LEARN SERIES Control System Strategies Save Money Written by Miguel Purdy, P.E.
CONTROL SYSTEM STRATEGIES SAVE MONEY WRITTEN BY MIGUEL L. PURDY, P.E.
How much do you spend each month or year to keep your per-
ishables fresh? From meats to dairy and frozen foods, to fresh produce and floral, it has been estimated to that between 30% and 50% of the electricity used in food retail is consumed by the refrigeration system. Ambient conditions that differ from the original design and equipment selection conditions adversely affect the energy used in refrigeration. Then, other inefficiencies creep in over time, such as dirty coils, burned up fan motors, etc., all the while driving up energy costs. Systems that were put in as the state of the art systems a few years ago must be refined, tweaked, managed, updated and replaced on a regular basis because of newer, more efficient control schemes that were not available at the time of installation. Reset First
points and maintain case or walk-in temperatures. This is called FloatWhat is the first step to improving ing Suction Pressure Control (FSPC). your refrigeration system efficien- For each 1 PSI increase in suction cy? Well, it is not upgrading or re- pressure, it is possible to save 2% placing the control system. The in compressor power. The control first step is system recommission- systems read the systems temperaing. Over time, with service calls tures and pressures then adjust the and owners keeping the system in set points to ensure that the refrigoperation, your systems drift away erant leaving the coils reach the sufrom the original specifications and perheat design parameters. set points. Recommissioning resets all of this and gives you some level Floating Head Pressure Control ground to work from when looking An additional control strategy is reducing the compressor discharge at the controls system. pressure or head pressure. This strategy is known as Floating Head Establish Control Strategies Pressure Control (FHPC). By allowThe next step is where monitor and ing the control system to reduce the control systems including energy head pressure, the system could management system come into save as much as 0.5% per PSI reducplay. There are many new technol- tion. At least one study found 14% ogies that help automate refrigera- savings of combined compressor tion control, monitoring and main- and condenser energy consumption for floating head pressure contenance scheduling. trols with variable frequency drives. Floating Suction Pressure Control Adjusting and maintaining suction Load Shredding pressures allows the system pres- Control systems do a great job of sure to float above established set making the system operate more
efficiently, but it can also perform other cost saving measures for your store. This is where load shedding comes into play. Suppose there are some functions that are not required to operate during a peak load time of day, such as anti-sweat door heaters, these loads can be turned off for that period of time. That will not only save some energy, but more importantly, it will reduce the electrical consumption at higher rate times. Control systems also can coordinate different aspects of the refrigeration system so some large loads do not operate at the same time, if possible, thus reducing the increased demand charges. Unified Systems Selecting the right energy management and control system can also unify other systems besides refrigeration, such as lighting and HVAC. A unified energy management and control system allows the building HVAC management system and the refrigeration control system to work together to keep the systems from fighting over the temperature and
January 2016
approach eliminates risk of system failures or inoperable systems for any period of time, while providing a fallback position with the existing control system, should a failure occur. While phased migration does have its drawbacks in terms of cost and time, the offsetting benefits include reduced risk and less downtime.
humidity conditions in the space. It can control the lighting within the store to conserve energy when spaces are unoccupied and when the store is closed, or there is less traffic.
Approach to Control System Upgrades The key to a successful upgrade of any refrigeration system comes from a thorough, front-end engineered approach. The methodology for the upgrade can be in the form of 1) a phased migration, 2) complete system replacement, or 3) a system upgrade. An important point to remember is that any new user interface must communicate with any existing controllers on a continuous basis.
an opportunity for savings of up to 335,000 kWh annually per site. This opportunity to save money was hidden because the building operators believed they already had the full benefits of controls.
Control systems have come a long way over the last few years. Is your system doing all that it can for you? Are you missing out on significant The approach of control system up- operational savings due to your curgrades or complete replacement rent control system, or maybe just offers benefits which include: 1) from the control scheme? A small increased asset protection, 2) in- investment could allow you to reap creased reliability, 3) improved effi- large paybacks to the bottom line. ciency, 4) faster information access, 5) better interface functionality, 6) The first step to improve your opimproved component communica- erational costs is to contract with tion, 7) reduced service and imple- a commissioning agent or firm to mentation costs, and 8) lower com- conduct a systems commissionponent costs over legacy systems. ing, then work with an experienced controls engineer to develop the Significant savings are possible controls system strategy that is configured to best serve your system Some controls manufacturers have needs. stated that controls systems can save at least 15% on the electric bill due to better capacity control, set point shifting, scheduling, load shedding and enterprise wide energy management. The payback for such systems can be 1½ years through energy savings alone, not to mention the reduction in unplanned maintenance calls.
Could your facility use an extra $35,000 added to the bottom line each year? One study found in one of the largest supermarket chains, a survey of 50 stores showed the majority had A phased migration is often the best control systems but that the control approach to large scale systems strategies were not implemented such as large grocery stores. This correctly. These misgivings provide 1 Based on 335,000 kWh x $0.1045/kWh = $35,007. National average electricity cost = $0.1045/kWh 2 Supermarket Controls and Commissioning: Uncovering Hidden Opportunities, Diane Levin and Lawrence Paulsen, Portland Energy Conservation, Inc., 2006 ACEEE Summer Study on Energy Efficiency in Buildings.
About the Author
Miguel L. Purdy, P.E. is a licensed Mechanical Engineer who has over 25 years of refrigeration system design expertise and leads the refrigeration design team at HFA. Miguel.Purdy@hfa-ae.com (479) 273.7780
CONTACT US HFA-AE.com (479) 273.7780 HFA is a full-service design firm providing Architecture, Interior Design, MEP Engineering, Fire Protection, Fueling Design, Refrigeration Design, Structural Engineering, Civil Engineering, and Landscape Architecture services to the retail, commercial and assisted living markets throughout the U.S. and holds professional licenses in all 50 states and the District of Columbia.