ThermalStorage:ChilledWater:Stratified
Used in:
Supply side of Chilled Water Loops
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ThermalStorage:ChilledWater:Stratified
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Used in:
Supply side of Chilled Water Loops |
The Stratified Chilled Water Storage component divides the water tank into multiple nodes of equal volume. The nodes are coupled by vertical conduction effects, internode fluid flow, and temperature inversion mixing. It simultaneously solves the differential equations governing the energy balances on the nodes using a numerical method. The system timestep is divided into many small substeps that allow the simulation to capture events that occur on a very short time scale. The chilled water is “used” by drawing from the “Use Side” of the water tank. The tank is indirectly charged by circulating cold water through the “Source Side” of the water tank. Control is based on cycling flow through the source side. When the tank temperature rises above a “cut-in” temperature, source side flow is requested. Source side flow will continue until the tank is cooled to below the tank set point or “cut-out” temperature.
For heat gains from the ambient environment, the ambient air temperature can be taken from a schedule, a zone, or the exterior. When used with a zone, the skin gains are removed from the zone heat balance as negative internal heat gains.
See also:
The name of the Chilled water storage tank.
Select the type of Chilled water storage tank from the list:
For a discussion of the applications, advantages and disadvantages of the two water heater types see the Chilled Water Storage overview topic.
The Nominal cooling capacity describes the typical cooling capacity that the chilled water tank will provide (in W or Btu/h). Since this is a passive device, the actual cooling capacity depends on water temperatures and flow rates. However, this field is used to describe the chilled water tank’s nominal cooling capacity for supervisory control where plant operation schemes require a cooling capacity to model how equipment is dispatched.
This field is used to autosize the Source Side Design Flow Rate. The field is used if the Source side design flow rate is set to Autosize and the water tank’s source side is on the demand side of a plant loop. This is the time, in hours, that the chilled water tank is to be indirectly cooled from 14.4ºC to 9.0ºC using the Design loop exit temperature of in the associated Plant loop.
The volume of the storage tank (in m3 or gal).
The height of the tank (in m or in).
For the 2-Horizontal cylinder tank shape (see below) the height of the tank is the measure in the axial direction, i.e., the height if you were to stand the cylinder up on its end. This field is autosizable.
The tank shape determines the size and skin losses of the stratified nodes. There are two options:
Select the schedule which specifies the chilled water temperature setpoint (in °C). This setting is also known as the “cut-out” temperature.
The delta temperature difference (in Delta °C or Delta °F) between the setpoint and the “cut-in” temperature at which the storage tank will request cooling. In other words, the “cut-in” temperature is Setpoint + Deadband.
The temperature (in °C or °F) at which the tank water becomes too cold. No source side flow is allowed when the tank temperature is below this limit. The minimum temperature must be lower than the setpoint temperature at all times.
This setting is used to describe the location in the tank where the temperature is sensed for control decisions. The program will associate one of the nodes with this height and use that node’s temperature for control decisions. The location is described from the bottom of the tank (in m or in).
The Ambient temperature indicator specifies how the ambient air temperature will be indicated. Select from:
Select schedule which specifies the ambient air temperature around the tank for skin gains. This field is only used if the 1-Schedule Ambient temperature indicator is used.
Select the zone specifying the ambient air temperature around the tank for skin gains. This field is only used if the 2-Zone Ambient temperature indicator is used.
The gain coefficient from the ambient air temperature (in W/K or Btu/h-°F) . This coefficient is often referred to as the UA for the overall tank thermal performance with respect to heat gains from the tank’s skin.
This field specifies the heat transfer effectiveness between the use side water and the tank water. If the effectiveness is set to 1 then complete heat transfer occurs, simulating perfect mixing of the use side water and the tank water. If the effectiveness is lower, then the use side outlet water temperature will not be as cold as the tank water, simulating a heat exchanger.
Select the availability schedule for the use side of the water tank. If the schedule’s value is 0.0, then the use side is not available and flow will not be requested. If the schedule’s value is not equal to 0.0 (usually 1 is used), the use side is available.
This autosizable setting is used to specify the design flow rate through the use side of the chilled water tank (in m3/s or gal/min). For autosized tanks, sizing results are reported in the EIO file.
The height of the use side inlet to the tank (in m or in). Normally this value will be the same as or close to the height of the tank and cannot be higher than the tank height. A value of autocalulate sets the Use side inlet height to the height of the tank.
The height of the use side outlet from the tank (in m or in). The outlet height cannot be higher than the tank height.
This field specifies the heat transfer effectiveness between the source side water and the tank water. If the effectiveness is set to 1 then complete heat transfer occurs, simulating perfect mixing of the source side water and the tank water. If the effectiveness is lower, then the source side outlet water temperature will not be as cold as the tank water, simulating a heat exchanger.
This field contains the name of an availability schedule for the source side of the water tank. If the schedule’s value is 0.0, then the source side is not available and flow will not be requested. If the schedule’s value is not equal to 0.0 (usually 1 is used), the source side is available.
This autosizable setting is used to specify the design flow rate through the source side of the chilled water tank (in m3/s or gal/min). Sizing results are reported in the EIO file.
The height of the source side inlet to the tank (in m or in). The inlet height cannot be higher than the tank height.
The height of the source side outlet from the tank (in m or in). The outlet height cannot be higher than the tank height. A value of autocalulate sets the Source side outlet height to the height of the tank.
The inlet mode of entering fluid from the use and source sides. There are two options:
An additional destratification conductivity (in W/m-K or Btu-in/h-ft2-°F) is added to the fluid conductivity of water (0.6 W/m-K) to account for vertical conduction effects along the inside of the tank wall, and perhaps other vertical components such as a dip tube pipe or anode rod.
The number of stratified nodes in the tank. There must be at least one node. The maximum number of nodes is 10, although this limit can be increased by editing the IDD.
An additional heat gain coefficient (in W/K or Btu/h-°F) added to the skin gains for each node to account for thermal shorting due to pipe penetrations, tank feet, and any other loss effects.