Building Automation: Controlling Demand Response
Lately, there has been a lot of interest and discussion about DR. In case you haven’t followed it, the concept is being promoted by utilities and others as a way to better match the demand for electric power with supply. When electricity is in high demand, such as on a hot summer day, the utilities cost for generating (or purchasing) this “peak” power gets progressively more expensive.
In the extreme case, when peak power becomes increasingly difficult to provide, blackouts may occur. Of course, the utilities can always build more power plants … just not in my backyard!
One alternative to increasing the supply of power is to simply reduce the demand. DR allows commercial building owners to sign up for a program that commits them to reducing demand on request (i.e., demand response). The owner typically gets paid a fee to be part of the program and may get additional payments if (and when) they are requested to reduce demand. These programs can work manually, with the building engineer receiving a phone call or fax, or ideally can be automated so that they signals are sent electronically to the BAS which then reduces demand through a set of pre-defined sequences.
Responding to the DR signalGiven the current scarcity of peak electric capacity in many regions, and the expectation that this will only get worse, DR appears to be a great idea. These programs can be financially attractive to suppliers, contractors, and owners. Controlling demand to better match supply also helps the environment. But is it really a good deal for building owners and occupants? The answer, of course, is that it depends on what you do once you get the DR signal.
A building that has been designed for DR can readily drop electric loads with little impact on the occupants. This is done by gradually dimming lights, using stored thermal energy (i.e., ice or chilled water storage) instead of or in addition to mechanical refrigeration, or by using on-site generation. These options allow for rapid, automated DR and it is unlikely that the occupant will ever notice.
Unfortunately, we are seeing owners that are attempting to implement DR in buildings that are not designed for it. This includes strategies such as raising comfort cooling setpoints, shutting off lights, or raising chilled water setpoints. Making this type of change is more likely to cause notice by the occupant and, in the worst case, will result in lost employee productivity. Savvy owners realize that the annual cost for the employee is over 100 times the cost of power for the building and that even small impacts on productivity can quickly outweigh the financial benefits gained in incentive payments.
Ideally, we believe that buildings need to be designed with DR in mind. This includes dimmable lighting systems and thermal storage, along with real-time data connection with the utility and the controls needed to implement the DR strategy. So can DR be added to existing buildings? Yes, if the right systems are installed; otherwise, the only option may be to either shut off lighting or increase setpoints. We would urge extreme caution before proceeding with this approach and carefully weigh the potential impact on comfort and productivity against the possible savings from participating in the program. ES