Heatcraft Refrigeration Products H-ENGM0408 Use of the Psychrometric Chart, Definitions, 7000

Page 37

Use of the Psychrometric Chart

From two known properties of air, its condition can be located on the Psychrometric chart and all remaining properties can then be found by reading the appropriate scale.

Figure 1 Illustrates a condition plotted at the intersection of its dry bulb and wet bulb temperatures. The dry bulb temperature is represented on the chart by the vertical lines with its scale across the bottom. The wet bulb temperature is read along the saturation line and is represented on the chart by the solid diagonal lines. Enthalpy at a saturation, for a given wet bulb temperature is read from the diagonal scale at the left using the diagonal lines extending from the saturation line.

Figure 2 Illustrates a condition plotted at the intersection of its dry bulb temperature and relative humidity. Relative humidity is represented on the chart by the curved lines which are marked in percent relative humidity.

Figure 3 Illustrates a condition plotted at the intersection of its dry bulb and dew point temperatures. The dew point temperature is read along the saturation line at the intersection

of the Horizontal Humidity line. The value of the specific humidity is read from the scales at the right in either pounds or grains of moisture per pound of dry air by selecting the appropriate scale.

Figure 4 Illustrates the determination of specific volume from the chart. Specific volume is represented by the broken diagonal lines marked in cubic feet per pound of dry air. Intermediate points are read by interpolation between the lines.

Figure 5 Illustrates the use of sensible heat factor to determine the air conditions required to satisfy a specified space temperature and load conditions. The sensible heat factor is the ratio of internal sensible heat to internal total heat load of the space being conditioned. A straight line from the sensible heat factor scale through the circled point of the chart to the slope line from the space condition point to the saturation line. Air supplied to the space at any temperature condition located on the ratio line (and in the proper volume) will satisfy the room load.

Example — Using the point which is circled on the Psychrometric Chart, the following values are obtained:

 

 

 

 

 

Dry Bulb Temperature

 

 

 

80.0ºF.

Wet Bulb Temperature

 

 

 

67.0ºF.

Dew Point Temperature

 

 

 

60.3ºF.

Relative Humidity

 

 

 

51.1%

Specific Humidity

 

 

78.1

 

A) 0.01115 lbs./lb. dry air =

SR/lb dry air

7000

B) 78.1 grains/lb. dry air

 

 

 

 

 

Enthalpy at saturation

 

31.62 BTU/lb. dry air

Specific Volume

13.83 Cu. Ft./lb. dry air

Figure 6 … *Air Conditioned Process

1.Cooling and Dehumidification — A decrease in both dry bulb and specific humidity represented by a line sloping downward and to the left. Total heat content (both sensible and latent heat) is decreased.

2.Sensible Cooling — A decrease in dry bulb and sensible heat content represented by a horizontal line directed to the loft

along the constant specific humidity line. Specific humidity and dew point remain constant.

3.Evaporating Cooling — (Air passed through spray water or wetted surface at wet bulb temperature) – A decrease in dry bulb (reduced sensible heat content) and an increase in dew point and specific humidity (increased latent heat content) represented by a line sloping upward and to the left following a constant wet bulb line – no change in total heat content.

4.Humidification — An increase in the specific humidity as a result of moisture added, represented by a line directed upward.

5.Heating and Humidification — An increase in both sensible heat and specific humidity, represented by a line sloping upward and to the right.

6.Sensible Heating — An increase in dry bulb and sensible heat content, represented by a horizontal line directed to the right along the constant specific humidity line, Specific humidity and dew point remain constant.

7.Chemical Drying — (Air passed through a chemical drying agent) – A decrease in dew point and specific humidity, represented by a line sloping downward and to the right.

8.Dehumidification — a decrease in the specific humidity as a result of removing moisture, represented by a line directed downward.

Definitions

Dry Bulb Temperature — The temperature indicated by a thermometer, not affected by the water vapor content air.

Wet Bulb Temperature — The temperature of air indicated by a wet bulb thermometer; the temperature at which water, by evaporating into air, can bring the air to saturation adiabatically at the same temperature.

Dew Point Temperature — The temperature to which water vapor in air must be reduced to produce condensation of the moisture contained therein.

Relative Humidity — The ratio of actual vapor pressure in the air to the vapor pressure of saturated air at the same dry bulb temperature.

Specific Humidity (Moisture Content of Humidity Ratio) — The weight of water vapor per pound of dry air.

Sensible Heat — Heat which when added or subtracted from the air changes only its temperature with no effect on specific humidity.

Latent Heat — Heat which effects a change of state without affecting temperature, as in evaporating or condensing moisture.

Enthalpy (Total Heat) — The sum of sensible and latent heat. In the chart, enthalpy represents units of total heat content above an arbitrary base in terms of BTU per pound of dry air.

Specific Volume — Volume per unit of weight, the reciprocal of density, in terms of cubic feet per pound of dry air.

Sensible Heat Factor — The ratio of internal sensible heat to internal total heat load.

Ratio Line — The line extending from the space condition to the saturation line at a slope determined by the sensible heat factor.

