How to Calculate Energy Savings in a Building

By Daniel on February 8, 2010

It’s an age old dilemma for efficiency advocates: how do you calculate how much energy you didn’t use or how much money you didn’t spend? You can’t put a yardstick up against something that doesn’t exist.

We tend to rely on models and predictions of what might have happened, and calculate the savings based on that hypothetical case.  But it all feels a bit like a house of cards, with our arguments and calculations set on a soft foundation.  Even if stakeholders understand the base-case model (many don’t), they may be skeptical of the savings estimates.

To gain confidence and a voice in energy decision making, we need a few improvements:

  1. A simple model for the base case, that anyone can understand with a brief explanation.
  2. A way to compare different models to each other, so we can choose the best one.
  3. An measurement of the uncertainty in our models and predictions, to set boundaries on our confidence.
  4. A quick way to calculate the difference between the model and what really happened, also known as “savings.”

Here’s my workflow for addressing some of these problems and needs, using my own home’s energy.  The process needs improvement, but I think it’s a start.

This method assumes you’re familiar with a bit of weather normalization.  If not, check out my previous article on how your energy use changes through the seasons.

First, plot your building’s energy use versus the monthly average temperature:

Electricity Consumption vs. Temperature

In the graph above, I’ve plotted all of my house’s energy data before September of last year – data for the baseline months before I insulated the attic and bought a new programmable thermostat.  I’ve normalized the kWh consumption to a 30-day cycle for consistency.  And remember, I’m using color intensity to give a sense of time; darker blue points are more recent.

You’ll note that there’s a distinct “curve” shape to the data, where my house consumes substantially more electricity in the cold-temperature months, less between 60 and 70 degrees, and a little more when it gets hot.  This mirrors the energy consumption of my heat pump in cold and warm months.

It’s clear there’s a relationship between temperature and electricity use, so we can make a model of this relationship.  “Make a model” is a fancy way of saying “fit a line.”  This is not a simple linear (straight line) relationship, though.  A polynomial (curve) fits much better.

Polynomial model of energy consumption

Nice.  Now we’re getting somewhere.  Check off requirement #1.

The line, and the 95% confidence intervals shaded in light blue, give us a way to predict how much electricity I would use if the month were 56 degrees.  How?

That line is an equation.  Specifically:

30-Day Normal kWh = 1912.9792 – 17.5737*AverageTemp + 1.2035871*(AverageTemp-61.491)^2

All we have to do is plug 56 into the equation for the AverageTemp and we get approximately 900 kWh.  Great!

Our “model” of energy use has some additional benefits.  It comes with an R Square value of 0.96, which means our model can explain 96% of the variation in the data.  Put another way, 96% of the change in my monthly electricity bill is captured by the equation above, and is explained just by the temperature change.  Only 4% of the variation in my bill is caused by other factors – the randomness inherent in our daily habits, how hard the wind blows, and who stands with the refrigerator door open.

We could add other factors to our model, like how many nights we cook every month, or change the type of curve we fit, and these would possibly improve our R Square.  But it’s very simple to find out the temperature, and I’m happy with the fit.  We’ll leave it alone.   Still, it’s nice to know we could develop better models and objectively compare them with one another based on R Square and other metrics.  Check off requirement #2.

Okay, let’s go ahead and add in my September-January data (red crosses) to see where it falls on the model.

Electricity Model with Savings Period

Eyeballing the data, it looks like the September data point is close to the prediction and lies inside the blue shading at 70 degrees.  Moving left through the colder months, the deviation starts to stand out, and we see that the red points don’t fit well with the previous model.

Keep in mind – we’re looking only at the vertical distance to get a sense of the changes.

Vertical distance = kWh savings

Thankfully, we don’t need to measure each point individually with a ruler, we can use our model curve to speed up the process.  Just use the equation for the line to calculate the difference between the model and each point.  In effect, we’re flattening out the curve, removing the effect of temperature on electricity consumption.  The result is called the “residual” – the 4% of variation left over when we remove the 96% of variation accounted for in our model so far.

Residuals from the Electricity Model

Requirement #4 – Check.

