Cool-roof impacts on a School-building thermal and energy performance in

Greece

Cooperation between EU and Mediterranean partner Countries in the Energy Sector- International Workshop

G.M. Stavrakakis, Division of Development Programmes-CRESA.V. Androutsopoulos, Energy Measurements Laboratory-CRES

Project overview

Scheduling of cool-roof application and of measurement procedure.

Installation of monitoring equipment.

Onsite thermal and energy inspection (collection of data and

interviews with end-users).

Development of the building energy simulation model.

Validation and calibration of the model with comparisons between

simulated and measured thermal indicators.

Estimation of temperature difference between the situations before

(ex-ante condition) and after (ex-post condition) the application of

cool roof on the pilot building.

Evaluation of cool-roof impacts on thermal comfort and energy

performance through whole-year building energy simulation using

the model developed.

Collation of simulated results for different conditioning scenarios to

determine under which conditions the cool-roof contributes to total

primary energy savings.

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Project

Cool Roof Impacts on

BUilding’s Thermal

PErformance (CRIBUTE)

Partners

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Pilot building characteristics [1/2]

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Pilot building characteristics [2/2]

Building occupancy schedule: 9 Sep. to 15 June: All rooms are operating all working days (all days except weekends) from 08.00-16.00, except of 15 days in end December/early January, and in April due to Christmas and Easter holidays, respectively.

16 June to 30 July: Ground-floor is in full operation as the aforementioned working days, while the 1st

floor remains unoccupied.

1 Aug. to 9 Sep.: The School remains unoccupied (Summer holidays).

Appliance System Properties Operation schedule

Heating Central heater unit: natural-gas

boiler

Terminals: Radiators

Auxiliary units: two circulators

Heater installed

capacity: 220 kW

Heater internal

efficiency: 89.8%

Circulators’ capacity:

400W

Well-insulated heater

and network tubes

Set-point: 20oC

07.30-11.30 on

working days

Ventilation 2 ceiling fans in each occupied

room

Installed capacity of

each fan: 82 W

All winter working

hours only when

ambient air

temperature reaches

29 oC or above

(observation obtained

during onsite

inspections in relation

to measurements)

Cooling 1 AC split unit in the PC room Cooling capacity: 6.7

kW Input power: 2.57

kW EER: 2.6

Set-point: 26oC

All summer working

hours

Lighting ~ 24 fluorescent lamps in each

occupied room

T8 36 W Winter: All working

hours

Summer: 07.30-10.00

on working days

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Application of the cool roof

Material properties:

Emissivity: 0.89

Reflectance: 0.89

Thermal conductivity (W/(mK)): 0.87

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Measuring procedure

Measurements of Thermal Performance Indicators (TPIs) in both

the Pilot and the Reference Building.

The data logging of the sensors readings was performed on a 10 minutely basis in a flash memory card.

Two phases are distinguished:Phase 1 (ex-ante): From June 23 to July 9, in which both school buildings are monitored to gain knowledge about their thermal behavior.Phase 2 (ex-post): From July 11 to July 29, in which both school buildings are again monitored after the application of the cool roof on the roof of the 7th

school class rooms.

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Numerical model

Systems and Occupancy properties & Schedules

Pilot building (ex-ante)=Reference building

Pilot building (ex-post)

Impact:

TPIs difference between the Reference and the Pilot building in the 2nd Phase.

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Model validation/calibration

Parametric cases:•Insulated envelope. •Non-insulated envelope.•Partly-insulated 1: Insulated brick-wall and roof and non-insulated bearing structure.•Partly-insulated 2: Non-insulated wall and insulated roof.

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23-Jun24-Jun25-Jun26-Jun27-Jun28-Jun29-Jun30-Jun 1-Jul 2-Jul 3-Jul 4-Jul 5-Jul 6-Jul 7-Jul 8-Jul 9-Jul 13-Jul 14-Jul 15-Jul 16-Jul 17-Jul 18-Jul 19-Jul 20-Jul 21-Jul 22-Jul 23-Jul 24-Jul 25-Jul 26-Jul 27-Jul 28-Jul 29-Jul

Tem

pe

ratu

re (

oC

)

