Simulation of a small size solar assisted adsorption air conditioning system for residential applications

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1 Heat Powered Cycles Conference Simulation of a small size solar assisted adsorption air conditioning system for residential applications Salvatore Vasta, Andrea Frazzica, Gaetano Maggio, Alessio Sapienza, Gaetano Cacciola

2 MAIN GOAL Simulation a small size solar assisted adsorption air conditioning system by means of a TRNSYS mathematical model capable to dynamically calculate the behaviour of each component of the system. The small size adsorption chiller has been modelled on the basis of experimental data collected on a laboratory prototype developed by CNR ITAE Summary o Aim and background o Support of the activity o Lay out of the system simulated o Adsorption chiller o Test o TRNSYS mathematical model description o Study of the performance achievable o Conclusions

3 Aim and background Solar thermal energy utilization has seen a considerable development number and size of applications grow up. One of the potential and more promising application of thermal solar energy use is building air conditioning highest cooling demand in the buildings occurs when the solar energy availability is the highest. The peak load on the electricity grid in summer critically increased especially in Mediterranean countries BUT. Application of solar cooling systems in the building sector has been limited to a small number of pilot and demonstration projects. CAUSES 1. Low level of technical/economic development of the thermally driven chillers 2. Large size of thermally driven chillers available on the market 3. High cost of the solar collectors 4. Very low cost of the electric cooling devices In such a background, small and cheap adsorption solar air conditioning systems show a high potential.

4 Support of the activity The work is partially supported by a national project which aim is the design and the realization of a small size demonstrative solar cooling system using a self made adsorption chiller (project duration 3 yr.) 1 st year 2 nd year 3 rd year Identification of the best adsorbent and heat exchanger concept (collab. Un. Messina) Adsorption HP realization System simulation by TRNSYS Acquisition of components (solar panels, heat storage reservoirs, control system, etc.) Model Validation Experimental Tests Executive design of the solar in laboratory cooling system Energetic, economic and exergetic analisys LCA- Life Cycle Assestment (collab. Un. Catania) Realization of the solar cooling system Field tests (climatizzation of an ITAE office

5 Lay out of the system simulated Thermal storage 3 4 Dry cooler 5 Adsorption chiller ack up boiler 2 6 Fan coil 1 Water pump Safety valve Tmax=130 C Water hummer arrestor Safety valve Pmax = 3 bar Ball valve Temperature sensor Expansion tank Flow sensor Pressure reducer Outgassing device 3-way valve Back vent Pressure gage Solar collectors The solar cooling system is also equipped with electric pumps, expansion tanks and several safety devices

6 Adsorption chiller Key features for solar cooling thermally driven by low temperature heat source (70 90 C), utilize cheap, safe and not polluting refrigerants and adsorbent materials do not present moving parts (low maintenance) A wide availability on the market of units with a small nominal cooling capacity is expected A relevant reduction of collectors cost is expected CNR ITAE adsorption prototype Type: 2 beds non regenerative Adsorbent: AQSOA Z02 Refrigerant: water HT level: C MT level: up to 45 C LT level: 5 20 C Cooling power: C (cond.) COP: 35 C (cond.) Cooling power: 1 45 C (cond.) COP: 45 C (cond.)

7 Adsorption chiller LAB test Aim: extract experimetal data to be used in the model Investigated condition A specific test bench was used in order to simulate the external heat source/sink, to measure the most relevant parameters and to perform tests at different operating conditions more than 6000 cycles were performed in different operating conditions

8 Cooling Power [kw] Test/ Power COP COP Average cooling power (kw) Power COP COP Delta T Condenser Evaporator [ C] T inlet condenser ( C) 0.0 The results of tests have been treated and a proper regression has been done in order to create a new library in TRNSYS environment (TYPE XX) to simulate the adsorption chiller behaviour as a function of the working condition

9 Model description/1 TRNSYS is a commercial software built to simulate the dynamic behaviour of power systems. Key features for this application Presence of dedicated libraries to model the different components (solar collectors, heat storages, absorption machines, etc.). It allows to model new components by writing the governing equations in Fortran language. Meteonorm data for the city of Messina Type 109 TMY2 the evacuated tube and flat plate solar collectors Type 538 and Type 540 the gas boiler Type 700 the thermal storage Type 60 the fan coils and the dry cooler Type 508 and Type 753 the thermal load corresponding to a 30 m 3 office room Type 56 The adsorption machine self made Type (Type 151)* * The new Type created calculates COP and cooling power as a function of the input temperature of the condenser and evaporator

