FrigoSim Instruction Manual

Brief Survey

When FrigoSim has started, you see three tiled windows, two narrow ones to the left and right, and one wide in the middle. The middle one is indeed the central one, in which the plant to be studied is visible, or eventually will be placed.

The window to the left is for storage of basis components. Any one of these components may be transferred to the plant to become a plant component, and any number of plant components may originate from one basis component.

The window to the right is for storage of fluids, both refrigerants and secondary fluids. Plant circuits (except power circuits) are filled from this fluid storage. It is not possible to enter the wrong kind of fluid into a circuit. You see that filling is underway when the fill symbol turns white and there is a line from the symbol to a connector (small square along the circuit lines). After releasing the mouse button the circuit gets the fluid colour and the fill symbol disappears.

In the central window we see plant components connected by lines through connectors. In addition we may see boundary condition symbols and control symbols, if these are chosen to be viewed. For some kinds of controls we also see sensor and control connections as dashed lines. As an alternative to the plant schematic, we may view state diagrams (Enthalpy-Pressure, Entropy-Temperature and Psychrometric).

The plant title is given on an elongated mustard-coloured button on top of all three windows. Also time and main simulation results are presented here. Pressing the plant title button reveals more details.

Most program functions are reached through the menu commands. Some of these functions are alternatively triggered by dedicated keys (short-cuts or accelerators) and mouse actions. The mouse left button is used for selecting an object for inspection or modification. Double-clicking directly enters the inner details. The right button is used for context-specific actions, i. e. the action depends upon which window that gets focus and whether an item is selected when clicking. The final result is a new basis component, fluid or plant component. Point, drag and release will move an item to a new position. The insert and delete buttons will respectively insert and delete an item.

To specify you own plant, you either start with a template or from scratch. In the latter case, please start simple, by one or very few components and build it from this on, being in control of the total specification. The user may specify a plant with few restrictions, but then errors are likely to be made, in particular under- or over-specification of the plant. In either case the program will tell you about it, but will not always be able to pin-point the problem at hand. The best help will be to simplify (if possible) or compare with similar template plants. Over- or under-specification of mass flow balance conditions will be indicated by black lines and connectors (if visible) for the corresponding circuit, if Preferences dialogue Deficiencies indicated box is checked. It may also be seen as non-quadratic matrices, when View|Equations and Variables is checked.

Prior to selecting a specific model to represent a component, you should study the properties of the model to learn how it functions.

Exercises

Let us do some exercises with FrigoSim. Please follow the instructions thoroughly, otherwise they will not function.

In the instruction text, when we write e. g. select File|Save, we mean you must push the File menu from the menu bar and then select the Save menu item. The text "Press Button text" tells you to press the dialogue button with the indicated text.

Inspecting Screen Items

Start FrigoSim and Select File|Example + radio button Plant template + list item Simple One-Stage Heat Pump . In the central window you now see a plant with 7 components, a compressor, a motor, a condenser, a throttle valve, an evaporator, and two pumps. In the left window you see 6 grey-coloured components. In the right window 2 fluid containers are visible.
Double-click the first symbol named "evap " of the left window named Basis set . You see a table-like structure with fields, push-buttons and a combo box (drop down item selection box). This structure, that enables the user to interact with the program, is called a dialogue. The dialogue title reads Basis Component of Model "Standard evaporator" , indicating the component model used for this basis component. The first two fields are for giving the basis component a name and an area (in the indicated unit). One push-button has the text Overall heat transfer coefficient. Pressing this brings you into yet another dialogue, positioned on top of the other. This is a dialogue for specifying/inspecting a function for the evaporator heat transfer coefficient. It indicates a constant value of 700 W/m2K. We will come back to this dialogue in later exercises. Please leave both dialogues by pressing the Cancel button or alternatively the Esc key from the keyboard.
Now double-click the green-coloured evaporator symbol in the central plant window. You see a plant component dialogue. The dialogue title is similar to that of the basis component: Plant Component of Model "Standard evaporator" . You see the name plus a descriptive text of the plant component. In addition you see a set of initial values for the component. These values are needed when FrigoSim starts the calculation involving this component. Normally the values only need to be rough estimates of the real values and sometimes may take any value when using simple input data. But in the event of later making a more accurate component description, you should always feed the component with reasonable initial quantities.

