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IDES-EDU modul

Lecture #11

Energy production

Community energy systems

Coordinator: Sašo Medved, UL

Contributor: Sašo Medved, Jure Vetršek, UL

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Note: Some of the pictures in the presentation are used from other sources which are citated. Some pictures are download from web and authors are unknown. We would like to thank all known and unknown authors. Some schemes are taken from marketing and technical material of different companies to improve the quality of presentation and we want to make acknowledgment to those companies. This presentation should be used for education purposes only.

Intro

Modern cities occupy substantially more space then they used to in the past. Suburbs area become integral part of the cities. 80 per cent of Europeans live in cities.

City can be treated as “black box”. Very different processes going on in the cities in order to ensure sufficient and continuously supply of food, water, energy (heat, cold, electricity, mechanical work) and materials to their inhabitance. Sustainability of the city can be measured regarding to the needed amount of the inputs and regarding to amount of the outputs which have different environmental impacts.

inputs outputs

processes

CITYenergy

materialswater

landenergy conservation

reuserecycle

gas, liquid and solidemissionsland occupied by building, streets, landfills,..

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Intro

Modern cities can fulfil needs of their inhabitancies and developed towards sustainable cities only if high efficient and sustainable community integrated utility systems are developed. This includes:

centralized supply of energy in form of heat, cold and electricityintegration of decentralized energy production systems with centralized; efficient water supply systems with low energy demand and low leaking;public transportation systems;solid waste treatment systems;waste water treatment systems.

Because of electricity supply systems are normally much larger then city itself, focus will be done on heat and cold utility systems and integration of the electricity production in those systems on city scale.

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The planning and decision making process

http://www.annex49.com/download/summary_report.pdf (page 56)

Planning of community utility systems LOTZ

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Community utility systems for centralized supply of energy

Dictrict heating / cooling system

District heating system with cogeneration of heat and electricity

District heating and/od cooling system – trigeneration systems

District heating system based on or with integrated

renewable energy sources

Advance district heating systems – low exergy systems

Development of community district heating system towards improved energy efficiency and sustainability

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District heating systems have some clear advantage regarding to decentralized heat production:

a larger central heating plant can achieve higher thermal efficiency then most smaller heat generators; with better partial-power efficiency;

emissions from central heating plant are easier to control and removal of pollutant more efficient; lower impact on environment, better quality of outdoor environment;

renewable energy sources can be utilized in large scale;

free space in building increase since boilers and fuel storages are not needed, lower maintenance and investment cost;

specific cost of equipment is lower, price of heat is lower as well; cost of operation can be even lowered by implementing cogeneration or trigeneration.

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But, district heating is rational in case of:

high thermal load density; this is characteristic for areas with high buildings and population density in cold climate; at least 50 buildings per ha and heat demand density up to 25 kWh/m2 of urbanized space covered by DH or where linear heat density is higher than 200 (500) kWh/m of pipeline per year.; in such case the capital investment for distribution system which usually present 50 to 75% of the total investment will be covered and district heat can be economically transported tens of kilometres;high annual load factor; this could be the case when district system operates with constant thermal power through whole year.

District heating systems

If we skip the Roman Empire, first district heating systems are in operation since mid of 19th century. Today district heating (DH) deeply penetrate in heat market. In Iceland 95% of all end-use heat is provided by DH in Denmark more than 60% in Sweden and Poland ~50% in Germany 12%. In St. Petersburg where largest DH system is in operation, 237 PJ of heat is delivery yearly, exactly that total final end use of energy in Slovenia !

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District heating systems – modes and components

One of the most common classification of the district heating system is based on temperature and sort of transport fluid.

The hot water or steam can be used as transport fluid. The later is common in industrial areas because steam can be used not only for heating or cooling but for industrial processes too.

Hot water systems are divided into three temperature ranges – high temperature supply temperatures over 175oC, medium-temperature supply temperatures in range between 120 and 175oC and low-temperature systems supply temperatures of 120 oC or lower.

The medium-temperature systems are common for district heating of residential areas because lower pressure and thermal loses and lower leakage. They are designed for a high temperature drop (50 to 60 K) in the building’s heating system heat exchanger to reduce flow rate of the transport fluid and pumping power.

