Air Conditioning, EER, SEER, SEER Ratings, BTUH, BTU/hr, BTU Air Flow Capacity Ratings, - Evaporator Heat Load - with Darrell Udelhoven

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 Solving ESP | ACCA ENERGY STAR pdf | Gurgling Pulsating Sounds at TXV | System Evacuation Procedures - Pulling a Deep Vacuum pdf
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Lot of HVAC Videos at bottom of this page!
The New Digital imanifold gauge estimates CFM and Provides Btu/hr Performance - On YouTube
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.

Using Goodman Manufacturing or other Expanded Cooling Data; e.g., using a 2-Ton 13-SEER, R410A, @75F 50%RH Indoors; "outdoor 90F," 'interpolate' between Charts 85F & 90F ambient, @800-CFM Mbh is 21.55, S/T is .765 * 21,550 is16,486-Btuh Sensible; 21,550 - 16,486 is 5,064 Latent. That's the simple close enough math...

You're going to gasp at what I suggest - however it will greatly improve a 3-Ton Return Air filtering situation, & blower efficiency. A filter grille, with a clean low resistant filter in accordance with Manual D, should stay within 300-fpm velocity. To achieve 300-fpm air flow velocity it will need 600-sq.ins., / by 144 or 4.1666-sq.ft of free air area. Therefore, 300-fpm * 4.1666-sq.ins. = 1250-cfm, that's 416.66-cfm per ton of cooling.

Hart & Cooley engineering data shows a 36X24  Return air filter grille with an Ak of 4.09-sf for 1227-cfm or, 3-ton of airflow at 300-fpm velocity through the filter. 1227-CFM / 300-fpm is 4.09-Ak sf.

That always calls for increased sizing for more Efficient Filtering & Return Airflow Efficiency. You will never get too much RA filter area, the more the better, because as the filter loads the velocity will go above 500-fpm velocity where the filter begins to allow too much debris blow-by.

Filter box depth sizing: Having a large filter/grille area is of little value if there is insufficient filter box depth, so that the RA duct is way too close to the filter/grille. Therefore, the depth of the filter/grille box &, when room permits, "being funnel shaped" to the 14” duct collar, is also important to efficient unrestricted airflow.

Figuring 650-CFM each Return Air duct run, that's 608-FPM Velocity. A 16" return duct flowing 650-CFM would produce 466-fpm velocity. Figure two 14” duct runs, if jammed too close to the filter, each duct collar opening would only be 154-sq.ins., which explains why the filter box depth is critically important to an unimpeded return airflow.

Filter mfg'ers ought to be required to list the sq.ft., free-air-area of their new filters! So, what is the free-air-area of the filter you are using?
CFM / fpm velocity = sq.ft. area. - Udarrell - Darrell

"What Percent of its Designed EER, SEER, and (BTUH, BTUhr, BTU/hr,) is your Air Conditioner delivering?"

Get a low cost Testo Tester & ballpark figure actual BTUH & EER - the information on it:

Everyone, very low cost anemometer to get airflow FPM Velocities, get it:

This should be helpful.

CFM X change in enthalpy X 4.35 = BTUH (Ballpark) Operating Performance & EER
"U Must Right Click Link & open in New Tab"
Wet Bulb Enthalpy Chart 
At least ballpark delivered performance for your customer's - Udarrell - Darrell

    keoffs are NOT blocked by the coil. In all cases, refer to the manufacturers’ data for static pressure losses to ensure the total system static pressure does not exceed 0.5” WC.
    Rules of Thumb for Duct Systems  - Hart&Cooley

    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. Inspector's should look into the boot areas for clues of problems...

    Rules of Thumb for Duct Systems  - Hart&Cooley

    Identifying your registers/diffusers & their (Ak) (sf) sq.ft. area, so you can multiply the FPM Velocity times the Ak 'sf' area to get the (CFM) Cubic Feet per Minute airflow from that register.
    Click on the categories to see the diffusers & Return-Air Grilles then find them on your downloaded pdf's engineering data.
    Hart & Cooley:
    Do a lot of Hart & Cooley engineering data searches, look at the registers & the Ak sq.ft. data to figure supply & return air grille & register's - delivered CFM.
    LOW AIRFLOW  <Click - this will help to open your eyes!
    WARNING: on units with a Thermostatic Expansion Valve (TXV), you cannot use the suction pressure to check the charge; many appear to be doing this; it tells you nothing. 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 it Right!

    * There is a TXV 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! * 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...
    Use my Superheat Subcooling Charging page!

    Below is an outstanding PDF "Basic AC Overview - "Specifications vs. Reality"
    by John Proctor, P.E., Proctor Engineering Group, LTD:

    HVAC TECH PERFORMANCE RATINGS  "AC Specs vs Reality" PDF - May not load?
    - It's Worth Your Time
    It’s 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 the duct system and the field-installation.

