CFM vs. SEER

[friesenk51]

Could somebody explain the differences between these two? Are they even related?

[LazyPup]

CFM is Cubic Feet per Minute, which is a measurement of tha amount of air a blower can move in a given period of time.

It is primarily used to determine the size of fan motor required to adequately move the air in your house by example,

If we had a room that was 10' x 10' with a 10' ceiling the area of the room is 100 sq.ft and the total volume is 1,000 cubic feet.

If we then wanted to design a blower system that could exchange the air in that room four times per hour, we would need a blower that could move 4,000 cu.ft of air per hour. Dividing 4,000 cu.ft per hour by 60min/hr would indicate that we need a fan that can move 4,000/60 = 66.6 cu.ft per minute.

When designing an HVAC ducting system they must begin by computing the total volume of the structure to determine the size of the fan motor. They must then compute the volume of each individual room to determine the size of ducting and air grilles to insuring a balanced air flow throughout the structure.

EER is Energy Efficiency Rating. Back in the fuel crisis days in the mid 70's people began to be very conscious of energy consumption. This was especially true in the HVAC and electrical appliance industries. In order to have a fair method of comparing one brand or model of HVAC equipment to another they came up with the idea of dividing the BTU output by the wattage input which yeilds the ENERGY EFFICIENCY RATING.
They could then mathematically compute the estimated annual cost of operating the equipment to get an annual EER rating. The annual EER rating was then compared to the national average cost of electrical energy to compute the average annual cost of operation, which is what we often see posted on electric water heaters, refrigerators or laundry washer and driers.

Relizing that most consumers are impressed by numbers even if they have no idea what that number means, in order to create a marketing tool the HVAC industry then took it to the next logical conclusion. An AC does not run constantly the year around, but rather only runs for the cooling season in an given region. They then took the annual EER rating and divided it by 12 months to create a monthly EER rating, which they then multiplied by the number of months in the cooling season at a given location.

In the early days of the pratice each manufacturer used the heating and cooling season at their principal manufacturing center to compute SEER. As you can easily see, even though the mathematical formula was the same a manufacturer in Chicago could show a much higher SEER rating than a manufacturer making an identical product in North Carolina or Alabama.

In an effort to be fair to all parties concerned, the industry has now settled on some finite standards based on national average to make the final computation. Thus when comparing units of the same output it can be said that on a national average a unit with a higher SEER number will consume less energy per anum to perform the same amount of work.

[kactuskid]

If you're trying to figure out how to size an air conditioner, then here's a link that'll explain and give you details as to how to :
http://hem.dis.anl.gov/eehem/95/950509.html