NEGST New generation of solar thermal systems Advanced applications Comparison of solar cooling technologies Vincenzo Sabatelli ENEA vincenzo.sabatelli@trisaia.enea.it NEGST Workshop - Freiburg - June 21st, 2007
NEGST WP5 Advanced application The overall objective of NEGST project is the development and market introduction of more cost-efficient ST systems, particularly for DHW preparation and/or space heating and cooling In this framework, the activities performed in WP5 aim at assessing the potential of ST for advanced applications, such as cooling and desalination NEGST - final project meeting - Rapperswil - January 17-19, 2007 2
WP5 final target An enlargement of the utilization field, traditionally limited to DHW preparation and/or space heating, could in fact positively contribute to support a further diffusion of ST systems and to promote innovative concepts The identification of the most promising technologies is a key step for effective future developments NEGST - final project meeting - Rapperswil - January 17-19, 2007 3
Main outputs Technical status report on solar cooling and desalination Report concerning suitability of different collector technologies for solar cooling and desalination Design software tool Feasibility studies in order to identify the potential areas for these applications NEGST - final project meeting - Rapperswil - January 17-19, 2007 4
Solar cooling potential Solar systems for DHW preparation are a mature technology and their applications already reach a satisfactory figure in many European countries The margins for a further market growth are rather limited, as well as the impact on global energy consumption In South Europe countries use of solar systems for space heating is not much attractive The application of solar collectors for air-conditioning of the buildings or, in general, production of cold water can have a high potential NEGST Workshop - Freiburg - June 21st, 2007 5
Status of cooling in EU-15 Energy consumptions for air-conditioning is ~10 5 GWh per year Spain and Italy together cover ~ 50% of the total EU-15 energy consumptions related to air-conditioning Spain, Italy and Greece are distinguished by the higher values per capita Other 13% France 12% Spain United Kingdom 8% Germany 11% Greece Greece 5% Italy EU Per capita consumption [kwh/y] Spain 24% 0 100 200 300 400 500 600 Portugal 2% Italy 25% Present distribution of apparent annual additional building floor area by country (Source: EECCAC study). NEGST Workshop - Freiburg - June 21st, 2007 6
Contribution of solar cooling Installations Presently, in the EU-15 countries solar energy contribution to airconditioning in buildings is really modest and is principally characterized by demonstration plants. Netherlands Austria Italy Portugal France Greece 2 2 3 3 4 6 Total installed capacity installed in Europe: 6.3 MW (estimated) Contribution to cooling total capacity is negligible Spain and Germany account for about 70% of the total installations in Europe Leading technology is absorption chiller 0 5 10 15 20 25 30 Employed technology NEGST Workshop - Freiburg - June 21st, 2007 7 Spain Germany Absorption chillers 60% # of plants 19 27 DEC Systems 28% Adsorption chillers 12%
Technologies for solar cooling Closed-loop cycles (Thermally driven chillers) Production of chilled water Any type of system for the distribution of cold can be applied Absorption (the most established technology) and adsorption chillers are both applicable Open-loop cycles (DEC systems) Direct treatment of ambient air System for distribution of the conditioned air is required Systems using solid or liquid sorbents are both available NEGST Workshop - Freiburg - June 21st, 2007 8
Absorption chillers Cooling cycle is based upon a sorption process in which a concentrated hygroscopic fluid absorbs the refrigerant vapour. pressure Q A1 condenser throttle valve pump thermal compressor Q drive generator solution heat exchanger throttle valve for the solvent evaporator absorber Q cooling Q A2 Systems are classified according to: temperature Source: NEGST WP5.D1 working pair (refrigerant/solvent) number of cycles (COP increases as well as the driving heat temperature) NEGST Workshop - Freiburg - June 21st, 2007 9