    Optimizing the Evaporator Heat Load at 75-F Room Temp will Optimize the Condenser BTUH Heat Load Output, Check your A/C - Chart below

    Especially if your system is oversized or there are a lot of low AC load days use an Adjustable Differential Room TSTAT.
    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 degree differential setting; heating equipment with TH set-point at 67 degrees F, temp drops 4-F from the 68-F over shoot, cycles on at 64-F and turns the heating equipment off at 68 degrees F, then the differential is 4 degrees F. Some have half degree increment settings over several degrees of differential spread. Mine has a SWING Setting of 1 to 9, I have it set at 8 for a long off time of two hours & one minute & a 20 minute on runtime in the heating mode. That was the settings & on/off times on January 25, 2012; 12:46pm noon hour; Temperature 30-F, wind chill 21-F; The performance of my new mere 57,300-Btuh Output propane gas furnace.
      Gurgling Pulsating Sounds at TXV: Low evaporator heat-loads lead to reduced liquid line mass and increased evaporator mass could be due to airflow problems. Eliminate low evaporator heat-loads before looking into adjusting the refrigerant charge.  Gurgling and pulsation noises at the expansion device can be caused by low evaporator circuit heat-loads, low charge, and/or non-condensibles and moisture in the system. Unbalanced airflow through the various distributor circuits of the evaporator coil will cause the TEV to close down refrigerant flow starving the coil. Piston-flow-rators will make it impossible to properly charge the system and cooling will be greatly compromised unless you eliminate the cause! "Put your ear on the liquid line at the evaporator coil."

      On every Rheem condenser cover it lists "non-condensibles and or moisture" as causes for a gurgling or pulsating noise at the expansion device. The entire evaporator circuits, may not become active for various reasons, - "the entire coil must become fully active for efficient performance."

      The purpose of these recommendations is to provide liquid refrigerant at the expansion device and provide efficient operation. Hopefully, this will aid your research.  If I can be of additional assistance, contact me.

      Too many do not properly purge & evacuate contaminated central air conditioning systems.

      The Triple Evacuation Method is normally done on central air conditioning systems:

      First, remove any valve cores with a special  valve core remover this will speed up the evacuation time. Back service valves two turns off their back seat.

      1) Re-claim unit charge (Recover all the refrigerant)
      2) Charge system to 150 PSIG with dry nitrogen and leak test
      3) On contaminated systems replace the filter dryers. Then Repair all leak(s)
      4) Evacuate system to 500 microns valve off & see if it holds 500 microns for ten minutes, if it holds, break the vacuum with dry nitrogen
      5) Evacuate system to a deeper 300 microns, valve off vac pump, & again break the vacuum with dry nitrogen
      6) Evacuate system to 300 microns and charge unit (Recharge with fresh clean refrigerant)
      7) Check to see if the Supply and Return air ducts were correctly sized & sealed by the original installer.

      Many HVAC contractors will consider this excessive time & effort for contaminated residential air conditioning systems, however it is a must for low temp applications.

      The “micron” is a metric unit of measure for distance. The micron is a unit of linear measure; one micron equals 1/25,400ths of an inch. Modern high capacity vacuum pumps help speed up the evacuation process.
      Air conditioner EER ratings, and BTUH Tons of Cooling Capacity ratings on Air Conditioning units are rated at an outdoor temperature of 95
      °F, and an indoor 80ºF dB 67ºF WB or, a 50% Relative Humidity.

      The SEER of a system is determined by multiplying the steady state energy efficiency ratio (EER) measured at conditions of 82°F outdoor temperature, 80°F dB and 67°F wB indoor entering air temperature by the Part Load Factor (PLF) of the system. (The PLF is supplied by the government.)

      Add to this the Part Load Factor (PLF):
      The SEER of a system is determined by multiplying the steady state energy efficiency ratio (EER) measured at conditions of 82°F outdoor temperature, 80°F dB/ 67°F wb 50% RH indoor entering air temperature by the “Part Load Factor” (PLF) of the system.
      The PLF is a measure of the cyclic performance (CD) of a system and is calculated as follows: CD is Cyclical Data
      PLF    = 1.00 -  (CD X's 0.5)

      cyclic performance (CD) value in the above equation has been determined by the government to be 0.25." The government contends that the PLF should equal: 
      [1.00  -  (.25 x .5)] = .125
      1.00 - .125 = 0.875, which yields: PLF  of 0.875

      The SEER rating is at only one set of conditions that are NOT typical of what we design for. Summer Outdoor Design varies however, we usually design for 75-F indoors NOT 80-F, also when systems' are downsized properly to achieve long runtimes the Part Load Factor becomes far less of a factor. Always go by the EER Rating NOT the SEER rating because as the SEER goes higher the EER ratio to it drops. Therefore, when the system is sized properly you have have a lot more   steady-state continuous runtime cycles & the PLF will be minimized.

      Proper system sizing for long runtimes along with a computerized variable speed blower motor to keep the evaporator's heatload capacity rating optimized, would help to achieve more of the BTUH, EER, & SEER Ratings of the unit!

      When selecting and installing a new unit. First, make all the changes you can to reduce the heat load/heat loss, --more insulation, etc. Then have a complete room-by-room Manual J. It was jointly developed by the Air Conditioning Contractors of America (ACCA) and the Air-Conditioning and Refrigeration Institute (ARI) heat load/loss calculation done on the house to insure correct sizing of the unit, then a Manual S for selecting the correct sized A/C equipment to meet the design load. Then use the Manual D for correct sizing of the Main and Branch Ducts. Manuals S and D were established by the ACCA. Use design outdoor conditions and daily temperature range exactly for your location per Manual J or ASHRAE Handbook of Fundamentals. 

      Otherwise, use the data for the closest location with a similar climate.
        Use standard 75°F design indoor temperature. Make sure the ducts are properly insulated and that there are no leaks. First and foremost on older systems, "both the condenser and evaporator coils and the indoor blower wheel must be clean and ducts properly sized to achieve optimal CFM airflow levels with NO air leaks." Thermostatic Expansion Valves (TEV/TXV) systems should be set for a minimum 9-Degrees Superheat. Print & use the linked charts below!