Date/Time

Results in the 1st-floor north measurement classroom of the pilot building

Pilot_North_Tair_exp Pilot_North_Tair_sim_no-insul Pilot_North_sim_insul

Pilot_North_sim_part-insul1 Pilot_North_sim_part-insul2

-6%

-3%

0%

3%

6%

9%

12%

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23-Jun24-Jun25-Jun26-Jun27-Jun28-Jun29-Jun30-Jun 1-Jul 2-Jul 3-Jul 4-Jul 5-Jul 6-Jul 7-Jul 8-Jul 9-Jul 13-Jul 14-Jul 15-Jul 16-Jul 17-Jul 18-Jul 19-Jul 20-Jul 21-Jul 22-Jul 23-Jul 24-Jul 25-Jul 26-Jul 27-Jul 28-Jul 29-Jul

Pre

dic

tio

n e

rro

r

Date/Time

Prediction divergence at the 1st-floor north measurement classroom

Error_North_no-insul Error_North_insul Error_North_part-insul1 Error_North_part-insul2

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Building thermal response

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13-Jul 14-Jul 15-Jul 16-Jul 17-Jul 18-Jul 19-Jul 20-Jul 21-Jul 22-Jul 23-Jul 24-Jul 25-Jul 26-Jul 27-Jul 28-Jul 29-Jul

Tem

pe

rature

diffe

ren

ce (oC

)Te

mp

era

ture

(oC

)

Date/Time

Floor-averaged temperature before and after the cool-roof

Pilot_Floor avg_exp Ref_floor avg_exp Ex-ante_floor avg_sim Ex-post_floor avg_sim DT_exp DT_sim

Both measurements and simulations converge to an indoor air temperature reduction after the cool-roof application of about 2oC, being most obvious during the first 10 days after the application. Interestingly, an increasing trend of the recorded temperature reduction is observed after the 23rd July reaching a maximum value of 2.6oC, contrary to the simulated reduction which presents a quite constant behaviour throughout the ex-post period.

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Impacts on building energy performance

Base-case: Pilot building with operating conditions and systems as observed during the inspection (free-floating 1st floor after 15th June). Scenario1: Pilot building with ACs instead of fans and the 1st floor is fully operating after 15th June until 30 July.

Adopted building part marked in pink colour

case

Scenario1

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Impacts on building energy performance

Base-case: Pilot building with operating conditions and systems as observed during the inspection (free-floating 1st floor after 15th June). Scenario1: Pilot building with ACs instead of fans and the 1st floor is fully operating after 15th June until 30 July.

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Building energy summary results

Impacts on EPIs

Base-case Scenario2

Building-block (below

cool roof)

Whole-building

Building-block (below

cool roof)

Whole-building

%ΔΕFans or %ΔEACs

29.28 7.19 18.57 5.64

%ΔΕheating -12.22 -3.65 -12.22 -3.65

% ΔEtot,prim -4.85 -1.43 7.41 0.41

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Thermal comfort impacts

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES

Conclusions

Indoor air temperature reduction below the cool roof (in summer): 2-2.6oC.

Associated heating penalty: up to 12%. Leading to not more than 5% increase of annual

primary energy consumption in the case of ceiling fans.

Ventilation energy demand in summer is significantly reduced after the application of the cool

roof reaching 30% in the case of ceiling fans use.

Thermal comfort on warm summer days is improved by at least 20%.

In the AC-use case, thermal comfort conditions are improved by at least 23% under a reduction

of cooling loads by 20%. Any heating penalty is fully compensated ensuring 4.5-7.5% savings in

annual total primary energy consumption.

Cool-roof: Energy-Saving and Thermal-Comfort Potential even in summer-paused buildings in

warm Climates => Efficient and affordable solution in the MENA (Middle-East North Africa)

Region.

Acknowledgments

The research work was funded by DOW Europe GMBH in the framework of the project Cool Roof Impacts on BUilding’sThermal Performance (CRIBUTE). The authors would like to thank Mr. Prokopis Perdikis from ABOLIN Co. for the identificationof the School buildings, for providing the properties of the cool material and for supporting CRES team during the energy andthermal inspections. The authors also thank Dr. Jouko Vyorykka from DOW Europe for coordinating the project, ensuringrequired resources and providing scientific advice, and Mr. Ioannis Melidonis from DOW Hellas for his market-orientedcontributions.

Dr. George M. Stavrakakis, Senior Research AssociateChemical Engineer, PhD, MSc

Division of Development ProgrammesCentre for Renewable Energy Sources and Saving (CRES) Email address: gstavr@cres.gr Postal address: 19th km, Marathonos Av., GR-19009, Pikermi, Attiki, GreeceTel.: +30 210 6603372Fax: +30 210 6603303

www.cres.gr

ΕΥΧΑΡΙΣΤΩ ΠΟΛΥ!

Cool-roof impacts on a School-building G.M. Stavrakakis & A.V. Androutsopoulos, CRES