has conducted several LEED- Existing Buildings: Operations & Maintenance (EB:O&M) feasibility studies for some existing office buildings, and compared the energy use of six existing facilities which achieved an Energy Star score of 70 or higher (meaning they are better than 70 per cent of North America’s buildings) with six LEED- New Construction (NC) and three LEED- Core and Shell (CS) certified buildings. The result was that the LEED certified new buildings performed better than even high performing existing buildings. Another lesson learned was that LEED-CS and NC buildings performed fairly comparably, highlighting the importance of base building systems like HVAC and lighting compared with tenant fit up items such as plug loads or appliances.

Energy Star is a database of the energy use of thousands of North American buildings, sorted by type. Buildings looking to qualify for LEED-EB:O&M certification must first prove they are in the top 30 per cent of North American buildings in terms of energy use by achieving an Energy Star score of 69 or higher. During an EB:O&M feasibility study, Enermodal performs a normalized energy analysis for the building using the Energy Star Portfolio Manager. This interactive energy management tool allows owners and facility managers to calculate normalized energy consumption across their entire portfolio or for an individual building. Portfolio Manager can help owners and facility managers set investment priorities, identify under-performing buildings, identify high performance buildings that are LEED-EB:O&M candidates, and verify the effectiveness of implemented efficiency retrofits.

How do you normalize a building’s energy performance?

 The most basic way to compare a buildings’ energy performance is to divide the total energy consumed by the building’s area (ekWh/ square metre). However, more information is needed to create an accurate picture of how buildings in an organization’s portfolio are actually performing. This additional information includes the following:

  • location
  • weather conditions
  • type of building uses
  • unconventional energy/process loads
  • office equipment/electronics
  • occupancy density and hours of operation
  • ventilation rates
  • building energy systems

As the graph comparing Enermodal’s LEED NC/CS projects with EB:O&M feasibility study shows, even high performing existing buildings achieving an average normalized Energy Star rating of the 75th percentile did not achieve the energy efficiency of new green buildings. It should be noted that EB:O&M improvements like re-commissioning have not been performed on the existing buildings which would improve building energy performance over time, although likely not to the level of the new buildings.

NC versus CS

An increasing number of building owners want to LEED certify their new construction projects, and some tenants are requesting green features in their space. However, in many cases, building owners are not responsible for fitting-out the interior space, and they do not know if their tenants (or future tenants) are interested in making this commitment. Fortunately, there is a certification that addresses this situation. LEED-CS essentially takes the tenant requirements from LEED-NC and either makes them less stringent or eliminates them altogether, while the requirements for the base building (and space that is fit-up by the owner) remain the same.

Many in the green building design community have wondered how LEED-CS buildings compare with LEED-NC in terms of energy usage. While the graph above only has a sample size of three LEED-CS certified buildings, it does show that these buildings performed similarly to their NC counterparts. This finding highlights the importance of base building improvements to HVAC and envelope relative to the tenant fit-up, such as lighting and appliances.

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