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Building Manager Green Tip

July 2012

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Why is Demand Response Beneficial?

Electricity demand plotted against daily max temperature

In most climate zones, electrical demand rises along with temperature as air conditioners ramp up to meet increasingly larger cooling demands.  The largest peak electric loads in a given year tend to occur in the mid- to late-afternoon during particularly hot sunny days in the Summer.  When this happens utility providers have to generate additional supply which tends to be generated using less efficient 'peaking' power plants.

According to data from the EIA, the average hourly demand for Massachusetts in 2010 over a full year was 4,886 MW, but the utilities need to maintain infrastructure with a capacity that is 279% higher (13,679 MW) in order to reliably meet peak Summer loads that may last only a few hours.  Keeping such capacity operational is very expensive, a cost that is passed through to consumers in both demand and consumption charges. By reducing peak loads facilities are able to save utility costs, infrastructure expenses, and carbon emissions!

Top 5 Load Reduction Strategies

    1. Raise Thermostat Setpoints to 78 Degrees or Higher - The key is to raise the thermostat right at the beginning of the demand response event so that the time the air conditioner is off is maximized.
    2. Unplug Unnecessary Plug Loads - Water coolers, coffee machines, printers, chargers, or other plugged in equipment that is not needed can be shut down temporarily.  If you have a laptop, work off of battery power. Don't open any refrigerators or freezers if it can be avoided to prevent the compressor from turning on.
    3. Turn off All Unnecessary Lighting - In many offices,  most of the ambient lighting can be shutoff while a few fixtures stay on to provide lighting for safety purposes.  Small, low-wattage desk lamps can provide additional lighting as necessary.
    4. Close Blinds - Even if direct sunlight is not shining on the blinds, creating even a porous airspace between the window and the blinds can contribute to a minor rise in insulation values.
    5. Reduce Elevator Use if Possible - Every time an elevator is used a motor with a relatively high electrical demand has to operate.  

Demand Programs at Harvard

Demand Profile on ISO New England Peak 2011

Harvard Engineering & Utilities coordinates demand response events across the university to save in both emissions and demand charges.  A reduction event that occured in July of 2011 correctly predicted the New England grid peak, and the 5.2 MW demand reduction saved the university over $200,000 in demand charges alone, a figure that does not include consumption savings.

Those on campus may have noticed a few events already occuring earlier this summer, specifically on June 21st and July 17th.  It's too early to tell whether one of these days will end up being the New England grid peak that is used to benchmark annual maximum demand, but initial results from the Blackstone North reductions profiled above indicated our program is sucessful in shedding loads. 

Green Building Services provides consulting services to ensure that the design, construction and operation of Harvard's built environment has minimal environmental and human health impacts, maximizes occupant comfort and generates an awareness of sustainable design and building operations. To learn more about our work and services, visit http://green.harvard.edu/gbs.