*NBS-M016 Contemporary Issues in Climate Change and Energy 2010 Introduction to Thermodynamics Combined Cycle Gas Turbines Combined Heat and Power Heat Pumps*Lecture 1Lecture 2Lecture 3

*10. Elementary Thermodynamics - History.Newcomen Enginepushes piston up 3) At end of stroke, close steam value open injection valve(and pumping rod down)4) Water sprays in condenses steam in cylinder creating a vacuum and sucks piston down - and pumping rod up2) Open steam valve1) Boil Water > SteamProblem:Cylinder continually is cooled and heated.*

*10. Elementary Thermodynamics - Watt Engine.Watt Engine1) Cylinder is always warm2) cold water is injected into condenser3) vacuum is maintained in condenser so suck out exhaust steam.4) steam pushes piston down pulling up pumping rod.Higher pressure steam used in pumping part of cycle.*

*10. Elementary Thermodynamics. Thermodynamics is a subject involving logical reasoning.Much of it was developed by intuitive reasoning.

1825 - 2nd Law of Thermodynamics - Carnot 1849 - 1st Law of Thermodynamics - Joule Zeroth Law - more fundamental - a statement about measurement of temperature Third Law - of limited relevance for this Course*

*10. Elementary Thermodynamics.Carnots reasoningWater at top has potential energyWater at bottom has lost potential energy but gained kinetic energy*

*10. Elementary Thermodynamics.Carnots reasoningWater looses potential energy

Part converted into rotational energy of wheelPotential Energy = mgh Theoretical Energy Available = m g (H1 - H2) Practically we can achieve 85 - 90% of this*

*10. Elementary Thermodynamics.Carnots reasoningTemperature was analogous to Head of Water Energy Temperature Difference Energy (T1 - T2) T1 is inlet temperature T2 is outlet temperature Just as amount of water flowing in = water flowing out. Heat flowing in = heat flowing out. In this respect Carnot was wrong However, in his day the difference was < 1%*

*10. Elementary Thermodynamics.Joule 1849 Identified that Lost Heat = energy out as Work Use a paddle wheel to stir water - the water will heat up Mechanical Equivalent of HeatBerlin DemonstrationSymbolsW - work Q - heatOver a complete cycleQ = W Heat in +ve Heat out -veWork in -ve Work out +ve FIRST LAW: You cant get something for nothing*

*10. Elementary Thermodynamics.Heat EngineFirst Law:W = Q1 - Q2so efficiency

But Carnot saw thatHeat Temperature What do we mean by temperature? Which should we use?Kelvin?Rankine,Reamur,Fahrenheit,Celcius,*

*10. Elementary Thermodynamics.Is this a sensible definition of efficiency?If T1 = 527oC ( = 527 + 273 = 800K)and T2 = 27oC ( = 300K)Note: This is a theoretical MAXIMUM efficiency*

*10. Elementary Thermodynamics.Second Law is more restrictive than FirstIt is impossible to construct a device operating in a cycle which exchanges heat with a SINGLE reservoir and does an equal amount of work on the surroundsThis means Heat must always be rejectedSecond Law cannot be proved - fail to disprove the LawIf heat is rejected at 87oC (360K)By keeping T2 at a potentially useful temperature, efficiency has fallen from 62.5%*

*10. Elementary Thermodynamics.The Practical efficiency will always be less than the Theoretical Carnot Efficiency.

To obtain the "real" efficiency we define the term Isentropic Efficiency as follows:- Thus "real" efficiency = carnot x isen

Typical values of isen are in range 75 - 80%

Hence in a normal turbine, actual efficiency = 48%

A power station involves several energy conversions. The overall efficiency is obtained from the product of the efficiencies of the respective stages.*

*10. Elementary Thermodynamics.

EXAMPLE:

In a large coal fired power station like DRAX (4000MW), the steam inlet temperature is 566oC and the exhaust temperature to the condenser is around 30oC.

The combustion efficiency is around 90%, while the generator efficiency is 95% and the isentropic efficiency is 75%.

If 6% of the electricity generated is used on the station itself, and transmission losses amount to 5% and the primary energy ratio is 1.02, how much primary energy must be extracted to deliver 1 unit of electricity to the consumer? *

*10. Elementary Thermodynamics.

