Coil:Heating:DX:SingleSpeed
Used in:
- PTAC,
- PTHP,
- Generic AHU,
- Unitary Heat Pump AHU
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Used in:
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The single speed heating DX coil model uses performance information at rated conditions along with curve fits for variations in total capacity, energy input ratio and part load fraction to determine performance at part-load conditions. The impacts of various defrost strategies (reverse cycle, resistive, timed or on-demand) are modelled based on a combination of user inputs and empirical models taken from the air-to-air heat pump algorithms in DOE-2.1E.
This alpha field defines a unique user-assigned name for an instance of a DX heating coil. Any reference to this DX heating coil by another object will use this name.
This numeric field defines the total, full load heating capacity (in W or Btu/h) of the DX coil unit at rated conditions (outdoor air dry-bulb temperature of 8.33°C, outdoor air wet-bulb temperature of 6.11°C, heating coil entering air dry-bulb temperature of 21.11°C, heating coil entering air wet-bulb temperature of 15.55°C, and a heating coil air flow rate defined by field “rated air flow volume” below). The value entered here must be greater than 0. Capacity should not include supply air fan heat. Rated total heating capacity should be within 20% of the Rated total cooling capacity, otherwise a warning message is issued.
This numeric field defines the volume air flow rate (in m3/s or ft3/min), across the DX heating coil at rated conditions. The value entered here must be greater than 0. The rated air volume flow rate should be between 0.00004027 m3/s and 0.00006041 m3/s per watt of rated total heating capacity. The Rated total heating capacity and Rated COP should be performance information for the unit with outdoor air dry-bulb temperature of 8.33°C, outdoor air wet-bulb temperature of 6.11°C, heating coil entering air dry-bulb temperature of 21.11°C, heating coil entering air wet-bulb temperature of 15.55°C, and the rated air volume flow rate defined here.
This numeric field defines the coefficient of performance (COP=heating power output in watts divided by electrical power input in watts) of the DX heating coil unit at rated conditions (outdoor air dry-bulb temperature of 8.33°C, outdoor air wet-bulb temperature of 6.11°C, coil entering air dry-bulb temperature of 21.11°C, coil entering air wet-bulb temperature of 15.55°C, and a heating coil air flow rate defined by field “rated air flow volume rate” below). The value entered here must be greater than 0. The input power includes power for the compressor(s) and outdoor fan(s) but does not include the power consumption of the indoor supply air fan. The heating power output is the value entered above in the field Rated total heating capacity.
This numeric field defines the minimum outdoor air dry-bulb temperature (in °C or °F) where the heating coil compressor turns off. The temperature for this input field must be greater than or equal to –20°C. The default value is -8°C.
Choose from two options:
If the reverse-cycle strategy is selected, the heating cycle is reversed periodically to provide heat to melt frost accumulated on the outdoor coil. If a resistive defrost strategy is selected, the frost is melted using an electric resistance heater. The default defrost strategy is reverse-cycle.
Choose from two options:
If timed control is selected, the defrost time period is calculated based on a fixed value or compressor runtime whether or not frost has actually accumulated. For timed defrost control, the fractional amount of time the unit is in defrost is entered in the input field Defrost time period fraction described below. If on-demand defrost control is selected, the defrost time period is calculated based on outdoor weather (humidity ratio) conditions. Regardless of which defrost control is selected, defrost does not occur above the user specified outdoor temperature entered in the input field Maximum outdoor dry-bulb temperature for defrost operation described above.
This numeric field defines the fraction of compressor runtime when the defrost cycle is active, and only applies to “timed” defrost (see Defrost Control input field above). For example, if the defrost cycle is active for 3.5 minutes for every 60 minutes of compressor runtime, then the user should enter 3.5/60 = 0.058333. The value for this input field must be greater than or equal to 0. The default value is 0.058333.
This numeric field defines the capacity of the resistive defrost heating element (in W). This input field is used only when the selected defrost strategy is ‘resistive’ (see input field Defrost strategy above). The value for this input field must be greater than or equal to 0.
This numeric field defines the outdoor air dry-bulb temperature (in °C or °F) above which outdoor coil defrosting is disabled. The temperature for this input field must be greater than or equal to 0 C and less than or equal to 7.22°C. The default value is 5°C.
The DX Cooling coil requires up to 6 curves be selected from the Curves database to define coil performance depending on the defrost strategy selected.
The Bi-quadratic, Quadratic or Cubic performance curve that parameterises the variation of the total heating capacity as a function of the both the indoor and outdoor air dry-bulb temperature or just the outdoor air dry-bulb temperature depending on the type of curve selected. The bi-quadratic curve is recommended if sufficient manufacturer data is available as it provides sensitivity to the indoor air dry-bulb temperature and a more realistic output. The output of this curve is multiplied by the rated total heating capacity to give the total heating capacity at specific temperature operating conditions (i.e., at an indoor air dry-bulb temperature or outdoor air dry-bulb temperature different from the rating point temperature). The curve is normalised to have the value of 1.0 at the rating point.
The Quadratic or Cubic performance curve that parameterises the variation of total heating capacity as a function of the ratio of actual air flow rate across the heating coil to the rated air flow rate (i.e., fraction of full load flow). The output of this curve is multiplied by the rated total heating capacity and the total heating capacity modifier curve (function of temperature) to give the total heating capacity at the specific temperature and air flow conditions at which the coil is operating. The curve is normalised to have the value of 1.0 when the actual air flow rate equals the rated air flow rate.
