|"Higher" or "Lower"
"Normal" (PRINT CHART)
||liquid High-Side||Sub- cooling||
|NORMAL - (norm) - LOW - HIGH - Variable||
|(1) Suction Line Restriction - Upstream
Between Service Port & E-Coil
Restriction - Downstream from
Service Port & Compressor Screen
|(2) Liquid Line Restriction - Poor humidity control||
|(3)Evaporator orifice oversized or bypassing - or TXV Overfeeding - Normal Charge - with orifice feed Poor humidity control||HIGH
|(4) Hot gas Disc. Line Restriction||
|(5) Inefficient Compressor - Also, see (3) Above - Poor humidity control||
|(6) Unbalanced heatload on Evaporator Circuits; or Insufficient Evap Heatload - Poor humidity control||
|(7) Insufficient Evap. Airflow, or
- Poor humidity control
Refrigerant Overcharge- High
or Low pressure - Variable
according Outdoor Ambient Temperature & to indoor heatload - non-TXV
|(9) Insufficient Low Charge -
- with orifice feed Poor humidity control
|(9a) Insufficient Low
Charge with TXV
||may be Normal
|(10) Excessive Evaporator Heat Load - Latent & Sensible + High Latent + high indoor airflow||HIGH
|(11) Ht Pump low head low sub-cooling; leaking check valve; both modes|SOV=switch-over-valve - rev/V leaking or bad coil||
|could be normal||LOW||LOW||LOW|
|(12) Very High Temp Ambient Air Entering Condenser or dirty - Low condenser airflow - with orifice feed Poor humidity control||HIGH||HIGH||HIGH||Norm/low||HIGH|
More authenticated survey test corroboration; the surveyed HVAC systems were systems that
they had complied with their program’s energy standards and "all had
received substantial incentive payments," but delivered
an average of only 63% of their
Rated Btu/Hr to the homes & 50% of the required airflow.
70% of homes in California are operating at 50% capacity. - California Energy Commission
http://www.law.cornell.edu/uscode/text/47/396 (8) public television and radio stations and public telecommunications services constitute valuable local community resources for utilizing electronic media to address national concerns and solve local problems through community programs and outreach programs...
First, always check for Return Air/Supply Air duct leaks, seal them with approved mastic, check CFM airflow rate and that the coil fins and blower wheel blades are clean! "Check for Insufficient Air Flow Across Evaporator Coil" - Check for: dirty filter, dirty lint clogged evaporator, blower speed tap selected, or belt and speed adjustments, blower motor, check any belts for wear and proper tension, dirt lint loaded blower wheel, and out of specs or wrong rated run capacitor.
NATURAL GAS or PROPANE
CFM = (Input BTU x thermal efficiency - Furnace OUTPUT) / (1.08 x temp-rise DT) or use 1.1
Note: Combustion efficiency can be used in place of thermal efficiency.
DT is the temperature rise across the heat exchanger in degrees Fahrenheit
This will give you an approximate CFM; although it will be very close to the actual if the measurements are made accurately and the input of the appliance is correct
For an electric furnace the airflow measurement procedure is the same. Allow the appliance to operate until the temperature rise stabilizes. Measure the temperature rise again out of the line of sight of the electric heater, along with the incoming volts and current draw in amps to the electric strip heaters. Enter the information into the following formula
CFM = (Volts x Amps x 3.41) / (1.08 x temp-rise DT)
CFM = (Input BTU x thermal efficiency - Furnace OUTPUT) / (1.08 x temp-rise DT) or use 1.1
Check airflow system static pressure. Verify Blower Performance --by checking blower air handler "Static Pressures with the specific model's Blower Curve Charts." At a specific heatload condition, Optimize the conditioned space's heatload on the evaporator coil to optimize the rated Btu/hr and EER, and/or SEER Ratings. Always Check comp. discharge line 6" from Comp 225°F or Less; cylinder walls 75°F higher!
Even experienced HVAC technicians are not properly charging the thermostatic expansion valve (TXV) refrigerant metered systems, because instead of only charging to the sub cooling standard they are interposing superheat into the equation leading to grossly miss charged and especially grossly under charged systems.
