Ventilation Energy and Environmental Technology
                                     from VEETECH Ltd.              Updated 12th November 2009

Comments: Thinking the Unthinkable

Is Tight Right for British Homes?

Damien Triltmand 2009
 

Key Points:

• Airtightness is not fail - safe;

• Appalling MVHR installation quality has been identified;

• 80% of the single-family houses monitored in Sweden did not meet minimum ventilation requirements;

• Air supply ducts contaminated by moisture can be “virtual incubators for microbial pollutants such as mould and bacteria” ;

• A relationship between allergic symptoms and low ventilation rates has been observed;

• So daft is the philosophy behind MVHR that the system must invariably operate throughout the whole year;

• Unable to demonstrate any effect of MVHR on overall energy consumption.

Current wisdom states that our homes must be airtight.  This, we are told, is to reduce ventilation heat loss and to recover heat by means of mechanical ventilation heat recovery (MVHR for short). Policy makers are seemingly so persuaded by the arguments of the mathematicians, that there is energy to be saved, that they appear to have embraced MVHR technology to the full. The future vision is that, in the name of zero carbon, we are destined to live in sealed boxes in which the air we breathe is mechanically fed to us through pipes. This ‘holy grail’ of energy saving has been around since the energy supply crisis of the 1970’s. During this period it became a popular concept in the cold climate regions of Scandinavia and Northern Canada. In principle, this seemed to be a sensible solution for locations where winters are dark, long and bitterly cold. 

Without airtightness MVHR will not work.  Failure to observe this number one rule simply means that air bypasses the heat recovery system, thus rendering MVHR a costly and energy-wasting accessory. Hence British Building Regulations are imposing ever-demanding requirements for building airtightness. MVHR also requires electrical energy. In cold climates, the difference between outside air temperature and indoor temperature is high which means that there is much energy saving potential to offset the electrical demand. In the UK, the temperature difference is much lower. Here, with good building design (such as sensible insulation and maximum utilisation of winter solar gain) the system often has little useful work to do. In addition, so daft is the philosophy behind MVHR that the system must invariably operate (and consume electrical energy) throughout the whole year (i.e. during the many months when heat recovery is simply not needed). This continuous operation is necessary because airtight buildings no longer have the natural porosity required to ensure safe, background ventilation.  In fact, airtight buildings are not fail-safe. A poor MVHR installation, a motor failure or even a failure to struggle into the roof-space to regularly replace clogged filters, will seriously inhibit fresh air supply. Apart from resultant allergic and ‘sick building’ symptoms, system failure could cost you your life. In this airtight environment gas cookers, portable heaters and open fires may rapidly be starved of oxygen, leaving the home filled with lethal carbon monoxide fumes.

So, with such onerous responsibilities, is it sensible to rely on the airtight approach? Sadly field evidence on the performance and safety of MVHR in airtight buildings is shocking. Installation surveys invariably show critical errors. Where these systems have been installed in houses that actually are airtight, critically low levels of ventilation and associated severe health problems have, all too often, been observed.

A field survey of heat recovery ventilation systems, commissioned by the Canadian Mortgage and Housing Corporation  (see reference 1), discovered that 12% of the systems investigated were not operating at all due to component failure including failed air supply motors.

Serious faults were found in many of the remaining systems including:

• Dirty filters, cores and fresh air intakes (over 50% of installations);
• Missing or compressed insulation on cold-side ductwork;
• Lack of grease filters in kitchen exhaust grilles;
• Lack of traps in condensate tubes;
• Potential pollutant sources in the vicinity of air intakes;
• The use of poorly installed flexible ductwork;
• A lack of airflow balancing.

In Britain, appalling installation quality has similarly been identified, along with negligible energy benefit. In a detailed and careful field trial of MVHR in Local Authority housing, Robert Lowe and David Johnston from Leeds Metropolitan University (see reference 2) reported that:

·        The supply and exhaust ductwork of several units were connected the wrong way round;
·        A number of the MVHR units and sections of ductwork were not insulated;
·        Condensate drains in general appeared to be installed with an insufficient gradient;
·        Some fans were wrongly commissioned resulting in these units consuming almost twice as much power as they should have;
·        In another case, extract airflow was twice as great as supply airflow, resulting in poor thermal efficiency.

