Mar 19, 2012 Sustainability News
Spelman College has entered the following video for Second Nature’s Climate Leadership Awards. Way to go Spelman!
The video gives an overview of Spelman’s sustainability initiatives featuring President Beverly Daniel Tatum, Art Frazier, director of Facilities and Management Services, and Spelman’s sustainability interns.
Mar 2, 2012 Editorials
Demand Controlled Ventilation (DCV) control strategies are utilized in many projects today to the energy used to condition outside air into the building. This energy reduction comes from utilizing lower outside air brought into a space or area when the amount of people is low or non-existent. This is especially useful for areas that will have minimal to no people for majority of the time but have a high amount of people for a short people of time. This can be a very useful energy reduction strategy when it is implemented correctly. But at this time, you see this strategy incorrectly implemented. The two most common errors in the implementation that I have seen is not having modulating outside air/return air dampers and having a very low carbon dioxide setpoint.
Many times you will see the engineer specify a simple balancing damper for the outside air. Using this type of damper does not allow you to bring in the extra outside air necessary to flush out the high carbon dioxide levels in a space. Even when the engineer specifies a modulating outside air damper, they typically do not provide the two outside air flow setpoints that are needed to properly control the system. The damper should have a minimum and maximum setpoints. The minimum setpoint should be based upon the minimum amount of outside air required by ASHRAE 62.1 to ventilate a space with no people. The maximum setpoint should be based upon the minimum amount of outside air required by ASHRAE 62.1 for a space with a full people load. Without having both setpoints, the minimum position with be set by the TAB contractor at the wrong minimum and when the DCV is used, the outside air damper modulates open and brings in excess amounts of outside air.
Another incorrect implementation of DCV is having a low carbon dioxide setpoint. Ambient carbon dioxide levels typically are in the 300-500 ppm range (this level maybe higher if the building is located near a major roadway). ASHRAE 62.1 recommends the setpoint for DCV to be 700 ppm above ambient carbon dioxide levels. Having a low carbon dioxide setpoint (say 700 ppm) means that you will start bringing in extra outside air when it is really not necessary. Bring in the unnecessary outside air leads to increased energy usage in the conditioning of this outside air. It is typically recommended that the setpoint by around 1100ppm.
DCV can be a good energy saving control measure….when it is implemented properly.