Loops Library
Loops are the subset of an HVAC system. They utilize hydronic equipment for heating, cooling and service water heating (DHW). The loop library allows you to create and manage these hydronic loops that will be applied to their project in the plants section.
“Loops are paths through which the working fluid is circulated in order to satisfy a cooling or heating load.” Loops can be divided into two sections: the Supply side half-loop and the Demand side half-loop. The supply side contains components (such as boilers and chillers) which treat the working fluid to a certain state and then send it to the demand side. The demand side has components (such as cooling and heating coils) that receive the working fluid and use it to satisfy the load.
The Loop Library contains six types of loops: Chilled Water Loop, Hot Water Loop, Condenser Loop, Mixed Water Loop, Heat Exchanger Loop and VRF Loop. Each loop contains specific components and controls that can be used to model almost every plant configuration.
To create a new loop library member or view the existing standard loops, click on one of the six loop types then click on the + Add Item button. You can also create custom groupings for organizing the library by clicking on the Add Group button. Loop library members can be added to custom groups by dragging and dropping. Right clicking on an existing library member allows you to rename, copy, delete, lock and unlock a loop library member.
Loop Types
Chilled Water Loop
The Chilled Water Loop uses equipment to produce and distribute cold water to cooling coils that have the load requirements from the building. Below is a simple line diagram for a chilled water loop.
Hot Water Loop Type
The Hot Water Loop uses equipment to produce and distribute hot water to heating coils that have the load requirements from the building. Below is a simple line diagram for a hot water loop.
Condenser Water Loop Type
The Condenser Water Loop uses equipment to expel the heat removed from the building to the atmosphere and return cooled water to the chiller in the chilled water loop. Below is a simple line diagram for a condenser water loop.
Mixed Water Loop Type
The Mixed Water loop uses cooling/heating equipment along with heat rejection and heating equipment to maintain a set range of water temperature for a system. Building loads can be met with several modes of operation depending on the outside conditions. The individual space equipment can switch between cooling and heating depending on space needs. The goal of the system is to recover heat or use “free cooling” whenever possible. Below is a simple line diagram for a mixed water loop.
VRF Loop Type
The VRF Loop is a combination of outdoor condensing units and other components that are tied to a group of indoor heating and/or cooling units via a refrigerant loop. Below is a simple line diagram for a VRF loop.
Heat Exchanger Loop Type
Heat Exchanger Loops transfer heat from one medium or loop to another for different purposes like energy saving, chilled water or ice storage, etc. Below is a simple diagram example of a heat exchanger loop.
There are eight different types of Heat Exchanger Loops depending on the placement of the heat exchanger and the loop types it connects
● Chilled Water Loop to Chilled Water HX
● Chilled Water Loop to Mixed Water HX
● Hot Water Loop to Mixed HX
● Hot Water Loop to Hot Water HX
● Condenser Loop to Condenser Water HX
● Condenser Loop to Chilled Water HX - some examples are free cooling applications.
● Mixed Water Loop to Hot Water HX
● Mixed Water Loop to Chilled Water HX
You can view the existing standard loops by clicking on one of the eight Heat Exchanger Loop Types. To create a new loop library member, click on the + Add Item button. You can also create custom groupings for organizing the library by clicking on the Add Group button. Loop library members can be added to custom groups by dragging and dropping. Lastly, right clicking on an existing library member allows you to rename, copy, delete, lock and unlock a loop library member.
Loop Library Member
The general library member information is displayed at the top of the screen. To build a loop, select components from the Plant Component Selection Bar to add to the plant diagram. The properties section displays all of the loop fields. It can be viewed by clicking on the bottom properties bar.
Plant Component Selection Bar
The selection displays categories of components that can be added to a loop. These categories are:
Each loop type will display the categories and components that are valid. Click on the category button to expand it and view the components that can be added to the loop. Select a component on the bar by clicking on it. The plant diagram will highlight the valid locations for placing the component on the loop. To drop a component on the plant diagram, click on one of the green dot locations. Below is a description of each category:
Pumps
The Pumps category in the Component Selection Bar displays the valid pump types that can be added to the loop. The available pumps for all loop types are shown below. For more information on each type of equipment see the Equipment Library.
● Constant Volume Pump Not-Headered
● Variable Volume Pump Not-Headered
● Constant Volume Pump Headered
● Variable Volume Pump Headered
Pumps that have been added to a loop will be displayed in the Properties Section under Components. Each component displays information from the equipment library member that has been selected. The library member may be changed but its information is not editable. The fields displayed for pumps are:
● Name
● Full Load Energy
● Pump Head
● Motor Efficiency
● Motor Heat to Fluid
● Flow Control
Equipment
The Equipment category in the Component Selection Bar displays the valid component types that can be added to each loop type. The available equipment per Loop Type is shown below. For more information on each type of equipment see the Equipment Library.
