Hotels near Vivarium Darmstadt

The room is cold, no room heater, I can not do much activities inside the room, no comfortable feeling. Coming back to hotel from activity outside in cold weather, I expect to get the warmth and comfort feeling in my room hotel but regret the room also cold. Even difficult to get to sleep because my body felt so cold, really terrible week to spend in this hotel. Could not get real sleep and rest while I have one week full day work in German, which required full rest, fresh mind and body. Deeply regret because the service is good and the staff are friendly but I will not choose this hotel again for my next year work trip.