By Nicole Imeson, P.L.(Eng.)

Through the Existing Building Commissioning (EBCx) process, energy analysis allows building owners to decarbonize their existing systems with less capital investment. "By crunching data on how we use energy, factoring in weather shifts, and understanding how our systems run (by calibrating the energy analysis to existing data), we uncover the shortcuts to sustainability," explains Jacob Komar, a mechanical engineer and Principal at Revolve Engineering in Edmonton, Alberta. He has spent the last 16 years modeling energy use in buildings, primarily focusing on Net Zero buildings and geothermal system designs. The energy analysis prioritizes savings based on cost-effectiveness and payback period while still maintaining or improving occupant comfort. For example, increasing cooling setpoints in the summer or decreasing heating setpoints in the winter would reduce energy consumption, but if these changes were drastic, the building occupants would start to notice. 

Utility Bills

At least one year of monthly utility bills — electricity, water, sewage, natural gas, etc. — are recommended to complete an energy analysis. Still, three years or more is best to establish trends and compare load profiles across various years. "Without first quantifying and understanding what the energy flows around the building look like, we can't make informed decisions," notes Komar. The commissioning provider (CxP) compiles the utility bills for the building and separates the data into various buckets; if the data is entered into a spreadsheet, this makes for quick work to compare several variables simultaneously.

The CxP should first look at the overall energy use intensity (EUI) to determine if it's above average in its market sector, which signifies energy-related cost savings potential. The EUI is calculated by dividing the total annual energy consumption (kBTU) by the total building size (ft2). This can be done in imperial or metric, depending on where the building is located and the units of the utility bills. The EUI should then be compared to benchmark EUIs for similar property types. 

Before diving too deep into the energy bills, the CxP needs to determine if any major changes occurred during the timeframe of the utility bills. For example, if the owner is providing the last three years of bills, but the boiler plant was upgraded last year, this will skew the data. This doesn't necessarily mean the analysis can't continue or will not be successful, but it will be challenging to assess potential energy conservation measures on the heating plant with limited data since the upgrade. In this case, it may be worth delaying the analysis until at least a year's utility bills can be provided for the heating plant. 

Comparing different types of energy used in the building as a percentage of total energy costs will show if one system or type of energy makes up a disproportionally large percentage of the usage compared to the output in the building. For example, suppose natural gas is used as the energy source for heating and does not serve any other purpose in the building, but natural gas represents most of the energy costs year-over-year. In that case, this is an area for improvement. If the natural gas usage is consistent year-round rather than dropping in the summer, this also requires further review.

Assessing year-over-year energy costs will show if there are significant deviations from the same period during the previous year. Since the price of energy changes with time, it's better to look at the number of units of energy used rather than just the cost for this comparison. This should also be compared to the weather data to check if the deviations are related to changing weather conditions.

Weather Data

Once the energy bills are plotted into the spreadsheet, the CxP downloads weather data for the location of the building over the time frame of the energy bills. There are a couple of different ways to do this. 

One is to look at heating and cooling degree days. Heating degree days are the number of hours per year — out of 8760 — a location was below a specific temperature, requiring heating to meet setpoint. Cooling degree days are the number of hours per year an area was above a specific temperature, requiring cooling to meet setpoint. Heating and cooling degree days are a great high-level look at how often a building requires heating and cooling. Thinking back to the natural gas example above, if the building only requires heating for 25% of the annual hours, but the natural gas bills represent 50% or more of the total energy usage, this area requires further review.

If evaluating the heating and cooling degree days indicates areas for further consideration or the scope and goals of the energy analysis require a deeper dive into the energy usage, the CxP should look for hourly temperature data for the building location. Hourly data records the temperature at a specific location for all 8760 hours of the year. It takes a little front-end work to download and clean up the data into a usable format, but building a template will facilitate easy use on future EBCx projects. 

The benefit of hourly weather data is it determines how many degrees the setpoint is above or below the outdoor temperature and how much energy it takes to heat or cool to the setpoint. This gives a much more accurate indication of energy usage since it determines when the building is in heating or cooling and how much energy is being used for this process. The weather data is then plotted against the energy usage to spot anomalies. 

Through the initial walkthroughs and interviews, the CxP understands how the building operates, which equipment serves each space, the types of systems used, and their sequences of operations. As the CxP compiles the energy usage and compares months, years, and weather data, they will look to the operating conditions to help explain any irregularities. If changes to the operation conditions don't align with the irregularities, this indicates a potential to reduce energy costs.

Low Hanging Fruit

The energy analysis will show many opportunities for energy savings throughout the building. During the analysis stage, the CxP keeps a running list of the potential measures for future consideration. Once the analysis is done, the commissioning team reviews the measures to identify low-hanging fruit — easy measures that can be implemented for little to no cost with a short payback period. "Energy analysis allows us to find low-hanging fruits and come up with innovative solutions that take into account the entire energy picture," says Komar. It's common for CxPs to separate the measures into a few different categories: low-hanging fruit, medium-cost measures, high-cost measures, measures that improve comfort but do not impact energy, and measures that reduce energy but may impact comfort. There also may be some overlap where a single measure will fall into a few different categories. 

Identifying the benefits of each measure, the cost to implement, the potential payback period, and the advantages and disadvantages of each measure will allow the owner to make educated decisions on how to proceed during the implementation phase. It will also allow the commissioning team to understand which measures can be implemented in-house, which require outsourced contractors, and which (if any) require design, permitting, or major system upgrades. 

Energy analysis is a great first step to decarbonizing existing buildings. By examining the energy usage across multiple years and comparing it to weather data and operating conditions, CxPs can spot anomalies to further review and discuss with the commissioning team. While some energy analyses look at major upgrades, several low/no-cost measures can often be implemented quickly and easily with big results.