There's been an interesting discussion recently about data analytics and software solutions that aim to improve the building energy-efficiency evaluation process. At the heart of this debate is what can be learned about a building without ever going on-site versus what can be gleaned from a traditional energy audit.

This certainly is an important issue. As organizations like utilities, energy service providers and building owners strategize how to evolve their efficiency programs to drive deeper energy savings at scale, they will need to leverage the right data and solutions at each step of their process.

A virtual assessment is defined as one that aims to identify the overall energy savings of a building by analyzing accessible data to determine how that building is consuming energy today, and then providing end-use operational and capital-related observations and recommendations of improvement without ever contacting the building. The data that could be leveraged here might be publicly available, such as assessor data or GIS information, 15-minute or hourly consumption from a utility, or all of the above. 

Of course, not all data sets are created equal. Combining data from different sources with varying depth provides a tradeoff between scalability and how effective the underlying analytics can be.

Virtual energy assessments are an extremely effective tool to help accurately identify and target buildings with high efficiency potential across a large portfolio. Prioritizing buildings by their energy-efficiency potential is critical to optimally focus resources across a large portfolio. As proof of this, Retroficiency has long touted the 70/30 rule of building efficiency: 30 percent of the buildings account for about 70 percent of the savings opportunity.

Few would argue with the significant value of prioritizing by efficiency potential, whether energy savings are used as a standalone ranking or are leveraged with other customer metrics and characteristics. Where the discussion gets more interesting is how the recommendations coming from virtual assessments and traditional audits should be leveraged. To understand that requires knowledge of the underlying building science and data that drive these types of recommendations.

As an example, let’s address the virtual assessment category that leverages 15-minute or hourly interval energy consumption data. With a year’s worth of interval data (35,040 data points) and a facility address, we can derive significant insight about opportunities that exist by combining advanced statistical methods with inverse and forward modeling techniques. Inverse modeling is a technique to solve for building parameters using known consumption. Forward modeling is used to vary these building parameters to estimate how a building could operate if it were efficient.

Looking specifically at HVAC -- when we pair granular consumption data (interval data) with hyper-local weather information, we can see how the building responds to changes in outside air temperature and humidity, among others. This tells us a lot about the performance and consumption of the building’s HVAC system. These insights include operational scheduling, or when the HVAC systems become active in the morning and how they ramp down at night; cooling equipment operating at low temperatures; as well as simultaneous heating and cooling during temperate periods.

Uncovering these opportunities provide good cause to focus on operational recommendations such as reprogramming a building energy management system (if one exists). Therefore, this type of analytics could drive a utility retro-commissioning program at scale.

Ideally though, these insights are also used to engage customers about a wide range of energy efficiency programs and serve as the tip of the spear in terms of getting more information about the building to achieve even deeper savings. This is when traditional audits and tools -- such as thermodynamic energy models -- can be extremely effective.

One reason is that a building is much like the human body, featuring a complex set of systems that work together, where a change to one part can influence another in ways that might not be obvious.

Let’s take a lighting retrofit as an example. Lighting retrofits are extremely popular because they commonly have attractive paybacks when replacing legacy equipment. Not only do new lights consume fewer watts per square foot, but sophisticated controls ensure the lights are only on when you need them.

But lamps emit heat, and new efficient lighting systems emit significantly less heat than their legacy technologies. So when you replace fixtures and/or lamps, it is likely that your HVAC system will need to work harder on cool days to heat the space, but work less on hot days to cool the space. These interactive effects could positively or negatively impact your potential lighting savings by 30 percent or more, which is significant when making an investment decision.

The total impact of interactive lighting effects has to do with building specific characteristics such as the type (or presence) of cooling and heating equipment and differences in the type, quantity, location, and controls of the legacy and retrofit lighting fixtures. The magnitude of the interactive effects can even vary based on the way air flows throughout the space. All of these parameters are best captured by an energy engineer with strong knowledge of the building, and are most accurately analyzed with a thermodynamic energy model designed to make sense of this complex system interplay.

Ultimately, virtual energy assessments are highly complementary to traditional energy audits. Because they are a fraction of the cost and can be delivered in minutes, virtual assessments enable us to determine the right buildings to focus on and provide insights to engage customers and get them moving effectively through the entire energy efficiency lifecycle. 

Virtual assessments can even spot opportunities that might be missed with a traditional audit because the objective energy data provides an inherently unbiased view of how the building is operating. On-site personnel sometimes do not fully understand how their building systems are actually operating.  

Traditional audits will continue to play a valuable role in building energy efficiency, providing a gold standard to fully develop energy conservation measures with sufficient accuracy and appropriate feasibility. The focus should not be on replacing this important step, but rather on making it faster, less expensive and more dynamic so that we can touch more buildings and reap benefits of these evaluations today and in the future.


Hugh Gaasch is responsible for development of Retroficiency’s Building Efficiency Intelligence platform as it relates to mining building energy use interval data to identify savings opportunities for customers; Chris Muth’s responsibilities at Retroficiency include product development, customer support and professional services, with an emphasis on working with customers to leverage asset data to rapidly evaluate buildings.