ERV - Energy Recovery Ventilation

ERV - Energy Recovery Ventilation

Preconditioning air before it enters
a DX rooft op system is not necessarily
a new idea. In fact, energy
recovery ventilation (ERV) has
been on the scene for many years. In recent
years, however, all the major HVAC
OEMs and nearly all of the smaller HVAC
manufacturers have engineered ERVs to
be a standard option on DX systems. Not
only do the OEMs off er it, but it also has a
growing popularity among engineers, mechanical
contractors, and building owners.
ERV AND HOW IT WORKS
According to the Air-Conditioning and
Refrigeration Institute (ARI), there are three
diff erent methods to precondition outdoor
air: heat pipe heat exchangers, plate heat exchangers,
and rotary heat exchangers.
Rotary heat exchangers, oft en the common
choice of manufacturers, are enthalpy
wheels consisting of sections of an energy
transfer matrix coated with a desiccant,
usually silica gel. Th e wheel rotates between
the incoming outdoor supply air and
the building’s exhaust air. It is positioned so
the outdoor supply air and exhaust air from
the building travel through it in opposite
directions through separate isolated ducts.
In the summer, the hot humid outdoor
air passes through the wheel before reaching
the DX system. As the air passes
through, the matrix absorbs heat and the
desiccant removes moisture, thereby preconditioning
the air for the DX system. As
the wheel turns into the exhaust duct, the
dry, cooler exhaust air passes through the
matrix, cooling the material and removing
moisture from the desiccant. (See Fig. 1)
In the winter, the process reverses with
the matrix warming and humidifying the
supply air. (See Fig. 2) Th e result is preconditioned
air that is cooled and dehumidifi ed
in the summer, and warmed and humidifi
ed in the winter. Th e wheel generally recovers
70 percent of the diff erence between
the incoming and outgoing airstreams.
Th is highly effi cient preconditioning essentially
eliminates the burden of conditioning
outdoor air from the DX system.
Accordingly, the ERV system is performing
work that is no longer required by
the mechanical system and performs that
work more effi ciently. According to ARI,
DX/ERV systems are up to 40 percent more
energy effi cient. Additionally, a DX/ERV
system requires less mechanical capacity,
lowering DX system cost that off sets most,
if not all, of the ERV system cost.
ERV’S NEW POPULARITY
So given these benefi ts, why hasn’t ERV
technology been a bigger success in the past
and why has it become so popular lately?
“When ERVs were originally released
on the market, they were not reliable,” said
Joe Finkham, general manager of ERV, Micrometl,
the company that assembles ERV
units for major DX manufacturers.
“Installations were generally done as retrofi
ts and the science of matching an ERV
with a DX system was far from precise. One
could easily miscalculate and lose control
over building space temperature, and many
installations did.”
Ted Cherubin is Carrier’s marketing
manager for package rooft ops and he agrees
with Finkham.
“Reception for ERV was poor for many
years,” he said. “Engineers did not understand
the technology and perceived it to
be ‘black art,’ even when it was successful.
Originally, all we had were paper simulations
that weren’t very credible, whereas now
we have sophisticated soft ware-modeling
tools. ERV was also sold as a separate unit
and engineers don’t usually like to take one
unit, combine it with another, and hope it
gets assembled correctly on the job. We’ve
now pre-engineered much of the DX/
ERV system, which greatly simplifi es the
engineer’s job and increases the reliability.”
Technology on the component itself
has also improved increasing the reliability
of the system. According to Randy Steele,
general manager, Airxchange, energy
recovery wheel manufacturer, “Th e original
‘heat wheels’ were almost impossible
to maintain leading to a large number
of failures in the fi eld. If there was ever a