Humidity effect calculator - window condensation

[P.Kelly]

I can't seem to find what I'm looking for. I'm hopeful that one of you might know of a tool/website/spreadsheet/formula.

Is there a way to *easily* calculate the impact of an aquarium on household humidity.

Eg. My home is 3300sq/ft, two story and is currently 54% relative humidity at 76 degrees F. If I add 200 gallons of water in an open aquarium and keep the aquarium at 79 degrees F evaporation will increase the household humidity by X?

I'm sure that I don't understand the complicated science behind evaporative cooling and humidity. I also know that temperature in my house can fluctuate a lot as I don't cool the house mid day and I open the house up at night to bring in cool air.

I'm asking this because I had a few hundred gallons in a previous, and smaller house, and condensation created mold problems around windows. I'm assuming that I may have similar problems again and am trying to quantify the problem.

I may be asking the wrong question. In which case I'm open to suggestions on how to figure out what to ask.

 

[Bob Nell]

I have no scientific explanation, but from my experience, your tank will be evaporating about 2 gallons per day. So you will have to consider that impact.
Other factors will be how new your home is and how well insulated it is.

 

[P.Kelly]

I have no scientific explanation, but from my experience, your tank will be evaporating about 2 gallons per day. So you will have to consider that impact.
Other factors will be how new your home is and how well insulated it is.

While I have dual pane windows, they are of the older non-thermo insulated aluminum frame style, so I think that is where some of the issue came from. Luckily, my home is also not horrible well sealed up, so I think I have enough air infiltration to keep from having air exchange problems.

I'll have to see if there is anyway to tell what 2 gallons per day will do to my humidity level.

 

[Sa6hir]

I've never had such a problem regarding mold and I've a 220g set up. I had it 2 years now my water temperature is 71 degrees F. Saying that my set up isn't open top and I have glass over the top to stop the condensation. I might be topping up with 25 litres every 2 weeks or so... also because you want an open top you could buy a dehumidifier that will help with condensation.


Sent from my iPhone using Tapatalk

 

[P.Kelly]

also because you want an open top you could buy a dehumidifier that will help with condensation.

Yes, that is an option, but not an energy efficient option. I'd rather first understand what aspects impact the window condensation most and see if there are other methods of avoidance or correction.

 

[Vinny Kreyling]

Window condensation is mainly because of a temp difference between in & out on the panes. I get it a lot in the winter under heavy drapery.

 

[jamie1981]

There are many variables that would come into play and you would need to know all these variables,

water temp
air temp
air humidity
surface area of water (not total gallons of water this would not affect evaporation rate)
surface agitation
air velocity over surface of water

If you are getting condensation on your windows and they are in good shape the humidity in the house needs to be lowered either via a HRV if you are in a cold climate or air conditioning or a dehumidifier in warmer climates.

 

[JZinCO]

I can't seem to find what I'm looking for. I'm hopeful that one of you might know of a tool/website/spreadsheet/formula.

Is there a way to *easily* calculate the impact of an aquarium on household humidity.

Eg. My home is 3300sq/ft, two story and is currently 54% relative humidity at 76 degrees F. If I add 200 gallons of water in an open aquarium and keep the aquarium at 79 degrees F evaporation will increase the household humidity by X?

I'm sure that I don't understand the complicated science behind evaporative cooling and humidity. I also know that temperature in my house can fluctuate a lot as I don't cool the house mid day and I open the house up at night to bring in cool air.

I'm asking this because I had a few hundred gallons in a previous, and smaller house, and condensation created mold problems around windows. I'm assuming that I may have similar problems again and am trying to quantify the problem.

I may be asking the wrong question. In which case I'm open to suggestions on how to figure out what to ask.

I took meteorology in undergrad 8 years ago. Here is what I remember.

Part 1: RH to mass per volume
Starting with the basics, RH is actual vapor density (AVD) over saturation vapor density (SVD). Saturation vapor density changes with temperature ( http://www.chemguide.co.uk/physical/phaseeqia/svpwaterplot.gif ). So, of course, as it gets warmer, the SVD increases, corresponding to a drop in RH. As it gets colder the SVD decreases and the RH rises. As an aside, the temperature for which the SVD equals the AVD, is the dew point (more on this in part 2)
Using the SVD, and atmospheric pressure (you can find a useful approx. given your elevation ASL), you can calculate the actual gH20/m3Air

Part 2: Add new mass per volume to new RH
Now, take the volume of your room. Determine how many gallons of water evaporate. Use the specific density of water to determine how much mass is added to your room's air. Calculate your new AVD (the prior AVD plus addition from evaporation), then divide that by the SVD (we are assuming your air temp is the same), to get your new RH

Note: This calculator will get you through Part 1. You'll have to backcalculate for Part 2.
http://www.cactus2000.de/uk/unit/masshum.shtml

The caveats:
Airflow--Of course, that room's air isn't isolated. You can estimate the exchange rate between that room and the rest of the house (and the outside for your HVAC) to get some RH reduction factor. Your HVAC system might actually have tags on it that specify the CFM air exchange rate. Simply use the RH of the rest of the house, the RH in the fish room, and the exchange rate to see how much the rest of the house relieved the fish room of humidity. The easiest way to do this is to figure out how much air is recycled within a day, how many gallons of water are evaporated in a day.
Here is a calculator that can help you incorporate the outside. http://www.lenntech.com/calculators/humidity/relative-humidity.htm

Insulation--Ignoring window insolation for a moment, if it is cold outside, your inside RH might be 50%, but once that inside air hits the window, if the temperature outside is below dew point, your will have condensate. To figure out if your window might condensate, sans insulation, determine the new RH (that is, including tank evaporation), then determine the dew point. That will tell you the outside conditions for which your window will have condensate. Of course, you still have insulation. I don't know how to include conductivity but the easy way is to, on the coldest days of the year, measure the room temperature right next to the window. Consider that temperature your dew point threshold for condensation.

Evaporation rate--In my explanation, I assume you know your evaporation rate (gal/day). The other posters hit on some of the difficulties to calculate this.

Sorry.. no easy answers and I'm probably only half aware, but hopefully close enough for an estimate.
The EASIEST way is to pay me to give me your house and tank specs. I can run a computational fluid dynamics model to figure this out for you

 

[JZinCO]

I hope you can now estimate the humidity.
As for solutions
1) in my experience, it's not conduction through the windows that creates the cold (low dewpoint) conditions on the surface of the window, it's cold air seeping around the edges. New trim or caulk goes a long way.
2) Increasing outside temp helps, as in moving down south.
3) Increasing air flow in the room and house, even a central fan or ceiling fan will do wonders, as will increasing passive air flow (e.g. in the tank is in the basement, open the door to the upstairs).
4) A tank lid
5) A bigger house or fish room
6) Put a sink for humidity in the fish room. Ideally in the stand by the sump or in the canopy (charcoal, rock salt, kitty litter)
In other words, increase the volume of air to lower vapor pressure, decrease the volume of water vapor, increase the window's boundary temperature.

 

[P.Kelly]

Wow, lots of good information and some reading to do. Thank you all. I live in Sacramento, CA. It rarely gets to freezing temperatures here but often below the dew point at night, at least half the year. I don't recall seeing condensate on my windows in the last house, but I think the aluminum frames transfer heat/cold better than the double paned windows. This is probably the issue. I'm hopeful that with a large house and a centrally located tank that gets plenty of air transfer throughout the house that issues will be reduced in the new house. I'll see if I can make heads and tales of the info provided above and arrive at any answers before I set up a tank this winter. Thanks!