There were a couple of moments when the PassivHaus study tour seemed to lose all contact with normality and enter into a surrealist daydream. Picture around 20 people, crammed into a cellar, with a few more hanging out in the passageway outside unable to get in for lack of space. We were listening, or trying to listen, to the architect, Carsten Grobe, who was explaining with the aid of a translator about the mechanical systems employed to heat the Passive House, which he had designed and built back in 1998 and in whose basement we were now standing.
One of our party asked what the carbon emissions were like for this house. Carsten gave a long and detailed explanation as to why the indoor air quality was very good and insisted that they had no problem at all with carbon emissions. It was an eloquent answer to a very different question.
You might think that this was just a translation problem and that he hadn’t understood the question. But similar misunderstandings happened throughout the tour. Whilst the Germans had no problem explaining how they have engineered these houses to reduce space-heating demand to an absolute minimum, they looked flummoxed when we started going on about carbon emissions or used the dreaded phrase “zero carbon.” I began to realise that these are concepts that the Germans actually felt uncomfortable about and it highlighted a surprising difference in emphasis between Germany’s PassivHaus builders and the UK’s “carbon busters.”
You see, it’s no accident that one of the key benchmarks for Passive Houses is a maximum allowance for space heating requirements for each house and it is expressed in kilowatt-hours per square metre per annum — 15 is the magic number they are looking for in this context. In contrast, the UK regs now work in terms of carbon dioxide emissions per square metre per annum. Whilst the two units are related, they are not the same, not by a long chalk.
The kilowatt-hour (kWh) has the benefit of being simple to understand. It’s the unit we buy our gas and electricity in, and the related kilowatt is the preferred unit of power for our boilers, fires and electrical equipment. Even light bulbs are routinely rated in watts. Most people are familiar and easy with the watt, the kilowatt and the kilowatt-hour.
Carbon dioxide emissions, in contrast, are much trickier. They vary a lot depending on the type of fuel being burned. A kWh of gas releases less than half the CO2 of a kWh of electricity. Every fuel has a conversion factor, related back to mains gas, and some fuels have several. So the fuel you choose to burn in your house has a critical effect on the CO2 emissions but no effect on the kWh you use. Consequently, Carsten Grobe saw no contradiction in using electricity exclusively to power his ventilation/warm air heating system and to heat his domestic hot water when the solar panels weren’t producing.
The three schemes we visited around Hanover were all different, designed to show the different aspects of PassivHaus living. Carsten Grobe’s selfbuild represented one strand, the upmarket detached family home: we also saw a block of flats in Hanover itself and a terraced house set out on the Expo site to the south of the city. The weather was wet — very wet in fact — but not particularly cold for February, around 7°C, and I was certainly a little surprised to find radiators on in both the detached house and the flat. In fact, I was surprised to even find radiators at all, though they were small and unobtrusive.
Most Passive Houses are built without radiators, except for towel radiators in bathrooms. They aim to maintain an even temperature throughout the structure and Carsten explained that the only reason they had a radiator in their house at all was for odd occasions when their elderly parents came to stay and they appreciated a bit of extra warmth.
But just because Passive Houses rarely use radiators, it doesn’t follow that Passive Houses are “Homes without Heating” as we sometimes think of them as being. The actual space heating arrangements vary from site to site but the overriding principle seems to be to
a) having insulated the fabric down to a very low U value and having designed out all thermal bridges
e) and you use a heat exchanger to take every available bit of heat from the extracted air and add it to the incoming air.
f) You then pass this pre-heated air through something called a post heater (a term I had not come across before) which brings it up to a comfortable temperature.
How much work this post heater has to do depends on how warm you like your house. The one in the terraced Passive House was capable of delivering 1.5kW and could produce an air temperature of 50°C if required. I was frankly surprised at this: it seemed to me that this was essentially a warm air heating system.
