Airtightness in Dwellings - Prepare to be Sick in your Airtight Home:
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,
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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" .
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