Several HVAC systems require field refrigeration piping to be designed and installed on-site. Examples include Condensing units, Direct expansion (DX) coil in air handlers, Remote evaporators with air-cooled chillers and Chiller with a remote air-cooled condensers. This Guide covers R-22, R-407C, R-410A, and R-134a used in commercial air conditioning systems. It does not apply to industrial refrigeration and/or Variable Refrigerant Volume (VRV) systems.
本应用指南中包含的信息基于 ASHRAE 制冷手册的第 2 章以及 McQuay 在此类设备方面的良好经验。
正确设计和安装的制冷剂管道系统应该：
- 使用限制压降的实用制冷剂管线尺寸，为蒸发器提供足够的制冷剂流量。
- 避免滞留过多的油，以便压缩机始终有足够的油正常运行。
- 避免液体制冷剂击打。
- 保持清洁、干燥。
制冷剂管道设计检查表
制冷剂管道设计的第一步是收集产品和工作现场信息。下面提供了每个项目的清单。本指南的其余部分将解释如何使用此信息。
产品信息
- Model number of unit components (condensing section, evaporator, etc.)
- 每个制冷回路的最大容量
- 每个制冷回路的最小容量
- 单位营业费
- 单位抽气能力
- 制冷剂类型
- Unit options (Hot Gas Bypass, etc.)
- 设备是否包括隔离阀和充电口
- 机组有抽气功能吗？
工地信息
- 管道如何运行的草图，包括：
- 距离
- 海拔变化
- 设备布局
- 配件
- 蒸发器管道连接的具体细节
- 管道铺设的环境条件
- Ambient operating range (will the system operate during the winter?)
- Type of cooling load (comfort or process)
- Unit isolation (spring isolators, rubber-in-shear, etc.)
典型的制冷剂管道布局
该图显示了安装在坡度上的冷凝装置，该装置连接到安装在屋顶空气处理装置中的 DX 盘管。
- A liquid line supplies liquid refrigerant from the condenser to a thermal expansion (TX) valve adjacent to the coil.
- 吸入管线将制冷剂气体提供至压缩机的吸入连接部。
该图显示了建筑物内带有远程蒸发器的屋顶安装式风冷冷水机组。
- 1. 有两个制冷回路，每个回路都有一条液体管线，将液体制冷剂从冷凝器供应到与蒸发器相邻的 TX 阀，以及一条吸入管线，将制冷剂气体从蒸发器返回到压缩机的吸入连接。
- 2、其中一回路设有双吸立管。
该图显示了屋顶上带有远程风冷冷凝器的室内冷水机。
- 1. 排气管路从压缩机的排气侧延伸至冷凝器的入口。
- 2. 液体管路将冷凝器的出口连接到蒸发器的 TX 阀。
- 3. 回路上的热气旁通管路从压缩机的排出管路延伸到蒸发器的液体管路连接处。
管道设计基础知识
良好的管道设计可以实现初始成本、压降和系统可靠性之间的平衡。初始成本受管道直径和布局的影响。管道中的压降必须最小化，以避免对性能和容量产生不利影响。由于几乎所有现场管道系统都有压缩机油通过制冷回路并返回压缩机，因此管道中必须保持最小速度，以便在满载和部分负载条件下有足够的油返回压缩机油槽。
一个好的经验法则至少是：
- 500 feet per minute (fpm) or 2.54 meters per second (mps) for horizontal suction and hot gas lines.
- 1000 fpm (5.08 mps) for suction and hot gas risers.
- Less than 300 fpm (1.54 mps) to avoid liquid hammering from occurring when the solenoid closes on liquid lines.
Hard drawn copper tubing is used for halocarbon refrigeration systems. Types L and K are approved for air conditioning and refrigeration (ACR) applications. Type M is not used because the wall is too thin. The nominal size is based on the outside diameter (OD). Typical sizes include 5/8 inch, 7/8 inch, 1-1/8 inch, etc.
Copper tubing intended for ACR applications is dehydrated, charged with nitrogen, and plugged by the manufacturer (see Figure below).
Formed fittings, such as elbows and tees, are used with the hard drawn copper tubing. All joints are brazed with oxy-acetylene torches by a qualified technician. As mentioned before, refrigerant line sizes are selected to balance pressure drop with initial cost, in this case of the copper tubing while also maintaining enough refrigerant velocity to carry oil back to the compressor. Pressure drops are calculated by adding the length of tubing required to the equivalent feet (meters) of all fittings in the line. This is then converted to PSI (kPa).
