How we research and check our figures
This page documents the numbers behind MistGuide: which formulas we use, which values are physical constants and which are planning assumptions, and how we check them. If you find a figure on the site that disagrees with this page, it is an error and we want to hear about it.
One shared engineering reference
Numbers that appear on many pages are maintained in a single internal reference and every guide is checked against it. That prevents the common problem of one page saying a nozzle flows 1 GPH and another saying 2. The main entries are summarized below.
| Figure | Value we use | Type |
|---|---|---|
| Low pressure | 40-80 psi, droplets roughly 50-100+ microns | Industry range |
| Mid pressure | about 100-300 psi, droplets roughly 20-50 microns | Industry range |
| High pressure | 800-1,000 psi (some systems to 1,500), droplets roughly 5-20 microns | Industry range |
| Nozzle flow, 0.012 in at 1,000 psi | 0.025 GPM (about 1.5 GPH) | Planning midpoint of published charts |
| Flow vs pressure | Proportional to the square root of pressure | Physics (orifice equation) |
| Pump headroom | 15-20% above calculated nozzle demand | Planning practice |
| Heat absorbed per gallon evaporated | about 8,700 BTU | Physics (latent heat) |
| High-pressure filtration | 5 micron sediment filter (some systems 1 micron) | Manufacturer practice |
| Open-air misting effectiveness | High pressure 50-70% of wet-bulb depression; mid 30-50%; low 15-30% | Editorial planning assumption |
Formulas used in guides and calculators
- Wet-bulb temperature
- Stull (2011) empirical formula from air temperature and relative humidity. Accurate to about 1 °C across normal outdoor conditions (roughly 5-99% RH).
- Heat index
- National Weather Service Rothfusz regression with the NWS low- and high-humidity adjustments.
- Saturation vapor pressure
- Tetens equation, es = 0.6108 exp(17.27 T / (T + 237.3)) kPa, T in °C, as used in FAO Irrigation and Drainage Paper 56.
- Nozzle flow at pressure
- Q2 = Q1 x √(P2 / P1), from Bernoulli's equation for a fixed orifice.
- Humidity after misting
- Evaporative cooling follows a line of constant wet-bulb temperature, so we solve for the humidity at the cooled temperature that keeps the wet-bulb constant.
When published figures disagree
Nozzle flow is the clearest example. Comparing several manufacturers' charts for nominally identical high-pressure nozzles at 1,000 psi, we found differences of up to about 40 percent for the same orifice size. Causes include different test pressures, different nozzle internals (impingement pin versus swirl designs), manufacturing tolerance on tiny orifices, and rounding. Rather than pick one catalog, we use a planning midpoint, publish the range, and explain how to measure a real nozzle in the orifice sizes and flow rates guide.
Droplet size claims have the same problem: some sellers quote a minimum, some a median (Dv50) and some a Sauter mean diameter, often without saying which. We report ranges and explain the terms in droplet size explained.
Planning assumptions, stated plainly
Some useful numbers cannot be measured once and applied everywhere. The best example is how much of the theoretical cooling an open-air misting system actually delivers; it depends on wind, layout, mounting height and where people sit. We publish conservative planning values, label them as assumptions wherever they appear, and let you change them in the cooling potential calculator.
Verification steps for every guide
- Figure check. Every number is compared with the shared reference or a cited source.
- Calculation check. Worked examples are recalculated independently.
- Consistency check. Related pages are compared so recommendations do not conflict.
- Safety check. Electrical, high-pressure, water hygiene and code guidance is checked against authoritative sources.
- Link and structure check. Internal links are validated automatically on every build, so a broken link cannot be published.