First; they never or rarely ever check or verify that there is the proper amount of cubic feet per minute (CFM) of airflow through the evaporator coil before attempting to balance the refrigerant charge; that should always be done first.
The thermostatic expansion valve (TXV) totally controls the superheat (SH) setpoint target; NOT the charging of the unit; a TXV set-point which could be a Fahrenheit set point of anywhere from 20°F down to 10°F on an air-conditioning system or 8°F SH on a heat pump.
The technician I witnessed had a wonderful digital readout manifold gauge showing superheat and sub cooling, the unit only had about 1°F sub cooling to begin with and he proceeded to get to a mere 4°F of liquid sub cooling adding one pound of R-22; the normal range is 8 to 12°F sub cooling (SC) on those older 12 SEER and lower systems.
That the technician erroneously said was that most TXV systems are targeted at 16°F superheat and so since it was at 14°F SH; and it was still hunting due to a lack of a solid liquid stream to the TXV; the reason that he falsely speculated that the system was over-charged was because it wasn’t holding his imaginary 16°F superheat target; that's because the TXV was a 14 or maybe 12°F or less superheat target-point TXV.
The TXV superheat target of this particular UNIT might be 14°F, or it might be 12°F or even 10°F therefore it is totally wrongheaded to be using it when charging to falsely think it would lower superheat & then to quit charging at a mere 4°F sub cool & NOT continue to the required sub cooling standard. To do so could leave a lot of new and older TXV controlled evaporator coils way under charged.
Troubleshooting an air-conditioning system using superheat and sub cooling:
Troubleshooting is a matter
of using temperature differentials; after
retirement, I've used temps for SC without using a
manifold gauge for many years. .
Sub cooling temperatures tell you if you have too much or too little liquid refrigerant in the condenser high side; superheat temperatures tell you if there is too much or too little liquid refrigerant in the low side, - in the evaporator coil.
A too high superheat and a too low sub cooling indicates you don’t have enough liquid refrigerant in the both sides therefore low on charge.
A too low superheat and a too high sub cooling indicates you have too much liquid refrigerant in both sides or an overcharge.
Both, a high superheat and a high sub cooling more than 15°F SC indicate a refrigerant system restriction; same with TXV system, TXV may not be able to bring SH down to its target.
System problems with a TXV metering device:
Refrigerant overcharge suction pressure normal & liquid pressure HIGH; superheat normal sub cooling HIGH; amps high and RH control normal
Refrigerant under charge: suction pressure normal; low liquid pressure; low superheat ;normal too high; sub cooling LOW; amps low; relative humidity control is normal.
Liquid restriction: suction pressure low liquid pressure low; superheat high sub cooling high; amps low and will eyes with poor real humidity control.
Low evaporator airflow: suction pressure low liquid pressure low superheat normal sub cooling normal amps low may ever me eyes with normal real humidity control.
Dirty condenser: suction pressure normal; liquid pressure high; superheat normal sub cooling normal ;amps high ;humidity control normal.
Low outside ambient temperature: suction pressure normal; low superheat; normal sub cooling; low amps; normal RH control.
TXV bulb loose: suction pressure & liquid pressure HIGH; AMPS HIGH; superheat & SC LOW; below sub cooling; HIGH amps; poor RH control.
TXV bulb lost charge: suction pressure low; liquid pressure low; superheat sub cooling HIGH; amps low; ICE/poor relative humidity control.
TXV bulb poorly insulated: suction pressure & liquid pressure HIGH; I superheat low sub cooling low; ;Amps HIGH; poor relative humidity control. - udarrell
Non-Condensables: suction pressure normal, liquid pressure normal; sub cooling normal; amps HIGH; poor relative humidity control sometimes normal control.
Try to check the run time and off-times of the air-conditioning system and write down the indoor temp & %RH -humidity & outdoor temperatures; it's best to do this on the hottest days & late in the afternoon around 4pm.
