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Old 07-25-2010, 09:06 AM   #1
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Reducing ESP in Cold Air Drop & Filter


I have two 20 year Bryant LP furnace/AC units. One is 3T and one is 3.5T. Both have the same blower. Just checked ESP with my newly acquired Dwyer A303 probe. Numbers for both systems are about the same. No issues on the supply side with almost all ESP loss across the coil (0.05 duct and 0.30 coil). I do have a problem on the supply running 0.45. I have 0.1 loss in the 8 x 25 cold air drop and 0.20 across my 16 x 25 filter. With a total ESP of 0.8" my blowers are delivering a little over 1200cfm. I am getting 19-20 degree air temp drop across both coils so overall I am probably ok. I wish I would have dione this 20 years ago so I could have been running on lower blower speeds, but too late for that now.

I did find one on-line supplier who sells cold air drop kits for $250. I could upgrade to 10 x 25 but I don't think I would ever recover the cost. However, I could easily increase my filter size to 24 x 24 by installing on a diagonal in the 8 x 25 drop. This would cut my filter ESP in half.

Is there any problem with installing the diagonal filter?

Another solution would be to install a MERV 4 filter, but in looking at them, I wonder if they would adequately protect my blower wheel and coil?

Thanks for your help.

PS I thought the orientation of the Dwyer probe was important but I didn't see any measurable difference in readings whether parallel or perpendicular to the air.

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Old 07-25-2010, 10:17 AM   #2
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Reducing ESP in Cold Air Drop & Filter


The A303(static probe) won't show a change in static readings from changing its orientation, due to its design.
A Pitot tube would.

A diagonal filter in a return drop. Often increases static. Since it restricts air flow at the points where it narrows the area between it and the duct.

A 25x10 drop will lower your drop static by a min of .05", to a max of probably .12". Varies with how your attachment is to the horizontal duct. And if your current drop uses a radius ell, or vanes, or is just squared.

If your supply static was checked with a dry coil(A/C not running). When its wet, it will increase. Might increase anywhere from .05 to .1" when wet.

Next. On a PSC blower. When you decrease static in the return, and increase air flow, the supply static will increase proportionally.

On a VS blower. If its moving set CFM, you won't see a static increase in the supply from improving the return. If it wasn't moving the CFM its set for. Then you will see a slight increase in static pressure.

VS blowers usually aren't moving full CFM at .8" static.

You may get a payback by using the larger return drop you posted. if your blower is a VS blower, then its amp draw will drop. Also, you'll use less gas for heating, since it will be delivering more of the heat to your house. And less out the chimney/flue then now. Along with a lower cooling bill.

How long for payback. Varies with each house/application.

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Old 07-25-2010, 10:54 AM   #3
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Reducing ESP in Cold Air Drop & Filter


Quote:
Originally Posted by beenthere View Post
The A303(static probe) won't show a change in static readings from changing its orientation, due to its design.
A Pitot tube would.

A diagonal filter in a return drop. Often increases static. Since it restricts air flow at the points where it narrows the area between it and the duct.

A 25x10 drop will lower your drop static by a min of .05", to a max of probably .12". Varies with how your attachment is to the horizontal duct. And if your current drop uses a radius ell, or vanes, or is just squared.

If your supply static was checked with a dry coil(A/C not running). When its wet, it will increase. Might increase anywhere from .05 to .1" when wet.

Next. On a PSC blower. When you decrease static in the return, and increase air flow, the supply static will increase proportionally.

On a VS blower. If its moving set CFM, you won't see a static increase in the supply from improving the return. If it wasn't moving the CFM its set for. Then you will see a slight increase in static pressure.

VS blowers usually aren't moving full CFM at .8" static.

You may get a payback by using the larger return drop you posted. if your blower is a VS blower, then its amp draw will drop. Also, you'll use less gas for heating, since it will be delivering more of the heat to your house. And less out the chimney/flue then now. Along with a lower cooling bill.