      Target Super Heat Chart and this Target Temperature Split for Airflow Chart

       A/C Trouble Shooting Chart


      3.5-ton system getting less than 1.5-ton of capacity!
      Low charge - plus
      Link below, 3.5-ton to less than 1.5-ton, too! -
      Way Overcharged !
      Excessively Hot Airflow Resulting in an Excessive Charge will greatly Reduce AC Capacity
      How installing a 3-ton system can become a 1.5-ton system of actual delivered heat transfer outside resulting in greatly reduced cooling of the  air in the conditioned space! (SURPRISE!):

      HVAC Techs - Checking the ACTUAL BTUH A/C PERFORMANCE
      Simple to ballpark actual performance: 
      Duct system CFM X* 4.5 @sea-level, or use X* 4.35 if 1000' above sea-level, X* change in wet bulb enthalpy = BTUH (Ballpark) Operating Performance. Home owners & anyone, it is easy & simple to do!
      "U Must Right Click Link & open in New Tab," look-up wet bulb enthalpy figures on chart," & figure wet bulb enthalpy 
      change. I know of NO HVAC Tech that performs this easy test, that even you can do. 
      PRINT & USE the linked wet bulb enthalpy chart below: 


      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.

      Additionally, for residential air-conditioning, "supply air diffusers" and "return air intakes" should be at the 8-foot ceiling level or 7-foot from the floor on side-walls where the warmest air is located, this is for optimal efficient heat loading of the evaporator coil during the cooling season. For air conditioning, both Supply and Return air grilles should never be at the floor level due to a mere recycling of floor level cold air.

      The greater the temperature difference between the Return Air (RA) and the Supply Air (SA) the more efficiently effective will be the heat loading of the evaporator coil. Additionally, the condensation of the latent moisture heat in the air will also be more effectively accomplished by utilizing a higher temperature difference.

      Flooded or Starved Evaporator Coils
      Optimizing the Evaporator BTU/hr Heat Input  NEW

      If you live in a high humidity climate, I would go for the 13 or 14-SEER unit with a variable speed control system, and in any climate with a Thermostatic Expansion Valve (TEV/TXV) refrigerant control on the evaporator coil. Also, a new high efficiency Variable Speed blower motor. Have a humidistat installed --wired in parallel with the room thermostat. (Both set-points have to be satisfied before the unit shuts down.) You will need a low cooling coil temperature and moderate airflow through it, coupled with long run cycles (proper equipment BTUH sizing) to get the humidity down to the 50 to 55% Comfort Zone!

      What makes things even worse is that a lot of furnace ductwork and registers, in older homes, were originally gravity flow systems, therefore there are no diffusers that throw the air up and across the rooms. Those supply air registers should be changed out, and then pressure drops should be kept at a minimum throughout the duct system, which helps provide more static pressure to the diffusers where that proper velocity & static pressure is needed for optimal throw upward and across the rooms.

      A/C OWNERS: Measuring the air temperature rise across the condenser coils is the easiest check point to determine the total amount of latent and sensible BTUH of heat your air conditioner is actually removing to the outside. You will enjoy doing it, doing it could lead to making changes that could considerably improve your Air Conditioning System's performance, thus improving your total comfort while in most cases greatly reducing your cooling bills.

      Unless the entire air conditioning system is engineered and designed so that the evaporator is absorbing its optimal designed latent and sensible heat load under your normal summer operating conditions, indoor near 76-F., with the outdoor temperature locally variable, --the air conditioner will simply be dropping below its BTUH rating and its Energy Efficiency Rating (EER) and SEER rating. The more often it operates well below its optimal btu/hr rating the further it will fall below its rated EER and SEER. Along with the -- Part Load Factor (PLF) due to oversizing the A/C equipment, resulting in short cycling and a dramatic drop of its Rated SEER!

      Optimize the entire air conditioning system and enjoy the EER and SEER you paid for, anything less will result in ongoing needless operating costs to you. Without a variable speed indoor blower the condenser temp rise differential split will drop down at lower indoor heat load levels. With optimal ductwork design coupled with adequate blower motor Horse Power and a clean blower wheel, clean indoor and outdoor coils, and full heat load airflow CFM through the evaporator coil, optimal heat absorption by the indoor evaporator coil will be achieved and thus discharged through the outdoor condenser coil. 

      "A lot of AC systems, with older furnace air handlers and duct systems, are not delivering anywhere near the A/C Unit's BTUH and SEER Ratings. This is primarily due to inadequate cubic feet per minute (cfm) of airflow through the evaporator coil, and/or dirty fins/coils and blower wheels.

      At 50% Relative Humidity the Sensible Heat Ratio (SHR) load is around SHR 70 to 75% depending on the unit's sensible design ratio. After taking the temp drop across the DX-coil here is the formula to find CFM.
      CFM = 4-ton unit (48000 X .70 or .75-SHF) / (temp drop 20-F X 1.08)
      (36000) / (21.6) = 1666-CFM / 4-Ton = 416.5-CFM per Ton

      Typical matched units from major manufacturers have Sensible Heat Ratios (SHR) in the 68% to 80% range (or 32% to 20% Latent). Proper mixing of the air and proper distribution to individual rooms is critical for comfort.

      It is better to use the condenser formula below to get an estimate of the BTUH transferred to the outdoor ambient.

      Additionally, even more common in northern areas of the USA, is the result of supply discharge air and return intake air being at the floor level where all the coldest air is merely being recycled through the evaporator coil. It is near impossible to fully heat load an air conditioning evaporator when the air flow is recycling too much of the cold supply air from the floor level. For air conditioning, the supply air outlets and air returns should be at, or near, the 8-foot ceiling level.