If you inspect the component after having performed a calculation, you will see that all or most of these values have changed. Some special quantities will not change during the simulation, unless changed by controls. Such quantities are called controllable parameters and are indicated by bold in the dialogue.
Push the button with text Basis component "evap". This will bring you to the basis component dialogue visited in point 2. So there is a direct link between the basis component called "evap " and the plant component called "Evap ". Press Cancel (only once).
Press Component quantities. This dialogue is for inspecting all quantities of the component. Note: You may not change any of these values, because they are calculated quantities. It is however possible to transfer the values to other programs via the clipboard. Just select the number text and press Ctrl+C. Press Exit and Cancel respectively in the Component quantities and Plant component dialogues.
Double-click the "R12 " symbol in the fluid window. You see the "R12 " as a selection among the range of available refrigerants. Some characteristic values of this fluid are displayed at the currently selected pressure. Changing this pressure value plus pressing the Update values button will display values at the new pressure. Press Cancel.
Double-click the "SeaWater " symbol in the rightmost fluid window. You see "SeaWater " as a selection from a list of available fluids. Some characteristic values of this fluid are displayed at the temperature Displayed temperature . Changing this temperature and pressing the Update values will display values at the new temperature. Press Cancel.
A third fluid representation is a user-specified fluid. Select Add|Fluid and then User's own data . In this dialogue you may specify a name, a description text, colour and properties of a fluid. There are 5 buttons for the specification of specific heat capacity, density, dynamic viscosity, thermal conductivity and thermal expansion. Each of these buttons accesses a function dialogue as we have seen before for the Overall heat transfer coefficient . The data can be saved to a separate file through the Save button. Press Cancel.
After getting used to the menu commands and double-clicking screen objects, you may start applying the right mouse button. Through this button you reach the most frequently used menu commands that are relevant to the accessed window and the object pointed to. For instance you may enter the plant component inspect dialogue directly by pointing to a component, press the right mouse button and select Inspect . Try out the various right button selections.

Performing a Simulation

Now we will try to perform a simulation. Select File|Reload (if not greyed) in case you inadvertently have made changes to the plant. Answer Yes in case you are asked to discard changes.
Select Perform|Simulation. You see a dialogue with the start time, stop time, time step and two push-buttons which we disregard for the moment. Press OK. You now see the plant being simulated. The solutions at the different time points will flash as the calculation carries on.
After the simulation has stopped, light blue and dark grey value tags are attached to the inter-component connectors. These show the temperature and power values at the corresponding plant sites. Double-clicking a connector displays more details.
Double-click one of the green connectors. This will display a dialogue with the title Secondary fluid circuit connector . This shows quantities indicating the state of the sea water flow at the selected site. Undisplayed values are either not calculated yet or not available. The position of the connector is also given. Press Cancel.
Double-click one of the red connectors. This displays a dialogue with title Refrigerant circuit connector . We see the state of the refrigerant at the selected site. Press Cancel.
Click the green evaporator using the right mouse button and select Inspect . The displayed dialogue shows all quantities of the selected component, i. e. variables, parameters and data, in this order. Test to see that the quantities can not be changed. Press Exit.
Select View|Variables. Press View all and OK. You now see more tags around the connectors: Magenta for entropy, yellow for enthalpy, red for mass flow rate, grey for vapor fraction, and green for pressure.
Select Inspect|Results. You enter Notepad showing a file with a number of quantities previously selected for output. Each quantity is headed by the corresponding component name, a dot, and the FrigoSim quantity name. This result file is in a format readily imported into a spreadsheet program. The quantity names must be selected to be legend texts. Exit from Notepad.
It is now not possible to save the plant by File|Save. FrigoSim considers the current plant values not to be the proper ones, since they have changed due to possible time variations in boundary conditions or controls. Hence they are not representative of the start time. If you want to make changes to the plant, do a reload first, by selecting File|Reload. Answer Yes if asked to discard previous changes.
If you do not want to see the (flashing) results of each time point (which also slows the calculation time), select View|Results on the fly, removing the menu item check mark. A simulation now displays a progress bar instead.

Inspecting Plant Examples

Ideal One-Stage Refrigerating Plant

Let us briefly inspect some of the included templates starting with the very simplest one. Select menu command File|Example + radio button Plant template + list item Ideal One-Stage Refrigerating Plant . This template shows a simple idealised cycle process. The plant items are 4 components, 2 boundary conditions and 2 enthalpy controls. The four components are the compressor "Comp " of basis component "comp ", the condenser "Cond " of basis component "dH ", throttle valve "ThrValve " of basis component "thrvalve " and finally evaporator "Evap " of basis component "dH ". The basis component "dH " is of model type Enthalpy adapter . This is a component model that indicates a change of enthalpy, however not setting the value of this change. The throttle valve is a specific model, but with the same properties as a Dew-point temp. adapter for refrigerant circuits . This is a model indicating a change of dew-point temperature or pressure. The "comp " basis component is a Reciprocating compressor , where the properties has been set to ideal values, i. e. no volumetric or power losses.
The evaporating and condensing temperatures are set by individual boundary conditions to 0 and 50 °C, respectively. The boundary condition symbols look like "flags". The light blue colour indicates that the dew-point temperature of the corresponding connector is set. Double-clicking the flag, enters a Boundary condition specification dialogue. The text field of this dialogue explains this boundary condition. The selector box is for selection of variable type of the controlled variable. The Boundary condition function button is for entry into a function dialogue for setting a variable boundary temperature. Press Cancel.
Finally we have the enthalpy controls, one at the suction port, the other at exit of the condenser. These are set to a constant value of 0, imposing no superheat and no subcooling, respectively. In FrigoSim such conditions have been related to separate controls, instead of always being built into the component properties. Some components models, performing phase separation, set the refrigerant state at the exit ports. For such components it will be incorrect to set the exit states through an enthalpy control.
Select Perform|Simulation and press OK. Check that the evaporating and condensing temperatures are 0 and 50 °C, respectively. What is the discharge temperature?
Select menu command View|H-logP diagram. You can see that the refrigerant conditions out of the evaporator and condenser are saturated.
Select View|T-S diagram and check that the evaporating and condensing temperatures are 0 and 50 °C respectively.
Select View|Variable and press Listitem}. The green lines of constant pressure disappear. Enter the Set|Preferences dialogue and check the Listitem} mark if not checked already. You now see that you can inspect the refrigerant name and conditions at all connectors.
Select View|H-logP diagram again plus View|Numbers. In this diagram you see both refrigerant name and conditions plus a larger set of conditions in all positions in the diagram. Note that the refrigerant library at combined high pressures and enthalpies may signal calculation failure stating Outside allowed range for refrigerant . Return to the plant layout by selecting View|Plant layout.

