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Wet bulb temp

I guess that's one way to remember it. So, should we all call it the wet blanket temperature from now on? Hmmmmmmmmmmmmmm

Comments

  • AC newbie
    AC newbie Member Posts: 11
    Wet bulb temp

    Hi
    New to the field and need to know how important wet bulb readings really are. No one I work with takes them or even knows how. What kind of tool is needed and why don't most guys have them?
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Temperature Primer

    Two important temperatures that are used by the HVAC technician are the wet bulb and dry bulb temperature of the air.

    The dry bulb temperature is the temperature obtained by using a regular thermometer. When we say that it is 75 degrees outside, we are talking about dry bulb temperatures.

    The other temperature, the wet bulb temperature, takes into account the relative humidity of the air and is measured with a wet-bulb thermometer. The wet bulb thermomter is basically a drybulb thermometer that has a cotton "sock" around the bulb that is soaked with distilled water.

    Here's the concept on how the wet-bulb thermometer works:

    As moisture evaporates, heat is absorbed from its surroundings. This concept is referred to as evaporative cooling. For example, when we are hot we sweat. When a cool breeze blows, we are suddenly cooled. THis is because the air moving across our skin causes the moisture (sweat) to evaporate. The evaporating moisture absorbs heat from our skin, making us feel cool.

    If however, the air was very humid, the air would not be able to hold the evaporating moisture from our skin. This is why we feel clammy when it is humid outside.

    Now, back to the wet-bulb and dry-bulb temperatures.

    There is a tool called a sling psychrometer that is made up of two thermometers, one wet-bulb and one dry bulb.

    The device is swung in the air for about a minute. As the thermometers are passing through the air, the dry bulb thermometer is taking the (sensible heat) temperature of the air. While this is happening, moisture from the wetted wich on the wet-bulb thermometer is likely evaporating. As the water evaporates, heat is absorbed from the thermometer bulb and the temperature of that thermometer bulb will drop to a temperature below that on the dry bulb thermometer.

    If the relative humidity is very low, the surrounding air can hold a lot more moisture and the rate of evaporation from the wick will be high and the wet bulb reading will much lower than the dry bulb reading. If the humidity is very high, very little moisture will evaporate and the wet-bulb reading will be very close to the dry bulb reading.

    If the wet-bulb and dry-bulb temperatures are the same, the relative humidity is 100%.

    The sling psyhrometer also has a feature that allows you to align the wet and dry bulb temperatures to determine the relative humidity.

    The relative humidity is important since the design air temperatures at which air conditioning systems operate is 50%.

    For example, at 50% relative humidity, the delta-t across an evaporator should be in the range of 17 to 20 degrees, under design conditions.

    If the humidity is high, expect the delta-t to be lower.

    If the humidity is low, expect the delta-t to be higher.

    Remember that the evaporator coil on an air conditioning system does two things. It dehumidifies and cools. If the humidity is high, more of the coil's capacity is used to dehumidify and less to cool. If the humidity is low, more of the coil's capacity can be used to cool the air, resulting in a higher delta-t across the coil.
  • Wethead7
    Wethead7 Member Posts: 170


    We currently provide one in each of our service trucks.


    Mike
  • bob_44
    bob_44 Member Posts: 112
    That's not the way

    I heard it. W.B. on the psychiatric chart really refers to Wet Blankets. Turns out that when W.H.Carrier was a young whippersnapper working for Buffalo Forge he and the Mrs. went on vacation in Mexico. He had not yet invented air cond. or the psych chart. They were staying in a little adobe hotel in the desert and he noticed that they had a wet blanket stretched across a window and a fan pulling air through it. The hotter it got the more wet blankets the innkeeper would hang across the window and the cooler the air. This is what inspired Dr. Carrier to invent the psych chart and why the W.B. stands for wet blankets. At least that is what I was told at a Carrier seminar on the high altitude psych chart. ;) bob
  • Empire_2
    Empire_2 Member Posts: 2,343
    Wet Bulb/Wet blanket

    Who cares...you are both right. The sock on the end of the psychrometer is the "Blanket"!!! "No disrespect intended." Both examples are very good to explain to the learning tech. If ya want, go into wet saturated vapor/dry saturated vapor. The young guy's need to know how and when the most work takes place. Do you agree???
  • Ray_7
    Ray_7 Member Posts: 16


    I have a Mannix digital psychrometer. I had to use it this week to get the indoor wet bulb reading as the dry bulb temp. wouldn't work with the freon temp./press. that was needed. With the humidity levels being high here in Ohio, the W.B. seems to be the better choice.

