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Solving Humidity Issues

If you live where it's hot and humid, an air conditioner will draw off moisture from inside air. If you live where it's cold and humid, heating will reduce the relative humidity of inside air. See: thermodynamic concept of relative humidity. But if the temperature outside is ideal or only slightly cool, then you do not want to apply heating or air conditioning.

With Outdoor Ideal Temperature

If the temperature outside is ideal, then a dehumidifier is likely needed? Before reading this section, read Whole House Ventilation,

Sealed Environment

If you have a mostly sealed environment, such as most modern living spaces, even a low powered and relatively silent peltier dehumidifier can have an impact. A few percentage points can keep dew and mold from forming.

Door sweeps, door shoes, or draft seals can be used to seal the gap between the bottom of the door and the threshold.

Open Environment

In an environment that isn't sealed, such as a room with a gap under an exterior door, then a low powered peltier dehumidifier can't reduce the humidity significantly, because outside air will be continuously mixing with whatever moisture is withdrawn. Water content per volume of air will remain relatively constant.

A compressor-driven dehumidifier will have sufficient power to affect interior air and surfaces, while also producing more heat and consuming more power. The unit can be placed outside with ducts for processing air.

To reduce power consumption and to have better control of humidity, sealing a house is highly desirable.

Automated Windows

In a living space where there is a constant source for increasing humidity, such as a shower or aquarium, less humid outside air can help draw out moisture.

Low cost bluetooth temperature and humidity sensors are available to keep track of indoor and outdoor readings. Their hygrometer function accuracy is limited but still useful. For example, to automate opening and closing of windows, or to turn on bathroom or ventilation fans, based on the indoor/outdoor humidity differential.

Air flow directional control is also important. Warm air, or moist air, or warm and moist air, they all rise because they are less dense than cold dry air. Having a high window or duct can pump humidity out.

Supply Ventilation

Supply Ventilation is covered in the article. Providing a ventilation fan for positive house pressure can be used in conjunction with air filtration.

I read somewhere that 15% of air should arrive from outside to keep internal air healthy. 15% is not very specific, but duct work could recirculate inside air and also pull a percentage from outside enough to maintain a slightly positive pressure. The duct could have a HEPA filter, negating the need for a higher amount of fresh air intake.

Dessicant Dehumidifier

Not anything I've seen, but an idea. For a supply ventilation home, have dessicant in the air intake duct. Air drawn from outside will have its moisture reduced. As the dessicant saturates and becomes liquid, have a drain for the liquid to flow outside into a sun facing receptacle, where it can dry for reuse. The receptacle could be a solar oven.

Mario S on YouTube explains how to use calcium chloride as a dehumidifier. “For basements use 5 gallon pails (of calcium chloride) for best results. Expect these to last 60 days or so.”

The dessicant will slightly increase the temperature of the air: “Physical adsorption of moisture is typically exothermic. The strength of the adsorptive bonds can thus be measured by the heat of adsorption. The higher the heat of adsorption for moisture on the desiccant, the stronger the bonding and the less easily that moisture can be subsequently removed.”

Avoid Basements

A basement can also increase living space humidity from the surrounding earth if the floor and walls are porous. Even if the basement is treated to prevent water vapor flow, the walls and floors of the basement will likely be cooler than the outdoor temperature, and this coolness causes an increase in relative humidity. Air with the same water content will be higher in relative humidity at a cooler temperature. See: thermodynamic concept of relative humidity.

With Outdoor Slightly Cool Temperature

Heat absorbed by the surfaces in a room will reduce the local relative humidity. Radiant heaters heat surfaces with infrared radiation. Surfaces can also be heated by solar energy to reduce humidity:

Passive Solar Heating

With Outdoor Slightly Warm Temperature

“Well water is around 55 degrees F …” Gary Ahlers at Quora.

Air Ducts

The following paragraphs for a supply ventilation system with air recirculation through a HEPA air filter, where outside air comprises a dynamic percentage of conditioned air to the house.

The percentage of outside air let into the system depends on:

  • outdoor air quality
  • desired interior temperature
  • the extent to which the home can be sealed.

Each floor or major space should have a floor-level conditioned-air-outlet, and a ceiling-level-exhaust either to the stairway or a dedicated exit to outside the home. The outlet and exhaust should be on opposite ends of the interior volume?

Recirculation can happen under internal doorways and along stairways to reduce the amount of ductwork needed.

Duct work can be built into the concrete floors. Less exposed surfaces within the home means less surfaces to clean. Ducts traveling between floors can be external to the house for easier servicing.

The ducts should be internally free of unlevel seams to allow easy cleaning, for example with a furry ball pulled by a string.

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engineering/hvac.txt · Last modified: 2023/08/19 00:08 by marcos