Arkansas HVACR NewsMagazine November 2021

HVACR NewsMagazine November 2021

Tech News

static is lower than 0.2 the distribution system is too large or may have uncontrolled air flow, such as a disconnected duct run, or inappropriate branch runs or terminal devices.

Part Three of Five-

Air Flow Through the Distribution System

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. This third article points out the distribution system. The distribution side is perhaps often overlooked due to the assumption no remedies are necessary. If the contractor takes the time to examine the distribution side, that means he will have to fix it. Over 80 percent of homes have inadequate or improperly designed distribution systems. Some distribution systems have suffered through three or four generations of equipment with no improvements to duct efficiency for the system. If I don’t fix the duct system , I guarantee the system will never perform. The system will never accept a full charge of refrigerant, fan flow will be low or excessively noisy, power consumption will rise and most importantly, comfort will take a nosedive. Static pressure is a quick way to verify distribution adequacy. We discuss TESP (Total External Static Pressure) many times and look generally pressure of 0.5. We find TESP by checking pressures with a manometer as described above provided by National Comfort Institute. If static across the filter is 0.15 or less and fan speeds are set appropriately for the outdoor matchup, supply static should no more than 0.4. Generally, if supply

As always, consult the manufacturers information, as some heat pump installations call for low supply side statics. The supply side must distribute air efficiently to high value targets. Those targets include upper floor ceilings, exterior walls, windows, and exterior doors. Contrary to popular belief, we do not simply cool the air within the space. Energy laden (heating) air is directed to targets just as Energy low energy (cooling) air is directed at the same targets. By loading insulated areas like ceilings and walls we maximize time off cycles. We should use high sidewall terminal device placement whenever possible. Sidewall grills are very efficient with low losses associate with throw and drop when properly selected. Where high sidewall placement is not achievable, curved blade