    Ray
  • AC newbie
    AC newbie Member Posts: 11
    So What

    > Two important temperatures that are used by the

    > HVAC technician are the wet bulb and dry bulb

    > temperature of the air.

    >

    > The dry bulb

    > temperature is the temperature obtained by using

    > a regular thermometer. When we say that it is 75

    > degrees outside, we are talking about dry bulb

    > temperatures.

    >

    > The other temperature, the wet

    > bulb temperature, takes into account the relative

    > humidity of the air and is measured with a

    > wet-bulb thermometer. The wet bulb thermomter is

    > basically a drybulb thermometer that has a cotton

    > "sock" around the bulb that is soaked with

    > distilled water.

    >

    > Here's the concept on how

    > the wet-bulb thermometer works:

    >

    > As moisture

    > evaporates, heat is absorbed from its

    > surroundings. This concept is referred to as

    > evaporative cooling. For example, when we are hot

    > we sweat. When a cool breeze blows, we are

    > suddenly cooled. THis is because the air moving

    > across our skin causes the moisture (sweat) to

    > evaporate. The evaporating moisture absorbs heat

    > from our skin, making us feel cool.

    >

    > If

    > however, the air was very humid, the air would

    > not be able to hold the evaporating moisture from

    > our skin. This is why we feel clammy when it is

    > humid outside.

    >

    > Now, back to the wet-bulb and

    > dry-bulb temperatures.

    >

    > There is a tool called

    > a sling psychrometer that is made up of two

    > thermometers, one wet-bulb and one dry bulb.

    > The device is swung in the air for about a

    > minute. As the thermometers are passing through

    > the air, the dry bulb thermometer is taking the

    > (sensible heat) temperature of the air. While

    > this is happening, moisture from the wetted wich

    > on the wet-bulb thermometer is likely

    > evaporating. As the water evaporates, heat is

    > absorbed from the thermometer bulb and the

    > temperature of that thermometer bulb will drop to

    > a temperature below that on the dry bulb

    > thermometer.

    >

    > If the relative humidity is very

    > low, the surrounding air can hold a lot more

    > moisture and the rate of evaporation from the

    > wick will be high and the wet bulb reading will

    > much lower than the dry bulb reading. If the

    > humidity is very high, very little moisture will

    > evaporate and the wet-bulb reading will be very

    > close to the dry bulb reading.

    >

    > If the

    > wet-bulb and dry-bulb temperatures are the same,

    > the relative humidity is 100%.

    >

    > The sling

    > psyhrometer also has a feature that allows you to

    > align the wet and dry bulb temperatures to

    > determine the relative humidity.

    >

    > The relative

    > humidity is important since the design air

    > temperatures at which air conditioning systems

    > operate is 50%.

    >

    > For example, at 50% relative

    > humidity, the delta-t across an evaporator should

    > be in the range of 17 to 20 degrees, under design

    > conditions.

    >

    > If the humidity is high, expect

    > the delta-t to be lower.

    >

    > If the humidity is

    > low, expect the delta-t to be higher.

    >

    > Remember

    > that the evaporator coil on an air conditioning

    > system does two things. It dehumidifies and

    > cools. If the humidity is high, more of the

    > coil's capacity is used to dehumidify and less to

    > cool. If the humidity is low, more of the coil's

    > capacity can be used to cool the air, resulting

    > in a higher delta-t across the coil.



  • AC newbie
    AC newbie Member Posts: 11
    So What

    > Two important temperatures that are used by the

    > HVAC technician are the wet bulb and dry bulb

    > temperature of the air.

    >

    > The dry bulb

    > temperature is the temperature obtained by using

    > a regular thermometer. When we say that it is 75

    > degrees outside, we are talking about dry bulb

    > temperatures.

    >

    > The other temperature, the wet

    > bulb temperature, takes into account the relative

    > humidity of the air and is measured with a

    > wet-bulb thermometer. The wet bulb thermomter is

    > basically a drybulb thermometer that has a cotton

    > "sock" around the bulb that is soaked with

    > distilled water.

