| ABSTRACT | | | | you off the hook, but you still need to quantify |
| Utility bill tracking is at the heart of an effective | | | | how much you saved, don't you? Management will |
| energy management program. Merely comparing | | | | only accept arm waving for so long. |
| utility bills can yield inaccurate indications of the | | | | You can quantify your savings by correcting your |
| amount of savings from energy management | | | | utility bill savings equation for weather. |
| programs due to the unaccounted influence of | | | | HOW WEATHER CORRECTION WORKS |
| weather or other factors. Correcting utility bills for | | | | Rather than compare last year's usage to this |
| weather data will give more accurate | | | | year's usage, when we use weather correction, |
| representations of savings that were accrued. | | | | we compare how much energy we would have |
| This paper presents the how and why of | | | | used this year to how much energy we did use |
| weather correction for those who want to | | | | this year. Many in our industry do not call the |
| become more familiar with the concepts and | | | | result of this comparison, Savings, but rather |
| methodology. | | | | Usage Avoidance or Cost Avoidance. But, since |
| WHAT UTILITY BILL TRACKING CAN DO FOR | | | | we are trying to keep this paper at an |
| YOU | | | | introductory level, we will use the word Savings. |
| Jim Faes from Jefferson County School District | | | | When we tried to compare last year's usage to |
| wrote to me "energy accounting is the backbone | | | | this year's usage. We used the equation: |
| of our school district's energy management | | | | Savings = last year's usage - this year's usage |
| program." Why would he write that? | | | | When we use weather correction, we end up |
| An energy accounting system is much like an | | | | with the equation: |
| airplane's control panel. In order to correctly | | | | Savings = How much energy we would have |
| navigate your airplane, you need to understand | | | | used this year - how much energy we did use |
| where it is, where it was and where it is going. If | | | | this year** |
| you fly the plane without the control panel, you | | | | **where this year's usage from the 1st equation |
| have a good chance of crashing the plane. It is | | | | is the same as how much energy we did use this |
| the same with energy management. You need to | | | | year from the 2nd equation |
| know where you are, where you were, where | | | | The next question is, how do we figure out how |
| you are going, and how where you are now fits | | | | much energy we would have used this year. This |
| with expectations of your progress. | | | | is done using weather correction as shown below. |
| With utility bill tracking systems, Energy managers | | | | First, we select a year of utility bills we want to |
| can: | | | | compare future usage to. This would typically be |
| - Enter target usage and costs and track their | | | | the year before you started your energy |
| actual performance against their targets | | | | efficiency program, or the year before you, the |
| - Discover large increases in energy usage and | | | | new facility manager, were hired, or some chosen |
| take corrective actions | | | | year. In this example, we would select the year |
| - Identify the buildings that are using more $ | | | | of utility data before the installation of the chilled |
| SQFT than the others, and concentrate energy | | | | water system. We will call this year the Base |
| management activities on those buildings. | | | | Year. |
| - Determine whether your meters are on the | | | | We graph Base Year usage versus weather (in |
| best rates | | | | the form of Cooling Degree Days or Heating |
| - Check to see if you are being billed correctly by | | | | Degree Days). The blue dots represent the utility |
| the utility | | | | bills. |
| - Create bills for your tenants (if you have any) | | | | Then we find the Best Fit Line between usage |
| - Determine whether you have saved any energy | | | | and weather. The Best Fit Line is the line that |
| from your energy conservation measures | | | | comes closest to all the utility bills. We can tell it is |
| - Aggregate your usage and costs and pass this | | | | the Best Fit Line by looking at some statistical |
| aggregated data to potential energy suppliers | | | | indicators (such as R2 value, Net Mean Bias Error |
| - Create utility budgets | | | | and CVRMSE, which are not covered in this |
| More generally, if you keep aware of the state of | | | | introductory paper) . |
| your utility accounting, you will know where your | | | | This Best Fit Line has an equation, which we call |
| facility is and how it is faring towards your goals. | | | | the Fit Line Equation, or in this case the Baseline |
| UTILITY BILL TRACKING: THE REPORT CARD | | | | Equation. Once we have this equation, we are |
