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THE AC/Heat Exchanger Thread (merged)

How to save energy through both societal and individual actions.

Re: Reducing energy consumption (AC's) in hot climates

Unread postby rockdoc123 » Tue 01 Apr 2008, 19:57:17

this all seems very climate dependant too me. I live in a place that has cold winters and hot summers. You can't have a house that "breathes" naturally to cool it in the summer as it is impossible to insulate it in the winter. What you can do which is cheaper and more energy efficient than AC is install an electric exhaust fan in your attic or invest in a window reverse circulation fan. I used both in the house we previously lived in and they worked quite well. The attic circulation fan you might turn on for an hour or so just as the sun goes down and it basically evacuates all of the heat that builds up and rises in the house. If you need a quick fix nothing beats one of these reverse circulation fans. Basically you fit the fan into a window where it is perfectly sealed (they come with a expandable frame that fits most window spaces, open a door to let in the cooler air and turn on the fan. It take about a half hour to an hour to fully change out the air in a fairly large home as I remember.
Alternatively if you live in a hot/humid country I think learning from the Spanish settlers is key. They built large haciendas that took advantage of breathable walls (adobe) and natural flow through circulation with large shaded courtyards etc. I've sat in several such courtyards and homes in Mexico and Colombia in 90+ temperatures and it has been quite pleasant.
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Re: Reducing energy consumption (AC's) in hot climates

Unread postby skyemoor » Wed 02 Apr 2008, 22:06:11

rockdoc123 wrote:this all seems very climate dependant too me. I live in a place that has cold winters and hot summers. You can't have a house that "breathes" naturally to cool it in the summer as it is impossible to insulate it in the winter.


RD,

I've seen solar chimneys that were shut up in the wintertime with an insulated panel, so they can be made to work in the summer and prevent infiltration/leakage in the winter.

Your discussion about the fans rings true, I've used something similar in the past.
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Homemade air conditioner

Unread postby Ayoob » Sat 16 Aug 2008, 15:18:41

Materials:

1. 5 gallon bucket full of ice and water
2. Aquarium pump, stuck to the bottom of the bucket
3. Plastic tubing from aquarium pump to copper tube coil
4. Copper tube coil zip tied to the back of a box fan
5. Larger plastic bucket to catch condensation from the apparatus

Method:

1. Stick aquarium pump to the bottom of the bucket with suction cups
2. Attach plastic tubing to aquarium pump
3. Attach copper tubing to the back of the box fan
4. Attach plastic tubing to copper tubing
5. Plug in aquarium pump and make sure cold water runs through the copper tubing
6. Turn fan on low
7. Enjoy nice cool breeze in the room

I keep about five 2-liters 90% full in the freezer for this situation. I'll fill the bucket with ice and water, and two hours later the ice is all melted and the water's warming up.

Before the last of the ice melts, I slip 1-2 frozen 2 liters in the bucket and let that suck the heat out of the water.

A frozen 2-liter will cool the room off for about half an hour or so. It takes a while for the 2-liters to freeze, so I keep a couple bags of ice handy too. As the day rolls on I probably dump another five or six bags of ice and cycle through all the 2-liters twice.

All told it probably knocks back the heat in my bedroom by about 15 degrees all day. The 105 degree heat becomes 90, which is a fucking godsend.

I only get the heat for 2-3 weeks out of the year and every year I think about blowing $800 on a window AC unit and I just can't pull the trigger on it. Not for 2-3 weeks.

Well, it's kind of like that. I don't cool off the whole house, just one room. I sure wouldn't do the living room/kitchen.. that would be crazy. I cooked breakfast in there, the dishwasher is running, the fridge is in there, etc.

But the bedroom, that I can keep separate.

Also, the fan doesn't blow through water, it blows through the copper tubing.

http://www.instructables.com/files/deri ... MEDIUM.jpg

Kind of like that, but I used a plastic bucket instead of a styrofoam cooler, and my copper tubing is in a relatively tight coil on the back of the fan instead of the rorschach test pattern that guy has.

