4.2.1 Air Permeability Testing
Air permeability testing for this project comprises of 5 distinct stages. Initially, upon completion in November of 2010, the housing in Phase 1 of the case study, the timber housing, was tested by a subcontractor, BSRIA, in order to meet with minimum building regulations. Three dwellings in Phase 1 of the Green Street case study were tested, of these three houses, two are part of the continuous monitoring phase.
The two remaining houses from phase 1 (not initially tested upon completion) were analysed by Dr. Edward Cooper of the University of Nottingham’s Architecture and Built Environment in secondary study in November of 2011 with the results available in Section 7.2.
At this point Phase 2 (masonry) of the Green Street site was complete and underwent a similar testing regime to Phase 1, upon completion, once again through BSRIA. Air tightness testing procedure was observed following a somewhat unusual process. A house would be tested and subsequently fail the test, the contractor would then enter the house with a foam gun and plug any apparent gaps in the structural envelope and the house would be tested again. This was repeated in each dwelling until all three passed under the threshold 3 m3/h.m2@ 50 Pa. The neglect of the remaining houses, despite the obvious
121 deficiencies experienced within the chosen test housing obviously raised some questions regarding the regulations of air tightness testing and the performance of the remaining houses not subjected to the remedial measures applied to the testing houses.
The unusually poor results from the Phase 1 housing and the continued neglect of untested housing in Phase 2 prompted stage 3 of the air permeability testing, a more in-depth study incorporating some independent testing of 9 houses in both Phase 1and2, by an approved and licensed air testing subcontractor, Aeratech Ltd. in May of 2012. The test houses were those originally untested by the house contractor upon the completion of the dwellings on the assumption that they should perform close to the completion tested housing in the case of Phase 1 and almost identical to the completion test results in Phase 2. The data from stage 3 of the testing showed a clear discrepancy between the theoretical results and the as-tested air permeability. These findings provoked stage 5, yet more testing in 3 Phase 2 houses, this time funded separately by the housing developer, BluePrint. Tests throughout all 4 stages were carried out using a positive pressure, blower door technique.
4.2.2 Co-heat Testing
There is no mandatory requirement to pursue whole house heat loss testing or “co-heat testing” (Wingfield, 2011), within the project briefing for In-Use Performance and Post Occupancy case studies (TSB (b), 2011). However this research project includes collaboration with other research projects in the University of Nottingham and involvement in a Building Research Establishment led project with partners from academia and testing agencies exploring the issue of co-heating testing in detail with the view to develop standard test methods, which measure a range of performance characteristics (NHBC, 2012). It is important therefore, to include some measure of co-heat analysis in the overall fabric testing of the case study.
122 Ideally the testing procedure should be completed in an unoccupied, just completed house, however, the practicality of commandeering a house for a minimum of 10 days during this stage of construction is almost impossible. The invasive and time consuming nature of this testing methodology restricts the sample size to 1 representative house from each typology. The representative Phase 1 house was tested in January 2011 and the Phase 2 house in November of 2011, both were tested post construction and commissioning, but before handover of the property to the new tenants.
The generally accepted framework found in work by Johnston, et al. (2012) details the following methodology.
Testing Period: Heating season – generally stretching from October/November to March/April time thereby ensuring a ΔT (temperature difference) of at least 10°C between inside and outside the dwelling.
Testing Duration: 2 weeks minimum, taking into account set up/take down time and the heat saturation phase at the beginning of the test when the structure is brought up to a steady state temperature.
Dwelling Access: Access to the building should be kept at an absolute minimum, with allowances made for equipment checking and adjustments. Dwelling Control: All windows and external doors must be closed, all trickle
vents, flues and mechanical ventilation systems sealed and switched off. All electrical appliances such as fridges, microwaves and ovens are to be turned off. Water traps and U-bends in kitchens, bathrooms, en-suites and toilets must be covered with water at all times. Internal drawers, cupboards and doors must be wedged open to allow the free movement of air round the dwelling
Equipment and Procedure: The dwelling is heated to a constant 25°C (or to a minimum ΔT 10°C ) using thermostat controlled electrical heaters and fans. The fans are used to circulate the heat throughout the house and maintain a constant temperature in all the rooms. The heaters and fans run through energy meters that record how much electricity they are using and then transmit the information to a centralised data logger for retrieval at the end of the test. Internal temperatures are recorded using temperature data loggers – in the case of this study this role is filled by the afore mentioned Tiny Tag Loggers (accurate to ±0.9°C over the range of -40°C to +85°C.)
