Mark Elton of Cowan Architects looks at the potential for Passivhaus technology in hospital estates, and urges the UK ‘to take note of what is already happening on the Continent to reduce unnecessary heating bills while improving patient and staff comfort for a healthier outcome’.
Winter is an appropriate time to think about the excessive heating costs that hospitals around the UK are racking up in order to keep patients comfortable all day, every day. However, in the Höchst district of Frankfurt, the world’s first Passivhaus hospital, the new Klinikum Frankfurt Höchst, is underway, with construction of the new 664-bed facility (which will be equipped with 10 operating theatres) due for completion in the first half of 2019, and it is time we took a note of this form of construction’s positive implications for both the public purse and patient and staff welfare, as well as the environment. The good news is that the potential for 80–90% savings on heating can be achieved with retrofit as well as new-build.
In the Sustainable Development Unit report, Securing Healthy Returns, published in June 2016, John Holden, director of Policy, Partnerships & Innovation for NHS England, acknowledges that ‘The evidence presented here shows that we don’t always have to choose between saving financial resources or protecting the environment – indeed, the most effective investments can often save money, improve health now, and safeguard the environment on which all future health depends. What’s good for the environment, and good for the patient’s health, can be good for the nation’s finances too’.
Impacts on many levels
Any building project, new-build or refurbishment, has an impact on the environment, both around and within it. This affects us on many levels:
However, with careful forethought and design, it is possible to mitigate the worst of a building’s impact on the environment, and even have a net positive impact.
Reducing energy use
Historically, by far the biggest environmental impact of any building over its lifetime is the energy used to heat or cool the spaces within it. Cutting down on this energy use should be one of the overriding considerations in the design of cost-effective, eco-friendly buildings, yet studies have shown that, more often than not, so-called low energy buildings have failed to deliver on their performance targets to the extent predicted by modelling. In the industry, this is known as the ‘Performance Gap’. It was in response to this that the Passivhaus design standard was developed in Germany some 25 years ago, seeking to address perceived shortfalls in design, construction quality, and modelling information standards. It is now the best researched, most rigorous design and quality assurance standard for buildings that there is.
A radical reduction in space heating demand
Many European cities now insist on Passivhaus standards for all new buildings (whether they be houses, care homes, hospitals, schools, offices, or community buildings), because the Passivhaus principles allow us to design buildings today that use around 80-90% less heat energy than conventional buildings. This design approach delivers buildings that are independently certified, never get too hot or too cold, cost very little to run, and that offer the very highest standards of comfort and indoor air quality for the minimum expenditure of energy and fuel costs.
How does Passivhaus design achieve this?
In essence, Passivhaus design is the partnership between sound architectural principles and advanced material science. It focuses on the absolute energy performance and comfort conditions of a building through the understanding and manipulation of a number of key design parameters:
All of these conditions are checked for compliance in advance through the use of the specialist software design tools, which include designPH and the Passivhaus Planning Package (PHPP). Trained Passivhaus designers use this software to input and record data on thermal performance for wall, floor, and roof constructions, ventilation design efficiency, fuel sources, and internal heat gains. A 3D model of the building can also be used to test the impact of form, shading, and window opening sizes and positions. Just as with any architectural design, Passivhaus buildings are shaped by the local context or streetscape, and by local views but, in addition, they are influenced by an awareness that building form also has a significant impact on energy use and construction cost.
The target for all Passivhaus buildings is to reach a level of efficiency whereby the space heating demand is reduced to just 10 watts per square metre (10 W/m2). Over the course of a year, the adjusted target is just 15 kilowatt hours per square metre per year (15 kWh/m2/yr – 1 kWh being equivalent to one unit of gas or electricity). To put this into a context, it equates to a large three-bedroom house being heated on the very coldest of winter days solely by a small fan heater. Insulation measures are particularly worthwhile in hospitals and other care environments – on account of their high temperature requirements and almost continuous operation.
