Affordable Air Conditioning

I never see ac units under around 5000 btu. Are there 2500 units etc?

I don’t know but there should be .

Never heard of the Davy principle, but I don't think this will work....you have to cool the entire room...You can lower the cost by sealing off air leaks making the room air tight and using R-30 insulation on the walls, floor and ceiling...a small 5,000 btu unit only draws about 600 watts and wouldn't need to run much if the room is properly insulated and sealed...

Davy’s safety lamp was used in mines before the advent of electricity. When a hot wick lamp is surrounded by a wire mesh, even if there are flammable gases such as Methane around, they would not ignite. This was called Davy’s safety lamp and was used extensively then.

in our homes, to prevent small insect entry,windows are sometimes covered with a mesh. There will be practically sealing of the air inside making it hot, humid and uncomfortable.

When you say it would consume 600 watts,that means in a day of 24 hours,14.4 KWH will be the consumption. With per capita earnings around Rs.2,000/- per month, and cost of electricity being Rs.5/- per KWH bill would itself be around Rs.2,100/- My figures are approximate but indicative. A small house hold in our country uses around 300 KWH per month and at lower levels of consumption, tariff is lower too. Hence my suggestion.

Yes I am familiar with the Davy's safety lamp....that does not apply here...the room must be sealed for the air conditioner to work properly....the ac unit will not run 24/7 if properly sized, and as you suggested, only at night...I have been an ac contractor for over 30 years...If the room is insulated and sealed as I have suggested the ac shouldn't run more than a few hours a night....the key to your success is proper insulation and no air leaks, this reduces the heat load and makes the room hold the cold longer....

Eliminate leaks. It's the same principle the whole world over. At these latitudes, the use of draught excluder around all external doors has been the solution to keeping the place warm, economically, for many decades, as has been the use of loft insulation, as indicated in the image.

Go for it.

Here is a link that may have some merit,but I am not sure about it's validity. =====================================================================================================https://www.geek.com/tech/eco-cooler-air-conditioner-cools-a-home-without-using-electricity-1657343======================================== You will have to copy and paste the links.--------------------------------------- And here is another one that may be expounded on.--------------------------------------------------------------------------- http://idxwebdesigns.com/canadian-students-have-invented-a-fridge-that-runs-without-electricity/--------------------------------------------------------------------------- and another one:------------------------------------------------------------- />--------------------- https://thefederalistpapers.org/us/breakthrough-israelis-invent-paint-cools-house-no-electric-bill-----------------------------------------------------------------------------------------------------------------------------------------------------------

Re:- Davy Lamps. The fine metal mesh cools the flame propagation front when it tries to pass through the mesh. The gas does combust within the lamp cage when it hits the flame inside = blue flame, which shows the miner gas is present and they are supposed to leave while the mine fans clear it.

Davy Lamp

The heat load is more important than the size of the room.Consider a small oven:It will take a large air conditioner to cool it even though it is asmall. Insulation of the area will pay many for itself many times over and continue to pay long after it's installation.Of course,like most other things,there is a point of diminishing returns. The ground temperature must also be considered.Swamp cooling is more efficient,but it does not work well in high humidity climates. Do you have plenty of water?What is the construction material of the buildings? Perhaps a double wall construction,with a porous out wall,and a non porous inner wall is a possibility. With a layer of wet absorbent material in between the inner and outer walls,the evaporation through the porous material will drop the interior temperature dramatically.

My point was to create a space within the bedroom that would be fraction of the total air space, so that the quantity of air cooled would be lower than the whole, of course with a little leakage of cooled air. Most members are suggesting that the room primarily should be better insulated, use alternate systems that do not need electricity, so on and so forth.

Iwould welcome any improvement over my suggestion or posts that say why it does not work.

<...why it does not work...> All things work after a fashion; this is really a question about economy of operation. In every case, the fewer thermal leaks in the cooled space, the better, because the equipment won't need to work so hard, and will therefore cost less to run.

The recommendations above are all valid.

The equipment needs to be some distance from the <...cooled...space...> as its noise output could disturb the occupant while sleeping, which means ducting the cooled air in from somewhere else, with attendant need to insulate the ducting.

We have split air conditioners where the compressor is situated away from the room and it does not at all disturb the people inside the bed room. Secondly, the bed area could very well be insulated with a simple overlapping cloth/felt entry/ exit.

