Zero Carbon or EcoBling?

By now, everyone should be aware that the UK is committed to reducing carbon dioxide emissions 80% below 1990 levels by 2050. Most people reading this blog will also be aware that carbon dioxide emissions arising from energy consumption in the buildings accounts for around 45% of the total.

Thus, one of the headline policies in the UK is that all new buildings should be constructed to zero carbon standards by 2020. However, by the time 2050 comes around new zero carbon buildings will only account for around 20% of the building stock, the remaining 80% are already in use today. The low carbon refurbishment of some 20 million existing buildings presents an even greater challenge for the construction industry than that of zero carbon new buildings. Further, in order to meet the commitment we will need to deliver over 2,000 low carbon building refurbishments every working day starting today.

Unfortunately, a number of recent studies of both low carbon housing and low carbon non-domestic buildings have shown that there is still a wide performance gap between the expectations of the construction industry and its clients and the ability to deliver real carbon savings. It is therefore vital that we embark on this journey of decarbonising the built environment with a clear understanding of what it will involve and which approaches deliver the best abatement at the lowest cost. Otherwise, we risk wasting time and money on initiatives that fail to achieve the end goal of reducing the overall amount of carbon dioxide emitted to the atmosphere.

Recently, the conjunction of local planning policies demanding on-site renewable energy generation and the generous financial incentives available for these technologies have created a perverse new market for small scale generation in urban locations. The most common approach now being taken to low and zero carbon housing is to use an electric heat pump in the winter and then provide the building with sufficient renewable generation to offset the electricity consumed by the heat pump over the course of the whole year. What we are seeing at the putative cutting edge of new building design will no doubt become the default approach for refurbishment too unless we do something about it.

Photo of PV shaded by taller building

Incentives encourage the installation of renewable technologies even where they are inappropriate.

In some instances I am even hearing now of projects that are abandoning super insulation and other passive energy conservation measures in order to pay for the revenue earning technologies. Under the right circumstances an owner could now be paid to generate heat that is wasted in a less well insulated building and paid again to generate renewable electricity to offset the wasted consumption and still qualify as zero carbon.

Subsidies aside, this approach to zero carbon, whether applied to new build or refurbishment, may not actually lead to zero emissions, as the assessment of carbon abatement does not take into account the different times at which the generation and the demands occur. The carbon intensity of grid-supplied electricity varies depending on the mix of generation required to meet demand. Generally, in the winter the carbon intensity is higher as more fossil fuel generation is brought into the mix to match the demand, whereas during the summer, when building attached renewables will be generating at their peak, the carbon intensity is low anyway.

Taken to the extreme, if we try to address low carbon refurbishment to meet our national targets using a mix of heat pumps and small scale renewable generators then we will simply exacerbate the problems. As more and more renewable generation is added to buildings, the carbon offset available for each individual generator will get lower and lower. On the flip side, a wholesale move to electric heating in the winter, even with the purported efficiency of heat pumps, will require a vast increase in generation capacity. Even if a substantial proportion of this demand can be met from large-scale renewables there will still be a requirement for backup generation to cover the intermittency of the renewable generators.

Then we need to consider the actual performance of heat pumps in practice. Ground source heat pumps provide pretty consistent performance throughout the year, but are expensive and require large areas of land for heat extraction. The performance of the more popular air source heat pumps depends on the external air temperature. The performance figures that are typically used to assess the carbon abatement potential are seasonal averages corresponding to outside air temperatures of 5°C to 7°C. With well designed, well insulated buildings there should be little demand for any space heating at these temperatures. In the future, heat pumps will be required to work mostly at outdoor temperatures below 0°C, when their performance drops rapidly. Thus, the instantaneous electricity demand from heat pumps during the winter could be much higher than anticipated at a time when the grid has higher carbon intensity.

A further problem with adopting small-scale renewable heat technologies to refurbish British buildings is that we have a history of building buildings that leak. The UK’s relatively benign climate means that, historically, we never really had to bother with insulation before energy conservation became such an issue, whereas our damp weather quickly leads to mould problems in buildings without good ventilation. Our standards of construction therefore reflect these very real drivers. However, this means that our buildings are generally too expensive to heat continuously, as the heat just escapes. Consequently we have adopted a pattern of intermittent heating following occupancy in homes and non-domestic buildings alike.

Intermittent heating requires a high intensity heat source such as a gas boiler, and a heating system that responds quickly, such as the traditional radiator. Low carbon and renewable heating systems work best when they are configured to deliver low intensity heat continuously to a well insulated, airtight building. To size a heat pump to deliver similar peak output to a boiler would be prohibitively expensive and lead to significant problems in its operation.

