Questions on Digi-Cabi

[cantaresg]

46%RH is high?

You don't need dry cab to store photography gears in store room if the RH is constant 46%.

Regards,
Arto.

If you check regularly at different time and find that the humidity is constant at 46%, you don't have to place the equipment in the dry cabinet. But if the storeroom is only dry only certain occasions. it is advisable to put it in the dry cabinet. Especially because it is more controlled.

 

[Artosoft]

I understand where you are getting at. Let's put it this way. There are 3 variables that will determine relative humidity. They are 1) actual moisture content, 2) temperature and 3) atmospheric pressure.

In my example above, I had assumed that the cabinet is air tight, so the actual moisture content and the atmospheric pressure remains constant. So the only variable is temperature.

On the other hand, Australia is a dry country, and I'm refering to the absolute moisture content wise. That's why in Australia, the temperature may be 23 deg celsius, yet the RH is only 50% or less.

This is also the reason why there can be water condensing outside the windows of air-conditioned building. Even in the dry cabinet, the humidity may be around 50% at 32 deg celsius, but if the air-con is turned on and if the dryer does not turn on in time, condensation may still occur in the dry cabinet.

So you will say: no need dry cab as it will make humidity RH inside higher than outside. Especially if you put it under air cond.
32deg 50%
31deg 53%
30deg 56%
29deg 60%
28deg 63%
27deg 67%
26deg 71%
25deg 75%
24deg 79%
23deg 83%

Manufacturer suggest 40-50%RH for photography gears.

Regards,
Arto.

 

[cantaresg]

No... this is not what i said. What I mean is this.

The dryer unit activates when it sense that the humidity has risen above the set-point. But usually the sensor in the dryer unit is quite slow in response. Usually the time taken for temperature to drop is faster than the time taken for humidity to drop, especially since the TS placed the dry cabinet near the air con. further, the hygrometer reacts slower than a thermometer usually.

If you have a digital hygrometer, put it near the air con. You will find that the humidity is quite high actually.

 

[Artosoft]

No... this is not what i said. What I mean is this.

The dryer unit activates when it sense that the humidity has risen above the set-point. But usually the sensor in the dryer unit is quite slow in response. Usually the time taken for temperature to drop is faster than the time taken for humidity to drop, especially since the TS placed the dry cabinet near the air con. further, the hygrometer reacts slower than a thermometer usually.

If you have a digital hygrometer, put it near the air con. You will find that the humidity is quite high actually.

IIRC, only the pro series (digi cabi DHC series) and the newest with single red LED have humidity sensor to control when its dehumidifier unit need to work (if the RH inside dry cab over certain point). The rest don't have humidity sensor, only humidity display (digital or analog), which is not give any feedback to dehumidifier unit. The rest (that don't have feedback control) only have knob to control dehumidifier unit power and doesn't react to humidity changing inside the dry cab. Which type of dry cab you are referring?

You know why we need humidifier unit (no, not dehumidifier unit, humidifier unit), the unit that use water, create fog or evaporate water into air? It is because humidity inside air cond room is lower. So when you sleep in air cond room, when you wake up, you feel your throat dry. This humidifier unit work by release water into air. This is not new technology. I don't know what kind of air cond you mentioned since your air cond can make humidity high. Maybe new technology :embrass: .

Have you ever noticed there are water come out from air cond unit? That's the humidity (water in the air) condensed into water. So what happen if 'water in the air' removed from air cond room? The room will be dry than outside (humidity lower).

Regards,
Arto.

 

[cantaresg]

Yes, you are right, the water condenses from the air con unit. That is because the air has been reduced to a temperature below its saturation point, or in other words, the humidity of the air that leaves the air con is about 16 deg celsius or lower, with a relative humidity of 100%. So water condenses. After leaving the air con, the air is gradually heated up by the surrounding, and the relative humidity slowly drops. So if you happen to place your humidifier near the air con, you find that the moisture you tries to add into the room has condensed back into water before it travels very far.

So when you place the humidity sensor near the air con, you will be measuring a much higher RH (but of course you need to wait some time to see the change if you are using the analogue hygrometer).

Most of the dry cabinets do not have a feedback control. What they do have, is a humidistat that stretches when humidity is high and contracts when the humidity is low (much like a thermostat). Typically, the response of such devices are quite slow. About 30 min as what I have tested.

 

[blive]

Got a Akurai dry cabinet from CP a few years back. Was working fine until recently, the RH lvl is hovering around 60 - 70. Without things inside, it can go down to 40-55. Its been like that for about a month already. Don't know what's wrong.

Anyone know how to contact Akurai? Is there a service centre?

Thanks.

 

[Artosoft]

Yes, you are right, the water condenses from the air con unit. That is because the air has been reduced to a temperature below its saturation point, or in other words, the humidity of the air that leaves the air con is about 16 deg celsius or lower, with a relative humidity of 100%. So water condenses. After leaving the air con, the air is gradually heated up by the surrounding, and the relative humidity slowly drops. So if you happen to place your humidifier near the air con, you find that the moisture you tries to add into the room has condensed back into water before it travels very far.

So when you place the humidity sensor near the air con, you will be measuring a much higher RH (but of course you need to wait some time to see the change if you are using the analogue hygrometer).

