Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

It's getting quite hot!

Status
Not open for further replies.

HugoC

New Member
Hi guys. Ok, I'm looking for a practical solution to a REAL need.

The situation:

My daughter, a Canadian (hence used to cool weather ;) ), works for a Canadian humanitarian organization (CUSO) in Accra, Ghana. Most probably she will be there for the next few years. She tells me that the home electrical power delivery is shut down for a period of 8 to 12 hours at a time, every other day or so, mainly at night. Hence, there are 2 problems she is faced with.

The needs:

1- Food conservation. Her fridge, being out of work at this rate, it's obvious it can't be of any practical use. But she (they) manage to accomodate themselves with local traditional food market, although....

2- The most difficult problem she really is faced with is with is getting good night's sleep due to high temperature and the impossibility to have the ceiling fan to work to get at least some form of breeze to freshen herself. Presently they are experiencing 38-40 deg C, daytime, and most probably around 30 and humid at night.

Shure, there is a simple solution around this. Using a gas power generator (such as Honda's). But remember, this is Africa, not USA or western Europe where on can just walk in a store and leave out with one of these. Anyhow, it seams there is none available in the area and , be it so, it would most probably be most prohibitive on her budget (and noisy for the neighbourhood!) to buy and/or operate one!

So the first idea that came to my mind was there could be a way to activate a fan powered from a 12 volts car battery. The battery would be recharged during the period the electricity would be back on. Talking the matter a bit with my daughter (I was in internet contact with her when I started writing this) she told me that she just learned that the locals have manage some way to achieve that through their own resourcefulness. Necessity is law!! I do not have all the details but it seams it goes something like this.

As I understand it, they would use a car radiator fan, the battery and the alternator, with its electronic regulator, to recharge the battery when the electricity is back on. I presume they are coupling the alternator to some a/c motor they found somewhere. I also assume it ain't a simple affair to get a suitable battery charger over there. But it wouldn't be such a problem for me to find the appropriate stock, here in Canada, and having it ship to her through CUSO forwarding facilities. At least, I 'think so' ;)

This being said, I don't know how many watt-hr a car radiator fan motor, operating for let's say 8 hours straight (a night of sleep), would drain out of a battery. In other word, what would be an average amp rating of such a motor operating at 12 volts?

But whatever this rating is, I'm pretty well shure that using it for that period of time would mean a deep discharge for any regular car battery, each and every time the fan would be operated like so. I'm aware that regular car batteries aren't made for that kind of deep discharges and more so on a repetitive fashion, over 800 time for the next 3 years we may assume here.

So I'm thinking of a system based on a deep discharge capable battery (with an adequate charger system) able to sustain 1000, cycles at an affordable cost, about 200-300US$.

- Is that wishful thinking that, with available consumer items, such a system could be built?

- Would someone know a good figure for a car fan motor amperage and how noisy it would be if used inside a room?
My guestimate is it would be about 5 amps. So 5Ax12Vx8Hr= 480 W-Hr per shift. So to be on the safe side, in this instance, the battery should be of at least 800 W-hr capacity.

I just learned that a gel battery system could do the job for the right price. What do you think?

As for the needs for the fridge, I have no idea at this time. I'm opened for all suggestions if any.

Thanks for giving a thought on this,

Hugo
 
The amount of energy required to turn a fan for personal cooling is no where NEAR what is required to turn a radiator fan for a car, in fact a car motor would likely give the user windburn.. Humans only need the slightest of air currents for personal cooling. What you want could probably be achieved using a few large rocks or any other available weight on a pulley/gear system from a decent height (tent height) with enough static resistance to keep it from unwinding all at once. If this is in the bush so to speak the first thing you need to avoid is electricity.
 
Modern people seem to forget simple mechanical methods of producing energy and rely on electricity FAR too often.
 
If you are going to buy a fan, why use one built for a car? There are many 12 volt fans made for boats and RVs. Some alternative energy sites might point you to a better value (enegy efficient). There are propane powered refrigerators and AC units, but getting a tank filled might be a problem.

Just a few thoughts...
 
Sceadwian said:
Modern people seem to forget simple mechanical methods of producing energy and rely on electricity FAR too often.

Well said. The first thing to come to mind for this problem is to rig a cord around the shaft or a pully wheel on the ceiling fan that pulls very slowly as a weight at the other end of the cord is allowed to fall slowly to the ground over the course of a night. I don't think it takes much energy to keep a ceiling fan turning so it would seem feasible to have a large stone taken to a high point, perhaps up a tree or top of the building, just by carrying it up or pulling it up with a rope and a pully. Alternately, a tree might be used as a spring. It would be quite clever to rig up a giant 'watch movement' that turns the fan blades slowly using the spring energy from a bent tree.
 
