The Physics
Hypertextbook
Opus in profectus

# Refrigerators

## Problems

### practice

1. Determine the following quantities for a window mounted, residential heat pump described in the table below:
1. the heat…
1. extracted from the environment per hour when the device is operated in heating mode
2. exhausted to the environment per hour when the device is operated in cooling mode
2. the real coefficient of performance…
1. in heating mode
2. in cooling mode
3. the ideal coefficient of performance for a 22 °C inside temperature and…
1. a −2 °C outside winter temperature
2. a +34 °C outside summer temperature
4. the velocity of the air blowing into the room when the device is operated in either mode
Residential heat pump
heating mode cooling mode both modes
heating capacity
7.9 MJ/hour
cooling capacity
10 MJ/hour
volts rated
115 volts
heating amps
7.6 amps
cooling amps
7.8 amps
air circulation
8.1 m3/minute
heating watts
743 watts
cooling watts
812 watts
width
66 cm
moisture removal
0.90 liter/hour
height
40 cm
depth
74 cm
2. Write something else.
3. Write something different.
4. Write something completely different.

### numerical

1. One millimole of a monatomic, ideal gas is run through a four-step cycle as shown in the table below.
1. Sketch the cycle on a PV graph.
2. Determine the absolute temperature of the gas when it is in states A, B, C, and D.
3. Determine ΔU, Q, and W for each segment of the cycle (A→B, B→C, C→D, D→A) and for the cycle as a whole (ABCDA). Include an algebraic sign with each answer. (Zero values do not get a sign.)
4. Determine the real coefficient of performance assuming the cycle is used as a refrigerator.
5. Determine the ideal coefficient of performance for this refrigerator.
6. How are the answers to the last two questions in apparent conflict? Why are they?
A four step closed cycle
state A B C D
P (kPa) 100 624 312 100
V (m3) 24 × 10−6 8 × 10−6 8 × 10−6 16 × 10−6
T (K)
path A→B B→C C→D D→A ABCA