Dealing with the poor state of the fabric of our buildings must be the priority in refurbishment, before we ever start to think of bolt-on technologies. Insulation and airtightness do not have the “EcoBling” attraction of small scale renewable energy, but will require just as much thought and ingenuity if we are to get it right.

When we try to retrofit high levels of insulation and air-tightness to traditionally constructed British buildings we can quickly run into problems with indoor air quality, condensation and even rot within structural timbers, not to mention bronchial health problems relating to mould. Improvements to insulation and airtightness therefore need to go hand in hand with provision for protection against condensation and controlled ventilation with heat recovery. Thus, an apparently simple measure actually introduces a whole family of additional requirements in order to maintain a safe and healthy internal environment. Is a serious mistake therefore to try and skimp on consideration of issues relating to the building fabric in order to pay for the low carbon technologies.

Therefore, when it comes to retrofit, we must not allow ourselves to become distracted by the apparent financial attractiveness of bolt on renewable energy technologies. It is conceivable that the conjunction of zero carbon buildings, the feed in tariff and renewable heat incentive could actually lead to higher emissions overall, whilst not addressing the root of the problem. The approaches we take in order to meet policy goals in the short term may not in fact be the most sustainable approach in the long term.

The problems facing us in dealing with the building fabric issues in our stock of existing buildings will require considerable effort, expense and innovation. Failing to deal with the building fabric issues will result not just in higher than expected emissions, it could exacerbate health problems and other social issues such as fuel poverty. We need to be aware that the directions we are taking now through expedience may not lead us directly to our hoped for destination and that we may have to change direction several times before we can reach our ultimate goal.

We would be much better off focusing our efforts on building refurbishments that address the fundamental issue of consuming less energy to create comfortable and productive internal environments, rather than continuing to delude ourselves that we can simply bolt expensive technology on top of already failing buildings. That way, the cost to decarbonise our energy supply, the only real way to achieve a low carbon economy, will be reduced in line with the energy we save.

23 thoughts on “Zero Carbon or EcoBling?

  1. Pingback: Allowable Solutions Consultation – silly policy, but still worth responding | Kate de Selincourt

  2. I do not know of a demand based passive vent system (apart from humidity led vents- these are available), and I cannot fathom how this should work, either with only wind as the driver. Energy demand of efficient MHRV is furthermore so low, and the COP (electric energy in to heating energy out) so high that I see very little incentive for inventing something that somehow works with natural forces. MHRV has the added benefit of being able to filter pollutants from outdoor air. At least here in NZ, 53% of people live in airsheds where the not-too-stringent national thresholds for ambient air pollutants are regularly exceeded. I would imagine this to be similar in the UK. So: letting in unfiltered air may not always improve indoor air quality. For passive vents to do some filtering, forces greater and steadier than wind need to be at work, as the pressure difference will otherwise not allow for reliable filtration. In high-rise buildings or severe climates this may be achieved with stack effects, but typically, mechanical forces are needed for this.

    • Thanks all, points well taken, I will leave the sun spaces in Hockerton! If then MVHR is the way forward for effective domestic ventilation, a related question re retrofits: would you agree that MVHR is generally only appropriate at an air tightness of 5 or worse, therefore we should be improving air tightness to at least this level (as well as insulation levels) before considering retrofit of MVHR (as well as ensuring it is carefully designed, installed and commissioned and occupants are fully trained)? Or would other factors such as poor internal air quality justify retrofit of MVHR in a more leaky building given the low energy cost?

      • Doug,

        balanced MHRV will improve indoor air quality – regardless of airtightness level. You are right, though, that airtightness is a precondition for the heat recovery to work to specs, and getting the high energy returns. In a retrofit, airtightness is indeed one of the major challenges. However: an n50 of 5/h is typically easy to achieve – but would not be good enough for optimal heat recovery. For this, you are looking at a n50 of 1/h or below, which is no longer simple, but achievable with careful design and implementation.

        I cannot relate to insulation being a precondition for MHRV to work. I do agree that insulation is typically the low-hanging fruit and should be done first in that case. However, as retrofitting insulation cost-effectively is a matter of timing and sequencing (e.g. insulating a cathedral roof when you need to re-roof anyway is a no-brainer, and fitting an external insulation finishing system when you have to re-paint and need a scaffold anyway is also quite cost-effective), the economic staging may not always allow the insulation to go in first. I do not see a problem with preferring the MHRV in these cases.

