Thank you so much for sharing these videos! I have a question : Let’s say the Supply Air is calculated to be 3200 CFM delivered to my house .And the Exhaust Fan removed 2000 CFM clean air to outside my house .Does the Supply Air change to be 5200 CFM (replacing the 2000 CFM EA)? , or Shall it stay constant = 3200 CFM? Case# 1 Exhaust Air goes out through the Return Air duct. Case #2 Exhaust Air removed outside directly in a independent duct without mixing with the RA. Thanks again,
Engineering team reply - Generally speaking the supply and return airflow will be the same, so if your house is supplied with 3200 CFM, the return will be 3200 CFM. Some of this supply air will be made up of outside ventilation air - 900 CFM for example, the exhaust air will be also be 900 CFM. The exhaust airflow is subtracted from return airflow to calculate the recirculation airflow which is 3200 - 900 = 2300 CFM. In some applications the supply airflow may be slightly higher or lower than the return air in order to control the pressure of a room to either positive of negative pressure relative to the adjacent rooms, for example, infectious isolation hospital rooms are controlled to a negative pressure so the return airflow will be slightly less than the supply.
Does a return opening have to go through a duct?? Coz' in our house for a few years now, my dad i think he came up with something regarding our ducted split AC (concealed) and I'd like to ask if it's right or is it going to cause the ACs to stop working any soon!.. Regarding the internal units; my dad who is not an engineer decided to make a gyps ceiling hiding two internal units for two ACs in our big space area inside the house but only one RETURN wich is NOT DUCTED or anything. The air just go inside the gyps ceiling which has two internal units with ducts to supply cold air, BUT no duct for the return. could that be right? Thanks..
Is it common for the return air not to be completely ducted on its way to the air handler? In my 1965 condo building each condo has its dedicated air handler (a hydronic heat pump) located in a common area closet hallway. Each condo shares this closet with 1 other neighbor and THEIR heat pump. The return air from my unit enters this hallway closet through a cavity up near the top of the closet wall. The cavity does NOT connect to the air handler via ductwork. It just enters the closet space to (eventually) find its way just outside the air filter used on the pump. I'm guessing there's no duct due to the very limited space of the closet...can't have a duct blocking access to the heat pump and there's not really any room for a duct to come out of the filter side of pump because the partition wall that separates it from my NEIGHBOR'S side of pump closet is only a few inches away. Are you familiar with this sort of ductless return air setup? Thank you!
This type of return is very common in commercial buildings as well. Often the cavity above the ceiling serves as a return plenum where the return air from multiple spaces is drawn through it and back to a common air handling unit that serves the various spaces. There are certain applications where this type of return is not allowed. For example, air returned from a patient room or laboratory must be completely ducted back to the air handling unit. This is because of the possibility of spreading gases or other hazardous contaminants between spaces. In this case, the return is labeled as an exhaust as its volume flow rate must be controlled to balance the space supply airflow rate and maintain proper space pressurization. We hope this helps.
Although it is sometimes desirable to filter return air at a return air grille, it is standard practice to filter all air at the air handler. This is necessary to keep the air handler coils clean.
Yes. The air handler diagram in the podcast was missing a detail. Both ventilation and return air should be filtered prior to reaching the heating and cooling coils of the air handler. Therefore a filter should have been included upstream from the coils.
I could have sworn the man who installed my handler last year said he closed off the return air in the garage because it wasn't allowed to recirculate?
That’s not surprising at all. Return air and ventilation air should never be taken from any place where exhaust fumes from vehicles may be present. That would include parking garages, passenger drop off/pick-up areas, and loading dock areas.
wow thanks for such a straight forward explanation without showing multiple calcs/tables
very simple yet powerful explanation for difference between exhaust, fresh and return air. thank you!
Jenni excellent information. thank you, you're an expert.
Hello, Very simple to understand. thank you very much
very very powerful interesting
God bless you Jenny
HVAC terms can be oh so confusing sometimes. Thanks for the clarity!
Very good explanation
thank you!!!!!!!
Thanks you
Thank you for this very helpful video. I was wondering what software are you using for illustrating your diagrams?
I use the Explain Everything app on the iPad to do the drawing and then Camtasia on my laptop to do the voiceover.
Well done
Thank you so much for sharing these videos!
