performance drop on filtrete filter

[SGKent]

when the ducting was installed in 2004 SMUD did a pressure leakage test on the new ducting to certify it for their rebate. Every joint was sealed with that mastic stuff and then some. Every clamp, seam etc. The leakage was almost unmeasurable with over 99% efficiency. SMUD commented that they had not seen such a tight system ever. I don't think leakage is the issue here. This is a 1400 sq ft 3/2 one story home on a slab. The attic is well vented and insulated. We have a whole house fan but when things like the forest fires come we can't use it. Same when the air is really dirty. One person in the house get asthma quite bad in those conditions.

Re TESP - The only pressure I have control over is the filter. That is what I am focused on. I have contacted my HVAC folks to inspect and clean the A coil. They are too busy right now and said they will happily get to it as soon as things slow a little for them. I suspect it needs a cleaning. That said, if the low pressure is inside the first few inches of the return inlet, and the high pressure is in the room, it is measuring the total pressure drop from the inlet to outlet. Think about it.

 

[metlmunchr]

Re TESP - The only pressure I have control over is the filter. That is what I am focused on. I have contacted my HVAC folks to inspect and clean the A coil. They are too busy right now and said they will happily get to it as soon as things slow a little for them. I suspect it needs a cleaning. That said, if the low pressure is inside the first few inches of the return inlet, and the high pressure is in the room, it is measuring the total pressure drop from the inlet to outlet. Think about it.

Total static is measured from the inlet to the outlet of the unit. The measurement is external to the unit itself rather than external to the unit plus the supply duct system as you suggest.

Any measurement taken prior to the fan, and referenced to surrounding atmospheric pressure will be a negative pressure.

The measurement at the unit's outlet with the same reference as above will be a positive pressure and is a measurement of the pressure drop thru the supply duct system and diffusers.

The total static is obtained by adding the absolute values of both readings. For example, 0.2" negative at the inlet and 0.2" positive at the outlet woud give you a total external static of 0.4".

Ideally, its easiest to use a manometer capable of directly reading differential pressure, but its also possible to do the same readings with one referenced to atmospheric pressure.

Obviously, you can't control the supply static pressure, but you need to know what its value is in order to judge the maximum allowable static pressure drop on the intake side so that you can keep the total static within the design limits of the unit.

Unless I've missed it, you haven't mentioned the size of your condensing unit. As I mentioned previously, the 1200 cfm @ 1/2" tesp would correspond to a 3 ton unit as most all equipment is based on 400 cfm per ton. In your area, where summer humidity levels are low, you have a low ratio of latent to sensible load. It would be unusual to have 3 tons on 1400 sq ft in that location.

That you measure a temperature drop of only 13.5* says something is wrong. Either the condensing unit is operating under capacity, or the system is handling too much air. If the system is handling too much air, then the pressure drop across the filter will be higher than it would be if the unit was handling the proper amount of air. With a low latent load percentage, you should easily get a temperature drop of 20* or more with a condensing unit operating at design capacity and a fan handling the proper amount of air across the evaporator.

There's a reason its called a hvac system. All things are inter-related. Making the assumption, for example, that more air is better (fan on highest speed for cooling) and if the temp drop is only 13*, it is what it is, only serves to ignore the fact that the system is possibly handling too much air and that this is a possible cause of difficulty in efficient filtering as well as the basic cause of higher pressure drops thru all parts of the system since the ducts are (or should be) sized based on system capacity and corresponding air quantities rather than the max cfm the fan can push thru the system.

FWIW, you can get a good idea of whether or not the evaporator coil needs cleaning by measuring the pressure drop across the coil. On residential units, the pressure drop should be 0.3" or less with the system operating and the coil wet. If its more than that, then its likely dirty enough to warrant the expense of cleaning. If its down in the 0.2" range or less, then cleaning is likely a waste of money.

 

[SGKent]

as I wrote prior. The condensing unit is 2 1/2 ton. The furnace is a 3 ton. That is how it was designed. The air flow of 1440 CFM comes from the chart the manufacturer, Carrier, has for that specific model at the specific differential. I also linked a screen capture of the CFM vs differential pressure, but here it is again.

View media item 94294

 

[TRWham]

You are moving too much air. It really doesn't matter how much air the blower can move- it should still be set up to balance as a system. That's why blower motors can be wired to run at various speeds, even on a single speed system. You match them to the application by setting the appropriate speeds (different for heating and cooling) during installation.