压降和温度变化
As refrigerant flows through pipes the pressure drops and changes the refrigerant saturation temperature. Decreases in both pressure and saturation temperature adversely affect compressor performance. Proper refrigeration system design attempts to minimize this change to less than 2°F (1.1°C) per line. Therefore, it is common to hear pressure drop referred to as “2°F” versus PSI (kPa) when matching refrigeration system components.
例如, a condensing unit may produce 25 tons (87.9 kW) of cooling at 45°F (7.2°C) saturated suction temperature. Assuming a 2°F (1.1°C) line loss, the evaporator would have to be sized to deliver 25 tons (87.9 kW) cooling at 47°F (7.2°C) saturated suction temperature.
Table below compares pressure drops in temperatures and pressures for several common refrigerants. Note that the refrigerants have different pressure drops for the same change in temperature. For example, many documents refer to acceptable pressure drop being 2°F (1.1°C) or about 3 PSI (20.7 kPa) for R-22. The same 3 PSI change in R-410A, results in a 1.2°F (0.7°C) change in temperature.
Note Suction and discharge pressure drops based on 100 equivalent feet (30.5 m) and 40°F (4.4°C) saturated temperature.
液体管线
液体管路将冷凝器连接到蒸发器，并将液体制冷剂输送到 TX 阀。如果液体管线中的制冷剂由于压力下降太低或由于海拔升高而闪蒸成气体，则制冷系统将运行不良。液体过冷是防止制冷剂因管路压力下降而闪蒸成气体的唯一方法。
The actual line size should provide no more than a 2 to 3°F (1.1 to 1.7°C) pressure drop. The actual pressure drop in PSI (kPa) will depend on the refrigerant.
不鼓励使用过大的液体管线，因为这会显着增加系统制冷剂充注量。这反过来又影响油费。
当液体制冷剂从冷凝器提升到蒸发器时，制冷剂压力降低。不同的制冷剂根据海拔高度会有不同的压力变化。具体制冷剂请参阅表 2。液体管路中的总压降是摩擦损失加上立管中液体制冷剂柱的重量的总和。
制冷剂 | Pressure Drop PSI/ft (kPa/m) Riser |
R-22 | 0.50 (11.31) |
R-407C | 0.47 (10.63) |
R-410A | 0.43 (9.73) |
R-134a | 0.50 (11.31) |
在这种情况下，只有过冷液体制冷剂才能避免 TX 阀闪蒸。如果冷凝器安装在蒸发器上方，则管道中液态制冷剂重量导致的压力增加将阻止制冷剂在没有过冷的情况下在适当尺寸的管道中闪蒸。
It is important to have some sub-cooling at the TX valve so that the valve will operate properly and not fail prematurely. Follow the manufacturer’s recommendations. If none are available, then provide 4 to 6°F (2.2 to 3.3°C) of sub-cooling at the TX valve.
Liquid lines require several refrigerant line components and/or accessories to be field selected and installed (Figure below). Isolation valves and charging ports are required. Generally, it is desirable to have isolation valves for servicing the basic system components, such as a condensing unit or condenser. In many cases, manufacturers supply isolating valves with their product, so be sure to check what is included. Isolating valves come in several types and shapes.
参考 这个图 :
- 从冷凝器开始工作，有一个液体管路过滤干燥器。干燥过滤器可去除液体制冷剂中的碎屑，并含有干燥剂以吸收系统中的水分。干燥过滤器可以是一次性的，也可以是具有可更换芯的永久性过滤器。
- 接下来有一个观察镜，技术人员可以通过它观察液体管线中制冷剂的状况。许多观察镜都包含湿度指示器，如果制冷剂中存在水分，该指示器会改变颜色。
- 观察镜后面是 TX 阀。
该系统可能的附件包括：
- A hot gas bypass port. This is a specialty fitting that integrates with the distributor – an auxiliary side connector (ASC).
- 抽气电磁阀。如果使用抽真空，电磁阀将位于 TX 阀之前，尽可能靠近蒸发器。
- Receivers in the liquid line. These are used to store excess refrigerant for either pump down or service (if the condenser has inadequate volume to hold the system charge), or as part of a flooded low ambient control approach. Receivers are usually avoided because they remove sub-cooling from the condenser, increase the initial cost, and increase the refrigerant charge.
Liquid lines should be sloped 1/8 inch per foot (10.4 mm/m) in the direction of refrigerant flow. Trapping is unnecessary.