(566 + 273) - (30 + 273) Carnot efficiency = ------------------------------ = 63.9% 566 + 273

so overall efficiency in power station:-

= 0.9 x | combustion loss 0.639 x | Carnot efficiency 0.75 x | Isentropic efficiency 0.95 x | Generator efficiency 0.94 | Station use = 0.385*

*10. Elementary Thermodynamics.Transmission Loss ~ 91.5% efficient

Primary Energy Ratio for Coal ~ 1.02

Overall efficiency 1 x 0.385 x 0.915 = -------------------------- = 0.345 units of delivered energy 1.02i.e. 1 / 0.345 = 2.90 units of primary energy are needed to deliver 1 unit of electricity.

*

*10. Elementary Thermodynamics.How can we improve Carnot Efficiency?

Increase T1 or decrease T2

If T2 ~ 0 the efficiency approaches 100%

T2 cannot be lower than around 0 - 30oC i.e. 273 - 300 K

T1 can be increased, but properties of steam limit maximum temperature to around 600oC, (873K)

We can improve matters by the use of combined cycle gas turbine stations CCGTs.

*

*10. Elementary Thermodynamics.In this part of the lecture we shall explore ways to improve efficiency

Most require us to ensure we work with thermodynamics rather than against it

The most important equation:

*11. Applications of Thermodynamics. Other modes of Electricity Generation: Open Circuit Gas turbinescEfficiency is low - exhaust temperature is high --- (T1 - T2)/T1 - similar to an aircraft engine*

*Practical Efficiencies:-Gas Turbine alone20 - 25%Steam Turbine alone35 - 38%CCGT 47 - 52%Combined Cycle Gas Turbine11. Applications of Thermodynamics. Combined Cycle Gas Turbines*

**ElectricityElectricity11. Applications of Thermodynamics. Combined Cycle Gas Turbines: Multiple Shaft ExampleGas turbineT1 = 950oC = 1223 KT2 = 500oC = 823K

Isentropic efficiency ~ 80%Steam turbineT1 = 500oC = 773 KT2 = 30oC = 303K

Output from Gas Turbine: 0.23 units of power to generator and 0.77 units to WHB Generator is ~ 95% efficient so output ~ 0.22 units Waste Heat boiler is ~ 80% efficient so there will be ~ 0.15 units lost with 0.8*0.77=0.62 units effective for raising steam. Shaft power from Steam turbine = 0.62 * 0.486 = 0.30 units with 0.32 units to condenser Total electrical output = 0.22 + 0.28 = 0.50units of which 0.03 units are used on station Overall efficiency = 47%

*Early CCGTs had multiple shafts with separate generators attached to gas turbinesSome had two or more gas turbines providing heat to waste heat boilers which powered a single steam turbineModern CCGTs tend to have a common shaft with a gas turbine and steam turbine turning a single generator.

Advantages of single shaft machines: tend to have lower capital costTend to have higher overall efficiencies up to 55/56% - e.g. Great YarmouthDisavantages:No option to run gas turbine by itself Gas Turbines can reach full output in a matter of minutes.Steam turbines take 12 hours or more

Gas Turbines tend to have higher NOx emissions and special provision is needed to reduce these levels e.g. injecting steam into gas turbine.

11. Applications of Thermodynamics. Combined Cycle Gas Turbines:

*Heat is normally rejected at ~ 30oCToo low a temperature for useful space heating

Reject heat at 100oC

i.e. Less electricity is generated, but heat is now usefulTypically there are boiler and other losses before steam is raisedAssume only 80% of energy available in coal is available.And technical (isentropic efficiency) is 75%Then for 1 unit of coal - electricity generated case 1 = 0.8*0.75*0.639 = 0.38 units case 2 = 0.8*0.75*0.555 = 0.33 units + up to 0.47 units of heat or up to 0.8 units in total. Typically 10% of heat is lost so 0.73 units available

12. Applications of Thermodynamics. Combined Heat and Power (2)

*The first Law of Thermodynamics states that we can neither create or destroy energy ie Work out = Heat in Heat Out Second Law states we must always reject Heat and efficiency = If we could utilise all of rejected heat

The 1947 Act stated Electricity must be generated as efficiently as possible i.e. Work/Electricity (not energy) was King

12. Applications of Thermodynamics. Combined Heat and Power (1)

*12. Applications of Thermodynamics. Combined Heat and Power (3)Back Pressure Steam TurbineITOC or Pass out Steam TurbineTo District Heat Main ~ 90oCNormal CondenserBoilerHeat ExchangerGas Turbine with CHP also Diesel/gas engine with CHPProblem:For most CHP plant, electrical output will be limited if there is no requirement for heat.