Cooling of Mackerel by Refrigerated Sea Water

Select menu command File|Example + radio button Demo plant + list item Cooling of Mackerel by Refrigerated Sea Water . You see a refrigerating plant cooling sea water which in turn is flooding a number of mackerels, represented by one component. The sea water is split into 10000 parallel courses, each "feeding" one individual fish. Double-click the "mackerel " basis component. In addition to the area, you see a Heat Conduction button. Pressing this enters a dialogue for a multi-layered one-dimensional structure. Here you may introduce more layers, delete some, and edit individual layers. Use the Insert button if you need to have a new layer between existing layers, while the Append button is used to extend the structure with one extra layer. Shapes can be slab, cylinder or sphere. For the last two an inner radius can be specified.
Now select the single layer and press the Edit layer button (or alternatively double-click the layer). In the layer dialogue appearing you may select size (thickness) and material of the current layer, how this layer is divided into node intervals and initial temperature values and time step. Values of density, specific heat capacity and thermal conductivity at average temperature (as indicated by First temperature and Last temperature ) for the selected material are displayed. An intrinsic material colour is also shown.
Plant components of "mackerel " basis component type (model 1D heat source/sink ) each calculates multi-layered one-dimensional transient heat conduction in non-linear materials with phase change. If you have a commercial license, the number of such components in a plant is only limited by the general component number limit of 200. The number of layers for each component is only limited by memory. The calculation is based on pure conduction in the layers (no convection). Leave all dialogues by Esc.
The sea water pipe component is a normal Heat exchanger with buffer , only with one particularity. Double-click the "channel " basis component and see that the Use boundary check box is marked. This enables attachment to "Mackerel " components or others of the same kind of model.
The sea water should only be cooled down to a specific temperature. If there is capacity surplus, a control is needed to reduce the capacity after having reached the required temperature. Double-click the yellow round symbol with attached dashed lines. You see a Regulator control dialogue.
Click the Requested quantity function and check that the the function is a constant 5 °C. The control states that the compressor through its controllable parameter Relative load is continuously controlled so that the Measured quantity inlet sea water temperature to tank is 5 °C. In the beginning it will set the compressor to maximum specified value (1.0) not obtaining the required value, but doing its "very best". When the criterion is reached the compressor capacity will be lowered to a maintenance level only to account for the load from the fish (still in need to be cooled).
Select File|Reload and OK to reset the plant, unless it is greyed.
Select Perform|Simulation + OK and see how the mackerel is cooled down to 5 °C. If you would like to study the details, just select the mackerel component and do a number of View|Zoom in 2x, before starting the simulation.
After the calculation, you may double-click the "Mackerel " component. This brings up the normal component dialogue. You see, however, that this component has one extra push-button Heat Conduction. Pressing this enters a dialogue for a heat conduction with a specific number of layers. By selecting a layer and pressing the Inspect layer button, you access a Layer inspection dialogue. Here you may inspect the material, the temperature distribution and also the current distribution of the thermal conductivity, the volumetric heat capacity, the internal heat generation (heat density) and heat flow density. These layer dialogues may also be accessed by directly double-clicking the layers on the screen, concurrently holding down the Shift button.

Two-Stage Refrigerating Plant with Open Flash Chamber

Select menu command File|Example + radio button Plant template + list item Two-Stage Refrigerating Plant with Open Flash Chamber . We see a two-stage plant with an open flash vessel at an intermediate pressure level. This vessel sets the enthalpies at the exit ports to liquid and vapor saturation respectively. Therefore enthalpy controls are not needed at the intermediate pressure level. Otherwise the rule of thumb is to have one enthalpy control for each pressure level.
Select Perform|Iteration to see how the intermediate dew-point temperature varies until convergence. You may also use the corresponding tool button for this menu command. Three iterations are needed per time step. The fourth iteration brings you to the next time point. An iteration is constituted by a number of mass flow rate balance calculations (one per circuit) and one subsequent heat flow balance calculation (for the entire plant). A number of such iterations is needed to reach a converged solution, due to non-linearities (state dependent component properties).
Double-click the connector at outlet of the upper throttle valve. What is the vapour fraction?

