Tech Tid Bits > Why TXVs? System Reliability, Indoor Comfort

Why TXVs? System Reliability, Indoor Comfort
06 Mar 2011

ICP recommends that thermo-static expansion valves (TXVs) be used with all of its new 13+ SEER systems. Why? Its not just for efficiency. The primary reason is reli-ability. TXVs offer better refrigerant control which will boost efficiency, but more importantly, helps prevent flood-back of refrigerant to the com-pressor. Compare to Piston Metering Device Lets consider the operation of a properly charged air conditioning system that is equipped with a pis-ton metering device, instead of thermostatic expansion valves. What happens when the indoor air filter on this system becomes full of dirt? Airflow in the system drops, resulting in colder indoor coil tem-peratures and a lower suction pressure. When the suction pressure drops, a larger pressure differential is exhibited across the fixed-orifice piston.

The high pressure differential causes more refrigerant to be pulled through the piston. The extra refrigerant is now entering a colder than normal indoor coil, and at this point, it is likely the refrigerant will not gain enough heat to completely boil off into a vapour. Eventually, this re-sults in liquid refrigerant flooding back to the compressor. In that same system, what happens if the outdoor coil is dirty? The system head pressure rises. If the indoor air filter begins to plug as well, the pressure across the fixed-orifice piston goes even higher. The compressor now sees BOTH high head pressure AND flood-back.

TXVs for ICP Product ICP specifies non-bleed, hard shut-off TXVs for all of its systems manufactured in 2006 and beyond. TXVs optimally regulate refrigerant flow and help compensate for pres-sures and temperatures that can go beyond the normal operating range of the system. The hard-shut-off feature helps prevent refrigerant migration to the indoor coil during shut down. If re-frigerant were left to migrate, refrigerant flood-back would occur at the compressor during start-up. This is not a good situation.

Think about this fact: 13 SEER systems that use 3/8 tubing in the outdoor coil require up to twice as much refrigerant as older systems. Add the use of a piston as the ex-pansion device, and the task of pre-venting refrigerant flood-back to the compressor becomes even more difficult. ICP systems use less refrigerant and use TXVs for expansion. Both of these help guard against flood-back and increase system life. However, the best reason is for customer satisfaction. Increased system efficiency, system reliability and indoor comfort are the many factors by using a TXV. Source: ICP Dealer Newsletter

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