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
[email protected] - 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