Author Topic: TEC or Other non-Aircon for Room Cooling  (Read 1051 times)

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Offline mengfeiTopic starter

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TEC or Other non-Aircon for Room Cooling
« on: May 27, 2024, 02:54:03 am »
ellow, has anyone done a good TEC cooling project + fan to cool like a 10square meter room?
is it even practical to use TEC for that type of cooling or any better ideas to keep a room where all walls are cement & is being bathed by the sun

it can get up to 45C in our area  :scared:

https://zoom.earth/maps/temperature/
« Last Edit: May 29, 2024, 01:36:50 am by mengfei »
 

Offline NiHaoMike

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Re: TEC for for room cooling
« Reply #1 on: May 27, 2024, 04:31:01 am »
any better ideas to keep a room where all walls are cement & is being bathed by the sun
Use aluminum foil to reflect away the direct sunlight.
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Offline ArdWar

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Re: TEC for for room cooling
« Reply #2 on: May 27, 2024, 04:53:12 am »
Why not simply using the usual commercial refrigeration cycle if you need room-sized aircon? Using TEC will not only horribly inefficient compared to refrigeration cycle but probably also give you (and everyone else) a lot of problem too with the required power.
 

Online Siwastaja

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Re: TEC for for room cooling
« Reply #3 on: May 27, 2024, 05:44:02 am »
Completely impractical. Efficiency is just way too low. Because the efficiency drops linearly as the hot side temperature rises, reaching 0 at 50-60degC dT, even getting 50% energy efficiency requires careful engineering: massive water cooling fan coil units.

Some 2kW cooling power is typically needed to make a difference. A compressor can do this well under 1kW electrical (and thus under 3kW dissipated); a Peltier solution would require at least 4kW power and thus dissipate 6kW of heat.
 

Offline Berni

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Re: TEC for for room cooling
« Reply #4 on: May 27, 2024, 06:00:37 am »
Classical phase change refrigeration cycle air conditioners are simply way more efficient.

Yes you could do it with peltier elements. However the number of peltier elements needed is huge to get the required cooling power. Then the inefficency means lots of power input to power it (so expensive to run due to the cost of electricity) and then you need a large heatsink to get rid of all that heat on the other side. Building this will be many times more expensive than a commercial unit and will be even more expensive to run due to the high power use.

The cheapest solution is to buy a commercial air conditioner. You can get a mini split unit for 300$ at a hardware store and they might include free installation with it. Or if you want it even simpler buy one of those american style window units, they don't need professional installation.

Only thing to avoid is floor standing AC units with a dryer hose out the back. Those have bad efficiency and need to have the water tray manually emptied all the time as they run.
 

Offline SiliconWizard

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Re: TEC for for room cooling
« Reply #5 on: May 27, 2024, 06:12:21 am »
ellow, has anyone done a good TEC cooling project + fan to cool like a 10square meter room?
is it even practical to use TEC for that type of cooling

No. You'd need a lot / huge modules for this, a LOT of cooling for the hot side, that would be very big and the overall consumption to cool a small room by a few Cs would probably be in the order of over 10 kW, probably even more, off the top of my head. And you'd get so much condensation that it would literally make your room wet.

or any better ideas to keep a room where all walls are cement & is being bathed by the sun

Well, plant some trees. There is unfortunately not many working solutions apart from a conventional AC unit.
 

Online Siwastaja

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Re: TEC for for room cooling
« Reply #6 on: May 27, 2024, 06:15:44 am »
Only thing to avoid is floor standing AC units with a dryer hose out the back. Those have bad efficiency and need to have the water tray manually emptied all the time as they run.

If you are emptying the water tray all the time, you are doing it wrong, and no wonder you are seeing "bad efficiency". Due to their obvious handicap (they suck a lot of hot replacement air), they try to limit the condenser air flow, and compensate by using a water pump to spray the condenser with the condensate water. Water evaporates, removes heat from the condenser, dropping condensing temperature and increasing COP. If you empty the water tray all the time, you are seeing at least some 30% drop in output power.

These units literally suck compared to real window units (or even better: split units), but they are still much more useful than most DIY contraptions.
 

Online 2N3055

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Re: TEC for for room cooling
« Reply #7 on: May 27, 2024, 06:23:21 am »
ellow, has anyone done a good TEC cooling project + fan to cool like a 10square meter room?
is it even practical to use TEC for that type of cooling or any better ideas to keep a room where all walls are cement & is being bathed by the sun

it can get up to 45C in our area  :scared:

https://zoom.earth/maps/temperature/

You need to insulate that wall and possibly put IR reflecting surface on it. Completely passive solution.
 

Offline mengfeiTopic starter

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Re: TEC for for room cooling
« Reply #8 on: May 27, 2024, 09:50:46 am »
thank you all for your valuable inputs & information  :clap:

the idea just came up since & still have a few peltiers lying around which i used to replaced my previous mini fridge & water cooler. I guess efficiency would really be a great problem not to mention the huge current to run these continually, I guess these where made for small/ minor cooling only.

we do have an inverter in one of our rooms but the children has always have it set at the lowest temp of 16C & at Turbo mode & still it's having a hard time cooling their room unlike when it was first installed last year(feb), now water drips  from it possibly from ice buildup.

i'll just add more insulation to the ceilings & walls then & probably get one of those Fans that you add water & ice.
Thanks again for the suggestions guys  :clap:
 

Offline Doctorandus_P

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Re: TEC for for room cooling
« Reply #9 on: May 27, 2024, 11:13:21 am »
Direct solar energy is around 1kW per square meter on the earth surface and 2kW / square meter in LEO.

