The project is an education sector retrofit and new-build Masterplan to deliver 3480 sqm of improved facilities for St Faith’s School, Cambridge. The works are divided into five phases spanning from 2010 to 2020 all using a traditional procurement route.
The existing buildings range in type from Victorian detached villas built circa 1885, single-storey classroom buildings built in the 1970s to more recent additions.
The aim of this project is to create an adaptation strategy for the School that will significantly reduce its overall energy consumption and enable it to cope with climate change, and extending the buildings’ design life. A key driver for the study is to provide an exemplar retrofit scheme, the lessons from which could be applied to other buildings of this kind across the UK.
Further project details
1. What approach did you take in assessing risks and identifying adaptation measures to mitigate the risks?
Literature and case studies reviews: research is ongoing to ensure that the team is adequately informed of the latest technologies to combat climate change.
Risk assessment workshop: during this workshop, all consultants discussed the risks associated with the project using the categories laid out in the Design for Future Climate report (Rated Table 1 Section 5) based on the three climate adaptation design challenges namely designing for comfort, construction and water.
Risk assessment register: this was developed as a working tool. The output of the risk register was then transformed into a risk vs risk magnitude bar chart.
TAS and PHPP modelling: using Prometheus weather data for the current weather scenario and future files for 2030, 2050 and 2080. The existing buildings and current designs have been tested for three probabilities of occurrence (of climate change) 10, 50 and 90 per cent. Test reference year (TRY) data for the high emissions scenario was used in all of the modeling.
SWOT analysis: strengths, weaknesses, opportunities and threats were assessed for a wide range of adaptations. This, along with a cost benefit analysis, assisted the team to collectively agree on the most promising measures to take forward for further testing, modelling and costing.
2. How have you communicated the risks and recommendations with your client? What methods worked well?
Client participation: the client is part of the project team and participates in all of the workshops.
Concise PowerPoint presentations: the outcomes from Milestone A1 have been presented to St Faith’s School during two of the team workshops (no 3 and 4). The presentations took the form of concise PowerPoint presentations with graphs, graphics and results of TAS and PHPP models. The outputs of the modeling of the buildings under study were very effective in highlighting specific problem areas within each building minutes of meeting: all meetings are recorded and minutes distributed to the team.
The client proposed using drop box to share the information and results as they were being obtained. All TAS and PHPP models were uploaded onto drop box and this encouraged more interest within the team.
The use of a collaborative medium for communication has provided for an efficient and time critical mechanism to relay key project information.
3. What tools have you used to assess overheating and flood risks?
Comfort
- PHPP (Passivhaus planning package) to establish building performance against PHPP criteria.
- Climate data convertor (CfSD): new software developed for this project that converts EnergyPlus weather files (.epw) to a format directly applicable to the Passive House Planning Package (PHPP). The convertor provides the climate data, heating loads W1 and W2 and daily temperature swing. CfSD are working on generating data for the cooling loads for future climate scenarios .
- TAS (Thermal analysis simulation) to thermally assess the building designs and identify problem areas and cross check results with PHPP results. PHPP considers the building in its entirety and does not focus on particular rooms. TAS modelling has been used to identify the problem areas, in particular which rooms are overheating.
- Dynamic thermal property calculator (ver 1.0) (Arup) was used to determine thermal mass properties of different forms of construction under study and check against manufacturer’s data.
Construction
- Trial holes: site base investigations to determine soil profiles.
- NHBC data for statistical risks of trees near buildings.
- Assessment of potential lowering of existing water table.
Water
- EA consulted in respect of flood areas: low risk so not part of the study.
- Water sensitive landscaping: the Huck Partnership have conducted a visual site survey to update the overall picture of the health of existing planting and trees. The existing vegetation was assessed for drought tolerance.
4. What has the client agreed to implement as a result of your adaptation work?
The client is keen to adopt adaptation measures which have a high cost benefit and are simple to implement providing the client with long-term resilience to climate change. A low embodied carbon design also plays a major role in influencing these decisions.
Detailed design work on the most promising options has only just started (April 2012). However, because of the tight programme, with the second stage of Phase IIA going on site this summer, the client is keen that detailed design of some of the adaptations recommended by the team are concluded in time for incorporation into the building contract. The following adaptation measures are likely to be adopted or have already been incorporated into the detailed design:
Comfort
- Natural ventilation (cross ventilation, passive stack and night purging). A fresh planning application is being prepared for Phase IIB Southfield where results from the TSB study are being incorporated into the new design.
- Mechanical ventilation with heat recovery is currently being tested for incorporation into the Phase IIB Southfield design. Coupled with more effective thermal design, findings from the research have shown that this approach is likely to reduce carbon footprint in the longer term and reduces heating loads, which is still an important consideration for the school in the future.
