District heating and cooling (DHC)

Transcription

1 District heating and cooling (DHC) Risto Lahdelma Professor, Energy technology for communities Tel: School of Engineering Aalto University Otakaari 4, ESPOO, Finland R. Lahdelma 1 Contents Course outline Schedule Fundamentals of DHC History of DHC R. Lahdelma 2 1

2 Course outline District heating and cooling (DHC), 5 cu Learning outcomes After this course, the students are able to Master production and transmission technology for DHC Evaluate DHC system in terms of technical, economical and environmental criteria both qualitatively and quantitatively Plan design and operation of DHC system Contents Economy of DHC system Use of DHC in buildings Transmission technology for DHC Planning and dimensioning of DHC Production technologies for DHC R. Lahdelma 3 Course outline Components Lectures (5 weeks, 20 h): Tuesdays and Thursdays Exercises: 3 weeks (4 mandatory assignment sets) Examination Material Lecture handouts in MyCourses Old book Kaukolämpötekniikka as supplementary reading New book Frederiksen & Werner: District Heating and Cooling Additional material posted in MyCourses R. Lahdelma 4 2

3 Schedule Lectures on Mondays 14:15-16:00, Room 150 K1 and xx (xx:15-xx:00, xx) 8.1. Introduction, DHC in Finland 10.1 DHC demand DHC demand in the building 17.1 DHC distribution (heat power, pump) DHC distribution (heat loss) 24.1 DHC network design Heat and cooling production 31.1 Economy of DHC (CHP cost allocation) 5.2. Economy of DHC (Investment and operation cost) 7.2 Guest lecture (may be relocated) Course exam Excercises in Maari A, starting week 3 Three groups 9-10, and :15-15:00 and 15:15-16:00 R. Lahdelma 5 Fundamentals of DHC DHC is a system for distributing heat and cooling from production facilities to meet residential and commerical heating requirements of customers The heat is typically used for heating space and water or as process heat for industry The cooling is typically used for cooling space, process cooling for industry, and cold storages (e.g. food) The goal of space heating and cooling is to create a comfortable indoor climate when outdoor temperature is lower or higher than desired indoor temperature DHC is typically assoicated with energy efficient production technologies such as combined heat and power (CHP) and combined cooling, heat and power (CCHP) and use of waste heat R. Lahdelma 6 3

4 Fundamentals of DHC Using free or otherwise wasted heat to satisfy heat and cooling demand - Excess heat from the thermal plant (combined heat cooling and power, CCHP) - Waste incineration - Excess heat from industrial processes - Waste biomass, solar heat - Natural geothermal heat - Free cooling sources: sea, lake and ground water DHC network cooling.html R. Lahdelma 7 - CCHP (combined cooling, heat and power) - Power (electricity - Heating - Cooling - further utilization of waste heat from turbine by absorption chiller - waste heat from the chiller can be used for heating domestic water by heat pump - More efficient than CHP (combined heat and power) Fundamentals of DHC R. Lahdelma 8 4

5 DHC production The traditional technologies for DH include CHP When electric power is produced in backpressure turbines, heat and/or cooling is obtained as a by-product Very high energy efficiency compared to separate production Heat-only boiler stations for peak heat demand The traditional technolgies for DC include Free cooling (natural sources such as sea water) Thermal activated technology (absorption chiller) Heat pump (compression chiller) R. Lahdelma 9 DHC production Novel techiques for producing DHC include Ground source heat pumps (cooling and heating mode) Use electric power to move heat from (heating mode) or to (cooling mode) some heat source such as the ground, a water system, sewage water etc COP-factor (coefficient of performance) = ratio of obtained heat / consumed power is typically Geothermal heat Geothermal direct-use plant (extract geothermal water from well) and geothermal water directly used for DH Geothermal (steam) CHP R. Lahdelma 10 5

6 DHC production Novel techiques for producing DHC include Solar DHC Heat from solar collector for DH Drive heat-driven (absorption) chiller for DHC requires some backup system because the sun is not always shining, working in conjuction with thermal energy storage waste incineration R. Lahdelma 11 Local production of renewable energy Idealistic scenario: buildings produce locally all energy they need from renewable sources Solar, wind, biofuels, ground heat, The demand varies in time, but not in coincidence with production Dimensioning the renewable source according to peak demand is very expensive Back-up energy sources are expensive if they are used only as backup What to do with excess production? No universal solution for efficient energy storage The renewable sources are not totally emission-free R. Lahdelma 12 6

7 Cooling and heating distribution are separated DHC distribution Tree-like structure R. Lahdelma 13 DHC distribution Heat & cooling is distributed to customers via a heating and a cooling network Water is used to distribute the heat and cooling via insulated pipes Heat In Finland pressurized hot water at temperatures up to 115 o C (supply) Temperature difference between supply and return is o C Steam is an alternative medium used in some other countries Cooling Supply temperature varies in different cooling systems»8 o C for absorption chiller»6 o C for compression chiller» temperature difference between supply and return is 8-10 o C R. Lahdelma 14 7

