Passivhaus overheating shouldn’t happen: it’s one of the criteria of the international Passivhaus standard. Even so, people sometimes ignore this requirement during the early stages of the design process.
Ground-breaking housing scheme captures one developer's journey to passive ... The just-finished second phase of Durkan Residential's ambitious Silken Park scheme in south-west Dublin bridges the gap between two extremes: while phase one was built to the 2002 building regulations, phase three - which will break ground next year - will comprise 59 passive certified units.
Anyone familiar with spending a hot summer's day in a caravan and then another in a stone house with closed shutters will appreciate the meaning of ‘Decrement delay’. The inside of the caravan closely maps the rise and fall in external temperature to provide the familiar stifling effect on the occupants .
Solar energy is a seriously underrated resource. More power from the sun hits the Earth in a single hour than humanity uses in an entire year, yet solar only provided 0.39% of the energy used in the US last year.
“As debate ramps up in Ireland about whether local authorities in Dublin should adopt the passive house standard, and the UK government scraps its plans for zero carbon homes, Dr Shane Colclough urges passive house advocates to prepare for the lobbying battles ahead by remembering the basic science behind the standard.”
Now nearing completion, the University of East Anglia's (UEA) most recent development, The Enterprise Centre, is on course to become an exemplar low-embodied carbon buildinq, pushing the boundaries for sustainable architecture.
The importance of good ventilation in classrooms has been recognised since Victorian times, but many of today's schools fail to reach even basic levels of indoor air quality. Ewen Rose reports on a growing health crisis.
Montgomery Primary School in Devon is the UK's first zero carbon, climate – change ready school. Andy Pearson takes a look at the fabric first, 'tea cosy' principles behind the design of this award-winning building.
When it comes to achieving outstanding results Montgomery Primary School, in Exeter, is top of the class. The UK's first zero-carbon school, it is also the country's first Passivhaus school and its first climate-change-ready school. If all that were not enough, this pioneering £8.9 m scheme was recognised by CIBSE at the Building Performance Awards 2014, at which it won the New Build Project of the Year award for schemes under £10m.
The zero-carbon target for the 420-pupil school was set by the client, Devon County Council, in 2008. The council had secured additional funding from the Priority School Building Programme - along with a grant from the Zero Carbon Task Force - to create an exemplar zero-carbon school that would help to increase knowledge and understanding of low-energy school design. The council worked with engineers Hamson JPA, and their architect and quantity surveyor affiliates at NPS Group, plus Exeter University's Centre for Energy and the Environment, to develop the design. The team set out to pioneer a new approach to primary school design. The simplest solution to meeting the client's zero-carbon aspirations would have been to construct a conventional Building Regulations-compliant building, which could be transformed into a zero-carbon solution using a biomass boiler for heat and hot water, and a green electricity tariff for electrical power. Such an approach was considered unsustainable by the design team.
'This solution is without value because it relies on the continued use of precious resources,' says the project's quantity surveyor, Chris Rea, from NPS Group. By contrast, Montgomery Primary School has been designed to minimise its use of resources, so that all energy for heating, lighting and power is generated on site.
“The space heating requirement of the school is now so small that the primary source of heat input is body heat from the pupils and teaching staff”
The starting point for the resource-lean design was to minimise fabric heat losses. The new two-storey school has been built within the grounds of the 1930s primary school it has now replaced. It is oriented north-south, with the majority of classrooms facing north and the more flexible teaching spaces to the south. A double height, central atrium-corridor divides the spaces. Passivhaus standards were adopted for the design of the building fabric. These set a limit of 120 kWh/m' /year primary energy use, and 15 kWh/m'/year for heating and ventilation - significantly lower than the 55 kWh/m'/year for a typical school. To meet the heating target, the school's walls have been assembled from highly insulated, precast concrete sandwich panels, comprising 100 mm of high performance, rigid foam insulation, sandwiched between a 100 mm-thick concrete inner leaf and 70 mm outer skin.
Concrete was selected for its high thermal mass, which was deemed essential in enabling the step-up from Passivhaus to zero carbon. Pressure to complete the 2,786m2 building in time for the school term forced the design team along the precast, modular route. At the time the modular fabric solution was being developed, building services design was not sufficiently advanced to enable these to be incorporated into the precast units.