You can see that we’ve flattened the line, and only the difference between each point and the model’s prediction is left.  You’d expect these residuals to look randomly scattered – if you see a pattern, your model missed something!

You’ll also notice that the baseline (blue) points are scattered around the zero line, deviating by plus or minus about 100 kWh.  You can make a measure of this variation, but we’ll just eye-ball it for now (I’m still working on Requirement #3)  and consider anything within those boundaries to be “normal” or expected.

You have no doubt noticed by now a couple of red crosses WELL below the line – those are my energy savings for December and January!  Multiply the residual by the price per kWh for that month (and yes, this changes…) and you’ll get this:

Savings over time

The line hovers around zero, meaning my model did an okay job at fitting the data.  It has a slight upward angle, indicating that my energy use was increasing over time, independent of the temperature changes.  Not good!

But take a look at the month after I insulated (the first red cross).  Energy use was below the expectation.  It’s not huge, but I wouldn’t expect a lot of savings in a month where my HVAC doesn’t run very often.

It’s not until December when you see some serious savings.  I attribute the $47 drop to a couple of things

  1. better insulation
  2. better control by the thermostat, avoiding the use of my auxiliary heat
  3. we traveled over Christmas and were gone for a week  :)

January’s savings weren’t quite as good, but still respectable for a single month.  I figure I’ve spent under $400 on insulation, thermostats, caulk and foam, and I’ve recouped about $100 of that in just five months.  Not bad, and I feel good knowing I can demonstrate the savings with some solid numbers, rather than guesstimates and a vague hunch.

Sadly, I’m excited to see what next month’s bill brings…

So the question is: how do YOU measure what didn’t happen?

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When the River Meets the Sea

By Daniel on January 28, 2010

the creek

We recently had some heavy rain, and the wooded path behind my house showed sinuous trails where the water carved its way between the leaves.  Thankfully, this path is not normally a river bed, but water is a powerful if fleeting force of nature.

All that water ran down the path, into the stream, and followed the road around the corner.  After that, my understanding is a bit dodgy.

The reason I’m curious about my raindrop’s destination is because I recently bought a power paint roller that pumps the paint out of the can and into the roller – no bending, no drips!  The downside is that you waste a fair bit of paint, and the cleanup instructions tell you to connect a garden hose to a port in the side of the painter, and just let the water flow.

Now, I don’t know about you, but I don’t have a hose inside my house, so if I cleaned the painter by the prescribed method, I’d be dumping latex paint onto the ground behind the house.  It would run down the path, into the stream, and we know where that leads… at least vaguely.

I’d argue that 90 percent of the people who buy this product would hook up the hose and let ‘er rip without thinking about where all of that material ends up.  InfoVis to the rescue!

Pierce County Washington has one of the coolest interactive maps I’ve seen in awhile.  Just double click on any point, and find out where water (or paint) falling in that location ultimately winds up.  If you knew your watershed – the series of rivulets and rivers that connect you with the ocean – would you think twice about what you added to it?  What about if you had to drink from it, or your food grew there?

Maybe you’re not a painter, but you might add fertilizer to your lawn.  Or, you may spread a few pesticides around the foundation to keep termites and roaches out out of the house.  Or, if you’re in North Carolina, you’ll certainly want to dump thousands of gallons of salt water on the roads every time the meteorologist thinks he sees a snowflake.

All of these things actions have a broader impact, and I’d love to see maps like this one for every region, so we could all appreciate our place in the water (and food) chain.  Seeing is believing, and maybe protecting.

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How bad could it be?

By Daniel on January 26, 2010

The Onion takes a shot at all of us who think our own insignificant actions don’t make a difference.

‘How Bad For The Environment Can Throwing Away One Plastic Bottle Be?’ 30 Million People Wonder

WASHINGTON—Wishing to dispose of the empty plastic container, and failing to spot a recycling bin nearby, an estimated 30 million Americans asked themselves Monday how bad throwing away a single bottle of water could really be.

