大型制药厂热电冷三联供
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吸收式制冷简介吸收循环是一个过程,制冷效果被通过使用两种流体和一些热量输入产生, 而不是如同在更熟悉的蒸汽压缩循环里的电输入。蒸汽压缩和吸收冷却循环在较高的压力经过制冷剂的压缩到一个低的压力和余热经过制冷剂的蒸发完成热的移动。 创造压力差并且循环这种致冷剂的方法是在两个循环之间的主要差别。 蒸汽压缩循环利用一台机械压缩机建立必要循环制冷的压力差。 在吸收系统,一种二元溶液或者吸收质用来循环制冷。 因为温度需求为循环在中低温热水范围内, 并且对于电能储蓄有重要的潜能,吸收制冷好像是地热的应用的一种好前景。 吸收机器在两个基本的构造今天是市场上可买到的。对于应用来说超过32F( 主要是空气调节) ,循环使用溴化锂作为有吸收剂,水作为制冷剂。 对低于32F的应用来说,氨水/水循环使用氨作为制冷剂,水作为吸收剂。 溴化锂/ 水循环机器图1显示一台典型的溴化锂/ 水机器(溴化锂/ 水)的图解。 过程在两个容器或者壳发生。 上面壳包含发生器和冷却器; 下面的壳,包含吸收剂和蒸发器。 热量供应在含有溴化锂/ 水溶液发生器中。 这一热量引起致冷剂在这一容器水中沸腾溶液到蒸馏状态。水蒸汽进入冷凝器部分在那里一个冷却的介质来把蒸汽冷凝到液态。水然后流动到蒸发器它经过在筒上方含有流体被冷却的区间。为了维持吸收器- 蒸发器壳的一个最低压,水在一个非常低的温度沸腾。这沸腾引起水从介质中吸收热被冷却,因此,降低它的温度。蒸发了水然后进入吸收器它被和在含水量中的非常低的溴化锂/ 水溶液混合的区间之内经过。这浓溶液 ( 浓溴化锂/ 水溶液) 容易吸收来自蒸发器区间的蒸汽形成稀溶液。这就是给循环取名吸收的原因。稀溶液然后被抽到发生机区间重复循环。如图1中所示,有三种流体循环外面的连接中: a)发生器热输入量,b)冷却水 , c)冷凝水 。由于每一个这些循环是一种特性机器额定下的温度。因为单级单位, 这些温度是 :0.12MPa的蒸气 (等效热的水) 进入发生器, 85F的冷却水,44F留下的冷凝水(制冷和空调工程师学会, 1983)。在这些状态之下,一个制冷系数 (COP) 大约可能在 0.65 到 0.70 (制冷和空调工程师学会,1983)。制冷系数可能被想到如机器效率的一种指标。它可以由所需要的热输入量除于冷却产量计算。举例来说,在一个 0.70 的制冷系数操作一个 500吨的吸收冷却器会需要:(500 x 12,000 Btu/h)/0.70=8,571,429 Btu/h 热输入量。这热输入量相当于0.12MPa 9,022 磅/小时的蒸气,或者1,008 gpm 240F 水在17F D T.双级机器能有效的提高机器的制冷系数。然而,温度需求为这些进入发电量温差范围内提供了很好的要求(350 F)。结果,双级机器会或许不被应用到地热应用。措施基于已经被发展 (Christen,1977) 描述单级吸收机的措施反应式,图 2 显示出在制冷系数和容量 (冷却出量) 与热水温度输入量的效应。进入热水小于220 F 的温度实际上造成设备容量的减少。温度造成设备容量减少的原因自然和输入到吸收式循环中的热量相关。在发生器中,热输入量在吸收剂/冷剂混合物中引起沸腾发生。 因为压力在发生器中总是不变的,固定在沸腾温度下。结果,那个进入热水温度的一个还原反应引起在热的流体和沸腾混合物之间的温差一个还原反应。 因为热传递直接地因温差而改变 ,由于进入热水温度在吸收致冷容量中有一个几乎线性的减少。在过去几年中,一个制造厂商已经为在较低的进水口温度增加措施修正小的容量单位 (2 到 10吨) 。然而,在大量输出中被修正机器的低温不仍然有效, 会可以应用在制度和工业型方案中。虽然制冷系数和容量也被其他的参数改变, 像冷凝器和冷凝水温度和流度估计,发生器热输入量在生产中有最大的影响。这是特别地重要的考虑关于地热应用。因为许多240 F和高于此范围的地热资源正在被调查因为使用有机的郎肯循环 (ORC) 的发电量方案, 空气调节应用在这个温度之下是有可能的。结果,在 180 到 230 F 范围中操作的冷却器 (依照图 2) 不得不在 400 和 20% 之间特大号中选择。同传统的系统相比这会容易增加资本支出而且减少回报。资本支出的增加会从较大的冷却塔成本出现,它起因于吸收设备的低制冷系数。单效设备的制冷系数大约是0.7。在相同的状态下面的蒸汽压缩机器的制冷系数可能是 3.0 或更高。结果,为每个单位的制冷,一个蒸汽压缩系统会必须在冷却塔释放 1.33个热量单位。对于一个吸收系统,在一个 0.7 的制冷系数, 2.43个热量单位一定在冷却塔被释放。这为吸收系统在冷却塔和附件增加重要的成本。为了要维持发生器中的热传递,唯一的温差可能在热水蒸气中被忽略。这是事实的一个结果机器本来设计来作蒸气的进量。热传递从那个浓缩蒸汽是一个常数温度过程。 结果,为了要有相等的效果,进入的热水温度会有高于饱和的温度在以定格的状态符合到进水口汽压。这要考虑到热水循环中的一些T。在锅炉中加倍了实施,这对工作费是小的影响。然而,因为T直接地影响流量率和抽泵能量,这是地热应用的主要考虑。举例来说,假如0.54的制冷系数和 15个F温差的地热流体, 250个 ft 抽水头和 65%冷凝效率,大约 0.20千瓦/ t泵压力被需要。这相当与大约 0.50-0.60千瓦/ t的一个大的离心机(只有压缩机消费).小的温差和高流动率在空气调节应用中关于吸收冷却器使用估计指出另外的考虑。 承担一个地热系统要设计一个新的建筑物的加热和冷却。因为供热系统与冷却器的在比较中可能被设计为了相当大的温差, 吸收应用的逐渐增加的成本会必须使用比较高花费和泵花费的需求。 一个第二应用为空气供暖需求设计而且使用一个较小的吸收机承担基本负荷。在这一应用,第二的电冷却器会使用到达好的效果。 从另一方面来说,成本支出会是增加的。大的吨数设备成本图 3 列举了一些在空间净化应用中一般大的吨数 (100个吨) 冷却设备的成本。图中显示出的吸收冷却器 (Abs。 chlr.),离心式冷水机 (Elec。 chlr.),冷凝器设备附件(冷却塔,冷却水抽水机和冷却水砂眼)的成本为了吸收冷却器附件 (Abs。 twr.)和离心式冷水机附件(Elec。 twr.)。 如图所示,吸收设计同电驱动冷却器冷却器相比它本身和它的冷凝器附件设备成本要高的多。 这些是最初的资本支出差别在一个地热实施中不得不节约。图 3. 电动和吸收冷却器和辅助设备的成本 .(Means,1996)小的吨数设备据目前我们所知,现在只有一家公司制造小的吨数 (20吨) 溴化锂制冷设备。 这公司位于日本,主要为太阳能应用生产设备。 现在,可提供的单位在 1.3,2,3,5,7.5, 和 10吨容量中。 这些单位可能被一起叠加提供达到 50吨的容量。因为单位是水冷却冷却器,同传统电蒸汽压缩设备相比他们需要较多的机械设备为一个给定的容量。 除了吸收冷却器它本身,还需要一个冷却塔。 被安装外部的冷却塔需要和内部的管子和循环泵相连。 因为吸收机生产已冷的水, 需要风机盘管输送冷却水到空气中。 绝缘管用来连接机器和盘管。 另外循环泵驱动冷却水循环。 最后,热水一定要供给到吸收机。 这需要第三蛇行管。图 4用来与传统的电冷却相比较评估小的吸收设备的经济效应 。这个图显示出同传统的制冷系统相比增加成本的使用吸收式设备所能节约的成本。明确的,图显示出多年来为五个不同的尺度单位下计算简单回报的电成本。 在每个情况,吸收系统 ( 在每年 2,000个满载小时) 每年的电节省费用同系统的逐渐增加资本支出成简单的回报价值关系。在这里同常规的吸收式系统比较的系统是一个屋顶组装机组。 这是最有效的不贵的传统系统。 一个比较成熟的吸收制冷系统 (VAV,4管冷却水等)会产生较吸引人的回报。