How long for payback. Varies with each house/application.
Thanks Beenthere. I measured with a wet coil. When I removed the filter, return ESP dropped to 0.25 but supply only increased 0.05 or less. I do have a PSC blower. I wonder why supply ESP didn't increase more?

Do MERV 4 filters do anything to protect the blower and coil?

I was hoping to get total ESP down to 0.6 so I could move the same cfm with less energy OR shut-off supplies in unused rooms to drive more cold air to the living areas. The Bryant literature talks about a multi-speed blower but I think multi-hp would be a better description.

Last edited by artbuc; 07-25-2010 at 10:57 AM.
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Old 07-25-2010, 10:57 AM   #4
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Reducing ESP in Cold Air Drop & Filter


Are they high efficient Bryant units with plastic venting. If so the heat exchangers are probably getting to the end of their life. May crack or have a problem with pinholes eaten thru them. Ductwork improvements would be more cost effective when the new furnaces are installed. Better airflow will increase the motor life and use less juice.
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Old 07-25-2010, 10:59 AM   #5
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Reducing ESP in Cold Air Drop & Filter


Your A/C coil when wet. Is equivalent to at least a MERV 6. So no, a MERV 4 won't do anything.

A PSC motor uses less electric at higher static pressures. More at lower static pressures. Since they are actually doing more work at lower static then they do at higher static pressure.

What brand of air filter are you using.

When you remove the air filter. Do the rooms that are lacking in air flow get alot, or alittle more air?
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Old 07-25-2010, 11:35 AM   #6
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Reducing ESP in Cold Air Drop & Filter


Quote:
Originally Posted by beenthere View Post
Your A/C coil when wet. Is equivalent to at least a MERV 6. So no, a MERV 4 won't do anything.

A PSC motor uses less electric at higher static pressures. More at lower static pressures. Since they are actually doing more work at lower static then they do at higher static pressure.

What brand of air filter are you using.

When you remove the air filter. Do the rooms that are lacking in air flow get alot, or alittle more air?
I use 3m Filtrete. I always used the red one (1250 I think). But for the first time I put in their lowest rated one which is designed for "high flow". 3M doesn't use the Merv system but I am guessing even their "high flow" filter is much better than a Merv 4 fiberglass job.

I get a little more air. I have the Byrant fan data. At 0.8 hi-speed, cfm is 1215 for 3T and 1250 for 3.5T. At 0.6 hi-speed, cfm's are 1440 and 1470. The Bryant data is with a filter. I assume the filter they are talking about is the fiberglass pad which came with the unit. It is still in the air handler. I should install it and see what happens. I assume it has very low pressure drop.

I think the reason I don't see a proportional ESP increase on the supply side is because it is so unrestricted. Basically everything is happening at the coil.

Re energy use, if I unrestrict the return, I can lower the speed setting which will allow me to move the same volume of air at lower ESP. This will consume less energy, but not enough to justify much investment. For example, at 0.6 I can move 1210 at med-lo speed compared to 1215 at 0.8 on hi speed.

Last edited by artbuc; 07-25-2010 at 11:40 AM.
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Old 07-25-2010, 12:21 PM   #7
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Reducing ESP in Cold Air Drop & Filter


The true supply static. Is the pressure between the coil and furnace.

So you need to measure the increase in supply static between the coil and furnace. See what it is with the air filter in, and with it out. You may be surprised at how restricted the supply is.

Remember. The A/C coil is external to the furnace. So you must measure between the coil and furnace to find the supply static the blower is working against.

I'd just use a general pleated air filter. It would be a lot less restrictive then the 3M your using, So you would move more air.


PS: If you post the supply static before the coil, along with the total static, and what CFM the blower data says its moving(never hurts to check it 2 or more times). I can tell you how much static increase in the supply you will have after fixing/modifying the return.
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Old 07-25-2010, 04:52 PM   #8
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Reducing ESP in Cold Air Drop & Filter


Quote:
Originally Posted by beenthere View Post
The true supply static. Is the pressure between the coil and furnace.

