外文翻译---关于综合运用局部和整体储存方式的储冰系统的应用.docx

河南科技大学毕业设计外文资料Performance of ice storage system utilizing a combined partial and full storage strategyAbstract A combined system is a new thermal storage strategy adopted in this study with which the two other known strategies namely, partial and full load, are compared. The results revealed that the combined system requires larger equipment size than that required by partial system to satisfy the same cooling load. Factors F and F that p f may be multiplied by the daily average cooling load to determine the optimum chillers size for a combined system are found. These factors are applicable for any cooling load and are based on a given chiller condensing and evaporating condition as used in this study. These factors are found to vary with the number of on-peak hours. Combined strategy required chiller size was found to decrease with decrease in on-peak period, hence the optimum chiller size for this new strategy was found to occur at zero on-peak hours, and i.e., when the combined system starts to operate as a partial strategy system. Keywords: Ice storage system1. Introduction Thermal storage is the temporary storage of high or low temperature energy for later use. Airconditioning system that employs thermal stor-age equipment incorporates two strategies, the partial and full load. For either of these strategies, investigations were made to determine thepossible saving in chiller size as compared with conventional cooling system. The partial andfull storage strategies were previously studied independently and the results obtained had shown that the chiller size required in partial strategy is smaller than that required in full strategy to satisfy the same cooling load. In this study a new strategy is adopted and investigated for chiller size determination. This strategy is named as a combined strategy system which includes both, the partial and full load,operating simultaneously. Hence, two sets of chillers are used in this new system, the first set operates continuously as a partial system and thesecond set operates during the off-peak period as a full system helping the first set chillers to meet the cooling load and charge the thermal storage reservoirs. The aim of this study is to find the optimum chiller size in a combined strategy system and to compare it with that of partial strategy at different on-peak hours to meet the same cooling load. Also, a relation between the optimum chiller size and cooling load is to be determined for general use at a set of governing conditions. To illustrate the combined strategy merits,three different case buildings with different cooling loads are investigated.2. Theory 2.1. Assumptions In this study, the following assumptions havebeen considered: 1) Air-cooled chillers with reciprocating compressors. 2) Evaporating pressure and temperature areconstants. 3) Refrigerant leaving the condenser and entering the expansion valve is saturated liquid. 4) Vapor leaving the evaporator and entering the compressor is saturated. 5) Refrigerant R-22 is used. 2.2. Conventional cooling system chiller In order to show the merits of a thermal storage system, the conventional system chillers capacity has to be determined for comparison.In common practice the size of these chillers is selected equal to the maximum cooling load which happens to be 28.67, 21.82 and 22.13 KW for cases (1), (2) and (3) respectively. 