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Here is information on Psychrometrics that should help remind the HVACR technician what this subject is all about... with perhaps a few tidbits the tech may not have known! Psychrometrics: the study of the physical and thermal properties of dry air and water vapor mixtures.
Degree of saturation (μ): See relative humidity.
Dew point temperature (tdp): Temperature at which water vapor starts to condense in the air.
Dry air: Air devoid of water vapor and pollutants. Dry air has relative humidity of zero.
Dry bulb temperature (tdb): Actual temperature of the air, as observed using a thermometer or temperature sensor.
Enthalpy (h): Total useful energy content in the air. It is the sum of the enthalpies of the dry air and water vapor.
Humidity ratio (W): The ratio of the water vapor in the air to the dry air. This value is often multiplied by 7000 grains/ lb and expressed simply as humidity in grains of moisture.
Relative humidity (RH): The ratio of the mole fraction of water vapor to the mole fraction of water vapor with saturated air. If you don’t like the term “mole fraction”, it is also the ratio of the partial pressure of the water vapor to the partial pressure of water vapor with saturated air. If you don’t like the term “partial pressure”, it simply refers to the fact that both water vapor and dry air exert a component pressure that sums up to the total air pressure. If you want to think of relative humidity as the ratio of water vapor in the air compared to the water vapor in saturated air, that’s ok, but it is not technically correct. This value is actually the degree of saturation, which happens to be close to the value of relative humidity.
Saturated air: Air having a relative humidity (and degree of saturation) of 100 percent. At this condition, air is also at its dew point temperature. See the “Concerning Dry Air and Water Vapor Mixtures” section below.
Specific heat ratio (SHR): The ratio of the sensible heat load to the total heat load. Matched air conditioning systems typically have SHRs in the 68% to 80% range. Systems having a low SHR will remove more moisture from the air than systems having a high SHR. SHR can also be used to determine the required supply air temperature to maintain a room at desired conditions.
Specific volume (v): The volume occupied by a unit mass of dry air.
Psychrometer: A device used to measure relative humidity. It consisting of two thermometers, one that measures wet bulb temperature, and the other dry bulb temperature.
Psychrometric state: The state of an air sample. It is represented as a point on a psychrometric chart.
Standard air (for fan ratings): Air having a density of 0.075 lb/ft3 at 70°F and 14.696 psia (29.921 in. Hg) barometric pressure. Used to rate fans in standard cubic feet per minute (SCFM).
Standard atmosphere: Reference for estimating properties at various altitudes. It is air at 59°F and 14.696 psia (29.921 in. Hg) barometric pressure.
Wet bulb temperature (twb): Temperature of a wetted wick thermometer exposed to high velocity air. It is normally used with dry bulb temperature to determine relative humidity.
It is a misconception that water vapor is somehow held, absorbed, or dissolved in the air. Water vapor is only a resident in the air, somewhat like dust. Air acts as a “transporter” of water vapor. But unlike dust, atmospheric water constantly changes state, and it is a major regulator of air temperature.
The term “saturated air” is a bit of a misnomer as it suggests water vapor is absorbed or dissolved in the air. In this context, “saturation” simply refers to the state of water vapor, and that water vapor and dry air behave largely independent of each other.
Adiabatic mixing: Mixing of two or more air streams while maintaining constant enthalpy (no heat loss or gain).
Cooling and dehumidifying: Reducing both the dry bulb temperature and humidity ratio of the air.
Evaporative cooling: Reducing the dry bulb temperature and increasing humidity ratio of the air while maintaining constant enthalpy (no heat loss or gain).
Heating and humidifying: Increasing both the dry bulb temperature and humidity ratio of the air.
Sensible cooling: Removing heat from the air without changing its humidity ratio.
Sensible heating: Adding heat to the air without changing its humidity ratio.
We hope this blog helps you in your HVACR career and you learned some valuable information along the way. If you need other helpful documents on HVACR related topics please visit our additional blogs below.
HVACR Tech Tip article contributed by John Withouse, senior engineer - refrigeration, Sporlan Division of Parker Hannifin.
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Superheat is the temperature of refrigerant gas above its saturated vapor (dewpoint) temperature. Superheat as it relates to thermostatic expansion valves, can be broken down into three Superheat categories:
Static Superheat – The amount of superheat necessary to overcome the superheat spring force biased in a closed position. Any additional superheat (force) would open the valve.
