Desert cooler with ducts to cool entire home

anupmathur

Super Moderator
Staff member
.......
Like I said, we can manage with our jugaad well enough, but sometimes I do wish we had a more professional player in this space.. ....
:)
Hehe, there are professional players! Just that they focussed on the least effective forms of a cooler, the small ones that are mounted on a trolley and are used indoors! :shock: :(

I also wish that one of these biggies would have the good sense to supply proper and professionally made desert coolers for the domestic space.
 

dzarg

New Member
@Mathurji
Here's the site for Ram coolers I found that might make some sense. I think if a company can get a chowk (that too in nagpur) named after it, then it must have a decent track record. :) Also I would intrinsically trust a company from Nagpur, having a good way to cool yourself there is pretty much a life or death question. :)

I especially liked the FAQs, there's some solid numerical data not just marketing jargon. for eg:
For every 100 square feet cooling area, allow 2 square feet of unrestricted air relief through windows or doors.
(They also offer 5 year warranties that seems pretty unheard of.)

Maybe worth trying? If any Nagpur based BCMtians can share their experience that'd be nice. I am particularly interested in their ducted models, because they have cooling pads on all 4 sides, that seems like a good idea. any thoughts?
 

anupmathur

Super Moderator
Staff member
....
Maybe worth trying? If any Nagpur based BCMtians can share their experience that'd be nice. I am particularly interested in their ducted models, because they have cooling pads on all 4 sides, that seems like a good idea. any thoughts?
In fact their ducted models are the only ones using fans of size larger than 21".
As for pads on all four sides, it hardly makes much difference.
All desert coolers in the US have cooling pads on four sides and downward blowing fans, since the coolers are mounted on roof-tops.

I see nothing special in their coolers except the fact that they have documented their products well.
There is no data other than the exhaust area required per hundred square feet! There is no study of relative humidity versus performance and cooling efficiency, and there is simply no study at all, no field measurements, no gathered data.
There is nothing to give them special status.
 

dzarg

New Member
I agree with you regarding the fact that a lot more data could have been provided.
I have yet to see an Indian manufacturer with such a habit, so if you do come across such a miracle then please share it with me. Until then it will be a trial and error process to see what works and what doesn't.
 

anupmathur

Super Moderator
Staff member
... Until then it will be a trial and error process to see what works and what doesn't.
Hey, it's not trial and error, as far as I am concerned. Have been using coolers for decades now! :)
I know exactly what will work and when.

What specifically are you interested in knowing?
 

dzarg

New Member
thank you for offering to share your hard earned gyan, I really appreciate your input.

I did have a few doubts:

- in terms of fan parameters:
What is the optimal rpm for a cooler fan that needs to cool an area of say 500 sqft? (assuming 40 degC external ambient temp, 20-30% external RH and avg 10ft ceiling height )How do you size the fan diameter and no. of blades?

- The wood wool mats that I am using are about 2mm thick, they are the standard size available in the market. They seem to sag unevenly after using for a few weeks, and I was wondering if placing 2 (in effect doubling the thickness) in each pad would be better.

- I have seen a few tall cooler models, that have a fan mounted parallel to the floor. (i.e the axis of the fan's rotation is perpendicular to the floor.) The cool air is then pushed out through a duct on top of the cooler. Is there any advantage to this?(maybe from having the 4th outer surface also covered with pads)
 

anupmathur

Super Moderator
Staff member
Your questions about the fan are not really relevant as there is little choice in the market. You are constrained to buy what the market offers. And it is indeed the best approach for keeping costs down.
Anything custom built costs disproportionately higher.

The fan should be of the largest size possible and should be used at the lowest possible rpm.
All branded fans have a CFM (or m³/hr) figure marked. This can be a good guide to select a fan that delivers the highest airflow at the lowest speed.
Amongst the best available in the market is the GE Alstom 24" 900 rpm fan. This needs the large box for which ready made cooling pads are not available. Each pad is individually stuffed with loose wood shavings, packed to your desired density/thickness.

The thickness of the stuffing should be at least half an inch. When I was using the smaller boxes (21" fans) I always installed two pads in each panel. I have mentioned this earlier on this thread.