 

[SGKent]

The Carrier dealer set up the system. I didn't. I'll mention it to my current HVAC folks when we inspect the A coil and clean if needed. I don't know if the AC can run lower speed than the high setting on the furnace. Maybe the manual will tell me. The more I am learning about the HVAC industry the more I am of the opinion that it is wham bam thank you mam when it comes to quality of service. Not everyone is that way but I sure have run into a lot of folks who are lately. I wasn't thinking of the GF folks who have offered help. It is better than one gets offered elsewhere. My current HVAC folks are great but my Carrier dealer is only interested in selling new systems. They hate working on used ones.

 

[metlmunchr]

I've been out of the business for 15 years, but during the 20 years I worked in it every day, all of the Carrier residential equipment with multi-speed motors used a Molex plug located near the fan for changing speeds.

There's one wire for the heat speed and another for the cooling speed, identified by color in the wiring diagram that's typically glued to the inside of the unit's access panel.

For 2.5 tons, the goal is to set the speed such that the unit is handling 1000 cfm at the existing total static pressure.

To get there involves some experimentation. Set up a gauge to measure the total static. Install whatever filter you've selected. Read the total static and go to the chart to read cfm corresponding to current fan speed and static.

If the cfm is too high, decrease the fan speed by one increment. Re-read the new static and the corresponding cfm for the new fan speed. Rinse and repeat until you have a combination of speed and static that equates as closely as possible to 1000 cfm.

The result will be a system that handles the proper amount of air and produces a temperature drop within the normal design range. Other added benefits will be operation with less air noise and better filtration due to lower velocity thru the filter(s).

Re your comments concerning the competence of today's hvac contractors, you are spot on in the majority of cases IMO. People who post here who are in the business aren't typical of the industry in general. The guys here are the type who have an interest in their trade and a willingness to share knowledge. Out in today's real world, the chance of the average hvac service numbskull having a good understanding of the operation of the stuff he's working on and how things are inter-related would be less than one in ten on a good day. If you want the system balanced for best operation and most efficient energy use, you may as well learn to do it yourself.

 

[SGKent]

I've been out of the business for 15 years, but during the 20 years I worked in it every day, all of the Carrier residential equipment with multi-speed motors used a Molex plug located near the fan for changing speeds.

There's one wire for the heat speed and another for the cooling speed, identified by color in the wiring diagram that's typically glued to the inside of the unit's access panel.

For 2.5 tons, the goal is to set the speed such that the unit is handling 1000 cfm at the existing total static pressure.

To get there involves some experimentation. Set up a gauge to measure the total static. Install whatever filter you've selected. Read the total static and go to the chart to read cfm corresponding to current fan speed and static.

If the cfm is too high, decrease the fan speed by one increment. Re-read the new static and the corresponding cfm for the new fan speed. Rinse and repeat until you have a combination of speed and static that equates as closely as possible to 1000 cfm.

The result will be a system that handles the proper amount of air and produces a temperature drop within the normal design range. Other added benefits will be operation with less air noise and better filtration due to lower velocity thru the filter(s).

Re your comments concerning the competence of today's hvac contractors, you are spot on in the majority of cases IMO. People who post here who are in the business aren't typical of the industry in general. The guys here are the type who have an interest in their trade and a willingness to share knowledge. Out in today's real world, the chance of the average hvac service numbskull having a good understanding of the operation of the stuff he's working on and how things are inter-related would be less than one in ten on a good day. If you want the system balanced for best operation and most efficient energy use, you may as well learn to do it yourself.

will add to the list of things to do. Sounds like a reasonable thing to do. I have all the factory literature on it. Guess I'll be reading and studying the manual as well as wiring diagram. Thank you

 

[lloyd 401]

I find this thread interesting as I work for 3M in a facility that manufactures the Filtrete media.

I dont know if the info you seek is available to the public but I can tell you that the labs run pressure drop tests regularly and at different stages of assembly.

Not sure why the 1900 filter would flow the best as we run several different weights and it's media isn't even in the bottom 2.

Sent from my SM-G950U using Tapatalk

 

[SGKent]

I find this thread interesting as I work for 3M in a facility that manufactures the Filtrete media.

I dont know if the info you seek is available to the public but I can tell you that the labs run pressure drop tests regularly and at different stages of assembly.

Not sure why the 1900 filter would flow the best as we run several different weights and it's media isn't even in the bottom 2.

