With either method done correctly the efficiency will be a tie. Good supply design and grille location and choice has the advantage of getting air everywhere that is is needed. Return location has far less influence on getting air where you need it. This is easy to prove with a cigarette (gasp) or a smoke pencil. I suppose confetti or powder would work also, but it would be messy.
Originally Posted by Brian GC
Do you think you could get the same results Cherokee got by re-locating supply registers, using different grilles, not increasing upstairs supply volume and using one downstairs return at floor level? Remember, he already had perfect air mixing in the mbrm with a ceiling fan and it did not help.
Originally Posted by lynn comstock
To answer the remaining questions:
Originally Posted by lynn comstock
1. The ducts are not in any exterior walls or attic in my house. The house was certified as a BGE energywise house when it was purchased and after my Energy audit about 3 years ago I have confirmed that it still meets the highest Energy Star ratings for air infiltration. That still doesn't mean that I haven't found and fixed a ton of problems and issue with poor design and construction. It just probably started life a bit ahead of the average home. Since my house was constructed in the late 90's most of the construction techniques have probably surpassed it by now.
2. Air is directed upward instead of out into the room. There are only two registers though in my room, which seems very low to me given the volume of air in there with a cathedral ceiling. Other factors making this room subject to more heat loss/gain then some is that the master bedroom floor is half over the hot garage and part of the wall is exposed to the hot garage attic. Given the cathedral ceiling, part of the upper walls are exposed to the hot attic, as well as all the ceiling area. The energy audit I did exposed all the problem areas where insulation had fallen down etc. and I fixed all of them, including rapping and aditional layer of R-19 unbatted insulation around the walls up in the attic to mostly increase the total R-value, but more imporantly make sure nothing could fall again.
Overall my house is very, very efficient with heat loss and heat gain. It has been 99 degrees here in the last month and when I leave at 7am, I am at 76 degrees in the house on the first floor. I have a setback of 85 degrees and it has never come on before the schedule kicks in around 4pm. In fact, I have never seen it reach over 80 on the first floor before it starts back up to cool the house down at the end of the day. I know this because I have Z-wave control system and can see my temperature on the first floor. It looks like I only used somewhere around 400kWh this month on A/C. Oh yea, I forgot to mention that all my windows have cellular shades that when closed increase the window total R value over 6, and they remain closed while we are not in the house to greatly lower solar gain.
Guys, I am not convinced what both of you are saying is mutually exclusive. I think the supply side location and volume of air is hugely important and probably more so than the return side. This can be proven by how a single return per floor design works, versus a multiple return. I would take a single properly sized return in the halway anyday over a multiple return system where they were dumb enough to run everything in the attic where the air reaches 140 deg F.
I think what the supply side guys are not acknowledging is the fact that any design flaw in the single return airflow, (ie my situation with very poor airflow from the one single return) can have a MASSIVE effect on performance of the entire system (ie 30% wasted energy). The other issue with a single return system is you absolutely can not shut the doors to the rooms if you want cooling unless you have a huge gap under the door, as you have just closed a box and increased SP thereby droping airflow dramatically (the blowing into a bottle analogy). In fact, I have actually verified that closing the doors / registers to unused rooms upstairs is counter productive in two ways. It drops the total CFM delivered to the upper floor considerably and secondly it allows that room to heat up so you now have un-insulated interior walls transferring heat into the rooms you are using.
Was your home in its present condition (as stated above) before you balanced the returns? Did drawing more return from upstairs make the biggest improvement?
Originally Posted by cherokee180c
Cherokee I admire how methodical you are. Perhaps you have mentioned already, have you had a room-by-room Manual J model done on your house? I am curious how well the cooling load correlates with the airflow supplied. Measuring the airflow may be the more difficult half of this comparison. Or more expensive, flow hoods cost a bundle.
Back when you posted KWH per day for a week before and after your change, did you have any suspicions about that last day being an outlier I wonder. Post #36. While you may have little desire to repeat the "before" scenario, it might add value to do some repetition of the "after" measurements.
Again, thanks for sharing your measurements. I feel we make a whole lot more progress when we do that.
Brian, I will try hard to be impartial in the future.