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1 Chilled Water Loop
A Air Cooled Chiller
B Water Cooled Chiller
A Absorption Chiller
B Engine Driven Air Cooled Chiller
C Engine Driven Water Cooled Chiller
D District Cooling
E Temperature Source
2 Hot Water Loop
A Boiler
B Water Heater
C District Heating
D Temperature Source
3 Condenser Loop
A Cooling Tower
B Fluid Cooler
C Evaporative Fluid Cooler
D Well
4 Mixed Water Loop
A Boiler
B Water Heater
C District Heating
D Temperature Source
E Cooling Tower
F Fluid Cooler
G Evaporative Fluid Cooler
H District Cooling
I Ground Heat Exchanger
J HX w/ Controls
5 Heat Exchanger Loop
A Chilled Water Loop to Chilled Water HX
a Air Cooled Chiller
b Water Cooled Chiller
c Absorption Chiller
d Engine Driven Air Cooled Chiller
e Engine Driven Water Cooled Chiller
f District Cooling
g Temperature Source
B Chilled Water Loop to Mixed Water HX
a Air Cooled Chiller
b Water Cooled Chiller
c Absorption Chiller
d Engine Driven Air Cooled Chiller
e Engine Driven Water Cooled Chiller
f District Cooling
g Temperature Source
C Hot Water Loop to Mixed Water HX
a Boiler
b Water Heater
c District Heating
d Temperature Source
D Hot Water Loop to Hot Water HX
a Boiler
b Water Heater
c District Heating
d Temperature Source
E Condenser Water Loop to Condenser Water HX
a Air Cooled Chiller
b Water Cooled Chiller
c Absorption Chiller
d Engine Driven Air Cooled Chiller
e Engine Driven Water Cooled Chiller
f District Cooling
g Temperature Source
F Condenser Water Loop to Chilled Water HX
a Cooling Tower
b Fluid Cooler
c Evaporative Fluid Cooler
d Well
G Condenser Water Loop to Mixed Water HX
a Cooling Tower
b Fluid Cooler
c Evaporative Fluid Cooler
d Well
H Mixed Water Loop to Hot Water HX
a Boiler
b Water Heater
c District Heating
d Temperature Source
e Cooling Tower
f Fluid Cooler
g Evaporative Fluid Cooler
h Ground Heat Exchanger
I Mixed Water Loop to Chilled Water HX
a Boiler
b Water Heater
c District Heating
d Temperature Source
e Cooling Tower
f Fluid Cooler
g Evaporative Fluid Cooler
h District Cooling
i Ground Heat Exchanger
6 VRF Loop
A VRF Outdoor Unit
B Water VRF Outdoor Unit
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Thermal Storage
The Thermal Storage category in the Plant Component Selection Bar is only available in the Chilled Water Loop type. The two available components are Ice Storage and Chilled Water Thermal Storage. For more information on each type of see the Equipment Library.
Heat Exchanger
The Heat Exchanger category in the Component Selection Bar displays the valid component types that can be added to each loop type. The available equipment per Loop Type is shown below. For more information on each type of equipment see the Equipment Library.
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1 Chilled Water Loop
A HX w/controls
B HX Waterside Economizer
2 Hot Water Loop
A HX w/controls
3 Condenser Loop
A HX w/controls
4 Mixed Water Loop
A HX w/controls
5 Heat Exchanger Loop
A Chilled Water Loop to Chilled Water HX
a HX w/controls
b HX Waterside Economizer
B Chilled Water Loop to Mixed Water HX
a HX w/controls
C Hot Water Loop to Mixed Water HX
a HX w/controls
D Hot Water Loop to Hot Water HX
a HX w/controls
E Condenser Water Loop to Condenser Water HX
a HX w/controls
b HX Waterside Economizer
F Condenser Water Loop to Chilled Water HX
a HX w/controls
G Condenser Water Loop to Mixed Water HX
a HX w/controls
H Mixed Water Loop to Hot Water HX
a HX w/controls
I Mixed Water Loop to Chilled Water HX
a HX w/controls
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Controls and Sensors
For Loops, the only available control is a Water Temperature Set point Controller. This controller can be connected to components added to the loop to sense the water temperature in that node. The control strategy can then be defined in the Properties section of the Controls tab.
Plant diagram
The plant diagram is a graphic representation of a loop. It displays the supply side components as well as a demand box. As components are selected in the component selection bar, the plant diagram will highlight valid locations for placing them with green dots. To drop a component on the plant diagram, click on one of the green dot locations. To delete a component from the plant diagram, click to select the component and hit delete. As components are added to the plant diagram, they will be added to the components tab of the properties section.
Each loop type in the Loop Library has business rules that will help create a valid loop configuration. When you are finished configuring your plant, click the validation button to display Validation Messages that will help you fix invalid configurations or missing data.
