Rooftop Units (RTUs): Retrofit to Achieve Energy Savings
Rooftop Units (RTUs) are among the most prevalent type of HVAC system in commercial buildings, cooling over 60% of the US commercial building floor area. Due to the age of many buildings, most of these units are 10 to 20 years old. With the increasing age of these units and advances in technologies over the past few years, many currently installed RTUs are using unnecessary energy.
Depending on the size and type of your building, a single rooftop unit could be wasting $1,000 to $3,700 annually. About 90% of currently installed RTUs use a constant speed fan. This means that the fan is either on or off, and for the most part it is on to help meet the building’s ventilation needs during occupied times. The excess energy consumed by running the fan at a single speed can be avoided with advances in control technologies.
Replacing RTUs with new, high efficiency models that have advanced controls built in is certainly an option, especially for units reaching the end of their lifecycle. In other cases it would be more financially beneficial to retrofit your existing RTU with advanced controls. Retrofitting can allow you to gain unit efficiency and save money, while avoiding early retirement of the equipment in which you initially invested.
Retrofit controls are best installed on RTUs that are less than 10 years old but could apply to well-maintained units that still have a useful life. In most cases, in order to take advantage of the efficiencies of a retrofit, the units should also have a cooling capacity greater than 5 tons. Simply installing a variable frequency drive for the fan motor, limits the potential energy savings, unit efficiency, and building comfort. An advanced RTU control system, such as Transformative Wave’s CATALYST, provides a wider range of features to enhance not only the fan but also the other factors that affect energy consumption and building comfort. The CATALYST includes all of the essential and desirable features the DOE suggests for an advanced RTU control system as described in the table to the right.
Through research conducted by the Pacific Northwest National Laboratory, the cost savings for a commercial building in the Baltimore region is 39 to 46% when an advanced RTU control system is installed, as shown in the graphic above.
Timing is Everything
Now is a great time to evaluate the efficiency of your building’s RTUs. The U.S. Department of Energy, ASHRAE, and the Retail Industry Leaders Association (RILA), have organized the Advanced Rooftop Unit Campaign (ARC) compiling information and resources into a convenient source for building owners and managers. To receive additional assistance from experts at the DOE national labs throughout the process, join the campaign. It is simple to join: sign up on the ARC Website, agree to be listed on the website, and pledge to adopt high-efficiency RTUs and controls in your facilities and then submit data and information about RTU replacements and retrofits. The Pacific Northwest National Laboratory offers a calculator that will help you evaluate the efficiency of your unit and compare it to potential upgrades.
Besides increasing the efficiency of your unit, you could benefit from tax incentives and rebates currently being offered in your area. These benefits can shorten the payback period of your investment, garnering you greater savings.