      The later model furnaces with bigger horsepower blower motors and blower wheels can result in too much airflow through the cooling coil, the result is that some incompetent, so-called, technicians end-up overcharging the system, trying to get a beer can cold suction line. The result is greatly reduced btuh system capacity and a deadly drop in the paid for SEER level!

      When supply discharge air diffusers and return air registers are at the floor level airflow must be at a much higher level to avoid mere recirculation (recycling) of the cold air back through the coil. Large floor fans can help circulate and mix the air to avoid stratification! For cooling, supply and returns at or near the ceiling level is the most efficient design.

      Solving the Mysteries of ESP - External Static Pressure
      ESP is the static pressure "external to the air handler." This is the reading that manufacturers' refer to in their fan performance data.

      The ESP is the pressure drop through ductwork (supply and return) only, and does not include pressure drop through unit components - heating coils, cooling coils, sometimes filters, & so forth.

      In other words, ESP is the sum of the static pressure drop in straight ductwork, and the static and dynamic pressure drops in duct fittings (i.e. elbows, tees, transition pieces, air outlets, etc.)

      "Consider that on High efficiency furnace there is a Condenser & an Evaporator that adds to the Supply Air Side Static."

      The Return External Static Pressure is measured as the air enters the return opening of the equipment, the Supply External Static Pressure is measured just outside the supply opening. Try to find the least-turbulent air to take the readings.

      To avoid turbulence take the readings 3 to 5 duct diameter inches downstream of turbulent areas.

      Bacharach says:

      Take your measurements on both the Return and Supply Plenums of the furnace, as it was shipped from the manufacturer (including the filter).  

      This means that if it was a gas or oil fired furnace, the measurement would NOT include the AC coil.  If a heat pump is being tested, the coil would be included.

      Drill two holes large enough to insert the static pressure tip, one on the supply side and one on the return.  Pressure measurements are then taken at each location.  The measurement on the return side will be negative with a positive reading on the supply but you disregard the positive/negative and just add the two numbers together.

      Once the ESP has been determined, look at the fan curve for that particular blower and determine the CFM from that chart.

      If the air flow is not per manufacturers' recommendations, it is near impossible to get the refrigerant charge correct.

      If you leave out the area up to & including the A-Coil where does that leave you? The area to the coil & including the coil can represent major Static Pressure problems!

      It will pay you to find an A/C tech that knows his field from A to Z.
      Darrell Udelhoven 

      In an oil furnace installation, a high static pressure can be partially due to the evaporator coil being installed too close to a big round heat exchanger. If you have room, a reducer transition should be stalled to funnel the air into the aperture opening of the A coil.

      Installing the coil on to of the furnace can cause high turbulence and back pressure, which combined with inadequate, (along with floor level intake returns) ducting coupled with long runs and other problems could increase the static pressure so high that your blower motor's HP will not move enough heat loaded room air across the heat absorbing evaporator coils and fins to fully heat load the outside condenser coil.

      Floor level supply and return air quadruples the problem. External Static Pressure (ESP) (Pressure reading before the E-Coil) needs to be kept within or below 0.5" Water Column for equipment 400-cfm per ton ratings, and for efficient operation of blower motor HP. When the Return Negative Air Static is reduced the SA ESP will be raised somewhat, however, the same HP blower motor, if rated for that ESP level, will deliver more Supply Air.

      It is very important to check the "actual" heat transfer cooling performance of your AC unit. There are several approaches, but we'll keep it as simple as possible.

      This method for testing the capacity of a system at the condenser unit doesn't require air flow testing equipment. However, you need to get the manufacturer's blower's Cubic feet Per Minute (CFM) data on the outdoor condensing unit's discharge airflow. The various A/C companies and/or service companies should also provide the A/C owner, the condenser CFM and air temperature rise. (The test standard rating conditions are taken at 95-F outside, 80-F inside, 50% RH inside.)

      This test only works on wrap-around condenser coil, top air discharge condensers' --first, check the condenser entering air dry-bulb temp., and the condenser dry-bulb discharge air temp., while moving the TH around in the air stream. This will usually be around a 18 to 28 degree condenser temperature split/rise. 

      You also need to add the additive heat of the condenser's compressor and fan motor. The indoor blower motor is also a heat contributing factor, not figured in this formula.

      Older units run a higher temperature split as they use a higher capacity compressors with less surface coil heat transfer area.  Reading the high-side saturation temperature of your manifold gage could be more accurate than the use of a thermometer for checking the discharge air tmperature.
      Techs should get the condenser air flow data in CFM from the manufacturer's engineering data. All the heat discharged by the condenser air flow also includes the latent heat of the evaporator's absorbed condensation heat, you can determine the total BTUH of heat discharged/exhausted by the AC condenser and thus determine if it is getting anywhere near its BTUH rating at your indoor thermostat setting. 

      (The below condenser temp-splits span 1.5 to 5-ton 12-SEER units. For the 12-SEER units, my figures get 17-F for a 1.5-ton and 23-F for a 2-ton condenser, 1400-cfm listed for both condenser fans). This is a good performance measure that should be part of any maintenance check since there are no duct variables to contend with, the coil is easy to inspect, thermometer calibration isn't much of an issue (if you use the same thermometer for both in and out air), wet bulb temp doesn't matter as you are measuring the latent heat removal too, and the compressor is closely matched to the condenser (the last can vary some with built-up systems of course). About the only thing to mess you up is a slow running condenser fan (a suspect if the motor runs real hot) or an incorrect fan blade or blade position to the venturi of the shroud (easy to inspect).

