3
ERV Questions & Answers
What is the difference between an HRV
and an ERV?
The core in an HRV (Heat Recovery Ventilator) trans-
fers heat from one air stream to the other. This is called
sensible heat. The term ERV (Energy Recovery
Ventilator) is usually used to describe a unit with an
enthalpic core that transfers moisture as well as heat
from one air stream to the other. This (moisture trans-
fer) is called
latent heat.
Enthalpic - what does it mean?
Enthalpy is the term used to describe the energy con-
tent of air. This energy is a combination of the sensible
and latent heat. Therefore, a core which transfers ener-
gy is called an enthalpic core.
Is an ERV better than an HRV?
NOT NECESSARILY!! In cold climates such as most of
North America, an HRV works better than an ERV. This
is because the air inside the home during the winter
months will be more humid than the outside air. An ERV
would transfer the latent heat (humidity) from the
exhaust air back into the incoming airstream. This will
aggravate moisture problems in the home and encour-
age the growth of mold and mildew. If the air in the
home is too dry for comfort, an ERV will not help. A
humidifier should be used to increase the humidity to a
comfortable level.
Where do you use an ERV instead
of an HRV?
An ERV is recommended for warm, humid areas with
heavy air conditioning use. As there is no defrost in an
ERV it is not recommended for areas where the temper-
ature drops below -4
˚
C (25
˚
F)
Why transfer moisture in the summer
(cooling season)?
The enthalpic core will allow moisture to be transferred
from a humid air flow to a dry air flow. This property is
useful in the cooling season if an air conditioning sys-
tem is used to lower the indoor humidity. You will then
have dry, cool air in the exhaust of the ERV, and warm
humid air in the supply stream. With these conditions,
the ERV will be able to transfer the moisture and heat of
the supply air to the exhaust air. In this way, the ERV
will supply to the home air which is cooler and drier than
outside. Remember that an ERV is not a dehumidifier,
and on its own will not take moisture out of the air.
So why use an ERV?
A properly operating air conditioner will not only lower
the temperature in your house, but will also lower the
humidity level. This prevents an uncomfortable cold and
damp situation. In fact, about 2/3 of the energy used by
the air conditioner system is to remove moisture.
Therefore, when ventilating in the summer, less mois-
ture brought into the home means less work for the air
conditioner, and energy savings for you.
During the winter, an ERV recovers some humidity
from the exhaust air, reducing the need for humidifica-
tion, if the required ventilation rate would make the
home too dry.
What's the difference between this type of
core and a rotary type?
Here's a list of characteristics of the fixed plate core.
1. No rotating parts, so maintenance is easy and the
unit lasts a long time.
2. It is very flexible in terms of installation.
3. The core can easily be changed.
4. Because the supply and exhaust air streams are
completely separate, there is very little cross leakage
of any dust or germs.
Can the core become clogged with dust?
Because the surface of the core is a turbulent flow
area, dust sticks to it easily; however, because the
inside of the element is a laminar flow area, virtually no
dust sticks to it.
What is the maintenance?
About once a year you should use a vacuum cleaner to
remove the dust from the core's surface. DO NOT
WASH WITH WATER!!
Is an air filter needed?
To prevent clogging of the core, an air filter should
always be installed on the supply and exhaust sides of
the core.
How much ventilation do I need?
During seasons when your windows and doors are
closed, the ERV should operate continuously when the
dwelling is occupied, and either continuously or intermit-
tently when not occupied.
For most installations the ERV will normally be set to
operate continuously on low speed with the option of
going to high speed as the need arises. For example; if
you are entertaining and there is a large number of
people present (some may be smoking), the unit
should be switched to high speed.
Your ERV may be equipped with automatic or manual
switches, but all ERVs will have a manual speed control
override.