The fridge problem might be solved with insulation, depending on its quality. It should maintain an acceptable temperature for 8-12 hours if you add a blanket around it and open only when necessary. Use a thermometer so she can tell when the temperature isn't cold enough. There are suitable natural and man made insulation materials everywhere.

You probably will get enough (maybe too much) air movement for personal cooling with a standard 80mm 12V computer fan (such as All Electronics CF-257 for $3). It uses 70 mA, so it would run up to 65 hours on a 4.5A/Hr battery.

This fan's drain is small enough that a small solar array (such as All Electronics SPL-6012 for about $30) or two could keep it charged.

I assume you can send a package of a few kg to her.
 
Especially not one with large blades which is most efficient, it needs to spin slowly. I often think these applications of potential energy as electrical or mechanical energy storage are far too often overlooked. You can find hand cranks on portable radio's and LED flashlights that provide mulitple minutes of use out of a short minutes worth of effort. Considering the cheapness of human muscle I don't think I'd have a problem moving a lot of smaller weights to get power for my activities (asuming the items were power savy)
 
Considering the objective is cooling, I hesitate to suggest physical activity as an energy source. I suppose you could lift the weights in the morning......
 
I wasn't even considering the fridge, insulation aside it takes a lot of energy to cool bellow ambient. The fan for human cooling is much simpler as it just helps accelerate cooling to ambient, or allowing natural perspiration to do the rest.
 
During huricane season, I place two 1 gallon jugs of water in my freezer. Power goes out, I move them to the refrigeration part. Also gives me two gallons of clean water. Never had to go a full 24 hours without power.
 
Once you're past 24 hours without power evacuation is usually more important than the temperature of the fridge.
 
The math?

A joule is the work used to lift 102 g one meter against gravity.
Assuming the mechanical requirement of the fan is 5 w-h (1 watt for 5 hours.)
A watt-hour is 3600 joules.
That's 18 thousand joules to operate the fan overnight.

Requires raising 1020 kg 1.8 meters?

Seems like too much - please correct me!
 
I know this is an electronics forum, so sorry for the lo-tech answer. I completely empathize with your daughter's sleeping difficulties - I need my sleep, too, and I'm much more comfortable in colder climates.

The answer is: dig a hole. According to my Dad (arguably the smartest person I've ever met, and I've met a lot of people), if you dig six feet below the Earth's surface just about anywhere on the planet, you can pretty much guarantee that the dirt down there will be somewhere between 6 and 10 degrees Celsius. Seemed a little weird to me at first, but it does explain why underground water pipes in Canada don't burst from freezing: it just doesn't get quite cold enough down there. I'd wager that the inverse is true in Africa: if you want to keep something below 10 Celsius, your best solution is to bury it deep.

Please don't think I'm trying to pass off a glib answer or have fun at your expense. I really think this is the best solution, given what your daughter has available. The easiest thing for her to do would be to find a basement somewhere to live. I know living in a basement isn't fun, but neither is losing sleep because you're too hot. If she's somewhere that doesn't have basements, I suggest she makes one. Seriously, this seems like the easiest solution to me. After you dig the hole (all you need is some shovels and friends), there's no expense or hassle to keeping things cool (like trying to find fuel or electricity). The only problem I can foresee is keeping moisture out, which with proper ventilation would solve the problem. No blackout hassles, and a guaranteed temperature for a goodnight's sleep. If she's there for as long as you anticipate, it will be well worth the effort. Try to find out as much detail about what the ground's like where she lives, research how to build a basement, and I'm sure you'll be able to come up with a good plan.

The easiest solution is for her to go where it's already cool. In Africa, that's underground.

Incidentally, this is also the quietest solution. The quietest solution for keeping food cool is to have a solar powered convection fridge kept in her basement. You could buy/construct the solar panels here and then ship them to her, but I don't know how easy it will be for her to get a fridge (she may have to compromise on that one). Sorry, but this also presumes that where she lives gets a lot of sun.

While my answers may require greater initial effort on her part, I think she'll find them the most satisfying since they ultimately permit greater independence from other factors.
 
