Quite so - and, as I recently wrote, the average obviously cannot be higher than the maximum - which is why I was surprised (at least, in comparison with my installation, which I would have thought was fairly typical) by aptsys's implication that the average PF in his installation is appreciably less than 0.85.
Since I haven't got a 'wired-in' monitoring system, I cannot tell you about the short-term fluctuation in PF in my installation. However, I can show you the short-term fluctuations in total consumption as determined by an assumption of a PF which remains constant (at the 'average' value) - as per the couple of graphs below from yesterday, which shows 'calculated' consumption for each minute over 3-hour periods. These don't 'prove anything', but show that short-term fluctuations in consumption (calculated using average PF) are relatively modest (and primarily due to on/off of individual loads). In the second graph, the hour or so for which I switched on 1kW worth of fan heater is obviously apparent but the short-term fluctuation during the entire period was, again, fairly modest.
I think that there is always some talking at cross-purposes in these discussions. As I always stress, my personal interest is in monitoring long-term trends in whole-installation electricity consumption - and for that purpose, data based on current-only measurements (together with knowledge of the 'average voltage' and 'average PF') is more than adequate.
However, as I keep saying, for the theoretical reasons that some people can't resist any opportunity to remind us about, current-only-based devices (like Owl) are unsuitable (and not intended) for measuring the true consumption (hence running cost) of individual items of unknown PF. If that is what one wants to know, then a cheap 'plug-in' energy monitor will provide that information.
Kind Regards, John
