Increasing AC Efficiency Using
Evaporative Cooling of Condenser Coil
This page gives the details on Chad's DIY scheme for significantly
improving the performance of a conventional AC system by providing
evaporative cooling of the airflow over the condenser coil.
Chad's method has the advantage over directly
spraying the condenser coil with water that it avoids mineral deposits
on the condenser coil that would eventually cut its efficiency.
Chad's system wraps evaporative cooling pads around the AC condenser coil.
Water is dripped down the cooling pads, and evaporation of the water cools the
air on its way to the condenser coil by about 15F. This increases
the capacity of the AC unit and significantly improves the efficiency of the AC.
See the pdf file and other supporting data below.
Evaporative cooling pads surround the
AC condenser coil.
Inside view of screens that
enclose evaporative pads.
Closeup of cellulose evaporative pads.
Pump and reservoir for the evaporative
cooling water.
The 21 yr old a/c system in the house developed what is believed to be an evaporator leak. The existing a/c was replaced with a new 2 stage SEER 16 and the 80% efficient 80kbtu ( output) natural gas furnace was replaced with a 95% efficient 2 stage 63kbtu furnace with a variable speed blower. The old system SEER is unknown but is believed to have been 10. The new system does a very good job of temperature and humidity control when coupled with a thermostat that commands dehumidification. The evaporative cooling system was not re-installed for 2 reasons: 1) the new condenser unit is of a different size and shape requiring time and new pads to redo it and 2) little desire to give a reason for warranty rejection should any condenser problems occur. Of note, there was a $200 upcharge to install an otherwise identical heat pump vs cooling only system. The heat pump was not installed as it would have not been eligible for significant utility rebates. For those using a propane furnace and a central air system, heat pump installation likely will have a very short payback when used with a properly configured thermostat.
The evaporative cooling system worked quite well over the year it was in use. It had some minor problems most of which were part of the design learning curve. The original A/C system finally performed acceptably once the evaporative condensing system was added. Unfortunately electricity savings is difficult to gauge due to significant differences in recent summer temperatures and the refrigerant condition of the system.
Problems:
1) water valve has corroded / collected contaminates. It typically would not flow but occasionally did not shut off. A filter and a valve intended for water would be recommended.
2) Algae buildup ( causes plugged water holes in distribution tube). Bleach was occasionally put in the basin and distribution holes manually cleared. Use of black hoses and reservoir would be recommended or possibly adding swimming pool copper based algae inhibitors in a slow release container.
3) cloth (tank top material) degraded and needs replacement. A synthetic material may be worth trying.
4) bugs / worms have gotten in to the system. The water should probably be filtered before going to the pads. Additionally, better shielding of the water system would aid in some of this.
5) Water loss: some water fell outside the catch basin. This had the effect of degrading the soil base which could cause problems long term. The basin and screen likely should be wider than the pads so that all falling water would be caught. The horizontal spacer tubes may be better placed inside the screen and a short spacer between the screen and the tubes to minimize water loss.
