Tag Archives: diy

What are the Differences Between Memory Foams?

Memory foam refers only to the “viscoelastic” behaviour exhibited by the foam. Memory foams can encompass a wide range of quality, durability, comfort, and other characteristics. Here’s a few things you should look for when considering the purchase of a memory foam product.

Density

This is the most reported memory foam specification, and while it isn’t perfect, it’s the one you
should look at most.

Density refers to the weight of a given volume. For instance, higher quality memory foams weigh
approximately 5 pounds per cubic foot (80 kg/m3) of volume or more. The reason density is a relatively good indicator is for two reasons:


First, memory foam density is typically increased by increasing the amount of additives to the foam mixture. These additives usually give it it’s “memory” effect. The higher the density, the better and more obvious this “memory” effect appears. Low density memory foams will deform quickly, and rebound equally as speedily. This means they will tend to feel more like “regular” foam and less like “memory” foam.

Secondly, increased density generally correlates with improved mattress life. Higher density foams will tend to last longer, and will not “collapse” or form dents where you sleep.

Note that softness was not mentioned! Remember, styrofoam has an extremely low density but would not be comfortable to sleep on. Lower density foams may be sold as "softer" but what they really are is simply a cheaper option for the manufacturer.

Be careful! Some unscrupulous dealers will put large meaningless numbers on their product which you may mistake for the density. Others may report the density as “pounds per TWO cubic feet” which has the nice effect of doubling the final number – but is a shameless attempt to deceive you. It is easy to check this – simply calculate the volume of your mattress, multiply by the density, and it should be quite close to the shipping weight. If it’s off significantly, this is a warning sign!

For instance, a 4″ thick queen mattress is 202 cm by 152 cm by 10 cm (yes, I’m from Canada). This gives us a total volume of 307,040 cubic centimeters, or ~10.8 cubic feet. If we assume it is made of 5lb/ft3 (80 kg/m3) memory foam, this means it should have a shipping weight of approximately 54 lbs (25 kg). A little bit either way shouldn’t be an issue, but significant deviations from this should be a warning sign.

I personally would not reccommend anything less than a density of five pounds per cubic foot. While this does eliminate a large number of products, it is still quite possible to obtain reasonably priced memory foam at this quality. This is a similar density to that used by high end memory foam beds (typically greater than 5lb/ft3 (80 kg/m3)).

Indentation Load Deflection

Specifications like this give engineers a bad name. While a valiant attempt at quantifying how “soft” a mattress is, the extraordinary variation in mattress composition and thickness makes it very difficult for a single number to accurately reflect a general quality like “softness” or “comfort”. Even if these numbers are produced, it then becomes difficult for the average person to say what number they prefer, and accurately compare between mattresses. It’s an extraordinary precise number that manages to be nearly useless from a consumer standpoint due to it’s precision. As such, the ILD is largely a quality control measure, more valuable to the manufacturer than the consumer.

ild

The test itself uses an “indenter”, shown on the right. This typically has a contact area of 50 square inches. The test involves pressing this indenter a specified distance into the foam, then measuring the force required to do so. A typical test is 25% deflection for a 4 inch sample, which means that the sample is compresses from 4 to 3 inches and force measured.

I don’t put much weight on this number for two main reasons. First, comparing ILD values is really only useful for foams with similar properties and manufacturing. Our entire intent is to compare between manufacturers, so this means ILD will give us little information.

This leads into my second point – it’s an extraordinarly limited test, initially designed for classic “elastic” foams. The major characteristic of memory foams is their viscoelasticity, which means that its response to load varies over time. The ILD test does not take time into account, which is fine for conventional “elastic” foams but completely misses the point of viscoelastic memory foams. As such, I do not view ILD as a useful “consumer level” metric. Choose based on comfort reviews and testimonials, not a single number.

Other Numbers

There’s a ton of different ways to measure foam, and as a result there’s a ton of numbers thrown around. They mean very little unless you are a chemical engineer dealing with the manufacture of these foams. The major measurement a consumer should pay attention to is the density, and following that reviews and testimonials on comfort.

Nerd alert: there are two valuable tests (creep and stress relaxation) typically done on viscoelastic materials that I haven’t bumped into for memory foams. If anyone has any quality data in this regard please contact me or post in the comments below.

