What setting would you choose low or intermittent??
Intermittent. Running the HRV 24/7 would just be a waste of energy. Even 20min of run time every hour is likely too much. Upgrading to the Platinum control or Ecobee would offer better programming options.
When would u usa high and low ?? Shouldn't high and or both be avoided in summer due to humidity ?
High if you have a house full of people, cooking and the windows are getting wet.
Low all other times.
I run mine 10 minutes an hour all year (ERV) and have it tied into the blower of my furnace to circulate the air around the house.
An ERV pre-treats the air by transferring some of the summer humidity it's bringing inside to the air it's exhausting. It doesn't get it all, but it gets some.
An HRV just brings all that humidity in from outside and dumps it inside. You'd be making your air conditioner work harder for sure. To some people, it's worth it to have fresh air inside.