INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Green Facades – How does plant choice affect wall cooling and wall
insulation?
Ross CameronUniversity of Sheffield, UKJane Taylor, Martin Emmett
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
The Context
• UK Victorian / Edwardian building stock• Brick dominated• Difficult to ‘retrofit’• Domestic properties – owned or rented• Replicated real houses???• ‘Down-sized’ – replicated ‘mini-buildings’ and
walls• Controlled environment studies
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
3 Experimental protocols
• ‘Mini-city’ – cuboids• ‘Stand-alone’ wall sections • Controlled environment cabinets
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Designing the ‘mini-city’!
• 20 Brick cuboids • 10 vegetated• 10 blank• Water tank in centre
– Winter studies
• Temp sensors 5cm from cuboid wall surface (and behind vegetation)
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
How do weather scenarios affect temperature profiles of air next to cuboids? (Mean data - Southern aspect)
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
How do cooling profiles vary with diurnal cycle?
• Wall system• Prunus v wet pot v blank
wall• Temp sensors for
air adjacent to wall
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Mean hourly air temperature for walls flanked by Prunus (South = Δ; North = ), ▲ Pot+media (South = □; North = ) or blank ■ Control walls (South = ○; North = ●). Data restricted to days with ≥ 5 h irradiance > 120 Wm2, August to September 2009. Bars = LSD (P = 0.05) blocked by
date. Residual d.f. = 30 each time. Ambient temperature – dashed line.
Prunus south aspect
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Wall surface temperatures
At discrete times thermal images showed a 10oC difference between vegetated walls and blanks• E.g.Wall behind foliage = 24.0oC, Control wall = 33.9oC Pot+media wall = 33.2oC; LSD = 0.81 (P = 0.05) d.f. = 12.
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
What are the implications to the cavity space within a wall?
• Phaseolus vulgaris
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Air temp – at wall exterior
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Cavity Air temp.
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
What types of plant are best at cooling?
Wall ShrubsClimbers
‘Functional’ plants
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Fuchsia
Stachys
Jasminum
Hedera
Prunus
Lonicera
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Controlled environment studies• Vegetated v non-vegetated walls• Warming programme with heater (300 W) within cabinet• Air and wall surface temperatures• Some programme runs with normal plants and some with leaves
covered with poly (1-acetyloxiethylene) to block stomata - inhibited 96-98% of normal ET (shade temps)
• Some runs with wet media only (evaporation)• Plant / pot temps stabilised at 18oC before placement in cabinets• Wall temps stabilised at 26.5oC and monitored change as plants
introduced. • Plants etc. weighed before and after to determine water loss
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Attained temp and water loss data for
• a = transpiring plant and media, • b = non-transpiring plant and media • c = media alone. • This allowed calculation of the cooling effect on the wall (oC) due to total cooling of
– planted trough – plant evapo-transpiration – shade and – media evaporation
• Plants destructively harvested and data for:– leaf number, total leaf biomass (dry weight), mean leaf dry weight, mean specific leaf
area, mean leaf thickness (individual leaf areas/leaf biomass) and total stem biomass (dry weight).
• Wall leaf area index (WLAI) was calculated as a ratio of total leaf area compared to exposed wall area and used to estimate the density of the foliage covering the wall.
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Temp. reduction on wall surface
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Temp reduction – per unit of leaf area
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Summer Cooling - Conclusions
• Vegetation can cool the air around a wall by 3-5oC in UK context
• Wall surfaces as much as 10oC different• Reduces cavity temp by 5oC in mid afternoon• Different plant species have different cooling properties
– Extent of cover – Depth of foliage – Some better at Shading– Some better at ETp cooling
• Water supply important in ensuring optimum performance• Green facades appear a viable retrofit option - UK
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Shrubs and Climbers Their role in thermal performance of built
structures in winter
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
What about reducing energy consumption in winter
– brick mini-building again?
• Replicated ‘mini-buildings’ with heated water tank within brick enclosure
• Water tank - Temp maintained at 16oC throughout• Energy use monitored over 2 consecutive winters
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Fig. 1. Energy use in Control (Blank) and Vegetated (Hedera) cuboids, during winter scenarios. Part-cover = foliage covering approx. 80%, and Full-cover = foliage covering 100% of cuboid. Bars = LSD values, df=79.
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Results
• Mean winter energy reduction = 38%– varied between 17% and 45% saving per week,
based on weather scenarios.• At 03.00 and 09.00 am cuboid wall
temperatures behind plants significantly warmer than ambient (mean 3.6oC)– not the case for blank walls.
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
How does species choice affect Winter insulation?
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Replicated ‘Cavity’ Walls
• ‘Dense’ Prunus v ‘Open’ Cotoneaster franchetti v Control (Blank)
• Late winter data• Wall surface and cavity temperatures
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Fig. 4. Cold, Non-Snow scenarios. Mean air temperature recorded at wall exterior (blue) or in wall cavity (shaded), as affected by species. Bars = LSD values Left = comparisons for exterior temperature, df=154 and Right = comparisons for cavity temperatures, df=107.
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Results
• Both the Prunus and Cotoneaster warmed the walls at night - Interior and Exterior
• Denser Prunus was more effective at warming the exterior.
• During sunny periods, however, plants particularly the Prunus inhibited solar gain to the wall.
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Winter - Conclusions
• Plants can insulate walls and improve temperatures / energy conservation in winter.
• The benefits are greatest under colder / more adverse weather conditions.
• Overall - – Plant species choice needs more consideration when
recommending wall screening plants.– Replicated ‘artificial’ buildings provided a high degree of statistical
robustness – need to scale up.
Thanks to Horticultural Trades Association, UK. for funding this research.
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK
Questions ?
INTERNATIONAL GREEN WALL CONFERENCE - 4-5th September 2014 - The Green Wall Centre, Staffordshire University, Stoke-on-Trent, UK