Manifold Feed/Return Pipes

[MortarThePoint]

I thought I would share by deliberations on pipes for the feed and return to UFH manifolds. I have an 11.2kW ASHP and two main Manifolds meaning the peak power a manifold is around 5500W. Based on a dT=5K, that works out as a flow rate of around 5.5W/(5K*4.2kJ/K.kg) = 0.26kg/sec = 943kg/h = 0.94m3/h.

 

My head calculations when considering a circulation pump were based on 28mm Hep2O. I was considering using 26mm multilayer pipe with compression fittings, but it turns out that would be much more resistive (~55% more) and the higher flow speeds would also be noisier. I expect a peak flow to a manifold of around the 946kg/h line of the table. For the multilayer pipe that works out as 4.27mbar/m or 154mbar=1.54m of head loss for a 36m run. Hep2O on the other hand the drop would be 0.276kPa/m=2.76mbar/m or 99mbar=1m of head loss for a 36m run. That's a 55% difference. If flowing 50% of the time, the difference in electricity use would work out as (24*365*50%) * ((0.26kg/3*9.81N/kg*0.55m) / 50%) = 12.3kWh/yr. Not much. I'd be more worried about being closer to the 1m/s advisory limit for flow rates based on noise.

 

The multilayer pipe has the advantage of holding a shape when bent to it and more reliable fittings. It doesn't suit my situation though as I can't easily change to the larger 32x3.0 size that would be needed. 28mm Hep2O looks to be the better choice.