123 Figure 4.1 Co-heat Test Equipment
External temperature is measured using the same equipment. A weather station should be mounted horizontally above ground level on a mast. It should be positioned to avoid any possible over shading or sheltering. A pyronometer is to be vertically mounted on the external south facing façade of the building, again free from any over shading. The daily electricity use is compiled and graphed relative to the average temperature difference between internal and external (ΔT) over the 24 hr period. The result is the HLC, a proportional value (W/K) which details how much energy is required to heat the entire dwelling per degree of difference between the internal and external temperatures. This value is adjusted to take into account the solar gains measured through the pyronometer. The final solar adjusted value is then compared to the design specified HLC where invariably dwellings perform below the pre-construction estimations. (Johnston D. , Fabric testing: Technical approaches and processes, 2010) (Wingfield, 2011) This gap between design and actual performance is caused by a variety of sources, ranging from the initial briefing process, design and modelling tools used, the build process and build quality, systems integration and commissioning, handover and operation through to the understanding, comfort and motivation of occupants. One of the objectives of this thesis is to understand
Heater Thermostat Circulating Fan kWh Meter
Not included in this
picture are the
datalogger and the
majority of the
individual temperature and humidity sensors placed throughout the house and outside. Internal thermostats within the heaters have been bypassed and the set-up relies on the thermostat pictured. In addition there was a pyronometer placed on the roof. Temp/Humidity Sensor
124 the extent to which specifically the materials and construction process contribute towards this gap between design and performance.
Combining Techniques: Ideally there should be an airtightness test immediately before and after the co-heat test, however, the limited access offered to this project did not allow for these additional tests within that timeframe. Combining the coheating test with other fabric analysis measures such as airtightness testing and thermography helps to gain a much better insight and understanding of the factors contributing to the heat loss identified though the coheating test, which by itself, has no way of identifying the contributing factors behind a design and as-built performance discrepancy. However, the practical logistics of organising so much equipment and the right expertise to converge in such a strict timeframe and under such a restrictive protocol is incredibly difficult – particularly if there are multiple properties involved.
A position paper entitled: “Designing Out Risk Using Post-Occupancy Evaluation Methods in Domestic Construction” (the abstract of which is available in Appendix B) was published by the author of this thesis detailing how the results of co-heat testing can be used as performance evaluation tool when comparing differing construction methods. Ultimately, this will form a fundamental building block in the case study evaluation, allowing for a direct comparison of the Phase 1 and 2 housing in this document. The position paper goes into more detail on the exact methodology of this process.
4.2.3 Thermography
The most important factor in qualitative thermography testing is an awareness of the environmental and material parameters that may affect the validity of the image. Requirements as set out by the TSB protocol (TSB (b), 2011, p. 10) seek to minimise the impact of these parameters by dictating a number of guidelines:
125 There must be an internal to external temperature difference of approximately 10°C or more for at least four hours immediately preceding the survey.
No sun should be incident on the facade for at least four hours immediately preceding the survey for low thermal mass structures and longer for high mass structures, ideally carried out before sunrise or late at night provided heating has been on to obtain a temperature difference.
Dry building surfaces with no rain during the survey Wind speed less than 8 m/s (light to moderate breeze).
Phase 1 testing took place in March of 2011, shortly after the dwellings were handed over to occupants. At that stage access to the properties was prohibited, therefore the initial study excludes internal images, instead focusing on the facades and party walls of the TPC housing. A second round of imaging was recorded in Feb of 2014, with access to the internal structure of the Phase 1 dwellings. Phase 2 testing took place during the coheating analysis in November of 2011. Both internal and external images are available. “The application and interpretation of thermal imaging requires a high level of expertise as factors such as direct solar radiation, surface dampness or surface emissivity can influence the image” (TSB (b), 2011, p. 10).
For all thermographic tests incorporated in this study the following conditions are recorded to aid in the analysis of the final images:
Sun Set Sky conditions
Atmospheric Temperature Relative Humidity
Emissivity
Distance from target
Internal Temperature of Dwellings Wind Speed
Ultimately the aim is to identify thermal anomalies in within the building envelope which may contribute to the gap between design and in-use performance. These anomalies may be caused by gaps in insulation layers, thermal bridging, and air movement within the structure or even a combination
126 of contributing factors. This study is particularly interested in contributing factors that are material or construction process specific.