ERV Questions and 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 transfer) is called latent heat.
Enthalpic - what does it mean?
Enthalpy is the term used to describe the energy content of air. This energy is a combination of the sen- sible and latent heat. Therefore, a core which transfers energy 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 win- ter 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 tem- perature drops below
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 mois- ture. Therefore, when ventilating in the summer, less moisture 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 leak- age 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 inter- mittently 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 con- trol override.
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