Essential question of humidity vs temperature
 

In climates, where it is too hot for comfort, we often need cooling - air conditioning - to keep us comfortable inside.

In almost all installations, a heat pump is splitting the energy of the air into hot and cold, directing the hot outside and cold inside. Most often, the air is cooled to not much over the freezing point (of water), and the temperature of the air is what is keeping the entire house cool - not just the air. Ideally. Ironically, at the same time as heat is expelled, heating up the outside even more, other energy sources are often used for hot water, like electricity, oil, propane ... what a waste!

Well, so far so good.

But really, we are so focused on temperature, for comfort. In the setup above, moisture is taken from the air inherently, as air being cooled off means decreasing the amount of moisture it will hold. As such, a normal air condition unit is also at the same time, a humidifier, hence, we don't really consider the humidity very much - the main parameter is TEMPERATURE in the control of our comfort.

But there is much more to comfort than just fahrenheit and centigrades.

HUMIDITY in itself is a highly forgotten parameter. Add to that CIRCULATION of air, and even think of different requirements for bedrooms, kitchens, gyms, offices ... there isn't just one golden target of temp/hum/airflow which suits all, different activities demands different environments.

In the winter mainly, we discuss WIND CHILL factors - more wind at the same temperature is factored, when a body is kept at a different temperature to the surroundings, ie the human body around 100F in much colder surroundings. The same goes for a building, whether heating in the winter, or cooling in the summer - more wind means more exposure - but ONLY when there is a difference in temperature. If the air temperature outside is close to the temperature of the house, more of less wind has no "wind chill" (or heating) effect.

The same for the inside environment of the house, circulation of air means (in most cases) more cooling of bodies - hence we often use plain fans, where real cooling isn't available, or in a non-A/C car, open the windows.

HUMIDITY ... just like the wind chill, you can make a table where temperature and humidity are interrelated to form an "index", like the Canadian Humidex: Humidex - Wikipedia, the free encyclopedia - (there are other ways of measuring it).

In other words, my claim is that for ENERGY CONSERVATION and INCREASED COMFORT, we should look more at air flow and humidity control, NOT just temperature.

If we can control the moisture content of the air, a much wider range of temperatures are comfortable. And frankly, coming from a hot moist outside into a cold, dry, drafting inside, can be quite a shock to the body, sometimes sparking summer colds, and other discomforts.

What we REALLY NEED is to find the "cheapest" way (energy-wise) to

REMOVE MOISTURE FROM AIR

Not heating, not cooling, not looking at the relative humidity, but how to wringe the air, the most energy efficient way. Add pain fans, which use a lot less energy than "real A/C", and we can have a comfortable environment using far less energy than a normal A/C HVAC installation.


So help me here, what is the best way?

• Silica / dissicant liquid?
• Solar heat driven heat pumps?
• Conventional electric dehumidifiers?
• Other solutions ... ?

My postulate is, that many buildings can save lots of electricity using less A/C, if we find a proper way to remove the moisture, and keeping the temperature HIGHER than the usual ~70F / 21C. Even 80F is comfortable, if the air is sufficiently dry. 90F is not optimum but bearable, if the air is really dry.

But we really need ... a reliable, cheap and efficient method, to remove moisture, which uses a minimum amount of energy.

Please add your comment below, with your best take on this.

Thank you.

Excellent topic Osolemio! Controlling humidity really can have a drastic effect on comfortability in a home, and you are right that most people don't even think about it.

My house has no central A/C system. I normally use window/box fans to pull air out of the 2nd floor windows during the night to cool things down. When it gets real hot I have a window A/C unit in my bedroom for comfortable sleeping.

This year I tried something new though. I put an additional window A/C unit in my kitchen downstairs. After I woke up in the morning I would close the house up and turn the A/C on for a couple hours (on a timer). This would help dehumidify the air, but not really drop the temperature of the room much at all. Admittedly we had a dryer year than normal, but even when the house got up to 80F/26.6C it was comfortable with just the ceiling fan circulating air. The window A/C unit didn't use a ton of power compared to a central A/C system, but if it were possible to remove the humidity another way I'd definitely look into it.

Xringer recently posted about a small device to absorb moisture. However, it looks like it uses an electric heating element to remove the moisture. Still, something to look into. Perhaps one could make a solar heater to heat things up to remove the moisture.
http://ecorenovator.org/forum/applia...ll-spaces.html

Also, to add a bit more. In winter time it is valuable to add some humidity back into the air to keep things feeling warmer. Obviously this is quite a bit easier than removing humidity.