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This is copy/pasted from a thread on another board. Use at your own discretion.
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Re: Homemade air conditioner

Unread postby Novus » Sat 16 Aug 2008, 15:44:04

Sounds terribly inefficient and a lot of work. Save yourself the hassle and buy this micro air conditioner for your bedroom. Costs about $140 with taxes and shipping.

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Re: Homemade air conditioner

Unread postby Tanada » Sat 16 Aug 2008, 16:35:52

Instead of all the messing about with a copper tube why not stop by a junk yard and pick up an AC condensor coil from a junk car? They cant be that expensive and they are already designed to transfer heat from fluid to air.
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Re: Homemade air conditioner

Unread postby 3aidlillahi » Sat 16 Aug 2008, 19:57:09

You're making your own AC so you have enough money for a 50" plasma? How did we ever get in this PO predicament, again?
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Re: Homemade air conditioner

Unread postby Keith_McClary » Mon 18 Aug 2008, 01:47:32

3aidlillahi wrote:You're making your own AC so you have enough money for a 50" plasma? How did we ever get in this PO predicament, again?

But if he has a 50' plasma he won't need a furnace. Think of the money he'll save.

Although, he might want to wheel the plasma outside in the summer and watch it out the window from his air conditioned room.

Also he should realize that any heat removed by his AC must be extracted from water (to freeze it) by his fridge and pumped into his kitchen.
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Re: Homemade air conditioner

Unread postby perdition79 » Mon 18 Aug 2008, 01:59:14

Cool, brings back old memories.

We made things like this homemade a/c when I was in middle school; it was good enough for third place in the science fair. Granted, we used 3 gallons of a 40% rubbing alcohol solution for the fan, ammonium nitrate fertilizer solution chilled with bags of ice and road salt for the heat sink, and copper tubing all around -- ammonium nitrate won't remove heat from water when plastic tubing is used.

That was fifteen years ago. Imagine trying to buy the supplies now! Guys with black suits would be knocking at my door in a matter of minutes, if I even made it out of the feed store!
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Re: Homemade air conditioner

Unread postby alpha480v » Mon 18 Aug 2008, 05:11:36

I think I could find a $100 for a cheap window unit instead of going through all that trouble.
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Re: Homemade air conditioner

Unread postby kpeavey » Mon 18 Aug 2008, 05:51:17

Gotta think bigger:
try a big tank outside stored in the shade on the north side of the house.
Add a pump in the 30 watt range, plumbed to a radiator/fan combo inside the house, a second radiator outside in the shade on the north side of the house, finally returning to the tank

some math:
150 gallons/hour @ 8#/gallon=1200 pounds/hour, can be increased with more flow/bigger pump.
20 degree temperature change, drawn from the inside air, =24k BTU/hour cooling ability

There are many different ways to configure such a jerry rigged contraption.
-more radiator
-more fan
-more flow
-The earth can be used as the thermal dump instead of the outdoor radiator. Burying some sort of heat exchanger underground at 4-6 feet will offer temperature stability much cooler than the outdoor temperature in the shade.
-The indoor radiator/fan can be part of a central air conditioning system.
-Add a solar thermal hot water system on the roof, get free hot water while removing incoming energy from the house

The only requirement for such a system to work is water at a lower temperature than indoors. The cooler it is (or the greater the difference), the better it will work.

some more math

window AC pulling 1500 watts/hour for 10 hours =15 kWH/day @ 12 cents/kWH=$1.80/day

30 watt water pump
100 watt fan
130 watts/hour for 10 hours=1.3 kWH/day @12 cents/kWH=$0.16/day

I use a similarly designed system to heat the greenhouse, costs me 15 cents/month to operate
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Re: Homemade air conditioner

Unread postby alpha480v » Mon 18 Aug 2008, 06:00:48

What's the Cost of the tank, piping labor to dig and install. How much is your time worth? Is all that really cheaper than running a window unit?
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Re: Homemade air conditioner

Unread postby Madpaddy » Mon 18 Aug 2008, 06:08:00

Ayoob,

Have you considered a cooling vest. We use similar products for certain jobs in the army and they work well.

