Carrier Infinity System with Excess Static Pressure
I'm a new member but have been monitoring the forum for information that would apply to my situation. I'll try to post enough information without just running on.
I was an owner/builder of my house and contracted to a local HVAC installer for my Carrier Infinity Hybrid system. Some system details:
Heat pump: Model # 25HNA660A003
Furnace (propane): Model # 58CVX110-1-22
Inside Coil: ADP M-215
The unit had high static pressure messages (around 1.3"WC) since it was installed. My main problem was in heat pump mode. The system would start heating on low stage, switch to high stage when it determined necessary, stage back down to low stage due to excess static pressure, then switch to the propane furnace because the heat pump couldn't meet the heating demand in low stage. I used a lot of propane my first year. I have since locked out the furnace until it gets to 30 degrees. This keeps it in heat pump mode but running on low stage most of the time.
My original installer (not an authorized Carrier dealer) gave up and told me to get an estimate from another company to fix it (he paid me the estimated amount with the agreement that he is done). I hired an authorized Carrier dealer to fix the problem. He enlarged/installed some more ducting and got the pressure down to about 1.1"WC. However, from everything I have read on this forum, this is still way too high. The target should be 0.5"WC and anything at or above 0.8 is too high. The new installer is implying that once he gets to 1"WC the system is good. Is this correct or should I hold my ground? The problem I have is a can't find any Carrier literature that states what an acceptable static pressure should be for my system, is there anything out there? The air delivery table in furnace installation manual does list 0-1.0"WC as the external static pressure range.
Thanks in advance for any help.
Pictures of duct system would help if that is possible.
' is still too high, as it doesn't allow for the air filter/filters to get dirty. You do have a return on both sides of the furnace, or its coing into the bottom of the furnace. Right?
Pictures are possible but not easy. The system is installed in the "attic" (uninsulated area above the ceiling). I may go up there this weekend, I'll see if I can take any meaningful pictures.
It is a horizontal system in the attic. I think the return comes in from either the end or one side, I'd have to look.
Either something is too restrictive to the air flow in your system(ex. Incorrect sized ductwork, too small/restrictive filter, dirty coil etc) or something is fouled up in the controls or blower motor in your unit.
I agree. It is either the ductwork undrsized, restriction somewhere, or bad information causing the controller to think the pressure is higher than it actually is. Several supply ducts/registers and another return have been added. The coil was inspected and found clean. One interesting thing is that the Infinity controller does not display the model and serial numbers of the furnace, just the capacity. I was told this was because the board had been replaced (I don't know if it was). I've wondered if it was somehow giving bad information to the controller. I'm really not trying to solve the problem, that is why I hired the Carrier authorized dealer. I'm just looking for a solid definition of what the static pressure should be. Right now I am just some customer saying anything 8"WC or above is too high without any documentation to back me up.
The static pressure need to be checked with a magnahelic to verify the static on the thermostat is correct .
5 ton coils are usually very restrictive to air flow. Often .3 to .46" PD wet. Add on a .03 for supply register, and .03 for a return grille, plus .07" for a cheap fiberglass air filter, and your already at .43 to .59" without any duct work. So .8" isn't too high for a gas furnace with A/C.
Do you think the three zones might be the problem?
The first problem you have is you purchased a high end Carrier system and than had someone install it who was not up to par to do it. If they did the ductwork than they should not be installing duct. If the ductwork is existing than the problem lies with the sizing of the system. You have not talked about square footage in your home and why a 5 ton was chosen. 3 zones? does this mean you have 3 separate supply trunks or an electronic zone damper system. As stated previously on a 5 ton system you should expect .5 static before even considering ductwork. Most duct designs out there are short on return. Have you run the system with the blower door off to see how much the static drops? You really need to give more information to allow anyone to give you advice on ways you can solve the problem. Also count how many supply registers you have in the house. On average each supply register should move 100 cfm. for a 5 ton system you would need approximately 20 runs for a typical setup.
The 5-Ton condenser is probably way too big for your home; however you could have them test-drop the CFM to an actual tested 330-CFM per/ton of cooling. (If it works okay; 330-CFM per/ton * 5-Ton is 1650-CFM that will help lower the coil's PD.)
Depending on the Make of that 5-Ton, depending on field conditions, the Btuh may be between or closer to 4-Ton capacity.(?)
It needs at least two very large (I mean large!) Return Air Filter grilles in the conditioned space with none in the air handler or duct system near the air handler. Use large low pressure-drop fiberglass filters...
For 1650-CFM; it will need at least 17 supply air branch runs to diffusers delivering an average of 100-CFM at around 600-fpm velocity.
I'd shoot for 0.5" & only up to 0.6" ESP Max.
Tell us where you live & all the details U can about your home, etc.
Last edited by udarrell; 08-30-2012 at 10:54 AM.
Reason: Clarity problems...
To high Static Pressure
How many returns do you have and what size are filter grills? Also what size is the flex running from the return grills?
Your duct work might be the problem.