I think it is a tricky question, ppm/h is a unit that hard to explain.

I suggest g/h or ppm CO2 in the exhaled air (in that case, you need the exhaled volume as well, so g/h is easier).

You can relate ppm and time if you are in a known volume closed room, but does not seem proper.

The concentration of the CO2 in the exhaled air is approximately the same all the time. If you need more oxygen, you accelerates the respiration. The CO2 concentration is limited by our lungs efficiency.

Mr. Hussein, I suppose that exercises mean physical effort. Yes, ppm/h is an uncommon unit but it is not quite complicated to find out the CO2 generation in liter/hour. Respiratory flow (air ventilated by the lungs for one minute in rest status) is: 500 ml (1 breathing volume) x ca. 14 breaths (1 insp.+1 expir.)/min ~ 7 l /min or ca. 420 l/h. Under physical effort the respiratory flow increases up to 80-100 l/min, that means 4800-6000 l/hr. This should be divided by 2 to get the expiration air flow, that is from 210 to max. 3000 l/h. Knowing that inspired air contains 0.03% CO2 but expired air contains 4% CO2, it means that CO2 generation (l/h) is got from expired CO2 minus inspired CO2:

210x4/100 - 210x0.03/100 ~ 8.37 l/h expired CO2 in rest status

3000x4/100 -  3000x0.03/100 ~ 119.1 l/h expired CO2 in maximum physical effort.

Certainly such calculation is approximate, the flow values taken into account are average values. Besides respiration, there is CO2 emission via perspiration, I have no any idea about this amount. I hope there is not any arithmetic error...