Thermal and Fluids

in Architectural Engineering

8. Refrigeration and heat pump

Jun-Seok Park, Dr. Eng., Prof.

Dept. of Architectural Engineering

Hanyang Univ.

Where do we learn in this chaper

1. Introduction

2.The first law

3.Thermal resistances

4. Fundamentals of fluid mechanics

5. Thermodynamics

6. Application

7.Second law

8. Refrigeration,

heat pump, and

power cycle

9. Internal flow

10. External flow

11. Conduction

12. Convection

14. Radiation

13. Heat Exchangers15. Ideal Gas Mixtures

and Combustion

8.1 Introduction

8.2 Vapor-compression refrigeration cycle

8.3 Heat pump

8. Refrigeration, heat pump, and

power cycle

8.1 Introduction

□We use refrigeration and heat pump cycle for

conditioning the buildings in every day life.

□ Renewable energy is also used combined with heat

pump.

- Examples: GHP system

Entropy M) W - Q ( ΔE

8.1 Introduction

Entropy M) W - Q ( ΔE

Source : KOTEC자료

8.2 Vapor-compression refrigeration Cycles

□ Refrigerator or Air conditioners are devices that do

move heat from law (Cold) to high (hot) spaces.

□ There are several types of refrigeration cycles

□ Vapor-compression refrigeration cycle is commonly

used in a wide range of application

- Example) Refrigerator in HVAC, Air-conditioner

Entropy M) W - Q ( ΔE

8.2 Vapor-compression refrigeration Cycles

□ In practical problems, - No device is to compress two-phase mixture

- A saturated liquid is expanded isentropically to a two

phase mixture

□ Because of these practical considerations, the Carnot

cycle is modified in two way,- two-phase mixture is moved to a saturated vapor before

the compressor

- A saturated liquid is expanded through irreversible

throttling valve.

Entropy M) W - Q ( ΔE

8.2 Vapor-compression refrigeration Cycles

□ The working fluid in a vapor-compression

refrigeration cycle is called as refrigerant.

- Example ) R-12, R-134a, ammonia, carbon dioxide.

□ The performance of a refrigeration cycle is evaluated

through two quantities

- COP or “Tons of refrigeration”

Entropy M) W - Q ( ΔE

8.2 Vapor-compression refrigeration Cycles

□ COP (Coefficient of Performance)

□ Typical values of COP are from 1.5 to 5.0

Entropy M) W - Q ( ΔE

process) cisenthalpi ( )(

)(

W

)(Q ; )(Q

)(WW

QQ

Q

W

4312

41

in

Ref

41L32H

12in

LH

L

in

Ref

hhhh

hhQCOP

hhmhhm

hhm

QCOP

L

L

8.2 Vapor-compression refrigeration Cycles

□ Tons of Refrigeration

- is measured early in the use of mechanical refrigeration

- means that the heat transfer rate required to freeze 1 ton of

0 ℃ water into ice at 0 ℃ in 24 hours

1 TON of Refrigeration is 211kJ/min

Entropy M) W - Q ( ΔE

8.3 Heat pumps

□ Heat pumps are devices that use QH,

□ Typical values ranges from 3.0 to 6.0

□ Heat pumps are more expensive and complex than

traditional gas, oil-fired heaters or electric resistance

heaters

Entropy M) W - Q ( ΔE

1

)(

)(

QQ

Q

W

Q

RefHP

12

32

LH

H

in

HHP

COPCOP

hh

hhCOP

8.3 Heat pumps

□ But, COP is always greater than traditional system,

and environment load is lower

□ because the COP and heating capacity decrease

as the source temperature becomes low, a back up

source of heat is often required.

- Examples) ground source, water source, river etc.

Entropy M) W - Q ( ΔE