| The following information has been provided to help users understand the various input fields in this program. |
| Design |
| Vent Outlet | The vent outlet is schematic only and no equivalent length is added for the outlet fitting except the outlet loss from the vent piping. The different representations are for schematic purposes only. |
| Branch | The addition of a branch inserts a "tee" and its equivalent length to the relief vent piping network. The size of the tee is assumed to be the same size as the downstream (toward the outlet) vent piping. If this is not the case, use a mid-pipe expansion. |
| Mid-pipe Expansion | The addition of a mid-pipe expansion inserts an expansion fitting and its equivalent length into the relief vent piping network. In general, expansions are added automatically before tees, but if an expansion exists after the tee this fitting must be used. |
| Pressure Relief Valve | A single or dual-assembly pressure relief valve. The schematic representation is a single relief valve, user control of whether it is a single or dual-assembly is provided in the details of the pressure relief valve. Once a pressure relief valve is added, the program will prompt you for the type of equipment that is protected. |
| End Cap | The end cap is used for future expansion or clean-out of the relief vent piping network. |
| Pressure Vessel | An ASME rated pressure vessel. |
| Compressor | A positive displacement compressor (reciprocating or rotary screw) and oil separator. Reciprocating compressors are typically fitted with internal relief and only the oil separator (ASME rated vessel) requires pressure relief protection. |
| Shell-n-tube HX | A shell-n-tube heat exchanger and surge vessel (if exists). The surge vessel is included because, if it exists, typically there are no isolation valves between the surge vessel and the chiller barrel. |
| Plate-n-frame HX | A plate-n-frame heat exchanger (surge vessel not included). |
| Generic Equipment | A user-defined piece of protected equipment. Some examples are product silos, etc. User will be prompted for required relief capacity in the details. |
| Specifications |
| Pressure Vessel Information |
| Descriptor | A user-defined name for the pressure vessel. |
| Next Fitting | The fitting downstream (toward the outlet) of the pressure vessel. |
| MAWP | The maximum allowable working pressure of the vessel in psig. The MAWP must be greater than or equal to the set pressure on the pressure relief valve. |
| Length | The length of the vessel (including the dished heads) in inches. |
| Diameter | The diameter of the vessel in inches. |
| Volume | The calculated volume of the vessel with 2:1 ellipsoidal heads. |
| Combustible Materials | If combustible materials are present within 20 ft of the vessel the IIAR 2 required pressure relief capacity on the vessel is increased by a factor of 2.5 for ammonia. An interpretation of this is available on the IIAR website. |
| Relief Conn. Size | The relief connection size on the vessel. This is required to flag and limit the application of pressure relief valves with inlet sizes larger than the relief connection size. |
| IIAR 2 Req. Cap. | The required pressure relief protection for the vessel based on IIAR 2. |
| Compressor Information |
| Descriptor | A user-defined name for the compressor. |
| Next Fitting | The fitting downstream (toward the outlet) of the compressor. |
| Compressor type | The type of positive displacement compressor (reciprocating or rotary screw). If a reciprocating compressor is chosen, it is assumed that it is fitted with internal relief and the required capacity for the compressor is based on the oil separator vessel dimensions. |
| Duty | The refrigeration duty of the compressor. The duty will dictate the mass flow rate of the compressor under the relief scenario. The mass flow rate is for the compressor at +50°F for high-stage duty, and at the saturated intermediate (i.e. system high-stage suction) for booster duty. |
| High-stage suction temp. | The saturation temperature of the high-stage compressors on a two-stage system. No input is allowed if the compressor duty is high-stage because the saturated condition for the relief scenario for a high-stage compressor is +50°F. |
| Displacement rate | The displacement rate (swept volume flow rate) of the compressor in cubic feet per minute. |
| Volumetric efficiency | The volume efficiency (if known) of the compressor at relieving conditions. If unknown, Appendix E in IIAR-2-2014 specifies the value of 0.90 (i.e. 90%). |
| Unload @ 90% of PRV | If the compressor automatically unloads at or below 90% of the pressure relief valve set pressure, IIAR-2-2014 allows the use of the minimum regulated flow through the compressor. |
| Minimum unload fraction | For compressors fitted with capacity reduction this is the minimum unload fraction at the relieving conditions. Contact the compressor manufacturer for more information. |
| MAWP | The maximum allowable working pressure of the oil separator vessel in psig. The MAWP must be greater than or equal to the set pressure on the pressure relief valve. |
| Length | The length of the oil separator vessel (including the dished heads) in inches. |
| Diameter | The diameter of the oil separator vessel in inches. |
| Volume | The calculated volume of the oil separator vessel with 2:1 ellipsoidal heads. |
| Combustible Materials | If combustible materials are present within 20 ft of the vessel the IIAR-2-2014 required pressure relief capacity on the oil separator vessel is increased by a factor of 2.5 for ammonia. An interpretation of this is available on the IIAR website. |
