Energy saving by evaporative cooling in AHUs

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Information about Energy saving by evaporative cooling in AHUs

Published on December 14, 2016

Author: CAREL_group

Source: slideshare.net

1. ENERGY SAVING BY EVAPORATIVE COOLING IN AHUs Raul Simonetti – CAREL Industries SpA (Italy) 1. Natural water evaporation & cooling 2. Water atomizers 3. DEC & IEC 4. Energy Saving by DEC/IEC in Australia

2. Natural water evaporation & cooling (1/2) • Water naturally evaporates when in contact with air • It requires energy: the latent heat of vaporization • Latent heat of vaporization  690 W/(L/h) • This heat is drawn also from the air, which is humidified and cooled (evaporative cooling)

3. Natural water evaporation & cooling (2/2) • The evaporation rate (L/h) is “proportional” to the contact surface air-water • The wider the surface, the stronger the evaporation, thus the heat taken from the air and the evaporative cooling – 1 L/h  0.69 kW of cooling – 100 L/h  69 kW of cooling – and so on

4. Water atomizers: description • They spray water in very tiny drops (5-50 µm) • The smaller the drops, the wider their total surface, the stronger the evaporation and the evaporative cooling • Small drops is better! • Input power: 0.5-10 W/(L/h)

5. Evaporation in AHUs/ducts (1/2) • Tiny drops fly with the air, do not fall • Evaporation takes time, thus some drops may not fully evaporate before the first device downstream (coil, blower, etc.) • Evaporation efficiency η = evaporated/sprayed water = 50%-95% depending on models and conditions °C before g/kg before m³/h m/s µm           η           Key:  = the characteristic increases  = the characteristic decreases

6. Evaporation in AHUs/ducts (2/2) • Non-evaporated drops must be collected and drained not to wet downstream • Drop separator (30-70 Pa) and drained drop pan are required

7. WUE: Water-Usage Effectiveness • WUE = evaporated water / input mains water • WUE = (evap.’d w. / sprayed w.) x (sprayed w. / input mains w.) • Typ. WUE with RO system: 10% to 48% • Typ. WUE with softener: 48% to 95% Water treatment Supply waterMains water Drain

8. DEC: Direct Evaporative Cooling (1/2) Evaporation in supply air : cooling + humidification

9. DEC: Direct Evaporative Cooling (2/2) Overall water consumption may be reduced To yield 1 kWhcooling, a chiller–based system uses: EERSI = 3 kWcooling/kWelectric [e] = 0.3 kWhelectric (= 1 / 3) Combined value for the water withdrawal of power plants in Australia: 46.0 L/kWhelectric 1 kWhcooling generated by a chiller system requires: [a] = 15.3 L of mains w. (= 1/3 x 46) If DEC does 1 kWhcooling, the evaporated water in air is: 1 L of evaporated water  0.69 kWhcooling 1.4 L (= 1 / 0.69) The amount of mains water supplied to the water-spraying system is: WUE of the water atomizer is equal to 80% [b] = 1.8 L (= 1.4 / 0.80) Input energy to DEC @ 10 W/(L/h) [c] = 18 Wh (= 1.8 x 10) Input energy saved [e-c] 0.282 kWhelectric/kWhcooling Mains water SAVED with DEC [a-b] 13.5 L/kWhcooling

10. IEC: Indirect Evaporative Cooling (1/2) • Evaporation in exhaust before heat exchanger (cross-flow or run-round coil): 1 + 3 below • Only sensible cooling is passed on to the supply • To avoid humidification (e.g. suitable for tropical climate)

11. IEC: Indirect Evaporative Cooling (2/2) Overall water consumption may be reduced To yield 1 kWhcooling, a chiller–based system uses: EERSI = 3 kWcooling/kWelectric [e] = 0.3 kWhelectric (= 1 / 3) Combined value for the water withdrawal of power plants in Australia: 46.0 L/kWhelectric 1 kWhcooling generated by a chiller system requires: [a] = 15.3 L of mains w. (= 1/3 x 46) Heat exchanger’s efficiency: 60% 60% If IEC does 1 kWhcooling to the outdoor air, the cooling of the exhaust air is: and the evaporated water in the exhaust air is: 1 L of evaporated water  0.69 kWhcooling 1.7 kWhcooling (= 1 / 0.60) 2.5 L (= 1.7 / 0.69) The amount of mains water supplied to the water-spraying system is: WUE of the water atomizer is equal to 80% [c] = 3.1 L (= 2.5 / 0.80) Input energy to IEC @ 10 W/(L/h) [d] = 31 Wh (= 3.1 x 10) Mains water SAVED with IEC [a-c] 12.2 L/kWhcooling Input energy saved [e-d] 0.269 kWhelectric/kWhcooling

12. DEC + IEC • DEC sprays to the required cooling OR the set %rh • IEC starts to do more cooling if required • Water saving: combination

13. Estimations of Energy Saving 50% To servers 22 °C 45 %rh From servers 32 °C 25 %rh • 3 data centres: 50 kW, 100 kW, 500 kW • Adelaide, Brisbane, Canberra, Darwin, Melbourne, Perth, Sydney • AHU: 24/7, modulating outdoor air for free cooling, EER = 3 • Water: 2.2 AUD/kL - Electricity: 0.276 AUD/kW • Installation: 2000 AUD per DEC+IEC

14. Energy Saving by DEC/IEC: ROIs

15. Energy Saving by DEC/IEC: comments (1/3) Internal heat loads ROI 50 kW 100 kW 500 kW Max 1 yr None Adelaide, Perth ALL but Darwin > 1 to 2 yrs Adelaide, Perth Brisbane, Canberra, Melbourne, Sydney ALL but Darwin > 2 to 3 yrs Canberra, Melbourne, Sydney None ALL but Darwin Darwin, given its outdoor conditions, might have a convenient ROI for internal loads > 500 Kw • Warm, not damp climate support energy saving by DEC/IEC • The higher the internal load, the higher the saving, the better the ROI • Overall water saving and CO2: next slides

16. Energy Saving by DEC/IEC: comments (2/3) • DEC/IEC uses water, but reduces electricity input • This reduces water withdrawals by the power plants • Overall water consumption is reduced: CITIES Electricity saved [kWh/yr] DEC/IEC [kL/yr] Withdrawal [kL/yr] Water saved [kL/yr] Adelaide 57,520 320 -2,647 -2,327 Brisbane 27,484 327 -1,265 -938 Canberra 33,038 186 -1,520 -1,334 Darwin 5,397 201 -248 -47 Melbourne 34,622 172 -1,593 -1,421 Perth 51,058 527 -2,350 -1,823 Sydney 31,893 362 -1,468 -1,106 Key: • Data “proportional” to 50kW heat load • 46 L per kWhelectricity

17. Energy Saving by DEC/IEC: comments (3/3) The saved electricity also reduces CO2: CITIES Energy saved [kWh/yr] CO2 reduction [ton eq. /yr] Adelaide 57,520 -49 Brisbane 27,484 -23 Canberra 33,038 -28 Darwin 5,397 -5 Melbourne 34,622 -29 Perth 51,058 -43 Sydney 31,893 -27 Key: • Data “proportional” to 50kW heat load • 852x10-6 ton eq. per kWhelectricity

18. DEC/IEC by water sprayers: conclusions • Cooling from water evaporation  690 Wcooling/(L/h) • Reduces electricity consumption because reduces the load of the cooling coils (chillers) • Suitable for Australia: YES • ROIs depend on installation and location, but may be 1-3 years for internal loads from 50 kW • Reduces water withdrawal of power plants and overall water consumption • Reduces CO2 from power plants

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