See the Adding loops and connecting components, Editing HVAC loop and component properties and the Condenser loops cooling tower tutorialsThe plant and condenser loop edit dialog incorporates two tabs, the first tab is General and incorporates loop characteristic and sizing data, the second tab covers Plant Equipment Operation allowing you to set up various equipment operation schemes for the loop.
See the Adding loops and connecting components, Editing HVAC loop and component properties and the Condenser loops cooling tower tutorials
If the supplied loop name is found to already exist, the software will automatically append an integer to create a unique name.
You can define the type of fluid used in the loop as a mixture of water and glycol along with the particular concentration being used. EnergyPlus will accurately model the thermal properties of the fluid based on glycol concentration and fluid temperature at each time step of the simulation.
Select the fluid type from 3 options:
When one of the glycol fluid types is selected above then you can enter the concentration of glycol in the loop fluid here. It should be entered as a decimal fraction between 0.0 and 1.0. A concentration of 0.0 refers to pure water. A concentration of 1.0 would denote 100% of the fluid referenced in the Fluid type input above.
This is the volume of the plant loop (in m3 or gal). This is the loop volume for the entire loop, i.e. both the demand side and the supply side. This is used for the loop capacitance calculation which updates the loop temperature from one time-step to the next and introduces some time delay between the supply and demand sides of the loop. The loop volume could be calculated from pipe size data but this is not usually known. If zero volume is specified the demand inlet temperature is set to the supply outlet temperature at the previous system time-step. If a very large capacitance is specified unrealistic time delay may result and there may be poor response to changes in loop setpoint temperature. If the loop volume is auto-calculated, the EnergyPlus provided calculation gives reasonable values for most system sizes. This calculation is described in the EnergyPlus Engineering Reference manual.
Two options are available:
The flow type is fixed as 1-Constant flow for DHW and condenser loops
This is the maximum allowable temperature (in °C or °F) for this loop.
This is the minimum allowable temperature (in °C or °F) for this loop.
This is the maximum loop flow rate (in m3/sec or ft3/min). This parameter is also used when the user chooses to auto-calculate the loop volume. See the Plant loop volume above and the EnergyPlus Engineering Manual for more details.
Note: This value is generally autosizable but only when the condenser loop does not contain any Vertical ground heat exchanger components. In cases where a vertical ground heat exchanger is included the Maximum loop flow rate should normally take the same value as entered on the ground heat exchanger dialog for Maximum flow rate and Design flow rate. The Condenser loop Maximum loop flow rate can be entered as higher than the ground heat exchanger flow rate but in this case it will be limited to that value during the simulation.
This is the minimum loop flow rate (in m3/sec or ft3/min).
The Load distribution scheme selects the algorithm used to sequence equipment operation in order to meet the plant loop demand. Currently, 3 schemes are functional:
The Plant loop demand calculation scheme determines the amount of heating or cooling necessary to bring the temperature of the Plant loop to its setpoint. When this value is determined then the Load distribution scheme explained in the previous section takes this value and distributes the load to the appropriate equipment. The demand calculation scheme determines how the load is calculated. See more information in the EnergyPlus Engineering Document. There are 2 plant loop demand calculation schemes:
2-DualSetPoint scheme in which the Plant loop requires that a 17-Dual setpoint SPM sets the high and low setpoint values for heating and cooling to implement a mixed water loop.
The water temperature (in °C or °F) at the exit of the supply side of the plant loop, Thus this is the temperature of the water supplied to the inlet of chilled or hot water coils in the case of plant loops or chiller condensers in the case of condenser loops.
This is the design temperature rise (for cooling or condenser loops) or fall (for heating loops) (in °C or °F) across the demand side of a plant or condenser loop.
This is the schedule that determines whether or not the Plant loop is available during the simulation. A schedule value greater than 0 (usually 1 is used) indicates that the device can be on for the timestep. A value less than or equal to 0 (usually 0 is used) denotes that the device must be off.
