According to Danish sensor manufacturer HB Products, its “defrost-on-demand” technology can reduce the frequency and duration of a refrigeration system’s defrosting cycles by 50% compared to standard timer-based control.
By monitoring the thickness of the ice on a system’s evaporators, HB Products’ HBDF defrost sensor and controller ensures a defrost cycle starts only when it is needed. The technology then stops the cycle once the ice is melted thanks to input from a temperature sensor located on the evaporator.
With fewer and shorter defrost cycles, end users can reduce energy consumption while increasing freezing capacity, ensuring a “fast return on your investment,” said the manufacturer.
“Experience from existing installations have shown energy savings up to 40%,” it added.
The HBDF defrost sensor was recently named Best Innovation in Industrial Refrigeration at the Grand Prix du Froid 2022 awards, which took place at SIFA 2022 (Interprofessional Refrigeration and Applications Tradeshow) in Paris in October.
Detects frost build-up
“The sensor has an isolated stainless-steel wire that is mounted between the fins on the air inlet side of the evaporator,” explained HB Products. “Another wire is connected to the chassis of the evaporator, which has electric contact with the fins.”
The manufacturer notes that the sensor requires a minimum fin spacing of 5mm (0.2in).
As frost builds up on the evaporator’s fins, the sensor detects a change in the electric charge of the evaporator. It then produces a signal to indicate defrost is needed. A temperature sensor detects when the defrost has been completed.
“The sensor can either provide a digital signal when the evaporator needs to be defrosted and when the defrosting is done, or it can provide an analog signal linear to the frost layer for a PLC [programmable logic control],” said HB Products.
The sensor works in ambient temperatures of -30 to 50°C (-22 to 122°F) and can be installed on both new and existing systems in less than an hour. According to the manufacturer, installation on an existing evaporator does not require the system to be shut down.
“HBDF is a unique but easily adaptable solution for automatic defrosting of evaporators,” said HB Products.
“HBDF is a unique but easily adaptable solution for automatic defrosting of evaporators.”HB Products
Similar products are available for cold storage applications that run just above the freezing point and for heat pump applications. The latter requires special conditions and larger fin spacing, noted the manufacturer.
Defrost-on-demand for ammonia-based systems
According to HB Products, Danish foodservice wholesaler AB-Catering has installed an HBDF sensor to get better control of defrosting for its ammonia/NH3 (R717)-based refrigeration system. The company also wanted to reduce the number of ice blocks building up on the floor below its evaporators.
“For years, AB-Catering struggled with the defrost cycles of its refrigeration system,” explained HB Products in a statement, adding that adjustments to the system were required at least twice a year.
The frequency of defrost cycles was previously “based on the evaporator [farthest] away from the compressor room to ensure complete defrost at every single evaporator in the room,” it added.
HB Products noted that the downside of this approach was that the evaporator nearest the compressor room would spend too long in defrost, which caused condensation at the adjacent ceiling to drip down to the floor and conveyor belt below, where it would then freeze in blocks.
AB-Catering worked with Danish contractor ICS to develop a solution to these issues. ICS, which has worked with HB Products for years, recommended the HBDF sensor as the “ideal” technology.