Closed Sorption Heat Storage

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1 Closed Sorption Heat Storage Potential and challenge of a closed sorption heat storage based on sodium hydroxide and water Benjamin Fumey Robert Weber Paul Gantenbein Xavier Daguenet-Frick Tommy Williams EMPA EMPA SPF SPF Kingspan

2 Current state of the art seasonal heat storage Solar collector field combined with sensible hot water storage, coverage approximately 90 % Pro known technology safe material Contra constant heat loss requires a large volume

3 Hot water storage volume In order to achieve 100 % solar fraction the last 10 % coverage requires a tremendous storage volume increase

4 Solution towards 100 % solar fraction Reduce time dependent loss Reduce storage volume allow storage geometries to easily adjust

5 Closed sorption heat storage Based on a continuous but not full cycle liquid state absorption heat pump Heat is not directly stored but the potential to regain heat from a low temperature source Heat losses are encountered in the conversion process but not during storage

6 Closed sorption heat storage Condenser Desorber Condenser Desorber Qc Qd Qc Qd P1 Pressure P Absorbate Path 4 P1 Pressure P0 Absorbate Storage Absorbate Path 4 Working Pair Storage Absorbent Storage Qe Evaporator Qa Absorber Qe Evaporator Qa Absorber T0 Temperature T1 T2 Sorption heat pump T0 Temperature T1 T2 Sorption heat pump with storage

7 Closed sorption heat storage Heat is stored by separation of substance Heat is retrieved by recombining the substances The process functions under exclusion of non condensing gasses Step 1: Step 2: AB (liquid or solid) + heat A (liquid or solid) + B (gaseous) B (gaseous) - heat B (liquid)

8 Closed sorption storage with NaOH and H2O Sodium hydroxide is cheep and readily available It has a high affinity to water Evaporation and condensation temperatures are fitting to conventional solar collectors and residential requirements NaOH. nh20 + heat NaOH + nh2o

9 Closed sorption storage main components Heat and mass exchanger Storage tanks for sodium hydroxide and water Material Suitable for vacuum technology Resistant to highly concentrated sodium hydroxide solutions Stable at temperatures up to 100 C

10 Principal performance CHARGING DISCHARGING Solution Storage H2O Heat Source / Load Converter Chamber 1 Chamber 2 Heat Storage (Geothermal heat exchanger) Solar heat Domestic hot water / Space heating H2O Vapor H2O Vapor Heat sink Heat source Solution Storage H2O

11 Regeneration mode Heat is supplied to chamber 1 Water vapor is driven from the diluted sorbent This water vapor is condensed in chamber 2 Heat is removed from chamber 2 to the environment CHARGING DISCHARGING Solution Storage H2O Heat Source / Load Converter Chamber 1 Chamber 2 Heat Storage (Geothermal heat exchanger) Solar heat Domestic hot water / Space heating H2O Vapor H2O Vapor Heat sink Heat source Solution Storage H2O

12 Regeneration mode The concentration is dependent on the temperature difference of chamber 1 to chamber 2 Both the sorbent and the water are stored separately Chamber 1 and 2 function as desorber and condenser respectively CHARGING DISCHARGING Solution Storage H2O Heat Source / Load Converter Chamber 1 Chamber 2 Heat Storage (Geothermal heat exchanger) Solar heat Domestic hot water / Space heating H2O Vapor H2O Vapor Heat sink Heat source Solution Storage H2O

13 Heating mode In chamber 2 water is evaporated using heat from the environment This water vapor is absorbed by the sorbent in chamber 1 due to the high affinity of water to sodium hydroxide CHARGING DISCHARGING Solution Storage H2O Heat Source / Load Converter Chamber 1 Chamber 2 Heat Storage (Geothermal heat exchanger) Solar heat Domestic hot water / Space heating H2O Vapor H2O Vapor Heat sink Heat source Solution Storage H2O

14 Heating mode Heat is released from the vapor to chamber 2 Heat is gained for domestic hot water and space heating Chamber 1 and 2 function as absorber and evaporator respectively CHARGING DISCHARGING Solution Storage H2O Heat Source / Load Converter Chamber 1 Chamber 2 Heat Storage (Geothermal heat exchanger) Solar heat Domestic hot water / Space heating H2O Vapor H2O Vapor Heat sink Heat source Solution Storage H2O