These days it is easy to fit a continuously variable electronic speed control. What this means is that sizing issues no longer exist. Buy the largest fan and box that you can afford and adjust rpm to control capacity.
A large fan noiselessly purring away is a far better solution than a small fan zipping at high speed to meet the demand.

The interesting thing about cooling with desert coolers is that any and every room of a connected/contiguous house can be cooled effectively, without the need for rooms to be 'in line'.
These fans 'pressurize' the house; air can flow effectively even if there is a U-turn involved. All that is required is to control exit paths (doors or window openings) to distribute the air flowing through each room.

Ducting can be used but in very short lengths. These fans are simple axial fans and cannot build pressure like centrifugal fans. The moment you look at centrifugal fans you are in the territory of industrial equipment and costs soar! Moreover, centrifugal fans are much noisier than axial fans and would definitely need to be mounted far away, like on the rooftop.

Ducting should be physically isolated from the cooler housing to minimize noise transmission. This is best done with a canvas ring or bellow as the coupling element between the cooler body and the ducting.
Some amount of acoustical absorbent is desirable in the ducting to reduce noise and resonance.

Having four cooling pads, as in top mounted fan boxes, offers larger cooling area (better cooling efficiency) and is an advantage. However, I have never felt the need for it.

The most important limiting factor for desert coolers is the relative humidity. The outlet temperature does not depend on the ambient temperature; it is determined by the RH only! Hard to believe? Well, that is how it is. :)

Once the RH crosses about 40% the efficiency of evaporative coolers drops off sharply. They become humidifiers, offering no appreciable cooling! :eek:
Ideally the RH should be 5 to 25%. Desert coolers put air conditioning plants to shame in such weather.
 

pushkark

Active Member
In Mumbai with humidity in excess of 70% the coolers are of no use. The only solution is using air-conditioners.
 

dzarg

New Member
Thank you for the detailed reply. Sorry for missing your earlier comment about the pads, it escaped my notice.

Going by your fan specification, is your cooler something like this?


Air Cooler (R-800)
Avail from us Air Cooler ideal to be used in offices owing to its effectual cooling, noise free operation and urbane humidity control panel.

Specifications :
High Efficiency cellulose pad (900 mm x 900 mm x 200 mm)
24” Exhaust Fan 900 rpm
Suitable for cooling room area 800 sqft.
Low Electric consumption(550 Watt)
Excellent carton packing
Supplied with remote control units
Frankes White color

Dimensions : W x D x H : 36 x 32 x 46 (inches)

Price : Rs. 25900.00 (Ex. Our works)
This seems like a pretty jumbo sized machine indeed! What do you do about it for the rest of the year when not under use?

The interesting thing about cooling with desert coolers is that any and every room of a connected/contiguous house can be cooled effectively, without the need for rooms to be 'in line'.
These fans 'pressurize' the house; air can flow effectively even if there is a U-turn involved. All that is required is to control exit paths (doors or window openings) to distribute the air flowing through each room.

Having four cooling pads, as in top mounted fan boxes, offers larger cooling area (better cooling efficiency) and is an advantage. However, I have never felt the need for it.

The most important limiting factor for desert coolers is the relative humidity. The outlet temperature does not depend on the ambient temperature; it is determined by the RH only! Hard to believe? Well, that is how it is. :)

Once the RH crosses about 40% the efficiency of evaporative coolers drops off sharply. They become humidifiers, offering no appreciable cooling! :eek:
Ideally the RH should be 5 to 25%. Desert coolers put air conditioning plants to shame in such weather.
Fully agree with you reg the fact that its possible to cool a bunch of rooms, although I haven't observed the U-turn effect (maybe because I have a lesser spec cooler). In my case all the contiguous rooms in a straight line get cooled. Nothing beats the cooler in summer (esp since the AC makes it even drier), plus the power savings are just incredible. I hope people in the non coastal regions come to their senses and use this more effectively. It drives me crazy to see all the heat islands and air conditioned malls that are sprouting all over, and apartment blocks stuffed with ACs.
 
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