TESTS ON AIR DISTRIBUTION PERFORMANCE IN BIG STORES

, Volue 7, Nuber 3, p.88-93, 26 TESTS ON AIR DISTRIBUTION PERFORMANCE IN BIG STORES P.F. Hu *, W. Liu +, Z.N. Jiang *, F. Lei * and F. Cai * * School of Enironental Science and Engineering, Huazhong Uniersity of Science and Technology Wuhan, Hubei, 4374, P.R. China + School of Energy and Power Engineering, Huazhong Uniersity of Science and Technology Wuhan, Hubei, 4374, P.R. China (Receied 2 Noeber 26; Accepted 28 March 28) ABSTRACT The objecties of this study were to ealuate the air distribution in big stores with floor area arying fro 389 to 576 2 based on easured data and to analyze the effect of soe factors on air distribution. Tests on teperature, air speed and huidity in the air conditioning enironent in three big stores in Wuhan, China were carried out. The standard deiation of teperature and air speed and ADPI were calculated. Correlation of the ariables with the acroscopic nubers describing air distribution including the ean speed, teperature difference between the ean inlet teperature and the ean teperature in the occupied spaces and the difference between the axiu alue and iniu alue in the were obtained. It was found that there is a serious uneen teperature and air speed distributions in these big stores.. INTRODUCTION Big stores are usually crowded and hae any counters. The teperature, huidity, air speed and their diffusion are relatiely characteristic and hae great influence on the cofort and health of the custoers and staff in the stores. There are any studies about the air speed and its fluctuation at a point but not any reports on the distribution of air speed and teperature in a plane, especially in big stores [-6]. This paper ais to test the distribution of teperature and air speed in big stores and analyze the relationships between the factors affecting the. 2. GENERAL INFORMATION OF THE STORES AND THE AIR CONDITIONING SYSTEMS Three big stores in Wuhan, China were considered. They are all-around and hae been built for 7 to years. All the stores are located on the site where traffic is conenient. The general layouts of the stores (only st to 5 th ) are shown in Table. The nuber of custoers and staff on each of the store was about 3 to 6 during the easured period. The general inforation of the air conditioning systes and the air distribution inside the stores are shown in Table 2. All the s are on the top of each. The return air is centralized. In each store, a reoling door is set to preent air leakage fro outdoor to indoor air. 3. MEASURING METHODS Oni-directional aneoeter Testo 4 ultifunction easuring equipent was used to easure air speed. Mercury theroeter was used to easure teperature and GJWS-2 teperature and huidity eter was used to easure huidity. The aneoeters and theroeters were calibrated by the anufacturer. The accuracy of the aneoeters was 2.5% for the range.5 to. s - and 5% for the range to 5 s -. The absolute accuracy of theroeter was.2 o C. The resolution of the aneoeter and theroeter was. s - and. o C respectiely. The easuring range of the aneoeter and the theroeter were.5 to 5 s - and to 8 o C respectiely. Tests were carried out fro June to August, 23, when the axiu outdoor teperature was generally fro 32 o C to 39 o C and the relatie huidity was 5 to 85%. The aerage relatie huidity is 44.%, 6.9% and 6.5% in the three stores. Measureents of the air speed were carried out at.45 aboe floor leel during a period of 3 inutes [7]. 45 to 5 positions in each were used for tests. There are 5, 7 and 7 stories respectiely for, B and C. Measureent s were ade only on fie stories ( st to 5 th ) in each store for coparison. 88

Table : General inforation of the stores Store Story Goods sold Area ( 2 ) st Cosetics, Jewelry, Foodstuff 576 2 nd Woen s wear 56 A 3 rd Men s wear 56 4 th Children s wear, Bedding 56 5 th Appliance 56 st Cosetics, Jewelry, Leather 48 2 nd Men s wear 4 B 3 rd Woen s wear 4 4 th Woen s wear, Woen s underwear 4 5 th Sportswear, Sports equipent 4 st Cosetics, Jewelry, Leather shoes 389 2 nd Woen s wear 389 C 3 rd Western-style clothes, Shirts 389 4 th Knitwear, Children s wear, Toys 389 5 th Appliances 389 Table 2: General inforation of the air conditioning systes in the stores Store Type of Position of exhaust A Diffuser Near the roof B Diffuser Door of the st C Slot Door of the st Height of the () Mean inlet teperature ( o C) Mean inlet speed (s - ) Diension of ( ) Distance between the (horizontal longitudinal, ) 2.8~3.6 6.5 4.95.36.36 4.8 3.8 3.6 9.6 2.88.36.36 7.5 3.5 3.2~3.6 2.5 2.8.8.5 3.5 2.8 4. RESULTS AND DISCUSSION The een situation of the diffusion of teperature and air speed can be described by the coefficient of uneen situation. The calculation procedure of the coefficient is as follows. The instantaneous speed u ( τ ) is expressed as the su of the ean speed u and the fluctuation u. The ean speed u is the aerage of the instantaneous alue at a point oer a tie interal fro tie τ to τ + τ: τ+ τ u = ( τ ) τ τ u d () τ Select n easuring points and easure the teperatures and air speeds on these points. The standard deiation of teperature and speed are: SDT SDV ( t t ) = i n ( u u ) = i n 2 2 (2) (3) where t (in o C) is the aerage air teperature in a zone; u is the aerage air speed (in s - ) in a zone; t i (in o C) is the local air teperature; and u i (in s - ) is the local air speed. 89

