SUPERMARKET REFRIGERATION


Rail heat revelations S


upermarkets aim to keep the room temperature below 25 °C, and most refrigerated display cases are designed for a maximum relative humidity (RH) of 60% (according to the EN ISO 23953 standard, Climate class 3 guidelines). If the relative humidity reaches the maximum level and the room temperature is at 25 °C, condensate will rapidly accumulate on the display case’s cold surfaces and glass. At room temperature below 25 °C, condensate is generated


Ejnar Luckmann


even before the relative humidity level reaches 60%. This creates a few issues. Firstly, it’s diffi cult for consumers to see what’s in the display case when the glass is clouded, and when they open the case, they risk getting wet. Secondly, and perhaps the most worrisome, is that condensate on the inside of the display case can cause bacteria to grow. If the water then drips down into the case, it can contaminate the food inside. To prevent condensation, most display cases are designed with a type of heating element, which heats the display case rails and glass. This is known as rail heat.


Rail heat control in the


Danfoss Smart Store In the Smart Store, we have four groups of low-temperature display cases controlled by eight AK-CC55 case controllers (Figure 1, #21-28). According to specifi cations from the supermarket chain that operates the Smart Store, rail heat should be set with 30% pulsing at night and 80% during the day. In the summertime in Denmark, humidity levels are so high that we need to control rail heat at a higher level than the specifi cations. During the wintertime, on the other hand, humidity levels are so low that we can control rail heat at the minimum level, even during the day. To give us better rail heat control, we chose the dew point control mode in the case controller. This mode controls the rail heat intensity based on the humidity level and store temperature instead of fi xed daytime/nighttime settings (Figure 2). If we look at the Smart Store’s total energy consumption,


Figure 1


low-temperature display cases and low-temperature cold rooms account for 14% of the overall energy used. Rail heaters account for a considerable portion of that 14% (Figure 3). In the Smart Store, we’ve installed 50 energy meters across electricity, hot water (for space heating) and chilled water (for air conditioning), and 3 meters for tap water. One of the electricity sub-meters is installed in front of the four groups of low temperature display cases (see Figure 1, #21-28) and the low temperature cold room (Figure 1, #100). This meter measures energy consumption for the fans, defrost, lights, rail heat and the controller/valve. By manually switching between 0 and 100% rail heat on the four groups of low-temperature display cases, we measured the rail heat load at 2.6 kWh. This means that if rail heat is at 100% ON all year, the energy consumption for these four groups of low-temperature display cases would be 22,776 kWh per year! As mentioned earlier, we need to control rail heat robustly when humidity levels are high. To fi nd the robust setting, we set rail heat to a minimum of 100% on two groups of low- temperature display cases (Figure 1, #25-28), while we controlled the other two groups (Figure 1, #21-24) using dew point control. By regularly comparing the moisture level in the display case where rail heat was set to 100% with the others with dew point control enabled, we could fi nd the robust dew point settings for the minimum and maximum rail heat. Based on this test, we set up rail heat control with a minimum


Figure 2 10 October 2025 • www.acr-news.com


30% rail heat at 2°C dew point controlled proportionally up to 100% at 11°C dew point. Figure 4 shows the energy


Download the ACR News app today


Rail heat, or anti-sweat control, has been a part of supermarket control systems for years. But why is this energy-saving feature often disabled or poorly set up? Ejnar Luckmann, Technical Manager, Danfoss Smart Store ADC explains how the Smart Store shows signifi cant energy saving potential without compromising robust control at high humidity levels.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40