Arduino "Swamp" cooler/heater control?

An evaporative cooler (AKA "Swamp" cooler) for those who aren't familiar are devices used in dry climates that basically suck dry air through a sponge like material saturated with water. Evaporation in turn cools the air which is then pumped in to the house to cool it. They use about 10% of the electricity of a traditional air conditioner.

The problem: there are no commercial controllers that intelligently juggle both the evap system and the furnace at the same time.

So, when you feel cold you turn on the heat. As it starts to heat up the evap cooler you forgot to switch OFF (Or perhaps more accuratley your wife :fearful:) turns on to try and cool it down.... and they both go to town battling each other until you wake up in the middle of the night to find out it is either freezing or muggy and hot as hell. (DAMHIK).

Annnyyyyway...... LOL, this sounds like a great Arduino project.

The cooler is directly controlled via 120V AC and has Fan High, Fan Low and Pump feeds. The furnace I think has the usual 24V (AC I think?) on/off circuit.

Unless I am missing something basic, an Arduino, a temp sensor and 4 SSR's and that should be about it? I Haven't used SSR's before... any caveats to watch out for? (I am comfortable wiring 120V AC circuits.)

My cooler has a unit in it that the fan and pump connect to. It is connected to a thermostat. The therostat lets my set the fan to low or high and turn the pump on or off. It is connected with a small 4 conductor cable (phone wire). Perhaps if you installed a controller like that in your cooler it would simplify your task as you wouldn't have to mess with 110 and the switching for the fan speeds.

Now that is interesting.... I wonder if it's a code (as in building code) thing because I've looked and shopped controllers a couple of times and they all have been mains level voltage. (Home Depot, Ace etc) (Denver CO here).

Is there some kind of module in the roof mounted cooler itself? Hmmm, I'd have to rewire a direct line but overall that's pretty easy. For that matter, I could mount the relay module in the cooler and use the same principle that way too. (BTW, reading up on SSR's indicates they aren't so hot for inductive loads like the motor. Good ole fashioned relays will do fine.)

The one I have now is digital, with an adjustable on temp but you have to set fan high/low and pump/fan manually using switches. The one before this one was a rotary temp dial but it automatically switched between high and low fan. I liked that, didn't like that it wasn't calibrated so any given position on the dial was at best a wild guess.

I'll look in to the remote possibilities, it may indeed be easier.

The controller I mentioned is in the cooler(Mastercool) and supplied with 110 from a nearby outlet. my thermostat has a switch for high and low fan and another for pump. I haven't measured the control voltages but i am sure could be switched with small inexpensive mechanical relays. I have also thought about having a temp and humidity sensor ouside to measure dew point and turn off the cooler and turn on the ac when dew point gets too high for the cooler.

also ssr's are also pretty costly compared to an comarable mechanical relay.

I think that a single smart thermostat which would control both cooler and heat pump functions would be more effecient and just cool. You could incoporate your heating instead of the heat function of my heat pump.

I just ordered some one-wire temp sensors (Which conveniently come in a sealed metal tube that's about 1/4x4" for poking through the ceiling) and two relay boards, one 4 and one 8 channel. The relays are rated 10A/250V which should be plenty.

Gist of the plan is to use 5 temp sensors and average them (Mostly for future development) to get "House temp" and then control the 4 relays to select Fan High, Fan Low, Water Pump and Heat. I just have a regular old gas fired furnace so on/off is all I can really control of that. It wouldn't seem to be that hard to add a humidity sensor and add in heat pump/AC Cooling too. It's another "stage" to work in but nothing that sounds too hard.

Later development may include vent baffles to control floor vent volume so I can do "Zone control" (I was looking at 12V car door lock actuators... only $6 @ Amazon). That will come in to play later once I get a basic temp control system in place.

Got me thinking!! I have two systems on my place and have to go from one to the other to make sure they are set the same (in terms of temperature and function). I am going to study repacing 4 thermostats with one and using your multiple temp sensor averaging for temp control.

For me the biggest issue is the disconnect between the cooling system and the heating. If both thermostats temp sensors read the same or even were off by some set amount I could probably stagger them (IE heat to 70 and cooler to 72) but they just don't. Having one homogenous system controlling both is the only fix I can come up with. The averaging is because the house was built in 1942 so some rooms cool faster than others.

Also in hopes of battling that is the idea of the vent baffles.... closing off "zones" as they get to temp but hold the furnace running until the remaining zones catch up or some such.

Now for the programming fun..... I'm off to research this "PID" thing...........

I have done a bit with PID. not an expert by a looong stretch but I'll help if I can. PID stands for proportioonal-integral-differential. The proportional term is how far the current, say, temp is from the set point. differential is the differance between the last and current temp (velocity of change). integral is the creep in temp over time so that if the temp is near the setpoint the small error will accumulate. Each is a coeffeciant in the equation that is calculated each time through the loop to determin the magnatude of the responce. i am not sure that PID is really applicable in your situation because the response is on-off (called bang-bang) not a PWM like response.

I'm coming to the same conclusion reading up on PID...... simple step points are much easier to code. PID is just overkill for the application.

With a bang-bang system it is important to build in some hysteresis so that the system doesn’t hunt. What i mean is if your set point for heat is 70° to turn on and off and it turns on, as soon as the temp rises just a bit it will turn off, then temp falls a bit on again. so make it turn on at 70° and off at 72°.

I’m interested in building something similar. I too have a 110V based wall switch (5 position). I wanted to be even more intelligent about how the thermostat operated the cooler.

Here are some features I’m considering:

  1. I want it to start the pump before it turns on the blower (so the pads can be wet instead of dry and just pulling in hot air).
  2. I also want it to stop the pump before it turns off the blower for the same reason (don’t waste the water already in the pad).
  3. I want to compare the indoor, outdoor, and target temperatures. If the outside air is sufficiently cold, why kick on the pump? Just suck in the already cold air.
  4. I’d like to monitor indoor and outdoor humidity to determine if it makes sense to turn on the pump.
  5. I’d like to implement schedules, and preferably auto learning schedules (think NEST thermostat).
  6. I want to implement multiple remote (probably wireless) temperature sensors inside the house.

Some amount of hysteresis in temperature (and probably humidity) is a must.

TroyO - I’m very interested in hearing how your temp sensors and relay boards work. Could you post links to the specific ones you ordered along with a review of how well they worked?

TroyO/groundfungus et al, Any updates on this thermostat project? I am also thinking of building something exactly similar. And James listed exactly the same additional features that I was looking for. Seems reasonably simple but your experience will be very useful ,instead of trying everything from scratch and stumbling upon the same hurdles that you guys may have run into.

One thing of note... Although, I believe most of them are 110V line voltage directly managed by the thermostat, there are some swamp coolers that have a controller next to the unit and their thermostat is simple 24V control wiring. Here is a good resource for simple wiring details