Ventilative Cooling issues in Mediterranean regions (The Spanish case) Servando Álvarez, José L. Molina University of Seville (Spain)

Transcription

1 Ventilative Cooling issues in Mediterranean regions (The Spanish case) Servando Álvarez, José L. Molina University of Seville (Spain)

2 Foreground A very powerful well known strategy to reduce the cooling needs of buildings is to use the low outdoor air temperatures during the night to cool either the indoor air (when the spaces air occupied during the night such as the bed rooms) or the structures of the building (for the other spaces of the building non occupied during the night). In many cases, the night-time outdoor air climatic conditions of many locations allow a significant compensation of the day-time solar and internal heat gains. The major concern is the ability of the building inertia to store cool during the night and to use during the day the coolness produced during the previous night.

3 E.P. Indicators in NZEB context pren ISO/DIS

4 Contents Cooling energy needs in the Spanish regulations Understanding the ventilative cooling Promoting the efficiency of ventilative cooling strategies Additional Capabilities in the National Calculation Tool in Spain Conclusions

5 Climate Severity Indexes for Winter and summer (Madrid as the reference) Winter CSI Summer CSI

6 The Climate in Spain Winter Zones Summer Zones Population TOTAL A - - 3,462, ,289 3,848,633 B - - 8,144,034 2,898,423 11,042,457 C 5,232,691 5,403,351 2,327,846 2,272,987 15,236,875 D 1,671,936 2,837,104 8,276,564-12,785,604 E 1,195, ,195,330 TOTAL 8,099,957 8,240,455 22,210,788 5,557,699 44,108,899

7 Cooling Demand (kwh/m 2 ) The reference energy needs in Spain (2006) for the 50 capitals of province (Appartment blocks) 25 Apartment blocks Heating Demand (kwh/m 2 )

8 Heating and cooling needs (Minimum requirements (2013) and foreseen NZEB requirements)

9 Cooling needs

10 Cooling Cooling needs = Heat gains Net Heat losses Gains [ Wh / m 2 ] no i 1 I i ne i j 1 Fs g A j, i A a a t Net losses [ kwh / m 2 ] ( ρ cp ACH V ) night DD night 24 Strategies: Solar control Night ventilation

11 Balancing global solar factor and night ventilation to comply with the limit values of the cooling needs in 2013 spanish regulations Global solar factors below 0.1 implies potential comflict with daylight issues. Natural ventilation is required in many combinations of orientation and window to wall área. Stricter values of the cooling needs (NZEB) will imply emphasis on night ventilation as solar alreay got its practical limit

12 Example of efficiency of night ventilation in Seville (zone 4)

13 Losses / Gains June July August Septem. 4 ren/h ren/h ren/h ren/h ren/h ren/h UF June July August September 4 ren/h ren/h ren/h ren/h ren/h ren/h Net losses [ kwh / m 2 ] ( ρ cp ACH V ) night DD night 24

14 The effect of the inertia If losses are higher than gains, why the building requires cooling?. Because only a small fraction of actual losses is used (Utilisation Factor) Because the actual losses are much lower tan the estimated losses (Ventilative efficiency) The actual losses and the Utilisation Factor depends to a big extent on the thermal inertia of the building.

15 Contents Cooling energy needs in the Spanish regulations Understanding ventilative cooling Promoting the efficiency of ventilative cooling strategies Additional capabilities in the National Calculation Tools Conclusions

16 The actual lossess The building is a very poor regenerative heat exchanger.

17 Temperatura (ºC) Efficiency of the building as heat echanger 26 Tinterior edificio Texterior Carga (noche) Descarga (día) t alm T alm T 0 0 T alm T alm ext t 17

18 Night ventilation: Heat dissipation A Effective thickness (cm) 2.5 ACH (h -1 ) 8 Convective Coef. (W/m 2 K) 2 CR m' c M C t p p alm NTU h S m Cp 18

19 Influence of the ACH A ACH Ԑ Q/Qa

20 Influence of the thickness A Thickness (cm) Ԑ Q/Q A

21 Influence of the convection coefficient A Convective Coef. (W/m2K) Ԑ Q/Qa

22 Temperatura (ºC) Night ventilation dependency Texterior Carga (noche) Tinterior edificio Descarga (día) t Outdoor climate (Tª at night-time). ACH. Thermal mass (inertia). Flow pattern (convective heat transfer coeficients). Time span between dissipation period and cooling needs period

23 Contents Cooling energy needs in the Spanish regulations Understanding ventilative cooling Promoting the efficiency of ventilative cooling strategies Additional capabilities in the National Calculation Tools Conclusions

24 Cooling the internal walls using night-time ventilation Outdoor climate (Tª at night-time). ACH. Thermal mass (inertia). Flow pattern (convective heat transfer coeficients). Time span between dissipation period and cooling needs periodc

