Condenser Vacuum Calculator

Inputs

Example data

Formula used

The calculator estimates condenser vacuum as the difference between atmospheric pressure and condenser absolute pressure:

• Vacuum = P_atm − P_abs
• P_abs = P_sat(T_cond) + ΔP_noncond

Saturation pressure of water vapor is approximated using an Antoine correlation:

log₁₀(P_mmHg) = A − B/(C + T_°C)

If altitude is selected, atmospheric pressure is estimated using a standard atmosphere approximation:

P = 101.325 × (1 − 2.25577×10⁻⁵·h)^5.25588 (kPa)

How to use this calculator

1. Select a method: enter condensing temperature, or use cooling-water outlet plus TTD.
2. Choose temperature units, then fill the visible temperature fields.
3. Pick an atmospheric input: altitude for quick estimates, or measured barometric pressure.
4. Enter a noncondensable/air pressure contribution to reflect leakage and venting.
5. Press Calculate to see results below the header.
6. Use Download CSV for spreadsheets, or Download PDF for reports.

Technical notes for condenser vacuum calculations

1) What this calculator estimates

Condenser vacuum is the pressure reduction below local atmosphere created when steam condenses. This tool estimates vacuum from atmospheric pressure minus condenser absolute pressure. Absolute pressure is modeled as the sum of water-vapor saturation pressure at the condensing temperature and a user-specified noncondensable contribution representing air leakage and vent limitations.

2) Inputs and practical ranges

For many surface condensers, a condensing temperature around 30–45 °C is common during normal operation, depending on cooling-water conditions. A terminal temperature difference (TTD) of 3–8 °C is often used for quick checks. Noncondensable pressure can be small (about 0.2–2.0 kPa) but rises quickly when air in-leakage increases.

3) Data points that help validate results

Saturation pressure increases rapidly with temperature. Typical values are approximately: 30 °C → 4.24 kPa, 35 °C → 5.62 kPa, 40 °C → 7.38 kPa, and 45 °C → 9.59 kPa. If you enter T_cond=37 °C and ΔP_noncond=0.8 kPa at near‑sea‑level atmosphere (about 101.3 kPa), the predicted vacuum will be close to 94–95 kPa (about 28 inHg).

4) Interpreting vacuum and troubleshooting

A lower-than-expected vacuum can come from warmer cooling water, higher TTD, or higher noncondensables. If vacuum drops while cooling-water temperature is steady, focus on air removal equipment, leaks at flanges and glands, and vent-line restrictions. If vacuum improves when load reduces, heat-transfer fouling may be dominating.

5) Reporting, consistency, and field checks

Use the same units and input method across sites to keep comparisons consistent. Prefer measured station pressure when available, especially at higher elevations where barometric pressure is lower. Exporting CSV supports trending, while PDF output helps attach calculations to commissioning reports and QA records.

FAQs

1) What is “vacuum” in this calculator?

Vacuum is the difference between atmospheric pressure and condenser absolute pressure. It represents how far below ambient the condenser operates, shown in kPa, mmHg, or inHg.

2) Should I enter condensing temperature or use cooling-water outlet + TTD?

Use condensing temperature if you have a reliable value from instrumentation or calculations. Use cooling-water outlet + TTD for quick estimates when only water temperatures are available.

3) What does the noncondensable pressure mean?

It is an allowance for air and other gases that do not condense. Higher values reduce vacuum and often indicate air in-leakage, insufficient venting, or degraded air-removal equipment.

4) Why does altitude matter?

Atmospheric pressure decreases with elevation. Because vacuum is referenced to local atmosphere, the maximum achievable vacuum in kPa is lower at higher altitudes, even with identical condensing conditions.

5) My vacuum becomes negative. What does that indicate?

It means the calculated condenser absolute pressure exceeds atmospheric pressure for the entered conditions. Recheck temperature inputs, noncondensable pressure, and barometric/altitude values.

6) Does this replace a full condenser performance test?

No. It is a screening and reporting tool. Full tests also consider heat-transfer area, cooling-water flow, cleanliness factors, and instrument accuracy under defined procedures.

7) Which pressure should I use: sea-level or local station pressure?

Use local station pressure when possible. Sea-level corrected pressure can misstate vacuum, especially at elevation, and may hide real performance issues during commissioning or troubleshooting.