The Bi-quadratic, Quadratic or Cubic performance curve that parameterises the variation of the energy input ratio (EIR) as a function of the both the indoor and outdoor air dry-bulb temperature or just the outdoor air dry-bulb temperature depending on the type of curve selected. The bi-quadratic curve is recommended if sufficient manufacturer data is available as it provides sensitivity to the indoor air dry-bulb temperature and a more realistic output. The EIR is the inverse of the COP. The output of this curve is multiplied by the rated EIR (inverse of rated COP) to give the EIR at specific temperature operating conditions (i.e., at an indoor air dry-bulb temperature or outdoor air dry-bulb temperature different from the rating point temperature). The curve is normalised to have the value of 1.0 at the rating point.
The Quadratic or Cubic performance curve that parameterises the variation of the energy input ratio (EIR) as a function of the ratio of actual air flow rate across the heating coil to the rated air flow rate (i.e., fraction of full load flow). The EIR is the inverse of the COP. The output of this curve is multiplied by the rated EIR and the EIR modifier curve (function of temperature) to give the EIR at the specific temperature and air flow conditions at which the coil is operating. This curve is normalised to a value of 1.0 when the actual air flow rate equals the rated air flow rate.
The Quadratic or Cubic performance curve that parameterises the variation of electrical power input to the DX unit as a function of the part load ratio (PLR, sensible heating load/steady-state sensible heating capacity). The product of the rated EIR and EIR modifier curves is divided by the output of this curve to give the “effective” EIR for a given simulation timestep. The part load fraction (PLF) correlation accounts for efficiency losses due to compressor cycling.
The 2 important rules to be followed when setting up this curve are:
The Bi-quadratic performance curve that parameterises the variation of the energy input ratio (EIR) during reverse-cycle defrost periods as a function of the outdoor air dry-bulb temperature and the wet-bulb temperature of the air entering the indoor coil. The EIR is the inverse of the COP. The output of this curve is multiplied by the coil capacity, the fractional defrost time period and the runtime fraction of the heating coil to give the defrost power at the specific temperatures at which the indoor and outdoor coils are operating. This curve is only required when a reverse-cycle defrost strategy is selected. The curve is normalised to a value of 1.0 at the rating point conditions.
This numeric field defines the crankcase heater capacity (in W). When the outdoor air dry-bulb temperature is below the value specified in the input field Maximum outdoor dry-bulb temperature for crankcase heater operation” (described below), the crankcase heater is enabled during the time that the compressor is not running. If this heating coil is used as part of an air-to-air heat pump (Ref. UnitarySystem:HeatPump:AirToAir or PackageTerminal: HeatPump:AirToAir), the crankcase heater defined for this DX heating coil is enabled during the time that the compressor is not running for either heating or cooling (and the crankcase heater power defined in the DX cooling coil object is disregarded in this case). The value for this input field must be greater than or equal to 0. The default value is 0. To simulate a unit without a crankcase heater, enter a value of 0.
This numeric field defines the outdoor air dry-bulb temperature (in °C or °F) above which the compressor’s crankcase heater is disabled. The value for this input field must be greater than or equal to 0.0 C.
The schedule that denotes whether the DX heating 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 must be off.
HVAC,Average,DX Coil Total Heating Rate[W]
HVAC,Sum,DX Coil Total Heating Energy[J]
HVAC,Average,DX Heating Coil Electric Power[W]
HVAC,Sum,DX Heating Coil Electric Consumption[J]
HVAC,Average,DX Heating Coil Electric Defrost Power[W]
HVAC,Sum,DX Heating Coil Electric Defrost Consumption[J]
HVAC,Average,DX Heating Coil Crankcase Heater Power[W]
HVAC,Sum,DX Heating Coil Crankcase Heater Consumption[J]
HVAC,Average,DX Heating Coil Runtime Fraction
This field is the total heating rate output of the DX coil in Watts. This is determined by the coil inlet and outlet air conditions and the air mass flow rate through the coil.
This is the total heating output of the DX coil in Joules over the timestep being reported. This is determined by the coil inlet and outlet air conditions and the air mass flow rate through the coil. This output is also added to a report meter with Resource Type = EnergyTransfer, End Use Key = CoolingCoils, Group Key = System (ref. Report Meter).
This output is the electricity consumption rate of the DX coil compressor and outdoor fan(s) in Watts. This rate is applicable when the unit is providing heating to the conditioned zone(s), and excludes periods when the unit is in reverse-cycle defrost mode.
This is the electricity consumption of the DX coil compressor and condenser fan(s) in Joules for the timestep being reported. This consumption is applicable when the unit is providing heating to the conditioned zone(s), and excludes periods when the unit is in reverse-cycle defrost mode. This output is also added to a report meter with Resource Type = Electricity, End Use Key = Cooling, Group Key = System (ref. Report Meter).
This is the electricity consumption rate of the DX coil unit in Watts when the unit is in defrost mode (reverse-cycle or resistive).
This is the electricity consumption of the DX coil unit in Joules for the timestep being reported. This consumption is applicable when the unit is in defrost mode (reverse-cycle or resistive).
This is the average electricity consumption rate of the DX coil compressor’s crankcase heater in Watts for the timestep being reported.
This is the electricity consumption of the DX coil compressor’s crankcase heater in Joules for the timestep being reported. This output is also added to a report meter with Resource Type = Electricity, End Use Key = Miscellaneous, Group Key = System (ref. Report Meter).
This is the runtime fraction of the DX heating coil compressor and outdoor fan(s) for the timestep being reported.