This space is not going to be hotter than the room, except for the biological heat of the sleepers. The thermostat control would be inside the space as well the grill with fan.

You don't want cold air blowing directly on a person, especially when the're sleeping...this would be detrimental to their health...the tent idea would not work well because the insulation would be lacking, leading to constant short cycling of the A/C unit...not good

The "little leakage" of the cold air is a problem for 2 reasons, the room never reaches temperature and the cooling unit runs non-stop, and the cool air hits the warm air and causes an increase in the humidity, a clammy uncomfortable environment to be in...

Forget the Davy safety lamp. The Davy lamp works because the wire gauze absorbs heat from an advancing flame (quenches it) so that the temperature falls below the ignition temperature of the explosive atmospheres sometimes found in mines. I don't see how it would work to keep cool air inside an enclosure.

https://en.wikipedia.org/wiki/Flame_arrester

However, if you have some type of insulated tent over your bed, you should be able to cool the air inside with less energy than cooling the entire bedroom. Possibly you could recirculate part of the air from your air conditioner, but if you're sleeping under it, you need some external fresh air and some leakage to exhaust the stale air. Ideally, you want your tent well enough insulated that the heat transfer is mainly through the exchange of air.

https://www.exploreoutdoorshq.com/camping/best-tent-air-conditioners/

Your problem will be with the ventilation. The smaller you make the space and the better you insulate it, the more stuffy and uncomfortable it will become. The only way round that would be a ducted ventilation system with an efficient heat exchanger.

The problem with building a warm refrigerator around a bed is the occupant inside the refrigerator needs to breathe. To make cooling/heating of any airspace as efficient as possible the air cannot exchange outside of the box, all refrigerators do this. Most rooms have a large enough volume that oxygen consumption and carbon dioxide buildup will not be a problem.

What might be a more practical and safe idea is a chilling blanket or pad for the bed.

You are forgetting that the body at rest produces 150 watts. With a couple sleeping in the "quranteed-off volume", you will need at least a 1000 BTU unit to prevent the volume from becoming uncomfortably HOT.

And with the 'two bodies' exercising, . . . as they may well do, . . . you will need a 2500 BTU unit.

Sounds like you want to put a screen door on a refrigerator.

Unless I am mis-reading the OP.

I think you nailed it....

This is a valid and oft suggested concept. I have even done it in my student days. All you need is 1000 BTU or so to cool the smaller space. With bubble wrapped ducts you can quieten the space by isolation. In fact, you can use a small dehumidifier to reduce the humidity in your segregated space so your normal cooling body based cooling works.

A dehumidifier is just an A/C unit that exhausts back into the room...it actually raises the temperature in the room...

You are right,but an air conditioner will decrease the humidity in the room as well as cool it.That is why they call it "air conditioning." Some people think a bigger A/C unit is better,but an air conditioner that is too large will short cycle,and never run long enough to reduce the humidity,resulting in a decreased level of comfort and wasted energy. Proper sizing of the unit is important,and requires some calculations involving number of heat/cool days per year. A very rough rule-of-thumb is 20 Btu's per square foot,but it is only a starting point for the calculations.Environment and ceiling height and number of windows and insulation,etc. are all important factors to consider.Manual "J" is the go to standard in USA.

I'm seeing lots of different approaches that all have validity and it would seem that each has a preference based on their historic experiences.

Insulation of the room space is always a good idea to preserve the value you have invested to condition the air.

Your proposal to reduce the volume is valid also meaning there is less to be conditioned.

It would also be beneficial to reduce the mass of the contents of the conditioned air space, since you will be trying to cool those items also from their daytime temperature. The wall materials will also play a significant role in this especially if they have residual heat from the day.

Room layout can assist. If you have wardrobes/cupboards located along the external walls, then with doors closed they behave like a thick layer of insulation for that portion of the wall.

The strategy with evaporative (swamp)systems is very different to what most people use in Western countries. You need to allow the air to escape so that fresh cooled air can enter the space. These however have limitations of the temperature drop achievable based on the relative humidity.

Where I am currently living we had multiple 45C+ days this summer gone and the evap was able to provide outlet air at around 35C. When the nights got down to 35C,the house was around 25C and we would turn it off. Morning temp around 28C.

While this is not the 20C that some would target, it is refreshing after time outside and not too shocky when you go outside again. Humans are wonderful at acclimatising to the environment, but gee that 10C difference is appreciated.