    >

    > Here's the concept on how

    > the wet-bulb thermometer works:

    >

    > As moisture

    > evaporates, heat is absorbed from its

    > surroundings. This concept is referred to as

    > evaporative cooling. For example, when we are hot

    > we sweat. When a cool breeze blows, we are

    > suddenly cooled. THis is because the air moving

    > across our skin causes the moisture (sweat) to

    > evaporate. The evaporating moisture absorbs heat

    > from our skin, making us feel cool.

    >

    > If

    > however, the air was very humid, the air would

    > not be able to hold the evaporating moisture from

    > our skin. This is why we feel clammy when it is

    > humid outside.

    >

    > Now, back to the wet-bulb and

    > dry-bulb temperatures.

    >

    > There is a tool called

    > a sling psychrometer that is made up of two

    > thermometers, one wet-bulb and one dry bulb.

    > The device is swung in the air for about a

    > minute. As the thermometers are passing through

    > the air, the dry bulb thermometer is taking the

    > (sensible heat) temperature of the air. While

    > this is happening, moisture from the wetted wich

    > on the wet-bulb thermometer is likely

    > evaporating. As the water evaporates, heat is

    > absorbed from the thermometer bulb and the

    > temperature of that thermometer bulb will drop to

    > a temperature below that on the dry bulb

    > thermometer.

    >

    > If the relative humidity is very

    > low, the surrounding air can hold a lot more

    > moisture and the rate of evaporation from the

    > wick will be high and the wet bulb reading will

    > much lower than the dry bulb reading. If the

    > humidity is very high, very little moisture will

    > evaporate and the wet-bulb reading will be very

    > close to the dry bulb reading.

    >

    > If the

    > wet-bulb and dry-bulb temperatures are the same,

    > the relative humidity is 100%.

    >

    > The sling

    > psyhrometer also has a feature that allows you to

    > align the wet and dry bulb temperatures to

    > determine the relative humidity.

    >

    > The relative

    > humidity is important since the design air

    > temperatures at which air conditioning systems

    > operate is 50%.

    >

    > For example, at 50% relative

    > humidity, the delta-t across an evaporator should

    > be in the range of 17 to 20 degrees, under design

    > conditions.

    >

    > If the humidity is high, expect

    > the delta-t to be lower.

    >

    > If the humidity is

    > low, expect the delta-t to be higher.

    >

    > Remember

    > that the evaporator coil on an air conditioning

    > system does two things. It dehumidifies and

    > cools. If the humidity is high, more of the

    > coil's capacity is used to dehumidify and less to

    > cool. If the humidity is low, more of the coil's

    > capacity can be used to cool the air, resulting

    > in a higher delta-t across the coil.



  • AC newbie
    AC newbie Member Posts: 11
    So What

    > Two important temperatures that are used by the

    > HVAC technician are the wet bulb and dry bulb

    > temperature of the air.

    >

    > The dry bulb

    > temperature is the temperature obtained by using

    > a regular thermometer. When we say that it is 75

    > degrees outside, we are talking about dry bulb

    > temperatures.

    >

    > The other temperature, the wet

    > bulb temperature, takes into account the relative

    > humidity of the air and is measured with a

    > wet-bulb thermometer. The wet bulb thermomter is

    > basically a drybulb thermometer that has a cotton

    > "sock" around the bulb that is soaked with

    > distilled water.

    >

    > Here's the concept on how

    > the wet-bulb thermometer works:

    >

    > As moisture

    > evaporates, heat is absorbed from its

    > surroundings. This concept is referred to as

    > evaporative cooling. For example, when we are hot

    > we sweat. When a cool breeze blows, we are

    > suddenly cooled. THis is because the air moving

    > across our skin causes the moisture (sweat) to

    > evaporate. The evaporating moisture absorbs heat

    > from our skin, making us feel cool.

    >

    > If

    > however, the air was very humid, the air would

    > not be able to hold the evaporating moisture from

    > our skin. This is why we feel clammy when it is

    > humid outside.

    >

    > Now, back to the wet-bulb and

    > dry-bulb temperatures.

    >

    > There is a tool called

    > a sling psychrometer that is made up of two

    > thermometers, one wet-bulb and one dry bulb.

    > The device is swung in the air for about a

    > minute. As the thermometers are passing through

    > the air, the dry bulb thermometer is taking the

    > (sensible heat) temperature of the air. While

    > this is happening, moisture from the wetted wich

    > on the wet-bulb thermometer is likely

    > evaporating. As the water evaporates, heat is

    > absorbed from the thermometer bulb and the

    > temperature of that thermometer bulb will drop to

    > a temperature below that on the dry bulb

    > thermometer.