So, as others have already mentioned here, this would overwhelm a few TEC's. What remains are the regular solutions:

* Remove direct sunlight (alu foil, shade from trees, etc).
* A sunshield with ventilation under the roof to prevent heat build up.
* Heat insulation / small windows.
* A lot of thermal mass that heats up slowly (Vent at night to cool down, keep windows and doors shut during the day)
* Regular air conditioning / heat pump.

Thermal mass is the most interesting option if there is a big temperature during day and night. The old fashioned way it just thick heavy walls, but you can also use an underground water tank with a heat exchanger and pumps.

How far are you away from the sea? What is the sea water temperature? If you pump sea water though an heat exchanger with a small pump and put a fan on it you may have an efficient solution. Sea water is harsh on a lot of metals, so it is not trivial to make a lasting system. It may be better to run water though a closed loop with two heat exchangers (One in the ocean, and the other in your room).

When this is done on a larger scale, it also has environmental issues. For example, rise of temperature of rivers because of cooling water from power plants is a well known and researched problem.
« Last Edit: May 27, 2024, 11:23:05 am by Doctorandus_P »
 

Offline Berni

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Re: TEC for for room cooling
« Reply #10 on: May 27, 2024, 12:01:06 pm »
Only thing to avoid is floor standing AC units with a dryer hose out the back. Those have bad efficiency and need to have the water tray manually emptied all the time as they run.

If you are emptying the water tray all the time, you are doing it wrong, and no wonder you are seeing "bad efficiency". Due to their obvious handicap (they suck a lot of hot replacement air), they try to limit the condenser air flow, and compensate by using a water pump to spray the condenser with the condensate water. Water evaporates, removes heat from the condenser, dropping condensing temperature and increasing COP. If you empty the water tray all the time, you are seeing at least some 30% drop in output power.

These units literally suck compared to real window units (or even better: split units), but they are still much more useful than most DIY contraptions.

I never owned a portable floor standing AC because i think they are a bad idea.

We have a multi split AC system at home and mostly end up running it in drying mode for about an hour or so on hot days. The house is reasonably insulated so the cooling it provides in drying mode is enough power to drop the temperature to a reasonable level then once it is turned off the dry air makes higher temperatures feel comfortable as you don't end up sweaty.

But it doesn't tend to get quite so hot here, so it has a easier job. Most of the time we just open windows at night to cool the brick walls down, so they hold the cold over the day. This is also the reason AC gets more used for humidity control than cooling (the cold night air is humid).
 

Offline NiHaoMike

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Re: TEC for for room cooling
« Reply #11 on: May 27, 2024, 12:18:14 pm »
Only thing to avoid is floor standing AC units with a dryer hose out the back. Those have bad efficiency and need to have the water tray manually emptied all the time as they run.
The newer dual hose units solve that problem, although those are substantially more expensive than equivalent window units so only a good choice if the window is incompatible with window units.
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Online Siwastaja

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Re: TEC for for room cooling
« Reply #12 on: May 27, 2024, 06:28:34 pm »
Whenever you can't install (apartment) or can't afford a split air conditioner, good old window unit (those that are really popular in the U.S.) is the best option, and they are surprisingly cheap. Sadly, they most come in certain form factors and for example here we have narrow and tall ventilation windows so that the typical U.S. style window air conditioner simply does not fit.
 

Offline hans

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Re: TEC for for room cooling
« Reply #13 on: May 27, 2024, 08:16:43 pm »
A TEC only has an efficiency in the order of dozens % to single-digit.
An airconditioner can move heat around at a EER at 2.6 (W/W) or more. => 1kW input, 2.6kW cooling out.

Its literal order(s) of magnitude more efficient.

Only thing to avoid is floor standing AC units with a dryer hose out the back. Those have bad efficiency and need to have the water tray manually emptied all the time as they run.

Unfortunately, in many countries split aircons are very hard to get for DIY installations. The only ones I see are for caravans and campers which are only 400-500W, from 12V DC, and still cost 600 euro.
In EU we also don't really have the classis sliding windows that can hang an window airconditioner like in US, unfortunately.

There is actually a mod for portable aircons, called a dual airhose conversion.
Normally those units operate so poorly because the single air outlet forces air outside the room, which creates an underpressure, and thus you will suck in outside air from cracks etc. in windows/doors. That's the outside air you want to keep out.

