Regular Guest
System:
<1 yr old a/c and furnace
Furnace: Carrier Infinity 58MVCO8O
A/C:Carrier Performance 24APA53OA003
Infinity Control
Carrier Media Filter Box 16x25
Filter: 4 inch MERV 8 Carrier FILXXCAR0020 (first one said FILXXCAR0016)
-I get the warning to change or clean filter after only about 2 months of use.
-When cooling when I set the fan to high, the airflow does not seem to move all that fast.
-The A/C does not quite keep up (maintain cool enough temp) on 90 degree days
I checked the A/C status with the Infinity controler, here are my results:
Fan set to auto, thermostat temp set to 71, outdoor temp 81, indoor temp 74.
Airflow CFM 875
Coil Temp 81
Outdoor temp 81
Blower RPM 720
Static Pressure .40
If I remove the filter from the cabinet:
Blower RPM drops to 657 and static press drops to .30
I tried setting the fan to high, it didn't change the #s
Correct me if I am wrong, but I think my static press is limiting my airflow, so in order to protect the system the blower never kicks in high RPMs...always under 876 when cooling.
I have already added a return when I had the system installed. Everyone of the installers (some from this forum) said my ductwork was OK.
I can (not so happily) live with the way the system works now (although it does not keep pace like my old oversized system).
2 questions;
1. Do my #s look OK?
2. Would using an even less restrictive filter help (only MERV 8 now)...any suggestions on a filter that would work?
Last edited by MiniSoCold; 09-02-2011 at 01:15 AM. Reason: sp
Professional Member*
Seems like Reasonable operation to me ( unless the unit is running > 14 hours a day).
You can not do Any better with filter selection.
Warning to clean filter Frequently is a bit troublesome.
I do not understand - my expectation would be to clean maximum of 4 times a year and change once a year.
Expectation of < 72'F is a bit extreme when it's > 90'F.
However, 71'F should be achieved a little after sunset.
Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities
God Speed, Jim. We'll miss you - 2-26-23
Your static pressure at 875CFM is fine. By calcs, it should only rise to .45" when the blower goes to 1000 CFM.
Professional Member
if the system was unhappy about the static pressure ithink it would tell you. you do not say the airflow increases with no filter. it sounds like the blower slowes to maintain cfm.
Regular Guest
I don't think the Infinity controler ever lets the static pressure go higher than .41 thus the blower never goes to 1000 RPMs, and never over 875 CFM to reach .45 static pressure when cooling. Thank you!
Professional Member*
I thought Infinity would allow static pressure of closer to 1.0". I think 0.50" is considered "nominal" for most any system near nominal rated cooling CFM. I'm guessing yours is 1200CFM. So it would be just a little high, but not too bad.
Beenthere, what's the max RPM for that motor? I'm guessing at least 1500RPM.
Professional Member*
Your filter choice is fine, your static at this point is fine your cfm is at 350 default. Have your dealer set it up for 400 cfm and that wil increase your sensible capacityOriginally Posted by MiniSoCold
God Speed, Jim. We'll miss you - 2-26-23
1200 or 1300 RPM. After that it won't report a static pressure as I recall.
AOP Committee/Professional Member*
In MN do you have medium heatloads with high humidity control problems?-I get the warning to change or clean filter after only about 2 months of use.
Pleated filters are face loading verses media filters that load through the depth of the media; therefore they may load faster even though they have a lot more sf of physical area.
-When cooling when I set the fan to high, the airflow does not seem to move all that fast.
-The A/C does not quite keep up (maintain cool enough temp) on 90 degree days
A setting of 71F on high heatload days is too low a setting, try 75F. On hot days, what temp does it achieve?
I checked the A/C status with the Infinity controler, here are my results:
Fan set to auto, thermostat temp set to 71, outdoor temp 81, indoor temp 74.
If so, that could be why they set it at 350-cfm per ton.
I don't have specific figures on your particular filter.
A 16X25X4 Merv8 figures at 1400-cfm & 492-fpm velocity, pd is 0.21", physical square feet is 18.8-sf'. Therefore, even at 1000-cfm if the rest of the duct system meets Manual D standards the static might well be within tolerances.
Merv8 filter specs - download the pdf:
http://www.google.com/url?sa=t&sourc...KP0L0IY5mN3PZw
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udarrell
Regular Guest
What size unit is it in ton for us non HVAC guys please?
Professional Member*
FILTER IS FINE ! !!
Translating ...
at 900 CFM the rated filter dP is only 0.087" ( not 0.21" @ 1400 CFM)
Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities
Regular Guest
What size unit is it in ton for us non HVAC guys please?
Regular Guest
Sorry double post.
Professional Member
It's 2 ton unit
Professional Member
If you you use MERV 12 (or higher) filter and you have old dirty returns you going to go through those filters pretty quick. (if returns are on the floor that does not help either.
You may look at cleaning your air ducts that will help in you situation.
My "old" 1994 2 ton comfortmaker keeping my 1100 sqft ranch at 70 on 100 day and cycling, with no problem and I'm like 500 miles south of you.
I use standard 1" Merv 8, 16x25 and they last like 3 month easy.
Professional Member*
2.5 ton
Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities
Professional Member
yep it's 2.5 my bad
AOP Committee/Professional Member*
Good point dan; a big drop in CFM results in a big drop in velocity through the filter & thus far less pressure drop.Translating ...
at 900 CFM the rated filter dP is only 0.087" ( not 0.21" @ 1400 CFM)
Without figuring the difference, I didn't think it would be that much.
At 900-CFM, being a little less than 0.10" is very good, especially if at 492-fpm velocity.
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udarrell
Regular Guest
Ok,
I will have my ducts cleaned, continue with the same type of filter, and not expect 71 Degree cooling on the 90 degree days.
15 years ago when I had a blower motor replaced, the guy doing the work told me there are huge differences in the effectiveness of different machines used to clean them. Any suggestions on what to look for in duct cleaning companies or equiptment?
Again I want to thank you guys. From reading these forums a year ago, I was able to choose a very professional instaler for my a/c and furnace. He did a load calc., Manual J, duct evaluation etc. One of the 5 bids that I recieved was from a larger company who would have just sold me an oversized system to match the size of the 24 year old one I was replacing. Without you guys freely sharing your knowledge I would not have known any better. When the inspector came to check on the work, he saw the name of the firm who did the work, and he told us up front he knew the work would be top notch from inspecting over the years. THANKS AGAIN!
Professional Member*
Does the infinity control have built in humidity control? If so try turning up the humidity setting to see if it speeds up the fan.
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