图 4.小的吸收设备上的简单回报与传统的屋顶设备相较。图是建立在充份的温度地热流体的有效为基础以额定容量允许之上的(190 F之上)。 除此之外,除了管道之外, 地热井和泵的成本是不用考虑的。只有制冷设备成本要考虑。 结果,图 4 的回报价值只有在地热资源已经被发展为一些其他的目的才是有效的 (空气供暖和水产业) ,而且唯一的可选决定是在电和吸收冷却的之间的选项。图 4 也小的吨数吸收冷却的经济效应只有在5到10吨容量需求和超过 $0.10千瓦/小时电力消耗才是是吸引人的。 图4是建立在一个年度冷量需求2,000个满载小时之上的。 这在最地理的面积需求的上端上。 为了平衡其他年度冷量的需求,只是乘以图4中实在的满载小时的简单回报系数再除以2,000。吸收式制冷机的性能建立在额定状态为了便于得到图 4 。应该指出的是,如同较大的机器,性能很重地依赖进入热水温度和进入的冷却水温度。 额定条件是建立在190 F进热水, 85 F 进入冷却水和 48 F 排除已冷的水。三个回路的流动率是建立在9F的温差之上的。图 4 举例说明进入热水温度和进入冷却水温度对小的机器性能的影响。 在进入热水温度小于 180 F时,实际减少是必要的。 初步的评估, 85 F 冷却水曲线是必要的。商业制冷许多商业和工业的制冷应用包括小于 32 F 的方法温度和多数是 0 F. 结果,溴化锂/ 水循环不符合要求,因为水作为冷剂。结果,所需要的流体在这些温度下是不会凝固的。这些应用最通常类型的吸收循环是水/氨循环。 在这情况,水是吸收剂,氨是制冷剂。在商业制冷应用中使用水/ 氨设备和地热资源为被许多其他的考虑如空气调节应用所影响。 图 5 这些举例说明这些中最重要的。 当冷冻温度减少, 所需要热水的温度是增加的。 因为大多数商业和工业的制冷应用在 32 F下发生, 所需的热输入量温度一定至少在 230 F. 应该记住所需的蒸发温度是在过程处理温度下面10到15 F。 举例来说,一个 +20 F的冷库将需要一个 5F 蒸发温度。研究表明最小需要的热水温度275F。 在这个温度范围内没有很多地热资源。 因为这个温度范围内的地热资源,有可能小的发电站将形成竞争除非叠加使用。结论在结论中, 当考虑地热/吸收冷却空气调节的应用时候应当评估下列几个因数资源温度实际的传递因数应用到设备应在温度少于220F时. 非常高的资源温度的重要部份或双级在低温制冷中被应用。吸收机热水需求量与空气供暖需求流量相较逐渐增加的井和泵成本应该被考虑到吸收机。制冷容量需求比较大的机器有比较低的成本逐渐增加在每吨的花费上。由于加倍的能量转移,这就造成一个积极的经济影响。空气调节年制冷负荷,满负荷运行或过程冷却,载荷系数明显地,设备的较高利用造成较快的花费。资源的抽泵动力往往在非常低的静止水平或下降。抽泵动力可能接近 50% 的高效率电冷却器消费。公用设备率由于很多的保护措施,高的公用设备率为消费和要求产生较好的系统经济性。 2004届 毕 业 设 计(论 文)题目:大型制药厂热电冷三联供工程设计研究班 级: 006102学 号: 00610117姓 名:高 小 平指导教师:肖 汉 才2004 年 6 月大型制药厂热电冷三联供工程设计研究摘要:热电冷系统利用吸收式制冷技术给设备供暖和制冷。利用现有热电联产系统发展集中供热,供电和供冷为一体的能源综合利用系统。该系统将溴化锂吸收式制冷机引入到热电厂的热电联产系统中,可增加热电厂的夏季热负荷,从而使冬夏热负荷平衡,保证热电厂更经济高效地运行。本文根据热电冷三联供节约能源的原理,对一座较大型的药厂进行工程设计研究,结合药厂对温度,湿度要求高的特点,进行详细计算,仔细论证,对制冷设备参数提出要求。通过调查和计算,将热、电、冷联产与热电和冷量分供系统加以比较,表明该系统不但可节能,而且具有增加电能生产和保护环境的效益。主题词:热、电、冷三联供;吸收;环保 Electricity Heat and Chilled Water Congenerating System in large-scale pharmaceutical factory is provided in the engineering design research.Abstract: Combined heat and power(CHP) systems often use absorption technology to supply heating and cooling to a facility.This paper puts forward an energy comprehensive utilization system, Electricity Heat and Chilled Water Congenerating System(EHCWCS).This system introduces H2O-LiBr Absorption Refrigenerating Machine into Heat and Power Plant to increase the heat load of the plant in summer,which can balance the heat load in summer and winter, so Heat and Power Plant can run in a high efficiency. This text is according to the thermo-electricity cold triple-generation system provide the principle that economize the energy, proceeding to a large pharmaceutical factory the engineering design study, joining together the pharmaceutical factory to the temperature, the degree of humidity requests the high characteristics, proceeding the detailed calculation, carry on detailed calculation, put forward the request to the refrigeration equipments in system parameter. The result of analysis states that this system can not only save energy, but also increase the output of electricity of Heat and Power Plant and protect environment. Theme words: electricity heat and chilled water congenerating; absorption; ervironmental protection目录第一章 绪论1第二章 工程概述2第三章 设计参数3第一节 室外设计参数3第二节 室内设计参数3第四章 负荷计算4第一节 冷负荷计算4第二节 热负荷计算8第五章 空调方案的选择及空气处理过程的确定10第一节 空调房间送风量和送风状态参数的确定10第二节 空调方案的选择12第六章 空气风系统设计及气流组织计算14第七章 方案比较17第八章 空调水系统设计18第九章 设备选型及安装20第十章 空气风系统设计及气流组织计算27第十一章 能效分析29设计总结及收获33致谢34参考文献35ABSORPTION REFRIGERATIONINTRODUCTIONThe