Theory and troubleshooting using short modules packed with images to make learning quick and easy.
The dry-bulb temperature is also referred to as the air temperature or ambient air temperature. The dry-bulb temperature is not affected by the moisture in the air. It measures the sensible temperature of the air.
It’s the temperature you’re usually referring to when you’re telling your friends how hot it is outside. The dry-bulb can be taken with an ordinary everyday thermometer.
The wet-bulb temperature is a measure of moisture evaporation. Basically how easy it is for moisture to evaporate.
Wet-bulb is measured by an ordinary thermometer with a wet cloth on the end. You can also use a sling psychrometer or digital psychrometer as well.
When the air passes through the wet cloth, moisture from the cloth evaporates into the air. This causes the air to reduce temperature. The temperature the air has reduced to is the new temperature the thermometer will read, and this will be lower than the dry-bulb temperature in most cases. If they’re the same, you have 100% relative humidity.
When our bodies overheat, it begins to sweat to reduce your core body temperature. Once the sweat is on your skin, it should evaporate which in turn will cool your body. However, when there’s more moisture in the air (high dew point) the sweat takes longer to evaporate and the warmer and more uncomfortable you become.
Relative humidity is the amount of water vapor in the air, expressed as a percentage, compared to the amount of water vapor it can hold at that temperature.
As air is heated, it expands. With this expansion, the amount of moisture it can hold also increases as there’s more space for the water to be placed within.
Temperature rise is the difference of air temperature between the conditioned return air and the heated supply air sent from the furnace.
Temperature rise is part of the initial setup of a furnace. Before taking a temperature rise reading, you will need to make sure you have a clean filter, proper gas pressure, combustion test, and correct furnace/duct/return air size.
Caution: It cannot be said enough how careful you need to be when drilling into a furnace to make pressure testing ports. Avoid drilling through the cabinet and hitting anything such as electrical, condensate traps, or the heat exchanger.
Static pressure is the resistance air faces when moving through a duct system or the balloon pressure outwards towards the walls of the duct.