2.3. Combined strategy system In a combined system where two sets of chillers operate in partial and full strategies atthe same time, it is important to find the minimum combination chiller size that will satisfy the cooling load at a set of conditions. These conditions are the evaporating and condensing pressure and temperature and the number of on-peak hours during which only the partial chiller is kept running. The procedure adopted in this study in finding the minimum chiller size may be summarized as follow: (a) An initial assumption of the partial chiller size is to be made. The chiller size thus assumed should be related, some how, to the cooling load.Two distinct values of the cooling load are the maximum and the average value and the later is chosen in this study. Hence the initial partial chiller size will be the average cooling load multiplied by a certain, arbitrarily selected, factor (Fp ). (b) Since air-cooled chiller is used, its condensing temperature would vary according to inlet ambient air temperature. Therefore the initial partial chiller size would be based on the condensing temperature at which maximum cooling load occurs. (c) Chiller capacity is then determined hourly and for the daily cycle at the different existing condensing temperature. (d) The difference between the daily cycle cooling load and the daily total partial strategy chiller capacity would be met by the full strategy chiller. The size of this chiller is assumed to be equal to the average cooling load multiplied by a factor (F) and must equal to the difference indicated above. If this condition is not satisfied then another value of (Ff) is selected. (e) The combined strategy chiller size obtained by the initial run with the assumed (Fp) and calculated (Ff) may not be the optimum.Therefore an iteration procedure is adopted and the factor (Fp) is changed progressively until a minimum chiller size is obtained. (f) In order to find the relation between optimum chiller size and cooling load at different on-peak hours, the above procedure is repeated for each on-peak period (starting from six and endingwith zero on-peak). For each on-peak period an optimum chiller size is to be determined. 2.4. Calculation procedure To start the calculation procedure, the size of the partial strategy chiller should be defined first. It shall be assumed that the size (Q sp) equal to the average cooling load (q av) for any of the three cases multiplied by an arbitrarilyselected factor (Fp). Qsp=q av .Fp (KWh) (1)Ref. 1 reported that rating of air cooling condenser is based on the temperature difference between dry bulb temperature of the air entering to the coil and the condensing temperature corresponding to the pressure at inlet. The air temperature inlet to the coil is typical of Baghdad area at the 21st of July. Ref. 2 stated that the evaporating temperature of a refrigeration system used for ice storoage, ranges between 4 and 12 C. In this study8C is used. Thus Qsp calculated by Eq. (1) shall be based on the maximum condensing temperature occurring during the daily cycle. Accordingly and with evaporating temperature indicated above, the partial chiller compressor displacement (V) is determined where mnis the minimum volumetric efficiency of the reciprocating compressor occurring at the highest compression ratio. Ref. 3 had reported the volumetric efficiencies against different compression ratios for modern high speed refrigerant 12 and 22 compressors. The hourly chiller capacity may then be calculated byand accordingly the total daily capacity may be determined by summing the hourly capacity calculated by Eq. (3) If the daily cycle total cooling load is obtained by adding up the hourly existing cooling load as given by then the cooling load which shall be removed by the full load strategy chiller (QfT ) is