Sent from my SM-G950U using Tapatalk

Thin media and many pleats. The thicker cotton or poly filters would not work with that many pleats due to the thickness of the material. Although I wish there was a simpler high MERV solution, the 1900 has the lowest drop of any filtrete filter per the data published on the filters. If I was doing it all over I would have had the system designed with more filtration area. It is too much trouble now on a 15 year old system. If I stay here and live that long I'll catch it next time around.

 

[danski0224]

Ductwork that is properly sealed may still have poor airflow characteristics (undersized, poor design) that makes the TESP high.

But, it's sealed up tight...

 

[DPelletier]

Good thread. In simple terms, I advise people to use low static (meaning low efficiency) filters and change them often as almost all residential equipment is incapable of dealing with the increased static caused by higher efficiency filters. Run stand alone HEPAs if you have a need.

The ductwork in most houses is rudimentary at best and undersized and restrictive at worst. The biggest mistake I see people make is shutting down registers to try to force air into a problem room or area which then increases static to the point the blower can't deal, airflow drops and the coil freezes....

Cheers,
Dave

 

[DPelletier]

I've been out of the business for 15 years, but during the 20 years I worked in it every day, all of the Carrier residential equipment with multi-speed motors used a Molex plug located near the fan for changing speeds.

There's one wire for the heat speed and another for the cooling speed, identified by color in the wiring diagram that's typically glued to the inside of the unit's access panel.

For 2.5 tons, the goal is to set the speed such that the unit is handling 1000 cfm at the existing total static pressure.

To get there involves some experimentation. Set up a gauge to measure the total static. Install whatever filter you've selected. Read the total static and go to the chart to read cfm corresponding to current fan speed and static.

If the cfm is too high, decrease the fan speed by one increment. Re-read the new static and the corresponding cfm for the new fan speed. Rinse and repeat until you have a combination of speed and static that equates as closely as possible to 1000 cfm.

The result will be a system that handles the proper amount of air and produces a temperature drop within the normal design range. Other added benefits will be operation with less air noise and better filtration due to lower velocity thru the filter(s).

Re your comments concerning the competence of today's hvac contractors, you are spot on in the majority of cases IMO. People who post here who are in the business aren't typical of the industry in general. The guys here are the type who have an interest in their trade and a willingness to share knowledge. Out in today's real world, the chance of the average hvac service numbskull having a good understanding of the operation of the stuff he's working on and how things are inter-related would be less than one in ten on a good day. If you want the system balanced for best operation and most efficient energy use, you may as well learn to do it yourself.

well said. I own a sheet metal/HVAC company that does mainly institutional work; our jobs are fully engineered, we retain the services of a third party air balancing and commissioning agent, etc. etc. ......typical residential HVAC system installations make me shake my head.

Dave

 

[DPelletier]

You are moving too much air. It really doesn't matter how much air the blower can move- it should still be set up to balance as a system. That's why blower motors can be wired to run at various speeds, even on a single speed system. You match them to the application by setting the appropriate speeds (different for heating and cooling) during installation.

yep; 400CFM per ton is normally what's required.

Dave

 

[SGKent]

so I am to swap the black and yellow wire to slow the CFM?

Yellow would give me 472 CFM per ton. This is a pretty dry climate and I understand from reading that 450 CFM is the target in dry climates. The next speed down is 406 CFM HOWEVER I think that the A-coil is a 3-ton coil they used with a 2.5 ton compressor. I vaguely remember something about that being said when the unit was installed to get the seer that was needed. If so, then the actual CFM numbers would be calculated against a 3 ton coil, med-high @ 393 CFM or medium @ 338 CFM. Right now it would be high @ 480 CFM (if it is a 3-ton A-coil).

View media item 94418

 

[DPelletier]

The real test will be to check the delta T but your likely OK with a bit of extra airflow. I've only ever used the Condensor size as the benchmark for CFM requirements, not the evap coil capacity.

Dave

 

[SGKent]

The real test will be to check the delta T but your likely OK with a bit of extra airflow. I've only ever used the Condensor size as the benchmark for CFM requirements, not the evap coil capacity.

Dave

Thanks Dave. Delta T appears to be about the same. The squirrel cage and inside of the air handler looked quite clean for 15 years use. Less dust than most people's desks in a week. I haven't checked the coil to see how clean it is but may do so in the next couple days. The humidity in the house is always around 50% so my guess is that if that drops then this was a move in the right direction. The delta t may rise as / if the humidity drops.