Fig 1 —

Fig 2 —

Fig 3 —

Fig 4 —

Fig 5 —

Fig 6 —

Dry Bulb and Wet Bulb

Dry Bulb and Relative

Dry Bulb and Dew Point

Specific Volume

Sensible Heat Factor

Air Conditioning Process

 

Humidity

 

 

 

* (See Above)

37

Image 37
Contents Engineering Manual Forward Table of ContentsWall heat loads Insulated block K factors TablesOpenings and infiltration Refrigeration Load Calculations Job SurveyAir Change Load Safety FactorProduct Load Daily figureHourly Heat Load Temperature above 32ºF 20-22 hrLoad Calculation Forms 50ºF. rooms and higher with coilExample 35ºF Convenience Store Cooler With Glass Doors Example 35ºF Beef Cooler Inches Type Ceiling Walls Floor Example -20ºF Ice Cream Hardening Freezer Example -10ºF Beef Freezer Gallons of ice cream @ Overrun Wall Heat Loads Appendix TablesEffective K Factor in Block Thickness of Insulation Allowance for Sun EffectFor long storage multiply the above values by VolumeStorage Room 40ºF .4ºC 50ºF ºCNot based on maintaining nutritional value Storage requirements and properties of perishable productsMaple Sugar Heat of Respiration Approx BTU / LB. / 24 Hrs Storage Temperature Degree F ProductºF. Other BTU / 24 HR Heat gain due to operation of battery operated lift truckHeat equivalent of electric motors Heat equivalent of OccupancyBanana Rooms Refrigeration Requirements Banana Ripening RoomRapid load selection for back bars Refrigeration requirements for hardening ice creamDesign Summer outside air and ground temperature design conditionsDry Bulb Temp State CityProduct Safety/Capacity Control Temperature DifferenceRefrigeration Equipment Selection Equipment BalanceType of Operation/Air Flow Derating FactorsRecommended Air Changes/Hour Effects of Altitude on Air Cooled EquipmentGeneral Guidelines Left Large cooler or freezer Right Unit Cooler Recommended Coil ReplacementLeft Cooler or freezer with glass display doors Right Recommended Line Sizes for R-134a Line Sizing+30˚F 150 200 10021/8 Expansion ValveEquivalent Lengths Recommended Line Sizes for R-22100 150 200 200 100 Receiver toRecommended Line Sizes for R-404A and R-507 30˚F 40˚F Recommended Line Sizes for R-404A and R-507Equivalent Feet of Pipe Due to Valve and Fitting Friction 134a R507 & R-404A Liquid Line Net Recommended Remote Condenser Line SizesRefrigerant Celsius Fahrenheit Celsius Temperature Conversion ChartFahrenheit Celsius FahrenheitConversion Factors constant Single Phase Loads Ohm’s Law for direct currentAir Coils = WattsEnglish to Metric Conversion Factors English Conversion Factors & DataDefinitions Use of the Psychrometric ChartSR/lb dry air 7000Atmospheric Pressure Appendix ChartsAt other altitude Courtesy of Ashrae Reproduced by permissionCourtesy of Ashrae Reproduced by permission Glossary of Refrigeration Terms Quick Selection Guide DimensionBtuh Load +35 Room +30 Room FloorTips for Quick Selection Guide Rapid Load Calculator for Large Coolers and Freezers Heatcraft Refrigeration Products LLC

H-ENGM0408, H-ENGM0806 specifications

Heatcraft Refrigeration Products offers a diverse range of commercial refrigeration solutions designed to meet various operational needs. Among their notable offerings are the H-ENGM0806 and H-ENGM0408 models, which stand out for their efficiency and innovative features.

The H-ENGM0806 model boasts a robust construction and high-performance capabilities, making it ideal for large-scale refrigeration requirements. This model is engineered with an advanced compressor that provides powerful cooling while maintaining energy efficiency. The unit operates at low sound levels, making it suitable for environments where noise reduction is essential, such as restaurants and grocery stores. Additionally, the H-ENGM0806 incorporates a reliable fan system designed to ensure optimal air circulation, promoting even cooling throughout the refrigerated space.

Meanwhile, the H-ENGM0408 model is designed for medium-sized applications that require flexibility without compromising on performance. This unit features a compact design, making it an excellent choice for businesses with limited space. Its energy-efficient compressor reduces operational costs, and its user-friendly digital controls allow for easy temperature adjustments and monitoring. The H-ENGM0408 is engineered to operate in various ambient conditions, ensuring reliability and consistent performance regardless of the environment.

Both models feature a state-of-the-art microprocessor control system that allows for precise temperature management. These systems not only optimize performance but also enhance the longevity of the refrigeration units. The H-ENGM0806 and H-ENGM0408 come with a robust evaporator coil design, facilitating rapid cooling and reducing the downtime associated with equipment maintenance.

In terms of durability, both products are constructed with high-quality materials resistant to corrosion and wear, making them suitable for demanding commercial environments. Additionally, they comply with industry standards and regulations, ensuring safety and reliability in operation.

In conclusion, Heatcraft's H-ENGM0806 and H-ENGM0408 models combine efficiency, flexibility, and advanced technology to provide reliable refrigeration solutions. Their thoughtful design and robust features make them ideal choices for businesses looking to maintain optimal temperature control while minimizing energy consumption and operational costs.