http://www.climatechsafety.com/LiteAir.aspx

Image

You can be cool anywhere and this model costs $129.
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Re: Homemade air conditioner

Unread postby pedalling_faster » Mon 18 Aug 2008, 09:01:03

i use the wet T-shirt technique, when it gets to 85+.

just dunk a T-shirt in the sink, wring it out, put it on.

when it gets into the '90's - i just take a shower once an hour.

when it gets into the 100's - i lay in the bathtub thinking about Peak Oil.
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Re: Homemade air conditioner

Unread postby Ayoob » Mon 18 Aug 2008, 10:57:29

kpeavey wrote:Gotta think bigger:
try a big tank outside stored in the shade on the north side of the house.
Add a pump in the 30 watt range, plumbed to a radiator/fan combo inside the house, a second radiator outside in the shade on the north side of the house, finally returning to the tank

some math:
150 gallons/hour @ 8#/gallon=1200 pounds/hour, can be increased with more flow/bigger pump.
20 degree temperature change, drawn from the inside air, =24k BTU/hour cooling ability

There are many different ways to configure such a jerry rigged contraption.
-more radiator
-more fan
-more flow
-The earth can be used as the thermal dump instead of the outdoor radiator. Burying some sort of heat exchanger underground at 4-6 feet will offer temperature stability much cooler than the outdoor temperature in the shade.
-The indoor radiator/fan can be part of a central air conditioning system.
-Add a solar thermal hot water system on the roof, get free hot water while removing incoming energy from the house

The only requirement for such a system to work is water at a lower temperature than indoors. The cooler it is (or the greater the difference), the better it will work.

some more math

window AC pulling 1500 watts/hour for 10 hours =15 kWH/day @ 12 cents/kWH=$1.80/day

30 watt water pump
100 watt fan
130 watts/hour for 10 hours=1.3 kWH/day @12 cents/kWH=$0.16/day

I use a similarly designed system to heat the greenhouse, costs me 15 cents/month to operate


I've thought about using that for my house later. The ground is about 58 degrees 6-8 feet down, so a water tank buried underground and using heat exchange could cool my house off very nicely in the summer. The hot season only lasts for a month or two.

Using a similar principle, I've heard of using a heavily insulated tank buried underground and heated can pump hot water through the house to warm it up in the winter. There are passive solar water heating kits that use black tubing on the roof of the house, and I can add an electric heater w/a PV panel to warm up the insulated tank. It's cool/cold here about 8 months out of the year, so I'd like to handle that problem as efficiently as possible.

I'm more concerned about heating in teh winter than cooling in the summer, though.
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Re: Homemade air conditioner

Unread postby kpeavey » Mon 18 Aug 2008, 14:38:20

alpha480v wrote:What's the Cost of the tank, piping labor to dig and install. How much is your time worth? Is all that really cheaper than running a window unit?


tank
a plastic trash can from walmart, 34 gallon, about 10 bucks

piping
the garden hose in your back yard
some fittings to get it hooked to a radiator, about 10 bucks

radiator
take the one out of the truck in your uncles yard that does not run
gas to uncle's and back, about 10 bucks

fan
new from the dollar store, about 10 bucks

labor
free, do it yourself

Total cost
if you already have a radiator, a fan, plenty of hose, about 10 bucks

Whatever system works for you and fits with your style will determine the cost. DIY will always be cheaper than hiring a contractor.

While such a system might be cheaper to operate than a window unit, there is the issue of comfort. The window unit can offer a steady stream of cool air which can also be adjusted up or down for flow rate and temperature. Rudimentary systems such as described above may not be as user friendly. This does not mean they don't work.

Ayoob refers to a ground temperature 6' down as being 58 degrees. That is correct for most areas of the world, 45-60 degrees. The exact temperature of a location is determined by factors such as moisture, soil composition, and climate, but is most often within the 50-60 range for most parts of the world.

A steady temperature of a large mass offers the opportunity to exchange heat. If the air in the house is warmer than the ground, heat can be drawn from the house. If the house is cooler than the ground, the house can be warmed. While it would take a substantial system to heat or cool a home using the earth as the only source/sink, it can be done, however you won't heat it above ground temp or cool it below ground temp.