User comfort the cornerstone
However, far from being just a numbercrunching exercise, the consideration of user comfort is the cornerstone behind Passivhaus. If building users are more comfortable in their working or resting environment, they are less likely to resort to the application of more heat or cooling to improve the situation. Studies have shown that we generally equate comfortable conditions with even temperatures and stable relative humidity, which means external walls and floors need to be sufficiently well insulated to avoid colder surface temperatures whatever the external conditions – this equates to a minimum thermal performance U-value of 0.15 W/m2K for external walls, floors, and roofs (although it is typically lower for overall energy conservation reasons), and 0.8 W/m2K for glazing and doors. This insulation needs to be contiguous, avoiding the all too common thermal bridges formed by structural elements in conventional construction. Windows also need to be triple-glazed, with insulated frames and glass spacers. Since external wall surfaces do not fall below 17/18˚, mould and condensation cannot form, and cold downdraughts are not induced, even adjacent to the glazing.
‘Build tight, ventilate right’
The level of airtightness required from the building fabric is perhaps the most significant difference between a Passivhaus building and conventional construction. Poor airtightness is one of the main reasons for the performance gap in other so-called low energy buildings, whereby the warm air within the property escapes through gaps in the construction under buoyancy and pressure differentials. UK Building Regulations permit a relatively high level of air leakage – Passivhaus compliance requires a standard some 16 times better (at least 0.6 air changes per hour, when tested at 50 pascals pressure). Typically, this is achieved through a detailed design and specification strategy from the outset, followed by careful and comprehensive installation. Components developed that are Passivhaus-compliant in terms of air leakage include window assemblies, membranes, tapes, and grommets. Testing of the assembly throughout the construction phase ensures that the quality and fabric integrity is maintained right through the fit-out and during the building occupation. This enhanced airtightness also helps with durability, as moist air is unable to penetrate the barrier and lead to condensation with the wall build-up.
However, improvements in building insulation and airtightness standards must go hand in hand with greater consideration being given to ventilation. In such cases, it is no longer healthy to rely on manual ventilation and draughts alone to remove poor quality air; nor will it be acceptable in energy terms to simply exhaust that warm air to atmosphere. By limiting the level of air leakage through the building envelope, it becomes viable to recover the heat energy from the exhaust air – a system known as heat recovery ventilation. The more airtight the walls, floors, and ceilings, the more efficient the ventilation system’s performance for the minimum of fan energy use. The best heat exchangers can achieve efficiencies of between 75% and 90%, with filtered, fresh air being supplied, slowly and quietly, to all occupied rooms to balance against the same volume of stale or moist air extracted from bathrooms or utility rooms. The energy used to run the fans is more than compensated for by the recovered energy from the heat exchanger. Dust and pollen filters, together with acoustic silencers and low air speeds, ensure that accommodation is always fresher, quieter, and cleaner, even in the harshest of urban environments, and all without any noticeable loss in temperature, even on the coldest of days. This is a huge positive for any healthcare environment.
Ignoring the associated heat loss for one moment, you can always open the windows if you want to, as all Passivhaus buildings have windows that open, not least for easy cleaning, and this may be of particular importance in the summer as part of a night cooling strategy. If opening windows is not practical, for reasons of noise, security, or weather, air quality doesn’t have to suffer.
Mechanical ventilation by default
There are additional advantages as the Passivhaus approach is based on mechanical ventilation supplied to all rooms by default, and this can capitalise on the healthcare sector’s move toward more flexible, standardised room sizes to maximise the usefulness of the accommodation throughout the building’s pattern of use. Issues of infection control or acoustic privacy can also be readily accommodated with dedicated fresh air supply and extract to each room.
Passivhaus in a changing climate
Climate change is expected to result in hotter, drier summers, with more intense and longer heatwaves. This can have serious implications for heat-related illness, particularly for vulnerable patients or older people, as they are more susceptible to the negative health effects of overheating. A recent study by the Joseph Rowntree Foundation, entitled Care Provision Fit for a Future Climate, identified many risks from overheating specific to the healthcare sector that would be exacerbated by climate change. The prevalent perception is that ‘older people feel the cold’, but there is scant recognition given to the risk of heat. The report goes on to identify a number of strategies for addressing them, such as improving awareness among residents and staff, better temperature monitoring and heating plant management, and the implementation of training and planning for extreme events.