Demand Side or Demand Box
The plant demand side contains equipment that places a load on the primary equipment. This might include coils, baseboards, radiant systems, etc.
Within the demand section, if you are using the Plant Wizard or are located in the Assign Loops section, you can view supply side components that the demand is connected to. An example would be a condenser loop that is connected to one or multiple chillers.
These assignments or connections can be viewed by clicking on the component or loop that it is connected to.
Supply Side
Supply side will contain primary equipment such as chillers or boilers on the supply side loop. Each supply side must be connected to a demand side and vice versa. You can select components by using the plant component selection bar. Each component has rules associated to them on where they can be placed within the diagram. Each valid location will have a green dot for placement. If the component location breaks a rule, then the validation rules will appear and will give a suggestion on what to fix in the particular loop.
Properties section
The properties section displays all of the fields that are necessary to define the correct operation of the loop and its components. Properties can be accessed by expanding the properties bar in the bottom left corner of the screen.
Loop Sizing
This properties tab contains the fields that are necessary to calculate plant loop flow rates and equipment capacities when auto sizing. This information is initially used by components that use water for heating or cooling such as hot or chilled water coils to calculate their maximum water flow rates. These flow rates are then summed for use in calculating the Plant Loop flow rates.
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Loop Sizing Method
This field controls how concurrence issues impact the plant loop flow rate. There are two options:
o Block - The cooling plant capacity is equal to the sum of the highest block load as simulated of the airside cooling coils as well as demand loads assigned to the cooling plant.
o Peak - The cooling plant capacity is equal to the sum of the airside cooling coil capacities or demand loads assigned to the cooling plant.
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Block Sizing Timestep
This is the number of timesteps used in a moving average to determine the design flow rate for plant sizing. This allows using a broader average over time.
Input Considerations: If you want to size a plant based on a larger timestep (e.g. 1 hour versus 15 minute time step increments), you would enter in a value that would be greater than 1 here. A good example would be wanting to size a plant based on a 1 hour average versus a timestep for simulation which is 15 minutes. A number of 4 would be entered (15 x 4 = 60 minutes) to size the plant based on one hour.
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Min & Max: 1 to 60
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Typical Range: 1 to 4
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Units: N/A
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Temperatures
Loop Temperature Difference
The design temperature rise (for cooling or condenser loops) or fall (for heating loops) across the demand side of the loop. This temperature difference is used by component models to determine flow rates required to meet design capacities.
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Input Consideration: Larger values lead to smaller design flow rates.
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Default values: Cooling loop: 10°F; Heating loop: 10°F; Mixed loop: 10°F; Condenser loop: 10°F
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Min & Max: -999 to 999
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Typical Range: -999 to 999
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Units: °F; °C
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Design Exit Temperature
The water temperature at the exit of the supply side of the plant loop. This is the temperature of the water supplied to the inlet of chilled or hot water coils and other equipment that places loads on a plant loop.
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Input Considerations: A higher or lower than normal temperature may impact equipment performance.
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Default values: Cooling loop: 44°F; Condenser loop: 95°F; Mixed loop: 90°F; Heating loop: 180°F
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Min & Max: -999 to 999
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Typical Range: 0 to 200
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Units: °F; °C
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Maximum Temperature
Defines the maximum allowable temperature for the loop.
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Default values: from template
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Min & Max: -999 to 999
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Typical Range: 0 to 200
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Units: °F; °C
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Minimum Temperature
Defines the minimum allowable temperature for the loop.
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Default values: from template
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Min & Max: -999 to 999
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Typical Range: -30 to 200
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Units: °F; °C
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Loop Sizing Factor
This is the factor to over or undersize the capacity of the loop. This is also more commonly known as a safety factor.
Default values from template
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Min & Max: 0 to 1000
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Typical Range: 100 to 200
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Units: %
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Fluid and Flow Rates
Fluid Type
This field determines the type of fluid for the loop: Water, Ethylene Glycol or Propylene Glycol. If Ethylene Glycol or Propylene Glycol is selected, the Glycol Concentration field becomes available. Ethylene Glycol or Propylene Glycol is used as an anti-freeze.
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Default values: water
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Glycol Concentration
Only appears when Ethylene Glycol or Propylene Glycol is selected for the fluid type. As an example, a mixture of 60% ethylene glycol and 40% water freezes at -49 degrees F.
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Default values: 30%
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Min & Max: 0 to 100
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Typical Range: 20 to 40
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Units: %
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Ice Tank Sizing
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Default values: 10 hr
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Min & Max: N/A
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Typical Range: N/A
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Units: hours
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Components
The Components tab displays the information of the components that have been added to a loop. The components will be displayed on a table grouped by the category from the Plant Component Selection Bar: Pumps, Equipment, Thermal Storage, and Heat Exchanger. When expanded, each component will display pertinent information about the selected equipment library member. A different equipment library member can be selected but the library member information cannot be edited on this screen.
