Great presentation. Will's Climate Comfort LLC out of New Jersey. I have argued this very fact so many times and distributors, other contractors and worse, home owners don't get it. Thank you. This will make my job much easier once I share your presentation.
Nobody like the bypass damper but it is an necessary eval to make the air noise at a register tolerable. This is an eye opener to start working with variable speed motors. Now give us these results. Thanks, NAS
Removing the bypass on a tiny window shaker with only two zones may not be a problem, but it certainly is on 10 ton and up with five plus zones. These are not used for energy savings, but to protect the equipment from high static pressure, and insufficient heat transfer when zones are closed.
It doesn’t have to be 10 ton big system. Same problem will happen on a small resi system. If you don’t move that heat out of the main trunk it’s gonna trip the high limit on a cold -10 to -20 night.
This illustration is done with either a "OPEN" or "CLOSED" damper - nothing in between. So, of course you will have some significant losses - and it is "DUMB". BUT...this is not the proper way to do it in the field, nor have I come across one that is either on or off like that. However, BAROMETRIC or Static Pressure control dampers only lower the main trunk supply static pressure enough to maintain proper airflow through the calling zones and across the coil. Of course, a similar approach would be to have a calibrated ECM (variable speed) blower or Multi-Speed (2 or 3 speed) blower to provide close to optimal static pressures and CFM's in calling zones. However, as with many older systems out there, many blowers are set on max speed to be able to provide proper airflow over the coil AND to be able to provide all zones with proper CFM. In this case especially, a properly setup barometric or static pressure controlled damper is the best solution. So, I do not agree with your assertion that "Bypass Dampers are Dumb".
You correctly point out that his test doesn't duplicate a correctly installed bypass damper. I still think that a better way to achieve the same ends is to adjust the non calling dampers to bleed air. I still think that bypass dampers are dumb.
@@Marty1911 Totally agree with you, I’ve been doing it for years without a bypass. Just bleed some of the air to other zones and call it a good system instead of having that dumb idea of bypassing
I'm sure it was a quick solution to a persistent problem that some zone control systems didn't want to handle in the past and it stuck around like a bad rumor. Haha
I like old school engineering with a mock up setup to prove a point with a set of DOEs( Design of Experiments) . As many have pointed out the test is flawed and usually the bypass is weight or spring loaded to dump a certain amount of air into the return . One of the main considerations in a home environment is comfort . Noise , airflow have to be optimised and they become priority The gentleman in trying to help but responding to the comments and actively engaging with the viewers would have been nice
Thank you for your explanation and math examples. I understood everything you explained and as a teacher see the need for our kids to practice paper pencil real world problems.
I'm only a home owner but I see a flaw here based upon my experience. These are equal sized zones with no backpressure. I have three zones: the smallest is two guest bedrooms (500 SF) in a walk out basement, next is the balance of the basement (1,500SF) and finally the main floor (2,200SF). Without a bypass my furnace sounded like a jet engine and made noise (vibration) when heating the smallest zone only.
Your thoughts on ewc smart bypass? Have one that has failed electronically and they're very expensive. Ideas on something else as i really have to have bypass on this 5 zone.
Great little demo, but something is wrong. When the bypass damper is open, some of the low temperature (42deg ) supply air is mixing with the Return from the space, so the return air temperatures listed should have been lower. With all ducts equal size in this demo, there should be around a 50% mix of 42 deg & 72 deg air, so it should have been around 57-60 deg Mixed air entering the coil. Delta T would drop affecting all calculations as well.
Neat demonstration, however, it does not (as pointed out below by several others) make the case for closing the bypass period. It does appear, at first blush, that routing a portion of the cold air back into the return flow would be wasteful and reduce the temperature over the coil. Problem is, the experiment is as simplistic as it is creative (mechanically converting a window unit to a 'central' distribution system. I suspect that a multi-zone system would employ either atmospheric or digitally-controlled dampers along with variable speed fan(s) to maintain optimal flow though each zone as the calls for each zone are made. It is obvious that, if one is pushing sufficient air to cover an entire system, shutting down half the supply would effectively (attempt) to push all that air through half the system and increase velocity and volume significantly. So, reducing the air flow into the (effectively blocked) system would seem obvious. If you cannot reduce the fan speed (thus pressure), the bypass does work - with the downside of using the same energy to do half the work and (potentially) reducing the temp over the coils long before the desired temp at the registers/room(s) is reached. One would have to agree that a simple manual bypass down in the basement is a jury-rigged approach / solution to a complex issue - not to mention the chore of going dow to the basement or crawling in the attic to turn that bypass damper one way or the other!