Water is an awesome resource with all its properties. My favorite property is the ability of water to absorb and radiate heat. Add a pump to move water, heat can be moved between locations. To heat or cool a space, its a matter of flow rate.
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Re: Homemade air conditioner

Unread postby Ayoob » Mon 18 Aug 2008, 14:48:05

It's not so much about the setup cost or the time, it's about heating or cooling your house independently. If I was so inclined, I would pick up a radiator and use that, but I already had the copper tubing so I just went with that.

I remember calling the power company and asking how much it cost for me to run my box fan one time. I'd turned it on in early June and it was late August. The customer service rep said it was probably about a nickel an hour. The fan was $20, so I figured a nickel an hour is 24 nickels a day... about a buck a day... June, July and August added up to about 90 bucks.

Wow.

So running the fan cost me four and a half times the cost of the fan itself?

I could have picked up a timer and shut the fan off at 9AM (time to go to work) and have it fire up again about 4PM to cool the place off when I got home, and I could have skipped the most expensive part of the juice, AND not even noticed it was ever off. My power bill probably would have dropped by 50-60 percent.

Running a heat exchange system cuts my power bill by 70% or so for heating and cooling, which is a huge savings for me. Now if I can figure out how to use passive solar to heat my bathwater, cooking, dishwashing, etc... I'm in the pink!

All of a sudden, my long-term vision of living an energy-extravagant lifestyle with minimal energy inputs can become a reality. I just have to piece it together one bit at a time.
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Re: Homemade air conditioner

Unread postby smallpoxgirl » Mon 18 Aug 2008, 16:18:28

Ayoob wrote:Running a heat exchange system cuts my power bill by 70% or so for heating and cooling


Not unless you're using someone else's freezer to make the ice. For starters, unless your freezer is outside, the heat that it extracts from the water, it just dumps right back into your house. Kpeavey's setup would make a lot of sense, but trying to use your freezer to air condition your house is just screwy.

You are aware how much heat a 50 inch plasma TV puts out right?
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Re: Homemade air conditioner

Unread postby kpeavey » Mon 18 Aug 2008, 19:10:24

spg wrote:You are aware how much heat a 50 inch plasma TV puts out right?

There is a shadow outline of my brother burnt into his recliner. :-D

Ayoob wrote:So running the fan cost me four and a half times the cost of the fan itself?

It's not the cost of the thing, its the cost of running the thing.

Incandescent light bulbs vs compact flourescent is a perfect example.

CF
bulb $4 for 8000 hours of life
25 watts/hour
200 kWH for the life of the bulb
12 cents/kWH=$24
TOTAL $28 =0.0035/hour

Incandescent
bulb, 50 cents, 4 for $2, 2000 hours of life each, 8000 hours total
60 watts/hour
480 kWH for the life of the 4 bulbs
12 cents/kWH=$57
TOTAL $59 =0.0074/hour
more than twice the cost, and you change the bulbs 4x as often

many people look at a 50 cent bulb next to the $4 bulb and calculate a savings of $3.50. I explained this to a lady friend once, she insisted it did not cost that much to run a bulb and there was no way she was paying $4 for a light bulb.

Compact flourescent bulbs make an excellent christmas gift. Sent a dozen to my mother. Her light billl dropped $20/month, says she'll never go back.

PASSIVE HOT WATER
A few years ago I was down on my luck. I shut off the hot water except for just before I used the bath. I was out in the yard, picked up the hose to water some plants, about burned my hand on the thing. Water was screaming hot. I grabbed a 5 gallon bucket to measure the volume, got the bucket half full, about 2.5 gallons from a 50' hose. Not a whole lot, but enough to do the dishes. I ran the hose into the house, did the dishes. By the time I was done with a load of dishes, including hot water rinse, the water was hot enough to refill the sink for another load. I alled a buddy who ran an apartment complex, had lots of hose, he dropped off 150'.