ITOC provides greater flexibility

*12. Applications of Thermodynamics. Combined Heat and Power (4)ProcessIntegrated Electricity Generation, Process Heat, Space Heat and Air compression at ICI Wallerscote Plant in late 1970s

*GeneratorGeneratorSteam TurbineGas TurbineFuel in 239 MWGT Temp 1127oC 12. Applications of Thermodynamics. CCGT with CHP (1)Heat Lost 24 MWUseful Heat 98 MWElectricity 55 MWElectricity 62 MW

*9. Applications of Thermodynamics.Combined Heat and Power

*12. Applications of Thermodynamics. Example of Small Scale Scheme (4)In most cases, CHP plant is based on an approximate summer time heat load with supplementary heating provided by normal boilers in coldest months of year

Chart1

84009200

84006600

84002100

7500April

5500May

4000June

4000July

4000Aug

6500Sep

8400100

84002100

84007000

Heat from CHP

Supplementary Heat

kW

Heat Supply

Sheet1

MonthTemp.Space Heat Demand (kW)Total Heat Demand (kW)Electricity (kW)CHP Heat available (kw)Useful CHP Heat (kW)Supplementary Heat Needed (kW)actual electricity that can be generatedSupplementary Electricity Needed

[1][2][3][4][5][6][7][8] = [4] [7][9][10]

Heat from CHPHeat from CHPSupplementary Heat

Jan1.91360017600780084008400920060001800

Feb4.51100015000720084008400660060001200

Mar965001050068008400840021006000800

April12350075006250840075005357***893

May14150055005800812055003929***1871

June16040005200728040002857***2343

July17040004800672040002857***1943

Aug16040004800672040002857***1943

Sep13250065005200728065004643***557

Oct11450085006200840084001006000200

Nov965001050068008400840021006000800

Dec4.11140015400780084008400700060001800

GWhGWhGWhGWhGWhGWhGWh

TOTALS78.4853.7568.3458.9719.5142.1211.63

Imported ElectricityCHP electricity

Jan18006000

Feb12006000

Mar8006000

April8935357

May18713929

June23432857

July19432857

Aug19432857

Sep5574643

Oct2006000

Nov8006000

Dec18006000

Sheet1

00

00

00

00

00

00

00

00

00

00

00

00

Heat from CHP

Supplementary Heat

kW

Sheet2

00

00

00

00

00

00

00

00

00

00

00

00

Imported Electricity

CHP electricity

kW

Sheet3

* Electricity generation in summer is restricted and import is highest when demand is least12. Applications of Thermodynamics. Example of Small Scale Scheme (5)

Chart2

18006000

12006000

8006000

8935357

18713929

23432857

19432857

19432857

5574643

2006000

8006000

18006000

Imported Electricity

CHP electricity

kW

Electricity Supply

Sheet1

MonthTemp.Space Heat Demand (kW)Total Heat Demand (kW)Electricity (kW)CHP Heat available (kw)Useful CHP Heat (kW)Supplementary Heat Needed (kW)actual electricity that can be generatedSupplementary Electricity Needed

[1][2][3][4][5][6][7][8] = [4] [7][9][10]