Is anyone aware of a source for dessicant that you might use in a semi-large dehumidifying system?

Bumping for ideas.

There are gas fired whole house dehumidifiers which are more efficient than AC units. Otherwise it's probably most efficient to get minisplit with a really high SEER. I don't see dessicant as the way to go. My dehumidifier can remove multiple gallons of water from my basement a day in the summer. How many cubic yards of dessicant will one need to cycle through (some in use and some spread out in the sun drying out) to make this possible? Think of the labor involved in hauling 2 or 3 yards of this stuff outside each day and spreading it out in the sun? what if you don't have any sun for several days. What if it's also humid, maybe because it's raining, and thus even more humid.

Thank you for your answers so far - it is an interesting subject, with huge potential, for global energy savings, comfort as well as for economics.

Adding moisture in the winter, as mentioned by Daox is just as important, depending on where you live. Adding moisture is easier, and it does make it possible to have a lower temperature inside and still not freeze. It is important to have a system to keep the moisture more or less constant during the year - the latter is also important for the well being of a house structure. Not too dry, not too moist, and all will be good!

After all, when we speak of "heating" and "cooling", "humidifying" and "dehumidifying" ... we are really talking about keeping it CONSTANT inside, or near constant. We add heat to counter a temperature fall in winter, or cool down, to counter a temperature rise in summer. Likewise with the humidity.

To solve the humidity issue - finding a smart way to add or remove humidity in a cheap and clean way, is the way forward, both for comfort, building preservation, energy saving and economy.

I don't think anything involving combustion of fossils is the way forward, though, no matter how efficient.

Usually, at times when you require cooling (or dehumidification), there is lot's of sunshine available. Turn that excess energy into cooling/dehumidification, and the world can save immense amounts of energy. We just have to find an efficient and sustainable way to exploit and control it.

But we also need to educate people and developers about humidity. An example:

Another place to live, built in 2005, with a central air-condition, and the problem is still the same, "faulty" type of A/C design: It has two modes it cycles between, as the temperature changes:

1) Very cold, dry air is pumped in, as long as the thermostat says "it's too hot"

2) When the thermostat says the set temperature is reached, the ventilation keeps going, but now with hot ambient (and humid!) air, until the thermostat again says "it's too hot"

The result is a cycling between "dry fridge" and a very humid hotter air, where everything becomes sticky. Both of these are quite uncomfortable, one too cold, the other too humid.

Instead, the A/C should have cycled on when it's too hot, but completely off until again required. Pumping in ambient hot/humid air is counter-productive and downright stupid, in all regards. I wish I could re-rig the A/C, but for now, where cooling requirements are less, a solution is to keep the A/C running in one room only, at lowest fan setting. This room is then quite chilly, but the air spreads to the other rooms, which are then quite comfortable - and not too humid!

When it is really bad, it becomes so humid that normal stationary paper loses that crackling sound when you handle it. On the other hand, when it is really hot outside, it's not a problem, as the A/C keeps in the cooling mode (as long as the fan setting is low). The problem is mainly present at times of fall/spring intermediate ambient conditions.

Why does your ventilation system stay on after the A/C is turned off? I haven't seen any systems that do that. Most turn off not to long after the A/C unit turns off, and after the a coil (heat exchanger) warms up so you extract all the cool from the system.

Plants!

This MUST be the solution, and how much more green can you get?

Plants take up CO2 (but only as they grow), and produce oxygen - opposite that of humans - and this is essentially the basis of our ecosystem.

There are plants in the desert, as cactus, that survives by taking moisture from the air. I wonder if this process has a net absorption of moisture, or maybe it just cycles back to the air?

If the moisture in the air combines with CO2 to make a dryer and more oxygen rich air ... then it is a question of finding the plant which is most efficient at just this process. And I think, looking in a desert would be a good start.

Any takes on this?

As with the salts used for drying, if the process does not have a NET absorption of moisture, then it is only useful if the plants/salts are cycled to give off moisture outside of the environment which we want to dehumidify ...

I hope there are some users out there who can bring more into this subject ...

Reduce your home's indoor humidity... with plants? - The Year of Mud: Cob & Natural Building

Interesting stuff, I will keep looking into this ... it's all new to me

This is the type that is built into the building, a central system and not a window mounted unit in each room. It's all great, but it alternates between ambient air (when the room is cold enough) and cooled air, when there is need for cooling.