        As for the training required: yes, in the olden days ventilation systems were not exactly user friendly or built with comfort and acoustical performance in mind. In the past, hardly anyone bothered with making maintenance an easy job, either. But things have evolved, and a large, responsible fraction of the ventilation market is nowadays offering systems that are very easy to operate and maintain. Anyone who manages to use a smart phone can operate one of the good ventilation systems with ease. And if you adhere to certified Passive House requirements, air flows are well adjusted on commissioning for optimal performance. You still have to do filter changes, but the good systems will send you an email or text when these are due. And all you have to do is pulling out a cassette and shoving a new one in. Evolution! Once in a while, the ducting should be checked and cleaned if necessary. This is easy if you are designing systems with maintenance in mind, and in case you do one of the Certified PH Designer courses, your instructors will dwell quite a bit on how to do this. With the right systems designed and commissioned by the right people, you really can sit back, relax and enjoy continuous fresh but pre-warmed air. You can even open a window at will – all this will incur if you keep it open for longer is a spike on your power bill. Open Passive House days in November are a great opportunity to check all this in real life.

  3. Doug, great overview, hope someone from central gov follows your blog! Re comments about domestic ventilation and lack of progress compared to comnercial sector, do you know of any domestic automated passive vent systems (eg actuated windows/vents linked to aq and internal/external temp sensors)? I wonder what the energy demand of such a system would be relative to MVHR, especially if could use a thermally separated south-facing sun space to pre-heat air in winter where possible? Also what might be the energy + aq + overheating mitigation benefits, user perceptions and costs of retrofitting such a system to suitable existing homes? A worthwhile action research project?

    • Doug (McNab)

      Uni of Nottingham has a number of examples that fit your description. To my mind this is a daft approach for the reasons Kara mentions plus:

      Much, much, more expensive
      More to go wrong (sensors, multiple window actuators etc)
      Buffer zone separates main space from outdoors (in a bad way)
      Buffer zone hot in summer cold in winter.

      Despite all this and the fact that there are examples to visit and kick the tyres, such relics of the 1970s are still being built.

    • Hi Doug, Unfortunately I can’t imagine that anyone from Central Govt does follow me, and if they did I suspect that their perception filters around Zero Carbon are so dense that the message wouldn’t penetrate.
      There were lots of experiments with passive solar design in the 70s and 80s including housing projects like Hockerton and the Berm House at Caer Llan (which gets a mention here: However, as Kara points out, most domestic buildings do not have enough height to generate stack effect and therefore any form of passive ventilation is based more on hope than verifiable performance. There was a brief fashion for passive stack ventilators for domestic bathrooms and toilets, but I think that that probably went the way it deserved to. Finally, as Nick says, there is the complication of controls and multiple possible modes of failure. On the whole I believe that it is better to leave the complicated passive systems to commercial buildings with maintenance systems.
      On the other hand heat recovery ventilation systems must be evident and legible to the owners of homes. Feilden Clegg Bradley experimented with whole house heat recovery ventilation decades ago in the first Milton Keynes EcoHouses. Unfortunately after a couple of changes of ownership the new occupants didn’t even know that the systems existed and so they were never maintained or even switched on.

  4. Nice ventilation discussion, love the quote Kara.

    Doug, the generals are clearly to blame for the silly strategy and for ordering us to do wrong things (to stick with your analogy).

    Recent history and psychology literature is full of examples of how rare it is for people to stand up and say no when told to do bad and stupid stuff that they would not not normally imagine agreeing with. This does not however excuse such actions.

    If the problem is the fear of loosing work by challenging the flawed brief then surely in this age of blogs and Twitter we can escape the Prisoner’s Dilemma by all agreeing together as a profession that something is bollocks.

    Professionally I have a vested interest in this not happening!

  5. Hi Doug,

    this is part of my doctoral research, which will be published if and when my examiners give the green light. The German Passivhaus Institut has publications in the same vein -unfortunately only in German, and more theoretical (I actually measured IAQ in new houses). But at least here in NZ there is some historical research attesting poor indoor conditions of houses as far back as the 1940 – I am quite certain you find similar closer to home (in my thesis, I quoted from e.g. Bedford, T. (1948). Basic principles of ventilation and heating. London: H.K. Lewis, and Tomlinson, C. (1850). A rudimentary treatise on warming and ventilation. London: Weale. I particularly liked a quote from Prof Jacob from Yorkshire College in Leeds:
    “Real ventilation is so uncommon that there is no general popular consensus on the subject. The architect usually thinks this object has been attained if some of the windows can be opened. Some think that the presence of “ventilators”, especially if they have long names, and are secured by “Her Majesty’s letters patent,” ensures the required end. We may as well attempt to supply a house with water by making a trap-door in the roof to admit the rain. ” Jacob, E. H. (1894). Notes on the ventilation and warming of houses, churches, schools, and other buildings. London: Society for Promoting Christian Knowledge., p. 28).
    In NZ, about 50% of houses in the late 40s were identified as having severe problems with mould and other indoor air contaminants – despite being significantly more air leaky and having no or very little insulation (the lack of insulation was in fact identified as one cause of the problems encountered; the other being the lack of continuous ventilation). Air leakiness is simply no substitute for purposeful ventilation, as it cannot be tailored to changing meteorological conditions or occupancy. Houses need to be as airtight as possible – for a myriad of reasons that have very little to do with energy – and be well ventilated. The ventilation could be done manually, but getting this right is just as tedious as doing all your laundry by hand, as you’d have to time window opening frequencies and sequences in line with changing conditions and loads. Trickle vents are only a solution if there is another driver for air exchange apart from wind (which is again unreliable). With low rise buildings in a temperate climate, stack effects will not be this driver. Would anyone buy a car when the manual reads: to ventilate, open windows wide occasionally? Probably not. We rightly expect better from a car. We should expect better from a house.

