[Equipment] How much water will normally be used by a humidifier

[Otil]

Dear all

A few weeks ago I started to use a humidifier together with my Dreamstation. I usually set the machine to preheat 30 minutes before going to sleep and refill the tank every day.

However, I’m a bit surprised that I typically only use in the area of 20-30 ml per night. Is that normal, or am I getting to little moisture during sleep?

Thx in advance...

[Walla Walla]

If you live in an area of high humidity it's normal not to use much. Assuming it's in Auto mode. The two things that affect it are humidity and air pressure.

[SarcasticDave94]

My observations via posts here on Apnea Board are that water use can vary, even from one night to the next.

Esample my own use:

My own water use is about 2/3 tank every night, but it has been only 1/2 a tank on occasion. It also has been on occasion almost the whole tank. My humidifier setting would range from 4-8 at its extremes, but I typically stay between 6-8. Always in the manual mode. Stuffy, runny nose to a too dry nose being the change in setting reasoning.

[1holegrouper]

A lot of variables come to play. The design of the CPAP equipment itself is meant to cover a broad range of situations. Factors that influence water amount usage are:

- humidification setting level (I use auto)
- the mask you use (does it leak, are the exhaust ports in their design venting out a generous amount of air?)
- the humidity level in your room (which can change in seasons)
- your pressure settings (obviously with more pressure more air is being moved across the water and thus more water is needed)

[silentsnore]

The key variables are the environmental temperature and humidity - assuming fixed pressure/temp/humidity settings on the machine, the water consumption would be higher when ambient humidity is low and/or ambient temperature is high.

Just my recent example - last couple of nights the room humidity was lower than usual, and instead of typical consumption of 1/4-1/3 of the tank, it was almost 2/3 empty each morning.

[Walla Walla]

Actually the temperature doesn't matter. Just the relative humidity and amount of air flow over the water (pressure).

[Otil]

The humidity in my bedroom is in the area of 60% and my pressure is mostly between 7 and 9.
The 20-30 ml water used per night is under 1/10 of the water capacity in the tank - I find it very low for my settings.

Until now the humidity has been on level 3 - to night I will try to increase it to 5...

[Walla Walla]

60% is considered somewhat high humidity. Be careful about increasing your humidity too much or you might end up with rainout. Which is getting actual water in your tube and mask.

[mesenteria]

Actually the temperature doesn't matter. Just the relative humidity and amount of air flow over the water (pressure).

I believe this to be incorrect.  I think you have neglected 'vapour pressure' which is temperature and pressure dependent, not just pressure dependent.

Let us suppose the room air temperature is a comfortable 19 deg C with relative humidity of 50%.  This means the air is capable of taking on more moisture.  If you increase the temperature of the air in the hose, you will have dropped the relative humidity.  That is, there is no reservoir. The air flowing through the hose will seem drier.

Keeping everything the same, no reservoir, but we drop air temperature by draping a cold wet cloth over 60% of the tube's surface, the relative humidity of the air passing through the tube will rise and we'll get more condensate in the tube.  Condensate is not humidity any longer, and will not contribute to the comfort of the breather.

Now let's add the reservoir with given water surface area and ambient temperature.  It will have a vapour pressure of X at the water's surface.  If you raise the temperature of the water, but do not heat the tube (it is ambient throughout), you will necessarily evaporate more water which will raise the relative humidity in the air passing into the tube for a given air temperature.  The air in the tube will be cooler than the air passing over the water's surface and will begin to condense water inside the hose again.  If you heat the tube, there will be less or no condensation which will increase the comfort of the person using the equipment up to a point.  

If this is not so, there is no point in heated tubes or heated reservoirs...no?  So, yes, relative humidity is important, but so are absolute moisture content and temperature.

[Sleeprider]

I think "relative humidity" takes into account temperature and vapor pressure.

Relative Humidity is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature. Relative humidity depends on temperature and the pressure of the system of interest. The same amount of water vapor results in higher relative humidity in cool air than warm air.

I'm going to go with you are both correct and just need a hug.