Raising Secondary ΔT From 6 K to 12 K Drops Two Pipe Sizes

The secondary duty at a liquid fraction of 0.95 is 11,785 kW [MODELED]. Hold that number still and change only the temperature difference: 1,782 m³/h at 6 K, 891 m³/h at 12 K [MODELED]. Flow is duty divided by specific heat and by ΔT, so the two endpoints are exactly half. The velocity screen then moves the zone ring two nominal sizes in the tabulated series, from DN300 down to DN200 [MODELED]. ΔT is the second blocking item after liquid fraction. It has to close before any pipe size is drawn.

The Velocity Screen at Split and Detour Drops Two Sizes

Flow does not pick a pipe size. A velocity band does. Total flow divides by three zones and then by two directions around the ring. The 1,782 m³/h case gives 594.0 m³/h per zone and 297.0 m³/h in the worst ring span. The 891 m³/h case gives 297.0 and 148.5 [MODELED]. Each candidate size is then checked twice: once at the normal split, and once at the isolation detour where the whole zone duty travels one way.

At 6 K the screen lands on DN300, running 1.06 m/s normally and 2.12 m/s on detour. DN250 is rejected there because its detour velocity is 3.00 m/s, exactly on the limit [MODELED]. At 8 K the intermediate size is DN250. At 10 K the answer is DN200 at 1.41 and 2.82 m/s, with 6% [MODELED] detour margin at the 0.95 liquid fraction. At 12 K it is still DN200, at 1.17 and 2.35 m/s, with DN150 ruled out at 4.03 m/s [MODELED]. Two steps of ΔT therefore move the ring by two sizes and leave a size in hand.

The 10 K row is the one the hydraulic basis currently writes downstream numbers to. That row is not a freeze of ΔT. It is the working substitution until the supplier letter arrives.

The Unit Tapping Drops One Size, Not Two

Only one size separates the tapping cases: DN200 at 6 K and DN150 at 8, 10 and 12 K [MODELED]. The tapping is sized on nameplate full flow rather than on the running split. Recommendation R-05 keeps it there: connections and secondary pumps are selected on nameplate, not on the normal parallel-running flow, because parallel operation is a control strategy and may not reduce the selection basis.

So the ring and the tapping respond differently to the same open input, and only the ring carries the two-size swing. Anyone tracking ΔT through the package by watching the unit connection will see one step and miss the other.

The cabinet branch is a third object. It can be standardised at DN50 across 8, 10 and 12 K, and only moves to DN65 at 6 K. That freeze is allowed before cabinet count closes. The ring is not.

Two Sizes Change Gallery Height and Hanger Load

Conclusion 13 lists what travels with the size: cross-sectional area up by a factor of 2.2, pipe weight and insulation area up by roughly 1.5, hanger and support loads and tray or gallery clearance rising with them, and floor-to-floor height and gallery layout changing directly [MODELED]. The 2.2 is reproducible from the tabulated bores — 314.76 mm against 211.58 mm, squared, is 2.21 [MODELED].

The space basis converts that into a dimension. Its ceiling band for the supply-and-return liquid run is set on DN200 at 0.50 / 0.65 / 0.90 m [MODELED]. Closing ΔT at 8 K or 6 K raises all three envelopes of that band by about +0.05 m and +0.10 m respectively, with hanger loads and insulation area following [TARGET]. The same document records the hydraulic prohibition as an inherited blocking condition: with ΔT open, no gallery section and no floor-to-floor height may be issued [FACT].

The liquid band is also the object the space basis ranks as physically un-reroutable once its elevation is set. Slope, flood weight, and air pockets lock the run. Two pipe sizes is therefore a collision priority and a hanger load, not a procurement preference.

Hangers Are a Common Cause Under All Three Zones

The structural basis carries the same dependency as a verification condition: ΔT closure, and with it the DN200-to-DN300 range, is what finalises the liquid band. Ten items currently sit in that verification list [FACT]. All ten are unobtained. The more uncomfortable entry is conclusion S-09. If the non-structural component importance factor is judged to require post-earthquake functionality, the seismic bracing of filled liquid piping becomes part of the availability chain rather than a compliance detail. One seismic event can damage the bracing of all three zones at once.

Zone redundancy is a hydraulic property. The supports are a common cause that sits underneath all three zones. The structural author asks for their zonal independence to be argued rather than assumed to be inherited.

The hanger control case is not the operating weight. Flooded and hydrotest line load is the case the structural basis records as easiest to miss and largest in consequence. At 30 percent, every hanging-load field is still empty. Steel tonnage, cost, and foundation reaction have no input basis. Two sizes changes the missing number. It does not fill it in.

Limits and open items

Confirmed on the current record: taking ΔT from 12 K to 6 K raises the zone ring two nominal sizes; total flow halves across that range at the stated duty; the size is set by a velocity screen applied at the split and at the detour; the unit tapping moves by only one size; no gallery section and no floor-to-floor height may be issued while ΔT is open. [FACT]

Modelled and not frozen: 11,785 kW secondary duty, 1,782 and 891 m³/h, the 594.0 / 297.0 and 297.0 / 148.5 splits, the velocity pairs, the 6% detour margin, the 2.2 area factor, the 0.50 / 0.65 / 0.90 m band, and the +0.05 m / +0.10 m lifts. The equal split across three zones and both ring directions is a premise. Ring hydraulic balancing is recorded as not started. The 0.95 liquid fraction is a hydraulic calculation value, not a supplier freeze. [MODELED]

Held open: ΔT is item H-04 and it is not the facility's to choose. Closure requires the information technology equipment supplier's written allowable cold-plate temperature difference and maximum allowable return temperature [HOLD]. The recommended design point of 10 K [TARGET], and the DN200 that follows from it, are a facility-side recommendation pending that confirmation, not a selection. The liquid fraction that sets the 11,785 kW duty is separately unfrozen, so both flow endpoints move together with it. The non-structural component importance factor has not been judged. The ceiling-band movements carry assumed support and valve allowances.

The 6 K end of the size table is also the end the hydraulic basis records as vetoed on other grounds: eight units at full load draw 464 kW [MODELED] of secondary pump power against a 385 kW [MODELED] electrical allowance, and 571 kPa [MODELED] sits on typical cold-plate and dry-break working limits. That veto is not a pipe-size freeze. It is a reason the 6 K column is not an operating case waiting for a larger gallery.

Nothing above reflects Engineer of Record review, supplier confirmation, commissioning acceptance or observed operation. No pipe size here is a procurement release.

Whether the DN200 Gallery Still Issues at 6 K

The condition that changes the result is one-sided. If the supplier allows 12 K, the ring stays at DN200 with more margin and the band stays where the space basis drew it. If it returns 6 K, the ring goes to DN300, the ceiling band grows, and the gallery section and floor-to-floor height that were waiting on this input have to be drawn to the larger case — a building consequence, reached through a velocity screen, from a number owned by a rack vendor.

The useful test is not whether DN200 appears on a current sketch. It is whether anyone will still issue that sketch if the supplier's letter comes back at 6 K.

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Source: K&K Data Service Inc., “Raising Secondary ΔT From 6 K to 12 K Drops Two Pipe Sizes,” https://www.kkdatasvc.com/lab/hydraulics-and-transients/delta-t-from-6-k-to-12-k-drops-two-pipe-sizes/.