Post tagged with "air-conditioning"


Westward bound: How the US population’s gradual migration has lowered home energy usage

  • By Katie DeWitt
  • November 26, 2012

Since its inception, the US population has progressively migrated westward. And more recently, thanks to the advent of air conditioning, we’ve moved southward. These trends, according to new data from the U.S. Energy Information Administration (EIA), have decisively shaped residential energy consumption patterns in recent decades.

The EIA’s data release suggests that our geographic shifts have been associated with a relocation toward warmer conditions, which has in turn meant lower demand for energy-intensive home heating. This phenomenon has been an important factor in dampening per capita energy consumption over the past 50 years – even as the average home’s square footage has been increasing.

The map below gives a sense of Americans’ westward and southward migration over time: in 1790, the country’s so-called “mean center of population” was in Maryland; in 2010, it was situated in southern Missouri.

Source: U.S. Census Bureau, Mean Center of Population for the United States: 1790 to 2010.

While in 1960, only 31.2% of the U.S. population lived in the warmest states (as defined by a temperature measurement called degree days), this share of the population rose to 43.4% by 2010. On the other hand, the share of the population living in cooler states declined from 59.7% in 1960 to 48.3% in 2010.

The shift toward warmer climates has naturally entailed greater demand for air-conditioning.  But because space heating generally requires more energy than space cooling, the total residential energy load from heating and A/C has actually gone down since 1960, as heating needs have decreased relative to cooling needs.

This isn’t to say that warmer is necessarily better for the world’s energy future. The recent spike in air-conditioning load in the US and internationally—due to a combination of intense summer temperatures and a greater ability of developing-nation households to afford air conditioners—has the potential to put strong upward pressure on residential energy demand in the coming years.

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Hot and heavy energy usage: How the demand and price for electricity skyrocketed on a 100° day

  • By Barry Fischer
  • September 5, 2012

The passage of Labor Day sadly marks the end of backyard BBQs and pool parties, but for many people it may also come as a relief: a brutally hot summer is finally coming to an end.

The first half of the year was the hottest ever recorded in the contiguous US. July 2012 became the hottest July on record. And in communities across the country, more than 27,000 daily high-temperature records have been broken or tied so far this year.

Across the river from Opower headquarters, Washington DC faced 11 consecutive days that hit or exceeded 95 degrees…it was the city’s most intense heat wave in 141 years of keeping temperature records.

Thankfully, air conditioners keep us cool and comfortable during these sizzling summer days. More than 60% of US households now have central air conditioning, up from 23% in the late 1970s. But the luxury of A/C comes at an obvious cost: higher electricity consumption.  Exactly how much higher? We found that the average home’s electricity usage on a 103°-high summer day is up to 40% higher than during a typical summer day.

How do we know? We cracked open our data warehouse to examine anonymized energy usage data across 18,000 homes from 3 different cities in the western part of US, which has faced blistering temperatures this summer.  In particular, we explored a few key questions about energy consumption on hot days:

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When the blackout hit, I blacked out my windows and was 33% more comfortable

  • By Barry Fischer
  • July 2, 2012

Like 2 million other electricity customers in the mid-Atlantic region this past weekend, I lost power.

A weekend with 100-degree temperatures is not the best time to be without air-conditioning. But, it got me thinking…is it possible to keep our homes cool in the absence of electricity?

Then it hit me: Don’t let the sun shine into the house. Close the blinds.

Indeed, simply closing window blinds or drapes can reduce solar heat gain into the house by 33-45%. So then, isn’t it a good idea on all hot summer days to close the window blinds when we leave a room for a while?

Yes–I’m going to do it more often. Less electricity needed for A/C use + increased comfort = Nice.

And if you are especially ambitious about blocking out the sun on hot days, you can consider strategically planting a tree to shade your most sun-exposed windows. Field studies conducted in Sacramento have found that “shade trees” can reduce cooling costs by 30% and overall summertime electricity costs by more than 5%.

The only catch: the shade tree needs to remain standing after storms…

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