All components except for Heat Exchangers and District Cooling/Heating are in the library. To view details on each input field, please go to the equipment library section to view them in more detail.
Heat Exchangers
A fluid-to-fluid heat exchanger is designed to couple the supply side of one plant or condenser loop to the demand side of another plant or condenser loop. This heat exchanger is fairly general and can be configured for use in any application where any two loops need to be connected together. The only constraints are that one side must be connected to the supply side of one loop and the other side connected to the demand side of a different loop. Because the heat exchanger is intended to be generic, its two sides are distinguished by the nature of loop side being connected. One side is called “Loop Supply Side” to indicate the heat exchanger is situated on the supply side of a loop. The other side is called “Loop Demand Side” to indicate it is on the demand side of a loop. The heat exchanger is intended to act as a supply component for the loop connected to it as the “Loop Supply Side” and as a demand component for the loop connected to it as the “Loop Demand Side.” From the point of view of the heat exchanger model itself, the Loop Demand Side fluid serves as the source/sink to supply heating/cooling to the fluid in the Loop Supply Side.
Model Type
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Default value: Ideal
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Description: Below are the selection types for the model.
● Cross Flow Both Unmixed: Specifies a single-pass, cross-flow heat exchanger. The effectiveness will be calculated using a cross-flow heat exchanger correlation for both streams unmixed.
● Cross Flow Both Mixed: Specifies a single-pass, cross-flow heat exchanger. The effectiveness will be calculated using a cross-flow heat exchanger correlation for both streams mixed.
● Cross Flow Supply Mixed Demand Unmixed: Specifies a single-pass, cross-flow heat exchanger. The effectiveness will be calculated using a cross-flow heat exchanger correlation for flow mixed on the Loop Supply side and flow unmixed on the Loop Demand Side.
● Cross Flow Supply Unmixed Demand Mixed: Specifies a single-pass, cross-flow heat exchanger. The effectiveness will be calculated using a cross-flow heat exchanger correlation for flow unmixed on the Loop Supply side and flow mixed on the Loop Demand Side.
● Counter Flow: Specifies a counter-flow shell and tube heat exchanger. The effectiveness will be calculated using a counter-flow shell and tube heat exchanger correlation.
● Parallel Flow: Specifies a parallel-flow shell and tube heat exchanger. The effectiveness will be calculated using a parallel-flow shell and tube heat exchanger correlation.
● Ideal: Specifies an ideal heat exchanger. The effectiveness will be set to ‘1.0’ and the specified UA will be ignored. The heat transfer rate will be calculated as the maximum possible heat transfer rate.
UA Value
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Default value: Autosized
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Min & Max: 0 to no maximum
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Typical Range: 100,000 W/K; 180,000 W/F
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Units: W/K; W/°C; W/°F
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Description: This numerical field is used to specify the overall U-Factor Times Area (UA) for use in the calculation of the heat exchanger effectiveness. If Ideal is specified as the heat exchanger type, the effectiveness will be set to 1.0. When set to autosize Heat Exchanger U-Factor Times Area Value is calculated based on an effectiveness of 1.0 where capacity is such that the temperatures in the plant for the two loops can be maintained.
Control Type
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Default value: For uncontrolled HX – Uncontrolled, For HX with Controls – Cooling Setpoint Modulated, For HX Waterside Economizer – Cooling Setpoint On Off With Component Override
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Description: This field is used to specify how the heat exchanger is to be controlled during operation. Different applications for connecting two loops will require different control behavior and different control options are needed depending on the desired behavior. There are the following eleven key choice options to choose from:
1. For Heat Exchanger Uncontrolled, the options are Uncontrolled, Sequencing with Modulated Flow, Sequencing with Max Flow
2. For Heat Exchanger with Controls, the options are Cooling Setpoint Modulated, Cooling Setpoint On/Off, Dual Deadband Setpoint Modulated, Dual Deadband Setpoint On/Off, Operation Scheme Modulated, Operation Scheme On Off, Heating Setpoint Modulated, Heating Setpoint On/Off and Uncontrolled.
3. For Heat Exchanger with Waterside Economizer, the options are Cooling Differential On Off and Cooling Setpoint On Off With Component Override.
● Uncontrolled - This control mode is applicable to situations where the heat exchanger is passively running all the time and always transfers as much heat as possible between the fluid streams. However there is one aspect of control in that it will only request flow on the Loop Demand Side when there is non-zero flow into the heat exchanger on the Loop Supply Side.
