Only
after you
have verified that all the coils are
clean & the
airflow is right-on,
can
you begin to
check the system's charge using
Subcooling method with a Superheat check.
Always check
the actual airflow
CFM 'before'
checking the charge, - get that Right First!
There
is a local TXV 1.5-Ton system that has very low airflow, actually less
than 200-cfm
per-ton of cooling,
they're
only checking the suction pressure & saying the charge &
everything is okay!
By the way, the furnace is a 112,000-btuh output & requires near
1200-CFM;
it is a CRIME to do such an A/C installation!
That
system has a
TXV & shows; 98-F
condenser saturation temp & 97-F liquid line temp near E-Coil,
a
mere 1-F Subcooling, it's
undercharged even with a mere 200-cfm per-ton cooling load!
Unbelievable, -
but it's happening out there!
Check the
Superheat & the Subcooling as outlined below and always
compare to the charging
instructions that are with the equipment as some use the
Approach
Method
& other methods may vary the operating figures & Target figures
vary somewhat from Super Heat & Sub Cooling
methods!
Those varied methods will usually be close to Super-Heat (SH) &
Sub-Cooling (SC) results. I would always use the SH & SC method in
conjunction with the mfg'ers method to trouble
shoot the refrigerant system.
Let's say
with a
TXV according to the Target Super Heat &
your collected data indicates a starved evaporator coil & a
normal or slightly off Subcooling, even if
you are
using a Mfg'ers
Approach Method do NOT automatically believe that it is undercharged.
One
company is
reportedly having problems with TXVs starving Evaporator
Coils,
or it could be a partially plugged TXV strainer/screen or other
restriction.
--------------------------------------------------------------------------------------------------------------
A new easy to use Super Heat
& Sub Cooling test instrument:
http://www.ueitest.com/ssm1/
To
Determine Super
Heat
(SH):
***
First, the
airflow through
the evaporator has to be absolutely correct blower wheel blades &
evaporator clean!
1.
Take
the Suction Saturation Temperature (SST) reading from
your manifold gauge.
2.
Then
take the Suction Line Temperature (SLT) as close to the
condensing section just before the serve valve.
Actually it is better to take it close to the TXVs power element, but
that is inconvenient.
3.
Take
the difference between the above readings (Suction Line
Temp 'minus' Gauge Saturation temp reading) = Superheat
4.
When
ambient air temperature (Outside air temperature) is 85
degrees or above the Superheat should be 8-12
degrees.
A/C
Thermostatic
Expansion Valves (TEV
/ TXV) should usually be set for a minimum of 7-F Degrees Superheat.
Some Heat Pumps with TXV's are set at 7 to 9-F Super Heat
or less because they have Suction
Line
Accumulators to store any spill-over liquid, which protects the
compressor.
For
TXV Subcooling, take the pressure of the liquid line note
the gauge
saturation
temperature.
Compare it to the actual temperature obtained near the
same point the pressure was obtained.
Thermostatic Expansion
Valves
(TEV
/ TXV) check with mfg'er Goodman concerning Superheat;
SH
varies by mfg'er Goodman TXV's are normally set between 7 to 9 or, 8 to
12-F; Goodman
TXVs are also adjustable. Always check Both SH & SC!
Heat
pumps with accumulators down to 7-F or less Super Heat.
This
linked page is strictly a SUPERHEAT
TABLE
Print these Tables & use them!
Print
this Two linked pdf pages: Target
Super Heat Chart and this Target Temperature Split for Airflow Chart
Here
is a formula for getting
the Super Heat Target - Within normal
perimeters:
((IWB)
Indoor Wet Bulb X's 3 -
80 - (OAT) Outdoor Ambient Temp) /
divided by 2 = Superheat Target
5.
If
Superheat is low then the evaporator is flooding.
Note: Do NOT adjust charge YET.
6.
If
Superheat is high then the evaporator is starving.
Note: Do NOT adjust charge YET!
7.
Do not
adjust charge UNTIL Sub-Cooling is checked.
