The Phoenix Psychrometric Calculator turns two readings you have already taken, air temperature and relative humidity, into the two numbers a drying job is managed on: specific humidity (grains of water per pound of dry air) and dew point. Phoenix part number 4024392.
It saves you working across a printed psychrometric chart, which is slow on site and easy to misread.
Quick and Easy Dew Point and Grains Calculations
- Provides accurate moisture content information in an easy-to-use tool.
- Helps avoid common data input errors.
- Accepts input data from 3% to 100% relative humidity.
- Accepts temperature inputs from 20°F (-7°C) to 120°F (49°C).
- Temperature and dew point are listed in both Fahrenheit and Celsius.
This handy tool gives you the moisture content information you need to determine a drying strategy and monitor the drying process.
With the Phoenix Psychrometric Calculator, you can accurately calculate dew point and specific humidity (grains of water per pound of air) without fumbling through awkward psychrometric charts. Simply set the temperature and relative humidity; the specific humidity and dew point temperature are displayed in their respective windows.
This moisture content information is crucial to the restoration professional in order to determine the drying strategy and monitor the drying process.
Important: It Calculates, It Does Not Measure
The previous version of this page, and some US listings, said the calculator "measures" air flow, temperature, relative humidity, dew point, wind chill and heat stress. That is not correct, and we have removed the list.
The calculator has no sensor. You take the temperature and relative humidity with a thermo-hygrometer or datalogger, and the calculator converts them to grains and dew point. It does not deal with air flow, wind chill or heat stress at all.
What You Need With It
- A thermo-hygrometer or ambient datalogger to take temperature and RH readings, for example the Tramex Feedback Datalogger DL-RHTA or the DL-RHTX.
- A moisture meter for the materials themselves, such as the Delmhorst BDX-20. Air readings tell you how well the air is drying; they do not tell you when the structure is dry.
How to Use It on a Job
- Take temperature and RH readings in the affected area, an unaffected area of the building, outside, and at each dehumidifier outlet.
- Set the calculator to the temperature reading.
- Set the relative humidity reading.
- Read specific humidity (grains per pound) and dew point from their windows.
- Record the results with the time and location, and repeat at every visit.
What you are looking for is the trend: grains in the affected area falling towards, then below, the unaffected area, and a clear drop in grains between the air going into a dehumidifier and the air coming out of it. A dehumidifier that is not lowering grains is not removing water, whatever it sounds like.
A Worked Example
Air at 25°C and 60% RH holds about 83 grains per pound (about 11.9 g/kg) and has a dew point of about 16.7°C. Any surface in that room colder than 16.7°C, such as a slab, a cold external wall or an air-conditioning duct, will collect condensation.
These figures are calculated at sea-level air pressure. Your reading on the calculator should be close to them.
Grains Per Pound or Grams Per Kilogram?
The calculator gives specific humidity in grains per pound, the unit used in US drying guidance and most restoration training. Some Australian reports use grams of water per kilogram of dry air instead.
There are 7,000 grains in a pound, so to convert, divide grains per pound by 7 to get g/kg. For example, 70 gr/lb is 10 g/kg.
Specifications
| Brand | Phoenix Restoration |
|---|---|
| Phoenix part number | 4024392 |
| CCW SKU | PRP4024392 |
| Inputs | Temperature and relative humidity |
| Outputs | Specific humidity (grains per pound of dry air) and dew point |
| RH range | 3% to 100% |
| Temperature range | 20°F to 120°F (-7°C to 49°C) |
| Units shown | Temperature and dew point in °F and °C |
| Power | None required. It has no electronics. |
| Accuracy and pressure basis | Not published by Phoenix |
Frequently Asked Questions
Does it measure humidity?
No. It converts temperature and RH readings you have taken with a meter into grains and dew point.
Why use a card calculator when my meter or app can do it?
It needs no battery and costs very little, so it is a reliable backup in every kit. It is also a good training tool, because it shows new technicians how temperature and RH together determine the moisture in the air. Phoenix has also published a Phoenix Psychrometric app for iOS and Android; check the app stores for current availability.
Can I use the results in a drying report?
Yes, as long as you record the meter readings they came from. Where a report needs logged data, an ambient datalogger gives you a continuous record rather than spot readings.
Does it work at altitude?
Psychrometric charts and calculators are usually based on sea-level pressure, and Phoenix does not state the basis for this one. For most Australian sites the difference is small. On high-country jobs, use a meter or software that corrects for altitude if precision matters.
Does it show g/kg?
Phoenix lists specific humidity in grains per pound only. Divide by 7 to convert to g/kg.
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