DEC systems Working cycle is based upon an evaporative cooling and dehumidification cycle via an hygroscopic solid or liquid material. Source: NEGST WP5.D1 COP is strongly dependent on external air conditions (temperature and humidity) Electrical energy consumption related to the ventilation system is significant Small capacity systems (<20 kw) are not commercially available NEGST Workshop - Freiburg - June 21st, 2007 10
Analysed cooling technologies The analysis has been limited to commercially available technologies DEC systems have not been included due to the mentioned limitations Single-effect H 2 O/LiBr absorption chiller Double-effect H 2 O/LiBr absorption chiller NH 3 /H 2 O heat pump NEGST Workshop - Freiburg - June 21st, 2007 11
Approach adopted H 2 O/LiBr absorption chiller and NH 3 /H 2 O heat pump, driven by any suitable low to medium temperature solar collector, are evaluated on the basis of the overall primary energy saving The inclusion in the investigation of both heating and cooling allows to select the best performing solar-assisted air conditioning system for each area, according to its global requirements To demonstrate that the feasibility of solar cooling is not limited to hot climates only, but it can be assessed in a wider European area, where cooling and heating are both needed
Description of the methodology a) Estimation of heating and cooling loads for a typical residential building located in sites representative of different European climatic conditions b) Calculation of the related primary energy consumption by an electrically driven VCHP, assumed as reference conventional heating and cooling system c) Definition of a reasonable fraction of the needed primary energy to be replaced by solar energy d) Evaluation of the collector area required to achieve the fixed primary energy saving by means of a software tool e) Comparison of obtained results estec 2007: June 19-20, 2007 - Freiburg 13
Description of the methodology φ f-chart method, applied to a general solar heating system, is used for the thermal analysis of each solar assisted air-conditioning system T > T min Thermal energy is delivered when the temperature is above a specified minimum useful temperature (T min ), depending on the type of application. An auxiliary heater provides the thermal energy, when the solar input is not sufficient to meet the load. The calculation method adopted in this analysis is well appropriate to assess the performance of thermally driven chillers which are characterized by a minimum driving temperature under which they cannot operate correctly. NEGST Workshop - Freiburg - June 21st, 2007 14
Hypotheses of the methodology For cooling cycles working only as refrigerator, the heat supplied by solar collectors is directly used to meet the load during the winter season (this can be achieved via common low temperature heat distribution systems for space heating) Cooling and heating (if applicable) COP are both constant during their working period. This assumption is not well-matched with DEC systems operational characteristics, being their performance strongly dependent on external air conditions (temperature and humidity). estec 2007: June 19-20, 2007 - Freiburg 15
Software tool Annual solar fraction for heating and cooling is calculated starting from monthly-based average meteorological data and building loads (input data) Solar fractions for heating and cooling are calculated on monthly basis Solar system is characterized by the efficiency of collector, backup unit, solar tank, and heat-exchanger Air-conditioning system is characterized by its cooling COP (and heating if reversible) and its driving temperature (both assumed constant during the working period) Result is a curve reporting the variation of the primary energy saved, with respect to the reference conventional system, as a function of the collector area estec 2007: June 19-20, 2007 - Freiburg 16
Software tool Solar system and thermal chiller parameters NEGST Workshop - Freiburg - June 21st, 2007 17
Software tool Weather and building data NEGST Workshop - Freiburg - June 21st, 2007 18
Software tool Main outputs NEGST Workshop - Freiburg - June 21st, 2007 19