    >

    > If the relative humidity is very

    > low, the surrounding air can hold a lot more

    > moisture and the rate of evaporation from the

    > wick will be high and the wet bulb reading will

    > much lower than the dry bulb reading. If the

    > humidity is very high, very little moisture will

    > evaporate and the wet-bulb reading will be very

    > close to the dry bulb reading.

    >

    > If the

    > wet-bulb and dry-bulb temperatures are the same,

    > the relative humidity is 100%.

    >

    > The sling

    > psyhrometer also has a feature that allows you to

    > align the wet and dry bulb temperatures to

    > determine the relative humidity.

    >

    > The relative

    > humidity is important since the design air

    > temperatures at which air conditioning systems

    > operate is 50%.

    >

    > For example, at 50% relative

    > humidity, the delta-t across an evaporator should

    > be in the range of 17 to 20 degrees, under design

    > conditions.

    >

    > If the humidity is high, expect

    > the delta-t to be lower.

    >

    > If the humidity is

    > low, expect the delta-t to be higher.

    >

    > Remember

    > that the evaporator coil on an air conditioning

    > system does two things. It dehumidifies and

    > cools. If the humidity is high, more of the

    > coil's capacity is used to dehumidify and less to

    > cool. If the humidity is low, more of the coil's

    > capacity can be used to cool the air, resulting

    > in a higher delta-t across the coil.



  • AC newbie
    AC newbie Member Posts: 11
    So What

    > Two important temperatures that are used by the

    > HVAC technician are the wet bulb and dry bulb

    > temperature of the air.

    >

    > The dry bulb

    > temperature is the temperature obtained by using

    > a regular thermometer. When we say that it is 75

    > degrees outside, we are talking about dry bulb

    > temperatures.

    >

    > The other temperature, the wet

    > bulb temperature, takes into account the relative

    > humidity of the air and is measured with a

    > wet-bulb thermometer. The wet bulb thermomter is

    > basically a drybulb thermometer that has a cotton

    > "sock" around the bulb that is soaked with

    > distilled water.

    >

    > Here's the concept on how

    > the wet-bulb thermometer works:

    >

    > As moisture

    > evaporates, heat is absorbed from its

    > surroundings. This concept is referred to as

    > evaporative cooling. For example, when we are hot

    > we sweat. When a cool breeze blows, we are

    > suddenly cooled. THis is because the air moving

    > across our skin causes the moisture (sweat) to

    > evaporate. The evaporating moisture absorbs heat

    > from our skin, making us feel cool.

    >

    > If

    > however, the air was very humid, the air would

    > not be able to hold the evaporating moisture from

    > our skin. This is why we feel clammy when it is

    > humid outside.

    >

    > Now, back to the wet-bulb and

    > dry-bulb temperatures.

    >

    > There is a tool called

    > a sling psychrometer that is made up of two

    > thermometers, one wet-bulb and one dry bulb.

    > The device is swung in the air for about a

    > minute. As the thermometers are passing through

    > the air, the dry bulb thermometer is taking the

    > (sensible heat) temperature of the air. While

    > this is happening, moisture from the wetted wich

    > on the wet-bulb thermometer is likely

    > evaporating. As the water evaporates, heat is

    > absorbed from the thermometer bulb and the

    > temperature of that thermometer bulb will drop to

    > a temperature below that on the dry bulb

    > thermometer.

    >

    > If the relative humidity is very

    > low, the surrounding air can hold a lot more

    > moisture and the rate of evaporation from the

    > wick will be high and the wet bulb reading will

    > much lower than the dry bulb reading. If the

    > humidity is very high, very little moisture will

    > evaporate and the wet-bulb reading will be very

    > close to the dry bulb reading.

    >

    > If the

    > wet-bulb and dry-bulb temperatures are the same,

    > the relative humidity is 100%.

    >

    > The sling

    > psyhrometer also has a feature that allows you to

    > align the wet and dry bulb temperatures to

    > determine the relative humidity.

    >

    > The relative

    > humidity is important since the design air

    > temperatures at which air conditioning systems

    > operate is 50%.

    >

    > For example, at 50% relative

    > humidity, the delta-t across an evaporator should

    > be in the range of 17 to 20 degrees, under design

    > conditions.