Plant with Pressure Drop in Distribution Line

Select menu command File|Example + radio button Plant template + list item Plant with Pressure Drop in Distribution Line . In this example you see a plant with a closed circuit at the warm side. Double-click the "Heater " component. The buffer temperature is set to 22 °C. This tells you that the heat is transferred to a sink at this temperature. The buffer temperature is a controllable parameter indicated by bold. This means that the quantity will stay at this value (22 °C), unless changed by a control. It will not be changed by the component itself. The controllable parameters are marked in the model descriptions.
If you implement e.g. a parameter control to a component, you will see a list of the controllable parameters of that specific component (normally only one such parameter).
Select Add|Control + Parameter control .
Click the parameter component combo box and scroll by ↓ and ↑ through the components, and see that several of them have a controllable parameter, among them the Air heater with its Buffer temperature . Press Cancel.
The "Pipe " component is a pipe with pressure drop. Double-click the basis component with the same name as the plant component, i. e. "Pipe ". The name of the basis and plant component may very well be identical. They belong to different Name spacesand will not be confused. Double-click the "Pipe " basis component (in the Basis set window). In the dialogue you see the data for "Pipe ": Diameter , Roughness height and Equivalent length . The value for the Roughness height is of course rather small given i m. Now press Cancel.
Select Set|Quantity units.
Select length in the Select quantity list box. You will have to scroll down the list box first to see the Length item.
Select unit microns (millionth of a meter). Press Exit. Now again double-click the basis component "Pipe ". Now you see a roughness height of 15 microns. Press Cancel.
Double-click the "Pumpk " basis component. You see a basis component with three constant data (Power fraction heating fluid 0.8, Lower number of revolutions 8.3, and Higher number of revolutions 25), two function data (Pressure increase and Efficiency ) and one integer data (Number of capacity steps 5). This specifies a component where 80 % of the shaft power is transferred to the pumped fluid. In 5 steps the number of revolutions may vary between 8.3 and 25 Hz (rps).
Press Pressure increase. You enter the Function dialogue. Press Draw and you see the pump curve in a graph. Press Edit if you would like to change these data. Press Cancel until having exited all dialogues.
You see a green-coloured boundary condition at upper left. This is for setting the reference pressure of the circuit. The components only operate on pressure changes. Double-click the green symbol and see that the reference pressure is set to 0.
Press File|Reload in case you have made some ill-conditioned changes.
Press Perform|Time step and FrigoSim will balance the plant at the initial time point.
Select View|Variables + Pressures , and press OK. You now see the pressures in the water circuit. The air circuit is not equipped with pressure values, because this circuit involves no components affecting the pressure. And no pressure boundary condition is needed here.

Cascade plant

Select menu command File|Example + radio button Plant template + list item Cascade Plant . This is a cascade plant employing ammonia (R717) for the lower-stage compression and R123 for the upper-stage compression. The flash chamber is evidently a closed chamber. The heat from the lower stage is transferred to the upper stage by heat exchange through a coil.
Select Perform|Simulation and study the results.
Select View|T-S diagram.

Ice Rink Refrigerating Plant with Small Heat Pump on top

Select menu command File|Example + radio button Demo plant + list item Ice Rink Refrigerating Plant with Small Heat Pump on top . This is an example of a refrigerating plant with a small heat pump residing on top. The refrigerating plant is an ice rink freezing unit with an air-cooled condenser. Some of the discharge gas from the two parallel compressors is fed into a flash tank. The vapour from the tank is sucked into a heat pump compressor, while the liquid part plus flash gas from the heat pump throttle valve are throttled back to the evaporator of the refrigerating plant.

Turbo Compressor Plant

Select menu command File|Example + radio button Plant template + list item Turbo Compressor Plant . This is a simple plant, only with a turbo compressor and a dedicated bypass control . The compressor is in addition controlled by a parameter control .
Double-click the parameter control having a graph-like symbol. You see by entering the function that the Prerotation vane angle is varied in time from 90° to 30°. Leave both dialogues.
Double-click the bypass control with the brown circle symbol. You see that this control sets up a link between the turbo compressor and the three-way valve Bypass valve . This link is also indicated by dashed lines in the layout.
The conditions for bypass are specified by the turbo compressor itself. Double-click basis component "turbo " and you see a rather complex component specification. The capacity and efficiency data are based on specifying nominal values and relative values from these. This facilitates adapting the compressor to a real plant: Only the nominal values need to be modified.
Press Relative volume flow and Draw and you see a set capacity curves. Note that the Relative pressure ratio axis is horizontal and the Relative volume flow axis is vertical, opposite of what is common. The curve set parameter is the Prerotation vane angle , with values 10, 30, 50 and 90°. Press Cancel and Minimum relative volume flow + Draw. You see the surge line, again with opposite axes of the normal graphs. This surge line is used by the bypass control, controlling the bypass valve so that the compressor relative volume flow is larger than its minimum value at corresponding pressure ratio (to prevent flow instabilities).
Exit the dialogues by Cancel and press File|Reload in case you have made some ill-conditioned changes.
Select View|Variables and Mass flow rates . Then press repeatedly Perform|Time step or corresponding tool button and watch how the bypass mass flow rate decreases as the prerotation angle goes from 90° to 30°.

