We have a special friend. His name is Erv, and he brings us fresh air into the house year round. Other people have the same friend, but they call him ERV, or sometimes by his full name: Energy Recovery Ventilator.
The ERV is a well appreciated equipment. Because our house is almost completely airtight, we need mechanical ventilation to remove the stale air and bring in fresh air. The ERV does just that, assures good indoor air quality, and in the process keeps us comfortable with the enthalpy wheel. It acts as a heat exchanger and removes excess moisture.
I like to put it this way: Using the ERV is like keeping windows open during the winter to get fresh air in, with the exception that it doesn’t get cold. It works so efficiently that it helps us to delay our heating season by up to four weeks.
The fresh air is distributed across our 1st floor apartment through a system of ducts, supplies and returns. I was about to embark on the ductwork installation project for the 2nd floor. But before doing so, I wanted to review our 1st floor ventilation system: What worked, and more importantly, what could we have done better?
Stale rooms (with a lowercase s)
The 1st floor ventilation system has fresh air supplies in key rooms to assure fresh air distribution across the apartment. A series of undercut doors, ‘indoor pressure balancers’ and ‘between room vents’ help move air from room to room and to eventually to the returns in the two bathrooms.
We can easily flush stale air out of the apartment by cranking up the ERV. However, if we run the ERV on the low setting (low airflow), the library and living room remain somewhat stale for longer than any other rooms in the unit.
In other words, the fresh supply air is not mixing sufficiently with the room air. The velocity from the fresh air supply in the foyer is good, but too slow when moving on to the library and living room.
To avoid something similar on the 2nd floor, I plan on adding a fresh air supply to the library and living room.
The first time we fired up our first floor ventilation system, it sounded like a roaring jet engine. That problem was quickly solved with two three-foot pieces of insulated flex duct connecting the ERV to the rigid ducts. I made sure we had a 90 degree bend in each flex duct, and our ventilation system fell completely silent – almost.
While the noise transmission from the ERV is under control, we still had some transmission from room to room. For example, the fresh air supply of the office and foyer are connected by a six foot duct. The noise transmission through this short duct is as such that two people – one in the office and the other in the foyer – could have a conversation with each other. The longer the duct between supplies, the more faint the noise transmission.
To minimize the room-to-room transmission on the 2nd floor, I plan on using a three foot piece of insulated flex duct with a 90 degree bend right after every supply to act as a sound muffler. This will also increase friction and reduce velocity, but I will try to make up for it through more generous duct sizing.
2nd floor ventilation layout
The plan below shows the 2nd floor ventilation layout with the improvements mentioned above:
- Using flex duct at each supply as a sound muffler to reduce room-to-room sound transmission
- Adding fresh air supplies to the library and living room to improve mixing with the room air and a more efficient flushing of the stale air, even at lower airflow rates.