Coil:Heating:Water
Used in:
- Air Handling Units
- Demand loops of Dual duct systems
- Air Distribution Units
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Used in:
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The simple water heating coil model provides sensible heating of the air. The calculations use the Effectiveness-NTU algorithm and assume a cross-flow heat exchanger.
An auto-generated name for the heating coil.
The type of a hot water coil must be:
In all cases it will also be possible to select 2-Electric in which case the Electric heating coil is used or 3-Fuel where the Fuel heating coil is used instead.
The user can choose one of:
If the 2-UA and Design water flow rate option is selected, you must input values for UA of the Coil and Max water flow rate of the Coil. If 1-Nominal capacity is chosen you must input a Rated capacity and UA of the Coil.
Rated capacity is defined as the heating capacity in watts of the coil at the rating points (i.e. the rated inlet and outlet water/air temperatures defined below). The rated capacity is used to calculate a water mass flow rate and a UA for the coil. The default is 1-Nominal capacity.
To autosize the capacity, choose 2-UA and Design water flow rate and use autosize as the inputs for UA, Maximum water flow rate, and Rated capacity. EnergyPlus will use the Sizing inputs to size the coil. The rated temperatures (see below) are not used in autosizing. These are used only when the user is specifying coil performance using the 1-Nominal capacity input method.
The maximum possible water flow rate (m3/sec or gal/min) through the coil. This field is used when Performance input method = 2-UA and Design water flow rate. This field is autosizable.
Enter the UA value for the coil needed for the Effectiveness-NTU heat exchanger model. An estimate of the UA can be obtained from:
where:
q is the heat transferred from water to the air in W;
Twater, avg is the average water temperature in °C; and
Tair, avg is the average air temperature in ° C. Or the LMTD temperature difference can be used. This field is only used when Performance input method = 2-UA and Design water flow rate
This field is autosizable.
The heating capacity of the coil (in W or Btu/h) at the rated inlet and outlet air and water temperatures. This field is used when the Performance input method = 1-Nominal capacity. This field is autosizable. The rating points are given in the four subsequent input fields.
The inlet water temperature (°C or °F) corresponding to the rated heating capacity. The default is 82.2°C (180°F).
The outlet water temperature (°C or °F) corresponding to the rated heating capacity. The default is 71.1°C (160°F)
The inlet air temperature (°C or °F) corresponding to the rated heating capacity. The default is 16.6°C (60°F)..
The outlet air temperature (°C or °F) corresponding to the nominal heating capacity. The default is 32.2°C (90°F).
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 Control variable defines how the coil is controlled. Temperature control is currently the only option.
The Action determines how the controlled variable (e.g. mass flow rate through a water coil) is changed based on the control signal. In a heating coil where water mass flow rate is to be controlled, the mass flow rate through the coil is increased when more heating is required, which increases the value of heat transfer from the water to the air stream. So this is considered a "normal" action controller and so the value of this field is fixed as 1-Normal.
This was again meant to be more generic but currently has only been used to control the water mass flow rate of a heating or cooling coil. This actuator variable is fixed as 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 hot water coils use complex models that cannot be inverted directly. Therefore, to determine the correct mass flow rate 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. 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.
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.
This is the ratio of convective heat transfers between air side and water side of the heating coil at the rated operating conditions. The default is 0.5. This ratio describes the geometry and the design of the coil and is defined by:
where 
is the fin efficiency
h is the surface convection heat transfer coefficient
A is the surface area
HVAC,Sum, Total Water Heating Coil Energy[J]
HVAC,Average,Total Water Heating Coil Rate[W]
HVAC,Average,Water Heating Coil U-factor Times Area [W]
Total Water Heating Coil Energy is the total amount of heat transfer taking place in the coil at the operating conditions.
Total Water Heating Coil Rate is the Rate of heat transfer taking place in the coil at the operating conditions. The units are (J/sec) or Watts.
This characterizes the overall heat transfer “UA” value, or U-factor times Area. The simple heating coil model adjusts UA value based on inlet temperatures and flow rates and this