Arkansas HVACR NewsMagazine May 2021

HVACR NewsMagazine May 2021

Tech News

of 3.5-inch thick pleated media with a total surface area that matches requirements in the chart. In general, the air intake of a furnace or air handler is too small to meet the cfm (400 per nominal ton) and velocity (300 feet per second) requirements by the manufacturer. This shortage translates to an intake area deficiency of approximately 30% for a nominal 1.5-ton system and to 47% shortage for a nominal 5-ton system. Columns I and J demonstrate the additional square inches necessary and the total area by square feet respectively.

find it is impossible to meet the criteria above without extensive costs or modifications. At the least, we leave the job educated on the shortfalls of the installed equipment with the understanding of the homeowner. When we present the problem in a well-defined scope for repairs, we may be surprised at the willingness of the homeowner to make those big changes to have an efficient and comfortable home. One final note. If a contractor chooses to ignore the geometry and physics of airflow, performance economy and

Required Added Surface Area Based Upon 400 CFM Per Ton @ 300 FPM

A

B

C

D

E

F

G

H

I

J

Filter size Filter Sq. in. Chassis Size Chassis Sq. in.

CFM Chassis Flow FPM Req. Area Size

Req. Area Sq. In. Add sq. in. Add sq. ft.

14"x20" 16"x20" 14"x25" 16"x25" 18"x25" 20"x25" 25"x25"

280 320 350 400 450 500 625

12"x18" 14"x18" 12"x23" 14"x23" 16"x23" 18"x23" 23"x23"

216 252 276 322 368 414 529

600 800

400 457 522 536 548 556 544

16"x18" 18"x22" 20"x25" 24"x25" 25"x28" 25"x32" 28"x36"

300 400 500 600 700 800

84

0.58 1.02 1.55 1.93

148 224 278 332 386 471

1000 1200 1400 1600 2000

2.3

2.68 3.27

1000

A- Represents nominal filter size generally purchased B- Represents gross filter dimensions C- Represents size restricted by the actual chassis frame D- Represenst actual square inches available for air flow

E- Represents required CFMflow through the heatpump or air conditioner F- Represents air speed through the blower G- Represents actual opening requried to maintain filter velocity at 300 fpm H- Represents return air gross grille area size I- Represents additional area required above chassis dimensions to maintain proprer volume and speed of air

J- Represents additional square footage required for proper filtration

With an ever-increasing emphasis on Indoor Air Quality and efficient energy consumption, media filters offer the best of both worlds when applied appropriately. We should benchmark static pressure across any filter combination at or below a .1 IWC. This translates to transitions for larger return air filtering on practically every job. During retrofit of furnaces and air handlers with platform returns, we may

longevity will be ignored as well resulting in unhappy customers and perpetual call backs. With current costs and complexity of evaporators being too dense to effectively be cleaned, filters remain the insurance policy to keep equipment operational for a longer period.

Tom Turner, Air Evangelist and Regular Contributor to the NewsMagazine