Expansion Valves (TXV) (TEV) Applications - set up an Adjustments
you choose air conditioners and heat pumps with thermostatic expansion
valve metering devices?
Expansion Valves have advantages in
nearly any climate zone where you have a variable temperature in the
summertime. The advantages
skyrocket when you live in a high humidity climate zone.
thermostatic expansion valve with a low eight (8) Fahrenheit superheat
set-point will keep the evaporator fully active at any temperature or
is critically important that the Thermostatic
Expansion Valve be properly matched
to the condensing unit and the evaporator used in that specific
There is a
wide variation in the tonnage applications that a particular
thermostatic expansion valve will cover. When the matched equipment
uses R-22 refrigerant, Goodman Manufacturing uses a one to 3-tonnage
thermostatic expansion valve. When matched with equipment using R410A,
they use a specific thermostat expansion valve for each tonnage up to
4-ton four and five-ton, which uses the five-ton TXV to cover both
Now let us
look at the technical aspects of the TXV versus the fixed piston
orifice when operating in different climate zones.
orifice system increases the head pressure and refrigerant flow rate
when there is high outside ambient temperatures; the TXV holes the same
superheat setting of 8-degrees Fahrenheit.
ambient temperatures are low, 70 to 75°F, the refrigerant flow rate
drops off and the superheat skyrockets. At 75°F outdoors and 78
indoor wet bulb, superheat skyrockets to 40° F.
increase in superheat means that your coil is going to be partially
filled with vapor that is being Superheated by the airflow through the
coil. This raises the temperature of that portion of the evaporator
coil and reduces the gross capacity of the coil.
thermostatic expansion valve will continue to keep the superheat at
8°F, thus you have optimal condensation of humidity and a full
capacity - heat loaded coil. The heat load absorbed by the evaporator
coil determines the heat that is exhausted out through the condenser to
the outdoors. Always strive to get an optimal heatload through the
talk about keeping the coil well below the dew point for optimal
condensation of moisture. Since the application temperatures and
pressures are higher with the new higher seer air-conditioning systems,
where humidity is a problem it would be wise to reduce these
cubic-feet-per-minute (CFM) airflow to 350-CFM.
evaporator coil with the low TXV 8°F setpoint and the oversized
evaporator coil with an abundance of fin surface coupled with the lower
velocity of the 350-CFM airflow across the coil will result in adequate
Checking Pressures -
Errantly Thinking it is a Fixed Orifice System
checking TXV controlled suction pressures for low charge keep in mind
that if the TXV controlled evaporator is receiving flash gas, suction
pressures can read normal.
Due to a low charged condenser, the TXV sensor bulb on the suction line
will cause the Power Element to be pushed down, - opening the valve and
this can raise the suction pressure and temperature readings to normal
The compressor cannot keep up & the evaporator temp & pressure
rises with too much vapor filling the evaporator coil, reducing its
capacity. The lack of cold vapor could lead possibly to an overheating
the compressor & its oil. Check the discharge line temp to see that
it is under 225°F.
For various reasons, many times TXV controlled evaporator's are not
listed in the installation instructions.
Every condenser & furnace should be labeled that it has a TXV
metering device, or the usual errant assumptions will ensue, that it
has a fixed orifice device!
techs came out to my brother's home to check his TXV AC system.
They checked the
suction line pressure per usual, that read close to 80-psig, and they
I wouldn't put any more Freon in there.
I said, that's a TXV controlled
system. They did not have any thermometer to check line temperatures; I
said, I the superheat should be
around 12°F on a TXV system. They said the superheat should be over
someone told them that before they came out. well, they left saying
would get Dan to come out, I will let you know, - but doubt that he
will ever show up. (More on these critically
important TXV application discussion topics soon)
are errors in this page it was typed with drag and voice software. My
hands and fingers are to miss the to type very much as I make many
typos now that I am constantly correcting! I have not checked this page
for errors you.
Udelhoven – udarrell Posted: 8/30/07
When the humidity is
its ratio of latent heat absorption.
Through Evaporator Coil (1987 Period)
and humidity load variations graph.
Air-Conditioning (ARI) Second Edition,
Page 624, ©
demonstration of how the latent heat capacity of the DX coil "increases
with the increase in room relative humidity.
A modern 2-ton 13-seer system would produce around .70 of a ton
or 8,400-Btu/hr, however at 70% Relative Humidity its capacity would
increase to around 1.1 ton or 13,200-Btu/hr or over half of the 2-tons
would be used for the latent heat-load. "That is around a 36% increase
in latent capacity" with some reduction in sensible capacity, --due to
a higher humidity!
& Air-Conditioning (ARI) Second Edition, C 1987
had higher condenser splits than 12-SEER and higher units.
graph, 90-db outdoor, 80-db indoors with 67 wet bulb or,
the condenser splits shown above graph.
Graph: 80-DB & 80-WB
is 100% Relative Humidity.
I assume no
responsibility for how anyone uses the information on my web pages
All HVAC/R work
should always be done by a licensed Contractor! This information is
only placed on these pages for your understanding & communication
with contractors & techs.
information is for the edification of contractors and techs. I
am NOT liable for your screw-ups, you are liable for what you do! -
Darrell's Refrigeration Heating and Air Conditioning -
Refrigerant Licensed - Retired
Darrell's Refrigeration Heating and Air Conditioning-
Contact me: email@example.com
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you'd like to contribute! - Darrell
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