| FOR FACILITIES AND FACILITY MANAGERS | | | | done with this regression process. |
| Energy Managers and some Facility Managers all | | | | Let's recap what we have done: |
| to often have to justify their existence to | | | | - We graphed a Base Year of utility data versus |
| management. How much did we save last year? | | | | weather data |
| Is that more than what we pay our energy | | | | - We found a Best Fit Line through the data. The |
| manager? Did your recommendations give | | | | Best Fit Line then represents the utility bills. |
| reasonable paybacks? Why do we even have an | | | | - The Best Fit Line Equation, which represents the |
| energy manager? | | | | Best Fit Line, which in turn represents the Base |
| There are several methods to determine whether | | | | Year of utility data. The Fit Line Equation |
| you have saved energy from your energy | | | | represents how your facility used energy during |
| conservation efforts, as described in the literature. | | | | the Base Year, and would continue to use energy |
| You can wave your hands in the air, and decide | | | | in the future (varying with changing weather |
| upon a number; calculate your savings based upon | | | | conditions) assuming there were no significant |
| data logger and control points; compare utility bills | | | | changes occurred in building consumption patterns, |
| to determine savings; and finally, employ a building | | | | such as new equipment, area or operating hours. |
| model. (These are referred to as Option A, B, C | | | | Base Year bills - Best Fit Line = Fit Line Equation |
| and D in the IPMVP, FEMP Guidelines and other | | | | In our example: |
| literature.) | | | | Baseline Equation = Fit Line Equation |
| Most likely, the simplest and most palatable | | | | Once you have the Baseline Equation, you can |
| method for the facility manager to determine | | | | determine if you saved any energy. |
| whether you are saving energy is Option C, | | | | How? You take a bill from some billing period after |
| comparing utility bills. Why? Well, although some | | | | the Base Year. You (or your software) plug in the |
| utility managers do present calculations given to | | | | number of days and the number of degree days |
| them by the friendly sales rep, this method is | | | | from the bill into your Baseline Equation. |
| hardly reliable, as they may produce inflated | | | | Remember, the Baseline Equation represents how |
| numbers. Placing dataloggers and using existing | | | | your building used to use energy in the Base Year. |
| control points seems easy enough, but converting | | | | So, with the new inputs of number of days and |
| these inputs into savings numbers can sometimes | | | | number of degree days, the Baseline Equation will |
| prove to be outside of the scope of the facility | | | | tell you how much energy the building would have |
| manager's skillset. Building modeling, while it can be | | | | used this year based upon Base Year usage |
| useful, requires hours of time to construct the | | | | patterns and this years conditions (weather and |
| model, and may represent how much the building | | | | number of days). We call this usage that is |
| should be using, and may not really represent | | | | determined by the Baseline Equation, Baseline |
| what the building truly is using. If those objections | | | | Usage. |
| hold, that leaves utility bills as the last remaining | | | | Now, to get a fair comparison of this year versus |
| method to quantify your performance as an | | | | last year, we compare: |
| energy manager. Plus, in the end, it is all about the | | | | Savings = How much energy we would have |
| utility bills, as the bills reflect how much you are | | | | used this year - How much energy we did use |
| paying. | | | | this yearor if we change the terminology a bit: |
| Since most facility managers are already tracking | | | | Savings = Baseline Energy Usage - Actual Energy |
| their utility bills, it is only one additional small step | | | | Usagewhere Baseline Energy Usage is calculated |
| to see whether you have saved any energy and | | | | using the Baseline Equation and current month's |
| costs from your energy management program. | | | | weather and number of days, and Actual Energy |
| Just compare prior year bills to current year's bills, | | | | Usage is the current month's bill. Both equations |
| and you will see if you have saved. | | | | are one and the same, Baseline = How much |
| Well, it isn't that easy. Let's find out why. | | | | energy we would have used this year, and Actual |
| WHY BILL COMPARISON DOESN'T WORK, OR, | | | | represents how much energy we did use this |
| WHY USE WEATHER CORRECTION | | | | year. |
| Suppose you want to see savings from the new | | | | CORRECTING FOR OTHER VARIABLES |
| efficient chilled water system you installed this | | | | Facility Managers in the industrial sector may want |
