(ii) EDUCATION AND TRAINING EQUIPMENT In a:cordancewidl die Electtomagnetic Compatibility (Amendmem) Regulations 1994 (SI No 3080) and EMC Directive 89/336'EEC andCE MarkingDirective 93/68/EEC. This~ complies with dieabove directives under die following clause: The use of the apparaws outside die classroom, JaOOratOry, sbldy area CK similar such pL1K:e invalidates confonnity widl die protection requirements of the Electtomagnetic Compatibility Directive (89/334/EEC) and could lead to prosecution. P.A. HILTON LIMITED Horsebridge Stockbridge, England. Tel No. National Ramsey (01794) 388382 International +44 1794 388382 Fax No. +44 1794388129 Mill, King's Hampshire, Sombome. SO20 6PX.
Transcript
(ii)
EDUCATION AND TRAINING EQUIPMENT
In a:cordance widl die Electtomagnetic Compatibility (Amendmem) Regulations 1994 (SI No 3080)and EMC Directive 89/336'EEC and CE Marking Directive 93/68/EEC.
This ~ complies with die above directives under die following clause:
The use of the apparaws outside die classroom, JaOOratOry, sbldy area CK similar suchpL1K:e invalidates confonnity widl die protection requirements of the ElecttomagneticCompatibility Directive (89/334/EEC) and could lead to prosecution.
P.A. HILTON LIMITED
HorsebridgeStockbridge,England.
Tel No. National Ramsey (01794) 388382International +44 1794 388382
Fax No. +44 1794 388129
Mill, King'sHampshire,
Sombome.SO20 6PX.
(ill)
INDEX
~SCHEMATIC DIAGRAM 1
SYMBOLS AND UNITS 2
SUFFIXFS 3
INTRODUCTION 4
5
5
6
8
9
10
11
12
THE IUL TON AIR AND WATER IlEA T PUMP
InstalJation and Commissioning
Specification
Description
Operation
Safety Devices
MaintenaIx:e
Fault Fmding
THEORY: The Heat Pump - Thennodynamics of Reversed Camot and
Yapom' Com~sion Cycles 13
USEFUL DATA 21
LOW GRADE ENERGY SOURC~ 22
23
24
26
32
3S
42
46
CAPABILITIES OF IDL TON AIR AND WATER REA T PUMP
1. Detennination of Power Input. Heat Delivered and CoPH
2. Production of Heat Pwnp Perfonnance Cmves over a range of sourceand delivery temperatures
3. Plotting the Vapour Compression Cycle on a p-h diagram andcomparing it with the Ideal Cycle
4. Production of Heat Pwnp Perfonnance Cmves t.sed on the HFC 134aproperties 81 a variety of evap(n1ing and condensing temperatures
S. Energy Balances for the comJK)nents and the whole cycle
6. Estimation of Volumetric Efficiency of the Compressor at a range ofpressme ~
7. Estimation of Overall Heat Transfer Coefficients in the Evaporatorand Condenser so
TYPICAL OBSERV AnON SHEET (blank) 54
TYPICAL DERIVED RESULTS SHEET (blank) 55
GRAPHS AND DIAGRAMS
p-h Chan for Rl34a (blank)
Wiring DiagnIm
Transfonner Connections
56
57
S8
~
II ba i
!~.11m1/
j~';3 ,;-J1
~Ijl -r
.II0Q.
il 1If Ui[f
I f
~~~ G
"
~~J -
J!J
"R"
P-If~
t~i
!:§
>
~~
W
InIL.,U
I.t'~
'5\I»
~ ~
r'" ~@ ~J
~
r ~
" 'e>I:I
- -j-i.
> c~t.n
~- --.~
,-c~
~j~--
..
;, I " ~
... '&
.. Ii
c ~
;
~_i
a--~
r:i
1r.-0
--I!f~ ..j-!ij~
!:i'il
1
~'-61,~V
I-
j~
2
SYMBOLS AND UNITS
Quantitv Fundamental~
Svmool
CoPH
Cp
Heat Pump Coefficient of PerfonTlance
Specific Heat Capacity ~dT
J kg"1 K-1
h
d1
W w. N m-1 or Pa
Wp
Q
q
r,s
t
T
U
J kg.l Ko1
OC
K
W m.2. Ko1
m' kg.)
J kg.)
m's.l
v
w
V
x s
11
9
Specific Enthalpy
Mass Flow Rate
Power
Pressure (Absolute)
Heat Transfer Rate
Heat Transfer per Unit Mass
Pressure Ratio
SpecifIC En~
Tcmpcranue (Customary)
Temperature (Ab~lute)
Overall Heat Transfer Coefficient
Specific Volume
W<Xk Transfer per Unit Mass
Volume Fk>w Rate
Time Interval
Efficicocy
Tempcranue Difference K
Presentation of Numerical DataIn dris manual. numerical quantities obtained during experiments. etc.. are ex~ in a non-dimensional manner. That is. d1e physical quantity involved has been divided by the units in which ithas been measured.
As an example:
Thisindicaresthat p . 150
10' N.--'
p . 150 x 10' N m-2
p = ISO kN m-2
or
alternatively
-Note: 1 Bar . 10' N mol = 10' Pa c 100 tN mol
3
SUFFI~ AND/OR STATES
1 HFCl34a at Compressor Inlet
2 HFCl34a at Compressor Delivery
3 ~l34a at Condenser Outlet
4 HFCl34a at Ex~on Valve Oudet
s Wat.er Inlet to COO1~ Cooling Coil and Evaporator Inlet
6 Water at Conoonser Inlet
7 WateJ' at Conde~ Outlet
8 Water at Evaporalm' Outlet
Ambient Aira
Condenserc
e Evaporaux-
HR' 1348r
Water (general)w
sat Sablration
t~
4
HILTON AIR AND WATER HEAT PUMP R831
INTRODUCTION
The VaJX)ur compression refrigeration cycle finds applications in countless indusbial. commercial anddomestic sinwiom throughout dJe world. In dJe majority of these applicatiom d1e emphasis is uponmaintaining a product or ~ a1 a low temperature whilst rejecting the heat ex~ted to a sink a1a higher temperahlre. This sink is usually the abnosphere.
However die vapom compression "refrigeration" cycle may equally be utilised to upgrade heat froma low grade "~" such as d1e aanosphere, a water c~ (river) or the soil so mat it may bedischarged at a more useful higher tempemtme fCK some other application. These applications may bespace heating, water heating or combined applications. FCX' example large dairy farms require chilledwater for cooling the milk and heated water for washing and cleaning of pipework. In theseapplications a heat plJDp can provide energy savings asswning that the scale and utilisation factorsjustify the increased capital cmts.
Similar app1k:ations can exist in chemical plant.
UDlradiD2 or HeatThe Clausius Swcment of the Secooo Law of Thennodynamics states that heat will not pass from acold to a hotter regioo witboot an "external agerx:y" being employed. This external agency may beapplied in the form of a high grMIe energy inlXlt of either "work" or a high grade heat inpuL The highgrwJe heat input may lake ~ fmm of either high tem~bJre combustion products, electrical energy(in the fonn of heat) or solar ~.
The Hilton Air and Water ~ Pump R831 is a V3JX>ur compression cycle unit utilising a small workinput to aansfer heat from either an air CI' water source evaporator to a water cooled condenser. Allrelevant Iempel'abJreS.pressures and power inputs are measured enabling the complete cycle to beinvestigated roth diagrammabcally and numerically.
HFC134aIn order to enable students to become familiar widt dte non-CFC refrigerants that are going to replacethe Ozone rr,pleting materials that have been canmon in the past. the Hilton Air and Water Heat PwnpR831 operateS (Xl HFC 134a. This is die Ozone friendly material designed to repla;e CFC12 whichbas been commonly used in danestic and c(XDmelcial refrigerators and air conditioning systems formany years.
HFC 1348 utilises 8 different oil to that used on CFC12 systems and in older to allow for the slightdiffCIaICes in die thennodynamic and chemical properties of the material purJX>se made expansionvalves. canpressors and filter/driers are used on the unit.
It is taential that no gas odler d1an fOCl34a is added to the R831 syStem and mat no mineral oil isadded to the unit The oil utilised is an Ester desipd exclusively for use with HFCI34a.
5
INST ALLA nON AND COMMISSIONING
Remove me unit from its packing case and visually inspect Any damage found should be reported tothe insurers immediately.
