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DESIGN OF A GAS-FIRED CARBON-AMMONIA ADSORPTION HEAT
PUMPSteven Metcalf, Ángeles Rivero Pacho, Bob Critoph
University of Warwick
i-STUTE, 9 March 2018
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• Box-for-box exchange for conventional gas boiler Retrofit market (> 90% of annual sales)
• Air source• 30% reduction in gas consumption• 7-10 kW (UK, 3 bedroom semi-detached house)
Heat pump concept
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Schematic drawing
Gas Burner
Hot Gases
Air-to-Pressurised Water Heat Exchanger
Warm Exhaust Gases
Inlet Air
Final Exhaust Heat Exchanger
AdsorbentBed 1Heated
AdsorbentBed 2Cooled
Condenser
Evaporator
Cooled Air from Evaporator
Return water from house
Ammonia
Cool Exhaust Gases
Ambient Air to Evaporator
Heated water to house
Focussing only on adsorption heat pump development
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Previous Generator Design
Shell and tube heat exchanger
150 mm
40
0 m
m
0.8 mm
3 mm1.2 mm
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Experimental Results (June 2016)
Experiment Model
Cycle Time
[s]
Load Inlet [°C]
Load Outlet
[°C]
Evaporating Temperature
[°C]COP COP
480 26.2 31.7 3.2 1.34 1.33
420 27.1 33.1 0.1 1.32 1.31
420 28.2 34 3.7 1.33 1.3
480 28.8 35.1 -1.6 1.3 1.3
420 32.9 37.9 3.9 1.255 1.29
360 33.4 38.8 4 1.23 1.27
540 37.6 42.7 1.9 1.244 1.25
480 38 43.4 1.8 1.233 1.25
300 40.5 46.7 3.5 1.19 1.21
Heating Power: 7.5 – 9 kWCOP: 1.19 – 1.34
Conclusion:
Machine performed as predicted,however, high manufacturing cost of the generators prohibited further development.
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New Generator Design
Shell and Finned Tube
Design Parameters:
• Tube diameter
• Tube pitch
• Carbon thickness
• Fin thickness
• Turbulator tube insert
Detailed simulations in Matlab
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New Generator Design
Target Performance:
• Heating Power 10 kW
• Total Generator Volume ≤10 litres
• Internal COP≥1.4
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Performance Predictions
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Large Temperature Jump Test100 mm Long Test Sample
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Large Temperature Jump Test
Vessel (Ammonia
Gas)
TP
T T
Water Flow
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Large Temperature Jump Test
Match obtained between experiment and model predicted pressure rise
Time constant ~50 seconds
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Machine Construction
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Hot off the press…
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Machine Construction
GeneratorsEvaporator
Condenser
Water valves
Water pumps
Ammonia Check Valves
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Machine Testing
System of Heating and Cooling Baths to provide:
- Up to 170°C Pressurised Water for High Temperature Heat Input
- 10 kW of heat rejection for the condenser and cooler
- Glycol flow down to -10°C for evaporator
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Conclusions
• Finned tube generator designs investigated with MATLAB model
• Performance verified with a sample section tested with the large temperature jump method
• Complete machine under construction as a test bed for generator and diverting valve designs
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Further Work• If the generator design gives promising results, the unit will
be packaged more compactly.
• A gas burner and air-source evaporator would be added and testing carried out in an environmental chamber.
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Thanks for your attention!