Zen practitioners in Japan are fond of practicing meditation under water falls (taki-shu-gyou 滝修行). One of greatest MMA fighters Rickson Gracie did dipping under ice-cold stream before some of his important fights (check out his workout video). Winter swimming is good for your health. All pointing to one direction: A feeling of intense cold can stimulate one's chi flow. How should one approach this method?
The best way is through doing cold shower, preferably starting in Summer. The natural bodily response to coldness is shivering, a tightening of one's muscles, so that heat will be generated and the body will be agitated to flight, i.e. move quickly away from the freezing environment. This natural response however cannot induce chi-generation.
To induce chi-generation under a cold shower, one MUST relax one's body (or muscles) and focus one's mind towards one's internal sensitivity. If one is successful, chi will be generated throughout the body to create enough warmth to combat the cold environment.
It is important to note that the speed of chi-generation (needless to say, together with its magnitude) is essential in the training process. Too slow a chi-generation (and too weak a magnitude) will likely result in shivering, a natural response which may lead to "getting a cold". The body needs to be trained in steps. The logic is always: Shower cold at some part of your body - do meditation under this condition - shower cold again (with or without increasing the affected areas) - do meditation again...
Remember: don't push to the state of involuntary shivering, but do push into its limit! Relax, focus and...enjoy!