Best wishes -- Pstu
Yes and Yes!!! But that is coming from a known design flaw issue where the idiots put the two main returns in series within a wall cavity without balancing the airflow. I did not move anything, I just re-balanced (skewing to the upper foor) by blocking off most of 1st floor return. I am not so sure the benefits would have been anywhere near as great had the system been perfectly balanced to start off with.
Yes, unfortunately the last day is an outlier as you pointed out. The day before that was actually even lower though so I took the most conservative contiguous data point. I tried to match average temperature conditions as close as possible between the weeks. The easiest way to tell the savings is real though is that I have 3 more weeks of data now and there are only 2 days above 60kWh at all with the highest being 64.5kWh. Go back and look at the before week and you will see there is no need to re-run. My billing cycle ends today, and it looks like I just had the lowest July electric bill since I finished my basement 6 years ago.
Guys, I am not convinced what both of you are saying is mutually exclusive. I think the supply side location and volume of air is hugely important and probably more so than the return side. This can be proven by how a single return per floor design works, versus a multiple return. I would take a single properly sized return in the hallway any day over a multiple return system where they were dumb enough to run everything in the attic where the air reaches 140 deg F.Watch it you are begining to sound like one of us "supply siders" because I agree with what you just said
I think what the supply side guys are not acknowledging is the fact that any design flaw in the single return airflow, (ie my situation with very poor airflow from the one single return) can have a MASSIVE effect on performance of the entire system (ie 30% wasted energy).
Again I agree if the return is not working then it is not going to work The point is to have the duct (not stud or joist space) install so it does the job it was designed to dop. No conflict with us "supply siders:
The other issue with a single return system is you absolutely can not shut the doors to the rooms if you want cooling unless you have a huge gap under the door, This is where you use ONE stud space to install transfer grills as you have just closed a box and increased SP thereby droping airflow dramatically (the blowing into a bottle analogy). In fact, I have actually verified that closing the doors / registers to unused rooms upstairs is counter productive in two ways. It drops the total CFM delivered to the upper floor considerably and secondly it allows that room to heat up so you now have un-insulated interior walls transferring heat into the rooms you are using. This observation is also in line with the "supply siders point of view as well
So your question is????
You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!
As you know, detail matters a lot.
- What is the elevation of the upper return relative to the floor upstairs?
- The sidewall grilles direct the air both up and out if they have flat blades, probably set at a 45° angle. A one-way curved blade grille is most commonly used in ceilings but will direct the airflow tight to the surface upward when it is installed on a wall. This maximizes the upward throw or distance that the air is pushed.
- Did you stop using the ceiling fan or change its setting in any way?
You have done a good job by being alert, thoughtful, and observant.
1. The bottom is about 6' off the ground and it is an 18" x 18" grill.
2. I don't have wall supply vents as they are in the floor.
3. Nope, my wife loves cold air blowing on her. Drives me crazy as she keeps it blowing all the time even in the winter.
Nobody can detract from the importance of the supply side but you are left with one hard question to answer. How did the power consumption drop by 30% and setpoint obtained 60% faster by simply drawing the return from upstairs vs. downstairs? There were no changes to the supply side or the envelope. The most obvious answer to me is that downstairs was not the most ideal location for a return for cooling. In other words return location matters a great deal, up to 30% or more.
Originally Posted by genduct
Yes, I fully agree. In this case, there is no doubt that a basically crippled single return on the upper floor is 100% responsible for a 30% waste of A/C energy. All I am saying is that if that return had been properly sized and balanced so that there was equal airflow to begin with on both floors, the improvement by skewing more airflow to the upper floor would have been less (maybe 10%, but this is just a guess). Remember I clearly stated in Post#2 that I estimated I had 90% of the air pulling from the first return in series (ie 1st floor) and only 10% from upstairs. When I physically blocked 90% of the first floor return, I flipped that ratio to highly skew to the upstairs.
There was one other benefit here that might have been lost in all the posts. When I blocked off 90% of the first floor return, I also increased the airflow pulled from the basement return as well, which also reduced the differential temperature between the basement and the first floor. The basement was always freezing and now it is only about 2 degrees colder than the first floor. I don't have good data for the basement temps though, but I can tell you it made a huge difference. I think I recall a data point from a few years ago and 4 degrees colder sounds familiar. The entire system is working so much more efficiently it is not even funny. It literally feels like a brand new HVAC system.