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Passivhaus - a visit to the UK by the founder |
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Author: Justin Bere
24 Nov 2008, 7:13 PM
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Wolfgang Feist likes to spend 60% of his working time at Innsbruck University in Austria and 30% of his time at the Passivhaus Institute that he founded in Darmstadt, Germany, although he prefers to avoid travelling and has only visited the UK once before. But his son is studying mathematics at Cambridge University and this was reason enough for him to make a short trip over here.
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Dr. Feist first visited the Martin Centre in Cambridge on November 20th at the invitation of Professor Alan Short and Director of studies Benedicte Foo, for a seminar with enthusiastic MPhil and PhD students from both the School of Architecture and the School of Engineering. The seminar was held in the tightly-packed Martin Centre Board Room, perfectly suited to host polite but intense debates, where a presentation becomes as much a discussion as a lecture; where you find yourself somehow equally and simultaneously aware of the speaker’s delivery and the participants’ collective and individual responses. Chairing the event, Professor Alan Short’s charm and informality created a relaxed atmosphere in which each small interruption added to the unique learning experience. Wolfgang Feist is also a master of such occasions and his delivery was fluent and inspiring.
Following a two hour session, which established the foundations of a new collaboration between the universities of Innsbruck and Cambridge, Dr Feist went to London, where he had a meeting with Liz Reason, (long time campaigner, policy analyst, strategist) CarbonLite Project manager for the AECB, who had invited him to deliver his first public talk in the UK.
The London talk had been planned as a presentation to just one hundred AECB members in a room at the RIBA. However, it seems that everyone under-estimated the interest in the event. Before the organisers had completed sending out invitations to AECB members, the event was fully subscribed and since the Florence Hall was booked out for a commercial event, it was clear that a larger venue was urgently required. This was found nearby at 229 Park Crescent Conference Centre and the result was that approximately three hundred architects, structural and services engineers, policy people, builders, manufacturers, critics, journalists and client representatives were accommodated in the packed-out hall of the conference centre.
Those who attend the huge annual Passivhaus Institute conference on the European mainland will know the wealth of research and monitoring that has been carried out on built Passivhaus examples since the early 1990s. Wolfgang Feist’s first talk to a UK audience could, in the time available, only outline and summarise the tremendous work that has been carried out so far by his research Institute; work that has been supported by the many architects throughout the world who have designed domestic, community and commercial buildings using the Passive House Planning Package (PHPP) software (available from www.carbonlite.org.uk).
The fundamental objective of Passivhaus design is to unambiguously cut energy consumption and to provide accurate design tools to measure the expected energy consumption in a clear, accurate, numerical way. These Germans really don’t have time for vagueness. They are, of course, at least as aware as anyone else of the requirements that are set out in our building regulations. The need to cut greenhouse gas emissions; the need to use renewable materials and technologies and to generate renewable power on site or at least locally where sensible as well as across the national grid; to provide provision for cyclists; to provide housing close to local community services including transport; for buildings to do everything possible to repair the damage that they cause to the natural environment and wildlife….etc. All that goes without saying, but however many of these other features are incorporated, the Passivhaus designer or developer will be unable to circumnavigate the essential Passivhaus requirement to produce a building designed to use less than 15kWh/m²/annum supplementary heat and no more than 120 kWh/m²/annum primary energy (total of heating, lighting, hot water, appliances and any cooling). No box ticking wood chip boiler, no nothing will let the Passivhaus architect, developer or builder circumnavigate this fundamental, verifiable bottom-line requirement for Passivhaus certification.
The reason for the focus on energy efficiency is to do with one planet living principles. If a building regulation concentrates on ‘low carbon’ alone, wealthy countries may end up using the land of poorer countries for their total food and fuel needs, rather than concentrating on cutting consumption. It would be wrong to think that our nation has plentiful land for biomass. For example, Professor Tim Lang has often pointed out that in the UK most of our food is grown on other peoples’ land and if we tried to feed ourselves with entirely home grown food, then the land available for large quantities of biomass would disappear.
German buildings use an average of 200kWh/m²/annum for space heating; most of that energy requirement is supplied by imported fossil fuel which damages the environment and the economy. The picture is similar in the UK. By contrast, Passivhaus buildings are designed to use no more than an average of 15kWh/m²/annum for space heating. (This is a critical figure because more than this would require some form of supplementary heating rather than using the ventilation system to carry the heat required for comfort).
In an earlier conversation Dr Feist explained that energy saving that reduces consumption of imported fossil fuel benefits the environment and is a boost for the regional economy that is then called upon to produce home-grown insulation and other products. The government should take note of this fact to stimulate the economy whilst saving money that will otherwise be paid to the countries that supply our oil and gas. Spending in such a way both saves money in fuel imports and earns money in low carbon manufacturing; Dr Feist pointed out that if the developed world had been doing precisely this for the last twenty years or so, both our environment and our economies would be in much better shape now.
Dr Feist showed a series of graphs that illustrate how in the same house design, some people will find ways to use more energy while others will find ways of using less. He explained that extensive research over many years has shown that in spite of the wide variation in user habits, the average energy consumption of Passivhaus developments has been found to generally speaking outperform design targets and even the highest energy user in a Passivhaus uses less energy than the lowest users of ordinary houses. Indeed the first ever Passivhaus development, DA-Kranichst has achieved an average of 9.2kWh/ m²/annum in monitoring from 1991-2008, less than expected and less than 1/20th of the typical German new-build house. In the UK our houses are very much draughtier than in Germany so in spite of the slightly milder winters we probably also average at least 200kWh/ m²/annum heating loads in the UK, giving us the same potential to reduce energy consumption.
