Chiller

Create Controlled Function

pandaprosumer.create_controlled_chiller(prosumer, cp_water=4.18, t_sh=5.0, t_sc=2.0, pp_cond=5.0, pp_evap=5.0, plf_cc=0.9, w_evap_pump=200.0, w_cond_pump=200.0, eng_eff=1.0, n_ref='R410A', name=None, index=None, in_service=True, period=0, level=0, order=0, **kwargs)[source]

Creates a chiller element in prosumer[“chiller”] and a chiller controller.

INPUT:

prosumer - The prosumer within which this chiller should be created.

max_q_kw (float) - Maximal cooling power of the chiller [kW].

OPTIONAL:

cooling_value_kj_per_kg (float, default 200e3) - Cooling Value of the refrigerant [kJ/kg].

efficiency_percent (float, default 100) - Chiller Efficiency [%].

name (string, default None) - The name for this chiller.

index (int, default None) - Force a specified ID if it is available. If None, the index one higher than the highest already existing index is selected.

in_service (boolean, default True) - True for in_service or False for out of service.

level (int, default 0) - The level of the controller.

order (int, default 0) - The order of the controller.

period (int, default 0) - Index of the period, default is 0.

OUTPUT:

index (int) - The unique ID of the created chiller.

EXAMPLE:

create_controlled_chiller(prosumer, “chiller_1”)

Controller

graphical representation here

Input Static Data

Parameter	Description	Unit
fluid_cp	Fluid specific heat capacity	kJ/kg.K
superheating_temp	Superheating temperature	°C
subcooling_temp	Subcooling temperature	°C
condenser_pinch	Condenser Pinch point	delta °C
evaporator_pinch	Evaporator Pinch point	delta °C
cd_coefficient	Cd Coefficient
evap_pump_power	Evaporator pump power	kJ/h
cond_pump_power	Condenser pump power	kJ/h
motor_efficiency	Motor efficiency
refrigerant_fluid	Refrigerant fluid

Input Time Series

Parameter	Description	Unit
time_series_file	Name of the file containing the time histories
setpoint_temp_col	Column header of Set point temperature	K
evap_inlet_temp_col	Column header of Evaporator inlet temperature	K
cond_inlet_temp_col	Column header of Condenser inlet temperature	K
cond_temp_increase_col	Column header of Condenser temp. increase	delta °C
cooling_demand_col	Column header of Cooling demand	kJ/h
isentropic_eff_col	Column header of Isentropic efficiency
max_chiller_power_col	Column header of Maximum chiller power	kJ/h
control_signal_col	Column header of Control signal

Output Time Series

Parameter	Description	Unit
delivered_power_chiller	Delivered power by chiller	kJ/h
unmet_demand	Unmet cooling demand	kJ/h
compressor_power	Compressor power consumption	kJ/h
eer	Energy Efficiency Ratio
plr	Part Load Ratio
evaporator_temp	Evaporator temperature	K
condenser_temp	Condenser temperature	K
evaporator_flow	Evaporator flow rate	kg/h
condenser_flow	Condenser flow rate	kg/h
evaporator_power	Evaporator power consumption	kJ/h

Mapping

The Compression Chiller model uses Generic Mapping Scheme.

Model

The model first checks whether the chiller is on. For the chiller to be on, all of the following conditions must be met:

The control signal is greater than 0.5.
The cooling demand is greater than 0.
The evaporator set point temperature is greater than the evaporator inlet temperature.

If these conditions are satisfied, a simple refrigeration cycle is calculated from the input data.

Evaporating Temperature

The model considers four possible pinch points — two in the evaporator and two in the condenser — located as shown in the referenced figure (Figure 8). In this figure:

\(Q_c\) refers to the cooling energy.
\(Q_h\) refers to the heating energy.

The evaporating temperature is determined by evaluating the two evaporator pinch points (inlet and outlet):

\[T_{evap} = \min(T_{set} - PP_{evap}, T_i - T_{SH} - PP_{evap}) \tag{15}\]

Where:

\(T_{set}\) : heat pump set point temperature
\(PP_{evap}\) : pinch point in the evaporator
\(T_i\) : evaporator inlet water temperature
\(T_{SH}\) : superheating temperature

With this temperature and saturation conditions, the evaporating pressure \(P_{evap}\) is obtained via CoolProp.

Condensing Temperature

The condensing temperature is calculated based on the pinch point at the condenser outlet:

\[T_{cond} = T_{in,cond} + \Delta T_{cond} + PP_{cond} + T_{SC} \tag{16}\]

Where:

\(T_{in,cond}\) : water temperature at condenser inlet
\(\Delta T_{cond}\) : temperature increase in condenser
\(PP_{cond}\) : pinch point on the condenser
\(T_{SC}\) : subcooling temperature

This temperature may later be corrected to ensure pinch conditions on the steam saturation line are met.

Compressor Inlet and Isentropic Compression

The refrigerant conditions at the compressor inlet are determined using:

\(T = T_{evap} + T_{SH}\)
\(P = P_{evap}\)

From this, CoolProp is called to compute thermodynamic properties.