Note:
When
charging a system using Superheat, you
are charging
the unit to the amount of air (CFM) and total heat load that is
crossing the evaporator coil
(Or, the amount of latent and sensible
heat load being absorbed by the evaporator coil).
Note:
Do not adjust charge based on Superheat on systems
with Thermal Expansion Valves (TXV, TEV's), (use Liquid Line
Sub-Cooling & Superheat to check the system.
TEV’s control the superheat; you should check the
superheat to see if the TEV is working properly.
Use
the manufacturers listed & Subcooling numbers, Goodman
Superheat Thermostatic
Expansion Valves (TEV / TXV) SH varies by mfg'er is normally set
between 7 to 9 or, 8 to 12-F; Goodman TXVs are also adjustable. Always
check Both SH & SC!
Brands vary; Some
14 SEER Goodman "TXV" A/Cs wants 7 to 9 degrees of Superheat and 5 to 9
degrees of Subcooling.
To Determine Liquid Line
Sub-Cooling
(SC):
*
First,
the
airflow
through a clean
evaporator should always be checked & be correct!
1.
Take the high side pressure and
convert it to temperature
using chart or gauge readings.
2. Then take the temperature of the liquid line as close to
the condenser as possible..
3. Take the difference between the above readings. (Saturation
Temp – Liquid Line Temp.).
Note: liquid line temperature at the
evaporator should be within 2 degrees of liquid line temperature at
condensing unit.
If not, could be a restriction or line set too long.
4. Sub-Cooling with a TXV, Goodman's around 7F +-2F
degrees, always check
with the mfg’ers for correct SC
5. Then using the information
from Superheat and Sub-Cooling we
can have some idea where to look for problems.
Example:
Suction Line Temp is -- 60 degrees @ condenser
Gauge Suction Pressure is --76-psig -- 45 degrees, Read Gauge Suction Saturation Temperature (SST)
65 degrees Suction Linee – 45 degrees = 10-F degrees Superheat - Adjust
charge to the
mfg'ers SH & SC
Settings
Liquid Pressure is -- 226-psig -- 110-F, Read
Gauge - Liquid Saturation Temperature
(LST)
Liquid Line Temp (LLT) is -- 105-F
110-F – 101-F = 9-F Sub-Cooling
- Adjust Refrigerant charge to the mfg'ers SC
settings; see that SH is within target range.
On
TXV metered systems the Subcooling should be within +/- 2-F of the
mfg’ers installation instructions.
==========================
Air
Conditioning Performance Diagnosis using listed (CT) Condensing
Temperatures
Using Goodman 16-SEER "Expanded Performance Data"
Find the correct (CT) Condensing Temperature with the following
known mfg’ers data.
Outdoor Ambient Temp (OAT) 85-F; IDB 75-F; IWB 63-F or 50%-RH.
Listed pressure is 316-psig, or 99-F CT; that is 99-F -85-F is a 14-F
SPLIT.
The delta T or temp-split should be within a 10-psig range or, +/- 2-F
degrees; I.E.; 95-F @ 97-F or 99-F.
The mfg’ers Supply Outlet should be able to provide Contractors &
Techs with those performance data charts.
Goodman has their “Expanded
Performance Data” on the Internet.
(1)
Unit owners get
a low-cost digital
flat-headed pocket Thermometer to use flat on the piping;
these test instruments will PAY big returns!
(2)Get a low cost Testo Tester &
ballpark
figure actual BTUH & EER - the information on it:
Testo 605-H2 Fast Accurate Wet Bulb
(3)Home owners; -a
very low cost anemometer to get airflow FPM Velocities, Info U Need:
http://www.amazon.com/Crosse-Technol.../dp/B0002WZRKE Search Hart&Cooley for the
Sq.FT., or Ak free-areas of diffusers,etc.
Get a low cost Testo Tester & ballpark
figure actual BTUH & EER - the
information on it:
Testo 605-H2 Fast Accurate Wet Bulb
-----------
This should be
helpful, as you can use this info to determine the actual realtime BTUH
output of your A/C system:
Take the Supply Air & Return Air wet bulb temperatures &
interpose them on the enthalpy chart linked below.
