Pressure Enthalpy Without Tears

1. Why would someone plot an HVAC system on a pressure-enthalpy diagram?

Create a visual representation of the system Estimate system capacity and efficiency Evaluate system deficiencies and faults All of the above

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2. Which of the following items do you NOT need to plot a pressure-enthalpy diagram?

High side pressure Low side pressure Compressor outlet temperature Evaporator outlet temperature

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3. The horizontal lines on a pressure-enthalpy diagram are:

Lines of constant enthalpy Lines of constant entropy Lines of constant temperature Lines of constant volume

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4. The vertical lines on a pressure-enthalpy diagram are:

Lines of constant enthalpy Lines of constant entropy Lines of constant temperature Lines of constant volume

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5. What does it mean if a point is outside the saturation curve and to the left of it?

The fluid is 100% liquid (subcooled) The fluid is at saturation The fluid is 100% vapor (superheated) The fluid cannot and does not exist

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6. What are the lines of constant quality?

Curved lines that drop off from the horizontal lines inside the saturation curve Slanted lines that determine the liquid/vapor content of a saturated fluid in 10% increments Slightly curved lines that rise from the horizontal lines inside the saturation curve Steeply curved lines that rise from the horizontal lines inside the saturation curve

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7. Which line on the pressure-enthalpy chart below represents the compressor?

1 2 3 4

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8. What is efficiency?

Getting the lowest up-front price possible How quickly we do work, regardless of the callback rate How well systems meet criteria for governmental incentives Ratio of output to input

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9. Which equation including net refrigeration effect (NRE) and heat of compression (HOC) represents coefficient of performance (COP)?

NRE + HOC = COP NRE - HOC = COP NRE / HOC = COP NRE x HOC = COP

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10. The trapezoid of an overcharged system will be __________________________ of the baseline "ideal system" trapezoid.

A little bit up and to the left A little bit up and to the right A little bit down and to the left A little bit down and to the right

Pressure Enthalpy Without Tears