Most of the dry cabinets do not have a feedback control. What they do have, is a humidistat that stretches when humidity is high and contracts when the humidity is low (much like a thermostat). Typically, the response of such devices are quite slow. About 30 min as what I have tested.

So the room with air cond (of course, closed door and window) will have higher humidity than outside or non air cond room :embrass: ?

Regards,
Arto.

 

[angelo]

So the room with air cond (of course, closed door and window) will have higher humidity than outside or non air cond room :embrass: ?

Regards,
Arto.

What is the diff between relative humidity and absolute humidity?

 

[Artosoft]

What is the diff between relative humidity and absolute humidity?

Read this :
http://en.wikipedia.org/wiki/Humidity#Absolute_humidity

Regards,
Arto.

 

[cantaresg]

So the room with air cond (of course, closed door and window) will have higher humidity than outside or non air cond room :embrass: ?

Regards,
Arto.

now, you have posted a very difficult problem for me. I don't know the answer as the question involves a lot of calculations, like what is the temperature of the air leaving the air con (we call that off coil temperature), the number of people in the room, the humidity of the surrounding environment etc. Suppose the air con you have has an off coil temperature of 18 deg, the relative humidity in the room is going to be very high, as compared to one whose off coil temperature is 12 deg celsius. An air con whose off coil temperature that is less than 15 deg celsius generally will make the room (in general) about 55% RH. But like I said earlier, areas near the air con may have a higher RH since it is much colder.

 

[cantaresg]

What is the diff between relative humidity and absolute humidity?

absolute humidity is the actual amount of moisture that the air is holding.

Relative humidity is the amount of moisture in the air relative to the maximum amount of moisture that the air can hold.

 

[angelo]

cantaresg and Artosoft, Thanks.

Correct me if i'm wrong. In summary, absolute humidity (AH) is the measure of actual amount of moisture in gases. As for relative humidity (RH), it is the ratio of actual amount of moisture to the maximum moisture capacity of a gases.

cantaresg, please help me to understand. Referring to your table below. I believe first column is the temperature and the second should be the relative humidity. Are you holding the absolute humidity as constant?

32deg 50%
31deg 53%
30deg 56%
29deg 60%
28deg 63%
27deg 67%
26deg 71%
25deg 75%
24deg 79%
23deg 83%

Artosoft, for your below statement. Are both countries having the same AH?

But, if you look into internet, the temperature and humidity in Singapore usually around 30degC and humidity >70%RH. And cold country like Australia, said IF 23degC, the humidity is around 50%. Your example shown different way, humidity rise up with the temperature drop.

 

[cantaresg]

Hi Angelo,
Yes, in this example, I have assumed that the AH remain constant. In any case, the concepts of AH is more relevant with people who design dry cabinets and dehumidifiers. On the other hand, for everyday users, RH is more important as this is the factor that determines whether fungus grows or other humidity related problems.

 

[angelo]

cantaresg, Thanks.

Sorry, more question.
- Is dry-cabinet air seal?
- Humidistat detect AH or RH?
- What is/are the diff between analog and digital dry cabinet?

 

[lcy]

You are right. I've the same problem with mohgui, got to as low as 20something RH. So I've check with Digi-Cabi and they told me to firstly power off and open the door. Let the RH rise. It should go up to about 60+. Then set the knob to about 8 o'clock and let the RH drop.It should reach about 40% - 50%. you can fine tune from there.

I've the same problem too. The humidity level is always hovering around 20% eventhough the knob is set at Pt A. Tried the above method and it did not work. Had to unscrew the dehumidifier and bring back to Digi Cabi for a exchange as mine was bought for more than a year. On-Site Service is only provided on the first year of purchase.

 

[Artosoft]

now, you have posted a very difficult problem for me. I don't know the answer as the question involves a lot of calculations, like what is the temperature of the air leaving the air con (we call that off coil temperature), the number of people in the room, the humidity of the surrounding environment etc. Suppose the air con you have has an off coil temperature of 18 deg, the relative humidity in the room is going to be very high, as compared to one whose off coil temperature is 12 deg celsius. An air con whose off coil temperature that is less than 15 deg celsius generally will make the room (in general) about 55% RH. But like I said earlier, areas near the air con may have a higher RH since it is much colder.

Ok. Now I've got what you mean. I agree with you, dry cab location just near the air cond (got direct cold wind from air cond) can make RH in dry cab drop too low when the air cond is turn off.

Thank you :thumbsup: .

Regards,
Arto.

 

[cantaresg]

i) Dry cabinet is designed to be air tight, so that moisture don't enter the cabinet easily.
ii) hygrometer measure RH.
iii) If the digital hygrometer provides feedback to the dryer, it is more responsive and accurate than the analogue dry cabinet. Otherwise, the only difference is that the hygrometer display on the digital cabi is more accurate. That's all.

Icy: Do you mean that when you open the door, the hygrometer still reads below 20%, or after the door is closed, the hygrometer reading drops below 20%?

Thanks, Arto.

 

[angelo]

cantaresg, Thanks.

 

[lcy]

Icy: Do you mean that when you open the door, the hygrometer still reads below 20%, or after the door is closed, the hygrometer reading drops below 20%?

The reading would raise to 60-70% if I kept the door opened. Everything is working fine now after I got the dehumidifier changed.

 

[yanyewkay]

dry cab setting problems again?

problem solved.