So you need to measure the increase in supply static between the coil and furnace. See what it is with the air filter in, and with it out. You may be surprised at how restricted the supply is.

Remember. The A/C coil is external to the furnace. So you must measure between the coil and furnace to find the supply static the blower is working against.

I'd just use a general pleated air filter. It would be a lot less restrictive then the 3M your using, So you would move more air.


PS: If you post the supply static before the coil, along with the total static, and what CFM the blower data says its moving(never hurts to check it 2 or more times). I can tell you how much static increase in the supply you will have after fixing/modifying the return.
I retook the measurements as carefully as I could. I am using a homemade manometer measuring the bottom of the meniscus against a grid with marks at 1/8 inch. Supply is measured between the blower and a wet coil. Return is measured between filter and blower.

Sup w/filter .32 Ret w/filter .38 Total ESP w/filter .70

Sup w/o filter .37 Ret w/o filter .27 Total ESP w/o filter .64

Blower cfm is 1335 at .70 and 1398 at .64.

Again, the Bryant chart says "AIR DELIVERY - CFM (With Filter)". I don't know what the "with filter" means. I assume it means that the actual air delivery at the same ESP w/o a filter will be higher than the chart. IOW, there is some filter ESP built into the data.

I don't know why these readings are slightly lower than what I took yesterday.

I removed the 3M 600 (approximately Merv 6) and replaced it with a brand new Flanders Merv 8 NaturalAire. Return ESP increased to .44.

Beenthere, I can't find any pleated filter with significantly less pressure drop than 3M at equivalent Merv. What are the "general" pleated filters you refer to? Thanks.
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Old 07-25-2010, 07:50 PM   #9
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Reducing ESP in Cold Air Drop & Filter


With filter, means with the air filter they supplied installed. You read the static before the air filter. Instead of after, as you have been doing. They have already allowed for it.

You should install it. And see what its pressure drop is. Then you add it to the reading you get with the other type of air filters installed. Measuring the way you have been(between them and the blower.

EG: If the factory air filter has a .07" PD. And you read .7" with it in. Your moving 1335CFM.

Then if you use a filter with a higher PD. You deduct .07" from your total static.
So if you were to use a filter with a .27" PD. You would deduct .07" from your static reading.

Here is a PDF, from one company. It has a list of filter sizes. And their pressure drop at X CFM.
http://www.google.com/url?sa=t&sourc...9wyNetFssJsZaQ


I get my air filters from a HVAC supply house. So I can't tell you what stores may have these air filters(as far as I know you can order from this company), or sell other low PD filters.
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Old 07-25-2010, 07:52 PM   #10
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Reducing ESP in Cold Air Drop & Filter


Is you manometer, a water manometer. And is it a U tube?

If its a U tube. Are you including the distance of both sides when you measure.
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Old 07-25-2010, 08:18 PM   #11
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Reducing ESP in Cold Air Drop & Filter


Quote:
Originally Posted by beenthere View Post
Is you manometer, a water manometer. And is it a U tube?

If its a U tube. Are you including the distance of both sides when you measure.
Yes, U-tube with water. Yes, measuring the total water column from both sides with one side open to the atmosphere.
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Old 07-25-2010, 08:20 PM   #12
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Reducing ESP in Cold Air Drop & Filter


Quote:
Originally Posted by artbuc View Post
Yes, U-tube with water. Yes, measuring the total water column from both sides with one side open to the atmosphere.
OK. Just wanted to make sure.
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Old 07-26-2010, 09:50 AM   #13
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Reducing ESP in Cold Air Drop & Filter


Quote:
Originally Posted by beenthere View Post
You should install it. And see what its pressure drop is. Then you add it to the reading you get with the other type of air filters installed. Measuring the way you have been(between them and the blower.

EG: If the factory air filter has a .07" PD. And you read .7" with it in. Your moving 1335CFM.
Bryant supplied filter has negligible PD just like a Merv 4 spun fiberglass job.
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Old 07-26-2010, 12:22 PM   #14
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Reducing ESP in Cold Air Drop & Filter


Probably is about a .07"

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