10 Model description/2 The model was developed in TRNSYS by a graphic UI Messina Control 1 Control 2 Coil Fan 1 Pump 4 Solar Collectors Pump 1 Pump 3 Adsorption Chiller Heat Storage Load Inner gains: 2.5 m 4.0 m 2 people 2 PC 1 lamp Pump 2 Control 3 Pump m Gas Boiler Radiator Fan 2 S = 10 m 2 V = 30 m 3 S window = 3 m 2

11 Study of the performance achievable/1 Several simulations have been carried: performance have been calculated during the summer 15 June 15 September Parametric analysis: 1.Collector type: evacuated tube / flat plate solar 2.Volume of heat storage, 3.Tilt angle 4.Total solar collectors surface. Performance has been evaluated by calculating, the fraction of the Solar Energy Supplied the ratio of the amount of heat supplied by solar collectors to the total amount of heat supplied. Thermal energy from boiler Thermal energy from sun TOTAL S.E.S (%) = Thermal energy from sun TOTAL

12 Study of the performance achievable/2 Evacuated type Solar energy supply Tilt angle Area: 3.2 m^2 Area: 6.4 m^2 Area: 9.6 m^2 Area: 12.8 m^2 Area: 16.0 m^2 Area: 19.2 m^2 Solar energy supply Tilt angle Area:5.2 m^2 Area:10.5 m^2 Area:15.7 m^2 Area:21.0 m^2 Area:26.2 m^2 Optimum tilt angle is 20 for both cases BUT influence of the tilt variation is more evident for the flat plate collectors Flat type a reduction of the fraction of solar energy supply by about 25% can be observed changing the tilt angle from 20 to 45, while for evacuated tube collectors it is only 2%

13 Study of the performance achievable/3 Parameter: - thermal storage volume ( m 3 ) - overall area of the solar collectors (up to 19.2 m 2 and 26.2 m 2 ) Solar energy supply Evacuated type Collectors area[m 2 ] Solar energy supply Flat type Collectors area [m 2 ] Heat storage volume:0.3 m3 Heat storage volume:0.5 m3 Heat storage volume:0.3 m3 Heat storage volume:0.5 m3 Heat storage volume:0.75 m3 Heat storage volume:0.75 m3 Evacuated-tube collectors allow to achieve a very high solar energy supply, 500 l of thermal storage volume ) Flat-plate collectors allow to reach a maximum value of solar energy supply equal to l of thermal storage volume Flat-plate collectors : a considerable reduction of the solar energy supply value can be observed when the thermal storage volume is reduced.

14 Study of the performance achievable/4 Evolution of the ambient and internal temperature calculated for an optimized solar cooling system (12.8 m 2 of evacuated tube collectors, 20 tilt, 0.5 m 3 of thermal storage July) Temperature [ C] th 18th 19th 20th 21th 22th 23th July July July July July July July Days Ambient temperature [ C] Internal temperature [ C] Note: 1.Adsorption machine works from 8 A.M. to 6 P.M 2.Solar cooling system is capable to maintain a comfortable internal temperature (25 35 C external temperature)

15 Conclusions/1 1. A model of a small solar air conditioning system based on a adsorption chiller developed by CNR ITAE, was implemented in TRNSYS 2. The model has been verified and several simulations have been done. 3. Results of simulations allowed to optimize the design 4. Results of simulations show that the optimized solar cooling system is capable to maintain a comfortable internal temperature (25 C) in a 30 m 3 office room, even if the external temperature exceeds 35 C 5.. See next slide

16 Conclusions/2 Model has been used to simulate and design a demonstrative solar cooling system that will be built up in Messina. N EVacuated type solar collectros N = 7 S = 20 m 2 Office container V = 30 m 3 CNR ITAE Institute

17 Heat Powered Cycles Conference Simulation of a small size solar assisted adsorption air conditioning system for residential applications Salvatore Vasta, Andrea Frazzica, Gaetano Maggio, Alessio Sapienza, Gaetano Cacciola