Let's say the air conditioner runs for 15
minutes then, off for 15 minutes before it restarts, that's a total of 30
minutes for complete cycle so you take 15 minutes and divided by 30
minutes and you get .5 or 50% runtime; let's say I have 2 ton air
conditioner; 80-F & 50%RH indoors & 95-°F outdoors could yield
24,000-BTUH; however, due to ductwork and other factors it would
not deliver to the rooms 24,000-Btu/hr instead figure 90% of 24,000 and
multiply that figure 21,600-Btuh delivered to & from the rooms by * .5
extrapolated that is only 10,800-Btu used per an hour to hold the 80-F
temp. Then you should perform a free online load-calc to verify how well
your A/C or heat pump is performing.
Another formula is the EER or 'Energy Efficiency Ratio' formula; the BTU/HR divided by the wattage used. Another way to use the formula is to take the BTU/HR and divide by the units EER Rating. SEER Ratings are rather irrelevant as in the field they never equal their LAB Ratings.
Let's say the air conditioner has a nominal rating of 24,000 BTU per hour divided by a 9.7 EER that is 2,328 Watts of power used. A technician can then take an amp-probe reading and multiply the amps times the checked voltage which will equal Watts the unit is actually drawing. From that reading you can figure what its actual EER is; 2,328-watts / by 240-volts would be 9.7-amps.
Another way to verify what your home's Btuh load is, is to do a load Calc; I'll provide you with the free online load Calc with which you can experiment with until you get a proper load Calc performed, which you will then have to print out because you cannot save your load Calc's.
You can also use a indoor humidity gauge and write down the humidity level while taking the temperature difference between the supply air and the return air in your home; then go outside and take the temperature of the discharge air and subtract the outdoor temperature from it.
On a 10 or 12 seer condenser the indoor split at 50% relative humidity and 80°F indoors should be around 19 to 22°F. The outdoor condenser split should also be between 19 and 22°F; the condenser fan is moving considerably more air through the outdoor coil than is moving through the indoor coil. A 13-SEER would be 20°F temp rise off the outdoor condenser; & a 21°F indoor temp-split.
Do the same with heating; say the gas furnace is an 80,000-Btu/hr at 95% efficiency which equals 76,000-output; if the runtime is 20-minutes on & 15-minutes off time before a restart, 20 + 15 is 35-mins total complete cycle time so, 20-runtime / 35 cycle-time is .57% * 76000 extrapolates to 43,320-Btu/hr used to maintain the Room-TH setpoint of say 70°F. If this were the coldest winter temp; then a 57000Btu'hr output furnace would be better sized, as it takes at least 3 to 5-minutes to reach nominal output each cycle; cooling mode takes around 7-minutes, therefore the Btu-output would be less than what I showed above for cooling & here for heating; short cycles are inefficient & costly.
Filter sizing: ACCA Manual D requires a low 300-fpm velocity through a new clean filter; a 60°F temp-rise maximum means the 76,000 will have close to 1200-CFM / 300 is 4-sf * 144 is 576-sq.ins of open-air-filter-area, media type filters only have a 65% open-air-area. 576 * 1.65 is 950-sq.ins of filter area. Two 16X25 is 400-sq-ins *2 is 800-sq.ins; still 150-sq.ins less than called for.
Above 500-fpm velocity debris blows through a media type filter. One 16X24 filter has a Ak of 1.84 @ 300-fpm it will only flow 552-CFM; @ 650-fpm it will flow 1196-CFM; that is 150-fpm above where debris begins to blow off excessively at 500-fpm velocity through the filter. Hart & Cooley Filter Engineering Data using media type filters. A 1" deep pleated filter has way too much pressure drop resistance, use 4 or 5" !
Totally Free Load-Calc
This Free online calc will help you determine equipment sizing & point-out areas that need efficiency retro-work - Once you calculate the page it saves the inputs for up to 24 minutes or, until you change inputs or close your browser.
You can easily reduce infiltration rates yourself, therefore, I’d use 0.4 ACH (Air Changes per Hour) be sure to add the (Air Changes per Hour) CFM into the ‘Fresh Air Recommended ‘line-slot, or it won’t figure the Infiltration & fresh air Btuh.
