Below is the current documentation for adding equipment, highlighting the available options.
- Compressor
This equipment is for the oil separator of a screw compressor. Calculation of the volume of vapor in the oil separator constitutes the bulk of the ammonia in a compressor package. All dimensions are assumed to be internal to the oil separator. Total volume calculated is the empty separator, while the displayed separator volume is the total volume with the oil volume subtracted.
The Head Ratio is the ratio of the separator diameter to its head diameter (twice the individual head dimension). Ellipsoidal heads with a ratio of 2:1 are the most common.
The Separator Length includes the shell length and both heads. The length of a 2:1 ellipsoidal head is ½ the diameter.
If the entered temperature is below the saturation temperature of the pressure provided, the density of saturated vapor at the given pressure is used.
Reciprocating compressors do not contain significant amounts of refrigerant, however they can be added as a user specified unit if desired.
- Condenser
For the purposes of determining refrigerant inventory in a system, we will focus on the normal operation and not the abnormal operation; however, the inventory under abnormal operation should be considered in the context of risk assessments and condenser siting.
Select “Specify Inventory” if you have the manufacturer data available.
In the event that operating charge data is not readily available, select “Specify Heat Rejection.” Two other rules-of-thumb can be applied to estimate evaporative condenser refrigerant inventory. The first rule-of-thumb says that the average density of refrigerant in the condenser heat exchanger is ~10 lbm/ft3. The condenser inventory is then the coil volume times that average density. The second rule-of-thumb says that a reasonable average charge is 90 lbm per million Btu/hr of rated heat rejection at a manufacturer’s specified condition.
Note: The rate of heat rejection is based on a 96.3 °F saturation temperature (a saturated suction temperature of +20 °F for an outdoor air wetbulb temperature of 78 °F).
- Evaporator
The majority of evaporators in industrial refrigeration service are aircooling plate-finned heat exchangers, but other common designs include: corrugated plate, plate-and-shell, scraped surface and others. This category will work for any of the heat exchanger types listed above. This tool has separate categories for shell-and-tube and plate-and-frame heat exchangers.
The refrigerant-side of evaporators for industrial refrigeration systems are usually configured in one of three ways: liquid overfed, flooded, or direct-expansion (DX). Evaporator manufactures do not catalog operating charge information for air-cooling evaporators, but this tool can help estimate the normal operating charge of refrigerant in evaporators.
Note: for gravity-flooded evaporators, the inventory of the surge drum itself is not included.
| Input Variable | Overfeed | Flooded | DX |
| Saturation Temperature |  | | - |
| Inlet Gauge Pressure | - | - | |
| Subcooling | | - | |
| Superheat | - | - | |
| Overfeed Ratio | | - | - |
| Evaporator Gauge Pressure | - | - | |
| Coil Volume | | | |
- Plate and Frame Heat Exchanger
Manufacturers typically list the volume on the refrigerant side in published literature and technical documents. The tool will list both the operating charge, as well as the maximum possible charge based on the volume entered.
- Shell and Tube Heat Exchanger
The tool allows you to select whether the refrigerant is undergoing a phase change or all liquid, such as in a subcooler.
This tool assumes a flooded liquid configuration for phase change refrigerant
Selecting “Ammonia in the Shell” assumes that ammonia occupies the space between the head and around the tubes. Any baffles or structural supports within the shell are neglected in the total shell volume used in the tool.
This tool should only be used in the absence of manufacturers published data.
- Pipe Section
When refrigerant is in a single phase (vapor or liquid), the total inventory in a pipe segment can be accurately determined. Estimating the inventory for piping with mixed phase refrigerant is much more difficult.
The “Two Phase” option requires an overfeed ratio, and is meant for use with overfed evaporators.
The “Condenser Drain” option requires a liquid percentage to indicate what percentage of the pipe is stacked full of liquid. This option could also be used for piping sections where there is an unexpectedly high level of liquid in what is normally two phase piping.
Note: the pipe size is presented as a Nominal Size, in inches, and a Schedule Number, in accordance with ASME Standard B36.10M.
- Vertical Vessel
For calculation purposes, all dimensions entered into the calculator are assumed to be internal to the vessel. If external measurements are used this will result in an over-estimate of the refrigerant inventory.
The Head Ratio is the ratio of the compressor’s diameter to its head diameter (twice the individual head dimension). Ellipsoidal heads with a ratio of 2:1 are the most common.
The Vertical Vessel Height includes the shell length and both heads. The length of a 2:1 ellipsoidal head is ½ the diameter.
The “Normal Operating Level” is used to calculate the operating charge as part of the Maximum Intended System Inventory. The “High Level Alarm Location” is used to calculate the Maximum Intended Inventory of the component. It can either be entered manually or calculated as a percent of the total vessel volume. The high level on a vessel is generally considered to be the height of the high level cutout on most vessels or 100% full in the case of high pressure receivers.
Note: If maximum liquid level is not specified, default maximum level is 80% of vessel height.
- Horizontal Vessel
For calculation purposes, all dimensions entered into the calculator are assumed to be internal to the vessel. If external measurements are used, this will result in an over-estimate of the refrigerant inventory.
The Head Ratio is the ratio of the compressor’s diameter to its head diameter (twice the individual head dimension). Ellipsoidal heads with a ratio of 2:1 are the most common.
The Horizontal Vessel Length includes the shell length and both heads. The length of a 2:1 ellipsoidal head is ½ the diameter.
The “Normal Operating Level” is used to calculate the operating charge as part of the Maximum Intended System Inventory. The “High Level Alarm Location” is used to calculate the Maximum Intended Inventory of the component. It can either be entered manually or calculated as a percent of the total vessel volume. The high level on a vessel is generally considered to be the height of the high level cutout on most vessels or 100% full in the case of high pressure receivers.
Note: If maximum liquid level is not specified, default maximum level is 80% of vessel diameter.
- Oil Pot
For calculation purposes, the oil pot is assumed to be a horizontal vessel with all dimensions entered into the calculator as internal to the vessel. If external measurements are used this will result in an over-estimate of the refrigerant inventory.
The Head Ratio is the ratio of the compressor’s diameter to its head diameter (twice the individual head dimension). Ellipsoidal heads with a ratio of 2:1 are the most common.
The Vessel Length includes the shell length and both heads. The length of a 2:1 ellipsoidal head is ½ the diameter.
An easy way to determine the amount of oil in the pot is to observe the frost level, since frost does not form where oil is present inside the vessel. Thus the calculator asks for the height of unfrosted oil pot from the bottom up to the top. The tool then assumes the remainder of the vessel contains liquid ammonia to determine the inventory. The small vapor space above the liquid ammonia is assumed as all liquid to be conservative in the calculation.
- User Specified Inventory
For particular sections of a refrigeration system, the inventory cannot be determined using rules-of-thumb. This may be caused by an unusual design, or the inability to provide necessary input parameters. If this is the case, the normal and maximum charge can be manually entered.
