Flow in each loop
within ±10 % of target10–25 % offmore than 25 % off— target
Checks
System curve and recommended pumps
Pump selection
Pump curves are approximations of each model's maximum-speed curve from the published shut-off head and maximum flow (estimated where marked). Confirm the selection in Taco's or Grundfos's selection software before ordering.
Loop table
Loop 1 is next to the supply connection. Head is in feet of the fluid being pumped.
How this is calculated
- Each loop is solved as a parallel branch between the supply and return headers. The flows are iterated until every loop's pressure drop matches the pressure difference between the headers at its own tee, and the loop flows add up to the total.
- Headers: 2-1/2″ × 3 mm stainless (57.5 mm bore), loops on 65 mm centres (from the XFM dimension table). Along the supply header the static pressure rises as flow peels off into the loops (recovery factor 0.8 of the velocity-head change); along the return header it falls as flow joins (loss factor 2.0, momentum balance). Header friction by Darcy–Weisbach.
- Loop branch: the XFM's rated Cv 6 per loop with both ball valves open. The ¾″ full-port ball valves are taken as Cv 25 each; when the return valve is replaced by a TacoSetter Inline 130 DN20 1″, the rest of the branch keeps Cv 6.4 and the TacoSetter 223.7566.519 (glycol scale 4–16 l/min, same data as 223.7566.334) adds Kvs 4.76 fully open (Cv 5.5).
- PEX: CTS SDR 9 bores of 0.475″ (½″), 0.574″ (⅝″) and 0.671″ (¾″), Churchill friction factor (laminar through turbulent), plus two compression adapters at K = 1.5 each.
- Fluid: water from standard property correlations; propylene glycol viscosity and density approximated from ASHRAE tables at the mean temperature. Temperature drop along the loop is not modelled.
- Balanced setters: the loop that needs the most pressure at its target flow (the index loop) stays wide open; every other setter is closed down to burn off the surplus. The setter is then adjusted until it reads the target flow. On glycol, read the setter through Taconova's glycol correction.
- Mains: supply and return PEX (CTS SDR 9 bores) or Type M copper (ASTM B88 bores) of the selected size, twice the one-way length, plus 8 velocity heads for fittings. Pump duty = manifold and loops + mains + the other losses you enter.
- Pumps: each model's maximum-speed curve is approximated as H = H₀ (1 − (Q/Qmax)²) from its published shut-off head and maximum flow; values marked est. are estimated where the manufacturer's figure was not available. A model qualifies when it gives at least 5 % more head than needed at the duty flow and the duty flow is under 85 % of its maximum flow; the smallest qualifying model in each line is shown.
- Ratings checked: 4.9 GPM per loop and 75 GPM trunk (Rhella XFM data), setter scale range, PEX velocity above 2 ft/s for air purging and below 4 ft/s for quiet running, and laminar flow.