Now I had enough volume to take a comfortable bath with plenty of hot water. I'd run the hose through the bathroom window, fill the tub until the hot ran out, wait for the hose to heat up again-about a half hour, and finish filling the tub. The hot water heater, and the bill that goes with it, had just become obsolete on sunny days.

At this point I have 500' of black PEP tubing, irrigation hose, in a coil in the driveway, about 7' across. A hose runs from the garden faucet to the coil, with another hose connecting to some plumbing in the greenhouse. From there I have CPVC with pipe wrap going under the house where it connect at the washing machine to the hot water pipes servicing the house. I shut off the valves at the hot water tank. When I turn the faucet at the sink, washer, tub or dishwasher, I have hot water coming out-FREE. High temps are in the 125-130 range, I've measured 131 degrees-HOT. Normal sun gives me 110-120. A comfortable bath for me is around 105, so I almost always have to add cold water. I can turn the faucet in the tub and get hot water for about a half hour before it starts to cool. Water temperature rises about a degree per minute, starting at about 70 degrees (city standpipe). To give me 105 degrees, about a half hour is needed. Another couple hundred feet of tubing and I should be able to run the water continuously, with the time it takes water to move through the tubing being equal to or greater than the time needed to heat the water. The result would be unlimited hot water, but I don't have that need at this time.

The cold season makes hot water difficult. Temps can reach 80 degrees in January, which makes for a cool bath. In the cold months I use the coil in conjunction with 55 gallon plastic barrel in the greenhouse. I have an 18 watt water fountain pump hooked up to the coil which returns back to the barrel. A timer turns on the pump when the sun gets above the trees, water starts cycling from tank to coil and back, warming up continuously. When the timer shuts off the pump, the tank often reaches 100-120 degrees. This heats the greenhouse all winter, giving off its stored heat over the course of the night. Costs me about 15 cents per month.

The next step would be hot water on demand.
Using the greenhouse heating setup, I need to add a heat exchanger to the barrel. Run a hose from the garden faucet to the barrel where it connects with copper tubing-already on hand, then hose from the tubing to the hot water connection. The pump heats up the barrel, when I open a tap inside the house water from the faucet should move through the tubing, heatig the water as it goes. The result should be hot water on demand. No more cold water after the sun goes down.

From that point expansion of the system is all about volume. More collector, more energy , more storage. Add another pumped loop from the tank to a radiator in the house, I should have it all: greenhouse heat, hot water on demand, space heating, all for the cost of materials and 2 pumps running as needed. The math says I need about 1000 gallons of storage, and 400 sqft of tubing. When done, the 2 pumps should do the job for about $2/month and give me dependable heat and hot water for several cloudy days. Add a 100 watt solar PV system, I'll be off the grid as far as heat.
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Re: Homemade air conditioner

Unread postby Keith_McClary » Tue 19 Aug 2008, 01:00:10

Madpaddy wrote:Ayoob,

Have you considered a cooling vest. We use similar products for certain jobs in the army and they work well.

http://www.climatechsafety.com/LiteAir.aspx

Image

You can be cool anywhere and this model costs $129.
I've been saving the fans from all my old computers just in case I needed them for a cool science project like this. Also I have not, of course, thrown out any old winter coats. Do you think I could make one of these cooling vests by cutting holes in a coat and duct-taping computer fans into the holes? (With suitable power supplies, which I also have saved, of course.)

Please reply promptly as we are having a heat wave here.
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Re: Homemade air conditioner

Unread postby aflatoxin » Tue 19 Aug 2008, 01:19:00

There are several facilities in Albuquerque that have big (10,000+ gallon) reservoirs that are turned into ice over the course of winter. I'm not sure if they are filled with water of some kind of salt. They are very cold at the end of the winter, as the heat pumps have pulled all of the usable energy out of the fluid.

Then, all summer long, the excess heat in the buildings is put into the tanks, heating the fluid and cooling the building. At the beginning of winter, the heated fluid from the summer is cooled again and the energy is used in the buildings.

I'm told that these setups can cut 25% of annual energy use needed to heat and cool the facilities.
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