Last edited:
It's not glib, there are people in the states makeing boatloads of money sellings systems that use this simple fact (putting cooling loops 6 feet bellow ground and passing the output through a compressor) works as both a heater or a cooler depending on how the external compressor/heat exchanger is configured. Never occured to me you could just dig a hole =) Simple, elegent, works. Cudo's to Hank.
 
Keep in mind that the earth at 6 ft or so below ground stays at a relatively constant temperature but only if relatively undisturbed. The ground loop is a relatively good example - bury the pipe and circulate fluid thru it and if you do not add or subtract heat the fluid and earth in immediate contact with the tubing remains at that constant temp. Start adding heat or subtracting heat and the fluid and ground does warm or cool. Here in Rochester the fluid from a ground loop pump will be well below 40 degrees F as winter progresses and up toward 70 or more well into the summer.

If you were to dig a basement and allow some warm air to circulate, the basement would warm somewhat - though it may remain siginficantly cooler.
 
Sceadwian said:
It's not glib, there are people in the states makeing boatloads of money sellings systems that use this simple fact (putting cooling loops 6 feet bellow ground and passing the output through a compressor) works as both a heater or a cooler depending on how the external compressor/heat exchanger is configured. Never occured to me you could just dig a hole =) Simple, elegent, works. Cudo's to Hank.
HVAC systems using compressors to cool and heat are known here as Heat Pumps. They work best if you can drop the coils into a water.

Wikipedia said:
Higher efficiencies are achieved with geothermal (ground-source or water-source) heat pumps, which transfer heat between your house and the ground or a nearby water source.

In Colorado there are examples of Mediterranean greenhouse that bury many feet of 4 inch plastic pipe under the greenhouse. Moving air heats the soil and cools the greenhouse by day and the reverse happens at night If you want to cool all the time you must need a quite large area to dump the heat.
 
It depends on the climate.

Deep underground the temperature will be roughly equal to the average annual temperature, here in the UK it's about 8 to 12 degrees (depending on where you live) C but in the tropics it's likely to be around 28 degrees C.

If you live in an extreem continental climate there will be variations in temperature, just not as much as outside, for example it might be 5 degrees in winter and 15 degrees in summer.
 
Tell her to relocate to a more comfortable climate! Ghana likely won't miss her. Not much is going to ever change there or in the nearby countries, just like it hasn't for hundreds or more years in the Middle East. They don't come to the water... they want the water to come to them.
 
The fan issue is best solved by using a normal ceiling fan and a power inverter. A fan might take 20W-60W. For a large 100AH deep cycle batt, 8 hrs is not unreasonable. However, that batt will require a lot of power to charge.

Solar is often a good choice. A car alternator might require an hour to charge that batt and thus might require a whole gallon of gas to idle like that.

This is a good setup because it makes a limited amount of 110V available 24 hrs a day and when you need 110V, you need it.

Fridge- well, there's super-efficient 12V fridges out there, they use Danfoss compressors. Expensive. Require 4amps when turned on, how often they spend on depends on interior temp setting, outside temp, and insulation. Unfortunately it would be easy to exceed the daily capacity of a medium-sized solar panel with this unless extreme measures are taken.

One alternative, very common, is an ammonia adsorption-based "Servel-cycle" fridge. "Dometic" is the primary mfg these days. It has no moving parts and requires no electricity. It runs off of a heat source which evaporates hydrogen out of the ammonia, they bubble through a series of cooling tubes, and get cold where they remix in a mixing chamber. It's a sealed system, you never see the liquid. Silent too. Most run off of propane for the heat source. A 5 gal BBQ tank would probably power one for months. People use these for hunting lodges and such all the time, they do work and are practical in SOME instances and I think you've got one. Many fridges for holding vaccines in third world countries are this type.

Many RVs, campers, camper vans (Volkswagon campers too) have used this type for decades. Unfortunately some are damaged, if run when not level it can stop flowing, overheat, and become damaged. It will take some looking but you should be able to find a working one at a reasonable price.

However, it is simply not efficient or powerful enough an effect to air condition a room. Its primary merit is that a 5-gal tank of propane holds the energy of about 3 tons of 12V deep-cycle batteries, or in some cases a plant might have waste heat (free!) of the appropriate temp to run the ammonia boiler. It still requires a LOT of liquid and a lot of cooling fins to be used for room air conditioning.
 
in the old days where i live the ceilings were high so the gradient of hot air woud be higher off of the ground and they used double hung windows where on one side of the house you would open the top of the window and the other side the bottom. this would cause a crossflow through the house as the heat rose up and out the upper window and outside air came in the lower. and don't forget the screens : )
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top