OK to delete an air return?

beenthere · Oct 5, 2009

Brian GC said:
As if that has any relevance. Try to keep up here.

The ceiling plays a roll in how the air moves. Maybe you should rethink your comparisons, before you make them.

Now you are a Hydro-Specialist?

It would if the room was 80deg. You should learn to ask the right questions before making presumptuous statements and off-topic, uwarranted digs.

See what being sarcastic gets you, just more sarcasm…but maybe you are just bored and enjoy it.

Somebody just said they use high/low returns with good result in a previous post. Why didn’t you jump all over them like you do me? You should learn to spread your love around.

If the room is 80°, then there is no need to use a heater to heat the water at the bottom. Since it would be heated by the room temp.

You try to make things up situations. And then when the answer doesn't suit you.
You change a parameter. Or, try to insult your way around you not knowing what your talking about.

I'm not against high and low returns.

But, I am against your cure all BS you spout about them.

Brian GC · Oct 6, 2009

beenthere said:
If the room is 80°, then there is no need to use a heater to heat the water at the bottom. Since it would be heated by the room temp.

You totally missed the point of the question and the analogy, but that’s OK.

beenthere said:
You try to make things up situations. And then when the answer doesn't suit you.
You change a parameter. Or, try to insult your way around you not knowing what you’re talking about.

The water in the glass is a very similar comparison to my point of removing the unwanted substance first. If you don’t get it, that’s OK too.

beenthere said:
I'm not against high and low returns.

Why, I thought you said they were of no worth. Maybe you could expand on that thought.

beenthere said:
But, I am against your cure all BS you spout about them.

I never said they were a “cure-all”. I said they will help a system when there is less than optimal air circulation, which is the case in most homes I’m in.

Brian

beenthere · Oct 6, 2009

Brian GC said:
You totally missed the point of the question and the analogy, but that’s OK.

No, I didn't.

The water in the glass is a very similar comparison to my point of removing the unwanted substance first. If you don’t get it, that’s OK too.

No, it was a bad anology.

Why, I thought you said they were of no worth. Maybe you could expand on that thought.

Just not against them. Don't install them as a rule. But, once in a while. A customer has a silly notion that they are needed. And is willing to pay for them. So I will install them.

I never said they were a “cure-all”. I said they will help a system when there is less than optimal air circulation, which is the case in most homes I’m in.

Brian

You have touted them as the way to make every air system work better.

Brian GC · Oct 6, 2009

beenthere said:
You have touted them as the way to make every air system work better.

Not every one, just every one I've seen.

I have always said that the better the circulation, the less effective low returns on a heating system will be. But, being positioned low can never hinder a system like being mounted high. It can only help it.

Brian

beenthere · Oct 6, 2009

Don't need high and low returns.

I only have low returns. Heats and cools fine.

Brian GC · Oct 6, 2009

beenthere said:
Don't need high and low returns.

I only have low returns. Heats and cools fine.

Try routing your low return to the highest point in the house and you will probably have the revelation X, me, and others have had. The higher your ceilings and return, the more it will likely hinder your system.

Brian

tinmandad · Oct 6, 2009

beenthere said:
Don't need high and low returns.

I only have low returns. Heats and cools fine.

Same here.
Around here we install low returns.
I don't have any scientific evidence of what's best, but, in 30+ years I've had no complaints.

Shophound · Oct 6, 2009

Brian GC said:
Because supply registers outnumber returns about ten to one.

That is a generalization and really isn't the point, is it? If you have one supply register in one room, and a large return air intake at the center of the house for the entire house (which is a very common setup in warm climate homes with slab foundations) you may or may not have pressurization/depressurization issues of each room depending on whether doors are open or closed, or whether each room has sufficient return air provision, such as jump ducts or bypass ducts, to allow sufficient return air to occur from the room when the doors ARE closed.

Therefore returns move about ten times more than a single supply register.

Another generalization. Are you speaking about one central return? Or several smaller returns distributed throughout the house? While one central return might see a volume rate higher than the largest supply register in the house, it can't touch the smallest supply register for velocity.