15 Output temperature The output temperature is dependent on the sodium hydroxide concentration in the sorbent, as well as the temperature of the evaporator Temperature TAout [ C] Maximum temperature at a concentration of 50 % Concentration wsh [kg NaOH / kg solution] TEout = 0 C TEout = 10 C TEout = 20 C TEout = 30 C TEout = 40 C

16 Capacity The heating capacity is dependent on the degree of sorbent dilution Volumetric energy density [kwh / l] One heat pump stage Concentration [kg NaOH / kg solution]

17 Capacity To determine the heat capacity the maximum sorbent concentration and dilution has to be found This in turn is dependent on the temperature of the water entering the absorber and the temperature of the liquid departing the evaporator Domestic hot water 40 C 10 C wsh = 50 % Heat Pump Water 5 C 2 C Vertical bore hole heat exchanger Space heating wsl = 25 % ΔTAE = 8 K

18 Capacity The capacity is dependent on the temperature difference between fluid departing the evaporator and the fluid entering the absorber Temperature ΔTea Temperature [K] K 12 K 8 K Concentration [kg NaOH / kg Solution]

19 Sum up The output temperature is dependent on the sodium hydroxide concentration in the sorbent, as well as the temperature of the liquid departing the evaporator The capacity is dependent on the sodium hydroxide concentration in the sorbent, as well as the temperature of the liquid departing the evaporator and the liquid entering the absorber This imposes limitations on system operation

20 Prove of Function Initial experience has been gained from a lab scale build financed by the Swiss Federal Office of Energy vacuum pump Burst safety valve Water valve Vacuum valve Water circular pump Water gear pump H2O ωweak = 0.35 kg/kg NaOH ωstrong = 0.5 kg/kg NaOH In Lye gear pump Out In Out In Out Heat sink In Out In In Out Heat source Out In Out Boiler

21 Prove of Function The laboratory system was successful in proofing the concept of the closed sorption heat storage

22 Prototype System In the frame of the EU project Comtes a prototype system is now under construction The aim of the project is to build a system able to provide 100 % solar coverage for a single family house built to passive energy standards and located in Zürich The system is based on a hybrid concept, consisting of sensible heat storage in water tanks and the closed sorption heat storage

23 Heat and mass exchanger development Falling film heat and mass exchanger To solar collector H2O Vapor From solar collector

24 Tank development Tanks are made of stainless steel

25 Tank development Tanks either hold concentrated solution and diluted solution or water A total quantity of approximately 8000l of diluted solution is required

26 Prototype System Solar collector system NaOH Absorber / Desorber Space heating Domestic hot water NaOH Condenser / Evaporator 55 C Buffer Tanks Buffer Tank 1000 L V10 32 C DHW 25 C Buffer Tank 1000 L SH V11 10 C Buffer Tank 1000 L Buffer V1 V3 V2 V4 V5 V7 V6 V8 V12 V14 Heat Exchanger V9 V15 P1 P3 P4 V13 P5 P6 V16 5 C GP 5 In Out In Out Heat Exchanger P2 D / A 2 Space Heating 3 Heat Exchanger 4 C / E 2 Tank 10x H2O Solar Collector Tank 1x NaOH VX1 Tank 7x NaOH VX2 VX3 VX4 Tank 8x NaOH DHW DCW VX7 VX8 PX3 1 PX1 PX2 VX5 VX6

27 Prototype System Water tanks are heated first Excess heat is used to charge the closed sorption heat storage By insufficient solar input the absorption heat pump is employed to gain heat at the desired temperature, either from the sensible heat storage or from the vertical bore hole heat exchanger

28 Prototype System

29 Outlook A next development step inside of the SCCER Improve heat and mass exchanger Decrease implementation of costly materials Improve overall system performance Increase concentration while preventing crystallization Decrease evaporation temperature while preventing icing Improve storage tanks by decreasing dead volume

30 Thank you Benjamin Fumey EMPA - Material Science and Technology CH-8600 Dübendorf benjamin.fumey@empa.ch

SOLAR COOLING TECHNOLOGIES

SOLAR COOLING TECHNOLOGIES S. SRINIVASA MURTHY Professor of Refrigeration & Clean Energy Technologies Energy Efficiency Summit 2010 Chennai Trade Centre, Chennai Department of Mechanical Engineering Indian