Duct system CFM X* 4.5
@sea-level, or use X* 4.35 if 1000' above sea-level,
X* change in enthalpy
= BTUH
(Ballpark)
Operating Performance.
"U
Must
Right Click Link & open in New Tab,"
look-up wet bulb enthalpy
figures on chart," & figure enthalpy change.
Wet Bulb
Enthalpy Chart
Rules
of
Thumb for Duct Systems - Hart&Cooley
DESIGN
AND INSTALLATION OF RESIDENTIAL FLEXIBLE DUCTWORK SYSTEMS
http://www.dca.state.ga.us/development/constructioncodes/publications/1ONE.pdf
Look
at the ducting, if it is not to code; make hard copies of this code
& give it to whoever does the ducting work
Make sure they redo it right!
Never
have flex duct interiors commercially cleaned, I just viewed Home
Inspection photos showing the interior damaged & insulation
plugging the duct.
Home Inspectors warn people because the duct
cleaner's tell them it won't damage the ducts. Some HI's
look into the boot areas for clues of problems...
=============================================================
------------------
Identifying your
registers/diffusers & their (Ak) sq.ft. area, so you can multiply
the FPM Velocity times the Ak to get the (CFM) Cubic Feet per Minute
airflow from that register.
Have or do a manual J heat-gain calc for each room. If a room calls for
3,000-BTUH; first divide 12,000-BTUH by the CFM PER TON you want to use.
I.E., Wet coil, 12,000/400=30-BTUH per each CFM; Wet coil
12,000/425=28.235294; 3000/28.235-= 106.25-CFM;
Dry coil,
12,000/450= 26.6666-BTUH; 3500 / 26.6666= 131.25-CFM
If register/diffuser has the same (Ak) free-airflow-area, as the duct
run!
Room calls for 3,500-BTUH, using 450-cfm per/ton dry coil or 26.6666-BTUH per CFM= 131.25-CFM.
I.E., 6" rd duct
.6*6=36*.7854=28.2744sq.ins/144=0.19635-sq.ft.; 131.25-cfm /
0.19635-sq.ft= or 668.4-fpm velocity.
SP2= 2-Ton {800-CFM / 650-CFM}2 = 1.2307692*1.2307692=1.5147928* old SP= 0.98"SP new;way too high!
SP2= 5-Ton A/C {2000-CFM / 1650-CFM}2 = 1.21212 * 1.21212= 1.4692363 * old SP .60" = 0.88" new; way too high.
SP2= 4-Ton {1600-CFM / 1350-CFM}2 = 1.85185*1.85185= 1.4046634*.65" old SP= 0.913" new SP2;way too high!
It is always better to add SA branch runs & more RA area, plus "a lot more RA filter area."
- SP2 ={(rpm2/rpm 1}2 X SP1 = SP2
-
Fan
amp-draw increases as to the cube of the cfm increase
- Amp2 = Amp1
(cfm2/cfm1)3 cubed *x Amp1= Amp2
Required
fan motor horsepower (hp) varies as to the cube of the rpm
speed:
- hp2 = {rpm2/rpm1}3 x hp1 = hp2
CFM Fan delivery varies
directly as to the fan RPM speed:
- cfm2 = (rpm2/rpm1) X cfm1 = cfm2
Duct
retro-work can solve the problem,
increasing blower HP alone won't usually work well!
A few calculations plus retro-work and presto, a matched airflow with
your systems'
heat absorbing coil capacities, delivering near its BTUH, EER, and SEER
ratings at normal room temperature settings! (Most don't)
- Required fan motor horsepower (hp) varies as to the cube of the rpm
speed:
- hp2 = (rpm2/rpm1)3 x hp1 = hp2
CFM Fan delivery varies directly as to the fan RPM speed:
- cfm2 = (rpm2/rpm1) X cfm1 = cfm2
Duct retro-work can solve the problem, increasing blower HP alone won't
usually work!