To determine the isentropic compression conditions, CoolProp is called with the inlet entropy and condensing pressure.

The enthalpy at the compressor discharge is calculated as:

\[h_{dis} = h_{suc} + \frac{h_{is} - h_{suc}}{\eta_{is}} \tag{17}\]

Where:

\(h_{dis}\) : enthalpy at compressor discharge
\(h_{suc}\) : enthalpy at compressor inlet
\(h_{is}\) : enthalpy of isentropic compression
\(\eta_{is}\) : isentropic efficiency of the compressor

CoolProp is again called with this discharge enthalpy and condensing pressure to obtain the discharge conditions.

Condenser Outlet Conditions

Condenser outlet conditions are computed with:

\(T = T_{cond} - T_{SC}\)
\(P = P_{cond}\)

Where \(T_{SC}\) is the degrees of subcooling.

Heat Production and Flow Rates

To calculate condenser and refrigerant flow rates, the demand is limited to the available pump power:

\[\dot{Q}_{loadef} = \min(\dot{Q}_{load}, P_{nom}) \tag{18}\]

Where:

\(\dot{Q}_{load}\) : heat demand (input 5)
\(P_{nom}\) : effective power of the heat pump under current conditions (input 7)
\(\dot{Q}_{loadef}\) : heat production at the current timestep

The refrigerant flow rate is then calculated using this effective load.

\[\dot{m}_{ref} = \frac{\dot{Q}_{load\_ef}}{h_{suc} - h_{cond\_out}} \tag{19}\]

where:

\(\dot{m}_{ref}\): refrigerant flow rate
\(h_{suc}\): enthalpy at compressor inlet
\(h_{cond\_out}\): enthalpy at condenser outlet

Condenser-side water mass flow rate is:

\[\dot{m}_{cond} = \frac{\dot{Q}_{load\_ef}}{C_{p,water} \cdot \Delta T_{cond}} \tag{20}\]

where:

\(\dot{m}_{cond}\): condenser water flow rate
\(\Delta T_{cond}\): temperature rise in the condenser (water side)

To verify the condenser-side pinch point above the dew line, the refrigerant enthalpy at saturation vapor (dew) point is obtained using:

\(P = P_{cond}\)

\(Q = 1\)

to get enthalpy \(h_{bub}\). Then, water temperature at this pinch point is:

\[T_{bub} = T_{in,cond} + \frac{\dot{m}_{ref} \cdot (h_{bub} - h_{cond\_out})}{C_{p,agua} \cdot \dot{m}_{cond}} \tag{21}\]

The pinch condition is then checked:

\[T_{bub} + PP_{cond} > T_{cond}\]

If this condition is met, the condenser temperature is redefined:

\[T_{cond} = T_{bub} + PP_{cond} \tag{22}\]

The cycle is then recalculated starting again from the compressor inlet.

Compressor power consumption:

\[W_{in,c} = \frac{\dot{m}_{ref} \cdot (h_{dis} - h_{suc})}{\eta_{mec}} \tag{23}\]

where:

\(\eta_{mec}\): motor or frequency converter efficiency

Partial load ratio:

\[PLR = \frac{\dot{Q}_{load}}{\dot{Q}_{max}} \tag{24}\]

Partial load factor (UNE14825 correction):

\[PLF = PLR \cdot (PLF_{CC} \cdot PLR) + (1.0 - PLF_{CC}) \tag{25}\]

Final heat pump power consumption:

\[W_{in} = W_i \cdot PLF \tag{26}\]

Pump consumption:

\[W_{Pu} = PLR \cdot (EvPuPw + CondPuPw) \tag{27}\]

Total consumption:

\[W_i = W_{in} + W_{Pu} \tag{28}\]

Condenser and evaporator powers:

\[\dot{q}_{cond} = \dot{m}_{ref} \cdot (h_{dis} - h_{cond}) \tag{29}\]

\[\dot{q}_{evap} = \dot{m}_{ref} \cdot (h_{suc} - h_{cond}) \tag{30}\]

Flow rates from energy balances:

\[\dot{m}_{cond} = \frac{\dot{q}_{cond}}{C_{p,water} \cdot T_{in}} \tag{31}\]

\[\dot{m}_{evap} = \frac{\dot{q}_{evap}}{C_{p,water} \cdot (T_{in} - T_{set})} \tag{32}\]

Output temperatures:

\[T_{out,cond} = T_{in,cond} + \frac{\dot{q}_{cond}}{C_{p,water} \cdot \dot{m}_{cond}} \tag{33}\]

\[T_{out,evap} = T_{in,evap} - \frac{\dot{q}_{evap}}{C_{p,water} \cdot \dot{m}_{evap}} \tag{34}\]

Unmet demand:

\[Unmet\ demand = \dot{q}_{load} - \dot{q}_{evap} \tag{35}\]

Compressor thermal losses:

\[Q_t = \frac{\dot{m}_{ref} \cdot (h_{dis} - h_{suc})}{\eta_{mec}} \cdot q_{loss} \tag{36}\]

Energy Efficiency Ratio (EER):

\[EER = \frac{\dot{q}_{evap}}{W_i} \tag{37}\]