8 DHC distribution Ideally the distribution network forms a tree-like structure rooting at the heat (cooling) plant and branches extending to customers Each line in the heat (cooling) network consists of two pipes: supply pipe to take the hot (chilled) water to customers, and return pipe to bring the cooled (heated) water back to the heat (cooling) plant This means that the same water circulates in the system R. Lahdelma 15 District heat consumption The customers use the district heat for heating space and water in residential buildings, and for process heat in some industries The district heating is connected to the central heating system of the building through heat exchangers Normally each building has two heat exchangers One for heating up tap water and One for heating the water that circulates in the radiator network This is an indirect coupling: the district heating water does not circulate in the radiators nor is it consumed as hot tap water R. Lahdelma

9 District cooling consumption The customers use the district cooling for cooling space residential and office buildings, cooling cold storages (e.g. food) and for process cooling in industrial processes R. Lahdelma 17 DH and DC in Finland short history First district heating (DH) in Finland was built 1940 for the olympic village in Helsinki Idea for CHP came from observation that industrial power production produced excess heat that could be used for heating DH was thus based on CHP in the very beginning Tapiola, Espoo initiated DH in 1953 Helsinki obtained wider DH in 1957 Cities of Mikkeli and Lahti got DH in 1958 R. Lahdelma 18 9

10 DH and DC in Finland short history DC is currently supplied in seven cities Helsinki (year 1998) Turku ( year 2000) Lahti (year 2000) Vierumäki (year 2002) Tampere (year 2012) Pori (year 2012) Espoo (year 2013) Customer willings to outsource heating and cooling production for DHC company Market share of DC in Helsinki is 30% R. Lahdelma 19 DC supply in Finland 180 DC supply in years (Finland) GWh year Source: Finnish energy institute R. Lahdelma 20 10

11 DC supply in Finland - Technology share DC supply in Finland in 2013 (169 GWh) Compression chiller 7.8 % Absorb chiller 17.1 % 48.8 % Heat pump Free cooling 26.3 % Source: Finnish energy institute R. Lahdelma 21 DC in Helsinki by HELEN District cooling is expanding rapidly It substitutes locally produced cooling It saves energy and conserves the environment It is produced in an environmentally benign way One of the Europe s largest DC suppliers Market share is 30% R. Lahdelma 22 11

12 Worldwide DC 4500 Cooling degree days in cities (average of 2014 and 2015) Source: International Energy Agency (reference degree 18 0 C R. Lahdelma 23 DH in Finland Today DH has very high market share in Finland DH accounts for about 50 % of the total heating market Over 70% of the district heating is produced very efficiently in combined heat and power (CHP) plants The main fuels for district heating are Natural gas Wood chips Coal Peat Municipal solid waste By-products of forest industry R. Lahdelma 24 12

13 DH in Finland Practically all urban areas are within DH R. Lahdelma DH in Finland - Heat-only vs CHP R. Lahdelma 26 13

14 DH in Finland fuel (TJ) R. Lahdelma 27 DH in Finland fuel shares (%) R. Lahdelma 28 14

15 DH in Finland - market share of fuels other peat wood coal natural gas oil R. Lahdelma 29 CHP in the Finnish Energy System CHP heat production is a low CO2-emission heating technology in Finland due to the variety of fuels and high power plant efficiencies (~90%). The present environmental discussion in Finland does not recognise this. Secondary heat 2% Biomass 23% Oil 4% Coal 25% Natural gas 28% Peat 17% District heat fuels in Finland in 2012 (includes also heat-only) R. Lahdelma 30 15

16 Benefits of DHC Environmentally friendly High energy efficiency Exhaust heat can be further utilized to drive absorption chiller Clean combustion technology Possible to use renewables (biomass, ground source, solar) Production can utilize different technologies CHP for base load, heat-only boilers for peak load Thermal storage for load shifting Common reserve capacity for all users Reliable Easy for the user supplier takes care of everything R. Lahdelma 31 Weaknesses of DHC Large investment costs, long payback times Network infrastructure Requires relatively dense urban structure Transmission losses 4-15% depending on network size an density R. Lahdelma 32 16

17 Condensing power plant Fuel 100 Condensing power vs CHP Power 40 Loss (condense) 60 Efficiency ~ 40% The largest share of the energy content of the fuel is lost with the condense Fuel 100 CHP Power 30 Heat 60 Loss 10 Efficiency ~ 90% A small amount of the power output is traded for a significant amount of heat R. Lahdelma 33 Separate heat and power production vs CHP R. Lahdelma 34 17

18 Preparing for the next lecture Review the following questions Describe the role of CHP in the DHC What are reasons for choosing CHP in the DHC system? (list at least three reasons) What are challenges for CHP from the viewpoint of DHC company for preparing final auditing report Discuss briefly the heat and cooling sources for DHC from the viewpoint of the sustainable development Sustainable dvelopment is the economic development without depletion of natural resources, ie, without using non-renewable natural resources R. Lahdelma 35 18