Replies

1. GBA Editor
   Martin Holladay | Feb 14, 2011 04:51am | #1

   Jeff,
   The basic problem with adding cooling to ventilation air -- or adding heating, for that matter -- is that ventilation air flows are low (generally 40 cfm to 80 cfm), while cooling or heating require much higher air flows.

   In the FHB article, I wrote, "If the Ultimate Air coil is supplied with 160°F water and 200 cfm of air flow, it can provide 8,700 Btu/hour of heat—not much, but enough for a small Passive House. Full heat output from the Ultimate Air coil requires 200 cfm of airflow. Since the typical ERV supplies only about 50 cfm of
   fresh outdoor air, you’ll need a second fan that can provide about 150 cfm of recirculated indoor air to the coil. The indoor air needs to be mixed with the ventilation air from the ERV to bring the total air flow across the coil up to 200 cfm."

   In general, cooling requires between 350 cfm to 400 cfm per ton of cooling, so a 3-ton system needs between 1,050 cfm and 1,200 cfm -- much more air flow than necessary for ventilation.

   I think it almost always makes sense to keep our heating and cooling delivery systems separate from our ventilation systems.

2. 
   user-600754 | Feb 14, 2011 03:58pm | #2

   Jeff,

   Like Martin said, you most likely wont be able to cover your A/C loads through your ventilation air. I have a Nilan VPL15 which is a ventilation system that has a heat pump instead of a heat/ energy transfer core like a traditional HRV/ERV. In the summer the heat pump will reverse to provide cooling. Since my ventilation air flow rate is low (~60cfm) it was only able to provide around 2k btu of cooling (not much!). If you live in a very mild climate it may provide enough cooling, but in western PA I doubt it would do the job. I solved the problem by adding a mitsubishi mini split which I have been VERY happy with, and highly suggest it if you are building a superinsulated house.

3. 
   9eug3rWHyE | Feb 14, 2011 07:55pm | #3

   Thanks guys. A Mitsubishi split system was my next choice. I'm just trying to keep the ductwork to a minimum.