Water
- Water conservation – rainwater harvesting: the school is located in the driest region in the UK and will suffer from reduced rainfall in the future. The client is keen to adopt a water conservation strategy. AFP structural engineers together with THP Landscape Architects have investigated the opportunities to incorporate the proposed pond within the surface water disposal system. Initial design work has identified that this is difficult to achieve due to relative levels at the proposed pond position and Phase IIA classroom extension. Further investigation into finding a workable solution to harvest the rainwater off the roofs and combine it with the pond design is ongoing.
- Green roof: Verve Architects have investigated the optimum type (mat, plug planting, seed, drainage system, substrate composition and thickness) and pitch for the proposed green roof to minimise need for irrigation on a south facing slope. Manufacturer’s Bauder and Blackdown have been consulted. They provided advice, literature and results from independent research on the benefits of different design options. As a result of this study, the proposed roof pitch has been reduced to 9 degrees, plug planting with 70 mm substrate and a drainage system has been selected and incorporated into detailed design for construction. Options for retrofitting onto existing roofs are still ongoing.
- Future tree and plant selection: the client has agreed to select any replacement trees, shrubs and ground covers from a list of plants adapted to the future climate. Replacement planting will be positioned to ensure the continuing availability of shade essential in keeping the external play areas cool in summer and maintaining biodiversity.
5. What were the major challenges so far in doing this adaptation work?
Establishing thermal conductivity values for existing materials: both TAS and PHPP software require the input of U-values for each building element. Determining the thermal conductivity values of certain existing materials was in some instances difficult.
Simulating the true benefits of green roofs: PHPP and TAS software are both not designed to model the benefits of green roofs. The software uses the thermal conductivity values of the soil and drainage mat layers in the U-value calculation. However, this does not describe the energy transfer through evaporation, reflection, convection and thermal mass.
Converting the EnergyPlus weather files to a format directly applicable to the Passive House Planning Package (PHPP). The Centre for Sustainable Design (CfSD) has created the Climate Data Convertor, which provides the climate data, heating loads W1 and W2 and daily temperature swing.
CfSD found that “when the convertor is tested using the Prometheus current weather file (1961 to 1990) for the 4 UK locations, the results show significant over estimation of sky temperatures… As a result of the higher infrared radiation intensity the convertor, using the Prometheus data, has consistently overestimated the sky temperature by a large margin. This finding raises a concern over the quality of the Prometheus infrared radiation intensity data. In order to provide a robust estimation of the sky temperature based on the Prometheus weather data, alternative methods which use input variables other than infrared radiation intensity are sought”.
The convertor adopts Aubinet’s three-variable model for sky temperature calculation as this outperformed all other models tested and its prediction error is practically always lower than four per cent.
Establishing cooling load data for future climate data: The models currently use the cooling load data from the PHPP climate data for East Anglia (available from the BRE website) for all of the future weather scenarios. The PHPP models are therefore using static cooling load data the quality of which is undetermined. So, CfSD are working on generating data for the cooling loads for future climate scenarios for inclusion in the PHPP models verifying the thermal mass properties of construction methods under consideration, e.g. Tradical Hemcrete and Tradis system using Warmcel insulation.
Budget constraints: the client has a fixed budget for every phase of the masterplan. The team is aware that there are limited funds to invest in expensive and complex adaptation strategies. So the strategies taken forward are the most cost effective and simple to adopt.
Programme constraints: Phase IIA has a fast-track programme, with insufficient time to incorporate any potential below ground structural adaptations into the foundations. The design required an off-site prefabricated system that could be erected within two weeks, which limits superstructure options.
Limited information on predicted wind speeds.
Rainfall predictions – data is not specific. It is also not clear how long prolonged dry periods will occur for predicting future water table levels.
6. What advice would you give others undertaking adaptation strategies?
Model the design in thermal modelling software as early as possible, and use it as a tool to test and develop the design to help achieve a building that is more resilient to climate change.
Early integration of simple cost effective solutions where appropriate, e.g. cross ventilation, thermal mass, superinsulation, and orientation of buildings. Passivhaus principles provide resilience to climate change.
Ensure that building designs can be adapted in the future as part of the building maintenance cycle and for example using windows for night purging.
Do not underestimate the role of green and blue spaces in keeping the external spaces cool especially where these form an important part of the building use, e.g. play areas in schools.
Consider other non-building design related measures too, e.g. changing the occupancy patterns where the building use permits.
Certain areas within the building may need individual solutions, primarily dependant on orientation, size of room and use.