If you select this option you can define the external temperatures below and above which, the plant or condenser loop will turn off as a deadband. The definition is different depending on the type of plant loop as shown below.
| Loop type | External cut-in temperature | External cut-out temperature |
| Hot water plant loops | The temperature (in °C or °F) below which the plant is on. | The temperature (in °C or °F) above which the plant is forced off. |
| Chilled water and condenser plant loops | The temperature (in °C or °F) is the temperature above which the plant is on. | The temperature(in °C or °F) below which the plant is forced off. |
Note: When either of the cut-in or cut-out conditions occurs they override the availability schedule. For example in the case of a hot water loop, when the Outside temperature operation check box is selected, if the outside air dry-bulb temperature is below the External cut-in temperature then the loop is cycled on (it is available) or if it is above the External cut-out temperature then the loop availability is forced off (not available), otherwise the loop availability is controlled by the Availability schedule alone.
Plant and condenser loops have a mechanism for controlling the operation of the loop to allow control over which equipment is available under what conditions. Since there may be multiple control schemes that are assigned various priorities associated with each loop, an overall operation scheme must be defined. Each operation scheme must have the type of operation scheme together with the name of the scheme and the schedule that defines its availability.
Note: The order in which the individual operation schemes appear in this list defines its priority relative to the others with the same scheduled availability. The first scheme appearing in the list is given the highest priority; the second scheme has second highest priority, etc. In other words, if according to its schedule, the first operation scheme is available, then it is used by the simulation to define how the plant or condenser loop operates. If it is not available, the second operation scheme in the list is checked to see if it is available until the highest priority scheme that is also available is found. To allow for simultaneous heating and cooling, there is one configuration where multiple operation schemes are available at a given timestep. This is allowed if a user inputs both a heating range based operation and a cooling range based operation with overlapping schedules. The simulation will look at the current loop demand to determine if the cooling scheme should be used or the heating scheme. In other cases, if two schemes overlap (are available at the same time), EnergyPlus will raise an error and the simulation will be aborted.
This is the number of operational schemes that are to be associated with the plant or condenser loop. A maximum of ten schemes are allowed for each loop. After setting the required number of schemes, the dialog will be automatically populated with sections for each scheme, the settings for each operation scheme being described below.
This is the type of control scheme used. The available options will depend on the current loop type. For condenser and chilled water plant loops, the options are:
for heating and domestic hot water plant loops, the options are:
for chilled water loops with Ice thermal storage components included, 2 further Scheme operation types are allowed:
Uncontrolled loop operation simply specifies a group of equipment that runs ‘uncontrolled’. If the loop runs, this equipment will run also, unless turned off by the loop flow resolver to maintain continuity in the fluid loop.
The 2‑Cooling load and 3‑Heating load options allow different load ranges to be defined and which items of equipment will operate for each range. If either of these options is selected, at least one operational range must be defined. For each range, there is a lower limit for the load range, an upper limit for the load range, and a list of the equipment items that will operate in this range.
This setting is only displayed if the Scheme operation type is set to 1-Uncontrolled. A list of valid items of plant or condenser equipment is displayed together with check boxes allowing you to define which items of equipment will be turned on for this scheme.
This is the schedule for the control scheme. This schedule consists of weeks and days, with the days containing “0 or 1” for each hour of the day. This binary schedule (0 for off, 1 for on) determines if the control scheme is operating for that hour of the day or not.
This setting is only displayed if the Scheme Operation Type is set to 2‑Cooling load or 3‑Heating load and is used to define the number of ranges required for the heating or cooling load scheme.
This setting is only displayed if the Scheme Operation Type is set to 2‑Cooling load or 3‑Heating load. This is the lower demand range (W) for the equipment defined for the current range. If demand is below this value, then the equipment will not turn on to meet the demand.
This setting is only displayed if the Scheme Operation Type is set to 2‑Cooling load or 3‑Heating load. This is the upper demand range (W) for the equipment defined for the current range. If demand is above this value, then the equipment will not turn on to meet the demand.
A list of valid items of plant or condenser equipment is displayed together with check boxes allowing you to define which items of equipment will be turned on for this range. This setting is only displayed if the Scheme Operation Type is set to 2‑Cooling load or 3‑Heating load.
Note: A priority drop-list associated with each item of equipment allows you to define the order in which equipment will be turned on when the loop demand is within this range.