Download Ventilation - Energy Systems Research Unit

Website: VENTILATION
The need to ventilate
The air renovation in the inhabited places is a physiological need. The breathing of the
occupants is translated in a consumption of oxygen and an expulsion of carbonic gas. The lack
of ventilation implies a decrease of the rate of oxygen, becoming the environmental air
harmful for breathing.
This decrease of oxygen is not the only factor that makes the air renovation necessary. Any
activity in a house produces dampness. The own fact of breathing contributes a substantial
quantity of water steam to the air, provoking an increase of the relative dampness and as
consequence of it, the appearance of condensations, formation of mildews and deterioration
of the finished ones.
To avoid these problems is necessary to ventilate. A good ventilation will allow:
- To contribute new air, necessary for the breathing.
- The evacuation of smells and / or toxic gases.
- To protect the housing of mildews and degradations due to the water steam.
Ventilation system
After a lot of research, we have decided to use an innovate solution which provides domestic
houses the combination of natural ventilation and heat recovery, known as Passivent iHybrid.
This solution provides the benefits of natural ventilation (a proven no-energy, highperformance and energy efficiency solution) and heat recovery (provides thermal comfort,
reduces heat loss in cold weather and improved comfort).
This iHybrid system is intelligent, that means it knows which mode it should operate in by
using sensors to monitor the external temperature.
When the external temperature is below 9ºC the system will switch the heat recovery fan on
to operate in Heat Recovery
Mode. The warm air being
exhausted passes through the
heat exchanger in the heat
recovery unit. At the same
time, the cold air which is
being brought into the house
passes through the heat
exchanger. The heat is
transferred to the incoming air
to provide warm tempered air
to the dwelling. Filters within
the heat recovery unit ensure
that unwanted pollutant do
not enter the home. Doing
that, a lot of advantages
appear as energy efficiency,
warm incoming air, reduced heating load requirement, fresh air, effective control of moisture
and relative humidity, thermal comfort for occupants...
On the other hand, when the external temperature is above 9ºC the system will switch the fan
off and activate innovate damper technology which diverts the exhaust air through the
ductwork used in Natural Mode. In
this mode, ventilation is driven
primarily by the natural stack or
convection effect by which warm air
rises, so no power is used during
operation.
Moisture-laden air is extracted
directly from wet rooms (kitchens,
bathrooms...) through ducting up to
a roof terminal where it is vented to
the outside. Wind blowing across
the roof provides additional suction.
Supply air is provided to the
dwelling
through
temperature
sensing wall vents.
This provides free fresh air, effective control of moisture and relative humidity, low
maintenance costs, automatic control, silent extraction...
Combining both worlds, the Passivent iHybrid solutions provides low annual energy use, low
annual running costs, lifetime cost savings, improved comfort, guaranteed ventilation, high
levels of indoor air quality, efficient operation...
Benefits

55% electrical consumption saving against mechanical heat recovery.
A temperature of 9ºC would be the optimum balance point within a dwelling. Based on this, it
is calculated that the iHybrid system will operate in Heat Recovery Mode for approximately
45% of the year. As a result, 55% of the electrical energy of the fan would be saved as it would
be switched off while operating in Natural Mode.

Less carbon emissions
Calculation show that carbon emissions would be reduced by approximately 8.5% using the
Passivent iHybrid system compared to a standard heat recovery system. This is because the
standard system uses energy all year round to bring in fresh air. While Passivent iHybrid uses
no energy for supply air while operating in Natural Mode.

Extended life expectancy and lower life cycle cistings
As the iHybrid system will operate in Natural
Model for 55% of the year, the heat recovery
unit will be switched off for this time. It is
estimated that this will prolong its expected
life to approximately 20 years compared to 10
years for a standard mechanical heat recovery
unit which will be working 100% of the time.
In addition, filter changes will be required less
frequently with the Passivent iHybrid system,
as they are not used while the system
operated in Natural mode.

Energy efficiency
With a standard
mechanical heat
recovery system, a
summer bypass will
usually be used to
bring air in from
outside without
passing over the
heat exchanger. To
do this the system is
continuously using
electrical energy.
In contrast the
Passivent iHybrid system uses no electrical energy in the summer to bring un fresh air when
heat does not need to be recovered.
Ventilation requirements
Ventilation requirements for comfort:
𝑄=
10 ∗ 𝐺 1
∗
𝐶𝑖 − 𝐶𝑜 𝜀𝑣
Where G is the pollution load, 𝐶𝑖 is the desired perceived indoor air quality, 𝐶𝑜 is the perceived
outdoor air quality, and 𝜀𝑣 is the effectiveness.
The results are:



2-bedroom house: 𝑄 = 105𝐿/𝑠 = 0.105 𝑚3 /𝑠
3-bedroom house: 𝑄 = 136 𝐿/𝑠 = 0.136 𝑚3 /𝑠
4-bedroom house: 𝑄 = 180 𝐿/𝑠 = 0.180 𝑚3 /𝑠
Power required
𝐹𝑎𝑛 𝑖𝑛𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟 =
𝑃∗𝑉
𝜂
Where P is the pressure drop, V is the ventilation flow rate and 𝜂is the efficiency.
The results are:



2-bedroom house: 𝐹𝑎𝑛 𝑖𝑛𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟 = 15𝑊
3-bedroom house: 𝐹𝑎𝑛 𝑖𝑛𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟 = 19.4𝑊
4-bedroom house: 𝐹𝑎𝑛 𝑖𝑛𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟 = 25.7𝑊
So, for the whole community:
𝑇𝑜𝑡𝑎𝑙 𝑓𝑎𝑛 𝑝𝑜𝑤𝑒𝑟 𝑖𝑛𝑝𝑢𝑡 = 6 ∗ 15 + 10 ∗ 19.4 + 4 ∗ 25.7 = 386.8𝑊
When the external temperature is
below 9ºC the system will switch the
heat recovery fan on to operate in
Heat Recovery Mode. Looking at the
table for Ayrshire temperatures we
can see there are 4 months were the
temperature is always above 9ºC
and 5 months were it is bellow 9ºC.
April, May and October have
temperatures higher and lower than
that value. We will assume that
approximately 50% of the time the
fans are on.
Total energy required in a year: 𝐸 = 363.8 ∗
8760
2
= 1593.44𝑘𝑊ℎ
References
http://www.passivent.com/
http://www.learn.londonmet.ac.uk/packages/clear/thermal/buildings/active_systems/mv/ind
ex.html
http://chestofbooks.com/home-improvement/repairs/Mechanics-Household/MechanicalVentilation.html
http://www.eurocable.es/esp/productos/vm_duo_mecanico.php?h=2
http://www.conaif.es/dinamico/editor/vetilacion.pdf
http://www.abe.psu.edu/extension/factsheets/g/G91.pdf