Use Air Conditioner to lower humidity

Hey, I’m looking to lower my humidity with my air conditioner during the summer. I have a z-wave thermostat that has values for both temp and humidity. What I’m looking to do is to keep the thermostat on cool until the humidity gets to 50%. However, I can only set the thermostat to a particular temp. I’m looking for a way to accomplish this with automation. Has anyone done this before? My idea is to set the thermostat for a really low temp and then set an automation to cut it off at 49% humidity. Then turn it back on at 51%. Does this sound okay or does someone recommend something different?

One option would be to use a Generic thermostat in combination with a Template Switch. Doing it that way not only handles the backend automation, but also makes available the climate/thermostat cards for use on the frontend.

  - platform: template
        value_template: "{{ is_state_attr('climate.example', 'hvac_action', 'cooling') }}"
          - service: climate.set_temperature
              entity_id: climate.example
              hvac_mode: cool
          - service: climate.turn_off
              entity_id: climate.example

When you set up the Generic Thermostat just remember that everywhere it mentions temperature, think of it as humidity… where it says “cold” think “dry” and “hot” think “humid”.

  - platform: generic_thermostat
    name: Dehumidification
    heater: switch.dehumidifier
    target_sensor: sensor.humidity_example
    min_temp: 45
    max_temp: 80
    ac_mode: true
    target_temp: 50
    cold_tolerance: 0.3
    hot_tolerance: 0
      minutes: 10
      minutes: 3
    initial_hvac_mode: "off"
    away_temp: 65
    precision: 0.1

Make sure the min_cycle_duration is set long enough for your ac equipment. The 10-20 minute range is generally safe for most equipment. My understanding is that you want to avoid short cycling, as it can cause an increase in wear on the ac.

Keep in mind that there is a limit to an air conditioner’s ability to efficiently remove humidity and, depending on the differential you’re trying to overcome and how often you plan on using it, you may find it more reliable and efficient to use an actual dehumidifier in addition to your ac unit.

1 Like

Thank you very much,

I’ll try it out

Let us know how this works out. I suspect that leaving the AC running until the humidity drops to 49% will result in the temperature dropping to a temperature that’s quite cold, the AC running much longer and raising your energy costs. I found that making some changes in my thermostat had a significant effect on humidity:

  1. Setting the fan to “Auto” instead of “Circulate”. The Circulate mode runs the fan 30% of the time when AC isn’t running with the intent to keep the air moving and make it feel cooler. But when the compressor stops running the coils are soaking wet with condensation and running the fan just evaporates that moisture and circulates it back into the house.

  2. Turning off “Extended fan run time in cool”. This option leaves the fan running for xx minutes after the compressor stops and also dumps all of the moisture on the coils back into the house.

  3. Changing the “Cool cycles per hour” from the default 3 to 2. This results in the compressor running longer and allowing it to remove more moisture,

I’m not an AC expert, and I haven’t tried to determine which of those 3 options had the most effect, but the humidity levels have measurable dropped since making those changes. Your results may vary.

The only proper way to dehumidify air is by cooling it down a lot, get rid of the condensate and reheat it again. That is, how professional HVAC systems, I’m maintaining, works.

It would be very difficult to achieve with a home air-conditioner. That’s all I can tell you, without talking about automations.

I don’t want to sound skeptic, but this is, how it works…

In the Resi market:

Semi Coupled systems can use functions to shed blower CFM (limited reduction) and or overcooling (3 degree max)

Highly Coupled systems have much greater control over blower, compressor and temperature.

In the Commercial market: (as BebeM mentioned)

All the functions of a highly coupled system with the addition of reheat and desiccant options.

Bottom line, there is a possibility you’ll damage your system trying to drive the temperature really low to achieve lower humidity levels. At least without any safeguards in place.

(You need to prevent low coil saturation temperatures / liquid flooding)

Thanks everyone. I’ve tried it out and it seems to be working okay.

Just for some background, I usually have my upstairs and downstairs units between 81 and 83 and supplement with ceiling fans. When lowering my target temp on the regular thermostat and using the Generic thermostat (as humidity target), my downstairs got to the target humidity when the temp was around 79-80. The upstairs has yet to reach my target humidity, but I did put a thermostat target of 77 degrees. So for now, the ac will turn off at either 50% humidity or 77 degrees, whichever comes first. So, I understand that this will use more electricity than I normally use. But I don’t think 77 is too low of a target temperature. I will continue to experiment to see how it does. Make sure it’s not cycling too many times or what not.