      You can use the high-side (SCT) Saturation Condensing Temperature on your manifold gage's dial, minus the outdoors-ambient Temperature; the difference gives you the condenser temp-rise or temp/split. There is NO excuse for not utilizing this important diagnostic check. Always use an accurate volt meter and amprobe to make sure you are not overloading the compressor's Wattage Service Factor and check the compressor discharge line to see that it is under 225-F. 

      First, figure the 'rated' gross capacity of the condensing unit. To determine the "Gross BTUH Heat Ejection" of the outdoor condenser: New Data = Let's take the total 'Watts' from the data sheets on an 17,500-Net-BTUH Heil condenser with a 2-ton DX evaporator coil with a TEV/TXV refrigerant control.

      Add the condenser motor heat: 1591-watts X's my low Power Factor of 0.90= 1432 X's 3.413= motor heat additive of 4887-BTUH + 17,500-BTUH = 22,387-BTUH Gross condenser heat ejection.
      22,387 / 1400-CFM of condenser fan = 16-F X's 1.08 = 17.3-F Rated Temp rise split off the condenser. A properly operating matched system should be within 10% of the condenser's gross temperature rise formula results.

      Source: of above & below formulas are listed in my ARI Reference Text book.

      Take the "listed watts" of the compressor and Condenser fan and multiply that wattage by the Power Factor, they used to use 0.90, then times 3.413 to get the BTUH heat additive of the motor, then add the listed BTUH of the condenser to that figure, and then divide by the condenser's CFM. Multiply that figure by 1.08 to get the temperature rise.

      Brother Don’s 17,500-Btu/hr Heil central A/C unit.

      1.08 *Xs 10-F split = 10.8 X 1400-cfm = 15,120-Btu/hr (outdoor) condenser, minus 4887-Btu/hr motor heat = 10,233-net-Btu/hr Xs .76 sensible = 7,777 sensible .24 X 10,233 or 2,456 latent heat transfer.

      7777/16-F indoor split = a mere 486-cfm | [I want 750-cfm; supply and returns at floor level!] Also, could be an unbalanced load on the evaporator circuits causing the TXV to shut down the refrigerant flow, among other things.

      For the uninitiated, Delta-T is the difference between the air temperature entering and leaving the outdoor AC condensing unit. This is a good diagnostic check because it measures the latent heat of condensation as well as the sensible heat absorbed by the vaporizing refrigerant in the indoor evaporator coil. I'm betting when you find out approximately how many BTUH that the AC system is actually transferring outside, you may be shocked by how far it is below its BTUH rating.

      His condenser usually has a 10 temp rise split, the evaporator appears to be under CFM heat-loaded or, it has an unbalanced heatload on the DX coil's circuitry allowing liquid refrigerant in the return line causing the TXV sensing bulb to reduce the refrigerant flow thus reducing the DX coil's heat absorption capacity. 

      The probable cause is "an unbalanced airflow/heatload through the evaporator coil. "I have a Thermo Pride OL 11 oil furnace. Those oil furnaces have a very large round heat exchanger that goes to near the top of the furnace, --due to a low basement ceiling the DX coil sets perhaps illegally close to the heat exchanger causing a few of the coil's circuits to be under heatloaded. Since the liquid refrigerant is not completely evaporated it will cause the outlet line that the TXV sensor bulb is on to be too cold and the TEV will shut-down the flow, which greatly reduces the BTUH capacity of the DX coil and the system. On piston refrigerant control systems, they may flood back liquid which could damage the compressor, unless the system is way under-charged. Thermo Pride could install airflow turning vanes just above the heat exchanger to funnel the air directly into the DX coil, instead of most of the airflow hitting the bottom of the DX's drain pan causing extreme turbulence back-pressure and an imbalanced DX coil circuitry heatload!

      Do your own figuring based on this formula. Get the Motor Power Factors (PF) of the compressor and fan motor from the manufacturers. (Above 0.85 factor could be close.)

      The chart split listed below is at Condenser Design conditions: Indoor Return Air 80-F dry bulb 67-F Wet Bulb or 50% Relative Humidity as you go up to 99% RH the condenser split could increase by up to 6-F; down as much as 4-F at a low humidity of 55-F Wet Bulb.
      Do your own figuring based on this formula. Motor BTU/hr additive = Watts X's PF x's 3.413 for Btu/Watts additive added to rated BTUH, divided by condenser fan CFM X's 1.08 =  condenser Temp-Split. Get the Motor Power Factors (PF) of the compressor and fan motor from the manufacturers. Some of the temp-split figures need correcting, will do ASAP. Some Splits rounded. < Click for Graph!
      Page 618, Refrigeration & Air-Conditioning (ARI) Second Edition, C 1987
      Those lower SEER units had higher condenser splits than 12-SEER and higher units.
      Sorry, I defiled the graph, 90-db outdoor, 80-db indoors with 67 wet bulb or 50% RH
      represents the condenser splits shown above graph. Graph: 80-DB & 80-WB line-intersect
      is 100% Relative Humidity. Typical matched units from major manufacturers have Sensible
      Heat Ratios (SHR) in the 68% to 80% range (or 32% to 20% Latent) when it is 95-F outside
      and 75-F with 50% relative humidity inside. Proper mixing of the air and proper distribution to
      individual rooms is critical for comfort.