Heating and cooling needs PALERMO LISBON ATHENS ROME Month Heating Cooling Heating Cooling Heating Cooling Heating Cooling [kwh/m²] [kwh/m²] [kwh/m²] [kwh/m²] [kwh/m²] [kwh/m²] [kwh/m²] [kwh/m²] JAN 12.26 0.00 12.40 0.00 17.04 0.00 25.13 0.00 FEB 8.64 0.00 9.47 0.00 15.82 0.00 18.81 0.00 MAR 6.49 0.00 8.10 0.00 16.28 0.00 10.92 0.00 APR 1.91 0.00 6.89 0.00 8.45 0.00 5.27 0.00 MAY 0.00 0.44 0.00 2.54 0.00 3.01 0.62 0.00 JUN 0.00 4.20 0.00 6.95 0.00 9.61 0.00 5.00 JUL 0.00 12.73 0.00 11.81 0.00 17.25 0.00 13.85 AUG 0.00 14.77 0.00 13.17 0.00 18.44 0.00 14.71 SEP 0.00 6.70 0.00 11.77 0.00 13.86 0.00 4.38 OCT 0.00 0.81 0.00 5.52 0.00 5.01 1.78 0.00 NOV 3.75 0.00 7.79 0.00 6.72 0.00 14.61 0.00 DEC 9.62 0.00 12.27 0.00 14.19 0.00 24.68 0.00 Total 42.65 39.64 56.92 51.76 78.50 67.17 101.81 37.95 estec 2007: June 19-20, 2007 - Freiburg 20
Solar heating and cooling systems Systems considered in the analysis and calculation parameters Type of cycle COP Cooling Driving temperature COP Heating Heat supply temperature Type of collector SE - H 2 O/LiBr 0.7 85 C - 45 C FPC SE - H 2 O/LiBr 0.7 85 C - 45 C ETC DE - H 2 O/LiBr 1.1 150 C - 45 C PTC NH 3 /H 2 O 0.8 180 C 1.6 180 C PTC estec 2007: June 19-20, 2007 - Freiburg 21
Main parameters used in the calculation TYPE OF COLLECTOR Flat plate selective (FPC) Evacuated tubular (ETC) Parabolic trough (PTC) collector parameters Test intercept [-] 0.78 0.76 0.74 Test slope [W/m²K] 4.3 1.8 0.56 Collector orientation South South N-S Collector slope 45 45 45 Concentration ratio - - 60 general solar heating system parameters Storage volume to collector area ratio UA of auxiliary storage tank Pipe heat loss 70 litres/m² Negligible Negligible Collector-store heat exchanger Tank-side flow-rate/area: 0.015 kg s -1 m -2 Heat exchanger effectiveness: 0.7 Load heat exchanger effectiveness 0.7 NEGST Workshop - Freiburg - June 21st, 2007 22
Results The energy assessment of each solar-assisted system is expressed by the required collector area per m² of floor area to be conditioned, together with the corresponding annual solar fractions, with reference to a given primary energy saving Solar cooling system PALERMO LISBON ATHENS ROME A c /A floor [m²/m²] f sol [-] A c /A floor [m²/m²] f sol [-] A c /A floor [m²/m²] f sol [-] A c /A floor [m²/m²] f sol [-] FPC + SE-H 2 O/LiBr 0.24 0.76 0.24 0.76 0.37 0.76 0.41 0.76 ETC + SE-H 2 O/LiBr 0.13 0.76 0.13 0.76 0.19 0.76 0.25 0.76 PTC + DE-H 2 O/LiBr 0.11 0.71 0.10 0.71 0.17 0.71 0.26 0.73 PTC + NH 3 /H 2 O 0.10 0.70 0.10 0.70 0.16 0.70 0.14 0.67 Primary energy saving with respect to the reference conventional system (cooling and heating COP equal to 2.5 and 3.0, respectively) is set to 70% estec 2007: June 19-20, 2007 - Freiburg 23
Economic analysis A comparative method is used: System cost-effectiveness can be inferred from the collector specific costs ratio (collector specific cost / FPC specific cost). If a realistic cost of the used collector with respect to FPC basic cost does not exceed this number the system appears to be more convenient. Solar cooling system Collector specific costs ratio [ / ] PALERMO LISBON ATHENS ROME FPC + SE-H 2 O/LiBr 1 1 1 1 ETC + SE-H 2 O/LiBr 1.85 1.84 1.91 1.69 PTC + DE-H 2 O/LiBr 2.30 2.38 2.14 1.62 PTC + NH 3 /H 2 O 2.33 2.51 2.30 2.88 estec 2007: June 19-20, 2007 - Freiburg 24
Conclusions NH 3 /H 2 O heat pump driven by PTC is the most effective airconditioning system in terms of required collector area per m² especially when the prevailing load is the heating load In this case NH 3 /H 2 O heat pump appears economically competitive if the PTC cost is up to almost three time as high as FPC cost Double-effect H 2 O/LiBr chiller driven by PTC shows comparable energy performance with respect to NH 3 /H 2 O heat pump when heating load is not much higher than cooling load Performances of single and double-effect H 2 O/LiBr chillers, driven by ETC and PTC respectively, appear comparable when the prevailing load is the heating load, thus singleeffect may be profitable from the economic point of view estec 2007: June 19-20, 2007 - Freiburg 25
For additional information NEw Generation of Solar Thermal systems Work Package 5 Advanced applications http://www.swt-technologie.de/html/negst.html Italian National Agency for New Technologies, Energy and Environment TRISAIA Research Centre Solar Collector Testing Laboratory http://www.enea.it - http://www.trisaia.enea.it NEGST Workshop - Freiburg - June 21st, 2007 26
End of presentation Thank you for your attention!!! NEGST Workshop - Freiburg - June 21st, 2007 27