Energy Recovery Ventilation

Another mechanical item we are looking into that I forgot to mention yesterday is the integration of a ERV (Energy Recovery Ventilator) unit into our HVAC system. It's a great strategy and I am excited about the possibility of doing it. I am not sure about the total cost of this addition and we'll have to see if it makes sense with our budget (in addition to whether or not we have the room for it). Although the HVAC unit that we have selected is a high efficiency unit (over 92%) and pulls in 100% fresh air for combustion, the ERV adds the heat exchange and the dehumidification element. Here is a link to an article (from back in 2000) that explains in detail how the whole heat exchange system works.

Make up air: Most of the time, houses (especially older ones) get fresh air from incidental air infiltration - leaks in the home's envelope (much like the 120 yr old old house we live in now!). Since many new homes are constructed so 'tight' (extremely well insulated), the only way to get fresh air into the house is opening the windows - which is not very energy efficient in the hot and cold months. So, installing a 'make-up air' vent brings in small amounts of outside fresh (albeit Philly) air. This vent will have an adjustable damper that will only allow air to enter the system when the unit is running. The main problem with this is that in the dead of winter and height of summer, the fresh air going into the unit can be anywhere from 10 degrees to 100 degrees and takes a lot on energy to bring it up or down to 70 degrees. But this is where a heat exchanger comes into play. The heat exchanger involves exhausting some of the stale air out of the house. The incoming air passes over outgoing air (exhaust) because one pipe is located within the other. When the two airs pass each other, there is a heat exchanger that takes the heat from the exhausting stale air and gives it to the incoming fresh air, without mixing the air. This is a way to preheat or precool the incoming fresh air and have your heating system work less. The biggest issue with this method comes during the summer: humidity. But there the ERV (Energy Recovery Unit) comes into play as it gets rid of the humidity.

The whole system makes a lot of sense and it's becoming more commonplace these days and getting more cost effective.

So, the way we see it is between the use of the "whole house fan" (discussed in a previous post) during the temperate months and our high-efficiency unit and possible ERV during the cold and hot months, we should be able to have some fresh air continually circulating through the home throughout the year using a lot less energy.