Using the controller for cooling house?
 

How about using your idea to pull hot air in winter but instead of connecting a fan to attic connect to a duct vent in floor and pull cool air from basement for free air conditioning? Also for using your controller for solar hot water pump could you either make a small 5 volt solar panel to run adruino and 12 volt panel for pump then change switch to 12 volt? Or even use 12 volt panel and reduce 12 to 5 volt going to adruino so you only need one panel, If solar hot water panel is warm enough to heat water you will have plenty of sun to power solar panel and you would have a system that would heat in case of poer outage. Just ideas I have been working on for myself, really like your controller also thanks

I did that until the basement was 76 degrees and I realized that it wasn't exactly free and the cool basement wasn't cool anymore. Works for a little while, maybe in the swing season for longer but no longer than a week. Neat backup plan for when the power goes out and your generator is 120v and can't power the a/c.

how are you progressing with the upgrade for this microprocessor-based controller? I am trying to get started with a similar design, but somewhat more complicated, for my geothermal heating system. Anything you've learned would be appreciated greatly.

Paul_L

I really haven't done anything with it since my last update. The original setup is still working great with my attic fan.

My plans haven't changed to upgrade it when I install my solar hot water. I just haven't gotten that far with the solar hot water setup yet. I'm hoping to get it up and running this fall so I have solar heat this winter.

What features were you hoping to add? I always like throwing around ideas that'll help improve a design.

attic fan differential controller questions
 

I know this thread is old, but I'm wondering if I, having no electronics training, could make a similar controller for my attic fan using the same approach. Any suggestions on how to go about this (or detailed instructions or plans!) would be much appreciated.

My fan currently has a control on it that turns it on when the temp. reaches a certain (hot) threshold, i.e., for summer time. However, I want to prevent ice dams in the winter, so am thinking that if I could make the fan turn on when a) the attic temp is above freezing, and b) outside temp is below freezing.

Welcome to the site wadevcamp.

The best way to prevent ice damning is really to air seal your heated space from your attic and add more insulation if necessary. This has the byproduct of lessening your heating bills too.

You could use this differential controller in that manner though. Having no electronics experience would make it a bit more difficult, but if you asked questions here I'm sure you could stumble through it.

A makeup air controller may be an cheap easy mechanical switch to preform the same task.

commonly used in commercial hvac setups its a adjustable temp and humidity switch that is usualy used to open a damper(but could control a fan) connecting outside air to the return of hvac. Sometimes used to allow air into a tight building for combustion(or generally make up for building air losses), sometimes just to improve HVAC eficiency. The idea is that sometimes outside air is more temperate than the return, so why not use it and save some btus?

Its been a while since i looked at one, but if i recall the cheap ones only did hot or cold settings on but not both. Some did comparative temp reads of outside and return air temps, and some had a single rheostat setpoint and some may output 24VAC for HVAC dampers and controls. But as i recall the cheap ones cost about fifty bucks wholesale.

Just remembered its called an economizer when used to temper with outside air, did a quick search and could not find the cheap mechanical ones, only the expensive microelectronic.

Google the air-2 controller to get a general idea. Its sort of a retail evolution of the thing.

You need an enthalpy control for the economizer operation.

Lately, I've been having some issues with my thermal differential controller. The fans will turn on and off a LOT unless it is really hot up in the attic. What I believe is happening is there is noise on the long sensor wire run to the kitchen which makes the temperature signal bounce around. I originally had this problem, so I put a small capacitor on the wire and it seemed to work... for a while.

Now, I am going about doing it the right way. I am reprogramming the controller to filter out the noise on the lines. This will be a completely free fix and require no new hardware, no soldering, no physical changes at all. The fix is pretty simple. I take a bunch of sensor readings and average them. This isn't a super precision thing, so it'll work just fine.

I did some quick and dirty reprogramming last night where I took 5 temperature readings and did some very poor 'averaging' just as a quick test and it made it 90% better than before. The fans kicked in and stayed on until it got close to the differential set point. Then, it started to turn on and off a bit. Not much, but a little better programming should virtually eliminate it all. This also means that I'll be able to get more heat out of the system because the fans will be running full tilt versus on and off.

Anyway, I am finishing up the programming soon and I'll post the new code when I find that it works good. I'm thinking 10 temperature readings should work out great, and get a true average of them. This also will eliminate the need for the capacitor shown in the schematic making wiring a little easier.

Yeah, I learned to do that with input readings back when I was in my teens. My dad had rigged up our Apple ][+ PC with a potentiometer on the railing of the floating dock behind our house (with a little mechanical linkage to amplify the rotation angle). The 200' 22awg wire between the PC and the dock was buried in conduit in a trench along with an 110V AC power cable. The potentiometer readings were quite unstable unless you used mathematical smoothing. After employing mathematical smoothing, we were able to write a BASIC program to predict upcoming tides.