Heat from CHPHeat from CHPSupplementary Heat

Jan1.91360017600780084008400920060001800

Feb4.51100015000720084008400660060001200

Mar965001050068008400840021006000800

April12350075006250840075005357***893

May14150055005800812055003929***1871

June16040005200728040002857***2343

July17040004800672040002857***1943

Aug16040004800672040002857***1943

Sep13250065005200728065004643***557

Oct11450085006200840084001006000200

Nov965001050068008400840021006000800

Dec4.11140015400780084008400700060001800

GWhGWhGWhGWhGWhGWhGWh

TOTALS78.4853.7568.3458.9719.5142.1211.63

Imported ElectricityCHP electricity

Jan18006000

Feb12006000

Mar8006000

April8935357

May18713929

June23432857

July19432857

Aug19432857

Sep5574643

Oct2006000

Nov8006000

Dec18006000

Sheet1

00

00

00

00

00

00

00

00

00

00

00

00

Heat from CHP

Supplementary Heat

kW

Sheet2

Imported Electricity

CHP electricity

kW

Sheet3

*12. Applications of Thermodynamics. Example of Small Scale CHP Scheme 6000 kWe (1)Hot water and process heat demand is constant over the year at 4000 kWHeat loss rate for buildings is 1000 kW oC-1Existing Heating provided by gas (80% efficiency).Mean space heat demand in January= (15.5 1.9) * 1000 = 13 600 kWThis is the balance temperature we shall discuss this in 2 weeks time. In such schemes approximately 1.4 kW heat is rejected for every 1 kW electricity generated. In this case 8400kW

MonthMean Temperature (oC)mean Electricity Demand (kW)11.9780024.57200396800412625051458006165200717480081648009135200101162001196800124.17800

*

Column [4] values

= col[3] + 4000

The 4000 is hot water and process heat requirement.

Column 3 values

= (15.5 col [2])* 1000

15.5oC is the balance or neutral temperature at which no heating is required. Incidental gains from appliance heat and body heat increase temperature to comfort level.

Column [5] is electricity demand from Previous SheetColumn [6] indicates the potential amount of heat which would be available. Typically it is around 1.4 times the electricity generation so Col [6] = 1.4 * col [5] subject to a maximum electricity generation of 6000 kWi.e. when electrical demand > 6000kW, only 6000 * 1.4 = 8400 kW will be available for heat.

Col [7] is actual amount of heat that can be usefully used. i.e if col [6] is greater than demand then the useful amount = demand

Maximum Electricity generation = 6000 kW electrical 8400kW heat12. Applications of Thermodynamics. Example of Small Scale Scheme (2)

MonthTemp(oC)Space Heat Demand (kW)Total Heat Demand (kW)Electricity(kW)CHP Heat available (kW)Useful CHP Heat (kW)[1][2][3][4][5][6][7]Jan1.91360017600780084008400Feb4.51100015000720084008400Mar9650010500680084008400Apr1235007500625084007500May1415005500580081205500June1604000520072804000July1704000480067204000Aug1604000480067204000Sep1325006500520072806500Oct1145008500620084008400Nov9650010500680084008400Dec4.11140015400780084008400

*

Column [8] is supplementary heat required from back up boilers

Col [8] = col [4] col [7]

Column [9] is actual electricity that can be generated.If the heat demand is greater than 8400, then units can be run at full output i.e. 6000 kW.If heat requirement is less than 8400kW, then output of generators will be restricted to a maximum ofCol [7] / 1.4

The totals represent the total amount of heat or electricity generated or required over the year. Using 30 day months the totals in each column will be: mean values * 24 * 30

Column [10] is additional electricity needed.Note: highest import occurs when electricity demand is least.

12. Applications of Thermodynamics. Example of Small Scale Scheme (3)

MonthTotal Heat Demand (kW)Electricity (kW)Useful CHP Heat (kW)Supple-mentary Heat (kW)actual electricity generatedSupplementary Electricity Needed[1][4][5][7][8][9][10]Jan1760078008400920060001800Feb1500072008400660060001200Mar105006800840021006000800April7500625075005357***893May5500580055003929***1871June4000520040002857***2343July4000480040002857***1943Aug4000480040002857***1943Sep6500520065004643***557Oct8500620084001006000200Nov105006800840021006000800Dec1540078008400700060001800GWhGWhGWhGWhGWhGWhTOTAL78.4853.7558.9719.5142.1211.63

Keith Tovey

*12. Applications of Thermodynamics. Example of Small Scale Scheme (4)In most cases, CHP plant is based on an approximate summer time heat load with supplementary heating provided by normal boilers in coldest months of year

