heat pumps theory e 2008-09

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Heat Pumps

Function of a Heat PumpEduard SchmalLeiter Systemtechnik

Hovalwerk AG, Austrasse 70, FL-9490 VaduzTel. +423 399 23 11 – Mobil +41 (0) 79 618 29 25 - Fax +423 399 23 34

eduard.schmal@hoval.com - www.hoval.com

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Hovalwerk AG / 13/04/23 Heat Pump Theory 2

Content

Physical basics Evaporation and condensation Function of a heat pump Evaporation in heat exchanger Important Components Refrigerant circuit COP – Coefficient of performance

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Thermo dynamical Machine

7.5 kW ecologically heating

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Basics: Pressure

P = F/A [N/m²] = Pascal [Pa]

1 bar = 100 000 Pa

1 mbar = 100 Pa

Altitude above sea level[m]

Air pressure[bar]

0 1.013

200 0.989

500 0.955

1 000 0.899

2 000 0.795

4 000 0.616

10 000 0.264

Normal simplified1 bar

In a closed system the pressure is identical!

(Pascal Law)

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Overpressure – Manometer

Overpressure = absolute pressure –1Absolute pressure = overpressure +1

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Manometer

Low pressure manometer

p0 / t0

High pressure manometer

pc / tc

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Electronic Manometer

More expensive; in fact the same measurement

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Basics: Temperatur

Heat is a measure of agitation of the molecules

0 °C - melting point of water

100 °C - boil temperature

Temperature differences are always in [K] !!

e.g.

Outside temperature : -10 °C

Inside temperature : +21 °C

Δt = 31 K

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Physical condition – Water experiment

Heat for evaporation

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Comparison Water and R134a

Pressure for evaporation at 5 °C:

Water 0.009 bar (vacuum!!!)

R134a 2.5 bar (overpressure)

t [°C] pabs [bar]

5 0.009

50 0.123

80 0.473

100 1.013

110 1.434

120 1.988

150 4.733

200 15.588

Temperature for evaporation at 1 bar:

Water +100 °C

R134a -26 °C

t [°C] pabs [bar]

-50 0.294

-40 0.511

-30 0.843

-26 1.026

-20 1.327

-10 2.006

0 2.923

10 4.149

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Evaporation and Condensation

Boiling / Evaporation Overheating

Under cooling Condensation Heat loss

Water at 2 bar

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Cold Vapour Process

p

boiling/vaporization condensation/liquefaction

vapour vapour

liquid liquid

Heat absorberHeat release

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Heat Pump with Refrigerant R 134a

Evaporation pressure 2.6 bar

Liquefaction pressure 13 bar

Condensation/ liquefaction

at 45 °C

Boiling/ evaporation at -

3 °C

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Refrigerant Circuit

Temperature of condensation and evaporation by measuring

the pressure with the manometer

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Heat Exchanger

Q = A x U x Tm

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Performance stream

Heat Exchanger:

Heat output from the medium with higher temperature = heat input from the medium with lower temperature.

Machine:Power input = power output

Energy variety are equivalent;

like electrical and thermal energy.

2,5 kW + 7,5 kW = 10 kW

10 kW40 °C

10 kW30 °C

7,5 kW2,5 kW

10 kW

Heat pump

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Evaporator – Condenser

+2°C

Heat loss

Under cooling

Over heating

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Machine for Heat Transportation

M

-3 °C

45 °C

Therefore it needs electric power

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Working Principle

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Source Side

Evaporation temperature

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Warm Side

Condensation temperature

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Heat Flow R134a – Brine/Water

tHG 70 °Ctc 45 °C

tFL44 °C

trl 30 °C

tvl 40 °C

CondenserCollector

Filter dryer

Inspection glass

Expansion valve

Compressor

Evaporator

to -3 °C tSG 4 °C

5 °C

0 °Cpc / tcpo / to

T=48 KTemp.

rise

+30 °C

+40 °C

+5 °C

+0 °C

Pc / tcPo / to

tHG

tSG

tFL

Determination

Overheatingü = tSG - to

Under coolingU = tC – tFL

Measurement

tc, to, tFL, tSG

HOTGAS

SUCTIONGAS

LIQUID VAPOUR

CONDENSATE

M

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Overheating, Heat Loss, Under Cooling - R404a

M

+49

to= -20-10

+85

tC= +50+49

OVERHEATING10K

°C

barPo= 2,05

pC= 22

HEAT LOSS

UNDERCOOLING

1K

EVAPORATORCONDENSER

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Balance – Range

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Balance

Performance e – it depends on the output and can be apply for selected data e.g (B0/W35)

e = QWP / PWP

Coefficient of performance CoP – consider the additionally power (like Pumps, Defrosting, controller)

CoP = QWP / (PWP + PV + PK + PSR + PA)

Seasonal performance factor = (QWP – QSPA) / (WWP + WPV + WPK + WSR + WA + WC)

QWP = Heat output heat pump

PWP = Compressor power input

PV = Power input part to overcome the pressure drop in the evaporator

PK = Power input part to overcome the pressure drop in the condenser

PSR = Power input part for control

PA = Power input (middle) part for defrosting

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Cold Vapour Process

QC = QO + P

QC

QO

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Compressor

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Performance Diagram: Heat Output

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Power Input

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Cooling Output

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Operation Range

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Expansion Valve

tSG [°C] = temperature of suction gas – has to be measured with thermometer (pipe)

tü [K] = tSG - tO ; tO – has to be measured with manometer

1. Thermostatic element

2. Injector

3. Valve body

4. Setting up shaft

5. Pressure equalisation (external)

6. Refrigerant (liquid)

7. Refrigerant exit

8. Temp. sensor

9. Membrane

10. Injector opening

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Expansion Valve

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Components

Valve

Rotaloc valve Inspection glass

Filter dryer

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Components

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Low Pressure Control

Switch OFF point – has to be set up with the difference scale

Switch ON point ca. 5K lower then the coldest source temperature

Suction pressure

Compressor off

Compressor on

Temperature increase on the source side

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High Pressure Control

Switch ON point has to be higher then temperature of the high-pressure side

Off = scaleCompressor off = scale

Diff. -Scale

Compressor ON

Max. pressure in standstill

(Summer)

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Diagram Log p, h – R134a

LIQUID

VAPOUR

WET-VAPOURp=ct.

t=ct.

h=ct. v=ct.

s=ct.

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Refrigerant Circuit

EVAPORATOR

M

CONDENSER

5

6712345

P [bar]

Abs.

H [kJ/kg]

2345

6 7 1

Energy delivery condenser hC

Energy absorption evaporatorPowerSupply

hP

e = hC / hP

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Log p, h - Optimisation

P [bar]

Abs.

H [kJ/kg]

hC

hP

e = hC / hP

hP

hC

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COP - Coefficient of Performance

CoP (Coefficient of Performance) = Heat Output / Electrical Energy*

1 High lift - Low CoP2 Low lift - High CoPE=B/AThe CoP depends on the temperature

lift!Norm-conditions for providing COP-

values Air/Water HP: A2W35 Brine/Water HP: B0W35 Water/Water HP: W10W35

Be careful when comparing CoP-Values!

*) Electrical Energy:- For the compressor motor- For the transport of the heat transfer mediums in the heat

pump (heat source and heating circuit)- For the the control

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Belaria® - Defrosting Process

Abtaufühler