In respect of energy benefit the authors state that: “We have been unable to demonstrate any effect of MVHR on the overall energy consumption of the field trial dwellings.” They also conclude that: “There appears to us to be little point in conducting research into the energy implications of mechanical ventilation systems of any type, without simultaneously addressing the problems associated with making houses airtight."

The problems associated with airtightness certainly need to be addressed because a further and, perhaps, a much more sinister nasty can lurk within mechanical ventilation air supply ducts. In our damp British climate it is an odds on certainty that the supply ducts will become contaminated with moisture. In a report entitled  “Is Your House a Sick House? The Mould/Air Conditioner Duct Connection” by Virginia Peart, of the University of Florida Institute of Food and Agricultural Sciences (see reference 3), the author states that air supply ducts contaminated by moisture can be “virtual incubators for microbial pollutants such as mould and bacteria.” This, the author points out, can lead to serious health implications. Such health problems have already been seen in Sweden, where a physician led study, by the Swedish National Testing and Research Institute (see reference 4), reported on the ventilation rates in 390 Swedish homes and associated allergic symptoms in children. This study found that 60% of the multi-family houses and 80% of the single-family houses did not fulfil the minimum requirement for ventilation rate required by the Swedish Building Code. It also went on to show that there was a ‘response relationship’ between allergic symptoms and low ventilation rates.

Everything points to the airtight home being a dangerous hazard to health. Nevertheless, having previously suffered from the untested housing disasters of the post war period, low-income families are destined to be the first to be shut away in these air-sealed environments. However, perhaps Housing Associations, Local Authorities and building developers should be wary. Any hint of installation inadequacy, system failure or duct contamination will undoubtedly lead to rich pickings for compensation lawyers, not to mention the risk of appalling health consequences for those with no choice but to live in such environments. 

It would seem that much of the current UK philosophy for low energy buildings stems from a time when scientists were  convinced of  an impending ice age. Now scientists warn us of global warming. Apart from poor indoor air quality and associated health problems, a further consequence of current housing design is severe summer overheating and a consequent increase in the use of air conditioning. In England’s and indeed, in Britain’s green and pleasant land, is there a place for air-sealed homes?

REFERENCES

(1) CMHC Research Highlights  "Field Survey of Heat Recovery Ventilation Systems", Technical Series 96-215 (1999).

(2) R Lowe  and D Johnston  "A Field Trial of Mechanical Ventilation with Heat recovery in Local Authority, Low Rise Housing, Final report, Centre for the Built Environment, Faculty of Health and Environment, Leeds Metropolitan University UK. (1997).

(3) Virginia Peart "“Is Your House a Sick House? The Mould/Air Conditioner Duct Connection”, university of Florida Report FCS3240 (2001).

(4) C. G. Bornehag  , J. Sundell  , L. Hägerhed-Engman  , T. Sigsgaard "Association between Ventilation Rates in 390 Swedish Homes and Allergic Symptoms in Children", INDOOR AIR:Volume 15(4) p 275-280 (2005).  

© VEETECH Ltd 2009 

Important Note: Comments are the views of authors and not necessarily those 
of VEETECH Ltd,

Further MVHR Case Studies 
point to an Energy and  Indoor Air Quality Disaster for Homes

• THE UNITED KINGDOM: Energy Saving Trust report CE130 “Thamesmead Ecopark – Case Study” reveals that, in this development of mixed heating and ventilation systems, energy measurements showed that the monitored dwelling fitted with MVHR had "the highest gas consumption" and that the heat recovery system "consumes more electricity than the fans" [of the other houses]. 
  

• THE NETHERLANDS: Reporting in the August 2009 Edition of the European Journal of Heating, Ventilating and Air Conditioning Technology, Atze Boerstra and Jaap Balvers from BBA Indoor Environmental Consultancy in the Netherlands report that "There has been considerable media coverage in the Netherlands on the health effects of balanced mechanical ventilation in homes, including reports on public television linking energy efficient houses with balanced ventilation to negative health effects". They continue by reporting that numerous cases have been encountered and  that "Investigation (inspection and measurement) supports the complaints and proves that the quality of the indoor environment is below standard." The reasons given are precisely the same as those given in "Is Tight Right for British Homes" .