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Old 04-03-2013, 02:57 PM   #16
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Humidity question


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Yep, been in the trade 38 years.

There are several HVAC tradesmen on this forum. We will all help if we can.
quick question. The filter drier on an a/c or refrigerator is used to remove any moisture buildup before the vapor enters the compressor, correct? So, that means its located on the vapor line?

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Old 04-03-2013, 04:29 PM   #17
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Humidity question


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I have another quick question. There is a clear vinyl tube coming from the return duct to round device. I believe its a pressure switch. What is that for? Also, when you increase the relative humidity on the humidistat does more water get produced for the evaporator pad or what actually happens when you turn the dial to increase humidity?
It does hook to a pressure switch. The blower has to be running for the humidifier to work. So they are using a pressure switch to sense when the blower is running.

When you turn the humidistat higher. It doesn't run more water per minute. It just keeps the humidifier running longer while the blower is running.
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Old 04-03-2013, 04:33 PM   #18
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Humidity question


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How come the humidifier air has to pass through the return side if the supply side air is what is being blown into the rooms? Reason I ask is because the return air is obviously cold.
Because air must go through the pad in order to pick up moisture. Since that humidifier itself doesn't have a fan to draw the supply air in and then blow it back out into the supply plenum. it needs the air to go through the pad and then into the return air. Where it will mix with all the return air, and increase the moisture content of the air that is not blown back into the humidifier.
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Old 04-03-2013, 04:38 PM   #19
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Humidity question


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quick question. The filter drier on an a/c or refrigerator is used to remove any moisture buildup before the vapor enters the compressor, correct? So, that means its located on the vapor line?
Filter driers are generally installed on the liquid line. Where they can be left in as long long term protection.

Suction line filter driers are used sometimes on systems that may have a lot of moisture(trapped in oil in the system besides the compressor) or other contaminates in the rest of the system. But suction filter driers are suppose to be removed after 72 hours of compressor run time. As they can clog easily.
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Old 04-03-2013, 06:41 PM   #20
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Humidity question


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Because air must go through the pad in order to pick up moisture. Since that humidifier itself doesn't have a fan to draw the supply air in and then blow it back out into the supply plenum. it needs the air to go through the pad and then into the return air. Where it will mix with all the return air, and increase the moisture content of the air that is not blown back into the humidifier.
But with cold water and cold air return how would you actually get that moisture? My humidifier is mounted on the supply plenum. So the hot air that passes over the pad collects that cold water, thus evaporating it, then that air is drawn through the bypass duct and into the cold return air?
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Old 04-03-2013, 07:23 PM   #21
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But with cold water and cold air return how would you actually get that moisture? My humidifier is mounted on the supply plenum. So the hot air that passes over the pad collects that cold water, thus evaporating it, then that air is drawn through the bypass duct and into the cold return air?
Cold air return is somewhat only a term. The air isn't cold, its room temp. The hot air evaporates the water. its carried into the return air. The return air's RH is slightly increased. Drawn into the furnace and blown into the homes rooms by the supply.

Its a gradual process.
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Old 04-03-2013, 10:08 PM   #22
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Humidity question


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Cold air return is somewhat only a term. The air isn't cold, its room temp. The hot air evaporates the water. its carried into the return air. The return air's RH is slightly increased. Drawn into the furnace and blown into the homes rooms by the supply.

Its a gradual process.
As I said before I started an HVAC program. I wanted to run by the a/c process and if you can let me know if I'm correct I would appreciate it.

Refrigerant enters the compress as a low pressure vapor and leaves as a high pressure high temp. vapor. It then travels to the condenser where the outside air that is in contact with the coils caused the vapor to condense into a high pressure low temp liquid. From the condenser it goes to a metering device just before reaching the evaporator. At the metering device the liquid is squeezed through a tiny hole where it is now at low pressure and still a liquid. Once it enters the evaporator it is a low pressure low temp. liquid and as warm return air passes over the coils the refrigerant absorbs that heat causing it to change to a low pressure low temp vapor. What is left over is cool coils that the air absorbs as it passes over. The low pressure low temp vapor then travels to the condenser where its heat is extracted to the outside through the condenser fan. As its heat is given up it changes state back to a liquid under high pressure low temp. After that it goes back to the compressor and the cycle repeats. Does this sound correct to you?
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Old 04-04-2013, 04:18 AM   #23
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Low pressure low temp vapor enters the compressor, it leaves the compressor as high pressure high temp gas and enters the condenser coil. As the gas cools in the condenser coil, it condenses and becomes a high pressure low temp liquid. It leaves the condenser and travels through the metering deice of the evap. After leaving the metering device it is a low pressure low temp liquid. In the evap it boils to a vapor absorbing heat from the air traveling over the evap coil. It leaves the evap as a low pressure low temp vapor/gas. It then travels to the compressor to repeat the previous cycle.