| Relief Conn. Size | The relief connection size on the oil separator vessel. This is required to flag and limit the application of pressure relief valves with inlet sizes larger than the relief connection size. |
| IIAR 2 Req. Cap. | The required pressure relief protection for the compressor and oil separator vessel based on IIAR-2-2014. Note that the larger of the two capacity requirements is used for a rotary screw compressor and oil separator package with no service valves between the compressor and the oil separator. |
| Pressure Relief Valve |
| Descriptor | A user-defined name for the pressure relief valve. Recommend using a descriptor that ties it to the protected device. |
| Next Fitting | The fitting downstream (toward the outlet) of the pressure relief valve. |
| Protected Eq. | The name of the equipment that the pressure relief valve protects. |
| IIAR 2 Req. Cap. | The required pressure relief valve capacity for the protected equipment. |
| Dual relief assy. | Is the pressure relief protection part of a dual-relief assembly with a three-way valve? Note that on a dual-relief assembly only one pressure relief valve is active at once and as such each pressure relief valve is required to have the required capacity to protect the equipment. |
| Radio buttons | A dual-relief assembly requires that both of the valves are connected to the relief vent piping network. Both valves are required to be compliant, as such, the worst case equivalent length of the branch must be specified. The worst case is typically the valve whose flow "turns" through the tee downstream of the pressure relief valves. The tee is automatically added when a dual-relief assembly is specified. |
| Pipe Information | The information on the branch piping from the pressure relief valve (or dual assembly) to the first header tee. Note that this is the first tee not associated with the dual-relief assembly). For example, a clean-out tee (and dirt leg) if present or the tee that connects the branch to the header. Recommend that if the branch piping size is larger than the outlet connection size of the pressure relief valve that the analysis starts at the outlet of the expansion fitting. Consider that most regular capacity relief valves have very little allowable length at their outlet connection size and adding the expansion to the larger size into the analysis may make it impossible to design a compliant relief vent piping network. Also recommend that for this scenario that the installer "bush up" directly out of the pressure relief valve. |
| Lineal ft of branch pipe | The length of straight piping in feet of the branch segment between the pressure relief valve an the next fitting (mid-pipe expansion or tee). |
| Nominal Pipe Size | The nominal pipe size of the branch piping in inches. |
| Pipe Schedule | The schedule of the branch piping. Note that the schedule influences the internal diameter of the piping and, therefore, influences the pressure drop associated with flow through the piping. |
| Number of 45° elbows | The number of 45° elbows in the branch segment between the pressure relief valve and the next fitting. The equivalent feet of these fittings are added to the branch total equivalent length. |
| Number of 90° elbows | The number of 90° elbows (assumed long radius) in the branch segment between the pressure relief valve and the next fitting. The equivalent feet of these fittings are added to the branch total equivalent length. |
| Valve Information | The physical description and capacity of the pressure relief valve. |
| Manufacturer | All currently available manufacturers' pressure relief valves for the industrial refrigeration industry are included in the database. If you are using a valve that does not appear in the database, specify other and fill in the required information to check compliance. |
| Model | Manufacturer model number of available pressure relief valves. |
| PRV Type | The type of pressure relief valve. The options are conventional, balanced, or pilot operated. The type influences the maximum allowable back pressure on the pressure relief valve. If a valve is chosen out of the database, the type is automatically chosen. |
| Pressure Set Point | The set pressure of the pressure relief valve in psig. |
| PRV Capacity | The capacity of the pressure relief valve in pounds per minute of air and standard cubic feet per minute (SCFM). If a valve is chosen out of the database, the capacity is automatically calculated at the specified set pressure from rating information cataloged by the National Board (NB-18). National Board information can be viewed at www.nationalboard.org. |
| Inlet/Outlet Size | The connection size of the chosen pressure relief valve. If a valve is chosen out of the database, the connection sizes are automatically entered. |
| Comb. Rel. Assy. | If a rupture disc is installed upstream of the pressure relief valve, the ASME Boiler & Pressure Vessel code requires that the capacity of the pressure relief valve be derated by 10%. |
| Adjusted capacity | The adjusted capacity of the pressure relief valve. Only different from the capacity of the pressure relief valve if a rupture disc is installed in combination with the valve. |
| Maximum allow. BP | The IIAR-2-2014 (Chapter 15) maximum allowable back pressure on the valve in absolute pressure (psia). The value is calculated based on the pressure relief valve's set pressure and valve type. |