The standard method of heating new homes in Germany is to use underfloor heating combined with a gas boiler. PassivHaus eschews this approach on the grounds that you don’t need a full heating system in a Passive House. But it seems to me to offer an alternative that is no cheaper to install and possibly burns more carbon because it relies on electricity to power the fans and the air heater. It would certainly be no cheaper to run because electricity is habitually three times the price of gas.
And yet Passive Houses sell themselves in part by saying that you can offset the extra costs of building to the higher standard by saving money on not having to install a full heating system. Hmm. I was beginning to have my doubts.
Carsten gave us another little trick used by PassivHaus designers. He said it was extremely difficult to get a really low theoretical heat demand from a detached two-storey structure as there is just too much external envelope in proportion to floor area. An easy way around this conundrum was to add a third storey, in his case a basement, and to include this in the heated envelope. The floor area goes up 50% whilst the space heating demand rises much less. As you are looking to meet a target expressed in kWh/m2/annum, the job of reaching PassivHaus standard becomes that much easier.
You could argue that this is daft and that the total energy load is actually increased in order to meet some notional standard. In fact, you’d be right but it’s a criticism that can be levied at most of the other energy rating schemes as well, certainly all the ones that work on a floor area basis.
Maybe, I am carping. I suppose I do carp rather a lot. But I know others were also uneasy. We had Julia Hailes, author of the Green Consumers Guide, with us in our party and she was flabbergasted to see that Carsten’s house was full of halogen and tungsten lights with not a CF bulb anywhere to be seen. There is in fact no particular requirement in the PassivHaus code to use energy efficient lighting or appliances: this seems bizarre. Julia also asked at one point just how you would incorporate a cat flap into a Passive House, a question that was met by complete bafflement from our hosts. Maybe the word cat flap was lost in translation, or maybe it was another case of different agendas.
The embodied energy question was raised several times by various delegates. Was the extra investment in, say, triple-glazing filled with krypton really worth it either financially or in terms of carbon emissions? Again, it seemed to be something that the Germans hadn’t addressed. They seemed to be solely interested in designing homes which required less than 15kWh/m2/annum for space heating: there didn’t seem to be any room for critical reflection about this.
The first day of the tour was spent in the hotel listening to various presentations. One of the most interesting presentations was delivered by John Willoughby, the energy consultant and sage, who gave a 20-minute slide show on the History of Low Energy Building in the UK. He ran through many projects starting with the Wallasey School (1961), the Wates House at CAT (1976 and still the best insulated building in Britain), various solar houses in the 1970s, the Pennyland and Linford projects in Milton Keynes in the 1980s, right through to Hockerton and Bedzed, both realised within the past few years. He also drew our attention to the increasing number of energy codes:
He suggested we were becoming good at standards but not very good at implementing them. He also referred to another energy sage, David Pickles, who I remember seeing give a talk once where he said that low energy living is 10% technology and 90% lifestyle. This little aphorism kept plopping into my head as we made our way around the three Passive House sites the following day. The German PassivHaus builders really didn’t seem to care about this aspect of energy efficiency at all: they just wanted to get their buildings up to PassivHaus standard and move onto the next one. PassivHaus seems to be very much an engineering concept, designed to provide comfortable space heating with the minimum energy possible. But that, unfortunately, is it.
So I came away feeling PassivHaus is a flawed standard. It’s very good on space heating demand (in advance of anything we have built in the UK, except for a tiny number of exemplar projects like Bedzed), but questionable on heat delivery systems, so-so on hot water heating and almost non-existent on lighting and electrical goods used within the home. What is more, there don’t appear to be any plans to update or improve the PassivHaus standard to take into account the rising concerns about carbon emissions. As such, I really don’t see PassivHaus translating wholesale across to the UK, but we can certainly learn a lot from what they have achieved to date.
The principle lesson perhaps being that, whilst it is all too easy for me to carp on about what is wrong with the PassivHaus standard, or why it is not quite the dog’s bollocks (try translating that!), they have built loads of them. And the more they build, the less theoretical it becomes and the more practical it appears. Whereas we may be full of good intentions, the Germans (and the Austrians, who seem to be even more enamoured of PassivHaus than the Germans) have now built around 6,000.
