add suggestion for ventilation class structure

CARA/temporary_ventilation.py

+from dataclasses import dataclass
+from abc import abstractmethod
+import numpy as np
+
+
+@dataclass(frozen=True)
+class Ventilation:
+
+    @abstractmethod
+    def air_exchange(self, room, time: float) -> float:
+        pass
+
+
+@dataclass(frozen=True)
+class PeriodicWindow(Ventilation):
+
+    period: int
+    duration: int
+    inside_temp: float
+    outside_temp: float
+    window_height: float
+    opening_length: float
+    cd_b: float
+
+    def air_exchange(self, room, time: float) -> float:
+        if time % self.period < (self.period - self.duration):
+            return 0
+
+        return ((3600 / 3 * room.volume) * self.cd_b * self.window_height *
+                self.opening_length * np.sqrt(9.81 * self.window_height * (abs(self.inside_temp - self.outside_temp))
+                                              / self.outside_temp))
+
+
+@dataclass(frozen=True)
+class PeriodicHEPA(Ventilation):
+
+    period: int
+    duration: int
+    q_air_mech: int
+
+    def air_exchange(self, room, time: float) -> float:
+        if time % self.period < (self.period - self.duration):
+            return 0
+
+        return self.q_air_mech / room.volume
+
+