The holes do not go anywhere and I am having trouble coming up with a reason why I shouldn't either repurpose them as part of a new Energy Recovery Ventilator install or otherwise insulate and seal them off.
The vents have been here since before I moved in and for whatever reason, I never gave them much thought beyond adding screening to them to keep out pests when I realized they were completely open on the bottom and had no idea about a lot of the inner-workings of home systems at the time. Recently, I've been thinking about adding an Energy Recovery Ventilator to get more fresh air in my home and thought these two vents on the front of my house might be from some variety of old leftover venting system that I could repurpose. As it turns out, the holes just lead to the empty wall cavities beneath my picture window and are completely surrounded on all sides by framing members (additional pictures below).
Does anyone have any idea what these holes might have been (or still be) for since there are no signs of any other tubing or cuts in framing to suggest there was ever any more tubing attached? As it is, I'm thinking about either repurposing the holes for my ERV (or minimally insulating and sealing them off). In case it helps, a large window or set of windows is original to the home's design (my house is a cookie cutter design and I have seen at least one home with the original windows), but I believe it may have been widened when a newer window was installed. That said, these vents sit pretty squarely beneath the window where I would bet they would have been beneath the original window's span as well.
I didn't take a picture of the left or down because there are obvious framing members at both points from outside the hole.