So I've read the bypass is to reduce pressure and make the system run quieter. Why not run 8" pipes instead of 6" and then cut air off to one zone when the heating/cooling is not needed in that area? I'm guessing you'd also need twice as much return air as well, which can be difficult.
Is it only dumb for Zoned Systems? What if you just need to balance a little bit of High Static pressure, is it ok to put a small bypass then? (On a traditional non-zoned system)
bypass dampers are not for energy saving. I have three zone system in my house amd it doesn't have bypass. When all zones are on it's perfect, but never are on at the same time, so it feels like the house is taking off. That bad. And also I'm gonna add a baromatric damper, not like that one on the video. it's a great experiment, but unless to me.
What about the fact that the wattage of the system is more when the bypass is closed? You are correct in that you are achieving a higher BTU, due to an increase in flow at the zones' supply with the bypass closed (therefore superficially increasing the SEER), but this would cause the overall system to cycle more than necessary; causing discomfort and shortening the life of the AC. Enjoyed your enthusiasm though! Keep it up :)
1>Your test is flawed, there is little to no static pressure on your test, hence no temperature change with bypass open. All HVAC systems are designed to have static pressure. Your results will be drastic! 2>Zone systems are usually installed 90% for comfort, not $$$ savers so ace the watts. 3>I did enjoy watching this video though :)
Common sense tells me the system will use less energy if all the air flow is being sent to the rooms (no bypass). But saving money is not the only reason for bypassing extra pressure in the system. Especially in the hot humid south where cooling a room more slowly does a better job removing humidity.
I love the fact that you built an example of a system to prove a point. Unfortunately all of your bypass damper open calculations are wrong due to the improper placement of the return temperature sensor. The return temperature sensor for your demonstration should be placed between the bypass damper and the evaporator.
Im a TAB Engineer and let me just say.. on a larger scale, we are usually very close to nameplate nominal amps at 100 - 106% airflow. if you want to save that 27%, put it all aside because in a matter of time you'll be buying a new blower motor for constant over-amping during full load time.
There is never really a clear cut yes or no. A bypass is not for savings it’s for pressure restraints. In my situation and (probably most) a bypass really isn’t needed. For the simple reason that the problem area is usually the furthest away. So if I have problems cooling the top floor, my bottom floor may shut off. The air then has to travel a further distance then if the top was cut off. That’s ok you lose force the further away the exit is. Now if I wanted to shut the top off and only cool the lower floor, that’s a problem and a bypass is needed. Some would do that to save energy if they didn’t want to top cooled. But I prefer a whole house comfort level. So I’ll never not want the top not cooling or hotter than the bottom. Well maybe in the winter. So bottom line depends on the scenario
The evaporator inlet air temp when the bypass is open should be the 50% colder than when the bypass is closed. I think the bypass air flow is not being measured properly because the bypass duct is right up against the coil inlet. I can't see how the return air and bypass air are being mixed but the 70 degree temperature measurement is a contradiction to the 50% rule. Accurate calculations need to be based on a real system with a thermostatic expansion valve that is reacting to load on the coil. Window AC units don't usually have a TXV. Units with a TXV will reduce compressor amps because the TXV valve reduces refrigerant flow as the suction temperature drops. I don't like the bypass and I think it is a waste of energy but this demonstration looks flawed to me.
Bypasses are dumb, but why did you use the sensible heat formula instead of total heat formula to determine your Btus? No consideration for latent heat.
Unless I'm missing something the percentage change (savings) should have been the New - Old / Old. You divided by the New (9.19). So my calculations for the savings was 38% (9:24) 48% (10:06) 28% (10:32). Someone check me please, but even though I'm pretty much exhausted right now, this is pretty much muscle memory for me, so unless I'm completely brain fried right now, I'm seeing different numbers.