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District heating systems – modes and components

building

Heat generator (coal, gas, biomass)

heat substations (heat exchangers) or direct connections

pipeline

Heat generator (coal, gas, biomass)

Smaller DH systems have one distribution loop because low heat losses

Large DH systems have severalpump stations and pipeline loops to avoid high pumping cost and heat losses

pump station

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District heating systems – modes and components

building

Heat generator (coal, gas, biomass)

heat substations with heat exchanger

nowadays steel or PVC (for lower temperature) pre-insulated pipes are used for distribution; the size is calculated regarding ot pressure drop not to be more 50 to 100 Pa/m.

direct connection to building heating system; no additional pump in heating system is needed

Despite the case on the photo, in most cases pipes are put into the ground and buried with the soil.

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http://www.pipesystems.com, REMINING LOWEX

Pipeline planning

Pipelines are planed regarding to optimization between cost of pipes and pumping costs.

Heat losses are calculated regarding fluid mass flow rate (velocity) and diamether; heat bridges and heat accumulation should be taken into account for detailed calculation.

Heat transfer fluid temperature drop in pipeline with DN 250

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District heating systems

As cities grow all the time, one of major difficulties in process of planning district heating systems is prediction of future heat consumption.

When the system is already build, there are still several options for connecting new settlements on existing district heating system:

by promoting and implementation of demand side management policy;by promoting low energy buildings with low temperature heating systems and retrofitting; buildings can be connected to return pipeline because temperatures of transport fluid are high enough for heating of such buildings; by integrating heat storage; heat storage decreases daily peaks of heat consumption and provides higher and more economical electricity production in cogeneration plants during day time.

DH in city of Ljubljana has 156 km long pipelines; hot water system (130oC/70oC); hot water storage tank with volume of 24000 m3 was build with thermal capacity 850 MWht.for peak-load clipping instead of build new boiler facility; 9% (2010) of heat was produced by co-burning of biomass chips and imported black coal.

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District cooling systems

In the cities with high buildings density and district cooling systems can be cost effective. Such a way of the cooling has several advantiges comparing to mechanical driven chillers presented in the lecture #6:

because saving in space, lower investment (chillers, condensing pipelines and cooling towers are not needed) and lower maintenance cost no problems with noise emissions from cooling equipment;no risk of legionnaires disease because no aerosols are emitted from cooling towers.

There are two types of district cooling systems, open and close:open systems are used in case of deep sea or lake water cooling, cold water with temperature 4°to 8°C from the depth of 50 to 100 m below the surface is pumped into the district system; such system operates in Stockholm since 1995 where sea water from Baltic Sea is used, in Toronto with cold water from 5 km off-shore and 84 m depth of Lake Ontario bellow the surface of Lake Ontario;

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District cooling systems

Similar project starts in 2007 at Cornell University, USA, using cold water from lake Cayugy.

In closed systems, coolant water is produced in central plant. Chilled water can be produced by electric-driven compressor. In central unit the peak electricity consumption is lower, as cold can be effectively stored.

Cooling energy can be transported by cold water, ice slurry, or brine to the buildings. By the use of slurry and salt water are the temperatures of the cold transfer fluid lower, smaller mass flow rates are needed for the same cooling load and pumping costs are therefore lower.

Sheme of distric cooling system in

Toronto, CAN

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District cooling systems

Supply temperatures are normally around 5° to 7 °C with return temperatures between 10° to 15 °C. Such low temperatures enable cooling and dehumidification of the indoor air.

When the heat from DH system is available at high temperature (>110 °C) even during the summer, the heat can be transformed into the coldness with decentralized absorptive cooling systems. In such cooling systems, called absorption cooling, cold is generated by the use of binary solutions, most common solutions of water and ammonia or water and lithium bromide. Such systems are described in lecture # 8.Although, the district cooling systems are the most widened in the USA, there are applications in Europe too. In Sweden the first system was built in 1992, today, however, over 20 systems of district cooling, with the whole length of 85 km, are in operation. In France 5 systems are working, among them the largest in Paris with its cooling power of 220 MW. In Germany, the most widespread are local systems of district cooling. They use absorbent cold-storage plants, which are connected to the hot water network of district heating.

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District cooling systems

Chillers in large DCS have higher COPs (see lecture #6) 5 to 7 comparing to smaller, compact units, but internal cold. water distribution system and final heat-exchangers are still needed.

Similarly to the DHS, metering must be established in DCS in order to billing the users according to actual cold demand.