      The condenser fan speeds are slower on several of the 10-SEER Tonnage Models.
      We are only trying to get a figure to go by for a comparison. When new condensers and Evaporator-coils "are installed on older air handlers" or due to ductwork even new ones, evaporator coils are usually NOT heat-loaded to the nominal BTUHR design of the system. (Additionally, always check voltage and then the amp draw!) The Base Spec sheets 12-SEER part no. 421 41 33301 03, Feb 2001. These are the Comfortmaker® units, which are nearly identical to Heil® units. I used the first rating on each tonnage class. While the "Performance Cooling Data" is listed at a 95-F outside ambient temperature, you can adjust the indoor airflow to get the Nominal BTUH Rating at the customer's normal indoor stat' temp' setting and the most outside temperature/degree operating hours. Take the "listed watts" of the compressor and Condenser fan and multiply that wattage by 0.85 X's 3.413 to get the BTUH heat additive of the motor then add the listed BTUH of the condenser to it, and then divide by the condenser fan's CFM. By using the various units' "base specification sheet data" from the dealer, you can determine if it is operating near its BTUH capacity rating. Some packaged units run a very high condenser discharge CFM airflow! Some "Condenser Makes" will have different temp-splits. The 2-ton 10-SEER, Janitrol; GMC; Goodman; with the U-29 E-Coil delivers less btuh, or 23000-btuh, I subtracted a reasonable amount from the total of the wattage and come up with 19 to 20-F temp-split. That is "if" its CFM is 1400, --get the figures on the "different Makes." The figures are used to provide an idea of what the condenser temp-split should be for use by the unit's owner and the service tech.

      The amp draw can vary from 5.7 to 10.7 amps on my Kenmore window unit's spec sheet. The nameplate rating is 7.5 amps at 115 volts, 10.5 that's 5 amps X's 115 volts is 575 watts, 7.5 amps is 862.5 watts or around 33% above the nameplate rating. [1.3 SF] It will handle up to a 120-F outside ambient.

      When I used a fan to increase the airflow through the evaporator coil both the temperature and the humidity dropped faster! This proved to me that low air volume may not increase the rate of dehumidification. Also, as the temp drops more moisture has to be condensed out by the evaporator to get the same percentage of humidity reading.

      Service techs, check the voltage at the unit and use your amp probe to see if the compressor is within its service factor wattage rating. Check the discharge line to see that it is under 225-F.

      The idea is to get some condenser temperature rise split perimeter curves with which to gauge its actual BTUH heat transfer performance, against your unit's Listed BTUH Rating. Then if the INDOOR AIRFLOW through the coil is optimal & Superheat and Sub Cooling are within specs, the unit should be getting its optimal BTUH and EER ratings for the existing conditions. 

      The larger your residential unit is the more apt the indoor air delivery system and blower will fall short of the required air flow. In some cases, even your 3.5 or 4-ton cooling system may only be delivering 2.5-tons of cooling BTUH capacity. 

      You need to know somewhere near at what BTUH capacity your AC is operating when the room temperature is where you normally have it and the outdoor ambient is near your average cooling day temps. With a Thermostatic Expansion Valve refrigerant control it may not freeze up but simple shut down the flow rate and back up liquid refrigerant in the condenser coil greatly reducing its capacity, as well.

      A few "important qualifications" are in order here: checking the condenser discharge airflow temperatures will not work on units' where "the blower is underneath and  blows the air up through a flat table top condenser coil because the temperature readings will vary across the entire surface of the condenser coil." You need to identify the liquid saturation sub-cooling temperature point on the coils where the "liquid should begin near the liquid line outlet. The highside manifold gauge will indicate the condenser temperature. 
      For efficiencies sake, do this immediately. Measure the Return Air duct/chase area. If it's a round duct measure the inside diameter, I'll give you the sq. ins., if square or rectangular multiple the two dimensions for sq. in. area. The Return Air throughput ducting area should exceed the Supply Area ducting. For Sq.Ins.of Rd duct, i.e., An 8" round duct: dia. 8 Xs* 8 = 64 Xs * .7854 = 50-Sq.In.
      On smaller systems, take your air conditioner's btuh and divide it by 150, (or dividing 24,000-btuh by 150 will give you 160 sq.ins., (14" Rd. duct,) close to a 0.05" return air duct Static Pressure drop) to get the amount of free air square inches for the Return Air duct system. It is best to use the manual D. I also use an ASHRAE Air Graphed Friction Chart, or use a Duct calculator based on the manual D.

       4 ton condensing unit, 48,000 btuh (450-cfm per ton) would need 254 sq.ins. or an 18" duct. A 5 ton 60,000 btuh (450-cfm per ton) calls for  314 sq. ins., or a 20" rd duct. 

      For a small 1.5-ton system I would go with 154 Sq. Ins. or a 14" Rd duct.

      After any duct work or other changes and before you make all the recheck tests, it is very important that your condenser coil and evaporator coil and indoor blower wheel be squeaky clean.

      Also, in older homes many times the supply and return air are both at the floor level rather than at the ceiling level, this colder air will tend to reduce the evaporator's heat load at standard CFM delivery rates, requiring an increased CFM. However, using air temperature stratification levels in conditioned areas with high ceilings allows the warmer air to act as an insulating barrier at the ceiling. View my other pages on static pressures, CFM air flow and AC efficiency. 

      Additionally, manufacturers could be helpful to the service and installation technicians if they would provide all the data possible with the units. The temperature rise across the condenser coil should be on the metal nameplate along with the CFM air discharge rate of the condenser.

      Also, a permanent indoor blower curve graph chart should be on the furnace or air handler's panel. This would save valuable time and give the technicians vital information with which to optimize the air conditioner's performance.