A very primitive but effective evaporative cooler ("Swamp Cooler")can be designed very cheaply by hanging wet blankets around the room and if you have a small fan,use it to blow air across the blankets. An oscillating fan would be better than a stationary one. If your relative humidity is low,this will work surprisingly well,but the temperature of the cooled air can never go below the wet bulb temperature,and this depends on the relative humidity. This is very effective in a dry climate but you do not state your location,so the results are uncertain but it is worth a try,and very inexpensive. We used to store milk and fresh vegetables in a root cellar,dug into a rocky hillside,with a small constant drip of water splashing onto a rock below.It was surprisingly cool inside. In very dry climates,the air can be 25 degrees F. lower than ambient.however when the Relative Humidity is around 70 percent, only 5 to 10 degrees F is possible,but even then it feels good. Hope this helps.Good Luck!

A plastic bag, rather than a net would be indicated. Just be sure you get the minimum number of air changeouts to maintain the oxygen level.

The Davy's lamp worked by chilling the flame with a cold wire mesh. The mesh would not restrict the outflow of cold air.

You might find that a dehumidifier may be a better approach to obtain comfort if the normal humidity is high.

I once made a hat of sorts from a length of clear plastic tube. Above the head was a large funnel (of sorts) where ice was placed as needed. Below was a drain for the drizzle of cold water..

I guarantee it works fine and that you would be the second person in the world to have this exclusive device.

(Cool the brain blood cool the body)

The best method to achieve a cool room is to prevent the heat from getting in.Then you don't have to pump it out via an air conditioning unit.If an ideal container is perectlly insulated,the temperature inside will remain constant.Heat flows from hot to cold.Cold is simply the absence of heat.Reduce the flow of heat to the inside of the container,and there will be less heat to remove.Therefor Even if you have to add it a little at the time,insulation gives the best return in investment in the long term.It constantly gives back.Shading of the building will also reduce the inside temperature.It can be up to 20F difference in sunlit and shaded objects.If you use an air conditioner,locate it on the shady side of the building if possible.This will improve the efficiency of the unit.Your heat source seems to be radiant as well as conductive and convective.Reducing any of these three will help.There are paints with an insulation factor of R5.They have ceramic crystals embedded,but they are rather expensive.Putting a reflective surface on the outside or inside will help reduce the radiant heat inside.Think foil or Mylar.Especially on the ceiling and walls,especially on the inside.The inside walls radiate heat that they absorbed during the day.If the local climate is low humidity,the wet blankets mentioned previously will certainly help.Even if the relative humidity is 70% they will help somewhat,but they can never get below the Wet Bulb temperature.Use a coarse fabric that will allow airflow to pass through.The effect will surpise you even with no external airflow,such as a fan.Hot air rises,so any vents to the outside should be as close to the ceiling as possible.

On the contrary, people at rest are ~~60 watt heaters, and they breathe so new air is needed.

There was an australian company that used a sealed unit for personal airconditioning that ran a vibrator on the 50 Hz AC, by use of a resonant system that used the third harmonic it ran at 150Hz in a standard air conditioning compression-expansion cycle to create a small cooled sleeping cocoon. I saw it about 15 years ago, I do not know if it prospered in the market place. The idea is valid, but it may have failed on low efficiency grounds.

If you have seen the small aquarium air pumps that work in this way, that will tell you how it worked - those of course are not efficient, but cheap and were not required to be efficient.

It seems to me that something like this could be engineered.

I was unable to find it via search, but I am not sure if I know the terms to search it under so I could find it.

here is one vibratory compressor

By"no external air flow" I meant no need for a fan to blow it past the wet blankets,not that fresh air was not needed.The cooling effect requires a certain amount of airflow for best effect because it increases the evaporation rate.I presumed the air flow from adjacent rooms would be sufficient,since there would be convection currents created by the falling of the cool air. It requires APPROXIMATELY 1000 btu's to evaporate a pound of water,depending on starting temperature of the water and other factors. Four gallons of water per hour evaporating will give ABOUT 8000BTU/hr.

CORRECTION: "Four gallons of water per hour evaporating will give ABOUT 8000BTU/hr." Should read"Four POUNDS of water....."...which is only approximately 1/2 gallon.

I believe the thumb rule is 975 BTU/LBM for a change of state of water.

Not if changing between liquid and solid. For liquid/vapor, it depends on pressure.

