Water consumption, energy consumption and velocity

The window cleaning robot is supplied with water by means of a water tank, and the capacity of the water tank is supposed to be sufficient to be able to clean a window without interruptions.

There are a few decisions and assumptions that had to be made in order to model the water consumption. The water consumption of the robot for a time step is taken to be 1/8640 L/s. This specific value for the water consumption is determined by looking at the amount of water a window washer uses per hour, together with the cleaning speed in terms of area per hour. According to an experienced window washer, the average cleaning speed is 50 m2/hr. In Moon’s analysis, it is given that five window cleaners cleaned a surface of 626.4m2 in 2 hours including preparation time and intermission time. This would mean that a single window cleaner would clean approximately 60 m2/hr. Given this number, the water consumption becomes 5/12 L/hr and thus 1/8640 L/s. Note that these numbers are of course fairly dependent on the size, height and difficulty level of the window, but for modeling purpose, the average seems to be a plausible choice.

The energy consumption is modeled in a similar way. The energy consumption of the robot for a time step is taken to be 73.5 W when it is cleaning (and thus consuming maximum energy). This number is determined by averaging over the power consumption of the three considered window cleaning robots. However, when the window cleaning robot moves over a window surface that has already been cleaned, it consumes less energy since it does not have to clean it. As mentioned before, this has to do with the fact that the friction force of the cleaning pad is not counteracting the vacuum anymore. The energy consumption during this motion is therefore estimated to be 50 W. The velocity of the robot is estimated to be 0.1 m/s, which is determined by looking at a comparable window cleaning robot (WINDORO). Accelerations of the window cleaning robot are not taken into account.