      These tests will reveal if the entire AC air handling System, ductwork, blower, etc., were properly sized and conditioned space loads balanced when installed. Later, if necessary, you can then make more refined changes to achieve the cooling and air flow you want to each conditioned space knowing that you are working with the full Nominal BTUH Rated Capacity and SEER that your AC matched System was designed to deliver.

      Some more component airflow variables are: disposable filters .05" to .30"; pleated filters .10" to .45"; Electrostatic filters .20" to .80", transitions, boots .05" to .35"; long air turning vaned elbows .01" to .10"; and duct length .05" to .20 of an inch of pressure drop. From the high end aggregate to the low end on all these components is a hugh pressure differential. It doesn't take much to get above .80".

      It is good to have a little extra blower horse power and cubic feet per minute of air flow to do your final room delivery balancing with. Every component in the air delivery system can be selected within pressure drop variables. 

      Here are a couple component variables you can select from to balance the delivery air flow and cooling. You can buy supply air diffusers and return air grilles for various rooms from .02" to .15" pressure drops. Put the lower pressure drop registers in the rooms that need the most airflow and higher pressure resistance ones where you need less airflow. 

      You will need a technician that knows how to diagnose the other numerous causes of low heat transfer. I will list only a few of them. 

      A rare situation could happen "in northern states" when there is too much air flow and a heavy heat load, --because an inexperienced so-called tech might keep adding refrigerant trying to get the Super Heat down and suction line colder -- which would overcharge the system filling too much of both coils with liquid refrigerant, thus greatly reducing their capacity to absorb and then dissipate heat.

      The piston/orifice must be checked for equipment model mismatch (the charts for orifice size are only useful when you have both the outdoor and indoor unit model numbers). I've found refrigerant flowrater pistons installed backwards allowing liquid freon to bypass the tiny orifice hole, -the results are very interesting! 

      A well informed tech knows how to use his amp probe, and pressure gages to trouble shoot conditions. He will evaluate the Suction pressure and Super Heat, Head Pressure and Liquid Subcooling, and check the indoor Static Pressure and air flows first, --so he knows the aforementioned checks will provide valid readings.

      A qualified tech is able to detect all of the many things that can destroy your units capacity and SEER efficiency. A few are: suction or liquid line restrictions, plugged cap tube, or malfunctioning TXV, hot gas discharge restriction, unbalanced load on evaporator coil, over or under charge of refrigerant, inefficient compressor. Dirty coils, dirty indoor blower wheel, clogged air filters, high back pressure supply air diffuser grilles, restricted return air supply, and so forth.

      If anyone has different formulas or figures please present them to me. I've been retired since 1994 so am leaving it to all you techs to contact AC companies and ask them to furnish the test information and to tap the air handlers so it would be easy to check static pressures ahead of the coil especially on oil furnaces.
      Determining which metering device the system has without physically looking
      If you do not absolutely know whether the metering device is a TXV, or a fixed orifice device or cap tube.

      Hook up your manifold gauges, block off considerable condenser air intake for a short time.
      If the suction pressure starts rising, you have a piston, or a cap tube.
      If only the high side goes up, you have a TXV.
      Double check using Superheat, if Superheat stays relatively stable when the pressures change it's a TXV.
      Have things with you in your van or truck to block-off the entering condenser air for a short time.
      Check every time you are not certain what metering device it has.
      There will be a lot of guessing in the future.
      You're going to gasp at what I suggest will greatly improve your (3-Ton) Return Air filtering situation, & blower efficiency...

      A filter grille, with a clean low resistant filter in accordance with Manual D, should stay within 300-fpm velocity.

      The formula is 300-fpm X's 4.1666= 1250-CFM or 3-Ton of airflow.

      The problem is that the filter Grille & the filter, both, reduce the free air area!

      Therefore, when you figure the area needed, they say, 2-CFM per, I'd use 1.25-CFM per, of the actual grille & filter area, not the outside measurements. 
      1200-CFM / 1.25 = 960-sq.ins., or two return filter grilles. You could even use two 500 or more, filter grille racks; sounds far out huh, but it will work just fine.

      Hart&Cooley usually just show the RA Grille sizing, Not the filter grille, plus the the filter's Ak sq., open area!
      That always calls for increased sizing for more Efficient Filtering & Return Airflow Efficiency.  ha...

      You will never get too much RA filter area, the more the better, because as the filter loads the velocity will go above 500-fpm velocity where the filter begins to allow too much debris blow-by.

      Filter box depth sizing

      Having a large filter/grille area is of little value if there is insufficient filter box depth, so that the RA duct is way too close to the filter/grille.

      Therefore, the depth of the filter/grille box &, when room permits, its funnel shape to the 14” duct collar is also critically important. Figuring 650-CFM each RA duct run, that's 608-FPM Velocity. A 16" return duct flowing 650-CFM would produce 466-fpm velocity.

      Figure two 14” duct runs, if jammed too close to the filter, each duct collar opening would only be 154-sq.ins., which explains why the filter box depth is critically important to an unimpeded return airflow. - Udarrell

      My Scan of My ThermoPride OL 11 Graphed Blower-Curve-Chart
      Thermopride OL 11 Graph ipg image - Thank you Dave Staso, CA. for the better expandable image!
      "After it loads Right click "Show Original Images" - Move cursor arrow over graph - Click + when 'over graph' for expanded image," then print on the highest quality setting.

      Every manufacturer should furnish blower curve charts with their units and also put them on the Internet for service tech's to download and print. Also, air conditioning codes should be updated in respect to proper sizing of the duct work which must include all the pressure inducing factors when sizing the supply and return ducts. Also, illustrate best furnace to evaporator coil transitions, especially on oil furnaces!  You should always keep the ESP to 0.5" or mfg'ers listing.