Not necessarily. The stagnant air is the desired warm air, stirring it is one way to get it to drop to the floor. Removing the lower strata of cold stagnant air is the other. Remember, cold air on the floor is replenished by slabs, windows, walls, leaks, drafts, opening doors, etc. So why not remove it first rather than stirring it into the room?

How about reducing the sources of replenishment, such as better windows, tighter walls, fewer drafts, etc?

Hypothetically imagine a 16oz glass of water with 60deg water on the lower half and 80deg water on the top half. The objective is to heat all the water to 80deg. You have a 1oz/min pump hooked up to an 80 degree water heater. That slow of a pump would not mix the water regardless of where the intake and outlet were located. Since the bottom, cold water is the unwanted water, would you draw off the bottom to remove the cold water first or would you mix the whole glass and begin removing 70deg water? IMO drawing off the bottom first would require only 8oz of water change to heat all the water to 80deg. To mix the water first would require more than four times the work which would make it far less efficient. Please comment of this example.

I used to take care of swimming pools. I'm the type of guy who isn't satisfied knowing just enough about what I set about to do. I'd read about the optimal way to set the supply jets in the pool, and then go do it. I'd read further to understand why. The jets were set in a certain pattern to assure the most thorough turnover of water for circulation and filtration possible for a given pool's configuration. I remember wondering how those small supply jets could somehow turn over the entire pool's water content and assure that at some point all of it passes through the filter. Set correctly, they in conjunction with the one central drain on the bottom, and the skimmers on top (which you and X might well seize upon to illustrate high and low returns

...except skimmers are only there to collect floating debris and provide a connection point for vacuuming the pool plaster) turned over the water sufficiently that (with D.E. filters) the water could clear itself overnight if it was somewhat turbid.

That's pretty amazing. A 25,000 gallon swimming pool can change over its entire volume just by little jets and drainage provisions. To wit, so can a house with supply and return air provisions.

Regarding your illustration, if you could get a jar to have 80 degree water on top with 60 degree water on bottom with no natural convective currents already circulating the water, that would be an amazing circumvention of physics.

Convective currents will be in place in any room that has a temperature difference in the air. If the top of the room had 80 degree air and the bottom of the room had 60 degree air, the 80 degree air would migrate toward the 60 degree air, as hot flows to cold. In the exchange of heat the cooler air would rise as it's warmed by the warmer air. The warmer air sinks as it is cooled by giving up heat to the cooler air. Just because the air on the floor isn't suitable for human comfort purposes does not mean it's not in motion due to convection.

Brian GC · Oct 6, 2009

shophound;4678622 said:
Another generalization. Are you speaking about one central return? Or several smaller returns distributed throughout the house? While one central return might see a volume rate higher than the largest supply register in the house, it can't touch the smallest supply register for velocity.

My only point was that the single return air extracts the sum total of all supply registers, be it twice or ten times the average supply. Its volume is far greater than the nearby supply registers. Therefore its affect on the central area would be significant if it was removing predominantly heated air when there was cooler air it could be removing instead.

shophound;4678622 said:
How about reducing the sources of replenishment, such as better windows, tighter walls, fewer drafts, etc?

That is the other half of the equation, but each heater setup should be optimally designed to be the best it can be regardless of existing leaks.

shophound;4678622 said:
Regarding your illustration, if you could get a jar to have 80 degree water on top with 60 degree water on bottom with no natural convective currents already circulating the water, that would be an amazing circumvention of physics.

Convective currents will be in place in any room that has a temperature difference in the air. If the top of the room had 80 degree air and the bottom of the room had 60 degree air, the 80 degree air would migrate toward the 60 degree air, as hot flows to cold. In the exchange of heat the cooler air would rise as it's warmed by the warmer air. The warmer air sinks as it is cooled by giving up heat to the cooler air. Just because the air on the floor isn't suitable for human comfort purposes does not mean it's not in motion due to convection.

That is why I called it hypothetical. I realize two temps of such deltas could never be so close to each other without convective interaction. But if you could have that condition my question was: would you rather draw off the bottom or stir the water first. I think you know extracting the cold first vs. stirring the water is the obvious and most efficient choice.