吸入管路
吸气管线允许来自蒸发器的制冷剂气体流入压缩机的入口。缩小吸入管路尺寸会迫使压缩机在较低吸入压力下运行以维持所需的蒸发器温度，从而降低压缩机容量。吸入管线尺寸过大会增加初始项目成本，并可能导致制冷剂气体速度不足以将油从蒸发器移动到压缩机。当使用垂直吸水立管时，这一点尤其重要。
Suction lines should be sized for a maximum of 2 to 3°F (1.1 to 1.7°C) pressure loss. The actual pressure drop in PSI (kPa) will depend on the refrigerant.
吸入管线细节
运行时，吸入管充满过热制冷剂蒸气和油。油在管道底部流动，并随着在其上方流动的制冷剂气体而移动。当系统停止时，根据环境条件，制冷剂可能会在管道中冷凝。如果系统重新启动时液体制冷剂被吸入压缩机，则可能会导致段塞。
To promote good oil return, suction lines should be pitched 1/8 inch per foot (10.4 mm/m) in the direction of refrigerant flow. Evaporator connections require special care because the evaporator has the potential to contain a large volume of condensed refrigerant during off cycles. To minimize slugging of condensed refrigerant, the evaporators should be isolated from the suction line with an inverted trap as shown in Figures below:
在通向压缩机之前，疏水阀应延伸到蒸发器顶部上方。
- 对于多个蒸发器，吸入管道的设计应确保压降相等，并且来自一个盘管的制冷剂和油不能流入另一个盘管。
- 可以在立管底部使用存水弯，以在冷凝的制冷剂流向压缩机之前捕获它。在适当尺寸的立管中不需要中间疏水阀，因为它们会导致压降。
- 通常，对于商业生产的空调设备，压缩机被“预装”到设备侧面的公共连接处。
- 吸气管干燥过滤器可帮助在制冷剂进入压缩机之前对其进行清洁。由于它们会产生显着的压降，因此只有在情况需要时才应添加它们，例如压缩机烧毁后。在这种情况下，吸滤干燥器通常在更换压缩机的磨合期后被拆除。吸滤干燥器会捕获大量的油，因此应按照制造商的规格安装它们以促进排油。
放电线
Discharge gas lines (often referred to as hot gas lines) allow refrigerant to flow from the discharge of the compressor to the inlet of the condenser. Undersizing discharge lines will reduce compressor capacity and increase compressor work. Over sizing discharge lines increases the initial cost of the project and may result in insufficient refrigerant gas velocity to carry oil back to the compressor. Figures below.
排放管线细节
Discharge lines carry both refrigerant vapor and oil. Since refrigerant may condense during the off cycle, the piping should be designed to avoid liquid refrigerant and oil from flowing back into the compressor. Traps can be added to the bottom of risers to catch oil and condensed refrigerant during off cycles, before it flows backward into the compressor. Intermediate traps in the risers are unnecessary in a properly sized riser as they increase the pressure drop. Discharge lines should be pitched 1/8 inch per foot (10.4 mm/m) in the direction of refrigerant flow towards the condenser.
Whenever a condenser is located above the compressor, an inverted trap or check valve should be installed at the condenser inlet to prevent liquid refrigerant from flowing backwards into the compressor during off cycles. In some cases (i.e. with reciprocating compressors), a discharge muffler is installed in the discharge line to minimize pulsations (that cause vibration). Oil is easily trapped in a discharge muffler, so it should be placed in the horizontal or downflow portion of the piping, as close to the compressor as possible.
多个制冷回路
为了控制和冗余，许多制冷系统包括两个或多个制冷回路。每个电路必须保持独立，并像单个系统一样进行设计。在某些情况下，单个制冷回路服务于多个蒸发器，但多个制冷回路绝不能连接到单个蒸发器。一个常见的错误是安装带有单回路蒸发器盘管的两回路冷凝装置。
该图显示了包含多个电路的常见 DX 线圈。隔行扫描是最常见的。可以将单独的盘管（每个盘管具有单个回路）安装在同一系统中并连接到专用制冷回路。
虽然最常见的空调应用每个回路都有一个蒸发器，但也可以将多个蒸发器连接到单个制冷回路。
Figure below shows a single refrigeration circuit serving two DX coils. Note that each coil has its own solenoid and thermal expansion valve. There should be one TX valve for each distributor. Individual solenoids should be used if the evaporators will be operated independently (i.e. for capacity control). If both evaporators will operate at the same time, then a single solenoid valve in a common pipe may be used.
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