What is Memory Foam?

Memory foam is actually a rather advanced material, and has only gone down in cost enough to be practical for personal use in the last ten years or so. More specifically, it is an open-cell foam with viscoelastic properties, typically manufactured using polyurethane. If this means nothing to you don’t worry, and read on!

Open Cell Foam

opencell

We can think of foam as a fluffy mixture of a solid (polyurethane in this case) and air. If the mixture is made up of many tiny bubbles, like in the sole of a tennis shoe, we can squeeze and compress this foam and the air will never come out as long as the bubbles don’t break. This is called closed cell foam, and is good for tennis shoes which need to protect our feet from harsh impacts again and again, but tends to be a bit stiff for beds.

Open cell foam is still a mixture of a solid and air, but in this case, all the little bubbles have even smaller holes in them! We can see this on the magnified picture on the left. This means we can squeeze and compress the foam a great deal, as the air will rush out just like water from a foam dish scrubber when you squeeze it.

This open-cell foam is soft and conforming to the body, and allows air movement through it which helps keep you cool and comfortable.

Viscoelasticity

Viscoelasticity is what makes makes memory foam have a “memory”.

A spring mattress is what engineers would call elastic. No matter how fast or how slow you put a certain load on the mattress, the spring still compresses the same amount in the end. The spring does not (or at least should not) soften or harden over time.


A memory foam mattress is what engineers would call viscoelastic. This is a combination of elastic properties (like a spring) and viscous properties (like oil or molasses). These viscous properties cause the foam to react differently depending on how fast you put weight on it. If you jump onto a memory foam bed, you can feel the foam slowly start to conform to your body as you sink in. If you get up quickly, there will be a dent in the foam in the shape of your body which will slowly disappear over time.

So who cares? Is a memory foam mattress just an expensive way to leave a cool handprint? Well, there’s more to it. Sleep comfort can be correlated with how pressure varies along the body during sleep. If the pressure changes rapidly with many individual pressure points (like sleeping on gravel, or that one spring that pokes out of the mattress), we’ll be very uncomfortable.

Memory foam does a very good job of reducing these “stress gradients”. Over a short period of time, the foam remolds to reduce these pressure points, something a typical elastic material cannot do. The resulting smooth pressure distribution provides a very comfortable sleeping surface.

Polyurethane

polyurethane

Without getting into too much chemistry, polyurethane is a polymer. This means it consists of very long chains of urethane molocules, which then become tangled together like spaghetti to produce a solid. To produce basic polyurethane foam, a reaction occurs where urethane is chained together into these long strings while water reacts with another compound to produce carbon dioxide. This combination of solid and gas gives us polyurethane foam.

One important advantage of polyurethane is that its properties are readily modifiable by adding different compounds to the mix. Typical polyurethane foam is not “memory” foam unless certain additives are incorporated which give it these “memory” effects.

Make Your Own Memory Foam Bed

High quality memory foam beds such as the Tempur line are incredibly comfortable, with a price tag of thousands of dollars to match. The construction of these beds is relatively simple however, evidenced by the number of “clone” beds on the market today. Unfortunately, some of these mass-produced “clones” have cut corners in quality, which can make selection challenging.

This page will tell you the typical components of memory foam beds, with instructions on how you can mimic each of these components with high quality substitutes. The cost savings can be significant.

For instance, I currently sleep on a queen size memory foam bed constructed in this manner. It cost me approximately $500, versus a memory foam mattress with comparable specifications which would have put me back over $1500.

It’s a lot easier than you might think – you need three layers. The major issue is quality control and determining the appropriate products which are the best value for each layer.

main-memory-foam


sub-memoryfoam

Memory Foam Layer

This contouring soft upper layer is what gives memory foam mattress their unique “feel”.

sub-foam

Base Foam Layer

This layer provides a supportive base which distributes your weight evenly across the bed.

sub-base

Platform Layer

A sturdy flat base supports the memory foam mattress and prevents a “hammock” effect.

The Black Beauty

As the summer progressed, I felt like I needed to improve my initial design. Luckily enough the science department had just thrown away an old freeze drying machine which had a perfect radiator. A few minutes crouched by the dumpster with some hand tools, some minor adjustments, and the Black Beauty was born.