…

According to the inner monologue of millions upon millions of citizens, while not necessarily ideal, throwing away one empty bottle probably wouldn’t make that much of a difference, and could even be forgiven, considering how long they had been carrying it around with them, the time that could be saved by just tossing it out right here, and the fact that they had bicycled to work once last July.

read the rest…

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Carbon Counters: Caveat Emptor

By Daniel on January 22, 2010

by jbushnell

It’s a perfect storm for developers of carbon accounting software: a brand new market, social and political pressure to comply, and a low barrier to entry.  And it’s worse than I thought.

A recent LinkedIn discussion pointed out that there are over 60 vendors offering carbon accounting solutions.  That seems like a lot to me, but I’m can’t say I’m surprised at the glut.  Carbon accounting requires some discipline and data management skills, but it’s not rocket science and many vendors can pretty easily churn out a carbon plugin for their current offerings.

In the greenhouse gas inventories I’ve prepared, I’ve chosen to learn the accounting protocols, develop the spreadsheets, and design a database to hold the information.  I did this so I could really understand the accounting, and to identify the best carbon abatement projects.  But more often than not, when an organization decides to measure its emissions, it falls to an already busy employee – a facilities manager or sustainability director.  They don’t have the time to develop a custom process, and so they look for turn-key solutions.

As much as I learned from the time I spent developing a carbon accounting system, I realize one major factor that is missing: institutional awareness.  The data, the methods, the conclusions, while all documented, reside with me, on my computer, and on my website.  I monitor air travel emissions, refrigerant leaks, and commuter activity, but I am not the person who makes decisions about travel budgets, maintenance, or public transit.  And while I can influence and inform those practices with my ideas and perspectives, there is still something of a disconnect between our carbon footprint and our daily decision making.

I think an institutional carbon tracking system would place the information in the hands of the people who can make a difference.  It would give maintenance workers a chance to input their own data, and track their progress.  It would give administrators a window into the environmental performance of their department or team.  In effect, it would make me obsolete.  A worthy enough goal in itself…

But which to choose?  I’m not prepared to answer that question, but I will respond with several more questions.  These come from Stephen Few, a leader in data visualization and analytics.  Few often rails against vendors for products that offer all sauce and no substance.  He recommends asking the following questions when you try to choose a visualization package.  I think the same apply to carbon accounting and probably any type of product or service you buy:

  • Does the vendor have deep expertise in the domains that its products support? Does it exhibit this expertise, not only in its products, but in its communications as well, including marketing materials and sales presentations?
  • Does the vendor invest in the development of features and functions in its products that actually work and are actually needed by more than a few users?
  • Does the vendor exhibit a commitment to designing products to be as easy as possible to use?
  • Does the vendor develop products that nudge users in beneficial directions (that is, in directions that actually produce results that effectively serve their needs)?
  • Has the vendor defined its potential users clearly enough and gotten to know them well enough to develop the product in relevant ways?
  • Does the vendor refrain from making marketing claims that are false or otherwise misleading?
  • Does the vendor know how to tell the story of what its product does, how it works, and why it’s good? If it doesn’t, this is a sign that it doesn’t have a clear story to direct its efforts into a coherent product.
  • Does the vendor make it easy for potential buyers to evaluate its products?
  • Does the vendor help its users develop the conceptual skills (not just skills in using the software) that are necessary to use its products productively? For example, if it produces data analysis software, does it offer instruction in the principles and practices of analysis?
  • Does the vendor take the time to develop user documentation that is really helpful, with clear explanations and meaningful examples?
  • Does the vendor’s support mechanism (phone support, etc.) demonstrate that it genuinely wants to solve your problems rather than only provide the minimum support that customers will find tolerable?

I suspect that many of the carbon accounting solutions would whither in the light of these questions.  Have you tried any of them?  And how did they work for you?

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Food, (shr)Inc.

By Daniel on January 20, 2010

Over the holiday weekend, I spent some time with friends one afternoon, and we decided to Netflix a movie.   Netflix is a verb now, right?

