PID implementation for a Humidity controller
Should I increase the period of PID execution time or
  


Something meaningful should be able happen between each sample.  I think one second much too close.  I would suggest starting with 10 seconds or more between samples.


  2.0 Should I retain the value of last calculated integral term ( or
  derivative) with the proportional term till the next addition of the
  integral ( or derivative).


P,I, and D should be calculated together in my understanding.  Using previous values will skew the process, it seems to me.  Previous values are already handled in I and D.


  But the problem is I cannot figure out how each terms are converted to
  the real output


Its not rocket science.  Its really up to your system and how you decide to plug in numbers for P I &amp; D.  For example, If you decide that an output value of >= 100 is off, and &lt; 100 on, P is adjusted until in the ballpark, and I and D to finish it up.

Find a copy of PID without a phd and study it well, if you haven't.