Of significance to architects, the report strongly recommends that the design of hospital and care facilities covers climate change impacts, for example location, orientation, and other physical measures to reduce solar and internal gains and avoid future overheating problems.
Stable internal temperatures
So how can Passivhaus design be the right solution, given that it involves high levels of insulation and airtightness? The thing to remember is that Passivhaus is about creating stable and comfortable internal temperatures all year round with the minimum of energy input. Insulation works just as well to keep heat out as it does to keep heat in – think of your highly-insulated fridge-freezer, for example. This is why the Passivhaus approach has been shown to work in places like the Mediterranean or even Indonesia. The problem tends to be that the energy sources that supplement your conventional heating system in winter continue to add unwanted heat in the summer. The internal energy gains from the use of appliances and lighting, from electronic equipment, or from hot water storage, therefore have to be accounted for to avoid excessive internal temperature rises in summer.
Most significantly of all, however, windows that provide those beneficial passive solar gains during the winter then present an overheating risk challenge during the summer months. For this reason, the Passivhaus standard places a limit on internal temperatures of 25 ˚C that should only be exceeded for a small percentage of hours in the year according to its modelling design software. To remain below this temperature cap, designers need to carefully consider shading and ventilation strategies that will combine to keep the building interior cool during heatwaves. Passivhaus buildings eschew large extents of east and west-facing glazing in favour of windows orientated to the south, where the higher mid-day sun angles allow devices such as overhangs, brise-soleils, louvres, shutters, and awnings, to be deployed to avoid excessive direct solar warming of the interiors. Windows can be designed to be left open in a secure manner overnight, perhaps with fixed external decorative guarding, which allows cooler night air to replace warmer internal air escaping via high level clerestory window or rooflights.
High external temperatures
Passivhaus also offers some advantages over conventional accommodation where external temperatures are high during the day – for example, the interior air at 21-24 ˚C can be used to cool down the fresh but warm incoming air. During late summer evenings, when external temperatures drop lower than internal ones, a summer by-pass can be engaged so that the cooler incoming fresh air directly lowers the temperature of the interior and its structures.
Other considerations include better planning and insulation of the hot water distribution network to avoid long, hot corridors, perhaps through shorter horizontal runs with more vertical stacks. The use of reflective facing materials can help, and, for courtyards and large flat roofs, planted green areas will absorb much of the solar impact, as well as enhancing biodiversity and the roof’s visual aspect.
Lasting retrofit to Passivhaus standards
The benefits of Passivhaus design for new buildings are unequivocal, but much of the healthcare estate in the UK is now quite old, with large amounts of post-war stock to contend with. The answer lies in refurbishment, or, more specifically, retrofit, which is the term used in the industry for energy efficiency upgrades to buildings. Retrofit typically involves adding insulation to walls, roofs, and, where possible, to floors, to eliminate heat losses, alongside window upgrades, and improvements to (or replacement of) heating and ventilation plant
The challenge for building operators is to undertake refurbishment that genuinely improves occupant health and wellbeing, significantly reduces operational running costs, and has a deep and lasting impact on carbon emissions, which may also align with social responsibilities. However, retrofit needs to be designed holistically and implemented to a high standard. The Intergovernmental Panel on Climate Change recently reported that ‘each building retrofitted in a sub-optimal way locks us into a high climate-footprint future’. The message is therefore to ‘do it once and do it well’ or, at the very least, to follow a strategy of retrofit stages that leads to the complete solution.
The Passivhaus principle relies on the ability to optimise a building’s form and orientation to maximise performance, but obviously this is not possible with retrofit, so the standard is adapted slightly to reflect the challenges of refurbishment, giving a certification standard known as EnerPHit. The ideal retrofit scheme involves a complete overhaul of the building fabric, which might involve wall insulation and cladding, air leakage reduction measures, window and door replacements, and the introduction of heat recovery ventilation. Most of these works can be undertaken externally if the style of the building and planning constraints permit. For older properties of heritage value, these upgrades will have to be carried out internally but, advantageously, this then allows upgrades to be undertaken on a room-by-room or wardbasis, which might be a more manageable solution for hospital estates.