absorption cycle is a process by which refrigeration effect is produced through the use of two fluids and some quantity of heat input, rather than electrical input as in the more familiar vapor compression cycle. Both vapor compression and absorption refrigeration cycles accomplish the removal of heat through the evaporation of a refrigerant at a low pressure and the rejection of heat through the condensation of the refrigerant at a higher pressure. The method of creating the pressure difference and circulating the refrigerant is the primary difference between the two cycles. The vapor compression cycle employs a mechanical compressor to create the pressure differences necessary to circulate the refrigerant. In the absorption system, a secondary fluid or absorbent is used to circulate the refrigerant. Because the temperature requirements for the cycle fall into the low-to-moderate temperature range, and there is significant potential for electrical energy savings, absorption would seem to be a good prospect for geothermal application.Absorption machines are commercially available today in two basic configurations. For applications above 32F (primarily air conditioning), the cycle uses lithium bromide as the absorbent and water as the refrigerant. For applications below 32F, an ammonia/water cycle is employed with ammonia as the refrigerant and water as the absorbent.LITHIUM BROMIDE/WATER CYCLE MACHINES Figure 1 shows a diagram of a typical lithium bromide/ water machine (Li Br/H2O). The process occurs in two vessels or shells. The upper shell contains the generator and condenser; the lower shell, the absorber and evaporator.Heat supplied in the generator section is added to a solution of Li Br/H2O. This heat causes the refrigerant, in this case water, to be boiled out of the solution in a distillation process. The water vapor that results passes into the condenser section where a cooling medium is used to condense the vapor back to a liquid state. The water then flows down to the evaporator section where it passes over tubes containing the fluid to be cooled. By maintaining a very low pressure in the absorber-evaporator shell, the water boils at a very low temperature. This boiling causes the water to absorb heat from the medium to be cooled, thus, lowering its temperature. Evaporated water then passes into the absorber section where it is mixed with a Li Br/H2O solution that is very low in water content. This strong solution (strong in Li Br) tends to absorb the vapor from the evaporator section to form a weaker solution. This is the absorption process that gives the cycle its name. The weak solution is then pumped to the generator section to repeat the cycle.As shown in Figure 1, there are three fluid circuits that have external connections: a) generator heat input, b) cooling water, and c) chilled water. Associated with each of these circuits is a specific temperature at which the machines are rated. For single-stage units, these temperatures are : 12 psi steam (or equivalent hot water) entering the generator, 85F cooling water, and 44F leaving chilled water (ASHRAE, 1983). Under these conditions, a coefficient of performance (COP) of approximately 0.65 to 0.70 could be expected (ASHRAE, 1983). The COP can be thought of as a sort of index of the efficiency of