Yes dpb; that could be true.
In the evenings which of course are longer in summer so lights go on later and evening is when it's almost always cool here.
So very rarely does anyone here have or use AC units (unless it is one of those reverse cycle heat pumps for heating the house in winter) and doubt even then that they would keep changing back and forth between heating and cooling modes?
Last few days of August (which we consider late summer) it's been around 15 degrees Celsius (Approx mid 60s Fahrenheit) during the day. Some 5 C, degrees cooler at night; or approx low 50s. F. No trouble sleeping! Lights go on later in summer/fall and do contribute slightly to home heat. In fact only today, Sept 6th, is it cool enough to even consider switching on any of the heating thermostats. It' s now past midday and haven't done so yet.
So we don't have any cooling load at all. Do occasionally run a dehumidifier in part of basement during the summer to keep down dampness due to warmer more humid outside air seeping in there.
Otherwise our almost completely in ground basement stays at around
55-60 deg F. most of the time, except very coldest and windiest weather when it may occasionally dip to around 50 deg. F.You have to think in terms of a climate that never gets warm enough (or only very rarely for a few days a year at most) to need any cooling. Only a short distance from the North Atlantic this is considered a 'maritime' climate; heat and cold being modified by the mass of the ocean.