OK, we need to disambiguate the terminology here. We are going to talk about the conept of active ventilation. We often talk about ventilating our attic. This makes sense with an unconditioned attic where moisture and air escape the home interior and we want that moisture out of the attic and so we ventilate it to help cool it as well as prevent moisture issues.
but that has nothing to do with the concept of ventilating the interior space and active the concept of mechanical ventilation.
Active ventilation helps solve these issues.
You don’t want your air coming in through all the cracks in the house and you don’t like the quality air in your neighborhood. Either you or family members are being sickly and you want to have a healthier home.[stextbox id=”info” caption=”Unhealthy homes can make you sick but you need to start at root causes to make homes and indoor air more healthy. ” bwidth=”2″]Make sure you see our orientation document. It helps you get your bearings on these complex issues. [/stextbox] [stextbox id=”info” caption=”Before you worry about active ventilation you need to deal with air leaks.” bwidth=”2″]You need to comprehensively deal with air leaks and then you will have control or more control of where your indoor air comes from. If you don’t get the house closed up, you get plenty of air exchanges you just might not like what is in the air. Leaking house need air sealing. When the air gets tight enough you begin to need ventilation. This is a gray issue tha you get to determine, but fix the air leaks first. We talk about air leaks here. [/stextbox]
You want to alleviate the air leaks in your home, but you know that this will mean fewer air exchanges and less fresh air, and so you would like to have plenty air coming in, only filtered air. You do not want contaminants coming in on the outside air.
Active ventilation is a big part of future home construction. Green homes now have active ventilation. The building science community has reached a consensus: build tight and ventilate right.[stextbox id=”info” caption=”A couple of reference points that relate to the broader implications to mechanical ventilation.” bwidth=”2″]Make sure you see our discussion on airborne contaminants in the home, and our discussion on where our indoor air comes from… These resources will give you background on active ventilation and why it might be a fit for you.[/stextbox]
What does active ventilation entail?
They are many variations on this so I am just going to discuss a simple and effective system that works well in a hot and humid climate like North Texas.
We will look at an Energy recovery ventilation EVR in North Texas in each of the seasons. We discuss the 3 seasons in Texas- heating season and cooling season and tween season in our discussion of where our indoor air comes from. You can see that discussion here. -LINK-
Basically an ERV has it own circulatory air system. You can pick up the stall air in your kitchen, in your living room, in your laundry room and you can deposit your fresh filtered air into your bedroom or anywhere you want. Now this is not a lot of air circulating in this system. This is not close to comparable to an air conditioner.
The mechanical ventilation system is just to get rid of stale air, and bring in fresh air. 12 cfm maybe. This is less than the average bathroom vent, and this is size by how much outside air you need. There are complex building codes here or coming to Texas for the details but you don’t need those details, your chosen expert can help you with that. But you don’t need to blow your hat off here. this is not even a breeze it is a whisper.
An ERV has a heat and moisture exchanger. In the cooling season, conditioned cool air would flow out of your kitchen or bathroorm and flow to the EFV where it would be run through a het exchanger where the indoor cool air would give up cool to the hot incoming air, and the income humid air would give up some of its moisture to the outgoing stale air.
The air masses are not mixed but run slowly through an apparatus that sort of works like a radiator to facilitate exchange of energy. I cannot explain how the system exchanges out moisture but a permeable surface is involved. In the cooling season, the hot humid air entering the ERV would be cooled and the humidity would go up, the cool conditioned stale air leaving the house would be warming up and getting drier. This would accomplish some drying of the incoming air, which is a good thing.
In the heating season cold dry air would be coming in and hot not as dry air would be going out. The dry air coming in would be picking up some moisture.[textbox] Confused about humidity? <> here are some answers about humidity and temeprature to help shed some light here. -LINK- 
The tween season is North Texas is more complex and more interesting.
There are so many days where we are not running our air conditioner. Maybe you do not have a state of the art variable speed fan anc compressor that can deliver just the amount of cooling you need at any time, or just the chosen level of humidity in the house- these systems are great and are worth the extra money you can spend on them- if they are sized properly and commissioned properly… we get into the details of HVAC systems here…
So maybe you are wanting filtered fresh air but in the tween season when the A?C is not runing or running as much, you are not getting the dehumidification ou are getting with the A/C. Air conditioners do not “cool” air, instead they are big dehumidifiers. Now if the house structure conspire with the mechanical system you can end up clammy and uncomfortable… we get into effective mechanical systems and being comfortable here.
But in the tween seasons between the heating season and the cooling season you can couple an ERV with a small dedicated dehumidifier and be cozy and comfortable and maybe even extend the season when you are not using your air conditioner. Used wisely, an ERV and a dehumidifier- acting in concert in a mechanical ventilation system, can save you money and make you more comfortable as well as give you filtered and clean air. However, do not think of mechanical ventilation as an energy saving device- it helps you send a quantity of conditioned air you paid to condition out and takes in unconditioned air you get to pay to condition.
Does a mechanical ventilation system make sense for you?
Make sure you get the air leaks stopped first. Don’t miss the info on air leaks here.
And one last caveat, mechanical ventilation is not a solution to musty air. That needs to be deal with first and dealt with decisively. Make sure you see the conversation about understanding water leaks, humidity, mechanical systems and moisture issues and unhealthy homes.
If you have a thought or a comment, add it below.