    >

    > If the humidity is high, expect

    > the delta-t to be lower.

    >

    > If the humidity is

    > low, expect the delta-t to be higher.

    >

    > Remember

    > that the evaporator coil on an air conditioning

    > system does two things. It dehumidifies and

    > cools. If the humidity is high, more of the

    > coil's capacity is used to dehumidify and less to

    > cool. If the humidity is low, more of the coil's

    > capacity can be used to cool the air, resulting

    > in a higher delta-t across the coil.



  • AC newbie
    AC newbie Member Posts: 11
    So What

    > Two important temperatures that are used by the

    > HVAC technician are the wet bulb and dry bulb

    > temperature of the air.

    >

    > The dry bulb

    > temperature is the temperature obtained by using

    > a regular thermometer. When we say that it is 75

    > degrees outside, we are talking about dry bulb

    > temperatures.

    >

    > The other temperature, the wet

    > bulb temperature, takes into account the relative

    > humidity of the air and is measured with a

    > wet-bulb thermometer. The wet bulb thermomter is

    > basically a drybulb thermometer that has a cotton

    > "sock" around the bulb that is soaked with

    > distilled water.

    >

    > Here's the concept on how

    > the wet-bulb thermometer works:

    >

    > As moisture

    > evaporates, heat is absorbed from its

    > surroundings. This concept is referred to as

    > evaporative cooling. For example, when we are hot

    > we sweat. When a cool breeze blows, we are

    > suddenly cooled. THis is because the air moving

    > across our skin causes the moisture (sweat) to

    > evaporate. The evaporating moisture absorbs heat

    > from our skin, making us feel cool.

    >

    > If

    > however, the air was very humid, the air would

    > not be able to hold the evaporating moisture from

    > our skin. This is why we feel clammy when it is

    > humid outside.

    >

    > Now, back to the wet-bulb and

    > dry-bulb temperatures.

    >

    > There is a tool called

    > a sling psychrometer that is made up of two

    > thermometers, one wet-bulb and one dry bulb.

    > The device is swung in the air for about a

    > minute. As the thermometers are passing through

    > the air, the dry bulb thermometer is taking the

    > (sensible heat) temperature of the air. While

    > this is happening, moisture from the wetted wich

    > on the wet-bulb thermometer is likely

    > evaporating. As the water evaporates, heat is

    > absorbed from the thermometer bulb and the

    > temperature of that thermometer bulb will drop to

    > a temperature below that on the dry bulb

    > thermometer.

    >

    > If the relative humidity is very

    > low, the surrounding air can hold a lot more

    > moisture and the rate of evaporation from the

    > wick will be high and the wet bulb reading will

    > much lower than the dry bulb reading. If the

    > humidity is very high, very little moisture will

    > evaporate and the wet-bulb reading will be very

    > close to the dry bulb reading.

    >

    > If the

    > wet-bulb and dry-bulb temperatures are the same,

    > the relative humidity is 100%.

    >

    > The sling

    > psyhrometer also has a feature that allows you to

    > align the wet and dry bulb temperatures to

    > determine the relative humidity.

    >

    > The relative

    > humidity is important since the design air

    > temperatures at which air conditioning systems

    > operate is 50%.

    >

    > For example, at 50% relative

    > humidity, the delta-t across an evaporator should

    > be in the range of 17 to 20 degrees, under design

    > conditions.

    >

    > If the humidity is high, expect

    > the delta-t to be lower.

    >

    > If the humidity is

    > low, expect the delta-t to be higher.

    >

    > Remember

    > that the evaporator coil on an air conditioning

    > system does two things. It dehumidifies and

    > cools. If the humidity is high, more of the

    > coil's capacity is used to dehumidify and less to

    > cool. If the humidity is low, more of the coil's

    > capacity can be used to cool the air, resulting

    > in a higher delta-t across the coil.



  • AC newbie
    AC newbie Member Posts: 11
    So What

    > Two important temperatures that are used by the

    > HVAC technician are the wet bulb and dry bulb

    > temperature of the air.

    >

    > The dry bulb

    > temperature is the temperature obtained by using

    > a regular thermometer. When we say that it is 75

    > degrees outside, we are talking about dry bulb

    > temperatures.

    >

    > The other temperature, the wet

    > bulb temperature, takes into account the relative

    > humidity of the air and is measured with a

    > wet-bulb thermometer. The wet bulb thermomter is

    > basically a drybulb thermometer that has a cotton

    > "sock" around the bulb that is soaked with

    > distilled water.