Assuming that no damage is found. proceed as follows:
PlJK:e the unit on a strong level bench where there is goOO light and ventilation. and close to:(a) A cold water SUWly capable of giving up to O.llilres S.l at 10m head(b) A drain capable of receiving the above flow rate(c) A single phase power supply (suitable for a 700 W load) aIxi earth.
2. C~t die 112" nylon reinforced h~ supplied to d1e 112 BSP fitting at d1e rear of the m-=hineusing the adaptor supplied. Note that the water SUPPLY connection is (Xl the eXb'eme LEFTwhen facing the rear of the machine. The DRAIN is to the RIGHT of the JOWly connection.
p~ the clear plastic drain blbe into the drain and secure to ensure that it is not ejected at highflow rates.
3. Ensure that the voltage label on the machine CCj&T~,xmds to die l<X:ally available supply.
In ~ where a transfonncr has been supplied the voltage on the machine shoold correspond tothe ootlet scx:kct on the lransform~. H a transfonner has been suWlied the ~ (power inlet)windings may have several line (live) tappings for connection to the supply. In this case. thevoltage of the Icxal SUWly should be ~ between line (live) am neuual and the lineconnected to the nearest w-u~,xmding voltage rapping. Neuual and earth connections to thelransformer shoold be made as labelled on the transformer.
It b egential for operator safety that the Green and yellow cable from the unit is connectedto an earthing or grounding point that complies with the local regulations.
The IX>wer cable from the ~hine. or if a transfonner has been supplied. from die ttansfonnerprimary (power input side) shoold be connected to a fixed elecbical supply via a fused outlet whichcomplies with me local electtical regulalions.
4.
The BROWN cable is die LINE (X' LIVEThe BLUE cable is me NEUTRALThe GREEN AND YE1l..OW cable is die EARTH.
It is e~ntial for operator safety that tbe Green and yellow cable from the unit is connectedto an earthing or grounding point that complies witb the local regulations.
s. Conn~t a shmt length of plastic hose to the condensate drain at the oottOm of the evaporatOr. Thismay be led to a coU~ting vessel or drain below this point
6
SPEcmCA nON
HK'l34a Tetrafluoroethane CF,CH:aFRefrigerant Used
Maximum condensing temperature limited by high pressure safetycut out to approximately 55°C. (Corresponds to 15 Bar absolute)
Condensing temperature
Glass reinforced plastic on which are mounted the following:Pauel
Hennetically sealed and fitted with oil cooling coil. Swept volumeIS cm' rev-I. ROfational speed approx. 2800 rev.min-1 on 50Hz.(3400 rev.min-1 on 60Hz.) Fitted with thermal overlolKl protection.
Thermostatically conb'OUed internally equalised. Conb'Ols 1OC134aflow rate to the evaporator.
Expansion Valve
Changeover Switch. SolenoidVaJv~ and Indicator Lights
Direct HFCl34a to eidter air source or warer source evaporator.
Evaponton:(i) Using air a beat source Continuous blbe - externally fmned - copper/aluminium galvanized
steel cOOS1nlction. Provided widt condensation drip uay and airfan.Multi-layer plate type heat exchanger. Externally insulated.(h) Using water as heat soun:e
NOD Return Valves To Jl'event back flow into idle evaP<X'ator.
INSTRUMENTS
Wattmeter Direct reading panel mounted WatUneter indicating JX)werconswnption (Watts) of compressor.
Water Flow Meters (2) To measme water flow dIrough water ~ evaporator andthrough condenser.
HFC134a Flow Meter To measme HFCl34a mus flow rate.
Multi Way DigitalTemperature Indicator
8 Type K dtennocouples located at relevant JX>ints connected to asingle digital temperature indicator widt channel ~lector switch.Resolution O.I°C.
To measure evaporator and condenser P'CSSIJres ~vely.Pressure Gauges (2)
Calibration 5.1. units.
CONTROLS
Controls cooling water flow rate 10 cOlxle~ and hence controlsconde~ pressure and condensing temperatwe.
CondeDser Cooling WaterControl Valve
Evaporator Cooling WaterControl Valve
Controls water flow rare 10 condenser and hence cootrols cvaporalorpressure and evaporating temperature.
7
Evaporator ChangeoverSwitch
Operates electric solenoid valves to select either air sourceevaporator or waler source ev8lX>r8tOr. Lights adjacent to meswitch ilKlicate which eV8JX>ratOr is in ~.
Selecting die air source evaporator also automatically turns on dieair fan.
SAFETYElectrical 1.
2.
3.
Combined main switCh and overload cut OULResidual current cin:uit breaker. This compares the incomingCmTent with tOO outgoing currenL In the event of these beingout of balance by more than 3~A as in a leakage to earthsituation, power is disconnected automatically.All components connected to a common earthing point whichin turn MUST be connected to a local earthing conductor tha1complies with local regulations.Compressor fitted with automatic reset high tempel3ture cutOUL
4.
Switches oft'the compressor if the condenser pressure exceeds 1400kN m-1 gauge.
HFC134a High Pr~ureCut-Out
DIMENSIONS HeightWidthDepdt .
Weight
SERVIC~ REOUIRED 220/240V. Single Phase. 50Hz.. OR 11OV. Single Phase. roHz.(Maximum load approx. 7OOW)
Cold Water A cold water supply capable of giving up to 0.1 litres S.1 at 10mhead.
Drain Capable of carrying the above quantity of wanned water to wasteor for cooling and ~ycling.
. O.46SmI.3OmO.6SSm
. S9 kg
8
D~CRlFflON(Refer ro Fig.! - Schcmabc Diagram)
HFCl34a vapolD' generated by absabtion of low grade heat in either the air or water source evaporatoris drawn into dJe compessor. This exlraction of heat from air or water reduces the temperatm'e of dJeair or water flow leaving the unit
The wm done on the gas by the COOlpreS.:)r iIK:reases the pressure and temperabJre of me refrigerantvap>ur. 'Ibis hot high pressure gas flows to a concenb'ic tube wafer cooled condenser.
In d1e cmdenser me gas is dcsuperheated and dlen condensed at essentially constant temperature.Befcxe leaving the colxic~ the liqujd refrigerant is slightly sub cooled below the satmationtemperatm'e for the condensing IX'CSSUIe and this liqujd then flows to a liquid receiver.
The liquid ~eiv~ gives a large volume into which excess refrigerant can flow during certain operatingcoIxIitions. In addition d1e receiver ensures that liquid is always available for changes in demand dueto evaporator loading.
The CtIDpIeSSOr motor hu winding resisrance losses, internal friction and the c<xnpression process isnot isentropic. All of th~ conditions result in some of the electrical energy inJX1t being converted intoheal The c<xn~ and motor are cootained within the hermetically sealoo Steel casing and nm inoil which during Donna! ~ration is warmed by ciICuiation aroImd the casing and coll«ts at the baseof the unit During normal operation some oil will be carried around the system and under certainCOIXIitions may appear in the variable area flowmeter as a di~louration to the flow. This is quitenormal and will disappear dming nmmal nmning.
As the compress« is designed specifically f(X' ~ IXIInP use a copper heat ttansfer coil is kx:ated atthe base of the compressor within the oil reservoir. By passing the cold water from the mains suWlythrough this coil befcxe the WaIa' is transferred to the conde~ the nonnally waste heat from the oilcan be a(kjed to that given up to the conoo~.
Sub cooled liquid HFCl34a at high presswe passes through a ~el mounted flowmeter to athennoswically conb'Olled expansion valve. On passing through the valve the pressme is reduced tothat of the evaporator and d1e two phase mixwre of liquid and vapoor begins to evaporate within mesel~ted evaporator.
Control of the heat pump is by variation of the evaporation tempemwre by the source air (cx water)tem~ and flow rate, and by variation of die condensing temperawre by the flow rare of thecoOOe~ water.
The range of source tempelabJre can be extended by directing WaDDed air from a fan healer 81 the airintake or by supplying warmed or chilled water to the source water inleL
Relevant system tempezanues are ~ by dam<x;Oupies and a panel mounted digital temperanueindiCator. The dtermocouples used are type K (Nickel-Chrome. Nickel-Aluminium).
Condenser and evaporator pressures are indicated by panel molDlted pressure gauges.
Walcr aIxI refrigetant flow rates are indicated by panel mounted variable area flowmeters.
The eJecttical input to me compressor motor is indicated by a panel mounted analORue meter.
9
OPERA nON
For normal ~ the unit requires connection to a mains supply,a cooling water supply,and asuiaable drajn. Details of the services ~uired are given in the Installation and Commissiooing sectioo,Page 5 and Specification, Page 6.