The uneen coefficients of teperature and speed in a zone are: σ = t σ = SDT t SDV u (4) (5) σ is a paraeter which is different fro turbulence intensity (Tu). Tu = u u 2 (6) σ (and SDV) reflects the een situation of the elocity in a plane while Tu is the agnitude of the elocity fluctuation oer an interal tie at a point. As to the cofortable air conditioning, the influence of huidity to cofort feeling is sall, so the coprehensie effect of air teperature and speed to theral feeling is considered. The effectie draft teperature [8] is: EDT = ( t t ) 8( u.5) (7) i i where t i is the local air teperature; t is the aerage air teperature and u i is the local air speed. Most people are cofortable where the effectie draft teperature is between.5 K and + K and the air speed is less than.35 s - [9]. ADPI is defined as the percentage of locations where easureents were taken that eets the preious conditions of speed and effectie draft teperatures. In general, ADPI should be higher than 8%. The ADPI in the stores are shown in Table 3. The percentage distribution of air teperature, difference between axiu and iniu air teperature in a t ax, ean air speed at a point u and uneen coefficient of air speed in a σ in the stores are shown in Figs. to 4. Though the alues of σ t (not listed here) are relatiely sall due to the relatiely large alue of t, the alue of t ax in ost stories are generally larger than 2 o C and σ is larger than.3. The alue of ADPI in half of the stories is less than 8%. It can be concluded that there is indeed uneen teperature and air speed distribution in these stores. The influencing factors are coplex, such as the design of air distribution, ealuation of lighting in each, changes of counter and goods arrangeent and the nuber of custoers. The standard deiation of teperature fluctuations SDT was found to hae a linear correlation with the teperature difference between the ean inlet teperature and the ean alue of the teperature in the occupied zone in a ( ti ) with a correlation coefficient of.73. It was also found that there is a linear relationship between SDT in a and the difference between axiu and iniu air teperature in a ( tax ) with a correlation coefficient of.73. The results are shown in Fig. 5 and Fig. 6 respectiely. The standard deiation of ean air teperature in a increased as the teperature difference between the ean inlet teperature and the ean teperature in the occupied spaces increased, or the difference between axiu and iniu alue of teperature in a increased. A linear relationship between the standard deiation of ean air speed in a ( SDV ) and the ean air speed in the ( u ) was deried with a correlation coefficient of.76. Further, the relationship between SDV in a and the difference between the axiu and iniu air speed in a was found with a correlation coefficient of.97. The data are plotted against ean air speed and difference between the axiu and iniu air speed in Fig. 7 and Fig. 8. SDV increased as ean air speed or difference between the axiu and iniu air speed in a increased. Table 3: The ADPI in the three stores (%) Story 2 3 4 5 Store A 55. 9.9 57.8 5. 66.7 Store B 77.7 96.3 66.7 87.6 Store C 85.5 66.7 75. 9

Percentage of easuring points / % 6 5 4 3 2 22 24 26 28 3 Air teperature / o C Difference of axiu and iniu air teperature / o C 6 5 4 3 2 st 3r d Story 5t h Fig. : Percentage distribution of ean air teperature Fig. 2: Difference of axiu and iniu air teperature in a Percentage of easuring points / % 5 4 3 2..2.3.4.5.6 Mean air speed at a point / s - Fig. 3: Percentage distribution of ean air speed at a easuring point Uneen coefficient of air speed. 2. 8. 6. 4. 2 st 3r d 5t h Story Fig. 4: Uneen coefficient of air speed σ Standard deiation / Standard deiation / Difference between inlet and ean air teperature in a / o C Difference between axiu and iniu alue of air teperature / o C SDT =.398 +.63 t i (r =.73) SDT =.675 +.28 t ax (r =.73) Fig. 5: Relationship between standard deiation and difference between inlet and ean air teperature in the Fig. 6: Relationship between standard deiation and difference between axiu and iniu alue of air teperature 9

Standard deiation / s - Standard deiation / s - Mean air speed in a / s - SDV =.24 +.565u (r =.76) Fig. 7: Relationship between standard deiation and ean air speed Difference between axiu and iniu alue of air speed / s - SDV =.3 +.449 u (r =.97) Fig. 8: Relationship between standard deiation and difference between axiu and iniu alue of air speed ax The standard deiation of air speed in a is related to the axiu and iniu air speed in the : SDV =.327 +.6627u ( r =.93) (8) SDV =.355 +.3336u ( r =.63) (9) in In addition, the air speed ariation at a easuring point during a period was inestigated. It was found that the standard deiation of air speed at a easuring point SDVp is related to the ean air speed (equation ()). Siilar relationships with different regression coefficient were found in preious studies [,2]. SDVp where ax =.223 +.2939u ( r =.8) () SDV p equal to the root-ean-square (RMS) of the speed fluctuation u '2. Coparing the relationship in Fig. 7 and equation (), it can be seen that the slope in equation () is larger than that in Fig. 7, so the fluctuation of air speed in a changed faster than that at a point when the ean air speed increased. The following relationship between ADPI and the teperature difference between the ean inlet teperature and the ean alue of the teperature in the occupied zone in a ( ti ) with a correlation coefficient of.66 was found: ADPI =.634.558 t i () 5. CONCLUSIONS Based on the easureents and analyses of air distribution in three big stores in Wuhan, the following can be concluded. The phenoena of uneen teperature and air speed distribution are coon and are relatiely serious in these big stores. The influencing factor is coplex. The designers and anageent of the air conditioning systes should pay ore attention to it. Designer should consider the nuber of custoers, lighting in each in a store as precisely as possible. The shelf in a store can affect the air distribution to soe extent, so designer should pay attention to the effect of shelf, including the possible position ariation of the shelf. Correlations between soe acroscopic nubers and standard deiation of air teperature or air speed in a in the store were obtained. It is helpful to know the air diffusion perforance, characteristics and effecting factors in the big stores. 92

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