Comparing the same amount of the heat and cold distributed to the users, mass flow rate of transport fluid is much greater in DCS due to the much smaller temperature differences between supply and return temperature (5-7°C; 10-14°C). To reduce cost of the network system and pumping cost, ice-water slurry can be use as transport fluid. 10% or so ice is added to the water and ice act as coldness latent storage. Because less turbulent flow, even pumping cost decrease.

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District heating system with cogeneration of heat and electricity (CHP)

Cogeneration or combined heat and electricity production is in principal efficiency improved production of electricity. Meanwhile efficiency of electricity production doesn’t differ from ordinary power plants, the heat which must be extract from thermodynamic cycle is used for heating. In most cases users are supplied with heat via DHS.

Diagrams that explain why cogeneration or combined electricity and heat generation is more efficient then separate production of those energy carriers. Despite lower efficiency of heat generation in CHP system comparing to contemporary boilers, this shortage is overruled by much higher overall efficiency of the CHP systems. It is evident that high efficiency of CHP can be archived only if heat is consumed by the users.

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District heating system with cogeneration of heat and electricity (CHP, coGEN)

Cogenerations in DHS are at scale of several 10s to 100s MW of electicity and heat.Note: in engineering practice therm “microCHP” is used for applications with electricity power up to 5 kWe, and term “miniCHP” for the system with electricity power > 5 kWe and up to 500 kWe. Such systems are mostly installed as decentralized units in buildings. See Lecture #If waste heat from CHP is used for supplying the DHS, CHP is usually sizing to meet minimum heat load, with backup boiler to additional heat supply. For example in the DHS in City of Ljubljana 98% of generated heat in CHP unit is used fro heating during the whole year.

In Europe since CHP Directive in the year 2004 (European Union’s Cogeneration Directive 2004/08/EC) was published, interest for CHP grows and today 11% of electricity in EU is generated using cogeneration. CHP is stimulated via feed-in-tariff subsidy systems in many countries. Nevertheless, differences between countries are large: in DK more then 50% of whole electricity production is done by CHP, in NL and FIN 35%, in Germany 12%.

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Best available technologies (BAT) for cogeneration

Internal combustion engine; The reciprocating engines used in cogeneration are internal combustion engines operating and could be a:

compression ignition engine; are predominantly four-stroke direct- injection machines fitted with turbochargers and intercoolers. Diesel engines will can run on oil or natural gas. Shaft efficiencies are 35 to 45%, and output range is up to 15 MWe. Engines up to ~ 500 kWe are derivatives of the automotive diesels and running at the upper end of their speed range, for larger engines marine diesels are used.spark-ignition engines; shaft efficiency is lower that for compression ignition engines (27% and 35%), and the output range is limited to ~ 2 MWe

Gas turbine; in gas turbine, the fuel is burnt in a pressurized combustion chamber using combustion air supplied by a compressor that is integral with the gas turbine. Hot gases enter the turbine at a temperature range of 900 to 1000°C and expand. Heat of exhaust gases (450°C to 550°C ) is used for heat supply.

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Steam turbine; have been used as prime movers for industrial cogeneration systems for many years. High-pressure steam raised in a conventional boiler expands within the turbine to produce mechanical energy, which may then be used to drive an electric generator. Typical inlet steam conditions are in range of 42 bar/400°C to 63 bar/480°C; in district heating cogeneration schemes, the turbine condenser may be operated near or even above atmospheric pressure, to ensures that the enough heat to supply the district heating circuit. Organic Rankine cycle; the Organic Rankine cycle (ORC) uses an organic, high molecular mass fluid with boiling temperature lower than the water. Therefore low temperature sources, such as industrial waste heat, geothermal heat, solar ponds can be utilized in a Rankine cycle. ORC systems has high partial load efficiency and load changing response. Some common fluids for ORC are toluene, butane, pentane, ammonia, refrigeration fluids or silicone oils.

Best available technologies (BAT) for cogeneration

Scheme of ORC cogeneration process. Source: (Quoilin & Lemort)

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Kalina cycle; the Kalina cycle is a thermodynamic cycle for converting thermal to mechanical energy, optimized for use of thermal sources at a relatively low temperature compared to the heat sink or ambient temperature. The cycle uses a working fluid with at least two components (typically water and ammonia), meanwhile the ratio between those components is varied in different parts of the system to increase thermodynamic efficiency.

Best available technologies (BAT) for cogeneration

Scheme of geothermal power plant with Kalina cycle in Husavik, Iceland (Exorka, Magnus Gehringer), put attention on cascade (temperature dependant) use of geothermal heat which is typical for all geothermal systems.