I have a question :
Let’s say the Supply Air is calculated to be 3200 CFM delivered to my house .And the Exhaust Fan removed 2000 CFM clean air to outside my house .Does the Supply Air change to be 5200 CFM (replacing the 2000 CFM EA)? , or Shall it stay constant = 3200 CFM?
Case# 1 Exhaust Air goes out through the Return Air duct.
Case #2 Exhaust Air removed outside directly in a independent duct without mixing with the RA.
Thanks again,
Engineering team reply - Generally speaking the supply and return airflow will be the same, so if your house is supplied with 3200 CFM, the return will be 3200 CFM. Some of this supply air will be made up of outside ventilation air - 900 CFM for example, the exhaust air will be also be 900 CFM. The exhaust airflow is subtracted from return airflow to calculate the recirculation airflow which is 3200 - 900 = 2300 CFM. In some applications the supply airflow may be slightly higher or lower than the return air in order to control the pressure of a room to either positive of negative pressure relative to the adjacent rooms, for example, infectious isolation hospital rooms are controlled to a negative pressure so the return airflow will be slightly less than the supply.
@@TitusHVAC
Thank you so much for your thorough explanation 👍
Supply leaks create a negative-pressure condition due to the room's ability to return more air (negative pressure from the blower).
Does a return opening have to go through a duct?? Coz' in our house for a few years now, my dad i think he came up with something regarding our ducted split AC (concealed) and I'd like to ask if it's right or is it going to cause the ACs to stop working any soon!.. Regarding the internal units; my dad who is not an engineer decided to make a gyps ceiling hiding two internal units for two ACs in our big space area inside the house but only one RETURN wich is NOT DUCTED or anything. The air just go inside the gyps ceiling which has two internal units with ducts to supply cold air, BUT no duct for the return. could that be right? Thanks..
This sounds like an issue you should address with a residential HVAC technician to see if your air is being distributed correctly.
Is it common for the return air not to be completely ducted on its way to the air handler?
In my 1965 condo building each condo has its dedicated air handler (a hydronic heat pump) located in a common area closet hallway. Each condo shares this closet with 1 other neighbor and THEIR heat pump.
The return air from my unit enters this hallway closet through a cavity up near the top of the closet wall. The cavity does NOT connect to the air handler via ductwork. It just enters the closet space to (eventually) find its way just outside the air filter used on the pump.
I'm guessing there's no duct due to the very limited space of the closet...can't have a duct blocking access to the heat pump and there's not really any room for a duct to come out of the filter side of pump because the partition wall that separates it from my NEIGHBOR'S side of pump closet is only a few inches away.
Are you familiar with this sort of ductless return air setup?
Thank you!
This type of return is very common in commercial buildings as well. Often the cavity above the ceiling serves as a return plenum where the return air from multiple spaces is drawn through it and back to a common air handling unit that serves the various spaces.
There are certain applications where this type of return is not allowed. For example, air returned from a patient room or laboratory must be completely ducted back to the air handling unit. This is because of the possibility of spreading gases or other hazardous contaminants between spaces. In this case, the return is labeled as an exhaust as its volume flow rate must be controlled to balance the space supply airflow rate and maintain proper space pressurization.
We hope this helps.
Question do you need filter in that handler because the return air has a filter
Although it is sometimes desirable to filter return air at a return air grille, it is standard practice to filter all air at the air handler. This is necessary to keep the air handler coils clean.
So the exhaust air mixes with the return air and ventilation air or also stated “outside side air “ ?
Also the exhaust air is the air that goes outside right through duct or some type of pipe like flue gas ?
Does return air pass through the furnace filter?
Yes. The air handler diagram in the podcast was missing a detail. Both ventilation and return air should be filtered prior to reaching the heating and cooling coils of the air handler. Therefore a filter should have been included upstream from the coils.
Can u pls explain how to calculate size of this mixing plenum
The plenum cross sectional area is typically that which will result in a 450 to 500 FPM face velocity through the filters and heat transfer coils.
I could have sworn the man who installed my handler last year said he closed off the return air in the garage because it wasn't allowed to recirculate?
That’s not surprising at all. Return air and ventilation air should never be taken from any place where exhaust fumes from vehicles may be present. That would include parking garages, passenger drop off/pick-up areas, and loading dock areas.