Hot Water Heat Pump – use with circulator and pre-heat – GreenBuildingAdvisor

Looking for any experience in using a HP HW heater in the following scenarios:

1) With a HW circulation loop (on timer, motion sensor or other smart use trigger)

2) With a Hydronic heating system where the hydronic HP is used to preheat the water going into the HP HW heater.

I have seen an article and presentation by John Siegenthaler where it looks like he did both with a Rheem HP HW heater that was per-existing in a church.

I ask because most the user manuals discourage using with circulation pumps (AO Smith, Rheem, and GE) and some prohibit use of preheat (GE is specific in use of solar or other preheating above set-point – with service agent claiming preheat would void warranty). I understand that running a circulation loop constantly would degrade the efficiency, but if its use is smartly targeted I would think there would not be any harm to the HP. Interestingly, Stiebel Eltron has you bring the recirc line back into the T&P port, I assume to keep from loosing stratification in the tank. Likewise, I can see how preheating above the set-point could be harmful, or with the single stage units it might cause short cycling, but with a variable speed HP on LG and GE, I don’t get why this wouldn’t be the optimal use?

For those wondering why not just use indirect HW from my Hydronic HP, it is because 1) I sort of want redundancy and 2) the hydronic switches to cold in the summer and HW priority with the potential of a second tank (or flipping the tank back and forth between hot and cold) is complex and expensive.

Hopefully someone has done this or can explain why the manufacturers don’t want me doing this.