In any case, we decided on Food, Inc., a documentary about our country’s agriculture system.  For those of you familiar with Michael Pollan’s The Omnivore’s Dilemma, this is basically a movie version of the book.  For those who are unfamiliar, the system goes something like this:

  1. Government subsidizes corn production, causing prices to go below production costs.
  2. Cheap corn!
  3. Farmers feed corn to cows, pigs, chickens, fish, and after lots of mysterious alchemy, to people in the form of High Fructose Corn Syrup and other interesting byproducts.
  4. Cheap food!
  5. Profit!
  6. Pay some lobbyists to take us back to step one.

Along the way, animals get sick, E. coli evolves into a super mutant, and 2/3 of Americans are classified as overweight.  Diabetes skyrockets.  Healthcare becomes expensive.

Was corn the gunman on the grassy knoll?  I can’t rule it out.

All joking aside, our food system causes serious problems, and these examples are just scratching the surface.  Who’s responsible, and what’s to be done?

I may not have posted on this topic if I hadn’t spotted the following infographic:

You’ll notice that in 1901, the average American spent about 40% of her income on food.  Now, it’s more like 10%.

You could argue that this is a huge boon for society, giving us the ability to feed the world at low prices.  No one needs to go hungry.

But I think it comes at a price;  instead of starving, we’re going bankrupt on medicines to treat diabetes, heart disease, and strokes.  And even though we’re fed, we’re not nourished.  There’s a big difference.

It looks like we’re devoting greater proportions our income to the transportation and “other” categories, and I’m left wondering – can transportation and “other” really replace what we’ve lost by eating cheap food?

At the end of the day, when I ask myself “Who is responsible for this?” I think the answer is, “all of us.”  We’re the ones that demand cheap food, that ignore the farm bill, and vote with our dollars.  I’d love to point to a foreign enemy or infectious disease as the culprit, but the paper trail on my credit card statement points squarely at the perpetrator:  me.

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5 Rules for Presentations

By Daniel on January 19, 2010

If you give presentations, and I suspect you do, there’s a lot you can do to make them more interesting, more engaging, and best yet, get people to respond with action.

The folks over at Duarte Design have put together a short list of 5 rules, and a slideshow that puts them to use.  As I’ve incorporated ideas from their book, slide:ology, I’ve gotten nothing but positive feedback from audiences.

Check out the video below, and pick up the book if you want to learn more.  As she states in the video, you should learn these principles because they will make your message stand out and reach the audience in a world of bad, boring presentations.  Who wants to be ignored?

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Picowatt – Smart Grid for the Rest of Us

By Daniel on January 13, 2010

If you read yesterday’s post on monitoring your smart appliances with new gadgets from the Consumer Electronics Show, you may have been left wondering, “What if I don’t want to replace all of my dumb appliances?”  I know I was.

Well, leave it to CES to solve problems created by CES.

The Picowatt, shown in the video above, is a plug/brick with WiFi guts. It can show you not only how much energy your appliances are using, but also lets you shut them down remotely.  It’s the holy grail of smart grid (information and control), without having to landfill your current fleet.

The 30% energy savings promised by the woman in the video seems a bit high to me, and you almost certainly won’t save 30% of your energy.  The savings would only be realized by someone on a time-of-use rate with their local utility if they programmed the device to shut down their appliances during peak loads.

It’s a worthy goal, and probably the wave of the future, but for now, most of us pay the same 8 cents per kWh, no matter what time it is.  So running the dryer at 3 AM costs the same as it would at noon.

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Consumer Electronics Focus on Energy

By Daniel on January 11, 2010

The Consumer Electronics Show is a yearly excuse for just about everyone to geek out.  It’s no surprise that the focus on energy efficiency and home management caught my eye.

First up,  Home Energy Manager promises to put your bloated house on an energy diet.  By linking to a series of smart monitors in each appliance, HEM lets the homeowner set a budget.  This approach is appealing for people who already budget their money, because now you can break down the “utility” line-item to identify some real-world strategies for saving.

Your house may spend more on running the dryer than the dishwasher, so a clothesline is a smart option.  Or maybe that beer fridge in the garage is past its prime and needs to be recycled.

The software will pilot in Houston this spring, and offers the additional benefit of weather forecasts and social networking.  Because you can never have too much social networking, I guess….

