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Virtual Assessment versus On-Site Audit: What’s the Difference?

With the increasing focus on finding solutions that reduce building energy consumption, efficiency remains the most cost effective way to deliver savings.  The challenge most energy managers face, however, is figuring out which buildings have the best potential for savings and then identifying the combination of measures that are most appropriate for each site.  This problem is exacerbated over a large portfolio.  Consider that very high potential buildings can have 40% or more savings potential, whereas low potential buildings can have little to no potential.

Software analytics combined with rapid building modeling offer new approaches to analyzing building efficiency much more effectively.  These approaches drive the two main types of energy analysis, virtual energy assessments and on-site energy audits.  A virtual energy assessment is an analysis of the energy efficiency opportunities in a building, or portfolio of buildings, that is conducted without ever going on-site. Often, these are referred to as ‘no-touch’ assessments because they require no contact with the building itself or its owners, managers or occupants.

On-site energy audits involve physical walkthroughs of a building, typically by a trained energy engineer or professional, to determine energy consuming characteristics and opportunities.

Understanding when and how to execute a virtual assessment versus on on-site audit is critical to successfully identifying the highest-ROI projects and achieving energy savings at scale. In this article, we will address several key questions to compare and contrast these two valuable pieces to the efficiency puzzle:

1)      At what point(s) do I use a virtual assessment versus an on-site audit?

2)      What data inputs do I need to collect or analyze to execute the evaluation?

3)      How much time does each require?

4)      What is the spectrum of tools available to help?

5)      What are the potential types of recommendations and outcomes can I expect from a virtual assessment versus an on-site audit?

When developing virtual versus on-site strategies, it is important to consider how one can use various evaluation techniques to optimize efficiency program resources while also sufficiently meeting objectives.

      Stage of Evaluation. A portfolio energy management program has several components before driving savings at individual buildings. First, a certain set of buildings must be prioritized, then there may need to be engagement at the local level, and finally the efficiency opportunities must be evaluated.

At the prioritization phase, energy managers may be dealing with dozens, hundreds or thousands of buildings. As such, a virtual assessment is necessary at this stage to gain insight into the potential opportunities at mass scale. Going to each building to conduct audits at $5K-$50K+ per building simply adds too much cost and time to the process.

A high-quality virtual assessment can help determine a building’s savings potential and provide considerable insights to opportunities that exist within. Knowing the possible opportunities beforehand allows organizations to hone in on specific insights about the building, potentially achieve immediate savings with easy to change operational behaviors, and keep an on-site audit more focused.

Once this has happened, an on-site audit is required to more comprehensively evaluate savings opportunities.  A trained energy engineer can properly collect data and assess its characteristics, assess feasibility, and then make the proper calculations to determine the cost effective savings potential of various measures.

Data inputs. At the core of energy efficiency evaluation is data, which allows organizations to identify and quantify opportunities.  There are two types of data that can be leveraged during the process, either energy consumption information or building asset data -which is specific information about the building itself, such as use-type, size and system details.

Buildings almost always have access to some form of consumption data, be it monthly or granular interval data (i.e. consumption data in 15-minute or hourly increments), but often no or limited access to asset data. Fortunately, when interval data is combined with analytics it can deliver significant insight about efficiency potential without ever going on-site. While in many markets interval data is only available on buildings above a certain demand threshold, the availability of interval data is increasing as a result of smart meter deployments throughout the country.

Eventually, building asset data will need to be collected, particularly for any retrofits/capital measures. Without an understanding of the current assets in a building one cannot accurately determine the installed cost or energy savings of a particular measure. For example, the payback of controls-based LED lighting must be compared to the current lighting in the building, such as T12s with no controls.  Asset information can be collected either before doing a building walkthrough or during the on-site audit phase on buildings that have demonstrated good potential.

Time Requirements. Virtual assessments and on-site audits differ considerably in terms of how long each takes.

Virtual assessments can take as little as minutes, which is important when deciding which buildings to target over a large portfolio of buildings. On-site audits on the other hand, can range from hours to weeks to even months. This variability stems from the types of recommendations being generated and the tools employed to execute the analysis.  Each of these will be addressed in the next two sections.

      Available Tools. The analysis for both virtual assessments and on-site audits are driven in part or in whole by some sort of software technology. These can range from basic spreadsheets to complex building-simulation software to emerging sophisticated energy analytics.

During the virtual assessment phase when pure consumption data is being analyzed, the options include energy analytics software and spreadsheets. Energy analytics can automatically correlate consumption data to multiple weather variables and GIS data, as well as large data-sets of similar buildings performing efficiently. Trained engineers can replicate some of these simpler analyses in spreadsheets, albeit at a much slower place.

Engineering calculations from on-site audits leveraging building asset data are typically executed in either spreadsheets, traditional energy modeling software, or new solutions that combine analytics with rapid energy modeling.

Spreadsheets can be used for most simple energy efficiency calculations like lighting projects, and can be practical for estimating the energy savings of individual measures. Spreadsheets, however, typically do not take in to account the ‘interactive’ effects of a building’s systems, such as how changing lighting equipment can influence heating and cooling savings opportunities, and can be complex and unwieldy when multiple measures are evaluated or advanced HVAC equipment is present.

Traditional building energy modeling can generate a very accurate representation of building consumption when used by a skilled professional, but requires significant time and cost when used for an audit. It is best to reserve usage of this type of software for certain situations that might arise during an investment grade audit (IGA) of a large, highly complex building.

Software that combines energy data analytics with rapid modeling can be used for on-site audits and is able to accurately evaluate a wide variety of energy conservation measures. These solutions help streamline data collection, make complex ECM calculations, and automate the time consuming reporting process.

Recommendation Objectives. Finally, before any energy evaluation is undertaken, those involved with the project should be able to answer a very simple question: ‘what type of recommendations and end results are we driving towards?’

The goal of a virtual assessment should be what we refer to as Energy Conservation Indicators (ECIs), insights about potential no- and low-cost operational opportunities as well as capital improvements to investigate further. Examples of ECIs are that building systems are coming on too early and staying on too late relative to occupancy, that there is simultaneous heating and cooling in the building, or that lighting, cooling, ventilation systems consuming too much energy relative to a similar efficient building along with the related data to support each. 

On-site audits should deliver Energy Conservations Measures (ECMs). ECMs are implementable recommendations that have been evaluated to the point where a building owner can cost effectively invest in a specific retrofit. In addition, depending on the programs available the   utility is able to pay a program rebate and claim savings towards their overall goals. Examples of ECMs include lighting fixture and controls upgrades, installing variable-speed drives on chillers, or optimizing outdoor air strategies using demand controlled ventilation or economizers.

ECMs differ from ECIs in that feasibility has been completely assessed and financial paybacks have been calculated.


Virtual assessments and on-site audits both play a critical role in helping drive building energy efficiency. Stakeholders must think strategically about when to employ each type of evaluation and determine what data and tools to leverage in the context of what the goal of the recommendation is.

Doing so will allow organizations to target the right buildings with the right opportunities, and drive deeper energy savings with each project.

Hugh Gaasch is the Vice President of Energy Engineering at Retroficiency

Richard Huntley is the Vice President of Sales at Retroficiency

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