added get_cop to heat_pump.py

oemof_heat_components/heat_pump/heat_pump.py

@@ -0,0 +1,47 @@
+# -*- coding: utf-8 -*-
+import pandas as pd
+
+def get_cop(heatbuilding, heatpump_type = "Air", water_temp = 60):
+    """ Calculation of the coefficient of performance depending
+    on the outside temperature
+
+    Parameters
+    ----------
+    heatbuilding: object
+        HeatBuilding object from demandlib.bdew countaining the index 
+        and outside temperature
+    heatpump_type: string
+        defines the technology used. Ground is more efficient than Air.
+    water_temp: int
+        temperature needed for the heating system
+
+    References
+    ----------
+    ..  [1]: 'https://www.researchgate.net/publication/255759857_A_review_of_domestic_heat_pumps'
+        Research paper about domestic heatpumps, containing the formulas used
+    """
+
+    cop_lst = []
+
+    if heatpump_type == "Air":
+        for tmp in heatbuilding.temperature:
+            cop = (6.81 - 0.121 * (water_temp - tmp)
+                   + 0.00063 * (water_temp - tmp)**2)
+            cop_lst.append(cop)
+
+    elif heatpump_type == "Ground":
+        for tmp in heatbuilding.temperature:
+            cop = (8.77 - 0.15 * (water_temp - tmp)
+                   + 0.000734 * (water_temp - tmp)**2)
+            cop_lst.append(cop)
+
+    else:
+        # TODO Raise Error
+        print("Heatpump type is not defined")
+        return None
+
+    heatbuilding.cop = pd.DataFrame({"cop" : cop_lst})
+    heatbuilding.cop.set_index(heatbuilding.df.index, inplace = True)
+
+
+    return heatbuilding.cop