A multi-scale approach has been formulated in a previous work。 The influence of HVAC system in supermarket on the performance of vertical open refrigerated display cabinet (VORDC) is considered。 The influence is evaluated by varying the supply air temperature and velocity at the diffusers of HVAC。 The computational results show that there is a direct interaction between the HVAC  system  and VORDC in supermarket。 When the supply  air temperature  of HVAC  system  decreases  from  19 °C to 16 °C, the electricity energy input in VORDC system decreases by 6。36%, and the highest products temperature is reduced by 0。18 °C。 When the diffuser supply air velocity of HVAC system increases from 83974

2。0 m/s to 3。5 m/s, the energy input in VORDC system decreases by 23。4%, and the highest product temperature  reduces by 0。4 °C。

1。Introduction

In the vertical open refrigerated display cabinets (VORDC), the air curtain not only provides cooling capacity but also establishes an aerodynamic barriers between conservation space and external environment [1]。 The thermal insulation performance of the air curtain has a great influence on the perishable food storage and energy consumption for VORDC。 The infiltration load through the air curtain is responsible for a major percentage, about 70% [2,3]。 Meanwhile, the energy consumption spent on food preservation is about 50% of the supermarket’s total energy consumption [4–6]。 In recent years, many experiments and numerical studies have been conducted to improve the performance of air curtains。 There are many interdependent factors which act simultaneously on of air curtains, such as discharged air parameters and ambient air conditions [7–10]。 Field and Loth [11] pointed out that the entrain- ment of ambient air was primarily due to eddy engulfment which arose from shear layer interactions and enhanced by high initial turbulence levels in the  curtains。 D’Agaro  et  al。  [12]  and Foster et al。 [13] developed a 3D CFD to predict refrigeration power within engineering accuracy。 Yu et al。 [14,15] proposed a two-fluid model to optimize the air curtain effectiveness。 The studies carried

out by Gray et al。 [16] and Wu et al。 [17] showed that a 70–30 distribution of flow between the air curtain and the rear duct per- forations yielded a performance that satisfies the standards。 Gaspar et al。 [18,19] developed a detailed CFD VORDC model including the internal ducts, fans and evaporator to get a global performance improvement。 Laguerre et al。 [20] proposed a mathematical model of heat transfer to predict the products temperature in an VORDC under different operating conditions, taking into account of the conduction, convection and radiation。 Chang et al。 [21]  developed a 2D CFD model of VORDC to evaluate the influence of light, veloc- ity in air curtains, ambient temperature and relative humidity on the food package temperature。

Furthermore, if the store indoor environment maintains at a lower relative humidity, it  will  result  in  a  higher  operating cost of HVAC system, but it could reduce frost formation on the refrigerator evaporator coil and anti-sweat heater。 When the store relative humidity was reduced from 55% to 35%, the majority of the refrigerated display cabinet would be saved 20–30% in compressor energy, 40–60% in defrost energy, and 19–73% in anti-sweat heater operation [22,23]。 Orphelin et al。 [24] developed a coupling model including display cabinets and the air-conditioning system to estimate impacts of temperature and humidity on the total energy balance of supermarkets。 Bahman et al。 [25] analyzed the energy saving in a supermarket  refrigeration/HVAC  system  using MATLAB software。

686 X。  Wu  et  al。 / International  Journal  of  Heat  and  Mass  Transfer  87  (2015)      685–692