There is one problem with his calculations. He is only measuring sensible BTU's and has not accounted for any latent BTU's. What about the extra latent capacity with the colder air? The EER calculation needs to take into account total BTU's which includes both sensible and latent BTUs. Plus with a supply air temperature between 39-42 degrees, he may have been partially frosting the coil. That would be additional latent BTU's not accounted for in his EER calculation.
never in the history of bypass dampers has there been a fully open or fully closed one. your missing the entire point of what it does. its supposed bleed off static pressure from the main truck of a system by sending the extra back into the return. to be clear , modern systems do NOT need a bypass damper. but if youve got an old as house from the 70s or 80s, and you dont want to upgrade your entire heating system, then throwing in some regular dampers inline into all the zones and installing a bypass damper is the correct way to go. after installing, you leave the bypass closed. then run the whole system wide open and adjust the weight position of the damper so it just barely starts to open. then back it off a pinch until its shut. its now set perfectly for the system. after that, you set thermometers in each room or zone and adjust the inline dampers until you get a uniform temperature or whatever youd like in each zone. Then, the bypass takes the extra pressure thas being kicked back from the semi closed dampers and sends it back to the return and keeps your system from burning out. your math is quite good and youre attention to detail is impressive. but to be honest, you just missed the biggest part of the equation. its the equivalent of trying to find the color of a circle. the math youre putting out has nothing to do with the procees you claim is "dumb". not trying to bash ya, you just dont understand the fundamental point in what a bypass damper does. it keeps you from burning out the heat exchanger or the cooling element of the system by relieving static pressure.
Bypass dampers are made to reduce noise by high static pressure that are produced when you reduce the duct volume by closing a damper in a duct . I have never considered a bypass damper or any zoning, for that matter as means to conserve energy. In multi zone configurations that incorporate more than three zones of different sizes a bypass of some kind would be essential. if only one zone is open and that zone was the smallest, without bypass and thermostatic freeze protection the unit would stop working altogether. This guy knows nothing about the application and design of a zoning system or the primary principles in dynamics of air flow as it relates to a air conditioning system.
What you seem to have missed is that when the damper is open, that zone will cool quicker than when it is closed. Nice try. By the way the variable speed fans are EXTREMELY EXPENSIVE.
bypasses are needed for humidification or for noise or pressure issues.....their is always pros and cons to things......should have done this experiment with a furnace in a house...would have been easier than this flawed set up you used here
I am not a fan of zoning, feeding a 140 sf room with a 5 ton condenser is dumb but somebody told the homeowner this would work great. I have seen so many mistakes in installation and so called professional opinions it makes no sense to me. Put in 2 or more systems without zoning and you will have the results you were looking for. Unfortunately builders do not want to spend the money to do that so they sell homeowners on this.
Ugh excuse me just a minute there, your not testing apples for apples sir. If 1 of your dampers goes closed that is 50% your bypass must go to 50% also your not recording cfm readings at all branches, you can't just arbitrarily say that 50% is 50%. If you have 1200cfm system and you close 1 200 cfm supply that doesn't mean you all of a sudden have a 1000cfm system, the air has to go somewhere, thus the bypass takes that additional 200 cfm's. Also you have 2 - 6" round supply branches and 1 - 6" bypass this is not accurate depiction of what you see in the real world, baypasses are much larger than supply branches. Lastly, all of this is mute if the blower is not modulating or on a frequency drive (separate vfd on a 3 speed motor best over ECM motor) Now that sir is where your energy savings come from if you don't slow down the fan you get no savings, but you still must insure that minimum cfm requirements across heat exchangers and coils are being maintained, and you cannot insure this without the awesome very much needed automated bypass damper.
This is just plain ignorance. Your are the reason i have to charge a customer $2000 to fix the zoned system on their new house because the coil keeps freezing. Stick to drawing pictures bud, let us worry about hvac! Im literally adding a bypass on friday.
Great presentation. Will's Climate Comfort LLC out of New Jersey. I have argued this very fact so many times and distributors, other contractors and worse, home owners don't get it. Thank you. This will make my job much easier once I share your presentation.
Nobody like the bypass damper but it is an necessary eval to make the air noise at a register tolerable. This is an eye opener to start working with variable speed motors. Now give us these results. Thanks, NAS
Removing the bypass on a tiny window shaker with only two zones may not be a problem, but it certainly is on 10 ton and up with five plus zones. These are not used for energy savings, but to protect the equipment from high static pressure, and insufficient heat transfer when zones are closed.