Next up, a related offering from Silver PAC, maker of all things remote.  Have you ever seen one of those remote controls that are bigger than my first TV?  It may have come from this group.

Called the SilverSTAT 7, the device also talks to your smart appliances via WiFi connections and displays your energy use on the thermostat.  The bait here is that the thermostat can talk with the local utility, giving you information to help shift your usage off peak when prices are lower.  It still lacks some automation, though, so you can’t take an entirely hands-off approach.

I do have to ding them for their use of “gauge-style” dashboard icons.  Gauges are generally considered to be a waste of space, but I guess they’re trying to give the people what they expect whether its good design or not.

And last, but certainly not least in our roundup, is the Mirasol display technology from Qualcomm.  Based on the way a butterfly’s wing creates vibrant, iridescent color without the use of pigments, Mirasol is a low-power display option that becomes even more visible in bright sunlight.  Other technologies rely on backlighting that reduces the image quality and draw power.

Check out the video below for a brief overview, and keep in might that the bright blue Morpho butterflies you see in the video are actually brown – it’s the prismatic scales on their wings that bend the light producing such a vibrant color.

via Paystolivegreen

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Division by Division

By Daniel on January 10, 2010

Burn by ktpupp

With the unemployment rate hanging like an albatross at 10%, the nation is looking for some fresh ideas for job creation.

Thus, on Friday, President Obama spoke about Green Job creation, fueled by a 2.3 billion dollar  tax credit to American manufacturers. According to the President,

“Through this initiative, we’re awarding $2.3 billion in tax credits for American manufacturers of clean energy technologies — companies that build wind turbines, and produce solar panels, and assemble cutting edge batteries. The initiative we’re outlining today will likely generate 17,000 jobs, and the roughly $5 billion more that we’ll leverage in the private sector investments could help create tens of thousands of additional jobs.”

Let’s do the math:

$3,200,000,000/17,000 jobs =  $135,294 per job.  Please sign me up for one of these jobs!

I’m growing very tired of politicians using “green” to cover over a host of fiscal sins, both because the programs are wasteful, and for the damage it does to the environmental movement.  If people are continually disappointed by “green” initiatives, it won’t be long before they refuse to support some very worthy causes.

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Free the Grid

By Daniel on January 7, 2010

Once that “Save the Whales” bumper sticker wears off of your 1984 Pinto, you may want to invest in a “Free the Grid” upgrade.

An electric grid is a difficult thing to manage, so its care has been traditionally left to the power companies.  The state government usually acts as overseer/dictator/blind eye, depending on where you live, and most of us were happily ignorant of how power reached our houses unless we had a outage or an extremely high bill.

But with the advent of affordable renewable energy, all that changed.  If you try to slap a solar panel on the roof, or put up a small wind turbine, you’ll find yourself in a regulatory briar-patch that will certainly leave you with a few scratches.

Many utility companies are resistant to letting the little-guy into their power playground.  It’s not without reason – variable sources of energy can make leveling the grid quite challenging.  But they also have a vested interest in keeping their monopoly: a kWh saved is a dime they don’t receive.

The Network For New Energy Choices releases a report card every year, grading each state on its interconnection standards and net metering protocol.  Some big no-no’s include:

  • Restricting eligibility to certain classes of electric customers
  • Limiting program eligibility based on the size of individual renewable energy systems
  • Preventing customers from receiving credit for excess electricity
  • Capping the total combined capacity of all customer-sited generators
  • Charging discriminatory or unclear fees and standby charges
  • Requiring — or allowing utilities to require — unreasonable, opaque or redundant safety measures, such as an external disconnect switch
  • Creating an excessively prolonged or arbitrary process for system approval
  • Requiring— or allowing utilities to require — different technical provisions that vary by state to serve a distribution grid that is homogeneous nationwide
  • Requiring — or allowing utilities to require — unnecessary additional liability insurance
  • Failing to promote the program to eligible customers

You can see that there are many creative ways to suppress and inhibit distributed renewable energy systems without expressly banning them.  My state, North Carolina, got a big fat “D” for its net-metering policies.  How did your state do?

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