Monday, July 25, 2011

Mist the Outside Central A/C Coil

To cool the outside air temperature, I originally thought of building a swamp cooler around the central A/C unit outside. That cost estimate quickly rocketed up into the $400 range. I'm all for advancing science and mankind's well-being but I don't want to blow that much money this early in the game.

I ended up going with a simple misting design (with 15-20 misting heads) that would allow for more airflow to the A/C coils. There are products on the web that do just that for about $100, but they are for smaller A/C units and adding enough misters for my size A/C unit add up to over $200. Plus I didn't like the toilet flapper float design they used for turning on and off the water supply line. 

For about $45 I built a misting system that uses an electronic sprinkler valve controlled by the existing HVAC thermostat.

The water feeds through from an unused hose bib near by into the sprinkler valve. 

How cool and and refreshing is this?  

The misting system reduces the outside air temperature, in turn reducing the pressure of the whole system, in turn reducing the air conditioner's power consumption 850 watts (or 21%) while it is running its cooling cycle. This results in a 4.8 kWh/day air conditioner energy savings.  

I still need to run a soft water line out to the misting system, before the A/C coil is sentenced to a corroded, rusty fate.

Between the A/C trellis shade (1.9 kWh savings), the A/C misting system (4.8 kWh savings) and the attic fan (4.7 kWh savings), our whole house net energy savings is 11.4 kWh/day or a 22% reduction. COOL! 

With the energy saved by not using an extra 11.4 kWh/day all summer long, I could drive an electric vehicle 3420 miles, or commute in it to work for 5 months, FOR FREE!

Update 7/27/2011: 

I have since plumbed our hose bib to the soft water line.  Now the misting system will not corrode the coil nearly as fast; maybe not at all.   

Update 2/18/2013:  
We have replaced our home's furnace and central air conditioner with a ground-loop heat pump.  I will not be able to report on any long-term damage caused by misting the cooling coils on the central AC.  Upon removing the A/C coil, it had some evidence of hard water deposits (probably from before the lines were fed with soft water) but was still in good working condition.  I resold it to recoup some of the costs of the Geothermal system.