job sheet 5 psychrometrics - lab-volt · job sheet 5 – psychrometrics © festo didactic 88271-20...

© Festo Didactic 88271-20 117

In this job sheet, you will evaluate how much heat is transferred by the heat pump to the air in heating and cooling mode using a psychrometric chart.

Energy transferred by the heat pump in heating mode

In this part of the job sheet, you will measure the temperature, speed, and relative humidity at the air intake and distribution register of the heat pump. With these values, you will plot the process on a psychrometric chart to find the amount of energy the heat pump is transferring.

1. Set the thermo-anemometer to measure air speed and relative humidity. Refer to instructions in Appendix D if necessary. The thermo-anemometer requires a few minutes to stabilize to the relative humidity measurement. Be patient.

Figure 83. Thermo-anemometer.

Psychrometrics

Job Sheet 5

OBJECTIVE

PROCEDURE

Job Sheet 5 – Psychrometrics

118 © Festo Didactic 88271-20

2. Perform the following settings on your training system:

Main power switch .............................................................................. Off

Thermostat ........................................................................ Heating mode

Temperature set point ....................... 5°C (9°F) above room temperature

Valve HV-1 ..................................................................................... Open

Valve HV-2 ..................................................................................... Open

Valve HV-3 ..................................................................................... Open

Valve HV-4 ..................................................................................... Open

Valve HV-5 ..................................................................................... Open

Valve HV-6 ..................................................................................... Open

Valve HV-7 ..................................................................................... Open

Valve HV-8 ................................................................................... Closed

Valve HV-9 ....................................................... No adjustments required

Valve HV-10 ................................................ Handle in horizontal position

Valve HV-11 ................................................................................... Open

Valve HV-12 ................................................................................... Open

Valve HV-13 ................................................................................... Open

Pressure gauge PI-1 selector switch ............................................... Right


Desuperheater On/Off switch ............................................................ Off

Priming tank three-way valves ......................................................

Pumping station three-way valves .............................................

Air distribution register .................................................................... Open

3. Set the main power switch to On.

4. Measure the length and height of the air intake as shown in Figure 84. Calculate the area.

Area of the air intake: __________



Figure 84. Air intake.

5. Wait until the compressor indicator light turns on. Before taking any additional measurements, wait another eight minutes for the system to stabilize.

Measure the temperature, air speed, and relative humidity. Complete Table 18. Be sure to measure the air speed and relative humidity as shown in Figure 85 and Figure 86.

Figure 85. Orient the thermo-anemometer as shown when measuring the air speed.



Figure 86. Make sure that the humidity reading on the thermo-anemometer is stable before taking measurement.

Table 18. Psychrometric test in heating mode.

Temperature at the air intake ( )

Relative humidity at the air intake

Air speed at the air intake

Temperature at the air distribution ( )

Relative humidity at the air distribution

6. Set the thermostat operating mode to Off.

7. Using the temperature and humidity values recorded in Table 18, trace the heating process on the psychrometric chart included at the end of this job sheet. Be sure to use the psychrometric chart that corresponds to the system of units that you are using.

8. Using the psychrometric chart, complete Table 19.

Table 19. Temperature, humidity, and enthalpy in heating mode.

Air intake Air distribution

Dry-bulb temperature

Wet-bulb temperature

Humidity ratio

Specific volume

Enthalpy



In the following steps, you will calculate the amount of heat gained by the air as it passes through the heat pump condenser (forced-air coil). First, you will have to calculate the mass air flow going through the condenser. Then, knowing the difference of enthalpy between the air intake and distribution, it is possible to calculate the heat gain.

9. Using Equation (5-7), calculate the mass air flow at the air intake.

(5-7)

where is the mass air flow at the air intake in kg/s (lb/min). is the volumetric air flow in m3/s (ft3/min). For your system,

assume that the volumetric air flow is 14.16 m3/min (500 ft3/min). is the specific volume at the air intake in m3/kg (ft3/lb). Use the

specific volume from Table 19.

Mass air flow at the air intake: __________

10. Using Equation (5-8), calculate the amount of heat that the air has gained in the heat pump.

(5-8)

where is the air heat gain in W (Btu/h)

is the mass flow in kg/s (lb/h)

is the air exit enthalpy in kJ/kg °C (Btu/lb °F) is the air intake enthalpy in kJ/kg °C (Btu/lb °F)

Air heat gain: __________



Energy transferred by the heat pump in cooling mode

In the following steps, you will repeat the previous experiment using the cooling mode. Depending on the current air conditions, this process may be a simple cooling process or a cooling process with dehumidification. You will trace this process on a psychrometric chart and calculate the amount of heat absorbed by the heat pump evaporator (forced-air coil).

11. Perform the following settings on your training system:

Main power switch .............................................................................. On

Thermostat ........................................................................ Cooling mode

Temperature set point ....................... 5°C (9°F) below room temperature

Valve HV-1 ..................................................................................... Open

Valve HV-2 ..................................................................................... Open

Valve HV-3 ..................................................................................... Open

Valve HV-4 ..................................................................................... Open

Valve HV-5 ..................................................................................... Open

Valve HV-6 ..................................................................................... Open

Valve HV-7 ..................................................................................... Open

Valve HV-8 ................................................................................... Closed

Valve HV-9 ....................................................... No adjustments required

Valve HV-10 ................................................ Handle in horizontal position

Valve HV-11 ................................................................................... Open

Valve HV-12 ................................................................................... Open

Valve HV-13 ................................................................................... Open



Desuperheater On/Off switch ............................................................ Off

Priming tank three-way valves ......................................................

Pumping station three-way valves .............................................

Air distribution register .................................................................... Open

12. Wait until the compressor indicator light turns on. Before taking any additional measurements, wait another eight minutes for the system to stabilize.

Measure the temperature, air speed, and relative humidity to complete Table 20.



Table 20. Psychrometric test in cooling mode.

Temperature at the air intake ( )

Relative humidity at the air intake

Air speed at the air intake

Temperature at the air distribution ( )

Relative humidity at the air distribution

13. Set the thermostat operating mode to Off.

14. Using the temperature and humidity values recorded in Table 20, trace the cooling process on the psychrometric chart you previously used for the heating process.

15. Using the psychrometric chart, complete Table 21.

Table 21. Temperature and enthalpy in cooling mode.

Air intake Air distribution

Dry-bulb temperature

Specific volume

Enthalpy

16. Using Equation (5-9), calculate the mass air flow at the air intake.

(5-9)

where is the mass air flow at the air intake in kg/s (lb/min).

is the volumetric air flow in m3/s (ft3/min). For your system, assume that the volumetric air flow is 14.16 m3/min (500 ft3/min).

is the specific volume at the air intake in m3/kg (ft3/lb). Use the specific volume from Table 21.

Mass air flow at the air intake: __________



17. Using Equation (5-10), calculate the amount of heat that the air has released in the heat pump.

(5-10)

where is the air heat loss in W (Btu/h)

is the mass air flow in kg/s (lb/min) is the air exit enthalpy in kJ/kg °C (Btu/lb °F)

is the air intake enthalpy in kJ/kg °C (Btu/lb °F)

Air heat loss: __________

18. Was the cooling process you experienced a simple cooling or a simple cooling with dehumidification?

19. Set the main power switch to Off.



Figure 87. SI units psychrometric chart.



Figure 88. I-P (inch-pound) units psychrometric chart.



Name: ______________________________ Date: ____________________

Instructor's approval: _______________________________________________

job sheet 5 psychrometrics - lab-volt · job sheet 5 – psychrometrics © festo didactic 88271-20...

Documents