It doesn’t have to be 10 ton big system. Same problem will happen on a small resi system. If you don’t move that heat out of the main trunk it’s gonna trip the high limit on a cold -10 to -20 night.
Right on John; the new gen of variable speed condenser/air handlers can be zoned well without foolish bypass.
This illustration is done with either a "OPEN" or "CLOSED" damper - nothing in between. So, of course you will have some significant losses - and it is "DUMB". BUT...this is not the proper way to do it in the field, nor have I come across one that is either on or off like that. However, BAROMETRIC or Static Pressure control dampers only lower the main trunk supply static pressure enough to maintain proper airflow through the calling zones and across the coil. Of course, a similar approach would be to have a calibrated ECM (variable speed) blower or Multi-Speed (2 or 3 speed) blower to provide close to optimal static pressures and CFM's in calling zones. However, as with many older systems out there, many blowers are set on max speed to be able to provide proper airflow over the coil AND to be able to provide all zones with proper CFM. In this case especially, a properly setup barometric or static pressure controlled damper is the best solution. So, I do not agree with your assertion that "Bypass Dampers are Dumb".
You correctly point out that his test doesn't duplicate a correctly installed bypass damper. I still think that a better way to achieve the same ends is to adjust the non calling dampers to bleed air. I still think that bypass dampers are dumb.
@@Marty1911
Totally agree with you, I’ve been doing it for years without a bypass. Just bleed some of the air to other zones and call it a good system instead of having that dumb idea of bypassing
I'm sure it was a quick solution to a persistent problem that some zone control systems didn't want to handle in the past and it stuck around like a bad rumor. Haha
I like old school engineering with a mock up setup to prove a point with a set of DOEs( Design of Experiments) . As many have pointed out the test is flawed and usually the bypass is weight or spring loaded to dump a certain amount of air into the return . One of the main considerations in a home environment is comfort . Noise , airflow have to be optimised and they become priority
The gentleman in trying to help but responding to the comments and actively engaging with the viewers would have been nice
Thank you for your explanation and math examples. I understood everything you explained and as a teacher see the need for our kids to practice paper pencil real world problems.
THANK YOU…THANK YOU!! I’ve been saying this for YEARS!
I'm only a home owner but I see a flaw here based upon my experience. These are equal sized zones with no backpressure. I have three zones: the smallest is two guest bedrooms (500 SF) in a walk out basement, next is the balance of the basement (1,500SF) and finally the main floor (2,200SF). Without a bypass my furnace sounded like a jet engine and made noise (vibration) when heating the smallest zone only.
Your thoughts on ewc smart bypass? Have one that has failed electronically and they're very expensive. Ideas on something else as i really have to have bypass on this 5 zone.
Great little demo, but something is wrong. When the bypass damper is open, some of the low temperature (42deg ) supply air is mixing with the Return from the space, so the return air temperatures listed should have been lower. With all ducts equal size in this demo, there should be around a 50% mix of 42 deg & 72 deg air, so it should have been around 57-60 deg Mixed air entering the coil. Delta T would drop affecting all calculations as well.
Good catch, John.
Neat demonstration, however, it does not (as pointed out below by several others) make the case for closing the bypass period.
It does appear, at first blush, that routing a portion of the cold air back into the return flow would be wasteful and reduce the temperature over the coil. Problem is, the experiment is as simplistic as it is creative (mechanically converting a window unit to a 'central' distribution system. I suspect that a multi-zone system would employ either atmospheric or digitally-controlled dampers along with variable speed fan(s) to maintain optimal flow though each zone as the calls for each zone are made.
It is obvious that, if one is pushing sufficient air to cover an entire system, shutting down half the supply would effectively (attempt) to push all that air through half the system and increase velocity and volume significantly. So, reducing the air flow into the (effectively blocked) system would seem obvious. If you cannot reduce the fan speed (thus pressure), the bypass does work - with the downside of using the same energy to do half the work and (potentially) reducing the temp over the coils long before the desired temp at the registers/room(s) is reached.
One would have to agree that a simple manual bypass down in the basement is a jury-rigged approach / solution to a complex issue - not to mention the chore of going dow to the basement or crawling in the attic to turn that bypass damper one way or the other!
From what I could tell the wattage was lower with the bypass open. Meaning ther was less stress on the blower motor
Yes, but if the lower wattage delivers a higher CFM of cool air, the thermostat will shut off the AC sooner, and savings are achieved.