    >

    > Here's the concept on how

    > the wet-bulb thermometer works:

    >

    > As moisture

    > evaporates, heat is absorbed from its

    > surroundings. This concept is referred to as

    > evaporative cooling. For example, when we are hot

    > we sweat. When a cool breeze blows, we are

    > suddenly cooled. THis is because the air moving

    > across our skin causes the moisture (sweat) to

    > evaporate. The evaporating moisture absorbs heat

    > from our skin, making us feel cool.

    >

    > If

    > however, the air was very humid, the air would

    > not be able to hold the evaporating moisture from

    > our skin. This is why we feel clammy when it is

    > humid outside.

    >

    > Now, back to the wet-bulb and

    > dry-bulb temperatures.

    >

    > There is a tool called

    > a sling psychrometer that is made up of two

    > thermometers, one wet-bulb and one dry bulb.

    > The device is swung in the air for about a

    > minute. As the thermometers are passing through

    > the air, the dry bulb thermometer is taking the

    > (sensible heat) temperature of the air. While

    > this is happening, moisture from the wetted wich

    > on the wet-bulb thermometer is likely

    > evaporating. As the water evaporates, heat is

    > absorbed from the thermometer bulb and the

    > temperature of that thermometer bulb will drop to

    > a temperature below that on the dry bulb

    > thermometer.

    >

    > If the relative humidity is very

    > low, the surrounding air can hold a lot more

    > moisture and the rate of evaporation from the

    > wick will be high and the wet bulb reading will

    > much lower than the dry bulb reading. If the

    > humidity is very high, very little moisture will

    > evaporate and the wet-bulb reading will be very

    > close to the dry bulb reading.

    >

    > If the

    > wet-bulb and dry-bulb temperatures are the same,

    > the relative humidity is 100%.

    >

    > The sling

    > psyhrometer also has a feature that allows you to

    > align the wet and dry bulb temperatures to

    > determine the relative humidity.

    >

    > The relative

    > humidity is important since the design air

    > temperatures at which air conditioning systems

    > operate is 50%.

    >

    > For example, at 50% relative

    > humidity, the delta-t across an evaporator should

    > be in the range of 17 to 20 degrees, under design

    > conditions.

    >

    > If the humidity is high, expect

    > the delta-t to be lower.

    >

    > If the humidity is

    > low, expect the delta-t to be higher.

    >

    > Remember

    > that the evaporator coil on an air conditioning

    > system does two things. It dehumidifies and

    > cools. If the humidity is high, more of the

    > coil's capacity is used to dehumidify and less to

    > cool. If the humidity is low, more of the coil's

    > capacity can be used to cool the air, resulting

    > in a higher delta-t across the coil.



  • AC newbie
    AC newbie Member Posts: 11
    So What

    > Two important temperatures that are used by the

    > HVAC technician are the wet bulb and dry bulb

    > temperature of the air.

    >

    > The dry bulb

    > temperature is the temperature obtained by using

    > a regular thermometer. When we say that it is 75

    > degrees outside, we are talking about dry bulb

    > temperatures.

    >

    > The other temperature, the wet

    > bulb temperature, takes into account the relative

    > humidity of the air and is measured with a

    > wet-bulb thermometer. The wet bulb thermomter is

    > basically a drybulb thermometer that has a cotton

    > "sock" around the bulb that is soaked with

    > distilled water.

    >

    > Here's the concept on how

    > the wet-bulb thermometer works:

    >

    > As moisture

    > evaporates, heat is absorbed from its

    > surroundings. This concept is referred to as

    > evaporative cooling. For example, when we are hot

    > we sweat. When a cool breeze blows, we are

    > suddenly cooled. THis is because the air moving

    > across our skin causes the moisture (sweat) to

    > evaporate. The evaporating moisture absorbs heat

    > from our skin, making us feel cool.

    >

    > If

    > however, the air was very humid, the air would

    > not be able to hold the evaporating moisture from

    > our skin. This is why we feel clammy when it is

    > humid outside.

    >

    > Now, back to the wet-bulb and

    > dry-bulb temperatures.

    >

    > There is a tool called

    > a sling psychrometer that is made up of two

    > thermometers, one wet-bulb and one dry bulb.