the machine. It is calculated by dividing the cooling output by the required heat input. For example, a 500-ton absorption chiller operating at a COP of 0.70 would require: (500 x 12,000 Btu/h) divided by 0.70 = 8,571,429 Btu/h heat input. This heat input suggests a flow of 9,022 lbs/h of 12 psi steam, or 1,008 gpm of 240F water with a 17F delta T.Two-stage machines with significantly higher COPs are available (ASHRAE, 1983). However, temperature requirements for these are well into the power generation temperature range (350F). As a result, two-stage machines would probably not be applied to geothermal applications.PERFORMANCEBased on equations that have been developed (Christen, 1977) to describe the performance of a single-stage absorption machine, Figure 2 shows the effect on COP and capacity (cooling output) versus input hot-water temperature. Entering hot water temperatures of less than 220F result in substantial reduction in equipment capacity. The reason for the steep drop off in capacity with temperature is related to the nature of the heat input to the absorption cycle. In the generator, heat input causes boiling to occur in the absorbent/refrigerant mixture. Because the pressure is fairly constant in the generator, this fixes the boiling temperature. As a result, a reduction in the entering hot water temperature causes a reduction in the temperature difference between the hot fluid and the boiling mixture. Because heat transfer varies directly with temperature difference, there is a nearly linear drop off in absorption refrigeration capacity with entering hot water temperature. In the past few years, one manufacturer (Yazaki, undated) has modified small capacity units (2 to 10 ton) for increased performance at lower inlet temperature. However, low-temperature modified machines are not yet available in large outputs, which would be applicable to institutional- and industrial-type projects. Although COP and capacity are also affected by other variables such as condenser and chilled water temperatures and flow rates, generator heat input conditions have the largest impact on performance. This is a particularly important consideration with regard to geothermal applications.Because many geothermal resources in the 240F and above temperature range are being investigated for power generation using organic Rankine cycle (ORC) schemes, it is likely that space conditioning applications would see temperatures below this value. As a result, chillers operating in the 180 to 230F range would (according to Figure 2) have to be (depending on resource temperature) between 400 and 20% oversized respectively for a particular application. This would tend to increase capital cost and decrease payback when compared to a conventional system.An additional increase in capital cost would arise from the larger cooling tower costs that result from the low COP of absorption equipment. The COP of singe effect equipment is approximately 0.7. The COP of a vapor compression machine under the same conditions may be 3.0 or higher. As a result, for each unit of refrigeration, a vapor compression system would have to reject 1.33 units of heat at the cooling tower. For an absorption system, at a COP of 0.7, 2.43 units of heat must be rejected at the cooling tower. This results in a