25 Activating the thermal inertia by increasing the convection coefficients

26 Activating the thermal inertia by increasing the convection coefficients Área de transferencia (m2) Coeficiente de Película h (W/m2K) Zona Pared Pared Pared Pared Pared Pared Pared Pared Pared Pared Pared suelo techo

27 rid rid Apr 12, 2004 FLUENT 6.1 (2d, dp, segregated, ske) Apr 12, 2004 FLUENT 6.1 (2d, dp, segregated, ske) Grid Grid Grid Apr 12, 2004 FLUENT 6.1 (2d, dp, segregated, ske) Apr 12, 2004 FLUENT 6.1 (2d, dp, segregated, ske) Apr 12, 2004 FLUENT 6.1 (2d, dp, segregated, ske) Grid Grid Apr 12, 2004 FLUENT 6.1 (2d, dp, segregated, ske) Apr 12, 2004 FLUENT 6.1 (2d, dp, segregated, ske) Convective heat transfer coefficient in night ventilation for different flow patterns Configuración 1 Configuración 2 Configuración 3 Configuración 4 Configuración 5 Configuración 6 Configuración 7

28 Activating the thermal inertia by promoting the ACH

29 Thermal Mass???? The thermal mass of the buildings is tipically concentrated in external walls, floor and ceiling slabs which are not usually touched by the air flow

30 Cooling floors and ceilings using night ventiltion

31 Thermodeck (cooling the building mass and day-time air for ventilation purposes).

32 Tubes with PCM Hollow core slabs with PCM

33 Night time PCM solid Opperation principle Intermediate Central hours PCM liquid

34 Cooling external walls using night ventiltion

35 Active façade (Summer mode) Fans Indoor Outdoor 35

36 Active facade (Summer mode) Frio Frio Calor

37 summer of 2015 in Seville

38 Evaporative cooling Potencial de enfriamiento evaporativo nocturno.- de 20ºC de foco frío se pasa a 14.5ºC 20 ºC 38ºC

39 Experimental set-up

40 Nozzels Experimental set-up

41 Temperature in the air layer without ventilation T. outdoor

42 Temperature in the air layer with mechanical ventilation and evaporation T. exterior

43 Diferencia entre temperatura difference indoor-outdoor (daily averages) Without ventilated facade T Ventilated facade without evaporation Ventilated facade with evaporation

44 Contents Cooling energy needs in the Spanish regulations Understanding ventilative cooling Promoting the efficiency of ventilative cooling strategies Additional capabilities in Spanish National Calculation Tools Conclusions

45 The national calculation tool

46 Additional capabilities in the national calculation tool The increased level of required values for limiting the energy demands of heating and cooling require expanding the scope and substantially relax the default values to be taken by calculation procedures. In the 2014 edition it has been included so-called additional capabilities that may be specific or generic. Specific are included explicitly in the program and require no justification. Generic require the use of a complementary software (or the existence of specific studies or curves manufacturers) to justify the use of values different of the default ones preset by the standard of calculation. These new values are more adapted to the characteristics of the building or to the passive or hybrid strategies employed. Additional generic capabilities fall into three categories: Building componentes Zone Multizone

47 CAG: Componentes Additional capabilities Component level

48 CAG: Componentes

49 Active facade (Summer mode) Frio Frio Calor

50 CAG: Componentes Additional capabilities Zone level

51 CAG: Zona

52 Activating the thermal inertia by increasing the convection coefficients Área de transferenci a (m2) Coeficiente de Película h (W/m2K) Zona Pared Pared Pared Pared Pared Pared Pared Pared Pared Pared Pared suelo techo

53 CAG: Componentes Additional capabilities Multizone level

54 CAG: Multizona

55 Ventilation strategy: multizone Air flow software Exterior Salón Dormitorio 1 Dormitorio 2 Dormitorio 3 Cocina Pasillo Baño Exterior Salón Dormitorio Dormitorio Dormitorio Cocina Pasillo Baño

56 Conclusions The roadmap of the 2020 compromises and beyond implies more and more strict regulations regarding cooling energy needs of buildings. The low temperatures during nigh-time can potentially elliminate the cooling needs of most buildings in most regions. The appropriate design of night ventilation strategies implies a wise use of the thermal inertia, which is extremelly difficult to get. Alternatives are night ventilation based on hybrid approaches as well as the use of innovative components for walls, roofs, floors and slabs. The evaluation and acreditation of solutions based on the thermal inertia of the buildings require the update of adaptation of calculation tools.

57 Venticool s position

58 Ventilative Cooling issues in Mediterranean regions (The Spanish case) Servando Álvarez, José L. Molina University of Seville (Spain)

59 The sole responsibility for the content of this presentation lies with the authors. It does not necessarily reflect the opinion of the European Union. Neither the EASME nor the European Commission are responsible for any use that may be made of the information contained therein.