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.

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

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.

Build tight, ventilate right.

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can't reduce the humidity significantly, because outside air will be continuously mixing with whatever moisture is withdrawn.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.

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 is covered in the energy.gov 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.

(under construction)

Not anything I've seen, but an idea. For a supply ventilation home, have a dessicant such as calcium chloride 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.” sorbentsystems.com

Unfortunately, in Peru calcium chloride is a controlled substance, I think because it gets used in the processing of coca into cocaine.

There are products for wall interiors and products for wall exteriors. Some are waterproof and/or make the wall vapor impermeable to varying degrees.

Not sure which products to use:

• hydraulic cement
• liquid rubber (foundation sealant)
• “pitch or coal tar are the traditional materials for waterproofing brick” Ross on Quora
• concrete sealer vs sealant
• silicate, silane, siloxane concrete sealers
• silicone micro emulsion
• waterproof wall putty

YouTube video by Apple Drains showing a sealant and drainage solution. This situation can be avoided by a foundation well above ground level.

Vapor barriers should be placed on the warm/humid side of a wall, so that the wall insulation does not build up condensate. In a temperate climate, that would be the interior. Vapour retarder latex primers, ecohome.net Does a latex primer keep mold from forming on the walls by not providing an attachment for mold growth?

Extraneous notes

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 may cause the floor and walls to become damp.

Air close to the basement walls with will be higher in relative humidity, and may reach the dew point. See: thermodynamic concept of relative humidity.

On rare occasion there is a geothermal gradient.

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:

signaturesustainability.com

Choosing an infrared lamp type, sundearheater.com. Not affiliated with any company, just the best info I was able to find for now.

“Well water is around 55 degrees F …” Gary Ahlers at Quora. This could be channeled through a heat exchanger in the ventilation system. You can also channel the water through a floor or wall, but in a humid climate, anything besides an arid desert, there would be condensate. In the ventilation system the condensate can be trickled outside.

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.

https://www.quora.com/Is-it-possible-to-heat-cool-my-house-by-simply-digging-a-deep-hole-in-my-garage-floor-and-blowing-the-air-up-from-the-hole-using-a-powerful-fan/answer/Erik-Hancock-3