Urban Design Mvhr Shading on the ArtHouse apartment scheme at Kings Cross UrBan REALITy Passive design for new London homes is being thwarted by external noise and the desire for glazing. Ashley Bateson says MVHR and shading are the most viable solutions R esidences in London are increasingly being built in noisy locations and on irregularshaped land. This often results in designs for single-aspect homes with faades exposed to traffic. At the same time, there has been a drive for large areas of glazing in new apartments, as it is perceived to be popular with buyers. These trends pose overheating risks for occupants, caused by solar gains from large expanses of glass and the restricted use of openable windows because of street noise. Single aspect designs also offer less opportunity for cross-ventilation. The London planning guidance1 states that developers should minimise the need for active cooling systems and consider natural means of maintaining comfort (London Plan policy 5.9). This mean designers need to consider passive measures such as shading. In reality this is hard to achieve. In many apartment buildings the proportion of glazing on the faade is more than 50% generally less than 35% in older domestic buildings. Population increase means there is a higher density of residential development in London, so less space for dual-aspect flats. Meanwhile temperatures are on the shading and openable windows for purge ventilation. Key lessons Early review of external noise and ventilation strategies will become increasingly important Natural ventilation strategies may be unacceptable from an acoustic perspective. MVHR is increasingly likely to be the future solution The use of external shading, light coloured facades, thermal mass and smaller areas of glazing should be evaluated as passive strategies to complement the MVHR system Dynamic thermal modelling is a useful tool to test the impact of passive measures at preplanning stage MVHR performance issues need fixing Impact of the future climate conditions, adaptation and microclimate will be increasingly important (including the urban heat island effect). cJ ASHLEy BATESoN MCIBSE is a partner at Hoare Lea. He presented on this topic at this years Technical Symposium. Selected papers are available here. Natural ventilation is not suitable, given the high levels of traffic noise, although modelling shows it would be effective rise. Most of the hottest years since 1850 have been in the last 10 years and average temperatures have increased by 0.5C since the 1950s2. Cities in particular are getting hotter and are susceptible to the urban heat island effect. CIBSEs overheating criteria for residential design states that operative temperature in living rooms should not exceed 28C for more than 1% annual occupied hours, while the Passivhaus Overheating Criteria says that air temperature should not exceed 25C for more than 10% of total annual hours. While it is difficult to achieve these targets in single-aspect flats in London without openable windows, the acoustic standards presented in BS8233: 2014 Guidance on sound insulation and noise reduction, make it impossible in many circumstances. This means designers have to turn to mechanical ventilation and heat recovery (MVHR) to prevent overheating and high noise levels. But there are issues The best solution comprises MVHR, external shading and openable windows around this technology, particularly around installation and maintenance. For example, filters critical to the performance of MVHR often become clogged and are not changed often enough by occupants.4,5,6 Other challenges in urban schemes are smaller dwelling sizes and internal heat gains from communal heating systems, which together raise solar and internal heat loads. case study Hoare Lea modelled a typical London residential development to test a number of scenarios. The project is a multi-storey apartment block with two elevations facing busy roads. (For full case study and references visit the CIBSE Journal website or via the app). Modelling revealed that natural ventilation is not suitable, given the high levels of traffic noise, although modelling shows it would be effective in minimising overheating risk. It showed that standard MVHR ventilation rates are insufficient to avoid overheating risk, but higher MVHR ventilation rates reduce overheating risk when used with shading. The best solution comprises large MVHR with high ventilation rates, external