Arkansas HVACR NewsMagazine May 2021

S tate, National, Chapter News Tech News

blocks the airflow causing less air to move over the coils which drives up the condensing temperature and head pressure.

So to put my money where my mouth is we picked a nice dirty coil and ran a full, white paper style test. For the sake of complete disclosure we used the fan curve charts to come up with evaporator air flow, which is fine because it was a before / after test. I used MeasureQuick for the calculations and my phone was giving me trouble and kept losing my manually entered data so I realized later that in my AFTER report the airflow was set to 750 and before was set to 700 so I went back in and changed the math so everything was apples to apples. Either way… the results are pretty self evident. You will notice that the “official” results below are slightly different than those in the screenshots at the top, and that math change is the reason. Equipment Cleaned 2-ton 1999 Trane R22 10 SEER “Spine Fin” Heat Pump Split system with a direct return operating and 0.4” WC total external static pressure on a PSC blower and a fixed piston type metering device. Test Process I Allowed the system to run 20 minutes continuously and took detailed measurements sufficient to compare wattage, total BTU/H removal and therefore the EER of the system using wireless connected digital instruments and the MeasureQuick app. We cleaned the condenser coil only while performing this test no other cleaning or servicing and making no adjustments to refrigerant charge.

Compression Ratio As the head pressure and condensing temperature increase the compression ratio increases (absolute head divided by absolute suction) which causes the amount of refrigerant the compressor moves to decrease resulting in both higher compressor amperage and lower system capacity. This effect is greater with TXV/EEV systems because the valve will tend to throttle down as the head pressure increases to maintain superheat further increasing the compression ratio. Evaporator Temperature On fixed metering device systems higher head pressure will also drive up suction pressure which will tend to keep the compression ratio slightly lower but will result in higher coil temperature and poor latent (humidity) control.