One of the first go-to strategies for increased energy conservation for any establishment with refrigerated cases is incorporating Floating Head and Floating Suction. Floating head and floating suction are managed through building controls. To learn more about Building controls check out our blog post from July 18, 2018, there is some great information on how building controls can improve operations and your bottom line.
Floating head or floating head pressure control is a fundamental Energy Management strategy which utilizes outdoor ambient conditions to adjust (or float) the condensing pressure/temperature in a refrigeration system. This is the pressure at which superheated refrigerant gas condenses to liquid to feed the loads on a refrigeration system. When a lower pressure is required to effect this change of state, less energy is required by the compressors to reach that lower level pressure. Condensing conditions are usually expressed in terms of temperature, as temperature and pressure are directly related when in this state. Generally, reduction of the condensing temperature yields a 1.3% energy savings per degree Fahrenheit reduced.
Floating suction or floating suction pressure control is an Energy Management strategy utilizing electronic rack controllers to automatically adjust the refrigeration system suction pressure setpoint based upon actual temperatures at the cases or walk-ins. Refrigeration loads (cases or walk-ins) are designed to maintain product temperatures based on specific constant suction gas temperature (again temperature and pressure have a direct correlation in the saturated vapor state of refrigerant). Compressors are run and cycled to maintain this suction pressure. Due to multiple related factors on system performance, when all loads are at or below their temperature setpoint, this pressure can be optimized to minimize compressor runtimes based on the cooling requirements of critical loads that are no longer satisfied. This “float” of the suction pressure setpoint has been proven to reduce the electric energy consumption of refrigeration systems by 1%-2%.
System Efficiency & Energy Consumption: Reduction in compressor power consumption resulting in electric energy cost savings. Depending on the size and configuration of the refrigeration system, this can net a savings of up to 20%. In a typical market, refrigeration energy consumption is on average 50-60% of the total usage.
Liquid refrigerant naturally subcooled, which helps cases perform more efficiently.
Prolonged compressor life (a result of lower compression ratios).
Rebates available from many electric utilities can help offset implementation costs and improve the ROI of implement these strategies.
Floating head control generally increases the energy consumption at the condenser. This needs to be managed through proper control of the fan motors.
Refrigerant charge requirements typically increase so systems need to be evaluated.
Expansion valves in cases need to be adjusted for proper superheat.
Setup greatly depends on the geographic location of the store, refrigeration system design and age of equipment.
This fundamental Energy management strategy is well worth the investment of time and money. Check out our recent post to learn more about How Energy Management Systems can improve your life by clicking this link.
Rick J Ferguson is an industry expert with over 30 years’ experience as a Refrigeration Engineer and Energy Management Consultant. He holds a Bachelor of Science degree from University of Portland in Mechanical Engineering and was one of the original founders of R3 Retail Development.