Pavement Heating by Heat Pump

Select menu command File|Example + radio button Plant template + list item Pavement Heating by Heat Pump . You see the component "Ground " being a 5-layered structure attached to the component "Climate ". The components are attached in a boundary (details about this in help text Boundaries for heat transfer ). Double-click the "Climate " basis component and note that the Use boundary box is checked. This is necessary for the "Climate " component to be attachable to the "Ground " component. Both "Climate " and the "Evap " evaporator are fed by outdoor air from the source component "Air ". Condenser heat is transferred to the ground by a pipe positioned just above the insulation layer.
Click the pipe component and select View|Zoom in 2x to clarify the details. Try to drag the pipe component. You see that it is indeed attached to the ground component and is not movable. The same is the case for "Climate ". Double-click the "Ground " basis component, press Heat Conduction, select layer no 3 (Insulation ) and press Edit layer. You see that the layer's Boundary box is checked. This is necessary for the "BPipes " component to be attachable to the ground at this position (at the beginning/top of the insulation layer).
Double-click the basis component "air " and subsequently the buttons Source temperature and Draw. The air temperature has been specified by a cosine function. Press Edit to see the parameters. The heat pump has no control. It operates at full capacity at any time.
Select Set|Quantity units and set the time unit to days.
Select Perform|Simulation and see how the ground temperature distribution change over a heating season from -100 days (22/9) to 100 days (10/4).

District Heating Plant with Intermediate-Temp. Heat Distr.

Select menu command File|Example + radio button Demo plant + list item District Heating Plant with Intermediate-Temp. Heat Distr.. This is a plant with a large central sea-water source turbo compressor based heat pump feeding heated water to a district heating line. Two peripheral heat pumps use this water as heat source, lifting the temperature to a required level, if necessary by using an oil-fired boiler. The central heat pump uses R134a as refrigerant, while the smaller heat pumps use R22. The supply and return pipes are modelled as Heat exchangers with buffer , both connected to a ground component at different positions (depths), similar to previous example. A climate component is attached at the top.
Select Perform|Time step and study the temperature levels. The heat starts from sea water at temperature 12 °C. The temperature supply to the district heating line is 40 °C. Heat losses reduce this to 36 °C, feeding the local heat pumps, which in turn increase the temperature to 68 °C.

Two-Stage Refrigerating Plant with Open Flash Chamber

Select menu command File|Example + radio button Plant template + list item Heat Pump with Two Parallel Aggregates . This is a plant with two parallel aggregates with individual heat source water supply, however connected by heating a water flow in series.
Select Perform|Time step and see how the identical aggregates differ in temperatures, mass flow rates and powers, due to differences in temperature feeding the condenser.

Refrigerating Plant with Two Parallel Two-Stage Aggregates

Select menu command File|Example + radio button Plant template + list item Refrigerating Plant with Two Parallel Two-Stage Aggregates . You see a two aggregate two-stage plant. The aggregate condensers are fed with the same water temperature, while the evaporators experiences different temperatures -35 °C and -25 °C.
Select Perform|Time step and study the effect of the differing source temperatures.

Plant for Heat Accumulation and Supply

Select menu command File|Example + radio button Plant template + list item Plant for Heat Accumulation and Supply . This is a plant comparing a heat accumulating tank with full mixing and one with stratification. For 12 hours both tanks are fed with water at 50 °C. Then they are fed by 10 °C water.
Repeatedly select Perform|Time step and see how the tanks perform.

Plant for Freezing Fish Meat

Select menu command File|Example + radio button Plant template + list item Plant for Freezing Fish Meat . This shows a plant that cools a brine for freezing salmon meat. The component "Freezer" is attached to a component "Salmon " consisting of two layers. One layer consists of Aluminium at thickness 5 cm, the other Salmon fish meat at thickness 30 cm.
Select Perform|Simulation + OK and see how the freezing develops. If your computer has reasonably high capacity, you may use a number of Perform|Time step.

Actual Plant Heating a Laboratory

Select menu command File|Example + radio button Demo plant + list item Actual Plant Heating a Laboratory . This is a plant that was established very early in the development of FrigoSim by a PhD student at Norwegian University for Science and technology, back in the 1980-ies. It is a plant with a major set of component models. New to this example survey are a Rotating heat exchanger with the name "VntHX ", a Superheat heat exchanger with the name "QCP ", a Suction heat exchanger with the name "SGHX ", an Oil return heat exchanger with the name "ORHX ", a Three-way valve for refrigerant circuit with the name "ManiE ", and a T-header for refrigerant circuit with the name "HEvap ". In addition there are two new control mechanisms, the valve control (2 occurrences) and the capacity control (one occurrence).
A valve control uses the same symbol as the enthalpy control, only has a visible control signal connection to a three-way valve. It is used to control the mass flow rate distribution between two parallel lines.
The capacity control is a concerted control of a number of components, in order to meet a time-dependent capacity requirement. The involved components have a visible control signal connection to the control. In addition there are measurement signal connections to two connectors, which must belong to the same circuit and have the same mass flow rate. Try to find all these signal connections on the screen.
Drag the control slowly to a new position, to increase the visibility. You see a connection to three components with names "Comp1 ", "Comp2 " and "RecF ". Between the two connectors there are three components giving off heat, "RecC ", "VntC " and "QCP ". The capacity measured by the capacity control is the sum of the capacity of these three components. The controlled components are controlled so that the total capacity meets the requirement of the control at any given time.
Select Set|Quantity units and SI units scaled . Double-click the capacity control symbol. You see a dialogue where the connectors, the capacity function, and a control strategy are specified or available.
Press Capacity function and Draw. You see a time variation of the capacity requirement during 24 hours. Press Cancel. Press Strategy and you see a dialogue with the three components and a strategy table (or matrix) with two levels. Clicking among the 6 entries of the table will show the meaning of the table symbols ('*', '>' ,'-' etc.).
Exit the dialogues and press File|Reload in case you have made some ill-conditioned changes. The two strategy levels are visible in the control symbol as the major red lines at the right. The minor red lines show the number of steps at each level, reflecting the component(s) regulated at that level.
Repeatedly select Perform|Time step and see how the signal line position at the red lines vary in time. This is of course due to variations in the capacity requirement.