● Operation Scheme Modulated - This control mode is applicable to situations where the heat exchanger is controlled by an operation scheme. When using this control mode the heat exchanger serves as a supply component. The operation scheme will dispatch a load request to the heat exchanger which it will try meet by conditioning the fluid stream connected as the Loop Supply Side. If the heat exchanger could exceed the load request, then the flow through the fluid stream connected as the Loop Demand Side will be modulated to just meet the load request.
● Operation Scheme On Off - This control mode is applicable to situations where the heat exchanger is controlled by an operation. When using this control mode the heat exchanger serves as a supply component. The operation scheme will dispatch a load request to the heat exchanger which it will use as an on/off signal to decide if the heat exchange should run or not. If it runs, it will run at full capacity and may exceed the load request.
● Heating Setpoint Modulated - This control mode is applicable to situations where the Loop Demand Side can provide useful heating to the Loop Supply Side. If the setpoint and inlet temperatures are such that heat exchanger could transfer heat from the Loop Demand Side to the Loop Supply Side to meet the heating setpoint, then the heat exchanger will run. The inlet temperatures must differ by more than the value set in the field called Minimum Temperature Difference to Activate Heat Exchanger for the heat exchanger to operate. If the heat exchanger could overshoot the setpoint, then the flow through the fluid stream connected as the Loop Demand Side will be modulated to just meet the setpoint.
● Heating Setpoint On/Off - This control mode is applicable to situations where the Loop Demand Side can provide useful heating to the Loop Supply Side. If the setpoints and inlet temperatures are such that heat exchanger could transfer heat from the Loop Demand Side to the Loop Supply Side to meet the heating setpoint, then the heat exchanger will run. The inlet temperatures must differ by more than the value set in the field called Minimum Temperature Difference to Activate Heat Exchanger for the heat exchanger to operate. If it runs, it will run at full capacity and may overshoot the setpoint.
● Cooling Setpoint Modulated - This control mode is applicable to situations where the Loop Demand Side can provide useful cooling to the Loop Supply Side. If the setpoints and inlet temperatures are such that heat exchanger could transfer heat from the Loop Supply Side to the Loop Demand Side to meet the cooling setpoint, then the heat exchanger will run. The inlet temperatures must differ by more than the value set in the field called Minimum Temperature Difference to Activate Heat Exchanger for the heat exchanger to operate. If the heat exchanger could undershoot the setpoint, then the flow through the fluid stream connected as the Loop Demand Side will be modulated to just meet the setpoint.
● Cooling Setpoint On/Off - This control mode is applicable to situations where the Loop Demand Side can provide useful cooling to the Loop Supply Side. If the setpoints and inlet temperatures are such that heat exchanger could transfer heat from the Loop Supply Side to the Loop Demand Side to meet the cooling setpoint, then the heat exchanger will run. The inlet temperatures must differ by more than the value set in the field called Minimum Temperature Difference to Activate Heat Exchanger for the heat exchanger to operate. If it runs, it will run at full capacity and may undershoot the setpoint.
● Dual Dead band Setpoint Modulated - This control mode is applicable to situations where the Loop Demand Side can provide either useful cooling or heating to the Loop Supply Side. If the setpoints and inlet temperatures are such that heat exchanger could transfer heat from the Loop Demand Side to the Loop Supply Side to meet the lower setpoint, then the heat exchanger will run. If the setpoints and inlet temperatures are such that heat exchanger could transfer heat from the Loop Supply Side to the Loop Demand Side to meet the high setpoint, then the heat exchanger will run. The inlet temperatures must differ by more than the value set in the field called Minimum Temperature Difference to Activate Heat Exchanger for the heat exchanger to operate. If the heat exchanger could overshoot the lower setpoint, or undershoot the higher setpoint, then the flow through the fluid stream connected as the Loop Demand Side will be modulated to just meet the deadband setpoint.
● Dual Dead band Setpoint On/Off - This control mode is applicable to situations where the Loop Demand Side can provide either useful cooling or heating to the Loop Supply Side. If the setpoints and inlet temperatures are such that heat exchanger could transfer heat from the Loop Demand Side to the Loop Supply Side to meet the lower setpoint, then the heat exchanger will run. If the setpoints and inlet temperatures are such that heat exchanger could transfer heat from the Loop Supply Side to the Loop Demand Side to meet the high setpoint, then the heat exchanger will run. The inlet temperatures must differ by more than the value set in the field called Minimum Temperature Difference to Activate Heat Exchanger for the heat exchanger to operate. If the heat exchanger runs, it will run at full capacity and may overshoot the lower setpoint or undershoot the higher setpoint.
● Waterside Economizer based on Differential Temperature - This control mode is applicable to situations where the Loop Demand Side can provide useful cooling to the Loop Supply Side. This mode is similar to Cooling Setpoint On/Off except that it ignores any cooling set point and its control is based only on the temperature difference between Loop Demand Side and the Loop Supply Side. The inlet temperatures must differ by more than the value set in the field called Minimum Temperature Difference to Activate Heat Exchanger for the heat exchanger to operate.