Chart1

84009200

84006600

84002100

7500April

5500May

4000June

4000July

4000Aug

6500Sep

8400100

84002100

84007000

Heat from CHP

Supplementary Heat

kW

Heat Supply

Sheet1

MonthTemp.Space Heat Demand (kW)Total Heat Demand (kW)Electricity (kW)CHP Heat available (kw)Useful CHP Heat (kW)Supplementary Heat Needed (kW)actual electricity that can be generatedSupplementary Electricity Needed

[1][2][3][4][5][6][7][8] = [4] [7][9][10]

Heat from CHPHeat from CHPSupplementary Heat

Jan1.91360017600780084008400920060001800

Feb4.51100015000720084008400660060001200

Mar965001050068008400840021006000800

April12350075006250840075005357***893

May14150055005800812055003929***1871

June16040005200728040002857***2343

July17040004800672040002857***1943

Aug16040004800672040002857***1943

Sep13250065005200728065004643***557

Oct11450085006200840084001006000200

Nov965001050068008400840021006000800

Dec4.11140015400780084008400700060001800

GWhGWhGWhGWhGWhGWhGWh

TOTALS78.4853.7568.3458.9719.5142.1211.63

Imported ElectricityCHP electricity

Jan18006000

Feb12006000

Mar8006000

April8935357

May18713929

June23432857

July19432857

Aug19432857

Sep5574643

Oct2006000

Nov8006000

Dec18006000

Sheet1

00

00

00

00

00

00

00

00

00

00

00

00

Heat from CHP

Supplementary Heat

kW

Sheet2

00

00

00

00

00

00

00

00

00

00

00

00

Imported Electricity

CHP electricity

kW

Sheet3

* Electricity generation in summer is restricted and import is highest when demand is least12. Applications of Thermodynamics. Example of Small Scale Scheme (5)

Chart2

18006000

12006000

8006000

8935357

18713929

23432857

19432857

19432857

5574643

2006000

8006000

18006000

Imported Electricity

CHP electricity

kW

Electricity Supply

Sheet1

MonthTemp.Space Heat Demand (kW)Total Heat Demand (kW)Electricity (kW)CHP Heat available (kw)Useful CHP Heat (kW)Supplementary Heat Needed (kW)actual electricity that can be generatedSupplementary Electricity Needed

[1][2][3][4][5][6][7][8] = [4] [7][9][10]

Heat from CHPHeat from CHPSupplementary Heat

Jan1.91360017600780084008400920060001800

Feb4.51100015000720084008400660060001200

Mar965001050068008400840021006000800

April12350075006250840075005357***893

May14150055005800812055003929***1871

June16040005200728040002857***2343

July17040004800672040002857***1943

Aug16040004800672040002857***1943

Sep13250065005200728065004643***557

Oct11450085006200840084001006000200

Nov965001050068008400840021006000800

Dec4.11140015400780084008400700060001800

GWhGWhGWhGWhGWhGWhGWh

TOTALS78.4853.7568.3458.9719.5142.1211.63

Imported ElectricityCHP electricity

Jan18006000

Feb12006000

Mar8006000

April8935357

May18713929

June23432857

July19432857

Aug19432857

Sep5574643

Oct2006000

Nov8006000

Dec18006000

Sheet1

00

00

00

00

00

00

00

00

00

00

00

00

Heat from CHP

Supplementary Heat

kW

Sheet2

Imported Electricity

CHP electricity

kW

Sheet3

*Electricity Out Irrecoverable Losses Useful Heat12. Applications of Thermodynamics. CCGT with CHP (1) large scale

*Gas turbine efficiency Electricity generated: 0.25 * 0.95 = 0.2375 0.25 0.750.125Irrecoverable Losses12. Applications of Thermodynamics. CCGT with CHP (2) large scaleEnergy to Steam Turbine= 0.75 0.125 = 0.6250.625

TemperatureTemperature (K)Inlet temperature to gas turbine1127 oC1400Exhaust temperature from gas turbine660 oC933Combustion Losses from stack, generator and WHB12.50%Note Error in Isentropic efficiency of both turbines75.0%HandoutGenerator efficiencies95.0%