They are also very keen to promote the PassivHaus concept to the non-German speaking world. To this end, the next PassivHaus annual conference will for the first time be bi-lingual in German and English. So if you want to go and learn more about it, you need to head for Bregenz in Austria on April 13/14.
It used to be the case that if you installed electric heating (rather then gas), and then invested the money saved on the lower installation costs in better insulation you had lower header bills then if you installed gas heating. I do not know if this is still the case in the UK, as the standard of insulation is now so match better in all new houses.
Also whenever I see cost comparisons of heating system, they never seem to take into account the cost of getting a gas system serviced each year, including the cost of the wasted day’s holiday you have to spend waiting for the service person to call. (Add in another day each year if you have an inside gas meter for your “meter safety check”, as the gas companies will not tell you what time they will come.)
 Interesting ... each of you, your hosts and you, had quite different perceptions ... one based on the success with the passivhaus standard, and the other from a country without such success.
That some visitors from our country would not understand that - for almost all fuels - an energy reduction without fail equates to a CO2 reduction, is difficult to imagine, not just for your hosts.
 As you wrote further down, CO2 emissions are a variable 'feast', depending on the type of fuel used. Moreover, CO2 figures don't mean anything to the average person (yet). What householders DO understand, especially those with the purse strings, is whether their energy use is reduced by 50%, 90% or whatever. That's why these energy consumption figures are used in Germany, in preference to CO2. Whatever fuel you are going to use, depending on what is available in your area, you want to use as little of it as possible.
The German energy facilities are different to ours, with far fewer gas connections, and more district heating.
So, yes, it is quite possible that Carsten Grobe was surprised about your CO2 questions and would have understood them as questions about air quality; especially as some of their ventilation systems are so sophisticated that they monitor CO2 levels in the indoor air and, when you have a party, automatically increase the ventilation rate according to need.
 "Carsten Grobe saw no contradiction in using electricity ... to power his ventilation [heat exchanger/heat-pump system] ...":
b) he is likely to be familiar with the exciting recent developments to harvest solar electricity cost-efficiently;
d) what fuel do YOU use for the controls and pumps in your (central) heating system, and for your compressors in your refrigerator and freezer?
 Well, if the Germans felt uncomfortable about the 'zero carbon' term, we do too, as it is usually a misnomer and misleading. All fossil fuels and biofuels produce CO2 (yes, biofuels also absorb some while growing, but that makes them 'carbon neutral', not 'zero-carbon').
 The passivhaus standard is only achieved if the building uses no more than 15KWh/m2/a for heating, and no more than 30 KWh/m2/a (or 120 KWh/m2/a primary energy at the power plant) for all appliances and lighting in the house; you will find more on the websites.
So, a building with built-in appliances which are not up to standard will not pass the final independent inspection and not obtain the financial rewards from the government for this standard - meanwhile, the standards of appliances are being driven up by law anyway.
 Low-energy light-bulbs: we don't know whether the homes are handed over with these bulbs provided. However, there is enough incentive in Germany, hence the good quality low-energy light-bulbs - obtainable even here for under £2 from Lidl. The problem may be that they can't generally be used with dimmer switches, and that it seems very difficult to find suitable lamp-shades, both there and here. Sad for all of us, isn't it, that this stands in their way!
 Yes, you will find a radiator in many passivhaus homes: a) it is a psychological reassurance which is still needed by some people at this stage; and b) it is of course true that the young, the sick and the elderly sometimes do need higher temperatures (and our visitors from Australia want 25oC ...). We have seen the particular building you referred to, and it was in fact laid out as 'life-time' accommodation which could be changed as necessary, and really did have grand-parents, parents and children living next to each other.
A building can still be a passivhaus building provided it meets the criteria and performance standard, even if the occupier decides later to 'embellish' it to satisfy their particular need or concern. After all, many people in Britain would laugh at the idea of a home without central heating. When they and their embellishments move out, the next occupier is able to still enjoy the benefits of the straight-forward passivhaus building.