Actual Plant Heating an Office Building

Select menu command File|Example + radio button Demo plant + list item Actual Plant Heating an Office Building . This is also a comprehensive plant. The news are the Pressure drop in refrigerant circuit as components "Dischar1 " and "Dischar2 ", representing pressure drop in the discharge line of compressors 1 and 2 resp. Then there is the Air cooler with given capacity as component "EvapBoil ", representing the boiler-room evaporator. The component "Receiver " is a Phase separator for refrigerants . It has the same properties as the Open flash chamber with three ports , but with a slightly different use. Finally we have the Back-up valve as component "BUValve ". This is a valve ensuring a minimum inlet pressure.

Adjacent cold room and freezing room with common condenser water supply

Select menu command File|Example + radio button Plant template + Adjacent cold room and freezing room with common condenser water supply . This is a demo plant using two temperature zone components as basis, one being a room, the other a freezer room.
Each of the zones has four walls, one common to both. The two rooms are refrigerated by one simple plant each. These plants use different refrigerants, R717 (ammonia) and R410A. The cold room is cooling 10 fillets of salmon and is controlled by a regulator control to stay close to 4 °C (1 K deviation allowed). The control is operating the rotational speed of the compressor. The freeze room is empty and is controlled to -30 °C. The 10 salmon fillets are represented by one using a Manifold for secondary fluid circuit split of the air flow from the room, and a Header for secondary fluid circuit to collect the air flows to one before release to the room.
The fillets are considered to be cylinder-shaped, and are placed outside the room only for better space and view. This has no implication for the calculation.
The ambient temperature is varing over the day and night as a simple sine function with average 20 °C and an amplitude 5 K, set by invidual parameter controls at the convective boundary component of each wall, these components setting the heat transfer coefficients to 5 W/m²K.

Building a New Plant from Scratch

Now we would like to take you through the specification of a plant from scratch.