Dr Feist’s energy performance claims are relatively easy to verify due to the tendency for Passivhaus architects to be very open with their building performance figures. It is for example easy to find all the performance data for the Hannover-Kronsberg Passivhaus project on the internet, in English.
Incidentally, in an earlier conversation, Dr Feist pointed out that energy measurements are usually slightly high in the first year, dropping in the second year as the building fabric dries out and the users settle into the building and by the second or third year, energy consumption has dropped close to its longer term average figure.
Dr Feist then explained the simple techniques necessary to achieve Passivhaus design. They are:
(1) Insulation (typically 30cm thick)
(2) Passivhaus windows (airtight, triple glazed with thoroughly insulated frames achieving an overall U-value of 0.8 including the frame)
(3) Airtight construction (max 0.6 airchanges/hr under 50 pascals pressure) with very efficient mechanical heat recovery ventilation. (Some mechanical HRV units have been tested at up to 92% efficiency by the Passivhaus Institute).
Assuming that these three main performance targets are met, together with detailing to eliminate cold bridging and numerous other detailed requirements prescribed by the PHPP software, it is possible to eliminate the need for a boiler and eliminate the need for radiators or underfloor heating. Dr Feist showed a famous Passivhaus graph that demonstrates how a little extra money spent on achieving the 15kWh figure makes it possible to save money by leaving out all this space heating kit. Therefore, when you spend just enough, the solution suddenly becomes economical in terms of capital costs. Now firms like Drexel und Weiss produce all the mechanical kit required to ventilate, heat water and top up the air temperature of a Passivhaus in a single compact unit. The heat pump required to maintain 21 degrees centigrade in sub-zero outdoor temperatures is the size of a refrigerator pump!
Because a Passivhaus is so extremely energy efficient, a domestic Passivhaus equipped with a heat pump can typically supply all its annual energy requirements for heating and plentiful fresh air with just 10 square metres of photovoltaics. Using a solar thermal panel to help heat the hot water, a further 3m² of photovoltaics are needed to provide the hot water requirements for the house. Again, I discussed the maths in an earlier conversation which is as follows:
Energy Harvesting
Solar Intensity UK approx 1000kWh/m²/a
PV system approx 10-12% efficient can harvest 100kWh/m²/a
Therefore 10m² provides approx 1000kWh/a
Air and Heat Energy Consumption
HRV approx 300-400kWh/a
Space heating: 120sqm x 15kWh/ m²/a = 1800kWh, divide COP3 = approx 600kWh/a
Therefore total approx 1000kWh/a
Domestic Hot Water
Domestic hot water: 2400kWh, divide COP3 = approx 800kWh/a. If a solar thermal panel provides approx 60% of the annual hot water requirements, the balance to be produced by the heat pump is 300kWh/a which approximately equates to a further 3 square metres of photovoltaics.
Dr Feist then pointed out that unlike passive solar buildings of the 1970s that usually had a conservatory on the front, architects have a great deal of design freedom with Passivhaus design, whether houses, schools, offices or factories. As a result there are some beautiful designs emerging from Passivhaus architects’ offices. One of the best shown was the Aufkirchen Passivhaus school near Munich. However, whilst the school was undoubtedly a very fine design, some of the pictures used to illustrate design quality were not very persuasive. I have visited more convincing designs by architects such as Hermann Kaufmann, an Austrian architect who also teaches in Munich University.
Dr Feist pointed out that unlike passive solar buildings, Passivhaus buildings can have windows on the north elevation. Again in an earlier conversation I commented on how difficult it is to get Passivhaus certification on a small freestanding house below 100 square meters if there is any north facing glass, due to the volume-to-surface-area-ratio. Dr Feist was aware of this difficulty and is already on the case. At the Passivhaus Institute he has people working on exploring ideas for a possible refinement to the PHPP software. I understand that this has something to do with reflecting the difference between the way in which a small Passivhaus performs if it is occupied by a family rather than by just a single occupier, since in a Passivhaus the heat given off by each person is of significant benefit. However he is aware that such an introduction could be abused and so will not introduce this refinement until this risk has been addressed.
Finally, Dr Feist invited the audience to attend next year’s 13th annual Passivhaus conference in Frankfurt (April 17th & 18th 2009). People who don’t speak German will as usual be provided with headsets, simultaneous translation and an English version of the book summarising all of the numerous technical presentations on offer.
Liz Reason subsequently gave a talk comparing certain other UK building codes with the Passivhaus approach, highlighting difficulties in the UK codes that have been introduced in relative haste. By contrast the Passivhaus code has passed the test of time and Dr Feist is very careful to ensure that it remains truly robust. It is the very robust nature of the concept and the software that led the RIBA in its recent sustainability review to describe Passivhaus as ‘the emerging European Standard.’ This may turn out to be a classic British understatement as in addition to the thousands of successful Passivhaus buildings in Europe, Passivhaus design is now being successfully used all over the world, with examples as far afield as Russia, Iran, the USA and, imminently, in the UK.
A brief response by a panel of experts followed and all seemed convinced of the need to see the Passivhaus standard made mainstream.
In answering questions, Dr Feist said that he thought that the UK construction industry will find the skills to build to Passivhaus standards. The first time we might have difficulty with air-tightness, but if we look and see where we went wrong, next time we will be better. “Practice makes perfect as you say.”
Credits:: Author: Justin Bere, November 2008.
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| Positive review of this story |
wipe0wt  |
14 Dec 2009, 8:01 PM |
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very good like it
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