After the great majority of heat has been transferred by the heat-exchanger from the outgoing stale air to the incoming fresh air, the small compressor (like in a fridge) in the exhaust duct beyond the heat-exchanger (hence the term "post-heater") extracts further heat when needed for hot water, or top-up heating on very cold days.
You could describe it as a 'supplementary (or residual) heat-exchanger' ... but 'post-heater' is perhaps easier.
 The cat flap ... your hosts' reaction is not a case of "different agendas", but perhaps a cultural difference. Anyway, specially insulated cat flaps have been used in passivhaus buildings in Germany, and are available from the UK!
 Yes, we do have too many energy codes here. Most may eventually disappear due to the wide and spreading acceptance of the low-energy and passivhaus standard.
Both your hosts and you start from your own assumptions made as a matter of course, and don't realise that the 'other side' is not aware of them at all!
Your hosts are not aware that Britain utilises none of the planning and fiscal incentive opportunities (as well as the next point below) that have led to such a rapid uptake of the passivhaus in Germany and Austria.
You, on the other hand, are not aware that the passivhaus standard QUITE INTENTIONALLY engages people and encourages their creativity by making no prescriptions beyond keeping within that all-important energy target – thus giving them complete freedom of choice over style, material or whatever; that the Passivhaus Institut is helping them to achieve this passivhaus standard cost-effectively with the passivhaus simulation software programme; and that, together with other groups, it is working continuously towards ever higher cost-effective energy reductions. The information we see on all the work that is going on is absolutely amazing.
 Incidentally, the conference in Bregenz in April is not the first bi-lingual annual conference, but we too recommend it to anybody who is interested – especially the site visits.
 All in all, you will see that we are very supportive of the Passivhaus initiative and have followed it for many years. Austria and Germany, and other countries, have recognised it as a viable and proven technology which could transform the energy requirement for buildings to a scale whereby the future need for new power stations could be questioned. This technology and experience is there to be had by us all.
It can only be Brian Rushbridge? Thanks for the detailed commentary and the help with the cultural differences.
I chose to build to PassivHaus standards for the very reasons Brian and Sibylle stated. It leaves your imagination and conscience free to determine your building materials and techniques.
I have found that if you investigate the passive houses built to-date you will find some amazing cost effective designs which improve on the basic standard.
The way in which you are choose to meet your buildings remaining energy requirements is also entirely up to you and your finances.
A concentrating solar pv system and hydrogen fuel cell would be ideal but at the moment a little too expensive. Although I'm working on it :)
Low energy light bulbs that are for use in dimmable (or normal on/off switched) lights are available. Manfacturer is www.megamanuk.com
hello just found your page while researching this concept and wondered what you thought of Richrd Hawkes House, (it is a passive house in UK built inside a large arch, see grand designs) and how it relates to your comments on CO2 emmissions?
I wouldn't be so enthused about gas heating. Gas is going to run out eventually and a fossil fuel can never be clean energy. We heat our house with infrared radiators, a low wattage solution from Infranomic. The price per radiator is about that of a central heating radiator, a bit less if you include the cost of labour for a corgi plumber to install it - these just plug into a standard socket. We aren't investing in gas which is unsustainable either. All our electricity is supplied by good energy - the only company to supply 100% renewable electricity so we aren't burning fossil fuels their either. I've lots of vices of course don't be fooled but not all electricity is bad and gas doesn't have a long-term future.
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"Also whenever I see cost comparisons of heating system, they never seem to take into account the cost of getting a gas system serviced each year, including the cost of the wasted day’s holiday you have to spend waiting for the service person to call."
I agree, they don't account for the maintenance cost of gas systems but highlight it when it comes to computing solar heating costs.
I think a lot can be said for the efficiency of homes. Effective insulation, energy efficient products and more general practice is one of the most sure ways of reducing the fuel bills and the amount of CO2 that your home needs.
"It was an eloquent answer to a very different question." - pretty much a diplomatic answer, which is trying to answer a question without actually answering it=)
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