Start FrigoSim, if not started already.
Select File|New. All contents of the three windows disappear. Also select Set|Quantity units and double-click the SI units item in the Select unit system box.
Select Add|Basis component and then Directly specified . You now see a dialogue with two list boxes, the first containing a number of model groups (corresponding to the ones found in help).
Select Compressors in the upper box and then Reciprocating compressor in the lower. Press OK. You now enter the Basis component dialogue for the Reciprocating compressor model. Specify all fields in succession, using "comp ", 0.01, 0.1 and 0.25. Note: A name may only consist of a maximum of eight characters. And a basis component name (as with fluid and function names) must only contain valid file name characters. The push-buttons are entries to Function dialogues. All fields and functions must be specified, except the price function. You specify this function if you wish to add the price of components of this basis component type to the total plant cost.
Press Volumetric efficiency. Functions are considered to be constants, unless you specify otherwise. So at entrance to the function dialogue for an unspecified function, you are directed to a field for a constant value. If you wish to specify a table or parameterised function, you specify this in the function type list box.
Select 1D table X-dependent for the volumetric efficiency and press Edit. You see a 2 x 15 edit fields with one column for x values (Pressure ratio ) and the other for function values (Volumetric efficiency ). Specify the points [1,0.9], [2.5,0.8], [5,0.75] and [20,0.6]. You do this most efficiently by typing:
1 Tab 0.9 Tab 2.5 Tab 0.8 Tab 5 Tab 0.75 Tab 20 Tab 0.6
Exit the 1D table dialogue by OK. You see the table as a graph in the function dialogue. Exit the dialogue by OK.
Press Isentropic efficiency, double-click 1D table X-dependent , enter the numbers [1,0], [1.5,0.5], [2,0.75], [3,0.82], [5,0.8], [10,0.6], [20,0.5] and press OK twice.
Now press Rel. part load shaft power, double-click 1D table X-dependent , enter the numbers [0,0.2], [1,1] and press OK. This function describes the compressor part-load properties, by specifying how the shaft power in fraction of the full-load shaft power depends on the partial load. Press OK again.
Finally you specify 4 as the Number of capacity steps . This is used in a Capacity control when the compressor is in a Regulated state. The capacity control searches for the proper step to meet a required capacity. The number should reflect the real compressor properties. In this case, we envision a 4 pistons compressor. Press OK to leave the basis component dialogue.
You see a marking symbol around the basis component just made.
Select Add|Component and specify the fields of the Plant component dialogue. Use "Comp ", Compressor , -5, 50, 1 and press OK. You now see a plant component symbol in the plant window, with the same appearance as the basis component.
Drag this component to desired position. Rotate the symbol 90° by selecting Edit|Rotate to next 90°.
Now we could continue building a complete plant. However, let us stop at this point and do the minimum needed to have a formally complete plant.
First we need a refrigerant. Select Add|Fluid and then Refrigerant .
Select R22 from the Refrigerants list box and press OK. You now see a marked fluid symbol in the Fluid window.
Select Add|Fluid fill. Now you see a new symbol in the upper-right corner of the plant window. This Fluid fill symbol can be used to fill the compressor with R22. Drag the symbol on to a refrigerant circuit connector with the symbol top being the hot spot. Release the mouse button when the symbol turns white and there is a connecting line to the connector. Now you have filled the circuit with refrigerant R22, making the compressor and connectors yellow.
Select Perform|Simulation. The menu command is disabled (greyed). This indicates that the plant specification is not complete. To complete we need two boundary conditions and one control.
Click the suction port connector. If in doubt on which to use, just double-click several connectors until you see one with the component connectors text Suction port .
Select Add|Boundary condition, specify the text Evaporating temperature
and press Boundary value function. Specify the constant -5 °C. Press OK twice. You now see a light blue symbol sticking out from the suction port connector.
Click the discharge port connector using the right mouse-button and select Add boundary condition . Specify a text Condensing temperature and a constant 50 °C as the boundary condition function.
Click the suction port connector again. Now select Add|Control and then Enthalpy .
Specify the fields of the Enthalpy control dialogue, e.g. "Super " and Suction superheat .
Select Superheat from the Type of enthalpy control radio buttons. Note that the function button text changes with the radio button selection. Press the function button Superheat function. Specify a constant 5 K. Press OK to exit the dialogues. You now see a small enthalpy-pressure diagram looking symbol for this enthalpy control. It has a red line parallel to the saturated gas (dew-point) line to indicate the kind of enthalpy control.
Select File|Save as and specify MyPlant.sim .
If you now select Perform|Simulation, you see that it is enabled, indicating that the plant specification is complete. Do this and press OK. The calculation is performed and a solution appears. The connectors are now equipped with tags for temperature (light blue),pressure (light green) and power (dark grey).
Let us now complete the plant with the other commonplace components.
Select File|Reload first, otherwise you will not be allowed to do any changes to the plant.
Instead of selecting Add|Basis component, you may point to the Basis set window and press the right mouse button.
Select Add basis component Directly.
Select model group Heat exchangers - Secondary fluid/Refrigerant and then double-click model Standard evaporator . Specify name "evap " and area 200 m2. Press Overall heat transfer coeff. and specify the constant 20 W/m2K. Press OK to exit both dialogues. You now see basis component number 2 in the Basis set window. Right-click the "evap " basis component and select Transfer to plant .
Fill in the fields of the Plant component dialogue by "Evap ", Evaporator and the values -5 °C, 0 °C and 100 W/m2K and press OK.
Select View|Zoom Out 2x to have more space.
Specify a condenser in a similar way: Select model group Secondary fluid/refrigerant heat exchangers and then model Standard condenser . Exit with OK. Specify name "cond " and area 10 m2. Press Overall heat transfer coeff. and specify the constant 800 W/m2K. Press OK to exit both dialogues. Drag "cond " basis component close to the plant window until a plant component dialogue appears. Fill in the fields of the Plant component dialogue by "Cond ", Condenser and the values 50 °C, 40 °C and 3000 W/m2K and press OK.
Specify a throttle valve by selecting model group Throttle valves and then model Throttle valve . Specify name "thrvalve ". Transfer to plant by one of the methods used above. Fill in the fields with "ThrValve " and Throttle valve and press OK.
Now finally we need a fan and a pump. Select model group Pumps and then model Pump with preset mass flow rate . Exit with OK. Specify the basis component name "pump " and press OK.
Transfer to plant and specify "Pump ", Condenser pump , the mass flow rate 2 kg/s and press OK.
Transfer basis component "pump " again to plant and specify "Fan ", Evaporator fan , the mass flow rate 4 kg/s and press OK. A fan is an air pump, so we need no particular models for fans.
Before proceeding, drag the components to proper positions and rotate by the F6 key if appropriate. Select View|Whole.
Point to the Fluid window , press the right mouse button and select Add secondary fluid . Select Air from the substance selection list box and press OK. Double-clicking a substance is disabled because some fluids require a concentration value.
Repeat the previous point, only this time selecting the Water substance.
Click the "Air " symbol in the Fluid set window.
Select Add|Fluid fill. Drag the fluid fill object to the fan and release it when it turns white.
Now right-click the "Water " symbol and select Transfer to plant . Drag the fill object to the pump and release it when it turns white.
Select File|Save.
Now is the time to connect the components. Click the fan outlet connector and drag it to the evaporator secondary fluid inlet. If you try the refrigerant inlet, you will not see a rubber string indicating a possible connection. When you release the mouse button, you see the evaporator filled with the light blue air.
Drag the evaporator refrigerant outlet connector to the compressor suction port connector and release it when seeing the rubber string. You now see an evaporator filled with the yellow refrigerant.
Drag the compressor discharge port to the condenser refrigerant inlet connector and release. The condenser is filled with the yellow refrigerant.
Drag the condenser refrigerant outlet connector to the throttle valve inlet connector and release.
Drag the throttle valve outlet connector to the evaporator refrigerant inlet connector and release. Now the refrigerant circuit has been closed.
Finally drag the pump outlet connector to the condenser secondary fluid inlet connector and release. Now all components have been fully connected. But it does not look very nice, does it? So how do we fix this?
Drag all connectors to a suitable position, disregarding the components. Then select Edit|Adjust components. Repeat this point, if you like.
When it looks reasonably nice, you may perfect it by first selecting Set|Autoadjust. Then drag all components until you are satisfied. A second Edit|Adjust components could also be appropriate.
Now we need to make the final specification adjustments prior to calculation. After introducing the evaporator and the condenser, the boundary conditions for evaporating and condensing temperatures must be deleted. Otherwise the plant will be over-specified.
Click the light blue symbol for the evaporating temperature boundary condition and select Edit|Delete. Repeat this with the condensing temperature boundary condition, only this time using the keyboard Delete. These operations are equivalent.
We now need to set boundary conditions on the open circuits inlet connectors. Click the fan inlet connector.
Select Add|Boundary condition, specifying text Inlet air temperature . Press the Boundary value function button and specify a constant 5 °C. Exit the dialogues by OK.
Repeat this on the pump inlet connector specifying the text Inlet water temperature and 40 °C.
We already have specified an enthalpy control for the lower pressure level. But we need an enthalpy control also for the upper pressure level. Click the condenser refrigerant outlet connector, select Add|Control and Enthalpy . Specify "Sub " and Subcooling and select control type Subcooling . Press Subcooling function and specify a constant 0 K (no subcooling). Exit the dialogues by OK. You see an enthalpy control symbol with a blue line parallel to the saturated liquid (bubble-point) line, indicating a subcooling specification.
Now the plant is again fully specified and we may do a simulation. Select File|Save first. Then select Perform|Time step and you see the result of the specification.
In addition to the minimum specification we have done now, we should normally specify a time span for the simulation, and specify quantities for output. Select File|Reload to prepare for some added specifications.
Select Set|Simulation conditions. Specify Stop time 86400 seconds (24 hours) and Time step 3600 seconds (1 hour). If you like, you may set hour as time unit first (Set|Quantity units), and then specify 24 and 1.
Select Output|Component quantities. You see the plant component Compressor selected in the Component combobox.
Select compressor quantities in the Quantities list box. These will be output to a result file of type rsl .
Click the component combobox and select other components to pick output quantities from. Before exiting the dialogue, the check the box for sorting the quantities by type and component should be on. This facilitates handling the results by a spreadsheet program. If you have established a column selction setup, but just need some extra quantities, you should turn off sorting before leaving. Otherwise the sequence of quantities could be changed.
Double-click the inlet air temperature boundary conditions and press Boundary value function. Change the function type to 1D table X-dependent and press Edit. Enter the [Time,Temperature]-points [0, 5] and [86400,-5] and exit the dialogues by OK.
Select File|Save.
Select Perform|Simulation and press OK. A 24 hours simulation will start, displaying results for every 1 hour.
The results are put to the file MyPlant.rsl . By selecting Inspect|Results you may study this file that shows hourly values of the selected output quantities. The file may also be input to a spreadsheet program. Try this if you have one.

