fix #11512: evap cooler docs — constant wet-bulb, not constant enthalpy

[brianlball]

Summary

Fixes #11512. Docs-only.

The direct evaporative cooler docs claim the process follows a line of constant enthalpy and treat constant wet-bulb as a close-enough proxy. The physics is the other way around: an adiabatic evap-cooling process follows constant thermodynamic wet-bulb temperature by definition (this is the defining process for Twb), and constant-h is the approximation — the outlet enthalpy differs from inlet by the enthalpy carried in by the liquid water before it evaporates:

h_sup,out = h_sup,in + h_water * (w_sup,out − w_sup,in)

Code is already correct — doc was inverted

The implementation holds Twb constant and derives W, h from it:

• src/EnergyPlus/EvaporativeCoolers.cc:1739 — CalcDirectEvapCooler (CelDekPad): OuletWetBulbTemp = InletWetBulbTemp
• src/EnergyPlus/EvaporativeCoolers.cc:3164 — CalcDirectResearchSpecialEvapCooler (ResearchSpecial): OuletWetBulbTemp = TEWB

Both paths use OutletTemp = TEDB − (TEDB − TEWB) · ε (wet-bulb-depression, not enthalpy-depression) and compute outlet enthalpy as a result via PsyHFnTdbW. Inline comments at both sites already state "WET BULB TEMP IS CONSTANT ACROSS A DIRECT EVAPORATION COOLER". Governing equation at evaporative-coolers.tex:26 (ε·(T_odb − T_owb)) is also a Twb-depression formula.

Changes

doc/engineering-reference/.../evaporative-coolers.tex

• Rewrite the inverted passage; add the enthalpy-balance equation and nomenclature
• Drop "or the constant enthalpy line" from the later paragraph that contradicted itself
• Fix two-stage section ("following a constant enthalpy line" → "constant wet-bulb temperature line")
• Fig 198 caption/label: Constant Enthalpy → Constant Wet-Bulb Temperature

doc/input-output-reference/.../group-evaporative-coolers.tex

• Prose rewrite only (I/O ref stays user-facing; equation derivation lives in eng-ref)
• Fig 145 caption/label updated to match

Image check

Examined image4790.png and image416.png. Diagonal lines on both are already labeled Wet-Bulb Temp [F] and the A→B process line is drawn along one of them. Images were already physically correct; only the captions were wrong. No image edits needed.

Label rename fig:psychrometric-chart-constant-enthalpy → fig:psychrometric-chart-constant-wetbulb — grep confirmed no \ref{} uses the old label anywhere in the repo.

Test plan

• Doc build: eng-ref LaTeX renders new equation block and updated caption
• Doc build: I/O ref renders updated caption
• Visual check: figure still appears correctly (only caption/label changed)

[mitchute]

@brianlball I made a minor touch-up here: 32c0810

let me know if that's ok.

[brianlball]

@mitchute I like it

[github-actions]

⚠️ Regressions detected on ubuntu-24.04 for commit 675ae29

Regression Summary

• ESO Small Diffs: 707
• Table Small Diffs: 393
• MTR Small Diffs: 525
• Table String Diffs: 177
• EIO: 397
• JSON Small Diffs: 2
• ZSZ Small Diffs: 72
• Table Big Diffs: 36
• ERR: 14
• MTR Big Diffs: 2
• EDD: 4
• ESO Big Diffs: 10
• SSZ Small Diffs: 13
• JSON Big Diffs: 2

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[mitchute]

More regression testing hallucinations... merging