Extensive evidence indicates that up to 35% of the energy used in this country is wasted every year. The waste takes many forms: lights and plug loads left on overnight, exterior lights and lights in daylit areas left on during the day, temperatures set too high or too low (particularly in unoccupied areas) and devices consuming energy when not in use.
So how can we identify and mitigate all of this energy wasted in buildings?
As the price of digital technology drops, new opportunities appear for analyzing and identifying savings in buildings. This article describes an approach that has recently become more cost-effective.
Continuous Auditing
All energy waste can be identified and eliminated only by continuously analyzing energy consumption at every end-use in a building. Continuous auditing is a method to achieve this goal. It consists of three steps:
- A certified energy auditor performs an initial energy assessment of a building.
- The building owner installs real-time energy monitoring (RTEM) equipment – ideally on all end-use circuits – and a networked thermostat system.
- The data is fed to a dashboard in real time, where the auditor can analyze trend data and look for anomalies indicating waste over the course of a year.
The primary benefit of continuous auditing is that energy waste that may not have been identified during an initial walk-through can be flagged and mitigated in real time, before it results in significant excessive energy costs.
Figure 1. Real-Time Monitoring Dashboard The green trend line (“range”) represents historical values, and the blue trend line (“usage”) represents the real-time usage for that day.
Figure 2. Real Time Network Thermostat Dashboard
The auditor reviews the data several times a week and coordinates with facility engineers and operators to mitigate energy waste. Over the course of 6 to 12 months, the auditor continues to monitor the building in real time, identifying energy conservation measures (ECMs) and waste based on new data. The net result is a building operating near its peak efficiency, over the course of all seasons.
While a comprehensive (or ASHRAE Level II) energy audit is very effective at determining the most cost-effective strategies for saving energy in a building, there are drawbacks:
- Most walk-through or Level II audits give the auditor an excellent snapshot of the building’s operations at that time, but not the full picture of changes in operations over the course of a year. For example, if the building is audited in the winter, the auditor would not likely see how the chilled water system functions.
- Savings calculations for ECMs are based on assumptions for inputs such as runtimes, temperature setpoints and use of override schedules. If these assumptions are not accurate, the savings may be overestimated or underestimated.
To achieve the maximum amount of energy savings with the most accurate calculations, it is essential to survey a building over all seasons, with accurate before and after data for all energy-consuming systems. With real-time information, data from all circuits is fed into a dashboard, where the energy experts can recognize when consumption is above normal, or above what’s expected, and then drill down to the specific circuit that is causing the energy waste.
Figure 3 shows how this approach revealed a significant amount of energy was being consumed at night by a school kitchen. Drilling down further into the data, the auditor identified a 6 kW food warmer that was cycling continuously at night, even though it was only used between 8 am and 1 pm. Because the indicator light had failed, operators couldn’t tell that the warmer was on. Shutting it down saved over 10,000 kWh per year.
Figure 3. Food Warmer Real-Time Energy Data
With continuous auditing, energy savings calculations are decidedly more accurate, since there are recorded data that will show exactly how equipment was operating prior to implementing a given ECM. If the continuous auditor knows exactly when a recommended ECM is implemented, he/she can record before and after data, and quantify the exact energy-saving effects of implementation. Therefore, measurement and verification (M&V) of implemented ECMs is built in, as post-implementation data can be compared to pre-implementation data using the dashboard.
Starting a Continuous Auditing Program
When performing an energy audit, you will typically find an initial set of no cost/low cost ECMs, which can save 5% to 10% of the building’s energy consumption. However, if you take the extra step to do continuous auditing, you should find additional savings opportunities each month to get to 20% total savings – or more – within a year.
For example, an initial ASHRAE Level 1 study of a city hall in Utah revealed approximately 8% savings in initial no cost/low cost ECMs. A full-circuit RTEM was installed and continuous auditing was initiated. Over the course of the first four months of analysis, a total of 40 additional no-cost/low cost ECMs were identified and recommended based on real time data. The total projected savings was 17%, summarized in Table 1.
Table 1: Continuous Auditing ECM Summary
Implementing a continuous auditing program with real-time energy monitoring and data analytics for a 12-month period can typically identify an additional 15% to 20% energy savings over what would be identified by a one-time energy audit. These savings are often implemented with little to no additional capital expenditures since they are generally based on enhancements to controls or behavioral changes, such as turning off computers at night.
The initial cost of continuous auditing includes the installation of real-time monitoring hardware and optional networked thermostats as well as the initial energy baseline assessment. The only other costs are small monthly fees for the monitoring service. The return on investment is typically one to two years.
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Eric Oliver, PE, CEM and LEED AP is VP of Energy Services for InScope Innovation. Contact him at [email protected].