I slowed the air speed down to 406 CFM per ton. We'll see what it does. Really quiet now. Measured the fan cap and it has fallen 25% so ordered one of those too. GenTeq. In. wc across the filter dropped from .18 to .15 in. wc. With the filter removed the duct still shows .05. When I get a chance I will check it between the bottom of the air handler and the top of the a-coil to see what it is. Can't get to inspect the coil today, have other errands.

The original question had to do with pressure drop across a filtrete filter. While this thread has morphed somewhat, I would say that the high pressure across the filters originally may have in part been caused by the high air flow. As the system appears to have been configured originally, it was moving as much air as a 3 1/2 ton unit so no wonder there wasn't enough surface area for the filters.

 

[SGKent]

I have put it back to high speed to be sure there are no freezes. Below are the numbers I took tonight. Late and totally confused. Had no idea there could be so much resistance somewhere in this system. These numbers are taken with the motor on high, and a fiberglass filter.

 

[LS6 Tommy]

A Delta T of 13.5-14°F is about 6° too low. Fan speed is definitely too high.

Tommy

 

[SGKent]

I am told that based on my measurements the external static pressure of the system in between .70" and .73". The label shows a max allowable of .50". Need to clean the coil I think if my HVAC folks won't get out here to check it.

 

[danski0224]

I am told that based on my measurements the external static pressure of the system in between .70" and .73". The label shows a max allowable of .50". Need to clean the coil I think if my HVAC folks won't get out here to check it.

Your evaporator coil has nothing to do with the problem.

Crappy, but well sealed ductwork.

 

[brewchief]

What does it change to when lowered to med- high?

Sent from my SM-G965U using Tapatalk

 

[DPelletier]

My 2 cents:

- delta T is too low; probably due to too much airflow. Try for 18-22 deg. F.

- high static could easily be because the ductwork was sized for a lower airflow. Lowering the airflow will help both the delta T and the system static. Your original issue with high static caused by the filters is also mitigated by lowering the airflow.


Dave

 

[SGKent]

Thanks. What do you suspect is the cause of the high static pressure?

 

[DPelletier]

...to much airflow for the duct size, not enough take offs, registers that are shut off, poorly manufactured fittings on the mains, dirty coil......could be any (or all) of those things.

Dave

 

[SGKent]

finished cleaning the evap coil. The filter has .02" in more across it than before so my guess is that the system is passing a little more air. Hopefully the delta t will improve and the static pressure drop a little. If so maybe I can lower the speed from high to medium-high and that will help a little too. Also there were some bent fins four or five spots the size of dimes to quarters. I used a fin comb of the correct pitch to straighten those up.

edit: delta t went from 13F - 14F to 15F - 16F.

 

[SGKent]

Resolved: Performance drop on filtrete filter

So here is the end result. Using fiberglass filters is the best solution because the pleated filters drop the CFM too much. After cleaning the evap coil the delta t got better by 2 F, going from 13-14 F to 15-16F. The Static pressure at the furnace outlet remained .45" but the inlet fell from .28" to .27". I lowered the blower speed from high to medium-high based on suggestions here, and the Carrier AC manual for my compressor that states use 400 CFM per 12,000 btu. The actual compressor is 28,000 BTU so that is 2.33 tons aka 2 1/2 tons. 2.33 x 400 = 932 CFM. 2.50 X 400 = 1000 so somewhere between 932 and 1000 is optimal. At the medium-high speed the furnace outlet fell to .40" and the inlet fell to .26" That is .66" external pressure. High but until the inlet ducting is changed it is what it is. At .66" the CFM from the performance tables shows 995 CFM. There is a footnote that if the internal filter is removed then subtract .1 so that makes the total .56" which is 1057 CFM. So - the CFM is set to somewhere between 995 and 1057 - which is right where it should be for 2 1/2 tons. At the new medium-high speed the delta t is now 20 f. Before the cleaning the delta t did not change much from the 13 - 14F regardless of speed.

Someday when we have time, I'll have the sheet metal improved to lower the pressure a little and maybe use a better filter. Thanks to all who made suggestions - Steve

 

[DPelletier]

Excellent; I think you've got it set up nicely now.

Cheers,
Dave

 

[SGKent]

Excellent; I think you've got it set up nicely now.

Cheers,
Dave

I think so too. Can move onto the next project now.