significant cost penalty for the absorption system with regard to the cooling tower and accessories.In order to maintain good heat transfer in the generator section, only small delta Ts can be tolerated in the hot water flow stream. This is a result of the fact that the machines were originally designed for steam input to the generator. Heat transfer from the condensing steam is a constant temperature process. As a result, in order to have equal performance, the entering hot water temperature would have to be above the saturated temperature corresponding to the inlet steam pressure at rated conditions. This is to allow for some delta T in the hot water flow circuit. In boiler coupled operation, this is of little consequence to operating cost. However, because delta T directly affects flow rate, and thus pumping energy, this is a major consideration in geothermal applications.For example, assuming a COP of 0.54 and 15F delta T on the geothermal fluid, 250 ft pump head and 65% wire-to-water efficiency at the well pump, approximately 0.20 kW/t pumping power would be required. This compares to approximately 0.50 - 0.60 kW/t for a large centrifugal machine (compressor consumption only).The small delta T and high flow rates also point out another consideration with regard to absorption chiller use in space conditioning applications. Assume a geothermal system is to be designed for heating and cooling a new building. Because the heating system can be designed for rather large delta Ts in comparison to the chiller, the incremental cost of the absorption approach would have to include the higher well and/or pump costs to accommodate its requirements. A second approach would be to design the well for space heating requirements and use a smaller absorption machine for base load duty. In this approach, a second electric chiller would be used for peaking. In either case, capital cost would be increased.LARGE TONNAGE EQUIPMENT COSTSFigure 3 presents some more general cost information on large tonnage (100 tons) cooling equipment for space conditioning applications. The plot shows the installed costs for both absorption chillers (Abs. chlr.), centrifugal chillers (Elec. chlr.), and auxilliary condenser equipment (cooling tower, cooling water pumps and cooling water piping) for both absorption chillers (Abs. twr.) And centrifugal chillers (Elec. twr.). As shown, both the chiller itself and its auxilliary condenser equipment costs are much higher for the absorption design than for electric-driven chillers. These are the primary capital cost differences that a geothermal operation would have to compensate for in savings.Figure 3. Chiller and auxiliary equipment costs - electric and absorption (Means, 1996).SMALL TONNAGE EQUIPMENTTo our knowledge, there is only one company (Yazaki, undated) currently manufacturing small tonnage (20 tons) lithium bromide refrigeration equipment. This firm, located in Japan, produces equipment primarily for solar applications. Currently, units are available in 1.3, 2, 3, 5, 7.5, and 10 ton capacities. These units can be manifolded together to provide capacities of up to 50 tons.Because the units are water cooled chillers, they require considerably more mechanical equipment for a given capacity than the conventional electric vapor compression