A few calculations plus retro-work and presto, a matched airflow with your
systems'
heat absorbing coil capacities,
delivering near its BTUH, EER, and SEER
ratings at normal room temperature settings! (Most don't)
======================================================
*You could ballpark the CFM
using the static test & a air handler graph. You could measure
the CFM delivered to each room with a hood Alnor Balometer,
it's
usually the best instrument to use, but not cheap. Measuring the air
velocity is a bit tricky because you have to use the
diffuser data which you don't always have available.
A rough ballpark formula to get the CFM: CFM = (velocity in (FPM) Feet
per Minute times the square footage of the duct area, you have to have
& use the diffuser data & get velocity there -for operating
conditions.) Taking the manifold gage head pressure & gage
condensing temp, is important data. Coupled with a TH condenser
temp-reading, if the condenser gage
pres/temp is too high compared to the TH reading, there may be
non-condensibles in the system.
Also,
there is a legitimate formula I use to determine the operating BTUH it
is delivering at all the data taken. All the mfg'ers ought to list the
condenser temp-split (it varies with EER & SEER) just like they
list the indoor split, it is valuable trouble shooting info.
You can also use the condenser temp-split (it contains both Latent
& sensible heat) combined with the indoor data to plot the indoor CFM. I
was never good at math, but those
equations have to balance, & they do work!
==================
The
A/C user need not know all the tech info, all they need to know are a
very few basic ways to identify that the system is not functioning
correctly so they can call
for a pro-tech to properly trouble shoot the system.
Now the reality is that you don't need a manifold gauge, - anyone can
Ballpark check the charge in respect to the indoor airflow with only a
little low cost MA-Line digital thermometer using some tubing
insulation on the sensor probe.
http://www.ma-line.com/HTML/L1_productmenu.html
You can't order it there.
However First, you check the discharge air temp off the outdoor
condenser, (that is the "Condensing Temperature (CT)," the higher the
SEER Rating the lower the outdoor normal temp/split above the outdoor
temperature will be.)
Then you either check the small liquid line tubing temp outdoors where
there is a tubing bend, or indoors where it bends to enter the plenum.
Indoors could be inaccurate as the tubing temp could vary higher or
lower depending on temp conditions the line is conducting.
Subtract the small liquid line temp from the CT & you have the
Subcooling temp which varies some from mfg'ers, but will be Ballparke 8
to 12-F Subcooled.
The condenser temp (CT) above the outdoor temp tells you how much
indoor sensible & latent heat, & the 3 motor heats it is
ejecting. The indoor humidity level has the biggest effect, the higher
the humidity the hight the split.
Now, indoors the higher the humidity the lower the temp/split between
Supply-Air & Return-Air.
At 50% indoor humidity the split should be Ballpark, around 18 - 20-F.
If blower wheel blades & all coils are relatively clean & the
split is well above 20-F, you have low airflow with a low heatload
through the evaporator coil.
If the indoor split
is way below 18-F at 50% RH, you either have way too much airflow
or some problems in the functioning refrigerant system.
To solve any of these problems you need to call a
knowledgeable HVAC TECH! - Darrell U
--------------------------
An Affordable Test
Instrument You Need!
All I had was the
Sling Psychrometer & spinning it was a bit time consuming, but I
used it religiously, it is information you need.
The Testo 605-H2 Humidity Stick
(wet
bulb), displays relative humidity,
air temperature and wet bulb temperature.
It is very affordable & because of its potential to help deliver
tons of other data everyone should have one!
For more information on it:
http://www.amazon.com/Testo-605-H2-H.../dp/B000774B6A
The other test data you need is the system's CFM airflow through the
evaporator coil, then with software I have you can peg the BTUH the
operating unit is delivering under those conditions.
Add to that a low cost Magnehelic gauge to read static pressures to
compare with mfg'ers blower performance charts; plus a velocity meter
& you have a ballparked CFM to plug into for the BTUH.
We could easily provide a detailed psychrometric print out of
exactly what the operating system is delivering including condensate
lbs/hr, & actual sensible & latent cooling BTUH & Ratio,
every data
detail imaginable.