simply the difference between the total daily cooling load defined by Eq. (5) and the total heat removed by the partial strategy chillers as presented by Eq. (4).Now the size of the full strategy chiller is to be determined using the same above outlined procedure. The procedure, again, shall be started by defining the full strategy chiller size. This may be accomplished by assuming that this chiller size (Q sf), based on the maximum condensing temperature, is equal to the average cooling load(qav ) multiplied by arbitrarily factor called (Ff). The full strategy compressor displacement (V) can now be estimated by And the hourly chiller capacity is Accordingly, the total capacity of the chiller when operating during the off-peak period onlywould be the sum of the hourly chiller capacity as calculated by Eq. (9) where n1 and n2 represent the start and end of the off-peak period during which the full strategy chiller is operated. The results obtained by Eq. (10) must equal to that given by Eq. (6) otherwise another (Ff) factor is selected and the calculation steps from Eq. (7) through Eq. (10) is repeated. Once this condition is satisfied the combined strategy chiller size would be the sum of the partial and full strategy chillers and may be expressed by It is to be understood at this stage that for a given on-peak period and for the initial selection of (Fp ) factor as used in Eq. (1), the combined strategy chiller size expressed by Eqs. (11) and (12) may not represent the optimum size. Hence an iteration technique, by which (Fp ) factor is progressively changed in Eq. (1), is adopted. With each new value of (Fp ) the whole calculation procedure from Eq. (1) through equation (12), is repeated. The iteration process continues until the combined system chiller size is minimum. Fig. 1. Variation of the optimum chiller size for the combined system with on-peak period.The percent reduction in combined system chiller size as compared to the conventional system chiller size to satisfy the same cooling load may be determined by When the above calculations and iterations are completed for a certain on-peak period, then another on-peak is used and the whole procedure is repeated all over again. 3. Results and discussion The optimum chiller size required in a combined system when applied to the three caseFig. 2. Variation of the chiller size reduction percent combined system with on-peak period. buildings under study, as calculated by Eq. (11),are listed in Table 1 and plotted in Fig. 1. The illustrations show the variation in the optimum chiller size when varying the number of on-peak hours from six to zero. The conventional system chiller size required for the three case buildings and the corresponding average cooling loads are also included in the same table for comparison. The results show that the combined system optimum chilled size decreases, as the numbers of on-peak hours are less. The minimum chiller size that would satisfy the cooling load is found to take place when the number of on-peak hours approaches zero. The zero on-peak hours indicates that only partial strategy chiller is in operation during the whole daily cycle. The percent reductions in chiller size when combined system is used at each on-peak period as compared to the conventional system chiller size are shown in Fig. 2. The figure clearly shows that the highest percent reduction achievement in chiller size is at zero on-peak hours. Also the figure indicates that percent reductions for all the cases are almost the same. The value of the factors F pand Ft at different on-peak hours are listed in Table 2. These values