June 2013 • 33
the equipment manufacturer before
upgrading to a MERV rating above 8.
• Ventilation. Fast becoming one of the
most talked about aspects of the HVAC
industry, make-up air, whether passive
or mechanical is now a requirement in
many areas. Regulations may vary by
jurisdiction but are based on calcula-
tions laid out in ASHRAE 62.2.
CODES ARE CHANGING
Commercial and institutional buildings
are currently subject to more stringent code
requirements than residential when it comes
to ventilation and make-up air. However, in
Massachusetts as in many states, bathroom
ventilation is required for new residential
construction. This requirement is meant to
address mold more than indoor pollution
as the bathroom fans operate only when
the bathrooms are used. Little attention
is paid to efficiency as the fans are taking
conditioned air from inside and replacing
it with untempered air, which enters the
home through openings in the building
envelope. In many cases, this will have a
negative impact on indoor air quality as the
incoming air is exposed to various wood
treatment products, insulation and other
materials that normally reside in a home’s
outer walls.
So how do we prevent the buildup of
these harmful pollutants in the air inside
of our homes? Well, the easiest and least
expensive option is to open the windows.
However, this is really not a practical solu-
tion during our long cold winters, and is
becoming even less so during the summer
months as more and more homes are being
centrally cooled. The EPA suggests tackling
the source of the problem, which makes lots
of sense, but may not be entirely achievable.
We are left with the mechanical option.
TEMPERERED AIR OPTIONS
Make-up air can be supplied in a number
of ways, but attention should be paid to
overall efficiency. Replacing conditioned air
with large amounts of untempered outside air
will adversely impact the home’s efficiency.
Using the tempered air to heat the incoming
outside air is a much more practical solution.
Heat recovery ventilators are designed to
exchange those expensive Btus fromoutgoing
to incoming air. Most HRVs operate at an
effective efficiency of around 60 percent and
can go go as high as 85 percent – meaning
that it will take that much less fuel to heat
the incoming air compared to bringing in
untempered air. The illustration at left shows
how an HRV exchanges the heat from the
outgoing air to the incoming air.
As you can see from the diagram, the
two streams of air do not mix but pass on
either side of an aluminum heat exchange
core, which transfers the heating/cooling
energy from the outgoing to the incoming
air. In summer, the HRV works in reverse,
removing heat from the incoming air and
transferring it to the outgoing air.
While HRVs are recommended in
northern parts of the US where the heating
season is longer than the cooling season,
ERVs are recommended in parts of the
country where high outdoor humidity
results in extended periods of air condi-
tioning and dehumidification.
Donna Carcerano, Benefits Administrator
New England Fuel Institute
238 Bedford Street, Suite 2, Lexington, MA 02420
(617) 924-1000