============================
It is
important to understand that "equipment ratings are only the
'potential efficiency' of that component of the system under perfect
conditions." Over half of the system’s efficiency depends on
correct equipment sizing run-time,
on the duct system sizing, i.e., on the quality of the complete
field-installation!
Especially
if your system is oversized or there are a lot of low AC load days use
an adjustable differential room TH.
TH
Differential: Differential is defined as
the difference between the cut-in and cut-out
points as measured at the thermostat
under specified operating conditions. For example, if the thermostat
turns the
COOLING EQUIPMENT on at 78-F & OFF at 75-F that is a 3-F degree
differential setting. This is a
good way to control high humidity problems & also improve SEER
performance; plus longer more efficient heating cycles.
What you want & need is right sized equipment operating
at
its
optimal ratings within varying conditions, for your optimal comfort
and
savings.
*CONDENSING
TEMP CT Diagnosis *
| Lennox TXV Subcooling
Approach |
| R410a
Evacuation
|
Differential
RM T- stat Improves SEER |*** Sizing
Units to Adequate
Airflow New ©
CHECK
RETURN AIR for HOT AIR LEAKS | Gurgling
sounds at TEV | Trouble
Shooting TXV Valves Affordable Test Instrument You Need
The
duct system airflow must be
checked & correct,
before performing any charging procedures!
My ordered procedure that must be followed
to achieve an optimally charged
efficient operating air conditioner.
Do not leave out any
of the
steps and always do these procedures in the
order sequence illustrated.
First,
check that there are NO air leaks in the Supply and Return Air
duct system.
Next,
Check to see if Indoor Squirrel Cage
Blower wheel blades
are
free of
lint or other build-up & Filter.
Before checking the
refrigerant charge always check the actual air flow with an anemometer
& apply the math shown below!
Check for
a dirty lint
clogged Evaporator Coil fins then check the Condenser Coil fins, check
both coils on the air entering sides as well as between the fins, -- clean if needed.
Take a
look at the ductwork for proper sizing and for leaks, Check
the External Static Pressure (ESP), check
the indoor Cubic Feet per Minute
(CFM) Airflow, then outdoor
condenser discharge
air
Temperature split (delta-T), then indoor
Delta-T, then after
15 minutes of run time before any charging
adjustments are made. On smaller tonnage equipment & in most
climates that are not overly humid, I like 425 to 450-CFM per/ton of
cooling
on a wet coil.
In
summer, Air conditioner & heat pump user's, this is a "Simple
Easy Safe Way" to Check an A/C's
Thermostatic Expansion Valve (TXV) metering system's refrigerant
charge & any A/C's Performance:
Record
the outdoor temperature, then "Take a thermometer & check the air
temperature coming off the outdoor condenser."
Locate
the small uninsulated copper line where it makes a bend, outdoors or
indoors,
so you can put a digital thermometer flat on it & insulate the TH
with
something (piece of the tubing insulation) read the temperature &
subtract it from the outdoor condenser discharge air temp.
E.g.,
condenser temp 110, line temp 100-F that is 10-F subcooling & 10 to
12-F is a normally charge system. If it's considerably less than 10-F
it could be low on refrigerant or need a Tech to check it; too far
above 12-F it's overcharged, call a Tech, could also be a restriction
in the lines.
You should own a low cost digital pocket thermometer: Now the reality is
that you don't need a manifold gauge, - anyone can Ballpark check
the charge in respect to the indoor airflow with only a little low cost
MA-Line digital thermometer using some tubing insulation on the sensor
probe. An A/C supply Outlet might sell you one or inquire at hardware
stores! Saves money on needless A/C Service Calls!
http://www.ma-line.com/HTML/L1_productmenu.html
Take the outdoor temperature & subtract it from the outdoor
condenser's discharge air temperature.
This temperature is standard for different SEER Rated units.
An older 12-SEER unit, with 50% INDOOR Relative
humidity ballpark should be 18 to 20-F temp split.
A 14-SEER will be around a 14 to 16-F temp/split. if too far above or
below those temps, call for an A/C Tech.