On top of the precast walls is precast concrete roof deck, blanketed with 200 mm of extruded polystyrene insulation. Underneath the building is a 150 mm layer of expanded polystyrene to insulate the cast, in-situ raft foundation and floor slab from the ground. 'We've adopted the same principle as a tea cosy, with insulation placed on the outside of the building to allow the thermal mass of the concrete structure to be fully exploited,' explains Rea.
Compliance with Passivhaus standards has ensured the school is exceptionally airtight. 'We followed the maxim "build tight, ventilate right",' says Rea. An air-seal barrier layer was defined in the modular wall, roof and floor constructions at the outset In addition, construction joints were carefully detailed and unavoidable service penetrations and other openings were kept as regular circles or rectangles to match the pipe or duct, and to make them easier to seal. To ensure the detailing was flawless, regular workshops were undertaken with all members of the construction team; for some of the more critical details, samples were prepared and tested on site to verify their performance.
The team's efforts were successful. The Passivhaus air-leakage standard is o.6 air changes per hour at 50 Pa; the focus on air tightness at Montgomery has enabled the building to achieve an impressive 0.28 air changes per hour at 50 Pa.
The fabric-first approach dramatically reduced the space heating requirement of the school. In fact, this is now so small that the primary source of heat input is body heat from the pupils and teaching staff.
A mechanical ventilation system with heat recovery ensures optimal thermal comfort is maintained throughout. Warmed fresh air is supplied to the teaching spaces. This returns to the air handling unit (AHU) through a high-level transfer grille into the building's central atrium-corridor, from where a high-level grille allows the air to return to the AHU in the plant room. This enables excess heat to be moved from high-occupancy spaces to spaces with a lower occupancy and a demand for heat.
Top-up heat is provided by electric heating elements mounted in the air supply ducts. The electric elements are set to operate on manual boost or fabric frost protection only. To protect against overuse, the boost feature is restricted to returning the room to the design set-point temperature. The advantage of this simple heating system is that it has zero losses when not in use and is almost 100% efficient in operation. 'Using electric heaters enabled us to offset this electricity using roof mounted photovoltaic panels.' says Rea.
The ventilation system operates in two modes. In winter, when heat is required, the building is predominantly mechanically ventilated using a variable air-volume strategy under control of the Building Energy Management System (BEMS). This uses temperature and C02 sensors to control dampers to alter the volume of air supplied. The BEMS also varies the speed of the fans in the building's AHU to minimise expended fan energy, while keeping the system in balance.
Energy consumption in the AHU is further minimised by a reversing regenerator unit. This uses two metal heat-exchanger packs to absorb heat from the exhaust air stream, and a series of dampers to reverse the airflow through the unit mechanically, once every minute. Initially, warmed exhaust air passes through one of the aluminium regenerator units, heating it before it is discharged. Simultaneously, cold supply air passes through the other, warmed, regenerator unit, where it picks up heat before it is supplied to the school. After 60 seconds, the control dampers reverse the airflow direction so that the regenerator warmed by the exhaust air now imparts heat to the incoming air, while its twin is regenerated by the warm exhaust air stream. The system is claimed to operate with 93% heat-recovery efficiency.
In summer, the building operates on a natural ventilation strategy. Each classroom has manually opening, triple-glazed windows that allow cool, fresh air to enter the room. This fresh air drives stale, warm air upwards to the transfer grille, and out into the central atrium-corridor, where large roof Iights open under control of the BM S to create a stack-driven, low-pressure, ventilation system. The effectiveness of the design was proven by modelling using IES: Virtual Environment software.
Summertime overheating of the highly insulated school is mitigated by the high thermal mass of the building fabric. In extreme circumstances, the natural ventilation system can operate overnight to remove excess heat to pre-cool the thermal mass for the following day.
In the same way that the building fabric was modularised, so too are the building services. Early involvement of the building services contractor, NG Bailey, enabled the ductwork and lighting assemblies to be supplied as modules and lifted into place. To reduce the lumen output of the lighting, the rooms all have light-coloured walls. In addition, absence detection and daylight sensors turn off lights in unoccupied spaces to minimise energy consumption.
