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Introd

Background

The traditional model of powgeneration and distribution ibased on the central thermalpower plant feeding an electgrid consisting of high voltagtransmission lines and lowvoltage delivery networks. Ttraditional model involvesinherent overall inefficiencieThe main source of inefficiein power generation is due twaste heat that must berejected by the thermal powplant (2ndlaw ofthermodynamics). As a resulcoal-powered plants typicalldeliver only about 30% of thcontained in the fuel as elect

users. The situation is improsomewhat with combined gapower plants, which can deli50% of the fuels energy to e

CHP - Making Use of Wast

The low efficiency of convengeneration and delivery procpushed the industry to consinear-site power generation (

referred to as DG distributgeneration) with the beneficiwaste heat for heating, domwater, or other thermally-actiequipment (i.e., sorption childesiccant dehumidifiers). Thpower generation is broadlyCHP combined heat and pBasically, CHP produces botshaft power and thermal enenear site, converting as muc

the input fuel into useful eneshown on the sankey diagraright.

DATASHEET 01

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cing CHP

er

lricale

is

.

cy

r

lt,

energyricity to end

veds cyclever up tond users.

e Heat

tional poweress hasder on-site oroften

d poweral use ofstic hotvatedlers, oris method oflabelled asower.h electric orrgy onsite orh as 85% of

rgy, asto the

In its simplest form, Ccombined heat and pogeneration), which mewaste heat from the prisatisfy the heating andwater needs of buildinHowever, sometimesused to denote combinheating, and power (Cgeneration, as depictegraphic.

Benefits

If used appropriately,increases resource enreduces CO2emissionCHP systems can alsoreliability by reducing obuilding's dependencepower grid, which is esin times of natural disa

outs. However, designito operate as a standb(island-mode) is difficul

CIBSE CHP Group

P refers toer (or co-

ns using theme mover toor domestic hots or processes.HP has also beened cooling,HP), or tri-

on the next

HP significantlyrgy efficiency and.

improve powerr eliminating aon the electricpecially importantters or grid black

ng a CHP systemgenerator

t and not

FEB 2012

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common, especially for retrofitapplications.

CHP System

A CHP unit comprises the following maincomponents:

()

A number of CHP prime movers areoffered on the market:

(5 20 )

(25 500 )

(500 100

)

(50 )

(1 10 )

Depending on the prime mover, CHP

systems can be powered by a variety offuels: ( )

/

()

The prime mover and fuel is carefullyselected following a detailed feasibilitystudy and sizing process. Common

factors affecting the selection will be theelectrical and thermal load profile,temperature at which heat must begenerated, fuel availability, any CO2emission reduction requirements,footprint, maintenance regime, cost,emissions, noise, and start up time.

Applications

Several variables must be considered in

determining an optimum CHPconfiguration (if it exists at all) for aparticular building or a scheme. Theseare the building heating, cooling, andDHW demand profiles, electrical demandprofile, utility pricing and contractualarrangements, availability and pricing ofCHP fuels, possibility (and pricing) ofreselling electrical power back to the grid,and, not the least, integration withexisting services. Non-monetary aspectsof systems should also be analyzed.These include power reliability andquality, grid independence, security,maintenance, and noise issues.

The economic viability of a CHP systemdramatically improves the longer thesystem operates (typically at least 4000 5000 hours per annum) and the more ofthe engines waste heat is utilised (ideally

100%). Therefore, buildings with aconsiderable and consistent demand forthermal energy are the most appropriatefor CHP applications in order to get the

Prime

Mover

Generator

Heat

Exchangers

/

Absorption

Chillers

Grid / Capacitor

Electrical Energy

Heating

Cooling

Hot Water

Mechanical

Energy

ThermalEnergy

Fuel

Energy

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best return on investment. Typically,larger mixed-use schemes are morelikely to offer a continuous thermaldemand profile. Nevertheless, heatutilisation can be increased with enablingtechnologies such as thermal storage,absorption chillers, or desiccantdehumidifiers.

Operation

Optimal CHP systems are sized to theexpected base heat load of the buildingor scheme to ensure maximum heatutilisation and full-load operation.Historically, there have been problemswith oversized CHP systems and this

should be avoided in mostcircumstances. In some cases, CHP hasbeen used to provide additional electricalsupply capacity where the costs of anupgrade to the existing mains supply areprohibitive. This means the unit is sizedelectrically and if the thermal capacity istoo high, some of the unused heat isrejected via heat rejection radiators.

The CHP unit is connected both thermally

and electrically to the buildingstraditional infrastructure. Thermally, theCHP is connected to the boiler headerreturn and can operate either in series orin parallel with the boilers, depending onthe design of the overall system.

On the electrical side, connection iscommonly made to the LV panel,although alternatively can be donethrough the HV ring through a step up

transformer. The CHP unit can act as astandby generator but this is not commonand can be difficult to implement. In suchcase, if properly coupled with the BMS,the electricity produced can be targetedto life critical systems.

The prime mover should be capable ofmodulating its output to the generator

depending on heat demand, whilstremaining synchronised with the(distribution network) mains three phasesupply.

Financial Aspects

Compared to conventional methods ofheat and power generation, theinstallation of a CHP system does havehigher capital costs. However, life cyclecosts will be advantageous, dependingon the spark gap - the differencebetween the CHP fuel price andelectricity. CHP payback shortens withincreasing spark gap, i.e. the electricityprice is high and the gas (or other fuel)

price is low.

Depending on fuel CHP may benefit froma number of financial incentives:

CHP systems can also be installed undera supplier finance arrangement whichrequires no capital outlay from the clientor through an ESCO company as part ofoutsourcing of utilities generation.

Bibliography

Additional information can be obtainedfrom:

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2) 176

3) 234

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5) ...

This datasheet was produced by the CHP Group of the Chartered Institution of Building Services Engineers(CIBSE) to inform building professionals about all forms of CHP. To join or contact the CHP Group go towww.cibse.org/chpor contact CIBSE, 222 Balham High Road, London, SW12 9BS (020 8675 5211).Acknowledgements to Gregory Zdaniuk and Huw Blackwell.