    • Kara
      I quite agree that we treat dwellings far too casually, whilst workplace regulations and the threat of legislation have forced significant advances in indoor environmental quality in commercial buildings, schools etc. Thanks again for your contribution, it is quite hard to keep up with all the research whilst trying to keep a business going. I wish you success with your examiners and look forward to reading your research in due course.

  6. Actually, it’s not the added insulation or airtightness that’s introducing these issues – indoor air quality in free-running houses is poor to begin with, regardless of how well insulated or airtight they are, and at least here in NZ even regardless of their mean air change rate. Houses I measured had mean air change rates between 0.18 and 1.3 per hour ( and a similarly wide range for air-leakiness) without notable differences in outcomes for IAQ. I explain this with the randomness of real time air exchange and fresh air distribution that comes with free-running ventilation. I would therefore argue that we are making houses better by adding insulation and airtightness, but: we are simply not going all the way when we omit a controllable, reliable form of ventilation.

  7. Could it be summed up with the mantra for resource conservation: reduce, reuse, recycle. Reduce by using insulation, improving airtightness and using more energy efficient appliances. Reuse is effectively taking the heat generated by appliance and solar gain (tied to point 1). And then recycle: using renewable energy to meet the residual requirements (whether this be locally, regionally or nationally generated should be based on a cost benefit analysis).

    • Thanks David, it feels like you’ve been reading my mind. My energy mantra, which I teach to students is:
      1. Conservation,
      2. Recuperation,
      3. Generation (but only as part of a nationally planned system).

  8. Doug – Great article.

    Re mould and health, recent research re connection between specific mould spores/fragments and health was found to be bad – No evidence to indicate metabolites/spore/fragments of any fungi/moulds are any worse than any other inhaled particulate.
    But I hear what you are saying…some of the internal environments produced as a result of misguided insulation are perfect for other forms of bad health.
    Re carbon – I have tried to find out how much energy is used to produce fibre glass and other forms of insulation – without success. Knowing the manufacturing process – I suspect a shed load !!

  9. Agree but what is depressing, and harder to forgive, is that many technically literate engineers and scientists go along with the fundamentally flawed concepts such as zero carbon buildings, RHI, Micro CHP etc. Surprising how many building service engineers for example will follow the latest political targets advising clients on how to tick boxes rather than how to build great buildings that need little energy.

    I know it is hard work to argue with planners for radical efficiency rather than tacking on PV to meet 10% of some of the estimated possible energy use for some aspects of a new building but if we all do it then surely sense can prevail.

    • It is hard not to get depressed, but we mustn’t blame the foot soldiers when the generals are the cause. Like most people in construction, the building services engineers must fight tooth and nail to win sufficient work to survive. The present procurement systems, driven by the public sector, penalise anyone who rocks the boat even a little. See my article Race to the Bottom. What we need most is whole system, joined up policy, but unfortunately that would require Government departments actually working together!

  10. Very refreshing Doug

    You hint at the fact that HP+PV doesn’t deal with winter peak demand which is also a capital expenditure issue. Will people realise that FITs is a Ponzi scheme before there is no cash in the pot to pay for real measures to stop the lights going out?

    I’m a cockup rather than conspiracy theorist but if you wanted to get public support for fraking and nuclear then it would be good to show that renewables can’t deliver. Zero carbon buildings is a great way to do that.

    What is a shame is that the rest of Europe seem to be going this way as well with near net zero – something they are also struggling to define!

    • Hi Nick. I don’t believe it is a conspiracy either (although the recent Part L shenanigans might be). I do think that the various incentives and policies are ultimately well intentioned, if misguided. I understand Systems Engineering, but I don’t think that there is anyone left in the Civil Service who does. If there was they would recognise that, if you are going to tinker with a small part of a complex system, you surely need to take into account how the rest of the system will rebalance itself.

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