Pop goes the Humidity

[TortyDxb]

I'm just curious b/c I lack the science.

I have a closed chamber enclosure in a small washroom for the nights. Substrate is coconut coir and humidity sits at 70 ish percent with a temp of 70 ish degrees. This is ok I believe.

In the room are some open pans full of water, the substrate is kept moist and inside the chamber there's also a shelf with an open container full of water.

Anyway, I wanted to push the temp up a little bit more to 80 + degrees. So I put a small 7 fin oil radiator thingy in the room, set it to achieve around 85 degrees, and got that temp without issue.

But...apparently the humidity has now disappeared? It is sitting at 50% in the enclosure- the sensors reading this are inside the closed chamber. This is despite new water containers inside the enclosure, wetter substrate, and I even put a pan of water on top of the radiator.

If anything a warmer room should be adding a lot more water to the air from all the containers full of water?

Is it just my humidity reader being weird? Can someone explain the science here?


Thanks!

 

[Clamhandsmcgee]

A picture would help me understand your setup. I have a few questions, is your air conditioning running/ heater in your house running? You have a closed chamber, I'm assuming that you have an oil heater running outside the enclosure. In a closed chamber enclosure, any outside humidity shouldn't effect the humidity inside the enclosure . Anyway, post a picture and maybe people smarter than me could explain better.

 

[Hugo's Home]

I can try to explain this the best I can. No your sensor isn't messing up unless it's one of those manual dials then I would suggest buying a digital sensor.
Warming the air doesn't add moisture to the air. It increases the potential to hold more water vapor in the air. So increasing the temp and the lower rh is due to the rapid increase in vapor pressure relative to partial pressure (this is what makes rh) thus seeing the lowering the RH (due to the equation) Now with the lower rh and the higher temps, the air has more "space" to reach saturation or 100% rh. It's not necessarily that the RH has dropped, well it has but its relative to the temp, the air just has more potential to hold more water vapor at that higher temp. It's just odd that with all the water your adding, the RH isn't increasing.
Add one thing, if the water molecules are moving faster due to the temp increase, you could increase the loss of water from your enclosure from non-sealed spots. Could explain why the partial pressure isn't increasing as rapid as the vapor pressure because of pressure/water loss but I see your adding a whole bunch of water so idk.
I think as long as the ac vents are sealed up and having the enclosure as sealed as you can, maybe it will just take time to reach a new equilibrium.
In my night box I can't keep rh above 60% usually around 40% (humidifier running full blast) due to the box not being as sealed as much it should be; the ideal partial pressure to match the vapor pressure just cant be achived in my setup.. yet..I'm going to rebuild the box for next winter.. The box stays between 80-85F.
Geez that was long but maybe it will help! Did the best I could!

 

[TortyDxb]

A picture would help me understand your setup. I have a few questions, is your air conditioning running/ heater in your house running? You have a closed chamber, I'm assuming that you have an oil heater running outside the enclosure. In a closed chamber enclosure, any outside humidity shouldn't effect the humidity inside the enclosure . Anyway, post a picture and maybe people smarter than me could explain better.

So it's a room behind the kitchen, about 16 square feet and 12 feet tall. No AC vents, does not cool, stays at about 70 degrees, oh and it has no windows. it's a utility room for the washing machine and storage shelves (brooms etc).

Yes i just put a small radiator in the room (not a fan type of heater) to bump up the temp a bit. I'm betting this is massive overkill but anyway I'm curious why extra heat has dropped humidity in the closed chamber by so much.

I'll do photos when I make it look a bit neater!

