I will have a very extensive home automation program running, on a Raspberry Pi, so I can utilize temperature, humidity, enthalpy(?), smoke sensors/detectors as inputs in the program sequences.
Automation is cool with all the new tech and with new toys sometimes people like to find ways to maximize what the toy does.
But, think of a refrigerator door. You can hook that up to automatically open based on heat gain within 2' of the door (so when somebody is standing there). But why would you, there are so many other variables determining when you choose to open the door and for how long you stare into the abyss.
So think of a WHF as that. It requires human decisions, but the kicker is, the whole (pun intended) purpose of a WHF is to open the windows
to bring in fresh/cooler air at a time the human chooses. From personal experience, I do not use the WHF when I smell a skunk has sprayed, nor when I smell leaves burning or the neighbor has a fire going, or when the town has fogged for mosquitoes. I also choose which window and height it's open based on security or visual access and adjust the fan speed based on how much air I can bring in (i.e. draw the blinds, leave only a sliver so no one sees any nekkidness, some rooms/floors closed depending where I'm at in the house). Some nights, however cool outside and how I currently feel about the humidity (i.e. one night 62% humidity may feel ok but another may feel sticky based on my clothes or what I'm doing), I'd just rather use A/C. So maybe I am missing something, but unless you have a separate wall damper in each room (and why would you do that?) I just don't see how an automated WHF can work. But again, as a nod to technology, you can hook up the WHF control to your wi-fi if you are too lazy to walk to the fan or reach for the manual control.
By the way, I am also considering running the WHF upon carbon monoxide detection and possibly by the kitchen smoke detector activation (as we're getting a half-useless range fan).
Again, without windows open, a WHF is useless. Just guessing without air intake from the window openings, it may pull maybe a hundred or 2 CFM, and pull it from whereever it can make it up from, not necessarily the place you are trying to exhaust. Think of the fire dept coming for a CO call, they will open your windows. So unless your windows are automated too, this feature would be useless. Am I missing something?
and regarding modifying my plans, at least to the point of separating the two systems (attic vs. whole-house fans), what about:
a variable-speed fan in the gables, no ductwork, but motorized shutters on the top floor of the house. In the summer, run the fan on slow speed, activated by attic temperature. Fall and spring, open the shutters and run the fan at medium or high.
You have two placements of attic WHFs. One is horizontal in the ceiling, so it directly pulls air from the interior. The other is a remote fan and ducted
to the ceiling. If it is not ducted, but only has the ceiling damper, then it becomes just an oversized power attic vent. You cannot control how much air it is pulling from the ceiling, it will pull the easiest path, which will probably be from the roof venting.
In attic-fan mode, would running the attic fan in reverse, drawing cooler air in, help in anyway? it would push hot air out the gable vents and eaves, correct? Since hot air rises, it wouldn't push it down into the house, would it?
AFAIK only certain styles of fans are reversible, they are lower CFM, need ducted, you should have a filter on it, and should pull air from the exterior wall not the general attic. A typical WHF has 4K-7K CFM (and disregarding that they will never meet the CFM based on attic venting or how much window is open) you do not want to push that much air into one point of the house without the equivalent and room-specific exhaust. Mechanical ventilation overpowers natural convection of hot air rising, but yes you would initially be pulling hotter air in from the attic in this situation.
It seems I need to do more research. I must admit ignorance of backdraft and enthalpy. But, and assuming I'm still interested in the benefits
WHFs accomplish their intended goals. You can do one, but keep it separate from venting the attic. If this is a new build, the roof should be designed for adequate passive venting first and foremost. Only if you have a hip with little ridge space or some shape of roof that does not allow high venting, should you then go to a power attic vent. So why are you intent on putting a power attic vent in from the get-go?