When the refrigerant leaves the condenser. It is a high pressure sub cooled liquid. When it leaves the evap it is a low pressure low temp super heater vapor. The refrigerant vapor entering the compressor, is also used to cool the compressor.
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Old 04-04-2013, 08:25 AM   #24
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Low pressure low temp vapor enters the compressor, it leaves the compressor as high pressure high temp gas and enters the condenser coil. As the gas cools in the condenser coil, it condenses and becomes a high pressure low temp liquid. It leaves the condenser and travels through the metering deice of the evap. After leaving the metering device it is a low pressure low temp liquid. In the evap it boils to a vapor absorbing heat from the air traveling over the evap coil. It leaves the evap as a low pressure low temp vapor/gas. It then travels to the compressor to repeat the previous cycle.

When the refrigerant leaves the condenser. It is a high pressure sub cooled liquid. When it leaves the evap it is a low pressure low temp super heater vapor. The refrigerant vapor entering the compressor, is also used to cool the compressor.
So, would you say my explanation was correct then?
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Old 04-04-2013, 09:24 AM   #25
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I thought you said you were going to an HVAC course. In 101 They should be teaching you the basics of how air conditioning works, vis a vis evaporation and condensation. There are some really good animated illustrations on the internet that show the cycle. Here you go.
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Last edited by jagans; 04-04-2013 at 09:28 AM.
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Old 04-04-2013, 10:03 AM   #26
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Humidity question


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I thought you said you were going to an HVAC course. In 101 They should be teaching you the basics of how air conditioning works, vis a vis evaporation and condensation. There are some really good animated illustrations on the internet that show the cycle. Here you go.
What was wrong with my explanation? Seemed to be correct based on the response from beenthere.
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Old 04-04-2013, 10:07 AM   #27
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Humidity question


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Low pressure low temp vapor enters the compressor, it leaves the compressor as high pressure high temp gas and enters the condenser coil. As the gas cools in the condenser coil, it condenses and becomes a high pressure low temp liquid. It leaves the condenser and travels through the metering deice of the evap. After leaving the metering device it is a low pressure low temp liquid. In the evap it boils to a vapor absorbing heat from the air traveling over the evap coil. It leaves the evap as a low pressure low temp vapor/gas. It then travels to the compressor to repeat the previous cycle.

When the refrigerant leaves the condenser. It is a high pressure sub cooled liquid. When it leaves the evap it is a low pressure low temp super heater vapor. The refrigerant vapor entering the compressor, is also used to cool the compressor.
What are you thoughts on reflective heat barriers installed on the attic floor? They said it prevents up to 95% of of heat loss and heat gain.
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Old 04-04-2013, 10:28 AM   #28
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Humidity question


If you are asking me, I have not done any research on reflective heat barriers, so I cannot say. I can say that at 66 years old I have learned that anything that sounds too good to be true, usually is. My rule of thumb when it comes to anything related to the building envelope is that most claims are made based on wild speculation and ignorance of the facts, and mother nature has a way of blowing away all of what the egg heads come up with in the lab, or more probably, at a sales meeting.

Common sense, and do the math based on facts is always the best way to go.
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Old 04-04-2013, 02:21 PM   #29
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Humidity question


The warm air from the supply side absorbs the moisture and is directed through the return air so the fan will pick iyt up and deliver to the occupied space. Also, thsupply side has a more positive pressure and is required to force the air over the humidifier pad then get cycled through the fan to the supply air registers.

The clear plastic tubing is the sensing line for the air proving switch. Once the induced draft fan starts the pressure switch senses the pressure differential/vacuum then allows the pilot to light..No air proving..ignition sequence not allowed. If prioven then pilot will attempt to light..if it lights then the pilot flame has to be proven before the main gas valve opens. This is to make sure there is a source of ignition when the main valve opens. Otherwise gas could accumulate and cause a fire or explosion if there is a delayed ignition from the igniter assembly. There are different systems and means for proving. Should learn about them in your course.
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Old 04-04-2013, 05:03 PM   #30
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So, would you say my explanation was correct then?

Except your last sentence or 2 has the low temp vapor going to the condenser coil then back to the compressor. Which is reverse of what happens.

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