 

[TortyDxb]

I can try to explain this the best I can. No your sensor isn't messing up unless it's one of those manual dials then I would suggest buying a digital sensor.
Warming the air doesn't add moisture to the air. It increases the potential to hold more water vapor in the air. So increasing the temp and the lower rh is due to the rapid increase in vapor pressure relative to partial pressure (this is what makes rh) thus seeing the lowering the RH (due to the equation) Now with the lower rh and the higher temps, the air has more "space" to reach saturation or 100% rh. It's not necessarily that the RH has dropped, well it has but its relative to the temp, the air just has more potential to hold more water vapor at that higher temp. It's just odd that with all the water your adding, the RH isn't increasing.
Add one thing, if the water molecules are moving faster due to the temp increase, you could increase the loss of water from your enclosure from non-sealed spots. Could explain why the partial pressure isn't increasing as rapid as the vapor pressure because of pressure/water loss but I see your adding a whole bunch of water so idk.
I think as long as the ac vents are sealed up and having the enclosure as sealed as you can, maybe it will just take time to reach a new equilibrium.
In my night box I can't keep rh above 60% usually around 40% (humidifier running full blast) due to the box not being as sealed as much it should be; the ideal partial pressure to match the vapor pressure just cant be achived in my setup.. yet..I'm going to rebuild the box for next winter.. The box stays between 80-85F.
Geez that was long but maybe it will help! Did the best I could!

Superb response, can't thank you enough. I'm sort of following most of the science here .

With all the extra water sitting about I'm beginning to think the petstore bought, 30 dollar, temp/humidity digital reader is wonky. I put the sensors (it came with two called 'in' and 'out') inside the enclosure hanging an inch from the top. It should be reading 70 percent plus humidity for sure. Yet as soon as I put the radiator on, humdity starts dropping (apparently inside the enclosure) which surely would take more time to be effected - it really is sealed well.

I think the digital reader is measuring outside temp/humidity at the display bit of it is near to the heater (at best) or just cr8p.

The thing about this is that I understand warming air, or a room doesn't automatically add humidity to it, but surely warming an already humid room (after adding even more moisture points to it) should?

 

[Markw84]

I'll try to explain for you...

Relative Humidity is exactly that = RELATIVE. That means it is the humidity in relation to the amount of water vapor air can hold AT THAT TEMPERATURE.

Perhaps what is not understood, is that air's ability to hold water vapor is dependent upon what temperature it is. For example at 86°, a cubic meter of air can hold 30g of water as vapor. But at 32° a cubic meter of air can only hold 5g of water as vapor.

So that 32° air with 5g of water vapor - is at 100% relative humidity. It would be forming "dew" and water would be starting to condense out of the air. If we heated that same air to 86° it would still have the same 5g of water, but since 86° air can "hold" 30g of water vapor, it only has 1/6th of the possible amount of vapor it can hold. So the relative humidity is now 1/6 or 16.6% relative humidity. So simply heating that air dropped the relative humidity from 100% to 17%.

In the winter, we have humidity issues in our homes because the air outside is cold and can hold little free water vapor. Even if it is raining outside and 100% humidity (because the vapor is actually condensing since the air cannot hold any more water = rain) if the temperature is 40° that 100% relative humidity is still a fairly small amount of actual water vapor in the air. As that air comes into our homes and is heated, the same amount of water vapor now shows 30% realitive humdity in our 75° home.

Rain actually occurs because warmer, high humidity air rises in the atmosphere and cools. If the warmer air from below has a high enough humidity - as it rises and cools, it eventually reaches 100% relative humidity and water vapor condenses as the cooler air can no longer hold the moisture in the air. And rain falls...

SO... As you heat a room, or enclosure - you need to add MORE water to the air to maintain the same relative humidity. At the higher temperature we are dealing with (80° or higher) it takes a lot of water. Without a pretty well sealed enclosure the effect of the warm humid air in an enclosure (or room) will constantly create a drafting effect drawing the warm, moist air out and drawing in the cooler air with less moisture. Through the smallest crack this can be substantial. So we quickly reach a point where we cannot maintain enough humidity at that temperature without better sealing the enclosure or room and stop the exchange of warm/humid air with the cooler/much less humid air.

 

[Hugo's Home]

I'll try to explain for you...

Relative Humidity is exactly that = RELATIVE. That means it is the humidity in relation to the amount of water vapor air can hold AT THAT TEMPERATURE.

Perhaps what is not understood, is that air's ability to hold water vapor is dependent upon what temperature it is. For example at 86°, a cubic meter of air can hold 30g of water as vapor. But at 32° a cubic meter of air can only hold 5g of water as vapor.

