Closed loop cirulation pump optimum location

[ruralboy]

Hi, as previously posted, we've located a oil boiler in a outhouse at our rural french house, and am currently connecting it to a heatbank quad coil tank heatbank heatstore tank in the loft of the house. Pipe run is 28M long and a head of 7M up so have sized a capable pump, although the circulation tube is only 16mm ID (though the burner has 12mm orifices on its connections anyway!). The loop is closed to the rest of the tank and the plan is to pressurise it to 1.1 bar filled with fernox and with a expansion bladder tank located at the highest point near the tank in the loft with a automatic air bleed valve and pressure relief right at the top.

Now Im getting conflicting advice on pump location. Would it be best from a efficiency and service life point of view to locate the pump in the loft near the tank so it sucks the water up, or down near the boiler so it pumps against the head of water. Two local artisans advise each option apiece.
The pump installation instructions just say to locate the pump neither at the lowest or highest points in the circuit. For reasons of sedimentation settlement for the lowest and air cavitation at the top. From a wiring point of view either is just as easy to implement, the switching wires already come down to the outbuilding to switch the boiler on/off.
Also should the pump be on the flow to or return from the tank, presumeably being on the colder return side would improve pump life?

Want to get it right, because this is v1, we're doing the same thing at our new house we're renovating although the head is only the first floor...

 

[Norcon]

An oil boiler with 12mm orifices ?.
And 28 M of 16mm (id) f&r ?

Can I ask what is the heat demand (kilowatts) of the property this is serving ?.
And what size is the boiler ?.

 

[ruralboy]

Peak demand is 9Kw, because we have previously ran on a 9Kw 3 phase immersion which could keep pace with the UFH even on the coldest days. Its still in place, but is just not cost effective and the new renters want to run off oil instead.

Boiler is a new lamborghini boiler with a 24Kw burner unit supplied as the matching units by the supplier. The fittings are (from memory, im not there right now) 3/4" but the actual size of the hole through the "tennis net" strainers on the orifices is 12mm which is what makes me more comfortable with the 16mm pex pipework diameter spec'd for the run.