 

[SGKent]

Conclusion. When this thread began the question was what kind of flow did Filtrete pleated filters have. The 1900 had the best flow for a Filtrete pleated filter but it was too high for the furnace so fiberglass was chosen. A Dwyer manometer was added to be able to see when the filter was dirty. Using that manometer measurements were taken that showed a need to tune the system. The Delta t was low, being about 13.5 +/- inlet temp to outlet temp. Changing motor speed made little change on Delta t. The evap coil was cleaned with a foaming cleaner purchased from Johnstone supply, rinsed with clean water using a pump up sprayer and then blown out using a long wand made from 1/4" copper tubing flattened on the end to make a fan of the compressor air. Small dents in the cooling fins were straightened using a fin comb of the correct number of teeth per inch. At high speed the Delta T rose from the 13.5 F to 15.5 F. Blower speed and CFM was calculated using ESP, and the fan speed dropped 1 speed from High to Medium-High. With this drop the Delta T rose to 20 F and the ESP was closer to where it should be max. I might note that before the coil cleaning speed changes had almost no effect on Delta T. Before and after drawings are shown below. I also learned a lot from the folks here and elsewhere about this process. For that I thank all who helped me thru this. FWIW I really didn't want to get this involved and tried to hire someone to do this for me but everyone was too busy right now due to summer increases in clients wanting services, or more interested in selling a new unit. In the end this system is working well. Humidity in the house is falling too more than before. We also find ourselves comfortable in the mid-70's instead of the low 70's. (Both of us have CPAP machines that put about a quart of water into the air each night, as well as showers and cooking adding water.)

BEFORE .73" ESP, 13.5 F Delta T

AFTER .57" ESP, 20 F Delta T

CFM Chart for this model

 

[SGKent]

an update - after studying the ducting installed in 2004 by the carrier dealer I came to the conclusion that the drop (3.25" x 14") to the return duct (12") from the back ceiling filter (12"x24"x1") was too small. That drop was only designed to carry 100 CFM. We increased the size of that return drop to 400 CFM to take full advantage of the back ceiling filter, and the 12" duct. That new drop lowered the TESP to .56" WC using the best MERV 13 Filtrete filter. The target was (from Carrier specs on the unit) .5" WC +.1" WC with the internal filter removed for a total of .60" WC total both on AC and heat. Heat speeds are lower than AC and are about .4" WC. Mission accomplished.

 

[fitter30]

Just because a unit is rated at 2.5 tons = 30k btu's that is nominal rating. Evap coil expansion device and efficiency of condenser has to be rated by the manufacturer in a lab and they have btu ratings of your extact mix of parts. If your looking for one of the best filter systems it will be a electronic air filter. Dust and pollen will be removed with a low pressure drop. Any filter system to get the most out of them blower has to run 24/7 and will only capture what it sees no different than your vacuum sweeper. This is just one brand.
https://www.honeywellhome.com/en/products/air-cleaners/f300-electronic-air-cleaner
Before changing blower speeds refrigerant charge, pressures, compressor efficiency and cleanliness of blower, coils need to checked out.
As for the competency of servicemen might help to ask for someone experience in air balance most techs don't have the tools or how to use them for looking at pressure drops or cfm.
Look at larger shops that have more money for training and tools.

 

[SGKent]

Just because a unit is rated at 2.5 tons = 30k btu's that is nominal rating. Evap coil expansion device and efficiency of condenser has to be rated by the manufacturer in a lab and they have btu ratings of your extact mix of parts. If your looking for one of the best filter systems it will be a electronic air filter. Dust and pollen will be removed with a low pressure drop. Any filter system to get the most out of them blower has to run 24/7 and will only capture what it sees no different than your vacuum sweeper. This is just one brand.
https://www.honeywellhome.com/en/products/air-cleaners/f300-electronic-air-cleaner
Before changing blower speeds refrigerant charge, pressures, compressor efficiency and cleanliness of blower, coils need to checked out.
As for the competency of servicemen might help to ask for someone experience in air balance most techs don't have the tools or how to use them for looking at pressure drops or cfm.
Look at larger shops that have more money for training and tools.

too many friends who had to keep a regular filter in the system to catch what the electronic system didn't, or catch it before the electronic filter. No faith in them. As to speeds and all that, I have the manual on everything that is installed and Carrier provides that info in the manual. This thread is 4 pages in now. Anyone here in HVAC could have offered to do the calculations for me for a fee and I would have been glad to pay them for their time at $100 an hour. No one stepped forward so I stumbled thru it myself and invested the money in tools to make measurements, spent days reading the specs and flows etc on different ducts, air pressure formulas etc.. I would much rather have paid someone to do it, and tried to find someone but none of the techs I talked to here even had a manometer. I spent $300 to get a good one.