● Waterside Economizer Integrated with Chiller - This control mode is applicable to situations where the heat exchanger operation is integrated with the operation of a specific chiller. Typically the heat exchanger and chiller are in parallel. When conditions are favorable for the heat exchanger to provide cooling to the Loop Supply Side, the heat exchanger is run and the integrated chiller is turned off. When conditions are not favorable, the heat exchanger is completely off and the chiller is allowed to run as usual. If it runs it will run at full capacity and may undershoot the setpoint. The chiller that is integrated with the heat exchanger is identified by entering the name of the chiller. The setpoint and control signal temperatures must differ by more than the value set in the field called Minimum Temperature Difference to Activate Heat Exchanger for the heat exchanger to operate.
Sizing Factor
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Default value: 1.0
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Min & Max: 1 to no maximum
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Typical Range: 1.15 to 1.25
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Units: N/A
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Description: This input field over sizes the heat exchanger to handle any condition.
District Cooling
Centralized source of chilled water, such as a district cooling system.
Nominal Capacity
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Default value: Autosized
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Min & Max: 1 to no maximum
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Typical Range: N/A
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Units: W; kW; tons; Btuh; Mbh
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Description: Contains the nominal demand that the district cooling will meet. This field is autosizable.
Capacity Fraction Schedule Name
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Default value: Available 100%
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Description: This input field contains the name of a schedule that describes how the nominal capacity varies over time. The capacity at a given point in time is determined by the product of the previous field and the value in this schedule.
District Heating
Centralized source of hot water, such as a district heating system.
Nominal Capacity
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Default value: Autosized
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Min & Max: 1 to no maximum
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Typical Range: N/A
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Units: W; kW; tons; Btuh; Mbh
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Description: This numeric field contains the nominal demand that the district heating will meet. This field is autosizable.
Nominal Capacity Modifier
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Default value: Available 100%
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Description: This input field contains the name of a schedule from the Utilization / Multipliers category in the library. It describes how the nominal capacity varies over time. The capacity at a given point in time is determined by the product of the previous field and the value in this schedule.
Controls
This tab displays the controls that have been added to the loop form the Controls and sensors category of the Plant Component Selection Bar. These control strategies allow for the equipment to follow certain set point temperatures. Each control added on the Plant diagram will display its required input fields depending on the loop type it is assigned to and the following Control Strategy options.
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Schedule
This controller allows you to enter a set point temperature either as a constant or through a pre-created schedule. The required fields will vary slightly depending on the selected Set point type.
Applicable Loops - Chilled Water, Hot Water, Condenser and all Heat Exchanger loops except Mixed Water to Hot Water and Mixed Water to Chilled Water.
Set point Control Type
The two options are Constant and Variable. Constant will maintain the same value during the whole simulation period. Variable requires the definition of a schedule that defines the set point value for different time periods.
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Default value: N/A
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Constant Control Set point
This is the set point temperature to which the equipment is controlling to. This may be similar or same as the design leaving temperature. This field is only available when “Constant” is selected for the Set point Control Type.
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Default value: Cooling: 44°F; 6°C, Heating: 180°F; 82°C, Condenser 85°F; 30°C
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Min & Max: 0 to 999°F
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Typical Range: 40 to 999°F
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Units: °F; °C
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Variable Control Schedule
Here a schedule can be applied to determine at what specific hours a piece of equipment needs to meet a certain set point condition. This field is only available when “Variable” is selected for the Set point Control Type. See Temperature Setpoint Schedules for more information on how to create the schedule.
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Default value: N/A
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Water Reset based on OA
The Outdoor Air Reset Set point Manager sets the supplied water temperature according to the outdoor air temperature using a reset rule. The reset rule is determined by 2 points: the water set point temperature at the outdoor high temperature (SATOH) and the water set point temperature at the outdoor low temperature (SATOL). If the outdoor temperature is above the outdoor high temperature, the water temperature is set to SATOH. If the outdoor temperature is below the outdoor low temperature, the water temperature is set to SATOL. If the outdoor temperature is between the outdoor high and outdoor low temperatures, the water temperature is linearly interpolated between SATOH and SATOL.
Applicable Loops - Chilled Water, Hot Water, Condenser and all Heat Exchanger loops except Mixed Water to Hot Water and Mixed Water to Chilled Water.
The required fields are:
Outdoor Air Reset
Here a schedule can be applied to determine at what specific hours a piece of equipment needs to meet a certain set point condition and when the temperature is reset based on the OA condition. See Outdoor Air Reset Schedules for more information on how to create the schedule.
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Default value: N/A
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Follow OA temperature
This set point manager is used to place a temperature set point that is derived from the current outdoor air environmental conditions. The outdoor air conditions are obtained from the weather information during the simulation.