    > The device is swung in the air for about a

    > minute. As the thermometers are passing through

    > the air, the dry bulb thermometer is taking the

    > (sensible heat) temperature of the air. While

    > this is happening, moisture from the wetted wich

    > on the wet-bulb thermometer is likely

    > evaporating. As the water evaporates, heat is

    > absorbed from the thermometer bulb and the

    > temperature of that thermometer bulb will drop to

    > a temperature below that on the dry bulb

    > thermometer.

    >

    > If the relative humidity is very

    > low, the surrounding air can hold a lot more

    > moisture and the rate of evaporation from the

    > wick will be high and the wet bulb reading will

    > much lower than the dry bulb reading. If the

    > humidity is very high, very little moisture will

    > evaporate and the wet-bulb reading will be very

    > close to the dry bulb reading.

    >

    > If the

    > wet-bulb and dry-bulb temperatures are the same,

    > the relative humidity is 100%.

    >

    > The sling

    > psyhrometer also has a feature that allows you to

    > align the wet and dry bulb temperatures to

    > determine the relative humidity.

    >

    > The relative

    > humidity is important since the design air

    > temperatures at which air conditioning systems

    > operate is 50%.

    >

    > For example, at 50% relative

    > humidity, the delta-t across an evaporator should

    > be in the range of 17 to 20 degrees, under design

    > conditions.

    >

    > If the humidity is high, expect

    > the delta-t to be lower.

    >

    > If the humidity is

    > low, expect the delta-t to be higher.

    >

    > Remember

    > that the evaporator coil on an air conditioning

    > system does two things. It dehumidifies and

    > cools. If the humidity is high, more of the

    > coil's capacity is used to dehumidify and less to

    > cool. If the humidity is low, more of the coil's

    > capacity can be used to cool the air, resulting

    > in a higher delta-t across the coil.



  • AC newbie
    AC newbie Member Posts: 11
    Wh

    > Two important temperatures that are used by the

    > HVAC technician are the wet bulb and dry bulb

    > temperature of the air.

    >

    > The dry bulb

    > temperature is the temperature obtained by using

    > a regular thermometer. When we say that it is 75

    > degrees outside, we are talking about dry bulb

    > temperatures.

    >

    > The other temperature, the wet

    > bulb temperature, takes into account the relative

    > humidity of the air and is measured with a

    > wet-bulb thermometer. The wet bulb thermomter is

    > basically a drybulb thermometer that has a cotton

    > "sock" around the bulb that is soaked with

    > distilled water.

    >

    > Here's the concept on how

    > the wet-bulb thermometer works:

    >

    > As moisture

    > evaporates, heat is absorbed from its

    > surroundings. This concept is referred to as

    > evaporative cooling. For example, when we are hot

    > we sweat. When a cool breeze blows, we are

    > suddenly cooled. THis is because the air moving

    > across our skin causes the moisture (sweat) to

    > evaporate. The evaporating moisture absorbs heat

    > from our skin, making us feel cool.

    >

    > If

    > however, the air was very humid, the air would

    > not be able to hold the evaporating moisture from

    > our skin. This is why we feel clammy when it is

    > humid outside.

    >

    > Now, back to the wet-bulb and

    > dry-bulb temperatures.

    >

    > There is a tool called

    > a sling psychrometer that is made up of two

    > thermometers, one wet-bulb and one dry bulb.

    > The device is swung in the air for about a

    > minute. As the thermometers are passing through

    > the air, the dry bulb thermometer is taking the

    > (sensible heat) temperature of the air. While

    > this is happening, moisture from the wetted wich

    > on the wet-bulb thermometer is likely

    > evaporating. As the water evaporates, heat is

    > absorbed from the thermometer bulb and the

    > temperature of that thermometer bulb will drop to

    > a temperature below that on the dry bulb

    > thermometer.

    >

    > If the relative humidity is very

    > low, the surrounding air can hold a lot more

    > moisture and the rate of evaporation from the

    > wick will be high and the wet bulb reading will

    > much lower than the dry bulb reading. If the

    > humidity is very high, very little moisture will

    > evaporate and the wet-bulb reading will be very

    > close to the dry bulb reading.

    >

    > If the

    > wet-bulb and dry-bulb temperatures are the same,

    > the relative humidity is 100%.

    >

    > The sling

    > psyhrometer also has a feature that allows you to

    > align the wet and dry bulb temperatures to

    > determine the relative humidity.