*12. Applications of Thermodynamics. CCGT with CHP (3) large scale steam turbine efficiency Mechanical power to generator = 0.425 * 0.625 = 0.2656Heat to Condenser = 0.625 0.2656 = 0.3594Electricity out = 0.95 * 0.2656 = 0.25230.3594

TemperatureTemperature (K)Inlet temperature to steam turbine577 oC850Condenser temperature95 oC368

*12. Applications of Thermodynamics. CCGT with CHP (4) large scaleStation use of electricity= (0.2375 + 0.25230) * 0.04 = 0.196Useful Heat = 0.3594 * (1 0.152) = 0.3048

Station use of electricity4.0%Distribution losses on heating mains15.2%

*Summary of SchemeFor each unit of fuelElectricity available = 0.470 unitsHeat sent out = 0.3594 unitsStation efficiency = 0.470 + 0.3594 = 82.9%But heat is lost form mains so only 0.3048 is actually usefulOverall system efficiency = 0.47 + 0.3048 = 77.5% 12. Applications of Thermodynamics. CCGT with CHP (5)

*NBS-M016 Contemporary Issues in Climate Change and Energy201013. Heat Recovery : Heat Pumps*

*Parallel Plate Heat Exchanger13. Heat Recovery Systems and Heat Pumps Cold Fluid InHot Fluid In

*Parallel Flow Shell and Tube Exchanger

Inefficient: maximum temperature achieved is ~ 50% of temperature difference13. Heat Recovery Systems and Heat Pumps Cold Fluid InHot Fluid InDistanceHot FluidCold FluidTemperature

*Contra Flow Shell and Tube Exchanger

Inefficient: maximum temperature achieved is ~ 50% of temperature difference13. Heat Recovery Systems and Heat Pumps Hot Fluid InDistanceHot FluidCold FluidTemperatureCold Fluid In

*Operation of Regenerative Heat ExchangersABBAStale air passes through Exchanger A and heats it up before exhausting to atmosphereFresh Air is heated by exchanger B before going into buildingStale air passes through Exchanger B and heats it up before exhausting to atmosphereFresh Air is heated by exchanger A before going into buildingAfter ~ 90 seconds the flaps switch over

*13. Applications of Thermodynamics.Heat PumpsSchematic Representation of a Heat Pump. IT IS NOT A REVERSED REFRIGERATOR.Heat PumpHeat Out Q1A Heat Pump is a reversed Heat Engine: NOT a reversed RefrigeratorIf T1 = 323K (50oC)and T2 = 273K (0oC)

**Responding to the Challenge: Technical SolutionsThe Heat PumpAny low grade source of heat may be used Typically coils buried in garden Bore holes Example of roof solar panel (Look East: Tuesday)A heat pump delivers 3, 4, or even 5 times as much heat as electricity put in. We are working with thermodynamics not against it.

*13. Applications of Thermodynamics.Heat PumpsPerformance is measured by Coefficient of Performance (COP)Theoretical Performance of 6.46Practical COP in excess of 3.i.e. Three times as much heat is obtained as work put in.Remaining heat comes from the environmentThe closer the temperature difference, the better the COPCan be used for efficient heat recovery Can recover the energy lost in electricity generation Will out perform even a gas condensing boilerWorking with Thermodynamics - NOT against it

*13. Applications of Thermodynamics.A heat pump refrigerator consists of four parts:-Heat Pumps and Refrigerators1)an evaporator (operating under low pressure and temperature)3)a condenser (operating under high pressure and temperature)4)a throttle value to reduce the pressure from high to low.2)a compressor to raise the pressure of the working fluid

*The Norwich Heat PumpOriginal Paper by John Sumner Proc. Institution of Mechanical Engineers (1947): Vol 156 p 338

*The History of the SiteThe building was unique - the very first heat pump in the UK.Installed during in early 1940s during the War.Built from individual components which were not ideal.Compressor was second hand built in early 1920s ! for Ice making.The evaporator and condenser had to be built specifically on site.Refrigerant choice was limited during War - only sulphur dioxide was possible.A COP of 3.45 was obtained - as measured over 2 years.Even in 1940s, the heat pump was shown to perform as well as, if not better than older coal fired boiler.

