The residential colleges consumed 10.6 percent less energy during spring break this March than they did last year, which brings the University one step closer to doubling the monetary support for sustainable energy it had expected to provide as a reward for conservation.

Under Yale’s Greenhouse Gas Reduction Strategy, students have one more month to produce a 10 percent improvement in the year’s total energy consumption compared to last year. If they succeed — and with the current savings standing at 9.3 percent, the race is coming down to the wire — the administration has agreed to invest in renewable energy certificates worth two-thirds of residential power usage. But while the overall campaign has already far exceeded its original 5 percent goal, a mysterious discrepancy in success rates among the colleges has left activists unsure of which factors most affect savings.

Sustainability efforts on campus have produced a major turnaround since November, when year-to-date savings stood at only 1 percent. Energy Manager Tom Downing said residential colleges have slashed energy consumption since then, recently culminating in the reduction of wasted power this month.

“Spring break was a victory,” Downing said. “Our initial hope this year was to make 5 percent, so if we make 10, this is all gravy.”

Activists have now all but secured sustainable energy credits — which allow providers of sustainable energy to sell their product at rates competitive with non-sustainable providers — worth one-third of college consumption as a reward for a 5 percent improvement.

Downing attributed the spring break savings largely to the weather, which was warmer than during the same period in 2005. But overall temperatures since September have been almost exactly the same as last year on average, so activist efforts and more efficient equipment are responsible for the success to date, Downing said.

New Haven Action Executive Director Whitney Haring-Smith ’07 said Yale is now experiencing the long-term effects of a campaign that began in September. Energy-saving efforts have included encouraging students to unplug their appliances during vacations and replace normal light bulbs with more efficient “CFB” bulbs.

“What we’re involved in is a marathon, not a sprint,” Haring-Smith said. “The steps that we took six months ago are reaping their rewards now.”

More recently, facilities officials have begun slightly changing temperature settings in dormitories and non-residential buildings during off-hours. For the latter category alone, a two-degree alteration is expected to save 7,800 metric tons of annual carbon emissions and over $1 million in operating revenues.

Despite their success in slashing consumption, activists said they are concerned by serious variations among the individual dormitories. Improvement rates range from 21 percent in Silliman College to negative 6 percent in Jonathan Edwards College.

Activists and University officials said they do not yet know what factors have caused the discrepancies. Some suggested that the Student Taskforce for Environmental Partnership has had more success raising awareness in some colleges than others. Two STEP coordinators are responsible for activities in each college.

“People definitely know who we are and ask us things,” said Charles Alvarez ’09, the coordinator for Silliman College. “I can’t say it affects how they live their lives, but something is happening.”

Alvarez also said college masters’ houses account for about 7 percent of residential college consumption, and some families are more cooperative than others.

The general attitude of each college’s student body is another potential culprit, Branford College Master Steven Smith said. Branford ranks second-lowest among its peers with a 0.8 percent improvement.

“I will frequently go into the common room, and the windows are open and the heating is up full throttle,” he said. “Maybe it is a culture thing.”

Heating requires the largest amount of energy in dormitories, though electricity and chilled water are also significant factors.

Downing said that while he doubts differing residential college “cultures” are responsible for the discrepancies, definitive answers will require an audit of each building at the end of the school year.

“There’s usually no magic answer; it just requires rolling your sleeves up and doing a lot of investigating,” he said. “We’re going to learn from the top five [buildings] and try to apply that to the bottom five.”

Though Yale has been successful in slashing its energy use so far this year, residential college renovations could actually increase power consumption in the long term, Downing said. Facilities workers are installing more efficient equipment in the renovations, but the savings are overshadowed by added square footage and new utilities, such as common room air conditioning.