Hi AC
There is a couple of reasons not to automatically turn down the recovery unit, and more specifically not using CO2 alone. Say you have a hot an humid day, and a cold night, but you are not at home. You would want the unit to run at a normal rate to avoid condensing on your windows and water running down into your window frame. If you come home to take a shower before leaving again you get the same situation. Then you have the situation where you just came home and you make food. To avoid the smell all over the house for hours until the CO2 level rises, you would want it to go a bit faster. Also, if you are like me, and smell like a week old dead cow after a full day of manual labor, some fresh air does not hurt (at least that's what the wife sais :-p ). Of course, you could have both CO2 and a humidity sensor, with a manual override, but now it is starting to become complicated.
Then, also to consider, is the fact that DC motors don't have anywhere near the life expectancy of an AC fan. It is also slightly less efficient, and if you count the conversion from AC to DC, even more so. More to go wrong also, which would happen when you are out of the house for a long time.
And, by the way, you will need some serious PC fans to get anywhere near the airflow and pressure you should have in a ventilation system. The AC ones used in professional PC racks would be more than sufficient, but I have seen none that is DC, and certainly none with a normal noise level.
At least here in Norway, you don't get this CO2 control for the HRV. I can see the efficiency benefit, but I suspect that it has more to do with selling point than actual usability. If you have a good recovery system there will be very little energy loss anyway. I actually have a problem with mine being too efficient (93% approximately). The air coming in to our bedroom when there is 0C outside (32F?) and normal temperature inside is <2C (4F) below the outgoing air. This keeps most rooms close to the average, which is a bit too warm for me to sleep in. If it is above freezing, we have to open a window a little. Also, air has little energy capacity, so a little change in airflow will not really affect things that much. I would suggest finding other places to save energy than reducing the amount of fresh air. My recovery unit is a medium setting now. I put it in low if we leave for a long time, and high if we have more than 8 guests. it is about 30% up and down in airflow for the different settings.
Ko_deZ
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