Note that if the cooling Waler tempetatUle is high (greater than 3OOC) then d1e output from d1e unit willbe Ied\ad and die ex~enta1 range redoccd. However the unit will contin~ to operate until mehigh IX'eS5Ure cut out operates at 1400 kN mo1 gauge pressure.
Assuming dJe unit is connected to suitable services t1D'D on the cooling water supply and adjUst thecoOOc~ cooling water flow and evaP<X8tor water flow to maximum. Turn on me main switch andthe COOl pI'eSS(X will start to ~ .
The eV8lXJr8fDr ~ is selected by die eva}X)ratOr changeover switch mounted 00 the front ~l TheeVa{XJralDr in ~ (Air or Water) is iOOicated by a small panel mounted lamp adjacent to die switch.
If the waIer ~ evaJX)rator is to be ~ then it will re n~essary to ensure that sufficient water is~ duoogh the evaP<Dfor to .-event ~zing. Freezing will be indir:-a!~ reSbicted cooling walerflow (the flow may stop completely) aIKI the inability to adjust the evapcntor pres5lD'e.
If fJeezmg should occur bJm off me ccxnpressor and adjust the evaporator water ~ to maximum.The CV8JX)raror is a plate type beat exchanger and should not be damaged by freezing but dlis cannotbe guaranteed if ~ occurs repeaIedly.
When initially nJmed on me fIOWmcler will show v8lX>ur bubbles. 1b~ should cease after 10-15minutes under oom1aI conditions. However under exueme operating conditions dlis time may be longeror shorter.
To increase the COIxSeDser pressme reduce the corxienxc cooling water flow rate.
With dJe w~ ~ evaporaIor ~leded. to increase the evaJX>l3tor pressure increase the water flowrate through the evaporator.
If the air QDCe evaporator is ~l~ted then it is ~ble to increase the evaporator pressure by directingwarm air (from an electric fan heater) to~ the evaporator inlet side.
The air ~tm:e evaporator preS8me may be redlx:cd by restricting the flow of air into the evaJX)ntor.A pi~ of paper or card may be used for this purpose. However it should be noted mat it is possibleto coUect ice on the air cvap<ntor if the air flow is restricted sufficiently.
To shut down the unit bIm the condenser cooling water flow rate 10 maximum to reduce the cond~pressure and then bIm off the main switch.
10
SAFETY DEVICES
TestiD2 8mb Pre8ure Cut-OutThis shoold be dme by a resoonsible DerSon at die beginning of each session and after every 25 hoUlSrunning.
With the unit nmning and the air evaporator selected, turn off the cooling water supply and observe mecoIxIeDa ~ure gauge. When it ~ 1400 kN mol, the cut-out shouJd opera1e arxI isolatecompress« mota. Turn on the cooling water and as me condenser pressure falls to betW~ 800- 1 (XX)kN mol the cmnpress<r motor should again 0peJ'ate.
If the cut-out fails to ~ at 1400 kN mol, the com~ should be tUrned off and me cooling watershould immediately be bD'Ded 00, and the ~ investigated. The cut out is mounted on the side ofthe small instnDnent conmle.
The unit must not be onerated with a defective him Dressure cut-OUL
The high pressme cut out should not nonnally rQJWre adjustment but if for any reason the unit requiresadjustment detains are given in the Maintenance sectioo on Page 11.
Testin2RCCBPeriodically the RCCB sbould be ~ by a competent persoo.
Remove the rear panel and switch on the m~hinc. Press the 8Pfea to Test" buuon on the RCCB. Thecoble unit shouJd inunediately switch off.
Switch the RCCB back 011 and replace the rear panel.
If tile RCCB fails to opezare tile device shoold be investigated by a competent electrician.
11
MAINTENANCE
LubricationAs me R831 utilises an hermetic compressor it is unlikely that any additional lubricating oil will berequired. If me System ~ lost sufficient oil to require recharging men it is likely d1at a major failurehas occm'red and me 1D1it will also have lost its refrigerant charge.
Note that as die unit operates on HFCl34a die unit should NOT be charged widl n~al CFC typemineral oil. The lubricant used is an Ester oil specifically designed for use with HFCl34a systems.
Refriaerant Cbarae <R134a)When the unit leaves P.A. Hilton Limited's factory, it has been cmectly charged and tested.
If a refrigerant leak is suspected it must be detected and ~tified.
Leak DetectionWith pressure in the system, inspect all jointS with either soap suds, or an electtonic leak tester.
Note that HFCl34a cannot be detected with a conventional electronic leak detector designed forthe CFC type refrigerants. The unit must be specifically designed for HFC use.
The leak must be rectified before recharging.
RecharRiDeGood refrigeration ~tise should be observed at all times during the recharging process.
Note dJat as the unit utilises HFCl34a and an Ester oil extta care should be observed regarding moiStureremoval and exclusion. Ester oil is panicularly hygroscopic (absorbs water) and a longer evacuationperiod should be used dIaD on CFC12 units to ensure all moisture is removed before recharging.
The charging point is located on die compressor casing and is a 1/4" Schrader fitting. This has aninternal spring looded valve widl a centtal actuator pin. By connecting a suitable charging hose widla pin depressing cenD'e to d1is valve die low pressure side of die system may be evacuated/charged.Connection to die high presstD'e side of die system may be made via die back seating valves on the inletand outlet of the liquid receiver.
Note that the unit has been designed specifically for operation with HFCl34a ONLY and shouldnot be charged with any other gas.
The original charge weight from full evacuation to fully charged is 1 kg of HFCl34a.
GeneralDust collecting among the connections and on the air source evaporator fins should be blown away bya dry compressed air jet, or preferably removed using a vacuum cleaner.
The ~el may be cleaned widt dilute detergent and polished with a dry cloth. Abrasives or solventsshould not be used.
12
FAULT FINDING
COlDD~r Does Not Start1. Check mat the unit is swirched on.2. Check d1at high pressIn cut-out has not Operated. Check condenser pressure gauge.3. Have elecU'ical ~1i0lW (internal and external) checked by a compcrcDt el~bician. An inrcrnal
wiring diagram is located at the rear of this manual.
Comoregor RODS Hot and Cuts Out On Hi2h Temoerature Cut Out1. The high temperature cut out is mounted on the compressor itself and will reset when the
compressa ~ng cools. However the symptoms can easily re confused wid! ~on of diehigh pressure cut out
If the high p'essure cut out has ~ men IX>w~ will be stopped at the high pressme switChterminals.
If an AC 2SOV voltmeter indicates d1at power is being supplied through to me compessor SWIertmminals and d1e compressor is not nmning men it is likely dlat me high temperature cut out hasoperated. If this is d1e ~ when d)C compressor cools me cut out should ~t aOO d)C compressorrestart
If the COOlpresscx fails to start after cooling then it is ~sible that ~ compressor has failed.Isolate d1e unit from the mains have a competent elecbician check the wiring up to the compresscx.
Exceaive Condenser Pressure1. Cooling water UX> hot2. InBquate cooling water flow due to low maim pessure. restriction in flow etc.3. Evaporator source temperature (air or water) UX> high.
Circuit Breaker Switch/Cut-Out Operates1. C~k mat cooling water flow is maximmn m dmt con<k:~ pressure is low2. Have a competent electrician check for short circuit
RCCB OoeratesThis may be a "nuisance" bip (one oft) or indicate a leakage to earth.
~ switching die lrip back on. isolate die unit from the mains and have a competent eleclricianc~ eanh continuity and the resistance between all comJX)nent lines and eanh. Line to eanhresislance should re in units of Meg Ohms. (1 x 1(1 Ohms)
If a fault exists die RCCB will operarc again when die unit is switched back on.
To switch the RCCB bIK:k on afta' a fault, isolate me unit from me mains. ~move me rear panel andturn the switch on the RCCB to ON.
13
THEORY
Thermodynamic Asoects or Heat PumosThe S~ond Law of Thermodynamics includes the statement. "It is impossible to ttansfer heat from aregion at a low temperature to another at a higher temperature without the aid of an external agency.".
Heat Pumps and Refrigerators are examples of ma:hines which transfer heat from a low to a hightemperature region and the "external agency" employed may be either work or high grade heat.
The First Law of Thermodynamics states dlat in a cycle the net heat transfer is equal to the net worktransfer. Thus, for a heat pump, Heat transfer at low temperature + Heat transfer at high temperatW'e= Work ttansfer. (The noImal sign convention must, of course, be applied.)