when multiplied by the average cooling load will yield the minimum combined system chiller size at a given on-peak hour. This is presented Table 2 Partial and full strategy system factors at different on-peak hours by Eq. (12). Any alteration in these factors will result in over estimated combined system chiller size. It is of interest to note that for the three different cases cooling loads the same values of Fp and Ff were found to appear for each on-peak period. From these results it may be concluded that these factors may be applied with any other cooling load to find the required minimum chiller size. This is true as long as the conditions are the same as those assumed in this study. 4. Conclusions 1) Combined strategy system requires less chiller size than conventional system does. A reduction of about 28% may be achieved. 2) Partial chiller strategy requires less chiller size than combined system. 3) Combined strategy chiller size was found to decrease with decrease in on-peak period. 4) Factors Fp and Ff found in this study can be used with any other cooling load to estimate the minimum required chiller size. Nomenclature F factor H refrigerant enthalpy KJ/kg Q chiller capacity KW qt hourly cooling load KW V refrigerant volume flow rate (m /s)Subscript Av average Com combined conv conventional f full storage mn minimum p partial chiller sf size of full strategy chiller sp size of partial strategy chiller Tp total chiller capacity for partial stratetotal time inlet to compressor state outlet from epansion valve state 关于综合运用局部和整体储存方式的储冰系统的应用 摘要对于两个已知的部分和整体储能战略来说，复合系统是一种新型的蓄热方式。结果表明。在满足相同的冷负荷时，复合系统比局部系统需要更大尺寸制冷机。我们采用Fp和Ff这两个系数乘以日平均冷负荷，来确定冷水机组最佳尺寸。这些因素适用于任何冷负荷，并且正在研究在给定冷水机组冷凝和蒸发条件下的使用情况。在峰值变化的数据中发现这些因素。发现联合储能策略要求冷水机组的型号随着电高峰期的降低而减小。因此，当联合系统作为部分储能策略开始运行，对于这项新战略联合冷水机组在用电高峰期的型号被发现。关键词：冰蓄冷系统1.导言蓄热是暂时将温度偏高或偏低的能源存起来以供日后使用。空调系统的蓄热装置表现为两种负荷方式，局部负荷和整体负荷。就某一方式而言，研究主要集中在与常规的制冷系统比较，能够节约的制冷机的空间大小。先前，已对局部和整体储存方式进行了分别研究，结论表明，在相同的冷却负荷下，采用局部储存方式的制冷机，其所需容积要小于采用整体储存方式的制冷机。本文中，采用了一种新的方式，并集中研究了所需制冷机的大小。此为同时运用了局部和整体负荷的复合系统。因此，在新的复合系统中，有两套制冷机。第一套作为局部系统长期运行，第二套作为整体系统只在非高峰时段运行，以配合第一套满足冷却负荷及控制蓄热装置。本研究的目的是寻找在复合系统中制冷机大小的最优值，并与峰值时段的局部运行方式进行比较，以达到满足同一冷却负荷的目标。同时，还研究制冷机大小最优值与冷却负荷之间的决定关系。为阐明复合制冷系统的优越性，对三幢大小不一，冷却负荷各不相同的建筑物作了分别研究。2 .理论2.1 .假设 本研究中，假设条件如下： 1 ）风冷冷水机组与往复式压缩机。2 ）蒸发压力和温度的常数。3 ）离开冷凝器和进入膨胀阀的制冷剂是饱和液体。 4 ）从蒸发器进入缩机的制冷剂气体是饱和的。5 ）使用R - 22制冷剂。2.2 .常规制冷系统机组为阐明蓄热系统的优点，必须确定应用常规系统的制冷机的容量以进行比较。在实践中，根据例一、二、三的最大冷却负荷，即分别是28.67，21.82和22.13KW，来选择相应2.3. 复合系统在局部式和整体式两套制冷机同时运行的复合系统中，找出在一系列条件下能够满足冷却负荷的最小型号的制冷机是很重要的。这些条件包括蒸发和凝结的压力和温度，以及仅有局部式冷水机组在持续运行的峰值时段的小时数。本文计算出合适的制冷机的最小值，过程如下：(a) 作关于局部式制冷机大小的最初假设。假设的制冷机大小应在某种程度上与冷却负荷相关。冷却负荷的两个值，即最大值和平均值。因此，最初的局部式制冷机大小应为平均冷却负荷乘以一个确定的，任意选取的系数（Fp）。(b) 使用空气制冷机时，其凝结温度随入口周围的大气温度变化。因此，当达到最大冷却负荷时，最初的局部式制冷机大小将取决于凝结温度。(c) 制冷机的容量持续变化，形成在不同的凝结温度条件下的日循环周期。(d) 关于日循环冷却负荷和局部式制冷机的日容量之间的差异在整体式制冷机这里找到了答案。整体式制冷机的大小假设等于平均冷却负荷乘以系数（Ff）并应该等于上文提到的差异。如果不满足本条件，则选区另一系数（Ff）。(e) 复合式制冷机的大小，通过以上假设的（Fp）和计算的（Ff）取得的，不一定是最优值。因此，重复以上程序，改变系数（Fp）直到制冷机尺寸的最小值。(f) 为明确在各峰值时段制冷机尺寸的最优值和冷却负荷间的变化关系，在各时段重复上述步骤（始于6点止于零点），将获得各峰值时段制冷机尺寸的最优值。2.4.计算过程在计算前应首先确定部分储能策略冷水机组的尺寸。假定它应承担的负荷的大小（Qsp）等于平均冷负荷（qav ）乘以三种情况中任意一个选择因子（Fp） 。Qsp=qav.Fp （KWh） （1） 参考（1）阐述了空气冷却冷凝器的评价是基于进入冷却盘管的干球温度和相应压力下的冷凝温度的温差。冷却盘管入口空气温度是典型的巴格达地区在7月21日的温度。参考 2 指出，采用冰蓄冷的制冷系统的蒸发温度介于-4和- 12。在这项研究中定为-8。因此，应根据等式（1）来计算发生在日循环最高冷凝温度下的总负荷Qsp。因此根据如上所述蒸发温度和局部机组压缩机的容量来确定 在往复式压缩机的容积效率最低时压缩比最高的。参考文献 3 阐述了容积效率与现代以R12和R22做为制冷剂的高效压缩机的压缩比成反比例。单位制冷量的计算可以由公式 计算得到，日制冷量由单位制冷的总和求得，依据公式（3） 如果日循环的总冷负荷可以通过单位时间制冷量的逐项相加有公式（5）而求得，那么应该从全部储能战略中冷水机组的负荷（QfT）减去的冷负荷等于每日总冷负荷由公式（ 5 ）计算得到的和从部分蓄冷机组中除去有公式（4）求的总的热负荷QFt=qT-QPT (KWh) （6）现在使用上述相同的计算方法来确定整体储能策略中冷水机组的型号。这个计算过程应该从确定全部储能了水机组型号开始。这我们可以基于最大的冷凝温度来完成假