Doing a quick sensitivity analysis of a plant

When a plant has been loaded or build, it is possible to experiment with it through a mechanism called Instant change. You may read a general description of it in the article Instant change mechanism.

Start FrigoSim, if not started already.
Select File|Example + radio button Plant template and select Simple One-Stage Heat Pump .
Double-click fluid SeaWater and change to Ethylene Glycol through the list box. Set concentration to 30 % or 0.3 if fraction unit has been set.
Select File|Save and specify a file name (you are not allowed to save back to the original template file).
Right-click the evap basis component and select Instant capacity change from the pop-up menu. A new window should now have appeared displaying a range of evaporator area values.
Drag the track bar to a new area value 1.48 m² and see the result on the plant temperatures.
Now push the + button. The total range is reduced to 1/10 of the original, and the resolution is 10 times up.
Increase the area to a value as close to 1.50 m² as possible.
Check the Keep final value checkbox. This is to preserve the final area value.
Click the cyan-coloured boundary condition symbol close to SWPump. You now see the instant change window dedicated to the input temperature of SWPump, with a range from 0 to 10 °C.
Reduce the temperature to 3.5 . Notice the effect on various plant temperatures.
Click the enthalpy control symbol (resembling a H-logP diagram) at inlet of compressor.
Increase the evaporator superheat value from 5 to 6 °C.
Finally click the Ethylene Glycol symbol in the Fluid set window.
Increase the glycol consentration from 30 to approx. 40 %.
The final discharge temperature from the compressor should now be 60.08 °C. This temperature is the result of a combined change of evaporator area, evaporator brine temperature input, change of evaporator superheat and finally the brine concentration.

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