Scheme of Kalina cycle; Source: (Quoilin & Lemort)

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Comparison of CHP technologies

ENGINE/PROCES FUEL USED

SIZE RANGE (MWe)

HEAT TO POWER RATIO

ELECTRICAL EFFICIENCY

TYPICAL OVERALL EFFICIENCY

Extraction steam turbine Any fuel 1 to 100+ 3:1 to 8:1 10 - 20% Up to 80%

Back pressure steam turbine Any fuel 0,5 to 500 3:1 to 10:1 7 - 20% Up to 80%

Combined cycle gas turbine

Gas, Biogas, Gasoil, LFO, LPG, Naphtha 3 to 300+ 1:1 to 3:1 35 - 55% 73 – 90%

Open cycle gas turbine

Gas, Biogas, Gasoil, LFO, Heavy fuel oil (HFO), LPG,

Naphtha 0,25 to 50+ 1,5:1 to 5:1 25 - 42% 65 – 87%

Compression ignition engine

Gas, Biogas, Gasoil, Naphtha, HFO, LHO 0,2 to 20 0,5:1 to 3:1 35 – 45% 65 – 90%

Spark ignition engine Gas, Biogas, LHO, Naphtha 0,003 to 6 1:1 to 3:1 25 – 43% 70 – 92% Organic Rankine cycle Any fuel 0,004 to 7,5 5:1 9-21% ~80%

Technology Steam turbine Gas turbine Combined

cycle Reciprocating engine

Investment cost (ECU/kWe) 1500-1000 1200-530 900-450 960-770 O&M cost 2,3-1,5 5,4-4,6 5,4-4,6 5,8-9,2 Cost per MWe (ECU/MWe) (price of fuel: 13,2 ECU/MWh lower heating value)

20-15 33-30 33-30 29-26

Simple payback time (operating: 7000 h/year, price of electricity: 77 ECU/MWh)

3,5-4 2-3 2-3 2-3

Life time 30 15 15 10

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District heating system with cogeneration of heat, cold and electricity (triGEN)

Electricity generation in cogeneration systems could be enlarged without of reducing overall efficiency if heat demand is enlarged, usage period is prolong and is heat demand is equally distributed thought the whole year.In DHS, this is only possible if surplus of heat is used to generate coolant water for cooling of the buildings. This can be done with so called absorption systems. Such systems were described in Lecture #8. Chillers are installed in the building, heat for operation is provided by DHS.

Technology (see lecture #8 for details)

Closed-cycle absorption (single-step)

Closed-cycle absorption

Closed-cycle adsorption

Refrigerant H2O NH3 H2O Absorbent LiBr H2O Silica gel Chilled fluid Water Water-glycol Water Chilled fluid temperature 6 - 20°C -60°C to 20°C 6-20°C Driving temperature 80 - 110°C 100 - 140°C 55 - 100°C Cooling water temperature up to 50°C up to 50°C up to 35°C

Cooling power range 35 - 7000 kW 10 - 10000 kW 50 - 430 kW COP (see lecture #8 for details) 0,6 - 0,75 0,6 - 0,7 0,3 - 0,7

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Since August 2008 Municipality of Velenje (SLO) headquarter building (area 23.485 m2, heat consumption 1546 MWh/a (65,8 kWh/m2a), cold consumption 1160 MWh/a 49 kWh/m2a), electricity consumption 68,8 MWH/a (3 kWh/m2a) is cooled by absorption cooling aggregate driven by district heat. Operator of DHS provides supply temperature in the range from 105°C to 110°C, the return temperature is 70°C to 75°C. Absorption chiller was made by BROAD (BDH84 X-87/1005-35/28-100), with COP 0,775 and nominal cooling power 980 kW. Total electricity load of chiller’s equipment is 5 kW. Total investment (including planning) was 1.175.039 € or ~1200 €/kWc.

District cooling systems – case study

Source: (Zager & Cvet, 2009)

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Source: The basic configuration of a central solar heating plant (Heller Alfred, 2000)

Biomass is mostly use renewable energy sources for DHS. Even so, low heat demand during the summer and not emission free operation of such thermal power plant, encourage the use of solar energy.Solar assisted DHS consists of a heat plant and a thermal solar plant. Thermal solar plant is composed of a large area of solar thermal collectors a heat exchanger that transfers heat to the heat storage tank or directly into distribution system. Storage tank is necessary due to intermittent nature of the solar radiation.