Many specialist products and techniques have been developed in the retrofit field over recent years, including high performance insulations that are pinned to the existing structure and can improve the thermal performance to the same level as new buildings. Typically, roof finishes are removed, insulation added, and new roof finishes replaced. Floors can be trickier, but in the worst case scenario an insulated ‘apron’ can be installed around the building perimeter to create a heat island underneath the existing structure. Improvements to air leakage levels are also a prerequisite for high performance and comfort, so that even in retrofits, very low rates can be achieved through analysis by an experienced retrofit designer.
A new approach, involving prefabricated retrofit, is gaining interest, where a new external skin is fabricated in its entirety under factory conditions (including linings, insulation, windows, and cladding), and tailored specifically to correlate to an accurate laser survey of the existing building. The new roof and wall panels are assembled on the outside of the building, with residents still in situ, with the only intervention internally being the removal and re-lining of the old windows. Air leakage and heat recovery ventilation distribution can all be dealt with in the new outer skin.
I used this method recently for a 1967 housing block in east London, and the potential is huge – with predicted energy savings in the order of 75-80%. This technique might just be the ‘silver bullet’: maximum performance and quality for minimum disruption – with the opportunity to transform tired old buildings – and certainly lends itself to overstretched hospitals that aren’t in a position to close entire wards or areas.
Following their lead
Greater energy efficiency is undoubtedly the path towards a healthcare estate that is more sustainable in terms of both its financial viability and its environmental impact. Heating and cooling plant and other services have an important part to play – efficient devices, whether in the form of lighting or medical equipment – not only save energy directly, but also simultaneously reduce the cooling demand. However, the replacement or retrofit of building stock to the Passivhaus standard provides the greatest opportunity for truly radical savings in running costs and greenhouse gas emissions. Benefits for a healthier living environment are proven to improve both patient and staff comfort, with significantly reduced absenteeism seen in Passivhaus offices and schools. The conditions for large-scale energy efficiency measures in hospitals are favourable; with the available technology, the energy demand can be reduced significantly in most areas. With our European cousins in companies and hospitals on the Continent poised to take full advantage of the benefits of Passivhaus design, it is time that we followed their lead.
About the author
Mark Elton, director, Cowan Eco Design, has been a practising architect for 22 years, with considerable experience in low energy architecture and retrofit on a wide variety of award-winning projects. His interest in sustainable design stems from a combined architectural and engineering education at the University of Bath, followed by a career in various London practices before joining Cowan Architects in 2016. Here he is working on bringing the synergies of Passivhaus technology to the practice’s healthcare sector client base.
An accredited European Passivhaus Designer, and a UK jury member for the 2014 International Passivhaus Awards, he believes that the deep understanding of building physics and detailing rigour that Passivhaus training brings, coupled with an extensive knowledge of building materials and their environmental impacts, can bring great credibility to the design process. He was a committee member on the RIBA Sustainable Futures group for six years, and continues to engage on RIBA matters relating to the retrofit agenda. He also acts as an architect representative on CIBSE’s ‘Homes for the Future’ group, and is a course tutor on ‘building fabric’ for the Retrofit Academy.
Throughout his career, Mark Elton has been responsible for a number of pioneering schemes, including the Arundel Great Court HQ and conference building in The Strand in London, and the University of Surrey’s School of Management. He has also gained experience in low carbon design through projects such as Cornwall’s Broadclose Farm, which won the Richard Fielden Housing Design Award.
He is recognised for his work on social housing retrofit projects, including the Edward Woods estate in Hammersmith, West London, which is highlighted in the LSE study, ‘High Rise Hope’, and Wilmcote House, the UK’s largest EnerPHit refurbishment project, currently on site in Portsmouth.
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