Save Energy and Cut Costs in buildings by Automating Building Energy Audits

Improved building energy efficiency is recognized as a societal benefit for a number of reasons, including; reducing energy costs, reducing combustion product emissions, and reducing dependence on foreign sources of energy.

However, energy is difficult to control.  If you insulate one wall in a building, the heat loss will occur through the other un-insulated walls.

The savings that may result from any energy saving building retrofit is also difficult to predict. Therefore, the dollar savings and return on investment (ROI) are not solid, and results only become apparent after an entire heating and cooling season passes, and that year’s energy bills are audited.

One building owner said to me: "If I follow all the recommendations that have been made to me by the "energy experts, I will need a line of fuel trucks in front of my building to take the fuel away they said I would save.” 

Also, not being able to more accurately predict the ROI of any energy saving retrofit has strained the credibility of many energy service companies (ESO’s) and because of this, many building owners simply shut down when the mention of energy savings occurs.

Moreover, detailed energy audits which attempt to provide:

  • a more quantitative evaluation of what energy savings are available
  • how one retrofit opportunity affects another
  • which combination of energy saving building retrofits provide the best energy savings for the dollar

can cost as much as $30,000 per building. The $30,000 energy audit only applies to a building before any energy savings retrofits are undertaken.
Data about building energy usage before, during and after energy savings retrofits are important to have.  With appropriate building instrumentation, predicted energy savings can be observed and verified as the retrofitting progresses.  Problems can be immediately identified and corrected.
Government agencies, that fund energy saving retrofits in the buildings they are responsible for, have problems which are similar to those of individual building owners.  For example, energy audits for say each of 300,000 buildings in NYC are unaffordable, time consuming and labor intensive. Moreover, there is a scarcity of real data that confirms that the agency-funded building retrofit programs have saved energy.

Technical Approach

Our approach provides quantitative information about a building, before, during and after energy saving retrofits.

The purpose of this program is to enable the rapid, automated performance of building envelope energy audits for numerous buildings at one time, at a cost of only a few dollars per building.

Before retrofitting:

Our new, patented, technology including rapid screening of buildings from an airborne platform, will:

  • Identify buildings which are the best (shortest ROI) candidates for retrofitting.
  • Gather important information about the envelopes of the buildings they are auditing before they start collecting the rest of the data.
  • Automate of as much of the additional data collection and analysis as possible to minimize costs and insure uniformity of results.
  • Perform more comprehensive energy audits.

To determine heat loss through a building's outer envelope[1,3,4], one must know the surface temperature, air temperature, surface properties, and the size of each surface element. Thermography obtains the element surface temperature and LiDAR (Light Detection and Ranging) concurrently determines the 3-D spatial measurements.  Thermographic images are superimposed on the LiDAR images by data fusion techniques and readily-available GPS information to form a detailed physical and heat emissions image of each building; software packages that accomplish this are available commercially for about $4,000-$5,000. The goal is a one-two inch resolution of building surface elements.  For example, with the proper lens focal length, a 1024 x 1248 thermographic camera can obtain a resolution of two inches and a swath width of 200 feet.  The resolution along the flight path of an airplane or helicopter equipped with LiDAR and thermographic sensors is dependent on the speed of flight, and, at low flight speeds and a nominal 500 m height, a two-inch resolution is realizable.  The determination of 3-D building geometry by thermography alone is possible, but the results are achieved by subtracting pairs of error-prone measurements that are close in value, compounding the errors in the resulting 3-D building measurements.  The addition of LiDAR can reduce these errors, thereby improving the accuracy of the measurements.

However, as there are millions of buildings of all types in the United States, and performing standard energy audits on all of them is impractical and unaffordable, it is highly beneficial to develop an enabling methodology to rapidly, efficiently, and inexpensively identify the best candidates for further, detailed energy audits and energy efficiency retrofitting.

The technology would be game-changing in the field of building energy conservation, which currently relies only on, expensive ground-based audits.  Given the dimensions and the outer surface temperatures of the envelope of a building, it is possible to compute the ideal energy usage for heating and cooling. Of course, the heating and cooling systems of real buildings always use more energy (the actual usage) than the ideal. The difference between the actual and the ideal energy usage represents the maximum potential energy savings that could be derived from building retrofits and the installation of improved control systems.

Although both LIDAR and thermography theory and technology are well developed (mitigating technology risk), their combination in the proposed system is novel.  Hence, while their technology readiness levels (TRLs) separately are probably TRL-9, the level of the overall system, including the aviation and data acquisition and processing systems, is estimated to be TRL-3 since it hasn’t yet been demonstrated.  It is expected to reach TRL-6 after the prototype system is demonstrated under actual conditions on a small number of buildings in a city or town, and progress to a higher level with further development.  Wide-scale implementation of this technology, coupled with follow-up remediation projects, could be game-changing in the building energy conservation field.  Currently, few energy audits include the building envelope because of the cost of collecting data, especially for irregularly shaped buildings.  In addition, ground-based surveys are costly.

The aerial collection of building envelope data represents a substantial improvement over conventional technologies used to baseline building efficiency.  For example, when done at a relatively low outside air temperature of 20 oF (-7 oC) and little or no wind, it enables calculation of the Thermal Resistance (R value), and heat losses/gains through the building’s surfaces.  Modeling a building as an ideal, highly insulated, air-tight building requires information about the building’s envelope. Comparing the ideal building results with actual monthly usage from the monthly energy statements enables the identification of areas of possible energy waste that should be further explored in a subsequent on-site energy audit.

During and After Retrofitting

Appropriate instrumentation will be installed as part of the energy savings retrofitting process.  Information such as:

  • Building inside temperature, relative humidity, carbon monoxide, and carbon dioxide at a representative number of locations
  • Boiler and chiller operating parameters, and operating times of each of the air handlers
  • Energy meter real time readings

will be logged automatically and made available to a computer program which will analyze the data and report on the success or failure of the retrofit as it progresses, and after it is completed.  This will enable knowledge based trouble shooting to QA and QC the retrofit work so corrective steps will be taken to insure the expected energy savings actually occur.