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Source: CSHPSS in Germany Solarthermie-2000 and Solarthermie2000plus Thomas Schmidt, Dirk Mangold SWT –Forschung http://www.solarmarstal.dk/default.asp?id=31760

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Germany is a world leader in development of CSHP. All systems have seasonal storage in order to extend the time of operation to the colder months. Four types of heat storages were tested:

hot water heat storage;ground heat storage with boreholes;gravel-water artificial aquifers,natural aquifers.

District heating systems with integrated renewable energy sources – solar energy LOTZ

Source: The basic configuration of a central solar heating plant (Heller Alfred, 2000)

Source: CSHPSS in Germany Solarthermie-2000 and Solarthermie2000plus Thomas Schmidt, Dirk Mangold SWT –Forschung http://www.solarmarstal.dk/default.asp?id=31760

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Source: CSHPSS in Germany Solarthermie-2000 and Solarthermie2000plus Thomas Schmidt, Dirk Mangold SWT –Forschung http://www.solarmarstal.dk/default.asp?id=31760

District heating systems with integrated renewable energy sources – solar energy LOTZ

Largest Central Solar Heating Plants in the world

No. Name SizeThermal Power

Annual production

Storage tank Storage type

m² MW GWh m³1 Marstal 18,048 12.9 8.2 2,100 Water tank

3,500 Sand/water10,000 ground pit

2 Kungälv 10,048 7 4.5 1,000 Water tank3 Brændstup 8,000 5.6 3.64 Strandby 8,000 5.6 3.65 Nykvärn 7,500 5.3 3.4 1,500 Water tank6 Falkenberg 5,500 3.9 2.5 1,100 Water tank

7 Neckarsulm 5,044 3.5 2.3 25,000Soil duct heat exchanger

8 Ulsted 5,000 3.5 2.2 1,000 Water tank9 Ærøskøping 4,900 3.4 2.2 1,200 Water tank

10 Friederichshafen 4,250 3 1.9 12,000Concrete tank in ground

Source: (Nielsen Jan Erik, 2008, PlanEnergi http://wapedia.mobi/en/Central_solar_heating>)

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Solar assisted DHS in Marstal on the island of Ærø (DK), is currently the largest CSHP in the world. It has more than 18000 m2 of solar collectors with yearly production around 8.2 GWh. The share of solar heating is 55%, additional heat is provide from biomass. The system has thermal storage in form of three tank all together 13600 m3 of capacity. The system has two modes of operation: summer and winter one. In winter mode the collector system is connected to the main waste oil heating plant where it preheats the return flow from the DHS. In summer mode the waste oil fired plant is not operating and only solar facility cowers all heating demand. As an emergency backup small heating oil boiler is used. In this mode the CSDHP is connected to the supply pipe of DHS.

Source: http://www.solarmarstal.dk/SUNSTORE%20.html

District heating systems with integrated renewable energy sources – study case LOTZ

The Municipality of Lienz has implemented a biomass district-heating power plant (Lienz I and Lienz II) with overall capacity of 44,5 MWh. Thermal solar system with 630 m2 of solar collectors was added as well as thermal storage with volume of 400 m3 for peak load clipping.Electricity is produced by ORC process (Organic Rankine Cycle) with a nominal electric capacity of 2,5 MWe.

District heating systems with integrated renewable energy sources – study case

Heating medium in boiler Thermal oil Yearly production of electricity

11000 MWh/a

Inlet temperature 300°C Yearly production of heat 74000 MWh/a

Outlet temperature 250°C Installed thermal boiler output 44.5 MWWorking medium - ORC Silicon oil Installed electric capa city 2.5 MWCooling medium Water Solar thermal collector 630 m²Inlet temperature 80°C Buffer storage 400 m³Outlet temperature 60°CNet electrical efficiency at nominal load 18,0% Investment costs 38.330.000 EUR

Thermal efficiency at n ominal load 80,0%

Heat exchanger for oil heating with flue gasses

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Source: CHP plant Lienz (Obernberger, Thonhofer, & Reisenhofer, 2002)

District heating systems with integrated renewable energy sources – study case

Solar collectors field

Heat storage

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Geothermal energy is wide use heat source in DH systems in countries where geothermal heat is available. In most cases DHS operates without additional heat source. Geothermal energy may be extracted from hot rock and ground water at depths of several hundred meters. Natural springs of geothermal water or pumping systems can be use as heat source. In later, geothermal water must be reinjected into the aquifer (thermal reservoir).