On-site renewable sources are used to enable the school to meet the zero-carbon, in-use target Photovoltaic panels were found to be the most appropriate technology to meet the school's predicted 166,000 Wh/y energy requirement. Around 900 m' of Sanyo HIT N-235 SE10PV of PV panels are located on the south-facing pitch of the roof. The electricity these generate is fed into the national grid.
Electricity generated by the PVs is not used to heat the hot water, although it is used for the trace-heating system, which keeps the water warm in the distribution pipe work. Instead, the hot water is heated throughout the year by a high-temperature, C02 air source heat pump, which picks up heat from the kitchen extract. Modelling showed this solution to have the lowest overall energy use of all possible options.
To enable the teaching and facilities staff to familiarise themselves with the innovative technologies and solutions employed at the school, the client specified an extended commissioning period in the contract. In addition, the team used the BSRIA Soft Landings approach for the handover and follow-up visits.
'The structure provided by this approach enabled the school staff, design team, client and contractor to work together to identify and resolve issues that - if left unsolved – would have compromised the school's low-energy operation and client's satisfaction with the scheme,' says Rea.
The design complies with the requirements of Building Bulletin 101: Ventilation of School Buildings. Unusually, the school has a 60-year design life. The scheme has been modelled by Exeter University and found to be sufficiently robust to ensure conditions remain comfortable, without overheating in the school, even as the climate changes up to 2080.
“The scheme is sufficiently robust to ensure conditions in the school remain comfortable. even as the climate changes up to 2080”
The scheme was completed in October 2011. Its measured energy performance figures are: 12 kWh/m'/year space heating and 167,358 kWh/ year total energy, including energy used in the kitchen. Despite these outstanding low-energy credentials the building has only managed a DEC band B because of its reliance on electricity for top-up heating. Monitoring has shown that, over the course of a year, the amount of electricity generated by the PVs is equal to that imported from the grid.
From the school's perspective, its carbon neutral performance means that the manager doesn't have to budget for heating and electricity costs over the coming year. Instead, any savings on the utility bills can be used to support future maintenance and educational budgets, to make the school a zero-carbon, self-sustainable, stand-alone environment of learning.
Pearson, A. (2014) ‘The full Monty’, CIBSE Journal, April 2014, pp. 4-8
Zero carbon is great as a political aspiration but will it stack up effectively as a policy? Richard Hillyard examines Government aims to impose zero carbon targets on the construction industry. Back in July 2007 the Government published the Building a Greener Future statement. This policy document announced that all new build homes would be zero carbon from 2016.
The definition of zero carbon requires new dwellings to take into account:
- emissions from space heating, ventilation, hot water and fixed lighting,
- exports and imports from the development (and directly connected energy installations) to and from centralised energy networks.
Note:- Expected energy use from appliances is excluded from zero carbon definition.
By following this policy the Government expects new buildings to have net zero carbon emissions over the course of a year.
The definition of zero carbon consultation subsequently introduced by the government, sought views on the Government's proposals. This consultation ran from 17 December 2008 to 18 March 2009 and goes on to explain how to achieve net zero carbon emissions.
The Government also announced that from 2019 all non-domestic new builds will also be required to have zero net carbon emissions, with earlier dates for schools (2016) and public sector buildings (2018).
Wisely, the government set boundaries to what it meant by zero carbon. The embodied energy content of construction materials is not covered, and neither is the transportation of materials. Additionally, transport emissions associated with developments are not included as the government intends to deal with these through other policy instruments.
Given these omissions, it could be argued that Government's proposals do not equate to zero carbon. Even if it is not possible (nor cost-effective) to construct a building without generating any greenhouse gases, how far could we get by dramatically improving the efficiency and sustainability of construction methods?
In any case, does it really matter? Less than one per cent of the UK's existing building stock is replaced every year, and it's been estimated by the Department for Communities and Local Government (CLG) that 87 percent of the current housing stock will still be around in 2050. That means that the UK cannot meet its carbon reduction targets without a far-reaching retrofit programme for existing buildings.
The UK Green Building Council's proposal for a Code for Sustainable Buildings will play an important role in improving the focus on energy efficiency in existing buildings. But this is just one of a hierarchy of measures that the Government says will be needed.