You can experiment with changing the design temperatures in both heat & cooling, (or start-over showing the New Retro-R-Values) also to see whether the equipment exceeds, at those particular temperatures & new retro conditions, (exceeds) the Btuh calculation load numbers, 'in each' of the 3 cooling categories; Total Btuh, Sensible Btuh & Latent Btuh
Simple easy anyone can do ways to check the performance of your central air conditioner so, if needed, you can call an Energy Efficiency HVAC Technician
If U want me to run a ballpark analysis of how your system is performing in respect to its 'Nominal Rated Btuh' we need at least the following numbers:
Performance Data Collection – Best Time to collect data is Late afternoon around 4:30 pm, when attic is HOT; also when outdoor temps are around 85; 95; 105F or, anywhere in between.
*All U need is a good thermometer (digital reading in tenths preferable) & and indoor Humidity Gauge
1) Helpful; Tonnage & SEER of Unit & outdoor condenser model number: __________________
2) TXV or, orifice metering device? _______. Only if U know…
3) Outdoor condenser’s discharge-air-temperature ______-F
Subtract Outdoor air temperature: _______
4) Need the ‘Indoor’ percent of relative humidity - away from Supply-Air outlets ______5) Indoor Return-Air Temperature ______
Subtract Indoor Supply-Air Temperature ______ -F
Indoor temperature-split _______-F
Need the above information for troubleshooting & performance analysis.
A Goodman 2-Ton 13-SEER condenser, 800-cfm indoor airflow; 80-F indoor dry bulb & 50% relative humidity; Indoor temp-split 18 to 19-F.
@ 85-F outdoors; 103.9-F - 85-F outdoors or around an 18.9-F temp-split;
@ Indoor 75-F & 50% RH condenser temp-split is only around 14.9-F.In summer an all electric farm home TWO Half-Ton Window A/Cs & basement large dehumidifier:
30, 2012; Darrell’s meter; 62610 – 62140= used 470-KWh * .0985= $46.295
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HVAC Efficiency Overview My Audio overview; listen while you do other things
First, Check Return Air (RA) at grille & at entry of blower for heat gain, due to Return hot Air leaks.
Where air handlers' are set over Return Air Chambers, check for air leaks through the sheet rock & down the wall studs from the attic - this is a fairly common condition that will overload the AC system with attic heat!
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Airflow has to be optimal within specs, before the refrigerant charge can be correctly balanced for efficient operation!
Check Return Air (RA) at grille & at entry of blower for heat gain, due to hot Return Air leaks.
Where airhandlers' set over Return Air Chambers check for air leaks through the sheet rock & down the wall studs from the attic - this is a fairly common condition that will overload the AC system!
efficiencies sake measure the
Return Air duct/chase
it's a round duct measure the inside diameter, I'll give you the sq.
ins. formula on another pages;
if square or rectangular multiple the two dimensions for sq. in. area.
The sq.in. Return Air throughput ducting area should equal or exceed
Supply Area ducting. In the far north smaller A/C units
the new larger heating blower units can mean too much CFM for the A/C's
smaller BTUH capacity. Thermostatic
Expansion Valves (TEV / TXV) systems should be set for a minimum
NOTE on 3 & 5 Above: If suction is high & head is low
it is not necessarily an inefficient
compressor, it could be (3) three.
Overcharge: amp draw is HIGH when under a
heavy heatload and can be LOW when overcharged but under a light heatload;
both the condenser and evaporator are then overloaded with liquid and
is not enough of a heatload to evaporate sufficient amounts of
refrigerant in the E-Coil to INCREASE PRESSURES and pumping WORK.
After any duct work or other changes and before you make any recheck tests, it is very important that your condenser coil, evaporator coil, and indoor blower wheel be squeaky clean.
Take the condenser entering air temp and leaving air temp, subtract for the temp-split. As a double verification: You can use the manifold gauge high-side (SCT) Saturated Condensing Temperature-dial-reading minus the outdoor-ambient temperature; the difference gives you the condenser temperature/split. There is NO excuse for not utilizing this simple btu/hr operating capacity diagnostic check. Always use an accurate volt meter and amprobe to make sure you are not overloading the compressor's amperage Service Factor and check the compressor discharge line to see that it is under 225-F.
the "Evaporator HeatLoad" will Optimize the Condenser BTUH HeatLoad