If it wasn't for the dewpoint of the ambient air, which is often way above the temperature of the room, then it wasn't any problem. But as you pull the humid air into a cold room, it condensates and makes for an uncomfortable environment - sticky and moist is not really what you want!

Regarding the plants ... I am thinking of certain types of plants where part of the plan absorbs moisture, while other parts expels it. This could be like a tree taking water using the roots, which in turn evaporates from the leaves (and other parts).

If you could have either part of the plant outside, and part inside, or have a kind of small green house around the part of the plant which expels moisture (and vent that outside), you could have the plant work for you - entirely for free!

Besides, many plants clean the air of certain pollutants, as well as increase oxygen leves. There must be a huge potential here ...

My plants shrivel up if I don't water them. And then, as you mentioned, the leaves expirate the moisture.

A former co-worker used to put tall cans spaced around in his shop. On the top was, I believe a funnel-shaped lid that had, if I'm right, calcium that would absorb the moisture. The moisture would collect and funnel down into the can, which could, in turn, be dumped later.

Before worrying about taking moisture out of the air, have folks given a thought to where it's coming from? As an energy auditor, I see a lot of houses here in Maine that have damp basements. Many run dehumidifiers. Many just put up with a musty smell that makes everyone sick. I tell people over and over: Use a fan over the kitchen stove, and in the bathroom. Get an energy star fan with a humidistat switch. Paint the basement concrete so it can't be a source for ground moisture evaporation. If you have a dirt floor crawlspace or basement (all too common here), put a membrane (usually builders plastic, but occasionally something better like EDPM) over it. Seal the moisture down.

I deal with a heating climate. Few of my clients use air conditioners before I get there, and I hope none do afterwards. If they do, I look for problems with ceiling/attic insulation. Fix that and AC isn't needed here.

If cool dry air comes into a house and warms up, the relative humidity drops. That makes the air suck moisture out of wood, skin, plants, whatever. When it escapes, at some point it reaches the dew point and water condenses out, regardless of venting.

In this maritime climate in the summer, if people have windows open, especially basement windows, the moist outside air comes in and condenses in the crawl space or basement.

So really the best way to dry air would be a heat exchanger system that first cools it, removing water, and then warms it again by running it past incoming air that's being cooled, or taking waste heat off the cooling machinery. Ideally, this would have very little energy consumption in the process. I'm thinking of the water purification distillation units in Gaviotas that left the clean water only 3°C warmer than the incoming water, despite having just been through a solar evaporator.

Bang!









Apparently "Bang!' is too short a message to post so I have to add this filler to get my "Bang!" out there.

I had a couple more thoughts.

If the machinery was outside the conditioned space, unlike a standard dehumidifier, you won't have the waste heat inside.

Also, from a simple thermodynamics point of view, you should be able to calculate how much water you're condensing out of the air.

Say you have 85° air with 100% humidity, and you hope to have 85° air with 50% humidity. You're removing 90 grains of water per pound of dry air. You're going from 180 grains total to 90 grains total. You're bringing the air down to 65°, where 100%RH means 90 grains of moisture as vapor, and the rest condneses, and then you're warming this air back to room temperature by cooling the air coming into the dehumidifier system.

A grain is .000143 pounds. A pound of air is about 13 cubic feet. Say your house is 2000 square feet, with 8' ceilings, and gets the recommended .35 air changes per hour natural ventilation. That's 5600 cubic feet. That's 430 pounds of air. That's .062 pounds of water to condense. The latent heat of evaporation is 970 BTU/lb for water, so we're talking about ~60 BTU per hour, which is virtually nothing.

EDIT: I found my math error: 5600 ft3 -> 430 #air -> 38800 grains h2o -> 5.54 #h2o -> 5400 BTU -> 1.6 kWh. Something like a 20 amp air conditioner, including equipment inefficiencies.

There will also be efficiency losses, and the air will be cooled in the process. If we can keep the cooling to 5°F, at .0182 BTU/(ft3*°F), that's another 500 BTU, and the room is down to 80°F, but up to about 57% relative humidity.

Somebody (STILL) check my math. If I want to be certain, I use a spreadsheet and a second person to check things. What I calculated is all air. If there are solid surface (through the insulation) heat gains, those will have to be dealt with separately. I also didn't account for the moisture you've added to the air from normal human activity, like breathing and doing dishes.