Opening Superheat – The amount of superheat necessary to open the valve to its rated capacity.
Operating Superheat – The superheat at which the valve operates at normal running conditions or normal capacity. The operating superheat is the sum of the static and opening superheat. The figure below illustrates the three superheat categories. The reserve capacity, as shown in the graph, is important since it provides the ability to compensate for occasional substantial increases in evaporator load, intermittent flash gas, reduction in high side pressure due to low ambient conditions, shortage of refrigerant, etc.
For more information, download TEV &AEV Theory and Application - Catalog E-1a.
Determine the suction pressure at evaporator outlet with gauge. On close coupled installations, suction pressure may be read at the compressor suction connection.
Use the Pressure-Temperature Chart to determine saturation temperature at observed suction pressure. For example, with a R-22 system: 54.9 psig = 30°F.
Measure the temperature of suction gas at the expansion valve’s remote bulb location. For example: 40°F.
Subtract saturation temperature of 30°F (step 2) from suction gas temperature of 40°F (step 3). The difference, 10°F, is the superheat of the suction gas.
Parker “sets” the thermostatic expansion valve superheat at the static condition described above. Turning the adjusting screw clockwise will increase the static superheat. Conversely, turning the adjusting screw counterclockwise will decrease the superheat. Parker valves can also be adjusted at the operating point, indicated above. When a system is operating, any adjustments made will change the operating superheat. The static superheat range of adjustment is 3°F to 18°F. One full turn clockwise will typically increase superheat 2°F to 4°F. Note: Refer to the valve’s installation bulletin for specific directions on superheat adjustment.
For more information, download TEV &AEV Theory and Application - Catalog E-1a.
For more details on Thermostatic Expansion Valves - Theory of Operation, Application, and Selection - Bulletin 10-9.
Article contributed by Glen Steinkoenig, product manager, Thermostatic Expansion Valves, Sporlan Division of Parker Hannifin.
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HVACR Tech Tip: 12 Solutions for Fixing Common TEV Problems
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13 Feb 2018
In 2017, many changes impacted the HVACR, HVAC climate control industry. New technologies emerged that not only changed the way we do business – most for the better! But also brought a shift in the way we do our jobs, our way of thinking. Flame-free refrigerant fittings? Changes in refrigerant choices for retrofits? Troubleshooting a refrigeration system in the field? The smartest technicians understand the importance of not only staying informed but having a go-to resource for reference while on the job. Our Climate Control engineers team are dedicated to bringing you the knowledge you need when you need it through this blog; so you can do your job smarter, more efficiently, more profitably.
Answers to your questions and solutions to your challenges can be found in the top 5 most read blogs in 2017 below which addressed -
As HVACR technicians, you need some ideas in your back pocket for basic troubleshooting in a refrigeration system. How about a simple chart that helps you diagnose a system with 3 data points for starters? Using this chart is simple and can greatly speed up the troubleshooting of a system while in the field.
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Refrigerant choices for refrigeration systems are undergoing significant change, including choices for retrofits and new systems. This article is Part 1 of a 3 part series addressing such retrofits and deals with the basics of refrigerant blends and temperature glide.
The thermostatic expansion valve (TEV) provides an excellent solution to regulating refrigerant flow into a direct expansion type evaporator. The TEV controls the flow of liquid refrigerant entering the direct expansion (DX) evaporator by maintaining a constant superheat of the refrigerant vapor at the outlet of the evaporator. To understand the principles of TEV operation, a review of its major components is necessary.
Six questions and answers that will help you learn the key points of what you need to know about flooded head pressure control.
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11 Jan 2018
The HVACR service technician uses an array of tools and test instruments to diagnose problems and evaluate system performance. One tool that is readily available, inexpensive and yet rarely used to its fullest advantage is the pressure-temperature card or P-T Chart.
Proper analysis of the pressure to temperature relationship can help service technicians diagnose a refrigeration system issue quickly. The ChillMaster P-T Chart allows quick pressure to temperature conversion by providing essential refrigerant data to mobile devices. Download the app today in IOS or Android version
Contractors and technicians will enjoy the P-T Chart’s user-friendly design and precise calculations based on National Institute of Standards and Technology (NIST) Refrigerant Properties. Other features include the ability to customize screens for certain refrigerants and preferred units of measurement.
