I did not know about the blower efficiency. Will have to check into it.
What should the static pressure be?
The installer was conserned about high readings and ran flex duct from the plenum to mixing boxes on the other end of the house to try to reduce the numbers.
I reallly hate to say this but should I have the duct system replaced with ducts designed for this system? If static pressure is really the cause of the high kWh consumption, that seems to be the only real solution.
If duct replacement is the only option, what are your opinions on flex duct vs fiberboard etc. The home has metal flex wrappped with insulation and a plastic outer layer other than all the flex duct that was installed......
Oh, we have been keeping the temp set at 79 degrees.
Then there's the one's whose bills are higher, slightly, but find that the whole home has more even temp's.
But yeah, the static has to be taken care of, no doubt.
many carrier dealers years ago thought infinity and ecm blowers would overcome duct issues this was not true. Now rule of thumb is to upsize duct work 25 % when using ecm blower. static pressure should be around .5
Why did they go to a 4 ton unit? Did they run a load calculation before installing it? There was a good chance that a 3 Ton may have been the ideal size. If the unit may be running at much lwoer, less effcient airflow levels to reach the desired humidity level... espceially if they matched it with a oversized indoor coil for a higher SEER rating.
Eneryg consumption may have also gone up, if you are keeping it cooler, lower humidity levels or the house is being cooled more evenly.
Also, if you have leaking ducts, a 2 stage system that runs constantly will suck in more humid attic air as well since it running longer.
Finally if you're old heat pump was a good quality 12 SEER unit, it may have dehumidified well, and ultimately a newer 16 SEER system, probably will only achieve an EER (effeciency at higher temps where you use the most energy) that only marginally better than your old unit.
My conditioned living space was enlarged since I purchased the home with the old 3 1/2 ton unit. The salesman felt a 4 ton unit would better suit our home size. He also said it would save us "lots on the electric bil".
As far as temp in the house, with the old unit I would keep it set at 75. With the new unit I keep it set at 79 hoping to save some money. It is comfortable when we first enter the house but feels warm after being inside for any length of time.
Guess I should have just kept my old unit :-(
Well, the 10 & 12-seer units were - good to go.
First, get the duct system sized for 0.5" ESP.
With a 4-Ton it will normally need two large Return air filter grilles with two entries to the air handler.
For fiberglass panel filters, about 69% is open-air-area (Ak) sq.,ft., area. (Using Hart & Cooley Engineering Data, with a RA grille.)
For a 5-Ton A/C at 2000-cfm/300-fpm = 6.666-sf *144 = 960-Free-air-area or (Ak);
the "Physical Area" to get that free-area is 960/.69 is 1391-sq.ins., or about 1400-sq.ins.
A 4-Ton needs at least 1600-CFM; You do the figuring..
Always use the above equation, many other methods won't always provide correct results.
Different filter types have different open-air-area (Ak) sq,.ft., areas; so U need to know the Ak or, test for 300-fpm through the filter with an anemometer.
In numerous situations, the Bryant 3 filter cabinet could be a good option! Link to cabinet filter system is above.
Do the RA filter Research it can help solve some major problems:
What is your humidity setting?
I am not a professional. I am a homeowner who has Carrier Infinity furnaces and AC condensers.
I also did not see a significant decrease in energy usage going from my 8 SEER 25 year old condensers. So you are not the only one.
Two things you should check. Is the fan set to auto? Is is very easy to push the top right button so that the fan is running continuously. I assume you are set up to cool to dehumidify. What is the humidity reading? What humidity settings do you currently have in the Infinity controller? The condenser (heat pump in your case) my be running for long periods of time in the low stage in an attempt to lower the humidity. A leaky house in the humid Florida climate would aggravate the problem.
You could try turning off the cool to dehumidify feature. I personally don't recommend it. In my opinion it is the best feature of the Infinity controller.
wow darrelll, so ur saying a 5 ton should have atleast 3 20x25 returns?
Originally Posted by udarrell
Three 20X25 is not 500-sq.ins each or 1500-sq.ins.; because actual physical filter area is approximately 19X24 or 456--sq.ins. * 3 is 1368-sq.ins.
Originally Posted by jrpsimivalley
Well, that is using ACCA Manual D's 300-fpm through a new clean cheap through-away filter.
We ought to check actual airflow through filters.
The physical required filter area depends on the performance data of the filter we are using.
Now, if there's a 90-ell near a duct insert filter, then part of the filter will have considerable more velocity through it the other portions with much less; Not a good situation.
Last edited by udarrell; 08-04-2011 at 06:34 PM.
I find this very interesting. Is it possible you could give more information on where the rule of thumb comes from. Jim
Originally Posted by jrpsimivalley
Two-stage, flex duct in the attic. That's probably your main issue. The lower air velocity in the ducts in low stage operation will allow it to pick up more heat, or conversely it will allow it to lose more cooling, to the attic air. Duct leakage losses will also be amplified. Adding duct runs in the attic in a case like this is an exercise in futility. It only worsens the problem.
Originally Posted by overheated in fl
Ok, so the installer has agreed to remove all the added flex duct they installed. They will also remove and replace (with larger flex duct) some of my original ducts leading to one of the air returns and to one of the mixing boxes. They are also going to add turning fins inside air return chase and Aeroseal the duct system. They feel my problem is a result of high static pressure and say enlarging the few lines should eliminate the problem. They are also saying, now, that my ducts should have been replaced but I was told they were fine before they did the job.
One other thing they noted was the unit is "slightly overcharged".
Hopefully this will solve some of my problems.