In die case of a heat pump (or refrigerator) using a work input, (i.e. die V81X>ur compression cycle),it follows that heat transfer at low temperature + work input = heat transfer at high temperature.
If the external agency is high grade heat (i.e. the absorption cycle). then heat transfer at low temperature+ heat ttansfers at higher temperatures = O.
The following notes awly only to the vapour compression cycle.
DEFINmONS
Heat PumoA machine whose prime function is to deliver heat to a high temperature region (usually aboveambient).
From the First Law of Thennodynamics it is apparent that a refrigerator must reject heat at a highertempelature and the heat pwnp must take in heat at a lower temperablre.
Thus, there is very little difference between the two plants, and bodt useful effects can be obtained fromthe same unit (e.g. a dairy has the need fm- refrigeration and hot water - both of which may be providedby dte same plant).
_Refri2eratorA machine whose prime function is to remove heat from a low temperature region (usually belowambient temperature).
Coefficient of Performance of a Heat Pum2 (Cop...)
Is the Ratio Rate at which heat is delivered-- - --
Power Input
Coefficient or Performance of a Refri2erator (CoP.)
This is the Ratio RefriRerator Rate or DUtYPower Input
The power on which die CoP is based and the Type of CoP should be clearly stated, since the powermay be:
(a) Elecb'ical power to drive the motor.(b) Shaft power to drive the compressor.(c) Indicated or piston power to compress me vapour.(d) Thooretical power of an ideal compress«.
14
PrKtX:al beat pumps can, under suitable MUmlla~s. deliver ~I)' m<n heat than is lakenin as high grade energy and can make a valuable conbibution to energy conservation and redtx:tion ingeneration of greenho~ gases.
The following notes awly to tat pumps driven by a work input
REVERSED CARNOT CYCLE (In&emal1y and Externally Revemole)
The ideal refrig«atlJr is represenred by the Reversed Camot Cycle in which heat is taken in from aCODSlant low tem~ somce at T L and is !ejected to a constant ~ temperawre sink at T H'
~T~
, ~~~=Ca'1denS8'1-
~
Evaporator
---,",~"-~
I Low T~ I
~ TL
12I--_I
HighPressure P.
Expander~
LowPreS8.Jr8 P L
Fig.l Fig.2
Fig.l illusllates a plant diagram and Fig.2 a axrespooding cycle 00 a T -5 diagram for a VIJX}tD'.
The cycle is . follows:
Wet V8JX>tD' at 1 is compesscd isentropically from a low pressure PI to a high pressure P2. Vapour at2 is ~ into a heat exchanger (condenser) and heat is rejected at constant pressme to a coolingmedimn (sink) so dIat d1e vaJX:.Jr coIKtenses and becomes satUJ3ted liquid at 3.
The high ~ sabIrared liquid is expanded isen~ically from p, to P. and me ~ting vezy WetvaJX)m' is ~ into a heat exchanger (eV3JX>rator) at Slate 4. In the heat exchanger the vapourevaporates at a low temperature taking in heat from the low temperature source and reaches state 1.The cycle now rqJeats.
Cycle AnalYsisHeat tmnsf~ in ~raIor. Q. = .[1 Tds
Q. = TL&
Q. = J'TdsQ. = -TH&
Heat Iransf~ in condenser,
Since the compression and expansion ~~! ale isen~ic ~ are 00 other beat transfers.
The net ~ transfer in the cycle, ~ . Q. + Q.
and from the First Law. W- . TL 4s - TH 4sW - = .CL..:..:JJ~
('I1Iis is . ve and IeplesenlS a wmk 1NPlTI')
15
Coemcient or Perfonn8nce
The Coeffk:ient of Perf(XD)al1CC of a Heat Pump is ~ ratio.
Heat delivered at a hiRh temoeratureWork. Input
Thus. for die Reversed Camot Cycle,
-T. A.rCT" - T.> A.
. -7'.~-:~ orCoP. . -2-T. - T£
The Coefficient of Perfcxmance of a Refrigerator is d1e ratio.
Heat taken in at low temoeratureWork Input
Thaw, for d1e Re~ Cand Cycle,0. T£ As T£CoP... . - . .W. (T£ - T.> As T£ - T.
Strictly .:cording to sign cooveDlim. this is negati~. but for coovenierx:e it is usually writtenT I which is positive.
TH - TL
THE mEALISED SIMPLE VAPOUR COMPRESSION CYCLE
AldtOUgb 00 refrigeraIm' (X' beat IXJmP can have a ~ffx:ient of perronnance higher d1an d181 of aReversed Carnot Cycle operating betWeen the same ~ and sink temperatures, the Carnot Cycle islmattIaCtive. This is Jargely became of the practicalpoblcms associated widt the design of an expan<k:rwhich would lake in high plesS1De liquid and pus oot very wet v8lK>ur at a low pessure whileprod&x:ing a smaJ1 work OOtpuL
There would also. of ~. be irreversibilities in any prxtical anempt to make a C8DOt Cycle.
In die m<xlem Vapour Compession Cycle. a dtrottling process is substiwted for die isenuopicex~oo process 3-4 in the Camot CycJe and aldtough the coeff1Cient of perronDance suffers due tothe introduction of d1is highly irreversible poccss. die reliability and simplicity gained far outweigh diesmall increase of work input ~uircd.
Cycle AnalYSisThe i~-ilL~1j plant and TIS diagrams are shown in FIgS.3 and 4.
AldlOUgh the dIrottling ~ is considered to be adiabatic. it is in fact inevcrsiblc and cnuopyin~ from s, to ~ during the expansion.
Q. = .p T41 = TL(s. - sJ
~ = ~ Tds = T~s, - sJ
16
1M ldeall8ed Vapoi6 ~..." Cyde. T
.. ~:~~~,Hol R.-1
q.... ~~ ~-~-..
Ex~'tVaiY8 ~
T'7
~-
TEYalXX'QIa' w~1
CD~e88a"4
I !Q4-1 I
~R8dCXt
Fig.4FiI.3Sinc:c 1-2 and 3-4 are adiabatic processes in the idealised cycle, me net woJt rransfer,
W . Q, + Qc. TL(.rl - "'J - Tp3 - sz>
The CoP. . ~W
and CoP... . ~
These expressions can be evaluated. but it is mm-e convenient in practice to illustrate cycles on p-hdiagrams. The corresponding p-h diagram is soown in Fig.5.
With reference to Fiore 5:
For the Compressor
~.J . ~ - ~ + w
If compression is adiababc, ~4 = 0,
w = b1-~,andW = lh.(bl-bJ
Note that dlis implies an input of work whichby convention is negative.
For the Condenser
~=~]=b,-~+W
but at die ~.D..-~ W - 0
b,-~and~ = dl.(b,-~
Note dial . this is a reja;tion of heal fnxn die system. by sign cmventioo this is negative.
17
p p:3
p P,4
Fig.5
For the Exoaosion Valve
~ = ~-hs+w
but w = 0 and the dU'Ottling process is adiabatic
.. . ~ :..,b.,
For the Evaoorator
~1 = CL = hi - h. + w
"""1:"--;1Q'-1w=o:. ~~,.,;.Jl. and Q. = dl,(hl - hJ
Note that d1is is a heat input to the system which by sign convention is positive.
[or ~.:!!:!)~-".
h,-~hi - ~
tic -CoP., = -;- -
18
THE PRACTICAL V APOUR COMP~ION CYCLE
Tbc prKtical cycle differs from the i~.wised cycle in the following ways:
(8) Due to friction. ~ will be 8 small press~ drop between the C<XDpressor discharge and~ valve inJet, and between the expansion valve outlet and the C<XDpIessor suction.
(b) The com~ion process is ncidJer adia~tic nor revelSible. (Iba'e will usually be a heat k>ss fromdie COOlIB'es5a' and. obviously. dJere are frictional effects.)
(c) The VllX>ur leaving d1e eV8pOIata' is usually slighdy superheated. (This makes ~ble automaticcontrol of die expansion valve and prevents compressor damage by ensming no liquid enters diesuction valve.)
(d) The liquid leaving die condenser is usually slightly sub-aX>led. i.e. it is red~ below thesat1D'Btion temperatme cODeSJX)nding widt its pressure. (This impoves the CoP and reduces thepossibility of the fonnation of VaJX>ur due to the pressure drop in the pipe leading to the expansionvalve.)