*The History of the SiteThe Norwich Heat Pump - note the shape of the columns

*The Norwich Heat PumpSchematic of the Norwich Heat Pump- from John Sumners Book - Heat Pumps

*The Norwich Heat Pump

*13.6 Types of Heat Pump For Space Heating Purposes: The heat source with water and the ground will involve laying coils of pipes in the relevant medium passing water, with anti-freeze to the heat exchanger. In air-source heat pumps, air can be passed directly through the heat exchanger.For Process Heat Schemes: the source may be a heat exchanger in the effluent of one process

Heat Sourceairwaterground

HeatSinkairair to airwater to airground to airwaterair to waterwater to waterground to watersolidair to solidwater to solidground to solid

*Some Examples13.6 Types of Heat Pump

Air to air:- Refrigeration vehicles, many simple heat pumps, most air-conditioning plants.Air to water:-Proposed UEA scheme in 1981Air to solid? May be relevant in a case where heat recovery from exhaust air is recovered - ?? A variant of ZICER - possible use in Academic Building East??Water to air Ditchingham Primary SchoolWater to waterNorwich Electricity Board Heat Pump during War; Royal Festival Hall. Southampton Geothermal Scheme.Water to solidProposed Duke Street Refurbishmentground to air? A scheme with cooling in summer and heating in winter with inter-seasonal heat storageground to waterENV demonstration scheme. No longer availableground to solidJohn Sumner's Bungalow: Now the preferred route for heat pumps except where water source is available

*

Readily Available Noise on external fansSource temperature low when most heat needed: hence performance inferior at times of greatest needSource temperature varies greatly:- hence cannot optimise design

not readily available

capital cost is great if retro-fitted source temperature normally higher than air or ground in winter: hence improved COP source temperature nearly constant: hence design can be optimised reasonable availabilitymoderate source temperature - better than air, worse than water moderate variation in source temperature: some optimisation possible 13. Heat Pumps: Heat Sources Air WaterGroundAdvantages Disadvantages

*relatively low temperature: hence good COPpossibility of heat recovery using mechanical ventilation. Possibility of use with air-conditioning and inter-seasonal heat store if used with ground source.

can only be fitted into hot air systems: cannot be used with most current Central Heating systems in UK. higher operating temperature: hence lower COPDifficult to incorporate heat recovery Cannot be fitted retro-spectively: must be installed at time of construction. more compact: can be incorporated with existing systems in use in UK Low temperature if installed as under-floor heating. Possibility of using heat store in fabric. 13. Heat Pumps: Heat SupplyAir WaterGroundAdvantages Disadvantages

*Ground LoopCompressorWinnington Tovey Heat PumpCondenserAir HeatingStale Air

*Absorption Heat PumpThe Win - Win opportunity More electricity can be generated in summer Less electricity demand in summer More income from exported electricity13. Absorption Heat Pump.

*13. Other Types of Heat Pump Diesel or Gas driven Heat PumpAdditional Heat can be obtained from exhaust gasesOther Types of Heat Pump

*Example: Using an Air-Conditioner in a Tropical Climate. Separate consumption into components: base load for lighting appliances etc. Air-conditioning load: Gradient of line = 75 kW oC-1Base LoadCooling LoadA large hotel complex

*Gradient of line = 75 kW oC-1But coefficient of performance is say 2.5actual cooling load is 2.5 * 75 = 225 kWoC-1

What is energy consumption for cooling over a period?Degree-days are a measure of cooling (or heating) requirementsHeating and Cooling Degree-Day data are often available.CDD: Base temperature is say 20. external temperature . 30 CDD = 10 for that dayExternal temperature . 40 CDD = 20Cooling degree days is sum of CDD over relevant period.

If CDD over period is 3000 (a typical value for some tropical countries)Total demand of electricity= 75 * 3000 * 24 = 54000000 kWh = 5 400 MWhIf Carbon factor is 800 kg / MWh,Total Carbon emissions = 5400 * 800 = 4320 tonnesExample: Using an Air-Conditioner in a Tropical Climate.

*13. Applications of Thermodynamics - Conclusions.Our Wasteful Society650 m21 m273 mWe behave as though we call in the RAFThe Heat Pump is the analogy with the crane

*