equipment usually applied in this size range. In addition to the absorption chiller itself, a cooling tower is required. The cooling tower, which is installed outside, requires interconnecting piping and a circulation pump. Because the absorption machine produces chilled water, a cooling coil and fan are required to deliver the cooling capacity to the space. Insulated piping is required to connect the machine to the cooling coil. Another circulating pump is required for the chilled water circuit. Finally, hot water must be supplied to the absorption machine. This requires a third piping loop.In order to evaluate the economic merit of small absorption equipment compared to conventional electric cooling, Figure 4 was developed. This plot compares the savings achieved through the use of the absorption equipment to its incremental capital costs over a conventional cooling system. Specifically, the figure plots cost of electricity against simple payback in years for the five different size units. In each case, the annual electric cost savings of the absorption system (at 2,000 full load hours per year) is compared to the incremental capital cost of the system to arrive at a simple payback value. The conventional system to which absorption is compared in this case is a rooftop package unit. This is the least expensive conventional system available. A comparison of the absorption approach to more sophisticated cooling systems (VAV, 4-pipe chilled water, etc.) would yield much more attractive payback periods.Figure 4. Simple payback on small absorption equipment compared to conventional rooftop equipment.The plot is based on the availability of geothermal fluid of sufficient temperature to allow operation at rated capacity (190F or above). In addition, other than piping, no costs for geothermal well or pumping are incorporated. Only cooling equipment related costs are considered. As a result, the payback values in Figure 4 are valid only for a situation in which a geothermal resource has already been developed for some other purpose (space heating and aquaculture), and the only decision at hand is that of choosing between electric and absorption cooling options.Figure 4 also shows that the economics of small tonnage absorption cooling are attractive only in cases of 5 to 10 ton capacity requirements and more than $0.10 kW/h electrical costs. Figure 4 is based on an annual cooling requirement of 2,000 full load hours per year. This is on the upper end of requirements for most geographical areas. To adjust for other annual cooling requirements, simply multiply the simple payback from Figure 4 by actual full load hours and divide by 2,000.The performance of the absorption cooling machine was based on nominal conditions in order to develop Figure 4. It should be noted that, as with the larger machines, performance is heavily dependent upon entering hot water temperature and entering cooling water temperature. Ratings are based on 190F entering hot water, 85F entering cooling water and 48F leaving chilled water. Flow rates for all three loops are based upon a 9F delta T.Figure 4 illustrates the effect of entering hot water temperature and entering cooling water temperature on small machine performance. At entering hot water temperatures of less than 180F, substantial