So I've read the bypass is to reduce pressure and make the system run quieter. Why not run 8" pipes instead of 6" and then cut air off to one zone when the heating/cooling is not needed in that area? I'm guessing you'd also need twice as much return air as well, which can be difficult.
Is it only dumb for Zoned Systems? What if you just need to balance a little bit of High Static pressure, is it ok to put a small bypass then? (On a traditional non-zoned system)
bypass dampers are not for energy saving. I have three zone system in my house amd it doesn't have bypass. When all zones are on it's perfect, but never are on at the same time, so it feels like the house is taking off. That bad. And also I'm gonna add a baromatric damper, not like that one on the video. it's a great experiment, but unless to me.
What about the fact that the wattage of the system is more when the bypass is closed? You are correct in that you are achieving a higher BTU, due to an increase in flow at the zones' supply with the bypass closed (therefore superficially increasing the SEER), but this would cause the overall system to cycle more than necessary; causing discomfort and shortening the life of the AC.
Enjoyed your enthusiasm though! Keep it up :)
Do a video on how you built that demo machine/system!
1>Your test is flawed, there is little to no static pressure on your test, hence no temperature change with bypass open. All HVAC systems are designed to have static pressure. Your results will be drastic!
2>Zone systems are usually installed 90% for comfort, not $$$ savers so ace the watts.
3>I did enjoy watching this video though :)
Common sense tells me the system will use less energy if all the air flow is being sent to the rooms (no bypass). But saving money is not the only reason for bypassing extra pressure in the system. Especially in the hot humid south where cooling a room more slowly does a better job removing humidity.
I love the fact that you built an example of a system to prove a point. Unfortunately all of your bypass damper open calculations are wrong due to the improper placement of the return temperature sensor. The return temperature sensor for your demonstration should be placed between the bypass damper and the evaporator.
Im a TAB Engineer and let me just say.. on a larger scale, we are usually very close to nameplate nominal amps at 100 - 106% airflow. if you want to save that 27%, put it all aside because in a matter of time you'll be buying a new blower motor for constant over-amping during full load time.
There is never really a clear cut yes or no. A bypass is not for savings it’s for pressure restraints. In my situation and (probably most) a bypass really isn’t needed. For the simple reason that the problem area is usually the furthest away. So if I have problems cooling the top floor, my bottom floor may shut off. The air then has to travel a further distance then if the top was cut off. That’s ok you lose force the further away the exit is. Now if I wanted to shut the top off and only cool the lower floor, that’s a problem and a bypass is needed. Some would do that to save energy if they didn’t want to top cooled. But I prefer a whole house comfort level. So I’ll never not want the top not cooling or hotter than the bottom. Well maybe in the winter. So bottom line depends on the scenario
Can I hire you to design an hvac system for my new house.
The evaporator inlet air temp when the bypass is open should be the 50% colder than when the bypass is closed. I think the bypass air flow is not being measured properly because the bypass duct is right up against the coil inlet. I can't see how the return air and bypass air are being mixed but the 70 degree temperature measurement is a contradiction to the 50% rule.
Accurate calculations need to be based on a real system with a thermostatic expansion valve that is reacting to load on the coil. Window AC units don't usually have a TXV. Units with a TXV will reduce compressor amps because the TXV valve reduces refrigerant flow as the suction temperature drops. I don't like the bypass and I think it is a waste of energy but this demonstration looks flawed to me.
First time in 30 years that i see someone that actually thinks the same way i do, 👍 good job
Bypasses are dumb, but why did you use the sensible heat formula instead of total heat formula to determine your Btus? No consideration for latent heat.
Unless I'm missing something the percentage change (savings) should have been the New - Old / Old. You divided by the New (9.19). So my calculations for the savings was 38% (9:24) 48% (10:06) 28% (10:32). Someone check me please, but even though I'm pretty much exhausted right now, this is pretty much muscle memory for me, so unless I'm completely brain fried right now, I'm seeing different numbers.
