Department of Mechanical Engineering
ME 322 – Mechanical Engineering
Thermodynamics
Lecture 30
Heat Pump Systems
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Heat Pump Systems: Thermodynamics and Design, Slides of Thermodynamics
A portion of lecture notes from a Mechanical Engineering Thermodynamics course focusing on Heat Pump Systems. It covers the concept of heat transfer rate for refrigeration, the heat pump cycle, and various applications and sources. Students will learn about the heat transfer rates, COP, and the role of heat exchangers in heat pump systems.
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Department of Mechanical Engineering
ME 322 – Mechanical Engineering
Thermodynamics
Lecture 30
Heat Pump Systems
Tons of Refrigeration
One ton of refrigeration is the heat transfer rate required to
melt 1 ton (2000 lbf) of ice at 32°F in 1 day (24 hr).
What heat transfer rate can accomplish this?
Btu
lbm
h sf Latent heat of fusion of ice (hf – hs) at 1 atm
Then:
Btu lbm-ft
lbm lbf-s Btu
2000 lbf 12, 000
24 hr ft^ hr
1 day 32.
day s
Q
Heat Pumps
How can the high temperature heat transfer be utilized? It
all happens at the condenser. A few possibilities are …
Cold air in
Hot air out
Heating Air Heating Water
Cold water in Hot water out
Hot
refrigerant
vapor
Hot
condensed
refrigerant
Hot
refrigerant
vapor
Hot
condensed
refrigerant
Department of Mechanical Engineering
ME 322 – Mechanical Engineering
Thermodynamics
Heat Pumps
Application: Residential heating
Isothermal Source Heat Pump
Q
Toutside
Qhouse
Qout
No auxiliary heat
source needed.
The heat pump
can always meet
the house load!
In principle, this is a great idea!
However it is cost prohibitive to
circulate refrigerant through the
isothermal source.
Qin
Source
Sink
Isothermal Source Heat Pump
Qin
Secondary heat transfer loop
(Some type of glycol mixture)
Q
Toutside
Qhouse
Q Qout
Evaporator
Department of Mechanical Engineering
ME 322 – Mechanical Engineering
Thermodynamics
Example
Heat Pump used for Heating and
Domestic Hot Water
Example
4 3
5
Q hw
Desuperheater
Given : A heat pump used for domestic hot water heating and
space heating as shown below.
R
SET 20 F
SCT 120 F
1
DSH 6 F T SET DSH
c 0.
x 4 (^) 0 x 3^ ^1
30,000 Btu/hr
Find:
(a) The heat transfer rate
available for hot water
heating
(b) The power requirement
of the compressor
(c) The heat transfer rate
from the source
(d) The coefficient of
performance for the heat
pump
Example
4 3
5
Q hw
Desuperheater
R
SET 20 F
SCT 120 F
1
DSH 6 F
T SET DSH
c 0.
x 4 (^) 0 x 3^ ^1
30,000 Btu/hr
h [Btu/lbm]
P [psia]^ 20°F
120°F
R
1
2
4 3
5
Example
4 3
5
Q hw
Desuperheater
R
SET 20 F
SCT 120 F
1
DSH 6 F
T SET DSH
c 0.
x 4 (^) 0 x 3^ ^1
30,000 Btu/hr
h [Btu/lbm]
P [psia]^ 20°F
120°F
R
1
2
4 3
5
Example
4 3
5
Q hw
Desuperheater
R
SET 20 F
SCT 120 F
1
DSH 6 F
T SET DSH
c 0.
x 4 (^) 0 x 3^ ^1
30,000 Btu/hr
h [Btu/lbm]
P [psia]^ 20°F
120°F
R
1
2
4 3
5
Energy sought = Q^ out Q hw
Example
4 3
5
Q hw
Desuperheater
R
SET 20 F
SCT 120 F
1
DSH 6 F
T SET DSH
c 0.
x 4 (^) 0 x 3^ ^1
30,000 Btu/hr
h [Btu/lbm]
P [psia]^ 20°F
120°F
R
1
2
4 3
5
Solution (Key Variables):
hw
out
sensible heat transfer rate ( )
latent heat transfer rate (no )
Q T
Q T
Heating and Air Conditioning
The reversing valve
reverses the roles of the
heat exchangers.
Reversing (4-way) Valve
CondenserEvaporator EvaporatorCondenser
Expansion Valve
Compressor
Refrigeration (Air-Conditioning) Mode Heat Pump Mode
Q
out
Q
in
Q
in
Q
out