Applicable Loops - Chilled Water, Hot Water, Condenser and all Heat Exchanger loops except Mixed Water to Hot Water and Mixed Water to Chilled Water.
The required input fields are:
Reference Temperature Type
The reference temperature type is the type of temperature value that the supplied water temperature will follow. The choice is either Outdoor Dry Bulb Temperature or Outdoor Wet Bulb Temperature.
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Default value: Outdoor Air Wet Bulb
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Offset Temperature Difference
This field provides a temperature offset that will be applied to the value of the reference temperature (outdoor air wet bulb/dry bulb). If this value is zero, and the limits are met, then the resulting set point will be exactly the same as the outdoor air wet bulb/dry bulb temperature.
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Default value: 10°F
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Min & Max: -999 to 999
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Typical Range: 0 to 10
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Units: °F; °C
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Maximum Limit Setpoint Temperature
This field provides an upper limit to the resulting set point value.
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Default value: From template, Cooling: 54°F, 12°C; Condenser: 95°F, 35°C; Heating: 180°F, 82°C
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Min & Max: -999 to 999
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Typical Range: 20 to 100
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Units: °F; °C
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Minimum Limit Setpoint Temperature
This field provides a lower limit to the resulting set point value.
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Default value: From template, Cooling: 44°F, 6.6°C; Condenser: 55°F, 13°C; Heating: 120°F, 49°C
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Min & Max: -999 to 999
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Typical Range: 60 to 200
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Units: °F; °C
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Dual Setpoint
This controller is available in Mixed Water Loops. It will allow for two set point conditions in the loop – high and low. The temperature of the water loop will float in between these values and either a boiler or cooling tower will be used to maintain the set points at their respective conditions.
Applicable Loops – Mixed Water loops, Mixed Water to Hot Water Heat Exchanger loop and Mixed Water to Chilled Water Heat Exchanger loop.
The required input fields are:
Setpoint Control Type
The choices for this input are either “Variable” or “Constant”. Variable allows to a variation in controlling temperatures throughout the day whereas constant is a fixed temperature throughout the day.
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Default value: Constant
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Constant Control Low Set point
This field provides a lower limit to the set point condition. This is only available when the set point type is selected as Constant.
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Default value: 60°F
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Min & Max: -999 to 999
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Typical Range: 20 to 100
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Units: °F; °C
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Constant Control High Set point
This field provides a high limit to the set point condition. This is only available when the set point type is selected as Constant.
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Default value: 90°F
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Min & Max: -999 to 999
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Typical Range: 20 to 100
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Units: °F; °C
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Variable Control Low Setpoint
Here a schedule can be applied to determine at what specific hours a piece of equipment needs to meet the low set point water temperature condition. See Temperature Setpoint Schedules for more information on how to create the schedule.
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Default value: N/A
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Variable Control High Setpoint
Here a schedule can be applied to determine at what specific hours a piece of equipment needs to meet the high set point water temperature condition. See Temperature Setpoint Schedules for more information on how to create the schedule.
Follow Ground Temperature
This controller is used to place a temperature set point that is derived from a current ground temperature. Vertical bore heat exchangers and horizontal bore heat exchanger use deep ground temperature (Site Temperature at Depth). Pond heat exchanger uses shallow depth ground temperatures (Shallow Site Temperature).
Applicable Loops – Condenser loop.
Reference Temperature Type
The reference temperature type is the type of temperature value that the supplied water temperature will follow. The choice is either Leaving Component Dry Bulb Temperature or Leaving Component Wet Bulb Temperature.
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Default value: N/A
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Offset Temperature Difference
This field provides a temperature offset that will be applied to the value of the reference ground temperature. If this value is zero, and the limits are met, then the resulting set point will be exactly the same as the ground temperature.
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Default value: From template
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Min & Max: -999 to 999
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Typical Range: 0 to 10
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Units: °F; °C
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Maximum Limit Setpoint Temperature
This field provides an upper limit to the resulting set point value.
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Default value: From template
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Min & Max: -999 to 999
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Typical Range: 20 to 100
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Units: °F; °C
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Minimum Limit Setpoint Temperature
This field provides a lower limit to the resulting set point value.
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Default value: From template
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Min & Max: -999 to 999
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Typical Range: 60 to 200
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Units: °F; °C
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Optimized Tower
The optimized cooling tower control for water-cooled chillers resets the leaving tower water temperature (the condenser water loop temperature entering the building) to minimize the sum of chiller plus tower energy each hour. Without optimization controls (fixed set point), the cooling tower will attempt to reach the set point condition, if possible, because the compressor is more efficient at lower condenser operating temperatures. However, there is a trade-off since lowering the tower leaving temperature normally increases the tower energy consumption (unless the tower is also given a more efficient unloading curve). The chiller-tower optimizing algorithm balances the trade-off so the net energy (chiller plus tower) is less than the non-optimized solution. In optimized mode, the tower leaving temperature need not be reset to its lowest design setting, and will often be higher than the non-optimized tower control. The optimum tower leaving temperature is calculated to minimize the total energy consumption of the cooling tower and chiller, using rated tower, performance data, rated chiller performance data, the hourly load, and the outdoor air wet bulb temperature that hour. Note: For water-cooled chillers, optimization is only supported for centrifugal, helical rotary and screw compressor types.
