The colder we can make our cold source (the bottom ice chest) the better is.
But you cannot make it colder. Assuming water is the working fluid, the lowest possible temperature of water is 0°C. Which means you can never make the water going through the radiator colder than that.
Good point! Well, in this case we want to be as close as possible to 0°C. But are we sure that water will not go below 0°C when there are several gel ice packs submerged?
Yes, water, it's the only fluid I saw in such projects and I can see why: the cold source is basically free from costs. Are there better alternatives?
Besides a well designed insulation, the coldness of the output airflow depends mainly from the cold source and the colder is the airflow, the faster are cooling times and this allows better energy balance along with power saving
Unfortunately, the temperature of the airflow has no bearing at all on efficiency of the system, other than personal comfort if you want to sit in the breeze.
I'm afraid we're again in thermodynamics territory which is in contrast with what seems obvious to expect. At least there is the advantage to get immediately some comfortable breeze without waiting for the time needed to cool down the room.
However, if I have understood well your previous statement, you seem to confirm what was my belief: getting the cold reservoir as close as possible to 0°C should be one of the target to reach.
The thermal camera screenshots I posted shows 67.9F (20°C) coming out from the reservoir and I'm not sure why such high temperature. The other project (the one with smaller motor and one air intake) shows a temperature of 1.5°C.
Given that both the configurations are pretty much the same along with the parts being used, I suspect that is the secondary air intake that ruins the internal temperature. It seems that for maximum efficiency, I need to identify the correct number of air intake and their dimensions. And such choice is strictly related to the blower motor size, its power, radiator type along with many other details of the cooling system. I think this will be the hardest part
To reduce the heat introduced from the air intake it came to my mind the idea to use a peltier module
Using a Peltier module can only make things worse. A Peltier module consumes electric power, and power is heat, and heat is not wanted. This is for the same reason that putting a refrigerator in the middle of a room with its door open will heat the room up.
Power consumption is something I must care about since low energy consumption is one of my main targets. The water pump is only 400ma, but the blower motor is 6A. I saw so many people talking about perltier modules power consumption and although I think to only need a 400mm block, the energy efficiency seems to depend from how the system is designed.
Apart from consumption, I suppose you refer to the heat side (the hot heatsink) of the peltier module system showed in my diagram, right?
What if we redirect the generated heat outside of the room just like does regular air conditioners?The modification of an existing window is a very cumbersome operation and not feasible. However, it should be pretty easy to get through a door with a small exit pipe with little or any modification at all. We could do the same even for whole working system although I believe it would be useless if we use a peltier module (which reduces the heat entering from the air intake through the cold heatsink).
Here is a simple calculation for cooling a room, if we assume the ice chest contains water ice. The calculation with gel packs will be similar, but I don't have the numbers for those. Also note that none of these calculations will involve the temperature of the cold air flow.
Firstly, assume a typical room size of 4 metres by 4 metres by 3 metres. We will assume the room is perfectly insulated and no heat can get in from outside (not true in reality, but gives a best case scenario).
The volume of the room is thus 4 x 4 x 3 = 48 m³
The density of air is 1.293 kg/m³.
Therefore the mass of air in the room is 48 x 1.293 = 62 kg
The specific heat capacity of air is approximately 1 kJ/kg/degC.
Therefore, suppose we want to cool the room down by 5 degrees C, then the heat removal required will be:
M cp ΔT = 62 x 1 x 5 = 310 kJ
This is the amount of heat to be removed to cool the room air down, one time only, by 5 degrees.
Next, consider the ice (the source of cooling).
The latent heat of fusion of ice is 336 kJ/kg. This is nearly the same as the heat removal calculated above.
Therefore, it will take about 1 kg of ice to cool the room down by 5 degrees, once, assuming the room has perfect insulation.
In reality of course, the room is not insulated, and it will keep warming up again. The rate of heating depends so much on the room, but let's assume it happens in less than an hour.
How much ice can you put in the ice chest? Maybe 10 kg? It depends on how big it is.
So I think the device could achieve a little bit of cooling, for a short while.
Probably it is better not to try to cool a room down, but rather to direct the cooled air directly at you, and just enjoy the cool air flow while it lasts.
My room size should be approximately the same (at maximum 30% smaller) and all the other parameters you mentioned match.
I'm afraid that trying to estimate whether it is possible to cool down a whole room to the desired temperature is a challenge.
For example the "Deluxe DIY Air Cooler!" project seems to have a similar room with an additional hallway of unknown size. It's unclear about the time needed, but he has been able to drop the whole room temperature from 27C to 25C. Whether 2C drops is the maximum achievable or not I don't know.
However, even if the desired temperature is only achievable on a limited area (let's say 2 cubic meters) it would not be bad although I designed the whole unit with in mind higher expectations.
It would be great if 1 kg of ice can cool the room down by 5 degrees.
The ice chest is 52QT, so I would say it should be able to contain around ten gel ice packs positioned vertically and probably additional 6-7 ones placed horizontally on top of them. Each gel pack is 1 liter and I can't find the weight on the specs.
Hard to estimate, but I believe it should be more than 10Kg. Problem is that the refrigerator does not have such capacity (unless I take off the frozen foods).
1 hour is the time lapse you estimate the unit will be able to keep the desired reached room temperature until the ice melt down and cooling capability ends up, is that right?
Cool air in the project I have just mentioned lasted 4 hours using 2 frozen gallon jugs and a couple of regular ice-packs with a temperature dropped from 27C to 25C. There are too many variables that makes impossible an estimate, but under the same conditions, given how my unit is designed and the parts being used, I would expect at least twice (at worse).
A follow up note. A small window air conditioner might be able to remove about 5000 kJ of heat from the room air per hour. This clearly is vastly more cooling than the little ice box thingy can achieve. So I would not expect too much from it in terms of actually cooling a room down.
Unfortunately in none of such projects I saw such data available, so I can't compare. Regular air conditioners have the advantage to transfer the heat outside the home. This is why I'm thinking to a peltier module integration. Probably my design for which I posted the diagram is not good because I suspect that the cold heatsink of the peltier system placed in front of the air intake still allows some heat penetration even if the heatsink is below 0C. There must be a way to completely redirect all the heat. Heat redirection should be probably the easiest task: a blower motor placed above the hot heatsink (rather than the black fan you see in the diagram), then a duct from the blower outlet until the room door, then a small adaptor that send the airflow into the slot located between the bottom side of the door and the floor (in this way I can even keep the door closed).
However, what I see with an 8 row radiator like mine seems to give good hopes:
Same location and conditions except that room temp dropped to 15C instead of 25C.
Unfortunately I can't do any reliable comparison with the unit running under the bigger blower motor (the one for which I posted the thermal camera screenshots) because it has been tested outdoor, but even in such conditions the guy was still able to cool an area.
So, before thinking to peltier systems and any other stuff I should focus on how to get all the available cold provided from the radiator because as is, with a 270CFM four inches blower, I suspect that a good amount of cold is lost.
If you have any suggestions, please kindly let me know.
Honestly I really don't know what to expect. Your calculations does not match at all what I see in similar projects, but it is better that I'm prepared even for the bad scenario you expect. And with this well in mind, I think that I should postpone the purchase of the temperature controller, am I right? If I will not be able to reach the desired temperature in the room, there is no point to regulate the blower speed based on the detected temperature because I will have to keep it running at full speed all of the time.
Edit: A controller could be helpful even in such case. I could use it to regulate fan speed to cool just the target area, no more and no less.