If the delta T is confusing and introduces convective principles then imagine the same test but with sediment on the bottom half and clear on top. Objective is to clean the water with a slow pump and filter. Would you draw the dirty water first or stir it first? Again, for quickest results stirring is not recommended for a stratified condition IMO.

Brian

beenthere · Oct 6, 2009

Brian GC said:
Try routing your low return to the highest point in the house and you will probably have the revelation X, me, and others have had. The higher your ceilings and return, the more it will likely hinder your system.

Brian

Tried that. made no difference.

My returns are flor returns.
I used thermopan. And created return chases up to 12" from the ceiling, just to see if it would make a difference in the summer.
It didn't.
My supplies throw the air to the ceiling. So I have good air mixure with room air. And it makes no difference summer or winter, for comfort.

If I had no throw from my supplies. Then it would be a way to cover up the problem of incorrect supply registers.

Shophound · Oct 6, 2009

beenthere said:
If I had no throw from my supplies. Then it would be a way to cover up the problem of incorrect supply registers.

You nailed it.

I've said it before and it is worth repeating: no intelligent conversation regarding air distribution throughout a residence can take place without a thorough understanding of both sides of the coin; supply air throw, drop, & spread, entrainment, convective currents within a space, and return influence and sizing. Throw in mean radiant temperature and humidity control for good measure, pertaining to the human comfort dynamic (which is what this entire discussion is for, anyway).

One can dream up a plethora of hypotheticals to favor their section of understanding, but such aren't necessary. The real-time dynamics are observable and do the job handily every day. Let these dynamics be the instructor vs. presupposition.

Shophound · Oct 6, 2009

Brian GC said:
My only point was that the single return air extracts the sum total of all supply registers, be it twice or ten times the average supply. Its volume is far greater than the nearby supply registers. Therefore its affect on the central area would be significant if it was removing predominantly heated air when there was cooler air it could be removing instead.

Providing no net loss through the envelope, and an adequate path back to the central return from all zones of the structure, the return will flow around the same volume of air as the aggregate of supplies. It will not, however, flow at the same VELOCITY. You must understand this important difference. Supply drop, throw, and spread receive attention by smart HVAC system designers due to VELOCITY as well as VOLUME. The VOLUME assures the proper amount of BTUs reaches the room to heat or cool it (in essence to offset heat gain or loss through the envelope). The VELOCITY assures air already in the room has an opportunity to interact with the conditioned air injected into the room.

Return paths provide a way for air to reach the air handler for conditioning. Period. That's all they do. You could isolate a room from the house and throw a supply in there without a return, but the only way you're heating or cooling it is shoving a bunch of air through the walls and ceilings to the outdoors. If the room was absolutely airtight, the supply wouldn't flow. It would be equivalent to placing a spray head on a garden hose that can be shut off, or connecting this same hose to a water and airtight tank. It will fill until the pressure within the tank equalizes with the water pressure in the hose. It then stops.

That is the other half of the equation, but each heater setup should be optimally designed to be the best it can be regardless of existing leaks.

To paraphrase Carnak: Building envelopes have a far greater influence over indoor comfort than any HVAC system design can.

We are so conditioned via our outdated construction methods to make up for it by high energy HVAC solutions. Once you experience living in a structure that does not undergo daily rapid changes in temperature and humidity, it changes how you think about building envelopes and HVAC systems. If anything, the HVAC system should be largely for conditioning ventilation air, offsetting internal heat gain (during cooling), and offsetting what reduced amount of heat gain or loss through the envelope occurs during extreme weather conditions. Instead, we have high horsepower HVAC systems struggling to maintain fickle human comfort requirements against Swiss cheese, marginally insulated envelopes full of thermal bridges and bypasses, topped with single pane glazing that are only a razor thin improvement over just leaving a window open.

That is why I called it hypothetical. I realize two temps of such deltas could never be so close to each other without convective interaction. But if you could have that condition my question was:

You can't, so the hypothetical falls apart. Stick to the real stuff. It will bail your butt out every time.

