Hi guys,
I want to take my old project for measuring the comfort of a room.
Which parameters should I need to measure in addition to:
Tell me what do you think about it 
elQuero:
- CO/CO2 (which is better?)?
CO sensors tell you whether you are being poisoned. CO2 sensors tell you how stale the air is. It is not a question of better/worse, they serve completely different functions.
Seems to me that you don't know what matters yet so I suggest you log everything that you think might be relevant and then try to correlate that data with a subjective assessment of how comfortable the room is. You need to know that in order to know the significance of your readings.
I suggest that air movement is also important - both in its own right, and to give you a measure of wind chill / cooling, which will have a huge impact on the range of comfortable temperatures. Also I think you will find there is interaction between the colour and brightness of the lighting, and the perceived warmth, which will affect the range of comfortable temperatures.
There is also the matter of where the room is located. Two rooms, as identical as possible, in different locations will not feel as comfortable to the occupants. Imagine one of them is a bedroom at your house, and the other is a hotel room 1000 miles away. They will not feel as comfortable, no matter how comparable the lighting, temperature, etc. Now, envision one of those rooms being a hospital room 2000 miles from home. Just not the same comfort level, no matter what you do.
This is a bit off topic but I found it interesting when I learnt about it;
Humans cannot directly detect lack of oxygen, that surprised me and I have been breathing for years. It is very rare in nature to be in a situation where there is insufficient oxygen in the air and, if there is, it is ususualy fatal so we never evolved the ability. Instead we detect CO2 produced when we "burn" oxygen in our bodies. This is a useful system because it ties directly into how much we are exerting ourselves and helps regulate breathing and heartbeat. The problem is if you remove the oxygen the CO2 is not produced, we then cannot indirectly detect the lack of oxygen and we just pass out.
There can be lack of oxygen for several reasons, e.g. reduced airpressure (as at high altitude), removal of oxygen (as happens inside steel tanks when they rust), replacement the oxygen (by breathing an inert gas like helium or halon from fire extinguishers).
CO is a clear, oderless, tasteless gas. In small amounts, as when smoking, it will cause long term health problems but you will be unaware of this happening. With larger amounts you might experience symptoms such as headaches but there would be a very fine line between that and enough to make you pass out and then probably die. The CO acts as a poison because it binds with the haemoglobin in your blood preventing it doing its job of circulating oxygen in the body. So if you inhale enough CO you will not detect the lack of oxygen, CO2 is not being produced so your CO2 sensing does not kick in and you just pass out and die.
Incomplete combustion in gas fires with poor flue gas extraction is a frequent cause of CO poisoning, but it can happen with wood, coal etc.
I have heard that if you pump CO into greenhouses plants such as tomatoes will concentrate the CO and become toxic if eaten, they are supposed to look unappetising though - don't know if this is true but it sounds plausible.
Well, maybe I should explain something more about this project...
1 years ago I've started this project as student in a projects competition: it was more like a game than a serious project, but I've ever thinked that it was a briliant idea.
Nowdays I've toke back this project because I want to turn it in a serious project.
There is also the matter of where the room is located. Two rooms, as identical as possible, in different locations will not feel as comfortable to the occupants. Imagine one of them is a bedroom at your house, and the other is a hotel room 1000 miles away. They will not feel as comfortable, no matter how comparable the lighting, temperature, etc. Now, envision one of those rooms being a hospital room 2000 miles from home. Just not the same comfort level, no matter what you do.
This device is like a knick-knack for living room. It has a minimal hardware interface (some LEDs) but you can interface to it via ethernet or USB for getting more informations, like historical graphs, realtime situation and set up the device for your specific needs (so PaulS, I think the problem you proposed can be solved by this way).
The first device version calculate a comfort index by measuring CO2 level, temperature, brightness and noise. The output was good for an inital prototype, but I always thought that these parameters weren't enough to achieve a reliable comfort index.
I understand from your answer that i should detect also lack of oxygen, and for detecting them i should detect the CO level. But can CO form multiple layers based on height? If yes i should detect it at more heights...
But can CO form multiple layers based on height?
Absolutely.
So, you seem to be trying to assign a relative comfort level based on environmental factors that the room owner might be able to alter, rather than an absolute comfort level, which includes a lot more than the environment factors.
Still, seems like an admirable goal. The web interface could include a lot of information about what the LEDs are showing, and what factors are being considered in assigning the comfort level.