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Here’s the overall view of the unit. A high speed fan pushes the air through the perfectly sized radiator, and water flow rate is controlled by a small hand valve.

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The radiator itself was horribly filthy when I first took it off, but a quick soak in some warm water and light detergent took care of it. The copper tubing inside the radiator is the exact same diameter as the copper tubing I used when I first built my original homemade air conditioner, so no need to change up the vinyl tubing.

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I placed the fan fairly close to the radiator itself, and it works great. I typically put the fan on the medium or low setting, as I notice little benefit from the high speed setting other than increased noise.

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The radiator was almost perfect, it only needed to be raised by a centimeter or so to align with the fan. Turns out old original Nintendo cartridges do the trick just fine. (For the record, that’s Teenage Mutant Ninja Turtles and Marble Madness. Don’t worry, I have other copies.)

5-dscf0686

Cold water is supplied from an outside garden hose. More detail can be found in the water supply section.


To calibrate the valves, the small hand valve inside is first opened wide and the garden hose opened or closed to find an appropriate upper flowrate. Then the hand valve may be used to vary the water flow or turn it off entirely.

6-dscf0688

The nice thing about this new setup is that all control is now done from inside the room. Starting and stopping the unit is far more convenient, which leads to more efficient water usage. The performance of the unit is drastically improved over the old design. Less water is needed, and the room cools quicker.

Homemade Air Conditioning Plans and Pictures
Original Design
Geoff’s Homemade Air Conditioner
Heat Exchanger Improvements
Water Supply Improvements
Technical Notes
Other Designs
Pete’s Homemade Air Conditioner
Anonymous’ Homemade Air Conditioner
Spencer’s Homemade Air Conditioner
Final Design
The Black Beauty

Pete’s Homemade Air Conditioner

Credit goes out to Pete H. in sunny England for this great build. This version of the homemade air conditioner removes the need to drain water outside by using an aquarium pump, and sits on a rotating base. Check out more homemade air conditioners here.

01_p_overall

Here’s the overall view of the unit. You can see the insulated polystyrene box containing icewater and the aquarium pump, along with the fan and attached copper tubing.

02_p_fan_front

Pete did a much neater job of attaching the copper tubing to the front of the fan than I did. Using copper tubing on both the front and back of the fan is a great idea, the more copper tubing, the more heat exchange possible.

03_p_fan_top

Here is a view of the unit from above, allowing us to see the copper coils on both the front and back.

04_p_fan_w_cooler

Here we can see the entire system on its rotating base, allowing directional cooling (most) anywhere in the room.

05_p_icc

This picture shows Pete’s innovation, the Internal Cooler Coil (ICC) ready to be installed. The water first runs through this coil, through the ice water, and then out to the fan. Pete and I are wondering if this actually increases performance at all, but it sure looks cool.


06_p_pump

Here we can see the aquarium pump submerged in the ice water. Pete aims to increase the power of the pump, and replace the polystyrene container with something more permanent. A small freezer with its heat vented to the outside would be ideal.

If you liked Pete’s design, check out Spencer’s heavy duty interpretation, or my final design.

Homemade Air Conditioning Plans and Pictures
Original Design
Geoff’s Homemade Air Conditioner
Heat Exchanger Improvements
Water Supply Improvements
Technical Notes
Other Designs
Pete’s Homemade Air Conditioner
Anonymous’ Homemade Air Conditioner
Spencer’s Homemade Air Conditioner
Final Design
The Black Beauty

Spencer’s Homemade Air Conditioner

Spencer from Ohio made this incredible build using some good old american muscle. This closed circuit version of the homemade air conditioner uses a radiator for efficient heat transfer, and looks awesome in the process.

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A spare radiator from a 1976 Triumph Spitfire ensures great heat transfer between the water and the air. A wooden frame supports the radiator and attached fans.

2-p5270014

Not just one, but two fans circulate air through the radiator and the room.

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Two water fountain pumps are used to circulate the water between the cooler and the radiator.


4-p5270016

Here we can see the warm water returning to the cooler. How does the whole thing perform? In Spencer’s words, very well.