If the delta T is confusing and introduces convective principles then imagine the same test but with sediment on the bottom half and clear on top.

No confusion here. I know what those convective currents are doing. They're in force whether the HVAC system runs or does not run. They're one reason a room is comfortable or uncomfortable between HVAC run cycles.

Objective is to clean the water with a slow pump and filter. Would you draw the dirty water first or stir it first?

This is no chicken or egg choice, Brian. You do both. If you draw from the same source, you must pump it back to the same source, unless you want to experience loss through leakage, which most of us tolerate.

Again, for quickest results stirring is not recommended for a stratified condition IMO.

Brian

From a grammar perspective, "stirring" is the opposite of "stratified". Stir up air that is stratified, it is no longer stratified. It is stirred up.

Brian GC · Oct 6, 2009

shophound said:
Return paths provide a way for air to reach the air handler for conditioning. Period. That's all they do.

Not entirely. They also establish the major are movement within the house. It can probably be witnessed best in a stairway when the return is upstairs. In this case you will see cold air within 12” of the treads moving downward and warmer air hugging the ceiling moving upwards. No matter how well you mix the downstairs air, the air that moves up a stairway toward the return will be the warmest air. 90% of my returns are upstairs so the upward (heat loss) draft is strong. But regardless of this draft, the cold air still falls down the treads. To pull downstairs air upstairs is to remove the warmest of air first and leave the colder floor air intact.

shophound said:
To paraphrase Carnak: Building envelopes have a far greater influence over indoor comfort than any HVAC system design can.

I could design a system so poorly that a perfectly sealed house would not heat, so that statement is untrue. Having a well sealed house is not adequate compensation for a poorly designed system. System design is still very important.

shophound said:
You can't, so the hypothetical falls apart. Stick to the real stuff. It will bail your butt out every time.

The hypothetical part is only to emphasize major stratification, you can imagine that can‘t you? I know 60deg water cannot sit next to 80deg water without influence, but stratification can occur in a house can’t it? In the example like the water in a glass simplifies a demonstration of how to remove the unwanted substance first rather than mixing and having to remove all 16oz many, many times to obtain your goal. In my example 80degrees could be obtained with about 10 – 12oz pumped through the heating system. Stirring the water first would require upwards of 50 - 100oz pumped.

Ideal and simplified (hypothetical) examples are used in the classroom all the time.

I do not have an engineering degree but I do have two brothers and a father who are engineers. I have always had that analytical mindset all around me. Not to get too personal but do you have an engineering degree or are you surrounded by engineers?

shophound said:
No confusion here. I know what those convective currents are doing. They're in force whether the HVAC system runs or does not run. They're one reason a room is comfortable or uncomfortable between HVAC run cycles.

Natural convective currents do not eliminate stratification.

shophound said:
From a grammar perspective, "stirring" is the opposite of "stratified". Stir up air that is stratified, it is no longer stratified. It is stirred up.

But as my water example shows, major stirring is not always the only or best way to heat a house.

Brian

Shophound · Oct 6, 2009

Brian GC said:
Not entirely. They also establish the major are movement within the house.

This point may be the "irreconcialable difference" between us, Brian. As long as you're eagle eyed focus is on return air dynamics, you'll say stuff like this. You have yet to show any indication you comprehend what we've been saying about supply side dynamics.

I see the whole picture. Supply and return. And how the building envelope fits in. I don't claim to have a fully mature understanding of it but I'm getting there. My job requires that I understand airflow dynamics, so I make a point to go beyond mere requirements and understand it in various applications, be it residential or commercial.

It can probably be witnessed best in a stairway when the return is upstairs. In this case you will see cold air within 12” of the treads moving downward and warmer air hugging the ceiling moving upwards. No matter how well you mix the downstairs air, the air that moves up a stairway toward the return will be the warmest air. 90% of my returns are upstairs so the upward (heat loss) draft is strong. But regardless of this draft, the cold air still falls down the treads. To pull downstairs air upstairs is to remove the warmest of air first and leave the colder floor air intact.