More than 70 refrigerants (traditional and natural) are featured in the P-T Chart. Extras included with the app - a training article “Using the P-T Card as a Service Tool.”
The app is available for both iOS and Android platforms. Click on your chosen platform to download the ChillMaster P-T Chart app for free.
Other helpful resources:
How to Use the Smart Service Tool Kit for HVACR Diagnosis
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Use of Suction Line Filter-Driers for HVAC Clean-up After Burnout
15 Nov 2017
The Suction Line Filter-Drier method of cleaning up a system after a hermetic motor burnout is favored by service technicians and recommended by manufacturers throughout the HVAC and refrigeration industry. This method gives the most practical and positive protection of the new compressor since the refrigerant lubricant mixture is filtered and purified just before it returns to the compressor. It is important that all contaminants remaining in the system be removed to prevent a repeat burnout of the new compressor. Suction Line Filter-Driers are designed specifically for clean-up after burnout with proven benefits.
The construction of the suction line filter-drier is not significantly different from the standard liquid line filter-drier. Both driers remove the important contaminants such as moisture, dirt, acid, and the products of lubricant decomposition. The suction line filter-drier utilizes the HH style charcoal core to obtain the maximum ability for lubricant clean-up and removing all types of contaminants.
The sealed models have an access valve (-T) at the inlet end to permit measuring the pressure drop during the first several hours of operation.
RSF shells have an access valve to measure pressure drop (see Parker Sporlan Bulletin 80-10).
Also, replaceable core Catch-Alls have a 1/4” female pipe connection (-G) in the endplate to permit the installation of an access valve to measure pressure drop.
If the proper style drier is not available, then a suction line filter-drier can be used in the suction or liquid line; and a liquid line filter-drier can be used in the suction line. The pressure drop characteristics of the two types of driers are essentially the same for a given line size.
The Catch-All Filter-Drier can be installed directly in the suction line by removing a portion of the line. After clean-up, the Catch-All Filter-Drier is generally left in the line. The cores in the replaceable model or RSF shell should be replaced with filter elements (RPE-48-BD or RPE-100) to obtain the lowest possible pressure drop.
A hermetic motor burnout produces large amounts of acid, moisture, sludge and all types of lubricant decomposition materials. To obtain the maximum ability to remove all these various types of contaminants, the Sporlan HH style charcoal core is preferred. If the HH style core is not available, the standard cores may be used.
OEM recommendations stress the importance of lubricant in cleaning up a system after a motor burnout. The lubricant acts as a scavenger, collecting the acid, sludges, and other contaminants. Therefore, the service technician should check the color and acid content of the lubricant. It must be clean and acid-free before the job is finished. The acid content can be checked with an acid test kit. For procedures for system clean-up please check pages 30 and 31 of Sporlan Bulletin 40-10.
This is frequently a difficult task. A lubricant sample can usually be obtained from the burned out compressor. To obtain repeated samples after the system is started up, install a trap in the suction line with an access valve in the bottom of the trap. This permits collecting the small amount of lubricant required for running an acid test. Another method is to build a trap with valves, and connections for charging hoses. Then refrigerant vapor from the discharge service valve is run through this trap and put back into the suction service valve. In a short time sufficient lubricant collects in the trap for analysis. For more information request Sporlan Form 40-141.
Most hermetic motors rely on refrigerant vapor for cooling. Any large pressure drop in the suction line could result in reduced flow of suction gas, and thus improper cooling of the new hermetic motor. Field experience has shown that if the filter-drier is properly sized, the pressure drop across it should not exceed the values given in the table below.
The pressure drop across the filter-drier should be checked during the first hour of operation to determine if the cores need to be changed. Any pressure loss in the suction line also reduces system capacity significantly. When an RSF shell or replaceable core type Catch-All is used, it is recommended that the cores be removed and filter elements installed when the clean-up job is complete. Obtaining a low pressure drop is particularly important for energy savings on supermarket refrigeration systems. Therefore, suction line filter-driers should be sized generously on these systems.
For more details on sizing and selection of filter-driers download Bulletin 40-10 (PDF)
Article contributed by Glen Steinkoenig, Product Manager, Contaminant Control Products, Sporlan Division of Parker Hannifin
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