After all of the trouble and expense to heat or cool the air in
our homes, the last thing we want is to let it get away. One of the
ways that we stop this is by the use of an Energy Recovery Ventilation
system. This is a truly unique device. As part of the plan for a
healthy home, we want to remove the indoor air, contaminated with
smoke,
allergens, cooking smells, etc. and replace it with fresh air from
the outside. In the old days most people would simply open a window
or turn on a whole-house ceiling fan.
Now picture your expensive conditioned air warming the outdoors.
Not very efficient!
An ERV is a device that captures the heat from the exhaust air leaving
a home and transfers it to the fresh air entering the building to
preheat the air and increase overall heating efficiency. The need
for ERVs has grown as new homes have become more air tight, in the
push for increased energy efficiency. A home that doesn't allow heated
or conditioned air to leak out still needs a source of fresh air
to avoid a buildup of moisture and pollutants.
How it works
A typical ERV uses two fans, one to expel household air and the
other to bring fresh air in. The key feature of an ERV is its heat-exchange
core, which transfers heat from the outgoing stream to the incoming
stream in the same way that a car radiator transfers heat from the
engine's coolant to the outside air. The heat-exchange core is usually
made up of multiple plates of aluminum or plastic separated by narrow
passages through which incoming and outgoing airstreams flow. As
the streams move through, heat is transferred from the warm side
of each passage to the cold, without the airstreams coming into direct
contact.
Depending on the model, ERVs can recover up to 85% of the heat in
the outgoing airstream, making them far more energy efficient than
letting air in and out through windows. In addition, an ERV filters
the incoming air to trap particulates such as pollen or dust.
Although an ERV can be effective in the summer months, when it takes
heat from incoming fresh air and transfers it to stale, air-conditioned
exhaust air, it's most important use is in colder climates during
the winter. A potential problem is buildup of frost inside the exchange
core if temperature falls below about 20° F. To avoid this, a
damper closes off the incoming cold airstream and routes warm air
through the core. After several minutes, a timer opens the fresh-air
port and allows ventilation to continue.
Reclaim and reuse the
conditioned air for a healthier environment
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Plenty of homeowner control
A typical ERV for residential use might move as much as 200 cubic
feet (5.7 cubic meters) per minute of air, but the fan speed can
be set to suit the air quality in the home. For example, a slow to
medium fan speed may be adequate for normal living, while a house
full of guests might require the highest setting. Controls are available
for intermittent and remote operation.
In addition to exchanging heat in the air, ERVs also include a humidity
regulator to remove excess humidity (or add humidity) to the air
that is being brought into a house. However, ERVs are not the same
as dehumidifiers. What ERVs do is transfer moisture from the humid
air stream – the incoming outdoor air in summertime – to
the exhaust air stream. ERVs may also be effective during the winter
the months. If indoor relative humidity tends to be too low, what
available moisture there is in the indoor exhaust air stream is transferred
to incoming outdoor air.