There is one problem with his calculations. He is only measuring sensible BTU's and has not accounted for any latent BTU's. What about the extra latent capacity with the colder air? The EER calculation needs to take into account total BTU's which includes both sensible and latent BTUs. Plus with a supply air temperature between 39-42 degrees, he may have been partially frosting the coil. That would be additional latent BTU's not accounted for in his EER calculation.
never in the history of bypass dampers has there been a fully open or fully closed one. your missing the entire point of what it does. its supposed bleed off static pressure from the main truck of a system by sending the extra back into the return. to be clear , modern systems do NOT need a bypass damper. but if youve got an old as house from the 70s or 80s, and you dont want to upgrade your entire heating system, then throwing in some regular dampers inline into all the zones and installing a bypass damper is the correct way to go. after installing, you leave the bypass closed. then run the whole system wide open and adjust the weight position of the damper so it just barely starts to open. then back it off a pinch until its shut. its now set perfectly for the system. after that, you set thermometers in each room or zone and adjust the inline dampers until you get a uniform temperature or whatever youd like in each zone. Then, the bypass takes the extra pressure thas being kicked back from the semi closed dampers and sends it back to the return and keeps your system from burning out. your math is quite good and youre attention to detail is impressive. but to be honest, you just missed the biggest part of the equation. its the equivalent of trying to find the color of a circle. the math youre putting out has nothing to do with the procees you claim is "dumb". not trying to bash ya, you just dont understand the fundamental point in what a bypass damper does. it keeps you from burning out the heat exchanger or the cooling element of the system by relieving static pressure.
Bypass dampers are made to reduce noise by high static pressure that are produced when you reduce the duct volume by closing a damper in a duct . I have never considered a bypass damper or any zoning, for that matter as means to conserve energy. In multi zone configurations that incorporate more than three zones of different sizes a bypass of some kind would be essential. if only one zone is open and that zone was the smallest, without bypass and thermostatic freeze protection the unit would stop working altogether. This guy knows nothing about the application and design of a zoning system or the primary principles in dynamics of air flow as it relates to a air conditioning system.
Amen
Thats why we call engineers "ruff drafters" and spend all our time arguing and fixing their mistakes!
@@Im-not-clever It's more importantly installed to relieve the static pressure and prevent short cycling rather than noice reduction.
What you seem to have missed is that when the damper is open, that zone will cool quicker than when it is closed. Nice try. By the way the variable speed fans are EXTREMELY EXPENSIVE.
bypasses are needed for humidification or for noise or pressure issues.....their is always pros and cons to things......should have done this experiment with a furnace in a house...would have been easier than this flawed set up you used here
Once you buy an ECM motor and a compressor due to failure caused by NOT having a bypass damper.......you'll kiss your "flawed savings" GOOD BYE.
I am not a fan of zoning, feeding a 140 sf room with a 5 ton condenser is dumb but somebody told the homeowner this would work great. I have seen so many mistakes in installation and so called professional opinions it makes no sense to me. Put in 2 or more systems without zoning and you will have the results you were looking for. Unfortunately builders do not want to spend the money to do that so they sell homeowners on this.
Useless. The bypass damper is not always fully open. Nothing proved
I missed my calling in life...
Wow you are way off base ! Your OUT !
Your test is really flawed
Shots Fired!
Ugh excuse me just a minute there, your not testing apples for apples sir. If 1 of your dampers goes closed that is 50% your bypass must go to 50% also your not recording cfm readings at all branches, you can't just arbitrarily say that 50% is 50%. If you have 1200cfm system and you close 1 200 cfm supply that doesn't mean you all of a sudden have a 1000cfm system, the air has to go somewhere, thus the bypass takes that additional 200 cfm's. Also you have 2 - 6" round supply branches and 1 - 6" bypass this is not accurate depiction of what you see in the real world, baypasses are much larger than supply branches. Lastly, all of this is mute if the blower is not modulating or on a frequency drive (separate vfd on a 3 speed motor best over ECM motor) Now that sir is where your energy savings come from if you don't slow down the fan you get no savings, but you still must insure that minimum cfm requirements across heat exchangers and coils are being maintained, and you cannot insure this without the awesome very much needed automated bypass damper.
Ok, This guy is acting like he knows what hes doing. Fake news
Zones are dumb in general
This is just plain ignorance. Your are the reason i have to charge a customer $2000 to fix the zoned system on their new house because the coil keeps freezing. Stick to drawing pictures bud, let us worry about hvac! Im literally adding a bypass on friday.
Everybody is an engineer lol