    >

    > The relative

    > humidity is important since the design air

    > temperatures at which air conditioning systems

    > operate is 50%.

    >

    > For example, at 50% relative

    > humidity, the delta-t across an evaporator should

    > be in the range of 17 to 20 degrees, under design

    > conditions.

    >

    > If the humidity is high, expect

    > the delta-t to be lower.

    >

    > If the humidity is

    > low, expect the delta-t to be higher.

    >

    > Remember

    > that the evaporator coil on an air conditioning

    > system does two things. It dehumidifies and

    > cools. If the humidity is high, more of the

    > coil's capacity is used to dehumidify and less to

    > cool. If the humidity is low, more of the coil's

    > capacity can be used to cool the air, resulting

    > in a higher delta-t across the coil.



  • AC newbie
    AC newbie Member Posts: 11
    Wh

    > Two important temperatures that are used by the

    > HVAC technician are the wet bulb and dry bulb

    > temperature of the air.

    >

    > The dry bulb

    > temperature is the temperature obtained by using

    > a regular thermometer. When we say that it is 75

    > degrees outside, we are talking about dry bulb

    > temperatures.

    >

    > The other temperature, the wet

    > bulb temperature, takes into account the relative

    > humidity of the air and is measured with a

    > wet-bulb thermometer. The wet bulb thermomter is

    > basically a drybulb thermometer that has a cotton

    > "sock" around the bulb that is soaked with

    > distilled water.

    >

    > Here's the concept on how

    > the wet-bulb thermometer works:

    >

    > As moisture

    > evaporates, heat is absorbed from its

    > surroundings. This concept is referred to as

    > evaporative cooling. For example, when we are hot

    > we sweat. When a cool breeze blows, we are

    > suddenly cooled. THis is because the air moving

    > across our skin causes the moisture (sweat) to

    > evaporate. The evaporating moisture absorbs heat

    > from our skin, making us feel cool.

    >

    > If

    > however, the air was very humid, the air would

    > not be able to hold the evaporating moisture from

    > our skin. This is why we feel clammy when it is

    > humid outside.

    >

    > Now, back to the wet-bulb and

    > dry-bulb temperatures.

    >

    > There is a tool called

    > a sling psychrometer that is made up of two

    > thermometers, one wet-bulb and one dry bulb.

    > The device is swung in the air for about a

    > minute. As the thermometers are passing through

    > the air, the dry bulb thermometer is taking the

    > (sensible heat) temperature of the air. While

    > this is happening, moisture from the wetted wich

    > on the wet-bulb thermometer is likely

    > evaporating. As the water evaporates, heat is

    > absorbed from the thermometer bulb and the

    > temperature of that thermometer bulb will drop to

    > a temperature below that on the dry bulb

    > thermometer.

    >

    > If the relative humidity is very

    > low, the surrounding air can hold a lot more

    > moisture and the rate of evaporation from the

    > wick will be high and the wet bulb reading will

    > much lower than the dry bulb reading. If the

    > humidity is very high, very little moisture will

    > evaporate and the wet-bulb reading will be very

    > close to the dry bulb reading.

    >

    > If the

    > wet-bulb and dry-bulb temperatures are the same,

    > the relative humidity is 100%.

    >

    > The sling

    > psyhrometer also has a feature that allows you to

    > align the wet and dry bulb temperatures to

    > determine the relative humidity.

    >

    > The relative

    > humidity is important since the design air

    > temperatures at which air conditioning systems

    > operate is 50%.

    >

    > For example, at 50% relative

    > humidity, the delta-t across an evaporator should

    > be in the range of 17 to 20 degrees, under design

    > conditions.

    >

    > If the humidity is high, expect

    > the delta-t to be lower.

    >

    > If the humidity is

    > low, expect the delta-t to be higher.

    >

    > Remember

    > that the evaporator coil on an air conditioning

    > system does two things. It dehumidifies and

    > cools. If the humidity is high, more of the

    > coil's capacity is used to dehumidify and less to

    > cool. If the humidity is low, more of the coil's

    > capacity can be used to cool the air, resulting

    > in a higher delta-t across the coil.



  • AC newbie
    AC newbie Member Posts: 11
    tools

    Which tool is better digital or the manual one you talked about. Any idea what they cost?
  • John Starcher_4
    John Starcher_4 Member Posts: 794
    Home-boy!!!!!!!!!!!!!!!!!!

    Glad to see you here, pal!

    Starch
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