1. as they monitor an increasing
number of parameters to ensure
the optimum indoor air quality
level, while further reducing
unnecessary energy usage. Demand
control MVHR will use sensors
in the dwelling or in the unit
itself to sample relative humidity
levels, carbon monoxide and
dioxide levels and VOCs against
occupancy, to switch fans down to
very low running speeds or even off
during prolonged periods of non-
occupancy.
The MVHR units of the future will
be ‘smart’ units that are able to
constantly monitor the ambient
conditions of the air and adjust
fan speeds and bypass conditions
to suit. These ‘smart’ units will be
able to assess the condition and
cleanliness of room vents and unit
filters and indicate to the user
when cleaning is required as well
as performing periodic system
tests to verify that all sensors, fans
and controls are working correctly
indicating to users when servicing
beyond cleaning is required.
Whenthese‘smart’systemsare
firstinstalledtheywillbeableto
self-commissionbyusingvariable
flowrateroomventswithintelligent
sensorsbuilt.Theywillbeable
toensurethatalltheroomsin
thesystemareventilatedtomeet
regulationsandensurethatair
qualityiskeptabovethethresholdset.
2016 is now less than five years
away and the government’s
commitment to net zero carbon for
all new build dwellings will require
ever more air tight buildings with
balanced demand controlled MVHR
systems. In turn, these systems will
be integrated ever more closely into
the heating systems used to keep
the property warm. So expect to
see air-to-air and air-to-water heat
pumps with incorporated MVHR
and an array of high-efficiency
photovoltaics connected to a grid-
tie inverter to keep the whole
system running. z
ecent changes to Building
Regulations Part F & L will
require that private new
build dwellings will be
25 per cent more energy efficient
than a similar property built to the
2006 regulations and that social
housing will have to go further still
with a 44 per cent improvement
in energy efficiency. Air tightness
is one focus point for improving
energy losses through the fabric of
a building and the target for most
domestic residential buildings
is being reduced. There is also
now a requirement for new build
properties to be tested, when
complete, to verify air tightness.
Typically an air tightness figure
of 5m3/hour/sq. m at 50 pascals
pressure will be applied to
the design although there are
provisions in the latest regulations
for even more air tight designs
which achieve 3m³/hr/m² at 50Pa.
The tighter the envelope of the
building the lower the heat loss
but also this reduces the natural
ventilation. Natural ventilation
and air movement helps improve
indoor air quality (IAQ) and remove
air pollutants such as airborne
humidity from showers and
washing, odours from cooking
and ECs and emissions of volatile
organic compounds (VOCs) from
furnishings and carpets.
With even modest levels of
building occupancy IAQ rapidly
deteriorates under these
conditions and requires the use of
a balanced mechanical ventilation
system with heat recovery (MVHR).
Such a system uses fans to exhaust
stale, moist indoor air from ‘wet’
rooms (kitchen, utility, bathroom,
en-suite, WC) and replaces it
with fresh outdoor air brought
in to living areas and bedrooms.
The heat from the exhaust air
is exchanged with the fresh air
through a heat exchanger without
allowing the airflows to mix. Thus
the energy required to heat the
fresh air is dramatically reduced,
often by over 90 per cent.)
MVHR is ideal for new build
housing where it can be designed
in and the insulated duct runs can
be integrated into the fabric more
easily than in retro fit applications
with existing housing. The unit
itself can be hidden away in a
utility room or loft and as long as
the filters and heat exchanger are
checked regularly and kept clean
the system should maintain a fresh
and healthy indoor environment
for many years.
So what about the current and
future developments in MVHR
that we can expect? Currently
manufacturers of heat recovery
units can have their MVHR
and MEV (Mechanical Extract
Ventilation – no supply air and no
heat recovery) tested to confirm
both the heat recovery efficiency
(e.g. 93 per cent) and the efficiency
of the fans used in the unit
(Specific Fan Power; sfp measured
in watts per litre per second; w/l/s).
This data is then published on the
SAP Appendix Q website (www.
sap-appendixq.org.uk) to enable
architects and designers to specify
a suitable unit to meet the required
SAP rating. The figure for the
specific MVHR unit can then be
entered into the SAP calculation for
the ventilation system in place of
the default figure.
What does the future hold? I
believe that in future we are likely
to come to view our ventilation
systems as life-support systems;