Homemade Air Conditioning Plans and Pictures
Original Design
Geoff’s Homemade Air Conditioner
Heat Exchanger Improvements
Water Supply Improvements
Technical Notes
Other Designs
Pete’s Homemade Air Conditioner
Anonymous’ Homemade Air Conditioner
Spencer’s Homemade Air Conditioner
Final Design
The Black Beauty

Anonymous’ Homemade Air Conditioner

This version of the homemade air conditioner implements two improvements, a flow valve and a condensation collector.

01_overall

Here’s the overall view of the unit. The condensation collector and flow valve are both visible. It’s a good idea to place the unit higher in the room like this, the action of the fan will circulate the hot air at the top of the room. Just make sure that your ceiling tiles aren’t flaking off abestos and you’re set.

02_fan_rear

This is the rear of the unit. You can see the copper tubing coiled along the back of the fan, attached by zipties.

03_condensation

The condensation collector sits below the unit. A towel catches any spare moisture not managed by the collector.

04_valve

Here is a closeup of the flow valve. This is extremely useful in managing flow rate, or stopping water flow entirely. If installed on the outflow side of the system, the flow valve allows the siphon to be restarted very easily once shut off. If the system lacks a valve such as this, air will bleed back into the tubing and make it more difficult to restart the siphon.

05_icebucket

An additional benefit of the ice water source is shown to the right. In extreme heat situations, one may sit in the ice water source for drastically improved cooling effect. Additionally, one could simply drink the beer cooling in the ice water. In heat waves, do your best to stay out of rehab.


06_outflow

Waste warm water is directed to a garden, no student ghettos here. Oh, how I yearn for the days of a mortgage and a house without concrete as a landscaping tool.

Homemade Air Conditioning Plans and Pictures
Original Design
Geoff’s Homemade Air Conditioner
Heat Exchanger Improvements
Water Supply Improvements
Technical Notes
Other Designs
Pete’s Homemade Air Conditioner
Anonymous’ Homemade Air Conditioner
Spencer’s Homemade Air Conditioner
Final Design
The Black Beauty

Technical Notes

technical_ac2

Several people have asked me if I have managed to quantify the performance of this system. I ran a few quick numbers – accuracy is not going to be great due to measurement error. In terms of rough numbers though, I’m pretty happy.

At a flow rate of 2 L/min (taken as the upper range of performance) inlet temperature is 16 degrees Celcius (C), and outlet temperature is 20 deg C. This corresponds roughly to 2000 BTU/h.

At a flow rate of 1 L/min (what I use for a hour before bed to cool the room off) inlet temperature is 16 deg C and outlet temperature is 21 deg C. This corresponds roughly to 1200 BTU/h.

At a flow rate of 0.5 L/min (what I would use for “maintenance” after cooling the room off if it’s a hot night) inlet temperature is 16 deg C and outlet temperature is 23 deg C. This corresponds roughly to 800
BTU/h.

In terms of BTU/$, I can’t complain. If I’ve made any errors in my calculations, feel free to chastise me.


UPDATE: My school requires me to write a “work report” for every term of outside work experience during the coop program. I felt the only logical choice was to do it on the infamous homemade air conditioner. Hopefully referencing yourself in your work report (PDF) is looked upon kindly by admin…

Homemade Air Conditioning Plans and Pictures
Original Design
Geoff’s Homemade Air Conditioner
Heat Exchanger Improvements
Water Supply Improvements
Technical Notes
Other Designs
Pete’s Homemade Air Conditioner
Anonymous’ Homemade Air Conditioner
Spencer’s Homemade Air Conditioner
Final Design
The Black Beauty

Water Supply Improvements

Having a large garbage can full of ice water in your room is a bit of a pain. I decided to modify the system to run off a garden hose, for increased reliability and to prevent late night stumbles from flooding my room.

01_hose

The system is fed from a tap on the side of the house. The hose is ancient so the connection is a bit leaky, but a bit of tape stopped that quickly. I added on some pipe insulation (~$1.50) around the garden hose to make sure the only thing warming up the cold water is my stupidly hot room.

The water supply in Waterloo is typically from groundwater sources, so the garden hose tends to be quite cold regardless of season.

02_into_window

The hose insulation ends under my window. The remaining length of garden hose is coiled and wrapped with towels to insulate.