Of course this will happen in multi story homes that experience a lot of temperature gradient due to various reasons. The people that complain most bitterly in either single story or multi story homes about temperature imbalances live in high ceilinged, highly windowed, Swiss cheese chimneys. They'll never be comfortable even if they brought a Hollywood wind machine in there to shove all the air around. These homes violate at least two points of my "quartet for indoor comfort" sig line.

I could design a system so poorly that a perfectly sealed house would not heat, so that statement is untrue. Having a well sealed house is not adequate compensation for a poorly designed system. System design is still very important.

Well sealed isn't the only aspect, albeit a large one. A well sealed, well insulated home that overall reduces heat transfer through the envelope significantly is a big deal, whether the home be single or multi-story.

And why would you even think of designing a poor HVAC system for a house with a great thermal envelope? When you say things like that it comes across as grasping at straws. You may not intend so, but that's how I read it. You weaken your position by appearing desperate to defend it.

Ideal and simplified (hypothetical) examples are used in the classroom all the time.

To illustrate the unfamiliar with the familiar, yes. I prefer examples that closely mimic reality, where it isn't hard for the student to make the connection. I also prefer illustrations that do not confuse concepts.

I do not have an engineering degree but I do have two brothers and a father who are engineers. I have always had that analytical mindset all around me. Not to get too personal but do you have an engineering degree or are you surrounded by engineers?

My uncle is a retired aerospace engineer. He likely could smoke my knowledge of aerodynamics pertaining to aircraft. However he's not a civil or a mechanical engineer. He asks me questions about HVAC because he knows I swim in it every day.
My specialty is HVAC management for critical environments, in particular an art museum. I not only need to turn wrenches, but understand how my building interacts with the indoor and outdoor environment. I need to understand airflow and heat transfer. Psychrometrics. Building envelopes. The curators and the director like that I know this stuff. So does my boss. I'm currently working on my degree, but that doesn't stop me from applying what I know, and acquiring what I don't know. I don't wait around for someone to tell me...I go find it when I need to know.

Natural convective currents do not eliminate stratification.

As a blanket statement you say so? Or in a given frame of reference? Pertaining to human comfort you may be right. Pertaining to sheer thermodynamics, maybe not.

Carnak · Oct 7, 2009

Brian GC said:
I could design a system so poorly that a perfectly sealed house would not heat, so that statement is untrue. Having a well sealed house is not adequate compensation for a poorly designed system. System design is still very important.

I doubt even you could Brian

Try this video out, has a pencil pusher who implemented some of the concepts developed in Canada's Advanced House Program. I was involved in this program, it was the step beyond the R2000 home which are the worlds most energy efficient and readily built homes, a light year beyond the average new construction quality happening in the USA right now.

Anyways in the late 90s there were major Ice Storms in eastern Canada, and this guy was keeping his entire home comfortable with passive solar heat, and a tiny gas fireplace on a millivolt system that just radiated and naturally convected heat. Power was out for about a week in winter conditions. Doubt it was more than 20,000 Btu input

This guy was worried about VOCs over a decade ago.

http://www.science.gc.ca/Videos/Earthtones/Advanced_House-WS34186CAF-1_En.htm?

Brian GC said:
I do not have an engineering degree but I do have two brothers and a father who are engineers. I have always had that analytical mindset all around me. Not to get too personal but do you have an engineering degree or are you surrounded by engineers?

I know a couple engineers, they design hvac, they are not chemical/electrical engineers with stop watches

Shophound · Oct 7, 2009

Great video! Enjoyable to watch and echoes everything we've been saying here.

Carnak · Oct 7, 2009

The R2000 program is almost 30 years old now. It is where the concept "the building as a system" came from.

http://r2000.chba.ca/What_is_R2000/brief_history.php

I must of done 50 homes built to this standard myself, and my father twice that many.

The main difference between R2000 homes and houses built to current Canadian codes are issues such as the air tightness are blower door tested as one part of the certification program and with R2000 you had to use heat/energy recovery ventilation.