Formula
for finding CFM Airflow
If you can
measure the air velocity coming from a duct, here is a rough
ballpark formula to get the CFM:
CFM
=
(velocity in (FPM) Feet per Minute times the square footage
of the duct area)
Example, 16" Rd duct
201-sq.ins. X's 0.00694 = 1.39494-sq.ft. X's Velocity
of
800-fpm = 1,116-CFM
Times 1000-FPM = 1395-CFM.
Branch ducts: 7" Rd duct 38.48-sq. ins. X's
0.00694 =
0.2670512-sq.ft. X's 500-fpm=133.5-cfm
However, times a velocity of 600-FPM X's 0.00694 = 160-CFM, the velocity is a big room CFM &
BTUH number changer.
-----------------------------------------------------------------------
Quick
Check for Sizing Units to enough Airflow
===================================================
TROUBLE
SHOOTING TXV VALVE SYSTEMS
Bulb location:
Some Mfg’s have there preferences, but a good rule of thumb is 10 or 2
O’Clock,
away from headers and heat exchangers, on a smooth clean surface.
Also, make sure the
cap tube is on top (horizontal
or vertical and never upside down).
Pressure drop:
TXVs like to have at least 100-psi
pressure drop across them to operate correctly. A
solid column of liquid (at the valve) is also a requirement.
Flood back:
Always make sure you have "the correct CFM airflow"
(clean coils,"
Clean fan blades
& fans running on correct speeds
and in the right direction) before you try adjusting a valve.
No flow: A plugged
screen is rare in air
conditioning, but happens often in refrigeration.
I have
seen the external
equalizer tube leak through in liquid
form and give the bulb a false reading (which causes hunting more so than no flow).
-------------------------------
TXV or filter driers
partially
plugged up stream from Service Gauge Port LOW SUCTION Pressure, if
downstream from service port partially plugged
Compressor Inlet screen high suction pressure.
In
HVAC-TALK These Posts Illustrate and Discuss these Test Results
Lennox TXV Subcooling -
Approach Method - pdf P- 8
http://www.davelennox.com/pdfs/installation_maintenance/Lennox-12ACB-IOM.pdf
Always
check both SH
& SC for trouble shooting
comparison to normal
parameters!
---------------------
Even on service calls where there
are cooling
problems the ductwork should have a quick Manual D performed.
Take the
ESP
static pressure & compare to blower graph or chart, also take the
FPM duct velocity.
For Room
Return Air balancing, i.e., -.01" IWC = approximately -2.48 Pascals, which is a more precise easier incremental
scale to read.
One inch water
column (IWC) equals rounded to > 250 pascals, 0.5" IWC is about 125 pascals; 0.25"
WC = 62.5 pascals; 0.125 = 31.25 pa.;
1 / 250 pascals =0.0040322
*X's -2.50 pascals = -0.01003657696655" IWC or
make
it - 0.01"
IWC for low Return Air room
pressure differentials; - use pascals.
Here
are some
examples of residential or light commercial in Inches Water Column
(IWC) Pressure
Drops. Check the engineering data as you design, and you
may be surprised.
This is mainly only the example of the Device
pressure losses.
Then do a quick
estimate of airflow
per equipment tonnage.
To find area of
a
round duct; Duct diam is 7"; 7"X7"= 49-sq.ins., X's .7854 =
38.04845-sq.ins divided/ by 144= 0.2672541-sq.ft. area X's FPM Velocity
600-FPM =
160.35246-CFM X30 = 4,810.5738
each 7" run X's 6 branch runs
= 28,863-BTUH, or airflow for 2.4-ton.
(12,000-BTUH
/400-cfm per-ton = 30-BTU per cfm ratio | / 450 = 26.666-BTUH per-cfm)
That would also
be
good for 2-ton; at 550-FPM velocity X's 0.2672541= 147-CFM X 30 =
4,410-BTUH each run X 6-runs = airflow for 26,460-BTUH.
*Never sell
units requiring more airflow than the duct system will support! - Darrell udarrell
|
MO
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