Coil:Cooling:Water
Used in:
- Air Handling Units,
- Demand loops of Dual duct systems
- Four-Pipe Air Distribution Units
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Used in:
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The water cooling coil provides detailed output with simplified inputs without the need for complex coil geometry definition. Instead the coil is sized in terms of auto-sizeable thermodynamic inputs such as temperatures, mass flow rates and humidity ratios.
Coil heat transfer (UA) values are calculated from the design conditions. A rough estimate of the coil area is provided along with percentage of surface wet and/or dry. This model uses the NTU-effectiveness approach to model heat transfer and has two types of flow arrangements cross-flow or counter-flow.
See the Chilled Water Loop and FCU Tutorial
See section “Cooling Coil Model” in the EnergyPlus Engineering Document for further details on this model.
A unique name for an instance of a cooling coil which is predetermined by DesignBuilder.
The maximum possible water volume flow rate (m3/sec or gal/min) through the coil. This value is autosizable and the default is Autosize.
The maximum possible air volume flow rate (m3/sec or ft3/min) through the coil. This value is autosizable and the default is Autosize.
The inlet water temperature for the design flow (°C or °F). This value is autosizable and the default is Autosize.
The inlet air temperature for the design flow (°C or °F). This value is autosizable and the default is Autosize.
The outlet air condition desired for design flow (°C or °F). This value is autosizable and the default is Autosize.
The highest value of humidity ratio possible for the Design inlet air stream. This value is autosizable and the default is Autosize.
The value of humidity ratio for the Design outlet air stream. This value is autosizable and the default is Autosize.
The coil has two modes of operation:
The difference between the two modes being, the simple mode reports the value of surface area fraction wet of the coil as dry or wet. The detailed mode give the exact value, however the execution time in detailed mode is noticeably higher.
The coil is operable in two modes:
Air-conditioning systems generally use cross flow heat exchangers, hence the default is set to 1-Cross flow.
Schedule that defines when the coil is available, i.e. whether the coil can run during a given time period. A schedule value greater than 0 (usually 1 is used) indicates that the unit can be on during a given time period. A value less than or equal to 0 (usually 0 is used) denotes that the unit is off.
The controller allows the flow of water through the coil to be controlled based on temperature and/or humidity ratio typically downstream of the coil.
The Control variable defines how the coil is controlled. Select one of:
Options 2 and 3 (the control variables involving humidity ratio) both have these requirements:
More information is available in the Humidity control section.
The Action determines how the controlled variable (mass flow rate through a water coil) is changed based on the control signal. In a coil where water mass flow rate is to be controlled, the mass flow rate through the coil is increased when more cooling is requested. In a cooling coil, an increase in water mass flow rate through the coil decreases the value of heat transfer from the water to the air stream (absolute value increases, but since cooling is traditionally described as a negative number, an increase in absolute value results in a decrease in the actual heat transfer value). Thus the cooling coil controller has Reverse action since an increase in flow rate results in a decrease in heat transfer.
The actuator variable must currently be use the keyword 1-Flow to control the water mass flow rate.
The coil is controlled by knowing the outlet temperature and/or humidity ratio specified by the setpoint managers, and setting the outlet conditions from the coil to meet these setpoints. The chilled water coils use complex models that cannot be inverted directly. Therefore, to determine the correct mass flow rate for the cold water the models are inverted numerically using an iterative procedure. The iterative solution uses an interval-halving routine and needs a termination criteria that is set here.
The convergence tolerance is the maximum difference between the actual temperature at the setpoint node and the setpoint temperature. This control offset is typically set to a small temperature difference, such as 0.01°C.
This value is autosizable and the default is Autosize.
This is the maximum water flow (m3/sec or gal/min) through the coil. Set to the maximum design water flow for the coil.
This value is autosizable and the default is Autosize.
Set to the minimum design water flow (m3/sec or gal/min) for the water coil, normally a shut off valve that is set to zero.
Following are the list of possible output report variables from this coil model:
HVAC,Sum,Total Water Cooling Coil Energy[J]
HVAC,Sum,Sensible Water Cooling Coil Energy[J]
HVAC,Average,Total Water Cooling Coil Rate[W]
HVAC,Average,Sensible Water Cooling Coil Rate[W]
HVAC,Average,Cooling Coil Area Wet Fraction
HVAC,Average,Cooling Coil Condensate Volumetric Flow Rate [m3/s]
Zone,Meter,OnSiteWater:Facility [m3]
Zone,Meter,OnSiteWater:HVAC [m3]
Zone,Meter,Condensate:OnSiteWater [m3]
HVAC,Sum,Cooling Coil Condensate Volume [m3]
Total Water Cooling Coil Energy is the total amount of heat transfer taking place in the coil at the operating conditions.
Sensible Water Cooling Coil Energy is the total amount of Sensible heat transfer taking place in the coil at the operating conditions. It only takes into account temperature difference in the inlet and outlet air streams at operating conditions.
Total Water Cooling Coil Rate is the Rate of heat transfer taking place in the coil at the operating conditions. The units are (J/sec) or Watts.
Sensible Water Cooling Coil Rate is the Rate of Sensible heat transfer taking place in the coil at the operating conditions.
It defines the fraction of total surface area of coil which is wet due to moisture condensation
on the surface of the coil. Value varies between 0.0 and 1.0. I
n addition, if a Water Storage Tank is used to collect coil condensate, then the following outputs will be available.
These reports provide the rate and amount of condensate from the coil. Condensate is water condensed out of the air as a result of cooling. The condensate volume is also reported on the meter for “OnSiteWater.”