I could work out this problem myself, probably, but I'm holding down three part-time jobs, and since I'm only a journeyman when it comes to this sort of applied engineering, I'd have to run my prospective signal plan by someone authoritative anyway. My hope is that you SMHRs would find this to be a worthwhile challenge.
Author's note: This diary was originally published to The KETI Program (Kossack Engineers) on 28 Aug 14. Many helpful comments - like this one - got close to the heart of the problem, but perhaps came up just short. Maybe there's touchdowns to be had this morning! Minor edits and updates were made to this republication effort which mostly address idiosyncrasies of time and place due to republishing.
So I did a whole-house renovation in 2010-2011, but I messed up. I put in good, solid, windows all around. Some of them don't open at all, however (to provide better insulation), and others are glass brick (surprisingly good R-value) - great for cold northern Ohio winter insulation, but in the summer, I get this:
What you're looking at is a clock in my bedroom indicating that it was 16 Jun 14 at just past 10pm at night. And yes, it was 104.6F degrees at that moment, and a few hours later the temperature went up to more than 107.4F! A sealed rather large ranch-style home with a broad roof that bakes in the sun - no one could have predicted that. Yeah, right lol!
Along with breathing new life into the 33yo ailing hardly-Energy-Star-compliant heat exchanger I use only for the air conditioning side, I figured the overarching solution would be a whole-house air evacuation system. Here's Sean "the Wookie" Caskey cutting a 2'x8' (16 sq ft) slot between the joists in the ceiling of my great room. Outside air is often pleasant and much cooler here in Northern Ohio than in my hothouse, and my expansive basement hovers around 61F in the summer because it's below ground.
The idea would be to evacuate hot air first out of my attic (adding life to my new tar shingle roof, btw) then evacuating my first floor, pulling in cool air to replace it, then supplementing with occasional air conditioning from the patched-up heat exchanger when absolutely necessary.
The Floorplan
(1) Cut a 16 square foot slot in my ceiling between the joists, as shown above. (2) Manufacture a very large, weatherproof wooden slot assembly and put it in the gables of my house at the very top right under the roof ridge. (3) Put a massive air fan behind it with a temperature actuated thermostat.
Now, here's the fun part. Even though I've screened off that ceiling slot (to prevent bugs and blown-in insulation from falling into my great room), I don't want it open year round. In fact, I only want it open when the big fan is on. Otherwise, I want it sealed by a 2'x8' insulated board which looks nice on my ceiling. To raise and lower that board, I'm going to use linear actuators with a 10" throw - something like this:
These devices will lift 400 lbs combined - more than enough to say the least - and I'll power them by means of an old computer 12v power supply. These are rated at about 400W - also more than enough.
Now, one last thing - the switching. I want the board to descend when the fan comes on and to retract it into the ceiling again when the thermostat cuts off. 12v all around, so I can use an everyday used or new automotive relay(s) for the job. Simple! Cheap! Now help me spec the right relay(s) for the job.
A relay, of course, has two "ends" - an input end and an output end. I want it to get signal from the thermostat side, and translate that into closed 12v circuit on the output side. These commercial linear actuators all have a great feature - they have a cutoff that turns off the motor once they're fully extended or fully retracted. Easy, and perfect for the actuators, but can I burn out a relay if it's always "on" for as long as 30-40 minutes? I think perhaps it should "know" to stop actuating after 10-20 seconds or so. And, of course, it should also "know" to actuate again for 10-20 seconds after it senses a power input cessation from the thermostat input side.
Anyone know of such a relay (or series of relays)? A "latching" relay has been suggested. How would I know if I've found one, and how would you describe the part I need to explain it to someone knowledgeable who might sell it to me? And can you suggest a simple wiring diagram? - one that even I can't mess up? :)
Welcome again to Saturday Morning Home Repair blogging, where we talk about fixing houses, the things in them that are supposed to work for us, and fixing them up. An ad hoc cadre of building professionals and gifted amateurs attempt to answer questions that arise from readers, and offer encouragement and advice for those inclined to do things for themselves, if they can. We all do a lot of things, collectively, and can probably help out with insights from our vast experience.
Or sometimes, we just gab.