Illustrative c5 cdu selection
323 kW exchanger duty; 213 kPa external circuit requirementmodeled
| Value kind | modeled — Interpret this value according to its displayed kind, scope, source, and as-of date. |
|---|---|
| Scope | Continue 5.1 with 320 kW IT heat on liquid, 459 L/min water (use the unrounded 5.1 flow), and a conservative 3.00 kW CDU/pump heat input assumed entirely into the TCS return before the exchanger. This rounds up the 2.61 kW pump-input screen in 5.13 and allows additional CDU heat. TCS supply is 35.0 °C; FWS inlet is 30.0 °C with the same 32.0 kW/K capacity rate. Assume candidate A and candidate B each transfer 330 kW at this application point, with 200 kPa and 240 kPa available external TCS head respectively at the required flow. These are synthetic candidate curves, not supplier offers. 5.13 derives 213 kPa external duty with a dirty external filter. Assume two independently isolatable B units, either capable of the entire stated duty; transition and common dependencies are unproved. |
| As of | 2026-09 |
| Source | Guide calculation from expressly assumed teaching inputs. Primary reference supplies method or equipment context, not evidence that this design was built or tested. |
| Derivation | Total exchanger duty = 320 + 3.00 = 323 kW. With heat-capacity rate 32.0 kW/K, the CDU hot inlet is 35.0 + 323/32.0 = 45.1 °C and FWS return is 30.0 + 323/32.0 = 40.1 °C. At the exact unrounded ports both terminal approaches remain 5.0 K. Each 330 kW thermal selection exceeds duty by 7 kW. The auxiliary heat is counted once; neither the 320 kW IT load nor the 330 kW selection is the CDU electrical draw. A fails hydraulic duty: 200 < 213 kPa. B has approximately 27 kPa head margin and its VFD is trimmed to the required operating point. Select B for the current piping arrangement, carrying the full 323 kW rejection requirement to 5.8 . Do not subtract the internal CDU loss from an already external-head rating. Two B units establish steady capacity only; their transfer, power and shared headers still need 13.5 acceptance. Flip. A becomes hydraulically eligible at external duty ≤200 kPa, provided its thermal and control conditions still hold. The 80.0 mm common-header alternative in 5.13 screens at 191 kPa and crosses that boundary, trading pipe space and capital against CDU selection. Use the ASHRAE CDU rating method to keep the comparison at identical ports. |
| Review | checking…cadence-derived review 2027-01-03 · standard cadence |
| Recorded changes | none recorded |
| Claim id | p5-c5-cdu-selection |
Where the guide uses it
Not quoted in a chapter yet; it is kept in the curated register.
← Full numbers register — every date-stamped figure in the guide, with revision history.