(e) Thm may be small heat inputs <X' k>sses to and from the surroundings to aU pans of the circuitdepending upon dteir temperatm'e relative to the sunoundings. The nett eff~t of these ")asses" orirrev~bilities 00 the cycle diagram is slX>wD in Figure 6.
D-b Dialram far SimDIe Practical Va DOur CamDressian Cycle
p
Fig.'
RECIPROCA 11NG COMPRESSOR PERFORMANCE
Refer to Fig.7
Froo1 FD'st Law
Q1-1 = ha - h. + w.
!{ flow is adiat..bC. Q1-1 = 0 and w = h. - ha
Notc dJa1 ~ to sign convention a wcxk input is regarded as negative.
19
However. most beat pump and refrigeralar canpressors run welllrove ambient tempeI3bDe and mere is I beat lramfer frtXn d1ecompressrx to die surroundings. In additim as me comp-essor ishermetically enclosed with the mOlar windings electrical (Currenttx Winding Resistance heating 1~ will be directly a(kJed to thesystem.
The end1a1ov chan2e ~ - hI is dlerefore the difference between theelectrical input and the tolal heat ~sfer fD die sunoundings andshould therefore not be re2arded as the work mout to a DI'Icbcalcomoress<r .
~ - hi = ~4 - W.
Fig.7
Volumetric EfficiencvThe volume of gas or V8fK>ur (measured at intake conditions) is less than the piston SWept volume forthe following reasons:
(a) L ~~DC past the pisux1 and through die valves.
(b) Pressure drop and temperatUle increase ~S the intake system, bom of which reduce vapourdensity .
(c) In a refrigerator compresscx. any droplets of refrigerant liquid roil as they meet the warm cylinder.Note that droplets should not ex.ist in theory if the exlliDsion valve is operating correctly andmaintaining a level of su~
(d) High pressure va~ left in the clearance volume after delivery expands and occupies a portionof the swept volume during d1C "suction" stroke.
The ratio Volume flow rate of ~DOur (meas/Ued at intake conditions) is called the VolumetticEfficieocy. Piston J'Wtpt \/Olume rate
It can be shown mat the theoretical volumetric efficiency of a reciprocating compressor is,
Yc ( 1 )1-- ry ',.-1.
where ~ is the ratio of clearance to swept volume.V.r, is ~ ratio of delivery JXeSSure to suctioo pressure.
20
n is die index II in die JX>lytropk law pV- = C which is a.uumed f(X' the expansion.
Howeva-. this axjX:~ion ~ lite eff~u of a. b 8KI c.
21
USEFUL DATA (See also S~on)
Comoressor Swept Volume = IScm3
Rotational Speed:-Rotational speed will vary widi compressor load and in particular die mainsFreq~ncy .
On 50 Hz supplies compressor rotational speed is typically 2800 rev min-1On 60 Hz supplies compressor rotational speed is typically 3350 rev min-1
Note: - As die com~or rotates at a higher ~ 00 60 Hz die refrigerantflow rate, heat delivered and compressor IX>wer consumption will behigher d1an on 50Hz supplies.
Mean heat b'ansfer area = O.0875m7.Condenser
Specific heat of water = 4.18 kJ kg-l
E vaoorata Mean heat transfer area = O.14mz
22
LOW GRADE REA T SOURCES
There is a very wide range of low gr.se heat ~UlCes available to practical heat pumps. The followingare typical examples.
~ from die abn~ is flee and available everywhere. However, it is subject to wide variatiomof tempcr3WrC and humidity. High humidity and low evaporator temperawres will result in evaporatoricing and ~ dIeD requires the complication of defrost cycles. These may either use reverse cycling(passing die hot high pressme gas dIrough the evalX>r8tor) or electric heaters. Either ~tion result ininaeased energy consumptioo for a given ovm11 ~ effecL
Air aW bas a low heat ca.-clty F unit volume and is a (XU cond~1Dr of taL Despite its ~tdisadvantages air is frequcody used as a low grade SOUICe, Imrbcularly in reversible summer/winterheating/cooling unilS.
A supply of warmer air or gas is ~etimes available from a variety of cooling or venlilaling processesand ~ can often be used ~ die source of low grade heal
~ as a low grade beat ~ may be available from rivers, lakes, the sea, wells. process cooling,domcsdc and indusaial waste eat.
Tbe SoU can be used as a source of heat providing that sufficient area is available relative to the depthof me evaJ)(Xating bI))e.,. There have been instances where the rate of heat exttaction at a particulardepth has been far greater than die incident solar energy resulting in a pernlafrost sitUation renderingthe heat JRlIDP useless.
Other sources of low grade heat include solar radiation, low presswe steam, process VapoUlS. flue orexhaust gases etc.
RefriaeratorsThe cooling eff~t of a refrigeraror (e.g. the heat extlacted frOOl a cold space) is also a ~ of low~e heal Nonnally a refrigerator rejects heat to cooling water or the aunosphere. By increasing thetcm~ at which d1is heat is rejectr.d. this heat will become ~ful. Although this will reduce d1eduty of the refrigerator and also its C~fficient of Perfonnance, a useful heat output can be obtainedfor little extta w<Xk input
Whatever the somce of low gra<k: heat, to be viable, the source must be reliable, at the high~t possibletemperature and "free".
23
EXPERIMENTAL CAPABILmES OF IDLTON AIR AND WATER HEAT PUMP
The unit povi<k:s a considerable amount of data, which, after analysis. provides all the characteristicsof a heat pump and the ~ compressim cycle.
Among the capabilities are:
Detem1ination of Power Input. Heat Ouqxlt and Coefficient of Perf(X'InaDCC.1.
2. Producaoo of Heat Pump Perf(X'ln8nCe CID'Ves over a range of source and delivery tem~
Plotting the V8JX>m' Compression Cycle on a p-h diagram and comparing it with the Ideal Cycle.3.
PrOOucDon of HQt Pump Perfonnance cmves based on die HFCl34a lX'OJ)erties at a variety ofevaporadng and cmdeming temperanues.
4.
EDtZgy Balances for die components and the whole cycle,s.
6. Estimation of Volumetric Efficiency of the Com~ at a range of pressure mOos.
Estimation of ~ Heat Transf« Coefficien~ in the E vaporaIor and Condenser.7.
It slX>uld be noted dIat due 10 manuf.:blring tolerances. die perfonnance of individual units may differfrom ~ given in die following pages. but tterKis and chaIaCteristics will be simi1ar.
NOte also dlat OPQ'ation of the unit on roHz electrical supplies will result in higher h~t ttansfers andhigher com~ power consumptioo.
24
1. DETERMINA nON OF POWER INPUT, HEAT OUTPUT AND COEFF1CIENT OFPERFORMANCE.
Procedure1. Turn on die ~ supply to d1e lmit and DJm on die main swiu:h.
2. Select the air evapnlm' by ~g the evaporator change over switch down.
3. Set die condenser gauge ~me to between 700 aIxIllOO kN/m-2 by adjustment of the condensercooling Wafer flow rate.
4. A1k>w the Wlit time for all of the system pammetelS to reach a stable condition.
Thenreccxd:
Calculations:
c~ E1~trical Power Input W = 450 W &US
Heat delivered to cooling ~ {r(Xn Comples8(X'.
Q~ . .c~. x (,. - t,). 20 x 10-s x 4.18 x 10-s(14.6. 133.7 WQItf
Heat delivcled to Condenser cooling WaIrJ'.
Q~ s M, Cp. x (" - tt>. 20 x 10-3 x 4.18 x 10'(31.8 -. 1437.9 WIIltJ
CoPH = Rate of Heat DeliveryCompressor Elecaical Power Input
If the heat delivered to the condenser m is considered. then:
COp. = ~W1437.9.450= 3.19
2S
If the total heat delivered to the wafer is considered. i.e. including the waste heat fmn the compressorcoo1ing coil. then:
4SO3.49
Hence by ex.1rXting heat frm1 die surrotmding air the heat pump is able ro deliver 3.49 times as mlx:hhot wata' at 31.8OC dIaD would be poaible by direct electrical resistance heating using 450 Watts of
power.
It is imlx.1ant to note dlat due to com~ ~ (Cumnf x resiswICe) l~ aOO friction 133.7 Wattsof me heat dclivemd would be lost if the compressor were air cooled rather than having the infernal
warercoolingcoil.
Similar tests may be carried out using water as me source of low gra(k; heat by selecting the waterheated evapcnror.