Prof. Dr. Páll Valdimarsson – lectured material at RES the School for renewable energy sciences, Akureyri, Iceland

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Reykjavik DHS design valuesBuildings are designed for 80°/40°/at -15 °C;DHS system is designed for -8 °C;Variation in estimated indoor temperature is calculated for cold spells;Heat stored in the building is the cold spellreserve;85% of the buildings is heated by geothermal DHS (240 000 out of 283 000 inhabitance);1500 MW heating power;5 kW per capita;20 W per m3 building volume;18 h storage capacity at average load;cost: 0,80 - 0,90 €/m3 ov building volume or ~ 100 €/year per fammily buildings.

Source: Prof. Dr. Páll Valdimarsson – lectured material at RES the School for renewable energy sciences, Akureyri, Iceland

District heating systems with integrated renewable energy sources – study case LOTZ

Modeling of DHS – case study: cogeneration modeLOTZ

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Proposed system with high temperature cogeneration

Modeling of DHS – case study: trigeneration modeLOTZ

Most of the energy used in the building sector is required to maintain constant indoor temperatures between 20°C and 25°C during the whole year. Because contemporary buildings have very low heating and cooling load, the supply temperatures of heat transfer fluid could be close to the desired indoor temperatures. Such heating and cooling systems are called low exergy (low-ex) systems. In such systems wide range of natural heat and cold energy sources can be applied in more efficient ways. This results, in case of DHS and DCS in lower distribution losses as well.

Low exergy district heating and cooling systems

Low-ex community suplly systems !

Source: IEA ANNEX 49

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http://www.annex49.com/download/summary_report.pdf

Low exergy district heating and cooling systems – concepts study cases

The thermal solar system in Okotoks complex (CAN) uses flat plate solar collectors and provides at least 90% heat for the space heating and 60% heat for domestic hot water heating for the 52 dwellings. This was achieved, despite winter temperatures as low as -33°C.

Source: REMINING-Lowex IBP

Low exergy district heating and cooling systems – concepts study cases

In Heerlen (NL) mine water is extracted from four different wells with different temperatures. The mine water in primary loop is extracted from the warmwells (~30°C) and distributed to local energy stations with heat pumps. Heat is transferred to the secondary energy grid in buildings. With temperature 35…45°C for heating and (16…18°C) for cooling.

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Low exergy district heating and cooling systems – concepts study cases

In Heerlen (NL) mine water is used for low-exergy (sometimes called high temperature cooling). DHW system needs higher temperatures (up to 65°C) and high efficient condensing gas boiler is used for this purposes after water was preheated by heat pump.

Source: REMINING-Lowex IBP

Source: Joao A. Peças Lopes

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Only integration of new energy production capacities is not enough - it must come hand in hand with energy efficiency measures.

Several energy sources and multiple technologies will be combined in synchronic and secure energy supply systems. Energy production sources will be placed much closer to the consumers.

Concept of smart grids, characteristic for electricity generation will penetrate also on the heat market.

No longer big production facilities, but flexible small units are evolving.

Future community integrated systemsLOTZ

Describe the community utility systems in the modern local communities !Explain how different actors influence on planning and implementing of energy community systems !Describe how performance of energy community systems could be improved !Explain how solar heating system could be integrated into energy community systems !Draw a scheme of large scale solar heating system connected to the energy community system !Explain the advantages of heat storage in energy community systems !Describe technologies for seasonal heat storage in energy community systems Define BAT for large scale cogeneration and district cooling !Explain how dispersed energy sources could be integrated into energy community systems and what are smart-grids !

Self evaluationLOTZ

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References

L.D.D. Harvey; “A handbook on Low-Energy Buildings and District-Energy Systems, Earthscan, UK, 2006

B. Sorensen; Renewable energy conservation, transmission and storage; Elsevier, USA, 2007

B. Lenz, J. Schreiber, T. Stark; Sustainable building services, Detail Green Books; Germany, 2011

K. Daniels, R. E. Hammann; Energy Design for Tomorrow; Edition Axel Menges; Germany, 2008

M. Santamoiris; Environment design of Urban Buildings, Earthscan, UK, 2006

ECBCS Annex 49; Low Exergy Systems for High-Performance Buildings and Communities, IEA, 2011

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