Arkansas HVACR NewsMagazine January 2022

HVACR NewsMagazine January 2022

Tech News

Part Four of Five-

Example: Nominal 3-ton flows 1200 cfm. 1200 cfm / 2 = 600 square inches of gross grille area. This gross grill area is valid for a standard stamped face grille. In certain circumstances where returns are space constrained, you may want to use a commercial type grille. AK factor can be almost double on the commercial grille allowing more air flow in a smaller space. Be aware, smaller spaces increase speed. We will tackle velocity next, but we must take note that anytime we exceed 400 FPM we generate too much noise at the return. Some companies use commercial returns as a standard offering to reduce static pressure and noise.

Cold Air (Return) Demand Tom Turner, Air Evangelist

In part one, we discussed the issue of air flow through the furnace or air handler and in part two we discussed the evaporator and proper selection for capacity. The third article pointed out the importance of the distribution system. This discussion includes a most difficult subject. Cold air (heating dominate climates) or return air (everywhere else) intake for the HVAC system. There are four obstacles to providing air access to the blower compartment via the chassis. Overall intake area- There must be adequate area for incoming air to the blower. This area must take account of added restrictions the grille applied, may bring to the equation. This is where understanding the characteristics of individual grilles is important. When measuring static pressure from inside the blower compartment to outside the return air including the filter values must be at .15 IWC or less. Grille area as related to free area or AK factor- Primarily understanding the AK factor gives us an idea of the free area the grille provides. In part one we discussed the chassis requirements for air. The formula for calculating the area needed, is a simple one. Half of the cfm required, equals the square inches of gross grill area.

Filter quality and area for slower air flow and greater filter efficiency- This topic is one of great consternation. With all the retrofit opportunities available, preexisting systems can pose the problem of uncovering the fact HVAC in often overlooked when the home is