They are negligible  compared to walls. (1000 watts)
	
	
		
		
			2)  Lets look at windows, specifically bedroom windows.  The minimum size is 5 sq ft on the ground floor, almost 6 on higher floors.  Lets take that minimal window and see what happens.  Local weather data says about 2000 degree days of heating and about 3200 of cooling.  The best windows I can find have an R-value of 5.  That gives a heating requirement of about 48,000 BTU and cooling of 76,800 BTU, for a total power use of 36 kWh for one small window.  .1 kWh per small window per day.  Your 1 kWh thus covers 50 sq ft of windows.  Few houses have that little in the way of windows.  And that's not counting any other use of power.
		
		
	 
 R-value of 5.5=0.97 m^2*K/(W*inch)
that means 1 watt for 1m^2 1 inch thick window at 1K difference,
for 20 degrees and typical 2 m^2 it will be 40 watts.
We will have 4 windows for my 70m^2 house. that's additional 160 watt to 1000 watt from the walls.
Conclusion - windows are negligible.
With all these additions I can give you 2000 watts of heat transfer. That's 100 watt for heat pump.
I just measured a typical window it's closer to 1 m^2, but that's OK, you can have 2m^2.
And then there are VIP windows, and if they are expensive (which they should not be) then you can still close your windows with additional thermal protection on a hot day. make it computerized/motorized