| January. A simple comparison of prior and post | | | | to correct for production rather than (or in |
| bills should show the savings right? Well, not | | | | addition to) weather data. This works if you have |
| exactly. Suppose last year had a relatively cool | | | | a simple variable that quantifies your production. |
| summer, and this summer was devilishly hot. | | | | For example, an automobile manufacturing plant |
| Would you see the savings? Maybe not. | | | | can track number of automobiles produced. If |
| There are a couple of ways we can plot the | | | | your factory makes several different things, for |
| usage from year to year. Suppose we just | | | | example, disk drives, desktop computers, printers |
| looked at the usage vs. time, like most people do. | | | | and main frame computers, it is difficult to come |
| We have marked two regions. The bottom | | | | up with a single variable that could be used to |
| (darker) region, we call non-weather sensitive | | | | represent production for the entire plant. |
| usage. This usage can be attributed to computers, | | | | However, if your printer manufacturing unit was |
| lights, constant volume pumps and other loads | | | | served by a different meter or submeter than |
| that are on regardless of what the weather is. | | | | the other units, then you could use the number of |
| For an all year operation, this amount is steady. | | | | printers produced as a variable for the meter (or |
| (In this case, the non-weather sensitive usage is | | | | submeter) that serves the printing unit. |
| very low, since this meter serves a mechanical | | | | WEATHER CORRECTION IN EXCEL VS. CANNED |
| plant. Typically, the non-weather sensitive usage | | | | SOFTWARE |
| would be higher.) | | | | Weather correction can be done in Excel, |
| We call the top (lighter) region weather sensitive | | | | however it can be laborious, and oftentimes may |
| usage. This is usage directly related to, in this | | | | not be as rigorous as when done using specialized |
| case, air conditioning the facility. Usage in this | | | | software. Excel will give regressions, fit line |
| region could be attributed to chillers, cycling chilled | | | | equations, and statistical indicators which show |
| water pumps, cooling towers, condenser water | | | | how well your usage is represented by the fit line. |
| pumps, condenser fans, and possibly fans and | | | | However, it is difficult to find the best balance |
| pumps that cycle or are on a variable frequency | | | | point in Excel, as you can in specialized software. |
| drive. | | | | Excel may force you have to choose just one |
| If last summer was cool, and this summer was | | | | balance point, and possibly then you would iterate |
| hot, then the non-weather sensitive usage would | | | | with different balance points, whereas canned |
| likely not change from year to year, but the | | | | software will allow you to easily find the best fit |
| weather sensitive usage would change. Notice | | | | line using different balance points. In addition, if |
| how in the second year, the weather sensitive | | | | you enter your weather data in high low |
| portion is much greater due to the hot summer's | | | | temperatures or average temperatures, it can be |
| increased cooling load. | | | | difficult to apply the correct weather data to the |
| Now suppose that the new chilled water system | | | | correct billing periods. Try it, and you will see. |
| reduced weather sensitive consumption by 20%. | | | | AVAILABLE WEATHER CORRECTION DESKTOP |
| With the weather variation, an annual comparison | | | | SOFTWARE |
| of the usage may not show any energy savings | | | | All of the major desktop utility bill tracking |
| at all.. (We removed 20% of the weather | | | | software packages will now correct for weather |
| sensitive usage from 2002 data, which is what | | | | data. Nearly all of them will correct for your own |
| we might see with a chilled water system | | | | variables as well. The major desktop programs |
| retrofit.) | | | | are Energy CAP, Metrix, Stark Essentials, and |
| Imagine showing management these results after | | | | Utility Manager Pro. You can find information on all |
| you invested a half million dollars. It is hard to | | | | of them online. |
| inspire confidence in management with graphs like | | | | CONCLUSION |
| that. So much for utility bill comparison. | | | | Weather changes from year to year. If wish to |
| To explain these results, you might provide them | | | | use utility bills to show energy savings from |
| with a graph of CDDs, and then they could see | | | | energy management programs with any degree |
| that, the post-retrofit year (2002) was indeed | | | | of accuracy, it is important to correct your utility |
| much hotter, and required more cooling and | | | | bills for fluctuations in weather. |
| therefore led to increased usage. This might let | | | | |