The garden hose is then connected to the vinyl tubing with duct tape, of course. It then leads through a small hole in my screen towards the fan. I must congratulate my landlord on the exceptional job he does on basic maintenance, such as exterior paint touchups.

03_inside

The tubing feeding the system cold water can be seen at the bottom of the window. Water circulates through the heat exchanger, and the warm waste water is pumped up towards the roof.

04_out_window

Another small hole was cut in the screen for the warm waste water line. It then passes an old bird’s nest (a necessary accessory for any student ghetto) and leads to the roof.

05_on_roof

The warm waste water is pumped onto this garish prefabricated roof, which covers part of the backyard. Hopefully, a side effect of this is a slight temperature drop on the roof due to evaporating waste water. This may have a minor effect on the outside temperature near the room.


You can also pump the waste water into your eavestroughs. This makes sure you’ll be draining to a location that won’t flood your basement.

06_waterfall

The water eventually drains off the roof. If you’re of the Zen persuasion, the gentle sound of running water will lull you off gently to sleep. If you aren’t, it may drive you absolutely mad until you realise that the sound of the fan drowns it out anyways.

07_bucket

The water drains to the same garbage pail, which can be dumped on the lawn or used for watering plants, if I had any.

Homemade Air Conditioning Plans and Pictures
Original Design
Geoff’s Homemade Air Conditioner
Heat Exchanger Improvements
Water Supply Improvements
Technical Notes
Other Designs
Pete’s Homemade Air Conditioner
Anonymous’ Homemade Air Conditioner
Spencer’s Homemade Air Conditioner
Final Design
The Black Beauty

Heat Exchanger Improvements

The major factor affecting the efficiency of the air conditioner is the heat exchanger. A radiator or evaporator coil would be ideal, but cost and availability are a concern. This page details my attempts to improve performance of my homemade air conditioner with minimal cost.

01_tinfoil

Strips of tinfoil were first used. You can see some of the copper coiled along the front, from an earlier attempt to improve the heat exchanger. This wins in the cost department, but ultimately the choice was made to discontinue the use of foil as it had the annoying habit of coming undone and buzzing like mad during the night.

02_coils_inprog

The decision was made to completely revamp the copper coils, and install the entire length of tubing on the front of the fan. You can see the recoiling in progress, I did a bit neater job this time (but not by much).

03_coils_done

Here’s the completed copper coil on the front of the fan. Cold water is fed from the centre to the outside. Again, I’m unclear as to what configuration if any (cold from the inside, cold from the outside) would lead to superior performance.

04_geoff_soldering

I decided to use wire to create a mesh on the front of the coils. (18 gauge wire, Radio Shack, ~$5 – I’m up to 30 bucks now!) This would increase surface area, intercoil heat transfer, and turbulence near the coils, hopefully increasing performance.


I first attempted to solder the wire to the tubing, a stupid attempt as the entire system is designed to efficiently transfer away heat. After several minutes of terrible cold joints, another approach was required.

05_geoff_working

I ended up weaving the wire from the centre to the edges, and back in. Approximately 10-12 passes were used per quarter section of fan.

06_ul_complete

Here’s a shot of the completed upper left quarter.

07_proper_tools

Weaving the wire is an unbelievably frustrating experience at times. The copper tubing usually has a slight gap between the white wire mesh on the front of the fan that the wire can pass through, but at other spots the wire will catch and start to unravel. It helps to have the proper tools (needle nose pliers, beer) to stay relatively stress-free. In this shot I’m halfway through weaving the lower right quarter.

Just be patient and you’ll be fine.

08_final_front

Here’s the fan as it stands right now. Saturday went from evening to night, and that means I need to go somewhere with cold pints and hot women. I’ll complete the remaining quarters tomorrow when I have a bit more time and patience.

Preliminary tests are very satisfactory. The cooling rate has increased, and the room will get a bit colder as well. This will help in extremely hot situations, where heat would leak into the room as fast or faster than the system could remove it.

Homemade Air Conditioning Plans and Pictures
Original Design
Geoff’s Homemade Air Conditioner
Heat Exchanger Improvements
Water Supply Improvements
Technical Notes
Other Designs
Pete’s Homemade Air Conditioner
Anonymous’ Homemade Air Conditioner
Spencer’s Homemade Air Conditioner
Final Design
The Black Beauty