The consultation document proposes a three-stage hierarchy for designers to achieve zero-carbon. The first step for energy efficiency requires compliance with Part L of the Building Regulations. This stage may also encompass other regulatory instruments, such as a mandatory requirement to design to Level 6 of the Code for Sustainable Homes.
The second stage proposed by Government is something called Carbon Compliance', which essentially is the use of on-site micro-energy generation. A report by the UK GBC Zero Carbon Definition Task Group believe over 80 per cent of homes in the UK to be unable to achieve zero carbon targets this way. The development of near-site and off-site low and zero-carbon energy generation is also being proposed.
Initially there were reservations over whether the use of biomass technologies could be included in the zero carbon strategy. However, the government appears to be in full support of using biomass systems both within new homes and as a source of direct heat from nearby off-site generation.
The third stage in the zero-carbon strategy is what is known as allowable solutions', which is a buy-out fund or form of carbon offsetting through high quality international investment in low and zero carbon projects.
This third way will, it is believed, only be permitted where energy efficiency and carbon compliance are unable to be achieved totally through on-site and near-site measures achieve the goal of zero carbon - in other words the residual emissions.
The government is proposing a system of credits to permit off-setting to occur. Credits will be awarded to developments that have a range of energy-saving criteria. For example, energy-saving appliances and low and zero-carbon technology capable of exporting energy to the grid will earn credits to enable an offset of residual carbon emissions.
The government would prefer off-site low and zero carbon technologies to be included in this part of the hierarchy by feeding into the national grid.
So will the policy work? The first two parts of the hierarchy - energy efficiency and carbon compliance - are signs of forward thinking. With a few tweaks, off-site low and zero carbon energy generation could play an integral part of reaching the zero carbon target, but only if the contribution from the grid can be guaranteed to be clean.
Other questions remain to be answered. For example, with allowable solutions, will off-setting contribute to reducing carbon dioxide emissions enough for claims of zero carbon to stack up - not just initially but over a sustained period? Or is it, as some might argue, just a way of covering up holes in the system, and easing collective guilt?
Off-site low and zero carbon energy generation technologies sounds like reasonable measures, but if they are supplying to the grid as opposed to supplying directly to a development, what guarantees will there be that this clean energy will not be lost in the overall electricity generation? This is a key issue, especially when it's mixed with the output from the proposed eight new coal power stations (each potentially generating eight million tonnes of CO2 per year) that the Government is keen to build.
These questions highlight the credibility gaps that still exist between intention and delivery in Government's push for a low carbon and sustainable energy future. Whatever transpires following the zero-carbon consultation, tackling the issue effectively will not only significantly affect the environment, but also our pockets.
Zero carbon targets on the construction industry, [Online], Available: http://www.bsria.co.uk/news/article/clean-home/ [18 March 2014].
With rising fuel costs and Arctic weather conditions this winter, the challenge of burning less fuel and keeping our homes warm has been uppermost in the minds of all homeowners. Thicker loft insulation and double-glazing are a must for existing houses but if you are building a new home, there are other steps which you can take to make dramatic savings on energy costs.
“Talking to an architect who specialises in low energy technology is a good starting point for the would-be house builder,” says Portadown-based architect Paul McAlister. “It costs about 10% more to build a lower energy house but this leads to an amazing 80% reduction in heating costs during the lifetime of the property which is both a huge financial and environmental saving.
“And there’s more money to be saved. Government grants are also available, such as those from Land & Property Services which offer free rates for five years to the occupier of a new zero carbon home and two years to the occupier of a new low carbon home.”
Paul has been advising clients on low energy housing solutions since 2006 and he has recently been certified as Northern Ireland’s first “Passive House Designer”. This is the worldwide gold standard in energy efficient house design.
“Since the sub-zero temperatures in December, we have talked to an increasing number of clients who want a low energy home as their number one priority. By including features such as triple-glazed windows and super insulating, it’s definitely possible to make long-term savings to fuel costs. It’s estimated that it costs £2,600 to heat a traditional house each year but by including the “Passive House” low energy features, fuel costs can drop to as little as £220 per annum.”
Loughgall businessman Fearghal McNeice is currently building a low energy house near the National Trust’s Ardress House.