      The evaporator must be mounted 4 to 6 inches above this model oil furnace to achieve adequate airflow!

      Also, air conditioning codes should be updated in respect to proper sizing of the ductwork, which must include all the pressure inducing factors when sizing the supply and return duct systems.

      We also need the pressure drop figures on the condensers in the high efficiency furnaces, --that should be a data tag requirement!
      Knowing the operating static pressure is a first order essential toward accurately identifying the operating CFM. If ductwork retrofitting doesn't solve the problem; Blower wheel RPM and blower motor Horse Power may need to be increased to achieve the optimal CFM to achieve your Unit's rated nominal BTUH and Energy Efficiency Rating. (80% don't).
      There ought to be a code requiring every manufacturer of an air-handler or furnace to provide capped hole taps ahead of the evaporator coil and ahead of the blower for easy static pressure testing access. 

      Read the pressure on the gauge, and record the reading on the supply side, then on the return side. Use a (+) sign before the positive or supply side reading to show where it was taken, and a (-) sign before the negative or return side reading. Add the two pressures. Disregard the positive and negative signs before the pressures, because both negative and positive pressures affect the fan as a force, so they must be added together to determine the total resistance the fan has to overcome. For example a +0.35" I.W.C. plus a -0.25" I.W.C. equals a total static pressure reading of 0.6" I.W.C.

      Record the pressure readings on a record sticker on the furnace plenum as a diagnostic report for future reference and use, and on the service invoice ticket. Any future changes in static pressure will reveal a change in the system that should be addressed. Our federal government along with every state and all the Electrical Utility Companies ought to be supporting the testing and upgrading of all air conditioning systems, new and old, in order to reduce electrical demand and brown outs. Check the temperature rise across the outside condensing unit, get in touch with a good AC tech if you even have a hint your system is not operating up to its optimal efficiency level.
      Call your local Utility Company and query them about their energy saving initiatives, if they don't have any, --request that they develop such programs ASAP.

      Click the link below for the evaporator temp drop graph.
      Air Temperature Drop Through Evaporator Coil (1987 Period)
      Indoor temperature and humidity load variations graph.
      Refrigeration & Air-Conditioning (ARI) Second Edition, 
      Page 624, © 1987
      I list any HVAC companies on any of my web pages they have nothing to do with the information I post on any of my Web pages, nor do I assume any responsibility for how anyone uses that information.

      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.

      This 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 Udelhoven

      Please write me if you have anything you'd like to contribute! - Darrell 
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    AC-trouble-shooting-chart.html  Techs
    Proper Duct Sizing of Residential Heating & Air Conditioning Systems  EFFICIENCY!
    Engineering for a "Comfort Zone Goal" NOT merely the SEER Goal
    Optimizing the Evaporator BTU/hr Heat Input 
    Optimizing Room Air Conditioner's EER Performance
    Half Ton Cools 900 sq. ft.@ 104 HT Index
    Is your 3.5-ton system getting less than 2-ton of cooling capacity?

    Oil Furnace Heat Exchanger Soot Cleanout  A Must for Safety & Efficiency !
    Air Conditioning EER - BTUH Levels - Evaporator (DX) Heat Load + Evaporator Air Flow
    Air Conditioning Engineered for Latent Heat Removal 
    For high humidity climates Discussion - Sizing SEER EER Latent Heat Loads
    Air Conditioning Optimizing Efficiency - Check-Up 
    Air Conditioning - Latent Heat Removal  For Comfort-Zone & Efficiency
      FINDING the LATENT HEAT of CONDENSATION of Your Air Conditioner
    System Evacuation Procedures - Pulling a Deep Vacuum pdf

  • Best Practices Guide for residential HVAC retrofit
  • New TEC Energy Conservation Testing Technologies
  • Energy Star 
  • SEER Ratings for Central Air Conditioners somewhat Nebulous 
    Heating & Air Conditioning Forum - Related to my SEER Page Above

       HVAC TALK HVAC Talk Community
    HVACR TALK FORUM  - Residential Problems - NEW
    HOME INSPECTIONS Learn about home inspections also HVAC inspections
    GARDEN WEB - Heating & Air Conditioning Forum
    DIY Do It Yourself Forum  - "Do It Yourself" TV - New
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    Getting it right makes all the difference in the world.
    This Energy Star ACCA pdf is interesting & confirms what many of us have been preaching, including educating the potential customers!

    Scroll down to page 5 Market Conditions, & study to learn how we can all profit, customers included...
    *Video checking static ESP *Video 2 checking static ESP View! I Got DSL 11/2010
    *Video measuring airflow Velocity W/ anemometer on a Return Air grille
    I'd use the .90% factor for open grille area - indicates what I'd want for 1.5-Ton of airflow; 294.7-fpm-Vel *X 2.376562=
    700-cfm | CFM= fpm*X sf-Ak open-air-area of grille

    *Basics Featuring the Testo 556 - Video of a very thorough Air Conditioning Testing setup 2/26/11

    Realtime HVAC A/C BTUH Performance Output (Part 1 of 2) YouTube Video

    *Realtime HVAC A/C BTUH Performance Output (Part 2 of 2)

    There are more ACCA links but this is a good starter document.

      Empowerment Communications
      Covering The Real Political Issues
      Darrell Udelhoven - udarrell
      Lancaster, Darrell Bloomington, Grant County, Wisconsin
      Posted: 04/03/03; Date Last Modified: 05/26/13