Q T ¼ ðqvAÞDAGðhRAG — hDAGÞ ð5Þ

Q T:SEN ¼ ðqvAÞDAGcP;MðTRAG — TDAGÞ ð6Þ

Q T:LAT  ¼ ðqvAÞDAGhfgðxRAG  — xDAGÞ ð7Þ

X。  Wu  et al。 / International Journal of  Heat and  Mass Transfer 87 (2015)    685–692 687

Fig。 1。  The length magnitudes in  supermarket。

3。Results and discussions

The main purpose of the paper is to investigate the influence of supply air temperature and velocity of the diffusers of HVAC system on the heat transfer and fluid flow performance of the VORDC。 Thus, the parameters of VORDC are set as constant in supermarket scale computations。 According to the Chinese Standard GB50736-2012, when the height of supply air outlet is less than or equal to 5 m in a comfort air conditioning system, the diffuser supply air temperature (DSAT) difference should not be greater than 10 °C, and the diffuser supply air velocity (DSAV) is appropriately 2–5 m/s。 So, the supply air temperature and velocity are about 16 to 19 °C and 2。0 to 3。5 m/s in the CFD models, respectively。 The computational conditions of supermarket scale models are described in Table  1。

3。1。Influence of supply air   temperature

Fig。  2。  Ambient  measurement  point  for VORDC。

The power requirements of HVAC unit can be pided into four parts: fan, boiler, chiller and radiator。 The HVAC energy consump- tion is calculated depending on outdoor conditions and parts of operating HVAC unit。 In this paper, only the energy  consumption of chiller is considered。 The power input to the chiller is expressed in  Eq。  (8) [31]:

Tout — Tsup

Fig。 3 shows three-dimensional isothermal surfaces of T = 20 °C, T = 22 °C and T = 24 °C in supermarket scale when the DSAT (Tsup) is given at 17 °C and the ambient temperature (Tamb) is 25 °C, which indicates the influence area of supply air of HVAC。 It can be clearly seen that the cold air discharged from the diffusers of HVAC system changes the temperature distribution surrounding the VORDC。

Fig。 4 shows the temperature fields under different DSAT of HVAC。 It indicates that the indoor  temperature  decreases  with the reduction of the DSAT and the temperature surrounding the VORDC also decreases, which will directly affect the operation con- ditions of the VORDC。 At the same time, it also influences the NIR of air curtains and products temperature inside the refrigerated dis- play cabinet。 Table 2 shows the influence of the DSAT on the tem- perature and humidity of measurement point and  RAG。

From Table 2, it can be seen that the ambient temperature of the

VORDC increases with the rising of the DSAT。 The ambient average

temperature increases about 0。16 °C at the measurement point。 As a result of entrainment of the air curtains, the increasing   ambient

Here, Pcond is an energy loss due to the condensation, when the sup-

ply air of HVAC system is cooled below the dew point temperature。

Pcond  can be described in Eq。  (9):

temperature causes air temperature rising at the RAG in the cabi- net-scale  model。  Fig。  5  presents  that  the  NIR  increases      from

0。285 to 0。305 with the rising of the DSAT。 This indicates that the

thermal insulation performance of air curtain decreases, which will

make the sensible heat load of the VORDC increase, as is shown in Fig。 6。