So that 32° air with 5g of water vapor - is at 100% relative humidity. It would be forming "dew" and water would be starting to condense out of the air. If we heated that same air to 86° it would still have the same 5g of water, but since 86° air can "hold" 30g of water vapor, it only has 1/6th of the possible amount of vapor it can hold. So the relative humidity is now 1/6 or 16.6% relative humidity. So simply heating that air dropped the relative humidity from 100% to 17%.

In the winter, we have humidity issues in our homes because the air outside is cold and can hold little free water vapor. Even if it is raining outside and 100% humidity (because the vapor is actually condensing since the air cannot hold any more water = rain) if the temperature is 40° that 100% relative humidity is still a fairly small amount of actual water vapor in the air. As that air comes into our homes and is heated, the same amount of water vapor now shows 30% realitive humdity in our 75° home.

Rain actually occurs because warmer, high humidity air rises in the atmosphere and cools. If the warmer air from below has a high enough humidity - as it rises and cools, it eventually reaches 100% relative humidity and water vapor condenses as the cooler air can no longer hold the moisture in the air. And rain falls...

SO... As you heat a room, or enclosure - you need to add MORE water to the air to maintain the same relative humidity. At the higher temperature we are dealing with (80° or higher) it takes a lot of water. Without a pretty well sealed enclosure the effect of the warm humid air in an enclosure (or room) will constantly create a drafting effect drawing the warm, moist air out and drawing in the cooler air with less moisture. Through the smallest crack this can be substantial. So we quickly reach a point where we cannot maintain enough humidity at that temperature without better sealing the enclosure or room and stop the exchange of warm/humid air with the cooler/much less humid air.

Muuuuchhhh better response explaining. Why I am not a teacher.

 

[TortyDxb]

I'll try to explain for you...

Relative Humidity is exactly that = RELATIVE. That means it is the humidity in relation to the amount of water vapor air can hold AT THAT TEMPERATURE.

Perhaps what is not understood, is that air's ability to hold water vapor is dependent upon what temperature it is. For example at 86°, a cubic meter of air can hold 30g of water as vapor. But at 32° a cubic meter of air can only hold 5g of water as vapor.

So that 32° air with 5g of water vapor - is at 100% relative humidity. It would be forming "dew" and water would be starting to condense out of the air. If we heated that same air to 86° it would still have the same 5g of water, but since 86° air can "hold" 30g of water vapor, it only has 1/6th of the possible amount of vapor it can hold. So the relative humidity is now 1/6 or 16.6% relative humidity. So simply heating that air dropped the relative humidity from 100% to 17%.

In the winter, we have humidity issues in our homes because the air outside is cold and can hold little free water vapor. Even if it is raining outside and 100% humidity (because the vapor is actually condensing since the air cannot hold any more water = rain) if the temperature is 40° that 100% relative humidity is still a fairly small amount of actual water vapor in the air. As that air comes into our homes and is heated, the same amount of water vapor now shows 30% realitive humdity in our 75° home.

Rain actually occurs because warmer, high humidity air rises in the atmosphere and cools. If the warmer air from below has a high enough humidity - as it rises and cools, it eventually reaches 100% relative humidity and water vapor condenses as the cooler air can no longer hold the moisture in the air. And rain falls...

SO... As you heat a room, or enclosure - you need to add MORE water to the air to maintain the same relative humidity. At the higher temperature we are dealing with (80° or higher) it takes a lot of water. Without a pretty well sealed enclosure the effect of the warm humid air in an enclosure (or room) will constantly create a drafting effect drawing the warm, moist air out and drawing in the cooler air with less moisture. Through the smallest crack this can be substantial. So we quickly reach a point where we cannot maintain enough humidity at that temperature without better sealing the enclosure or room and stop the exchange of warm/humid air with the cooler/much less humid air.

I just had a eureka moment, thank you- incredibly kind of you to do this- THANK YOU.`

 

[TortyDxb]

Just to finish this, I run the heater in the room before they go in now. This brings the room (and their enclosure to about 90 degrees but knocks the humidity to around 40-50%. Once they are in, it's lights out and heater off, and door to room is closed. Humidity rises to around 75-85% and temps settle at around 75 degrees which is acceptable.

I think the coir substrate is doing most of the work along with a spray down of the room/ enclosure a little once a day.