I was wrong. The latent heat of vaporization is 970 BTU/LBM. That is a constant except where my memory fades it to 975..

The real value is closer to 954 BTU per pound. Therefor,a gallon of water would be approximately 7961 BTU,at atmospheric pressure,so my math was wrong on the first calculation.

At what pressure?

The RATE of latent heat transfer is determined by many factors including pressure,air flow,relative humidity,impurities in the water,relative speed of the water to the surroundings,etc,etc. I simply stated the available BTU from evaporation if a gallon of water is completely evaporated in one hour. The pressure that was used to derive this value are well known to those familiar with the science to be at sea level, and standard atmospheric pressure,which is 101.325 kPa or 14.7 psi.and the starting temperature is 100C. I have always learned more from the questions than the answers. The questions make me re examine my statements in more detail. So feel free to ask more,so that we both may learn. Thanks for the feedback.

For a gallon of water to evaporate in an hour, the relative humidity would need to be extremely low....that doesn't appear to be the case here, it's a hot humid environment...even if the RH was low to begin with, in a sealed room it wouldn't be for long...Not to mention the perfect level of RH for comfort is 50%, any higher than about 70%, and you have mold and fungus growth...and you are putting your health at risk...not to mention it is physically uncomfortable...

I always enjoy learning from you guys.

As I read through this thread, I reflected on the water bed we had forty years ago, in Canada. There we needed warmth and the thermostatic heater did a great job, even if the room was cold. How about cooling a waterbed, in India?

If you've ever slept on a waterbed that had a failed heater, you know the outcome, so stiff and sore in the morning it takes a full day of rehab....waterbeds have heaters for a reason...

India is a big country,with at least 4 different climate zones.What is the normal temp and humidity in your location? This info will help determine the best method for you.

Right now shade temperature is 46 C and relative humidity around 50. Minimum temperature itself is around 23 C

i did try peltier modules. If you want cooling the hot side has to be quickly cooled. Otherwise it would fail. I did think of a number of them like a screen on the window and to be reversed during winter for heating. They consume lot of energy too and ultimately much too expensive.

usually the bed in our country would be placed touching the south wall and the west wall and the air conditioning unit situated near the roof on the south wall. Effectively only two sides of the bed are thus needed to be covered. My intention of this post was to find out from our friends the type of screen, whether mesh type or sheet and the material. But most of the replies veer from my requirement.

The link below looks promising,but my wet-sheet suggestion can probably achieve the same results using no energy. An enclosure similar to the one they use in the link above is what I had in mind as a canopy. At this point,I have no other helpful ideas that EXACTLY meet your requirements. Good luck.

Air which is colder than it's surroundings will fall vertically unless there is a side draft. You don't need an enclosure around the bed just a method of releasing a supply of cooler air immediately above the sleepers. Check out the web and U tube on how to construct a home made peltier air conditioning unit. 100watts should be enough for you needs. Positioning the unit so that it draws the air from a space cooler than ambient and ducts it to above the bed will help muffle the sound of the fans. There is no noisy compressor just (typically 4) silent Peltier units, a heat sink and fans to direct cooled air into your ducting and hot air away from the heat exchanger. If there is an air space below the house that would be ideal.

How many btu's do you think a 100 watt peltier unit would produce? Peltier units would be the least efficient means of cooling...

https://rimstar.org/science_electronics_projects/peltier_effect_module_cooling_efficiency_test.htm

Perhaps construct a canopy over and around the bed and keep it moist by using pre-calibrated drip nozzles,such as used in greenhouses to irrigate plants.Capillary action would tend to distribute the moisture Four pounds(1/2 gallon(approximately 2 liters) of water per hour evaporating will give ABOUT 8000BTU/hr.at 00% relative humidity.Less effective as RH increases. experimental placement and size of the drip or mister nozzles will determine the best results.Misters are also available which might be better for your purposes. ===============================================================================================================================================================================here is a link.Cut and paste---------------------------------------------------------------------------------------------------------------------------------------http://www.mrdrip.com/680--34-GPH-Barbed-Mist-Nozzle-Bag-of-5_p_332.html===============================================================================================================================================

It is a good idea to have comparatively smaller area to be cooled arrangement. It is absolutely correct that we waste lots of energy by cooling 5 times more air volume and also cooling the relatively hotter outer walls. There is already a product in market see it and let us try to improve on it. Visit https://tupik.in/ for Personal Bed Air Conditioner