26
1. PRODUCTION OF REA T PUMP PERFORMANCE CURVES OVER A RANGE OFSOURCE AND DELIVERY TEMPERATURES.
Procedure
Turn on me Wafer supply to d1e unit and turn on the main switch.1
2. Select the air CValJ(ntor by pressing me evaporator change over switch down.
3. Set the condenser cooling water flow rate to maximum and allow the unit time fm- all of the syStemparameters to rea:h a stable condition.
4. Mate me observations ~ out on Page 24.
S. It is assumed that die air source tem~bJre (laboratory room temperabJre) will remain sensiblyconstant during the tests. This tem~1Ure soould be recorded for reference.
6. Reduce the cooling water flow rate so that me condenser pressure increases by approximately 100kN/m1 gauge pressme d1en repeat the observations.
7. R~ this procedme until the condenser pressure approaches 1400 kN/m1 gauge pressme. Notethat die high pressme cut out is factory set to 0Ja3Ie 81 1400 kN/m1.
8. The series of observadons may be ~ 81 another constant air tem~ about lOK ooucrthan peviously tested by dilecting d1C warm ~ from a fan heater into the air eV8fX)ratm.For d1is IXDJX)se it will be necessary to measure dJe air temperature locally to dJe evaporator usinga suitable tbennoneter or meas1D'ing cEvX:e.
9. In additim die procedure may be repeated using water as the heat source by selecting the waterheated evaporator. It may also be possible depending upon locally available resources to carry outthese tests at a range of constant source temperabJres by using heated water.
In all ~ the limitation will be the high pressure cut out rempelatlR of 1400 kN/ml
The calculations ale similar to th~ caITied out for Experiment 1 on Page 24
Typical ~<Xmance cmves are shown on Pages 28 to 31.
30
Ncr-~000 -000
...0v.0: I
~
Heat delivered - W
atts-
- -
--
- N
N
0 V
\ 0
V\
0 0
0 0
~
~
~
~0
tV
~
0\0
0 0
0
Com
pressor Load - Watts
I
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u.0
~~
0'r\~~
il ~~
00M..-
iii L
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31
32
3. PLOTnNG THE V APOUR COMPR~SION CYCLE ON A P-H DIAGRAM ANDCOMPARING IT WITH THE mEAL CYCLE.
Procedure
1. Tmn on die Wafer sUWly to the unit and tmn on the main switch,
2. SeJect eid1er the air or waIeJ' evaJX>latCl" using the evaporator change over swiu:h.
3. Set the condenser cooling watec flow rate to approximately 50% of full flow and if using the watereV8fXJra1or set me ev8lXJr81or Water flow to an intennediate flow rare.
Allow the unit time for all of the system parameters to leaCh a stable condition.
HFCl34a TemperabD'e at ex.-nsion valveoutlet rc/OC -4.1
. Absolute ~. i.e. gauge pressure + atmospheric pressure,
Results: Refer co pressme - end1alpy diagram on Page 34.
The following assumptions ale made:(a) The ~ drop dn'Ough the condenser is insignificant due to moderate velocity. Th~ P2 - PJ.(b) The throttling process 3-4 is sensibly adiabatic. Thus h, - h4.
Location of stare JX>inlS:
(I) Is located by the intersection of Pt = 2SO kN m"2 and t1 & 2.4OC. (h1 = 301 k1 kg-1 and V1 =
0.084 m' kg-1)
(2) Is 1<x:aIed by the intersection of P7o = 756 kN mo2 and 1z . 64.2OC. ~ = 350 kJ kg"1 and V2 =
0.032 m' kg"1)
(25) Is ~~ by ~g constant en~y compession from state JX>int 1 to P2 . 756 kN mo2(~ = SJ Ch:ao = 328 kJ kg"l)
33
(3)(4)(4')
Is located by the in~bon of p, = 7S6 kN m,2 and t, = 27.2OC. (II, = 137 kJ kg'l)Is locatcd by the in~bon cX .. - -4.1OC aIK1 b, . 11..
Is located by the intc~bon of P. = 250 kN m'2 and h, = 11.. (S~ diagram on Page 34)
Comments
1.2 and 1.25The com ~ ptx:ess 1-2s is that which would take place in a reversible and ~bIIJjc (isenlropic)compress<r. In s~h a pI'(X:eSS. the work transfer would be equal to die enthalpy change (hI - ~.
The ~1Ua1 comr--~ ~ 1-2 JXocioccs a 1arg~ enthalpy change (hI - bJ. The reason for thisinaease is complex:
(8) The compression will be neidler reversible ncr ~~iabatjc. Frictional losses (bodt vi..:ous andmecbanjcal) will have 8 "heating" effect on the HFCl34a and will increase entropy.
(b) Valve and piston leakages are throttling processes and will caux entropy to increase.(c) The net heat transfer during the compression may be positive or negative.
Since the electric motor is within the same casing as the compressor, the I~ in the mOtor ~ ageneral rise of tQllpe~ in the region of die compressor. During stx:tion and die fIrSt pan ofcompression, it is likely that the beat transfer will be to (+) d)e HFCl34a. Towards the end ofcom~ it may be from (-) die HFCl34a as its tempelatm'e rises aOOve its surrowtdings.
It sbouk1 be ~Pwised d18t althoogb hi - ~ is die walk transfer in an isen~c compressor, hi - ~may be more or less dIaD die actual work transfer to the HFCl34a. according to die net heat transfer.
HThe vaJK)m' is de-su~bea1ed. condensed and then suIx:ooled at the high pressure. The heat rransfer~ - bJ hu been to d1e condenser water aOO is the ~ful OUtput of the heat pump.
HPoint 4 is k)CatM on the -4.1OC isod1erm and by die assumption of 11, = h.. Due to beat gains duringex~sion it is likely that h. is slightly greater than h,. but me eITOr is likely to be insignifJCanL
It will be ~n dw during the expansioo. the HK'134a changes from high pressure sub-cooled liquidto low pressme wet vSIX'ur widt a dryness fractioo of 0.20 (or 20% va(X)ur)
~The wet VaJX)Ur is converted to superbeared vapour and the enthalpy change (hI - hJ is caused by a heat
transfer from the low ~ beat ~urce.
The slight pessure drop P4 - PI is due to resistances in die evaporator and in the non-retmn valve.
Without this pressme drop, point 4 would move to 4' as in the ideal cycle. It will be noted that theeffect of d1is ~ drop is 10 increase the evaporation temperatme and thus reduce the temperabD'edifference between ~ soun:e and me refrigeranL
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35
PRODUcnON OF REA T PUMP PERFORMANCE CURVES BASED ON THE HFCl34aPROPER~ AT A VARIETY OF EVAPORATING AND CONDENSINGTEMPERA ~.
4.
Procedure1. Turn on the water supply to the unit and bJm on the main switCh.
2. Select the water evaporator by pressing the eV8lX>rator change ovez- switCh up.
Ensure the evlpcntor water SUWly is flowing at. (X' near, its max.imwn raIe.
3. Adjust the cOlKienser to a high water to a high flow raIe.
When stability is ~hed. note d)e condenser pessure (pJ aOO d)e evaJXntion temperawre (t,J.then make the observations set out on Page 37.
4.
5. Reduce die condenser water flow rate so d1a1 die condenser ~ure (P2> in~ byappoximal:ely 100 tN mol. Adjust the ~ water flow rate until r. returns to or near its initialva1~ When stability is ~bed repeat the omervanons.
6. R~ in iDcIements of approximalCly 100 kN m-l in me value of P1 unlil the pessure ~hesabout 1400 kN mol (gauge).
The test may oow be repeated 81 anomer conslant value of~. Warmed water may be used as dieheat Dm:e if available. (AllCm81ively die source water flow rate may be red1x:ed to decrease dievalue of ~.)
7.
If the evaporata water flow rate is too low it may freeze in the plate heat exchanger. Thebeat exchang~ is roOOst and no damage should result but re~ occurrences of this shouldbe avoided.
~:
Freezing will be indicated by the evaporator water flow ceasing 8Jxi lack of control of d1eev8lX>rator temperawre and 1J'eSSure.
Observations
See Page 37 for specimen observations.
Calculations (FCX' Test 6 - Page 37)
PI - 253 kN m"2 absolute
ts . -1.4OC
P1 . 1285 kN m"2 absolute
&a . SOOC
From p-h chart (Page 38) or tables:
hi . 298 kJ kg°i
~ . 358 kJ kg'l
h, = h. = 163 kJ kg"!
