Would a bigger Fan/Blower Help?

[BobM3]

I'd like more airflow from my home AC/Furnace. Easiest would be to put in a bigger fan and blower. My guess is that the exchangers are probably optimized for the motor and blower already installed so my heating and/or cooling power might not increase with the increased air flow. Any thoughts?

 

[pmover]

your guess is a safe assumption/conclusion. for the heating/cooling coil, the duty is fixed, so increasing the airflow will likely result in a change of air temp leaving the coil(s).
check filters and any other possible restrictions in duct system and the airflow may likely increase some; yet not impact the heating/cooling capabilities too much.

good luck!
-pmover

 

[MintJulep]

Your furnace was "rated" at some set of conditions that included an airflow/pressure drop. Those rating conditions may or may not be published somewhere, and may or may not be desirable real-world operating conditions.

From there the manufacturer probably established a recommended range of acceptable airflow or total external static pressure.

The first question to ask is: Is your system operating within that range?

 

[IRstuff]

One honest A/C guy points out that the flow resistance of your ducting and registers will limit the output of your A/C. Even at the reduced tonnage recommended by this guy, my registers whistle pretty loudly during A/C operation.

TTFN

 

[BobM3]

I had the ductwork cleaned out last week. I lubed the motor and checked its current draw and voltage. All looked o.k. When I had this furnace installed 6 years ago I wasn't impressed with the airflow. Newer homes in my area blow the curtains wildly off the walls when the A/C is on.

 

[IRstuff]

Not sure what your house size, etc., are, but I've got a 2200 sqft house with 4 ton A/C, and while I can't claim to blow the curtains off the walls, the A/C gets the house cold enough to shiver. My house is 30 yrs old this year

TTFN

 

[IRstuff]

One problem that could occur is that if your A/C is already oversized, your inside exchanger might be freezing up and limiting the air flow directly. Do you see lots of condensation coming from the drain line?

TTFN

 

[BobM3]

I do see a lot of condensation on the drain line. Maybe I should pull out the evaporator while the A/C is operating and check for icing? (Although heating air flow isn't that great either). I'll have to compare my tonnage/(house sqft) ratio to yours.

 

[IRstuff]

Are your registers free from blockage? When we got the house, some of the registers were covered with wallpaper, which they slotted, but...

TTFN

 

[pennpoint]

BobM3
Most, but not all heater/air conditioning blower motors are multi-speed. Suggest you seek (its a simple terminal change) if you have multi-speed type and switch to the highter speed to see if thats helps. Speed (RPM) is directly proportional to CFM. Double the speed = double the CFM.
You may still can realize some loss of cooling through the coil due to the higher air velocity. But you are ex-changing the air at a greater rate. Also...You may not be as cool but you feel cool because you feel a movement of air around you a "perceived coolness" so to speak. "Comfort is perceived"
NOTE: Horsepower increases by the square so the cost of moving that air increases. In winter switch back to lower speed to prevent occupents fron feeling stiffeled from heated air blowing around them.
Give it a try!

Best regards
pennpoint

 

[willard3]

BobM3:

Which system seems not to be working well, heating or cooling?

If you want to bump the fan speed, something must not be working.....else you'd leave the fan alone.

 

[BobM3]

Air flow isn't very good for either heat or cold. When the furnace was installed new the flow wasn't that great. I can live with slow heating but I'd like the cooling to be faster. The heat exchanger was replaced about a year ago - no change in air flow. I pulled the evaporator out a year ago for cleaning - didn't make much difference in air flow. I'm going to move some of the furniture farther away from the air return ducts. I'm going to find my square footage and tonnage and see how it compares to IRstuff's. I'd like the ability to use the setback feature of the thermostat to allow the house to get warm during the day but then be able to quickly cool it (or me) in the evening. Penpoint's "perceived cooling" sounds interesting. Maybe getting the air flow up (even if it results in less cooling power) will feel better.

 

[IRstuff]

Been there, done that ;-)

We lived without A/C in our house for three years prior to getting the A/C. Big ass fans moving lots of hot air around is marginally better than hot still air. Particularly if it's so hot that your perspiration evaporates immediately before you feel a wind chill effect from the moving air. Desert climes like Tucson and Las Vegas are like that. The hot wind really doesn't cool you down much.

If your registers don't whistle, then I'd agree that your air flow is insufficient.

How's the suction on the inlet side? Is the inlet grill blocked for some reason? Your fan should be capable of suctioning heavy cardboard against the inlet grill.

Have you replaced your filters?

Can't imagine anyone selling you an undersized fan when there's such a temptation to sell you an oversized fan ;-) The typical sales rule is 1 ton for 400 sqft.


TTFN

 

[willard3]

You can also do what is done commonly by manufacturers, put in a 2-speed motor and run high speed on cooling and low speed on heating.

Even better would be a VFD (variable speed drive), but there are control issues for the heating unit.

Make sure the entire system is clean before you make the changes....could be dirty filters.....

 

[thermcool]

There are chances that the cooling/heating power can increase with the increase in the flow rate of the fan. If you look at the refrigeration process and the air flow rate, for the increase in the air flow you will experience less degree of temperature rise in the air steam which will bring the evaporator temperature a bit high (due to the rise in the temperature at which the air is leaving the evaporator). Now with the rise in the evaporator temperature its internal pressure will also rise. This rise in the internal pressure will basically increase the enthalphy change occuring inside the evaporator (in the P-H diagram). Now if you look at the vapour density, in this case the compressor is compressing the dense vapour which basically increase the mass flow rate of the refrigerant mixture inside the cycle. Also, the volumetric efficieny will increase due to the rise in the evaporator pressure and the less expnasion of the charge present inside the clearance volume of the compressor. The overall effect will menifest in the form of increase degree of heating or cooling of the surrounding as more energy is being transfered from the evaporator to the room.