Routes for A/C improvements. Francis Meunier Emeritus Professor Cnam

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1 Routes for A/C improvements Francis Meunier Emeritus Professor Cnam

2 Reduction of A/C electricity consumption: a big challenge Many progresses can be achieved: - using renewable energy - in the process concept - in the design -in the component selection etc.

3 Solar A/C

4 Solar A/C results (Singapore)

5 Data centers Free cooling ASRHAE recommends Free cooling for data centers when: Dry bulb temp<35 C Dew point temp<21 C See example of Japan where free cooling is possible for more than 7000hours (green) or even 8000hours (bold blue)

6 District cooling 5km in Singapore 70km in Paris (Climespace) EER: 5-5.5kWrh/kWeh at 4.5 C Compared to 3.5kWhr/kWeh at 6.7 C -35% electricity consumption -50% CO 2 emissions -90% refrigerant leaks

7 Which heat sink the best for A/C? Generally, ambient air is used as heat sink with two drawbacks: Hourly and seasonal temperature variations High temperature in summer Contribution to heat island in summer (a few degrees in Paris) Ground, water (lake, river, sea) can also be used with advantages: Nearly constant and lower temperature No contribution to heat island but a small cool island

8 District cooling in Geneva Cool water extracted from the lake and then distributed to the disctrict cooling system through a heat exchanger. The return water is reinjected into the lake close to the surface In Geneva, the deep water lake temperature is around 15 C which allows free cooling

9 Principle of cool sea loop in the mediteranean sea : case 1 The 15 C cool sea water (at 30-50m deep) is used directly to fire heat pumps distributed along the sea loop. The return water is rejected close to the surface The heat pump provides cooling in summer and heating in winter The problem is corrosion for the heat pump

10 Principle of cool sea loop in the mediteranean sea : case 2 To avoid corrosion, an alternative is to use a titanum heat exchanger The return water is rejected close to the surface Doing so, the loop can be clean water loop Heat pumps are distributed where needed

11 Principle of cool sea loop in the mediteranean sea : case 3 Another alternative is to have a heat exchanger deeply located in the sea. The loop is clean water loop In that case, the heat is rejected deeply which may cause biodiversity problems

12 Example of pipes used for sea water loop

13 Advantages of the cool sea loop The heat pump (HP) can be fired with nearly constant temperature heat source With that nearly constant temperature heat source, the HP efficiency can be extremely high In Europe, during spring and end of summer, free cooling can be provided

14 High performance sea loop A/C With sea water at 25 C, EER>7 and seasonal ESEER>9 for 7 C chilled water Moreover free cooling chilled water possible Therefore reduction by a factor more than 2 of the electricity consumption

15 Geothermal springs in Malaysia and Singapore

16 Principle of geothermal A/C Broad absorption chiller Sorption chiller fired by geothermal energy Geothermal energy at a temp>70 C If temp C: adsorption chiller with EER= If temp>85 C: single effect absorption chiller with EER=0.7

17 Chilled water at 7 C with sea loop 100m 3 /h 90 C Broad Chiller 12 C 884kWr 80 C Geothermal energy 7 C Chilled water Sea loop HX 30 C 28 C

18 Drawbacks of absorption for geothermal A/C Geothermal drilling is very expensive It is all the more important to optimize the energy extracted from a geothermal source The 10 C temperature drop for absorption chillers is too small New processes providing higher cooling rates are needed Two possibilities exist

19 Adsorption chiller An adsorption chiller operating between 75 and 65 C has a lower EER: 0.46 But using the geothermal energy between 90 and 65 C results in a cooling rate of 1050kWr for 100m3/h geothermal flow rate instead of 884kWr

20 Advanced cycle with large temperature spread for geothermal A/C: higher cooling rate Geothermal heat rejection 60 C Geothermal heat input 90 C If EER=0.57, then cooling rate for 100m 3 /h equal to 2000kWr

21 Ab-Ad-sorption chillers in series 90 C 80 C 75 C 65 C Absorption chiller operating between 90 and 80 C in series with An adsorption chiller operating between 75 and 65 C With a 100m 3 /h geothermal water rate, the cold production will be 1250 instead of 884kWr, i.e. a gain of 50%

22 Potential of geothermal A/C With a 100m 3 /h geothermal flow rate at 90 C, it is possible de produce: 884kWr at 7 C with absorption 1050kWr with adsorption 1250kWr with absorption and adsorption chillers in series 2000kWr with an innovative adsorption process The electricity consumption is used only for pumping and then reduced by a factor of 5 to 10.

23 Ambitious improvements for drastic A/C electricity consumption reduction District cooling: 35% reduction Cool sea loop : 50% reduction Renewable A/C: 80% reduction Free cooling (cool sea loop) Solar A/C Gothermal A/C Several solutions exist based on the state of the art But innovative research still required to improve geothermal A/C

24 Thank you