Applicable Loops – Condenser loop, Condenser to Chilled Water Heat Exchanger loop and Condenser to Mixed Water Heat Exchanger loop.
Condenser Entering Water Temperature
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Default value: N/A
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Min & Max: -999 to 999
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Typical Range: 60 to 200
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Units: °F; °C
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Use System Defaults
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Default value: N/A
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Min & Max: -999 to 999
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Typical Range: 60 to 200
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Units: °F; °C
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Minimum Lift
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Default value: N/A
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Min & Max: -999 to 999
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Typical Range: 60 to 200
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Units: °F; °C
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Maximum Condenser Entering Water Temperature
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Default value: N/A
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Min & Max: -999 to 999
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Typical Range: 60 to 200
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Units: °F; °C
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Cooling Tower Design Inlet Air Wet-Bulb Temperature
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Default value: N/A
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Min & Max: -999 to 999
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Typical Range: 60 to 200
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Units: °F; °C
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Follow Return Temperature
This controller is used to place a temperature set point that is derived from the current loop return temperature.
Applicable Loops - Chilled Water, Hot Water, Condenser and all Heat Exchanger loops except Mixed Water to Hot Water and Mixed Water to Chilled Water.
Return Setpoint Control Type
The choices for this input are either “Variable” or “Constant”. Variable allows to a variation in controlling temperatures throughout the day whereas constant is a fixed temperature throughout the day.
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Default value: N/A
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Return Variable Control Setpoint
A schedule allow you to define variable setpoints. See Temperature Setpoint Schedules for more information on how to create the schedule.
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Default value: N/A
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Min & Max: -999 to 999
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Typical Range: 0 to 10
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Units: °F; °C
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Maximum Limit Setpoint Temperature
This field provides an upper limit to the resulting set point value.
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Default value: From template
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Min & Max: -999 to 999
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Typical Range: 20 to 100
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Units: °F; °C
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Minimum Limit Setpoint Temperature
This field provides a lower limit to the resulting set point value.
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Default value: From template
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Min & Max: -999 to 999
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Typical Range: 60 to 200
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Units: °F; °C
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Availability Manager
An availability manager sets flags telling a plant loop to turn on or off. Each type of availability manager contains a high-level on/off control strategy. The types are:
High Temperature Turn Off
This strategy is used to turn off a plant loop if a sensed node temperature exceeds the defined temperature limit. The required fields are:
Sensor Location
Sets the location of the sensor downstream of the selected equipment.
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Default value: N/A
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Temperature
The set point temperature at which the system is turned off.
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Default value: N/A
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Min & Max: -999 to 999
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Typical Range: 60 to 200
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Units: °F; °C
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High Temperature Turn On
This strategy is used to turn on a plant loop if a sensed node temperature exceeds the defined temperature limit.
Sensor Location
Sets the location of the sensor downstream of the selected equipment.
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Default value: N/A
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Temperature
The set point temperature at which the system is turned on.
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Default value: N/A
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Min & Max: -999 to 999
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Typical Range: 60 to 200
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Units: °F; °C
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Low Temperature Turn On
This strategy is used to turn on a plant loop if a sensed node temperature is below the specified temperature limit.
Sensor Location
Sets the location of the sensor downstream of the selected equipment.
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Default value: N/A
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Temperature
The set point temperature at which the system is turned on.
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Default value: N/A
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Min & Max: -999 to 999
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Typical Range: 32 to 90
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Units: °F; °C
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Low Temperature Turn Off
This strategy is used to turn off a plant loop if a sensed node temperature is below the specified temperature limit.
Sensor Location
Sets the location of the sensor downstream of the selected equipment.
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Default value: N/A
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Min & Max: N/A
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Typical Range: N/A
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Units: N/A
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Temperature
The set point temperature at which the system is turned on.
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Default value: N/A
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Min & Max: -999 to 999
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Typical Range: 32 to 90
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Units: °F; °C
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Validation Messages
Validation will be done every time equipment is dropped into the diagram as well as when properties are changed. The validation messages will show warnings or fatal errors within that particular plant section. Validation can be done by clicking the magnifying glass underneath the demand box. Once clicked, it will provide you with an explanation on why the loop did not validate and how to correct the issue. Each loop has special validation rules written.