“Employing the services and expertise of a professional within the architectural energy industry, such as Paul McAlister Architects, has been very beneficial,” commented Fearghal. “We are looking forward to much lower heating costs and the two year rates’ rebate was a very welcome added bonus!”
The message is clear. Think low energy as you plan your dream home and you can save pounds on your fuel bills in the future.
Author Paul McAlister
The first social Passivhaus development
'Tigh-NaCladach' (house by the shore), is the UK's first social housing Passivhaus development in Scotland. This affordable low-energy housing scheme effectively demonstrates how the Passivhaus standard can help meet the increasingly high levels of energy performance demanded of public housing. The high performance EWI system, StoTherm Classic, impact resistant to 50-60 joules - was specified for other Passivhaus developments in the UK. These include a domestic project nearing completion in the Cotswolds (the first completed house independently certified to the Passivhaus standard by the Scottish Passive House Centre) and the first commercial building constructed to Passivhaus standards, recently completed in Dover.
Existing buildings are also utilising the thermal insulation properties of EWI systems. With 20% of the UK's total carbon emissions coming from existing housing stock, the principles behind the Passivhaus standard are also applicable to homes in need of sustainable up-scaling.
One such retrofit/refurbishment project to embrace Passivhaus principles is the RlBA Award winning Zero Carbon house in Birmingham. The former two-bed, semi-detached Victorian house has been turned into a spectacular four-bed sustainable property. In order to achieve its zero-carbon status, Passivhaus principles were employed, incorporating StoTherm Classic to ensure excellent air tightness and thermal efficiency. The EWI system enabled the building to achieve an exceptional U-Value rating of <0.11 W/m2K within the building envelope.
As the changes in regulations continue to evolve, social landlords are continually required to ensure that social housing in the UK is up to standard. Passivhaus offers a proven and uncomplicated method to achieve energy-efficient sustainable buildings, and could very well provide the necessary specification to meet the increasingly high thermal efficiency demands of social housing.
The Passivhaus standard offers a well-established alternative to the Code for Sustainable Homes and the Building Regulations for sustainable design and construction. Denise Freeman investigates the emergence of Passivhaus in the UK and the benefits of external wall insulation and modern render systems. The term Passivhaus relates to the rigorous energy-efficient building standard developed in Germany in the late 1980s. Although it is considered to be a relatively new standard in the UK, Passivhaus is widely used throughout Europe. 17,000 buildings have been constructed using its design principles. The core focus of Passivhaus design is to achieve an extremely low-energy building that requires little energy for space heating and cooling. Buildings built to Passivhaus standards typically achieve a 44% reduction in carbon emissions compared to an average existing home.
Passivhaus is sometimes confused with Passive House, which typically relates to a building with traditional passive design features, such as the use of solar gain. Whilst Passive House design relies exclusively upon the orientation of a building and format, and uses fewer or no active mechanical and electrical systems. A Passivhaus building integrates some passive design features, but takes an active approach rather than a passive approach. In essence, the fundamental space-heating requirement in a Passivhaus building is managed by a mechanical ventilation and heat recovery system. This active approach also allows the Passivhaus designer to be more flexible with the building design. Current legislation stipulates that new build homes should achieve a minimum of level 3 under the Code for Sustainable Homes. However, this is soon set to increase with all new builds having to comply with code level 4 by 2013. Passivhaus is equivalent to code level 4. The sustainable methodology behind Passivhaus brings the housing sector a step closer to the government's zero-carbon idea, which is almost impossible to achieve without implementing Passivhaus principles.
A Passivhaus building must incorporate a number of core elements including exceptional levels of insulation, an airtight envelope, a heat recovery system and thermally advanced windows and insulated doors. In order to realise the extremely high levels of thermal performance that the Passivhaus standard requires, the external walls must achieve a U-value rating of <0.15W /m2K. This is achieved through the use of an external wall insulation (EWI) system. EWI systems are increasingly becoming a key element in the specification process with regards to high thermal efficiency requirements. Around 30% of the energy used to heat a typical home is lost through the external walls. EWI systems work by wrapping the building in a thermally efficient envelope, significantly reducing any energy loss. maximised and comfortable internal maintained all year round.