Isn't the biggest problem here that 'comfort' is entirely subjective? Two people, in the same room, will each have their own 'comfort' levels. I'm very sensitive to light levels, whereas my partner thinks nothing of sitting next to a very bright daylight bulb to do her needlecraft. On the other hand, she is much more sensitive to temperature changes than I am.
Two people, in the same room, will each have their own 'comfort' levels.
Then, you'll need two of OPs devices... 8)
elQuero:
I understand from your answer that i should detect also lack of oxygen, and for detecting them i should detect the CO level. But can CO form multiple layers based on height? If yes i should detect it at more heights...
NOT "CO"; you should be detecting "CO2".
Air temperature can vary with height and position, but it seems unlikely to me that you will find significant variations in concentrations of the different gases throughout a room, unless you have a really concentrated source (gas lamp, candle etc).
NOT "CO"; you should be detecting "CO2".
I don't know. Concentrations of carbon monoxide in a room can make it uncomfortable. In a permanent way.
Concentrations of carbon monoxide in a room can make it uncomfortable. In a permanent way.
Ditto CO2
Isn't the biggest problem here that 'comfort' is entirely subjective?
For avoiding this problem I assumed that
This device is like a knick-knack for living room
therefore there won't often be people without same habits.
NOT "CO"; you should be detecting "CO2".
I don't know. Concentrations of carbon monoxide in a room can make it uncomfortable. In a permanent way.
Ditto CO2
Maybe I should check both XD
I understand from your answer that i should detect also lack of oxygen, and for detecting them i should detect the CO level. But can CO form multiple layers based on height? If yes i should detect it at more heights...
NOT "CO"; you should be detecting "CO2".
Air temperature can vary with height and position, but it seems unlikely to me that you will find significant variations in concentrations of the different gases throughout a room, unless you have a really concentrated source (gas lamp, candle etc).
Well, in that question I was talking about CO, not the other parameters. I know that they can vary, but I also share your opinion that height variations for some parameters (like temperature, brightness, noise, etc) are negligible.
But gases may stratify and make the room uncomfortable: they can't be easly detected by humans, so this device might warn you before you fall asleep! I'm in the wrong way?
elQuero:
Well, in that question I was talking about CO, not the other parameters. I know that they can vary, but I also share your opinion that height variations for some parameters (like temperature, brightness, noise, etc) are negligible.
But gases may stratify and make the room uncomfortable: they can't be easly detected by humans, so this device might warn you before you fall asleep! I'm in the wrong way?
The quotes have got messed up somewhere, I hope I'm quoting you correctly. I think your comment above is the exact opposite of what I am saying.
CO is worth monitoring only so that you can sound an alarm if the level exceeds a (very low) threshold. It has nothing to do with comfort - CO will kill you without making you feel uncomfortable.
CO2 makes the room feel stale. It is worth monitoring as one of your comfort indicators.
I do not expect CO or CO2 concentration to vary from place to place within the room, except near a very concentrated source such as a flame.
I would expect temperature to vary throughout the room and to vary with height too. It is entirely normal and expected that the room will have hot and cold spots and these will affect the comfort.
Light levels obviously vary through the room and this will affect the comfort.
This sounds like a fun project, but I'm not sure what you'll do with the "comfort" data once you have it. A CO alarm would be useful, but I wouldn't want to rely only on a home built solution for that.
It reminds me of a question I heard asked of a dive computer salesman - "The computer captures the water temp, why doesn't it display it during a dive?". The answer was basically "You know when you're cold so we don't spam you with data you don't need". Similarly here, you know if you're comfortable, so what are you trying to get from the device?
If the reason for doing it is "Because I can", then that's fair enough of course.
The quotes have got messed up somewhere, I hope I'm quoting you correctly
Yes, you have tagged my correcty 
CO is worth monitoring only so that you can sound an alarm if the level exceeds a (very low) threshold. It has nothing to do with comfort - CO will kill you without making you feel uncomfortable.
A CO alarm would be useful, but I wouldn't want to rely only on a home built solution for that.
Maybe the CO detection isn't very usefull for my goal... 
If the reason for doing it is "Because I can", then that's fair enough of course.
My reason isn't only "Because I can", but i think that it could be an usefull part in a domotic project.
Think about a green house that can"understand" your needs, based by your preferences and, for example, the season, and adjust some environmental parameters (like temperature, etc) for make you feeling more comfortable. That was my main goal, I don't know if it has been already done.
This device is an important part of this main project that can help me developing a software that could do this (infact the main part is the software, not the hardware).
Now you can understand why i need to identify all the parameters i need to detect for recognize if a environment is comfortable.