derating is necessary. For preliminary evaluation, the 85F cooling water curve should be employed.COMMERCIAL REFRIGERATIONMost commercial and industrial refrigeration appli-cations involve process temperatures of less than 32F and many are 0F. As a result, the lithium bromide/water cycle is no longer able to meet the requirements, because water is used for the refrigerant. As a result, a fluid which is not subject to freezing at these temperatures is required. The most common type of absorption cycle employed for these applications is the water/ammonia cycle. In this case, water is the absorbent and ammonia is the refrigerant.Use of water/ammonia equipment in conjunction with geothermal resources for commercial refrigeration applications is influenced by some of the same considerations as space cooling applications. Figure 5 illustrates the most important of these. As refrigeration temperature is reduced, the required hot water input temperature is increased. Because most commercial and industrial refrigeration applications occur at temperatures below 32F, required heat input temperatures must be at least 230F. It should also be remembered that the required evaporation temperature is 10 to 15F below the process temperature. For example, for a +20F cold storage application, a 5F evaporation temperature would be required.Figure 5. Small tonnage absorption equipment performance.Figure 5 suggests a minimum hot water temperature of 275F would be required. There is not a large number of geothermal resources in this temperature range. For geothermal resources that produce temperatures in this range, it is likely that small scale power generation would be competing consideration unless cascaded uses are employed. Figure 5 indicates another consideration for refrigeration applications. That is the COP for most applications is likely to be less than 0.55. As a result, hot water flow requirements are substantial. In addition, the cooling tower requirements, as discussed above, are much larger than for equivalently sized vapor compression equipment.CONCLUSIONIn conclusion, it is necessary to evaluate the following factors when considering a geothermal/absorption cooling application for space conditioning.Resource temperatureSubstantial derating factors must be applied to equipment at temperatures less than 220F. Very high resource temperatures or two-stage are required for low-temperature refrigeration.Absorption machine hot water requirements compared to space heating flow requirementsIncremental well and pumping costs should be applied to the absorption machine.Refrigeration capacity requiredLarger machines have lower incremental capital costs on a $/ton basis. Coupled with the larger displaced energy, this result in a more positive economic picture.Annual cooling load for space conditioning, in full load hours or for process cooling, in terms of load factorObviously higher utilization of the equipment results in more rapid payout.Pumping power for resources with unusually low static water levels or drawdownsPumping power may approach 50% of high efficiency electric chiller consumption.Utility ratesAs with any conservation project, high utility rates for both consumption and demand result in better system economics.
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