Cooling and Heating
In HVAC systems, air is typically cooled by passing it over a cooling coil. Most cooling coils are finned-tube heat exchangers in which cool water or refrigerant flows through tubes,…
Measuring Vapour Pressure
Measuring vapour pressure is very difficult without complex laboratory instrumentation. However, it can be relatively easily derived from more measurable properties. The ratio between the weight of water vapour actually…
Measuring Dew Point
Two types of dew point sensors are commonly used today: a condensation dew point method and a saturated salt system. The condensation dew-point hygrometer is a polished metal mirror that…
Measuring Humidity
The instruments used to measure humidity are called hygrometers. The simplest form of hygrometer is called a psychrometer. It consists of two thermometers mounted on the same frame that can…
Measuring Wet Bulb Temperature
Wet bulb temperature is easily measured with a standard thermometer which has its sensing bulb encased in a wetted wick that is subjected to rapid air motion across its surface.…
MEASURING PSYCHROMETRIC VARIABLES
All psychrometric properties of air are determined by measuring two psychrometric variables: for example, if wet- and dry-bulb temperatures are measured, then relative humidity, vapor pressure and dew point. Many…
Vapour Pressure
Water vapour is one of several gaseous constituents of air, the other principal ones being nitrogen, oxygen and carbon dioxide. Each exerts its own partial pressure on the surrounding environment…
Specific Air Volume
Specific Volume is the volume that a certain weight of air occupies at a specific set of conditions. The specific volume of air is basically the reciprocal of air density.…
Dew Point
Dew point temperature indicates the temperature at which water will begin to condense out of moist air. When air is cooled, the relative humidity increases until saturation is reached and…
Absolute Humidity or Humidity Ratio
Absolute Humidity is the vapor content of air, given in grams or lb of water vapor per lb of dry air (i.e., lb of moisture/lb of d.a). It is also…