36
Evaporating temperallDe (tJ =-4.2OC
Condensing temperablre <..111285 kN m"2) = 49OC
Heat ttansf~ in condenser,- '",cia, - lLz>
- 5.5 x 10-3(163 - 358) x 10'- -Ian
This is.f!2m. me HFCl34a!g, the condenser WIler and by connection heal b'ansfer to the system andwmt b'ansf~ from the sySfCD1 are regarded as positive.
Elecbical input to compressor = 470 Watts(This is Ie~ as a wort input to me system)
HMt DeaW1wl~. - Work 1"""
1072--470
-2.28
It is of in~ to compare die aOOve with the CoP of the ideal cycle with isenlmpic com~on.
hi = 298 kJ tg"1 as befmeFrom p-h cban:
~ = 332 k1 q-1 Isenlropic line from ~, PI to P2
b, = b. = 163 kJ kg-I as before
332 - ~. 5.0This discrer-ncY in the Coefficien~ of ~mmance is largely accounted for by one of the variousl~ in the COOlpreBSOr unit aOO .-nicularly ~ l~~ in the el~bic motor.
Note. however. d1at the heat deli~ does not take into account the energy derived from the motorcooling coil whkh will improve the actual COPH,
CaJculated daIa is shown on Page 39 and the results are JX'esented graphically 00 Pages 40 and 41.
Similar results may be delcnnined for other evapcx-ating temperatures and when using dte air heatsource.
~... eIectticaIpower. 445W I Watts 400 4OS 430 460 470
HFCl~ ~
~ I tJ q-' 311 302 300 300 300 198~~.--~ I tJ q-t 348 350 3~ 352 354 358~ deliVer)
c~ oudetBvipCnlOl' inlet
))
~ - -., kJ q"a 131 138 143 148 153 163
40
Heat Delivered Watts
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N .N
~ .rf')
C"!('f") M ,.0
N~
Q)
~.~~
'f'f")
-~:~
.
i\,OI .--.~
I+~M
Ij-', ,,L--"}1
II
~~..==
rIJ..~
..w=~
~
~0u~~
Q)-Q)
>.--
Q)
0.
~Q)
:I:
~
"C'~1...'~~.-'
-~
Q~'=,~.
=:
~rj
==
e-
c.s-~
~
II//
'\,0I .To...:NI
~0u
1\0I .
TviN
. .
0 0 0~ 0 tr')N N ~~ ~ ~
SU'B M. palaA!Iaa :I,'BaH
00--
00('f')-
~ .N
.u0~~~~c..e~f-I'e;'~>.--~0~~~~
42
5. ENERGY BALANC~ FOR mE COMPONENTS AND THE WHOLE CYCLE.
Procedure1. T~ on me water supply to die unit and QJrD on the main swiu:h.
2. Select the water evapor8r« by pessing d1c eV8porara change OVa' switch up.
Set the evaporator wala' flow to ~ intermediate value.
3. Set die condenser cooling wafer flow rare to a similar value.
When the syStem hu been allowed time 10 ~h a stable condition record all of the valuesindicated 011 die observation sheet CIl Page 44.
4.
If die evaporat« water flow rare is too low it may freeze in the piare beat exchanger. Theheat exchanger is roOOst and no damage should result but repealed occurrences of this shouldbe avoided.
~:
Freezing win be mmr-!t~ by die evaporator water flow ceasing and la::k of coouol of dieevaporator tem~ and pessure.
Calculations
PI . 2S3 tN m-2
It . -1.4OC
P2 - 1285 tN m-2~ = SO.OOC
From p-b chart (Pagc 45):
. 298 kJ kg-!hs
~ . 358 tJ kg"l
h, . II. . 163 kJ kg"1
Compressor (Electrical) Power Input W = 470 Watts-
EV8oorat2r
j#Heat ttansfer!!Qm water soun:e.
~~"'TLJ
. 'ccp<" - r.>. 11.5 x 10-3 X 41~13.0 - (-1.2» W-mw
J.,.
Heat transf~ 12 HFCl34a.Q14-1 = .,cla. -11.>. ", x 10-'(2g& - 163) x 10' W
. 742 W
The discrep8Jx;y (59 W) may be attributed to instrument and observation errors and to heat b'ansferfrom the surrowxIings.
~43
Condenser
Heat transfer to water.. meCP<r, - ,.>. 7.0 X 10-J X 4180(49.8 - 16.4) W=mw
Heat transfer from HFCl34a. Q,,-s= m,(~ - h,). 5-')( 10-'(3-'8 - 163) )( 10' W= 1012 W
(A disa"epancy of 7S W)
Compressor
Heat lransfer to water.- '",Cp(I, - I,). 7.0 x 10-' x 41~16.4 - 13.0) 1f= 99.5 1f
~: Tbjs is ackted to die 977W above and contl'iootes to die useful output of die beat pump.)
Heal transfer from HFCI34a.
(J,,-2 : m,(hz - h., + W. 5.5 x 10-'(358 - 298) x 10' + (-470). -140 W
The mscrer-.ncy (40.5 W) may be accounted for by die heat loss from the ~g of die co~.
For the CYCleFrom me First Law of Themto<iynamics. in a cycle die Net ~t Transfer = Net Wcxk Transfer.
The calculated Heat Transfers (to or from the Rl34a) are:
In the evapaarDrIn the condenserIn the compessor
+742 W-1072 W
-~W
-
Net Heat Transfer - 470 W.This is exactly equal to the net work (EJectrical input) ttansfer at the com)X'essor.
Similar energy balances may be produced for other operanng conditions.
~n die air source is in ~. it is not possible to evaluate the heat transfer from the air since its massnow rate is unknown.
.
44
un. TON AIR AND WATER REA T PUMP
OBSERV A nONS Date:
1.05 Bar = IOS kN m-1 AilWater(delete)
Heat Source:Aunospbcric preaure:
21OCAtmospheric IcmpCl'aQJIe:
T- 1 2 L!- . l.-.:!.-. ,Electrical iJlpUt to
~i'JectrIcai W/Waua 470
m,/g .-1 So!MMlfJDwrale
~1«1ucd0DPIJIe~
" I kN mol ~ - -
COnIpI-eIICX'~"'a~ paI1Da
PI! kN m,z 2.13
COIKIeMer pup
p'a8...PI I kN moZ 11~
~ abldU1DpaIaIe
PJ/ kN m.a 12858FC134a
COI11R8IQrIucQOll
~ ,,/8(;: -1.4
I
Con.-t'IIOI'delivery~ ../8(: .0
~
CoIMienlod liqmd
aJ~'s/-C 44.8
EvaporalOr inlet
~ ../-C -4.2
dIc II .-1M8IIf»w,.. 7,0W8ter
C o~ CooIlDI 1D1et~ r,J8C 13.0
I ~ ~Oudet ~ r.rc 16.4
dIo liS-aM8II&w~ ~~
, J I JWater
CODde.-erC.IDI
,.rc1D1et~I 4
CoIIdeDIer outlet...~.am~ "lac 49.8
Ib./l so! 11.5MUI&w18kWaterSource
Ey8pontor
t "
lD1Ct~ c./-C 13.0I t
'a/8C -1.2Oudet ~
46
6. ESnMA'DON OF VOLUMETRIC EFFICIENCY OF THE COMPRESSOR AT A RANGEOF PR~SURE RA11OS.
Procedure1. Turn on die water supply to die unit and wm on die main switch.
2. Select either the air or water evaporatm- using the evaporator selector switch.
3. Adjust the condenser cooling warer flow rare to maximum and if using the water source evaporatoreosme an ~uate water flow rare to prevent freezing.
4. Allow the unit time for all of die system parameters to reach a stable condition, dlen Iecord thepammctcrs shown below.
S. Reduce the condenser cooling water flow rate so that die condenser pressure (pJ increases byapproximately 100 kN m-1. Allow die unit time to stabilise and dlen repeat the observations.
6, Repeat in increments of approximately 100 kN m-1 until the pressure reaches approximately 1400kN m-1,
Observations
Abnospheric temperawre:
Abnospberic pressure P.21OC= 1.05 Bar = 105 kN m-2
Tea 1 2 3 54 6
Mass flow rare dI, II s'\ S.9 6.2 6.6 7.1 7.3 7.4
COlJ¥r4a«~aaucCpellure
PI I kN m.a 140 tSS 170 200 210 22S
~sor SucttODabsolute ~~ PI I kN m-l 245 260 27S ]OS 315 330
Specific V ciunz atCon.-essor SucUon v/rD'kg o.~l 0.085 0.080 0.071 0.068 0.065
CalculatedData
VolumcaicEfficiency
76.7 15.5 75.4 72.0 70.9 68.711.