If you carry 0.07 air changes an hour for natural infiltration on one of these houses you will be conservative in your furnace sizing. The non certified homes you would carry about 0.3 ACH and be conservative.

The Advanced House Program, was diminishing returns when it came to thermal efficiency when compared to R2000. You could not really seal the houses up any tighter and not a big difference if your exterior walls were R30 instead of R22 or your attic was R60 instead of R40. It differed from R2000 mainly because it was a more green building program and focused on more energy efficient lighting and appliances. Advanced house was also into 'integrated mechanical systems" while R2000 just used conventional high efficency systems. - You would not have say "passive solar domestic hot water heating" tied into a forced air or radiant floor heating system in an R2000 home.

In heating climates, a Passive Solar design can greatly reduce heat bills. One home owner with a passive solar R2000 home used to annoy the hell out of me, they were having an intermittent problem with a GSHP system, and would only call to complain at night.

Turned out to be an intermittent short in the transformer windings. I was annoyed as they never called during working hours to complain, always after supper and they were 1 hour drive out of town.

This was happening when the weather was still in the single digits F, not the -20F and colder range that the systems were designed for. When the sun was shining, it actually kept the house warm to the point that the geo never had to run.

They would not know the heat was down until after the sun set.

Anyways, when a guy in Canada can keep his house warm in the winter for a week with no power and basically the sun and a 20-30K Btu gas fire place, it just baffles me at how people freeze in California because of a return grille.

Carnak · Oct 7, 2009

You could ball park furnaces sizes on new construction, prior to doing a load calculation pretty easily.

Just have to take the total square footage including the basements that were always heated and multiply by about 17 to get the heating requirement of a house built to code.

If it was going to be an R2000 home, just had to multiply by 13.

And this was for homes facing -24 to -30F ambients. Most common furnaces I ever sold were 60 to 75K gas furnaces, 80% and 90% efficiency.

Do the detailed room by room heat loss later in the design stage and almost every single time come up with the furnace sized to meet the "17" & "13" Btu/sq ft allowance. May get stung if they ended up with an atrium of glass or wanted to use a Jenn Air range or fancy Italian Stainless Hood in the Kitchen. Only end up eating a C-note on the ball park quote, the cost of the next larger furnace than what you quickly pre-estimated. and could then more than make it back by adding a 'make up air system' to handle the excessive intermittent exhausts that have no real business in the home in the first place.

It is amazing what you can do when someone builds a home that actually keeps the outdoors 'outside' of the home and you can control how outdoor air moves through the building.

So that is why I say, the way we build has the biggest impact. My own home and three adjoining units down here in the tropics are tight to the R2000 levels and they run some of the lowest indoor humidty levels found anywhere in the humid tropics and significantrly lower than most posts you see in here outside of people in arid regions.

When there are problems it is often the hvac that is the first to blame. A lot of times when you get to the root cause of the problem, it is because the house was a POS when it came to construction quality.

Shophound · Oct 7, 2009

Carnak said:
Anyways, when a guy in Canada can keep his house warm in the winter for a week with no power and basically the sun and a 20-30K Btu gas fire place, it just baffles me at how people freeze in California because of a return grille.

Shophound · Oct 7, 2009

Carnak said:
It is amazing what you can do when someone builds a home that actually keeps the outdoors 'outside' of the home and you can control how outdoor air moves through the building.

So that is why I say, the way we build has the biggest impact. My own home and three adjoining units down here in the tropics are tight to the R2000 levels and they run some of the lowest indoor humidty levels found anywhere in the humid tropics and significantrly lower than most posts you see in here outside of people in arid regions.

When there are problems it is often the hvac that is the first to blame. A lot of times when you get to the root cause of the problem, it is because the house was a POS when it came to construction quality.

Yep, yup, affirmative, aye, checkmate, slam dunk.

Imagine if HVAC design shifted from scattershooting attempts to counteract a poor building envelope to actual, accurate, efficient, and effective indoor climate control with low energy cost and high comfort.

Sure beats going round and round about return air grill locations. :gah:

OK to delete an air return?

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