Plalme lad.o 2.63 2.78 2.93 3.29 3.67 4.26
CalculationsSee test No 3 aoove
Compressor suction prCS8me Pi = 275 kN m-1
Compressor delivery pressure P1 = 80s kN m-1
t 47
PJ- -
PIms--275
- 2.93
Compressor P'CSSUte ratio. r,
Stale JX)int 1 may be plotted on the p-h diagram at PI and 1s and it is found d18t:
VI = ~m] kg"1
The volume flow rate at compressor suction.
VI = mr x VI
= 6.6 X 10-J x O.<*> ~J oS-I
= 5.28 X 10'" ~J ,-1
The C(XD~ swept volwne rate (asswning d1at it nms 812800 rev.min-I),
- ~ x 15 x 10" .' .1-1S)
= 7 X 10'" .' .1-1
Yola-.. flow ,. (at InID8 ~).Compr~r ~ WJlIIMe
- 5.28 ~ lO~Volumeuic Efficiency,
-7 x 10'"
- 7~.4"
A typical gmph showing the effect of pressure ratio on volurnebic efficiency is given 00 Page 49.
CommentsThe volumeUic efficiency of a compressor is a f1D1ction of:
{i} The pressme ra1io{ii} The clearance volwne ratio(iiI) The ilKlex of dte ex~oo process{iv} The pressme drq> due to resistances in the intake system{v} The temJx;ranJre rise in d1e intake system{vi} The mechanjcal condition of the valves and pisUXl seals
Considering (i), (ii) and (ill) only, it can be shown that the volwnebic efficiency,
- 1 - y~r(~)~ -Y.llpl
where ~ = Clearance VolumeV, Swept Volume
and n is die index of expansion.
In small CCII.lpressm y., is usually about 0.05 and n may be taken as 1.05.
¥.
.48
Substi!1l~n-! to' r, - 2.93 in this example we get1
11,. . 1 - 0.05[(2.93) i:m= 91.1S
- 1]
This COIDIXia-es widt an .:Wal ~timated volumeaic effici~y of 75.4'11.
The disaeJ8DCY is ~ to die 8ssuIDptjons made, insttument em:. and factors (iv) and (VI).
so ,TRANSFER COEFFICIENTS IN THE7. ~110N OF OVERALL HEAT
EV AroRA TOR AND CONDENSER.
Procedure and Observadoos as for S. Energy BaJances. Page 42.
CalcuJatioas - Follow the same procedure as outlined for S. Ena1Y Balances. Pages 42 10 45.
Evaporator t5-13 oa(Water
t4.-4~.-: M--'l4-c.-~I - - - - - 1- --."
te--12-C iI
i.!
Figure 15
The ~urtlJX)sition for die water and HFCl34a will be awroximalely as shown above. Howeverthe point P 81 which d1e evaporation phase change at constant remperabJre and supcrbeating beginscannot be !~&~. Therefcxe the best that can be achieved is to estimate as follows.
By refming to the p-h diagram Figure 13, Page 4S and Figure 16. we ~ that during the ~~ 4-1,the following propation of beat is transferred during comtant temperature evaporation.
296 - 163 = 98.5S- - 163
The beat transfer ra1e dming CvaJ)(nbon.. m,(A, - A.>. 5.5 x . -'(296 - 163) x 10'= 732W
From d1e proportion of heat transferred during constant temperablre evaporation,
The tan~ of die ~ at point p = 13 - (O.O1S~) x (13 - (-1.2» OC= 12.8OC-
51
Figure 16
Thus die logaridtmic mean remperanue difference dming evaporation
A-8e "2 1
. .,~(-1.2 - (-4.2) - (12.8 - (-1.4»
iii (-1.2 - (-4.2»)\ (12.8 - (-1.4»
3 - 14.2
~Ih)-11.2---1..55
- 7 :J11K
H we assume dw die phase change takes place in 98.5% of the ev8JX)raror length, the area involvedwill be 0.985 x 0.14 = 0.138 m2.
The Estimated Ovelall Heat Transfer Coefficient during ev8JX)ration can now be detennined.
U=-2-A 8.
- -.E3- --0.14 x 72717.3 W,,2 r-1
Note mat me evapa'atOr is a plate type heat exchanger which has a very high heat transfer area tovolume ratio. Thelef<Xe in physjcal tenDS the heat exchanger can be very small but due to its highsurface area and overall heat transfer coefficient can transfer a large amount of energy.
52
CoDdeaser
Condenser ! t7-49.8°CT Water
t3-44.80('
.-: t2.80.~I
t1 ! ~-T5- ~,~ -!~"
i :. I. .
t6-16 ,-c. ! iI ', I, .I '. Ii :, I
t,-C ~ ! :
I: HFCma
80.0
49.8
'36'93
448
17.7
16.4
Water
Figure 17
Figure 18
(In me coIkIenser me p'eSSIUe is approximately 1285 kN m-2 and the saturation temperature at thispressme is 49.3OC. Hence the pb&1C change fron vapom to liquid will take p~ at this tempelabJre.)
The tempembJre disttibution in die coodenser will be approximately as in FiIUle 17. Using much thesame pnx:ed1D'e as for die evaporator, it is found that.. = 17.7OC aJx1 1. = 43.6OC.
The Heat Tramfer during the phase change (refer to Figure 18),. mrCh. - II,). 5.5 x 10-'(325 - I'M) x 10' W=825W
Assuming d181 d1is takes pl.lK:e in 79.5 % of die tOIal aJa..
U.--2-A 8.
825.0.0696 )( 15.1785 W ..-2 K-1
CommentsAlthough a number of a.uumptions have been mOOc in these calculations. me values of U are ~Jefor cva}X)ralion and CO!!.d-.~lion in clean water-cooled beat excbang~.
S4
1m. TON AIR AND WATER MEAT PUMP
OBSERV AnONS Dare:
kNmo1 Heat Source: AirWater(delete)
Aboospberic pressure:
Aunospbcric tcmperacme: oc5 ,T8 J 2 s 4
Electrical iDPUt ~
~--EI«.1ricai W/Waas
"/1'-'Mus&wrak
~ aucdoo~peuare
PI ItN m~
I f
CCXJ¥eUOrlucbODa8i_p8Ime
PI I kN m-3.
COIKieDIer aUF
JRU~PJ/kNr
CmKicDler ablciute
paImePI! kN m-ZBFC134a
I~ aueCon~ ../-C
Con.,reIIcx' delivery~ ,,/-C
..
COIMieIlled liquid
~8blle../-C
EvlpOI'IfOr inlet
~ ../-C
IMaat1ow~ d'o I g ,-I
WaterCO~resIor
CocilDl
IDler temperabR r,/-C
..rcOudet~I I
d\ IS S.IMusOow~Water
CoademerCoQlal
lnletlempcl'abm ~rcCOIxIeDIeroadct
~.,/8C
"/11"MasstmwraleWaterSource
Ev~r,/8C1n1et=npcran=
,,/8(:Oodet ~
ssHILTON AIR AND WATER HEAT PUMP- - --
DERIVED RESULTS Date:
Ref:
1 2 3 4 5 ,Cc ~ Power Input W/Waus
hI I kJ q"11R'134a Propa1ies
b, I kJ q.1
h, = ~ I kJ q.1
VI ,m' q.1
Ev8pOr8tiOD T~ Ct/-C
('~-!at!.CX1 Te~ ..atp,/OC
Heat TJanIfer in EV81XDt«
To HFC134a = d1r(ht . h.)
Plan Waa = dIo x 4.18(is - r.)
0 / w
Q./W
Heat Transfer in Condenser
~ ID"Cl34a . ~ - b,) Q.,.z/W
Q./WTo Waa . dI., x 418CXt, - r.>
~-a I W
o-/W
HC81 TlanSfer in Commessa-
~-h'>-W
To Waa (in w cooler)= d1c x 4.18(.. - t,)
Total Heat Dcliv~ to Wiler
To W~ = d1; x 4.18(t, - r,) ~/W
Ovn1 CoPs . ,Qpw
~/m'1COIJIIKCIIorluclionvolumeflow rate VI = dI, VI
Swept YoI~ tale "(At SOHz). IS x If16 x~
60
V./m's
v ol~c efficielM:y .y..V.
11'"
~ ~ ratio= p.absolute
P.abIolute
r.
n 0 I :i ... ~ GO
m ~ ~
0 . I 9- i i ! ~ .- "' .... (' 0 a -c .i ~ !. Q C"I