By redirecting the inlet airflow for the condenser to a second airhose and drawing fresh air directly from outside, you can minimize this erroneous airflow and improve the efficiency quite drastically.
The most important thing is to watch out for overheating of the compressor/condenser coils as it now draws in hotter air from outside (which in hot climates is more challenging in the relatively modest "30C heatwaves" we have here). Don't go too restrictive on the inlet. I took a 150mm hose, just as big as the outlet, and did some temperature checks before I finally commissioned 2 units in my house. (I rent so this is my only option, unfortunately)

Emptying the condenser water is a waste. Many airconitioners have a drip tray that will 'overflow' into the condenser side helping it cool down extra through evaporation as well. I even saw some guy intentionally adding extra water to the condenser after a dual hose mod, because otherwise the aircon would hit thermal shutdown on really hot days (up to 40C here).

I've no idea why manufacturers create these portable aircons with a single hose from the factory.. It's not like 1 or 2 hoses is such a dramatic installation difference. Presumably people don't want to deal with air hoses and covers/seals at all.. (E.g. see BS like this: Evolar EVO-ES9000)

A few years ago I did see a few airconditioners with dual hose.. but in my ignorance I didn't get one. Since then they have gone 'out of fashion'. I only know of 1 mobile airconditioner available locally  that still features  this concept 'off the shelf': https://www.inventum.eu/klimaat-comfort/airconditioners/ac127wset/
But only with the optional booster kit. But that unit is not cheap.. the aircons I got are also 12kBTU but I got them for 120 euro as new in open box.
« Last Edit: May 27, 2024, 08:20:50 pm by hans »
 

Offline mengfeiTopic starter

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Re: TEC for for room cooling
« Reply #14 on: May 28, 2024, 04:12:03 am »
Last week I got a Floor standing fan that claims it can cool a room to 16C using the Airdisk cooling method by compressing hot air then releasing cold air!

& I thought hey! wait a minute that was invented by a young student form the Philippines.

https://timeskuwait.com/news/young-filipina-inventor-presents-new-environmentally-friendly-ac/ 

https://www.reddit.com/r/Philippines/comments/dkkb7n/airdisc_cooling_technology_filipina_inventor/

to my dismay it was just an ordinary thin floor standing fan that they sell here in china. I ask if i needed to put any water or ice to get to that temp & they said no as this is a new technology that they where using blah blah blah  :palm:

anyways does anyone know how's the project of Maria Palma going?
I really hope that goes into fruition. 
 

Offline ArdWar

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Re: TEC for for room cooling
« Reply #15 on: May 28, 2024, 05:16:02 am »
Airdisk cooling method by compressing hot air then releasing cold air!

If I understand correctly (no paper at all, patent description is useless, and news coverage is just marketing BS) it uses the same principle as aircraft air cycle machine. Neat trick if you already have compressed air to bleed off, but questionable if you have to purposely compress the air. I seriously doubt it can get anywhere close to refrigeration cycle in efficiency. I even doubt it get more than 1.0 COP. Granted it does away with the refrigerant.
 

Offline Berni

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Re: TEC for for room cooling
« Reply #16 on: May 28, 2024, 05:46:21 am »
The efficiency of refrigeration trough gas expansion is also very poor indeed.

You need to compress it to a very high pressure in order to get a useful temperature difference between input and output. This is like using an air compressor as an air conditioner. The compressor cylinders and tank gets hot due to compressing air, that heat dissipates away into the ambient air, then once you release the compressed ambient temperature air out the end of the hose, it gets colder than ambient.

This sort of cooling is actually used in practice for reaching cryogenic temperatures. There using phase change cooling gets tricky because once you get really really cold, things don't want to evaporate anymore(or things that do are difficult to condense), hence no phase change. So to get around the problem phase change cooling is used to get a high pressure gas very cold, then that gas is released to expand out, making it get even colder. In Joule Thompson cryocoolers this cold expanded gas is used to cool the still compressed gas even more, getting it even colder, getting the expanded gas even colder...etc This process has very poor efficiency. The only reason it is actually used is that it works down to really low temperatures.

If you want energy efficient, simple cooling with no refrigerant gas, you got water evaporative cooling. But the problem is that you need reasonably low outdoor air humidity for it to work well. Our climate doesn't lend itself well to it.
 
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Offline mengfeiTopic starter

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Re: TEC for for room cooling
« Reply #17 on: May 28, 2024, 06:48:30 am »
when i worked in Saudi our dorms where made of mud hence mudhouse  ;D

anyways we where using huge water coolers in our room like it's 1cbm
on the left, right & back it has somewhat of a haylike filter where water runs down via a pump & then a cylindrical fan blows out (into room) cool air, really cool eh pun intended  ;D
i guess these kind of water coolers are not suitable for humid places.

now china is showing, not sure if it's new, a water cooling system for the floors & ceiling that are panel types & uses pipes arrange in S shapes to run the water & it has it's own evaporator/ heat exchange unit set outdoors just like a split type aircon. not sure if practical use in homes

https://menred.com/article/5mg-Water-Cooled-Silent-Air-Conditioning-Panel.html

the Airdisk thing looks like a promising project  8)

 

Offline coppercone2

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Re: TEC for for room cooling
« Reply #18 on: May 28, 2024, 07:53:05 am »
there is this thing
https://www.sony.com.hk/reonpocket/en/

it might make the heat more bearable. It uses a tec and some neurophysiological trick.

But putting a ice back with a towel on it on your back would be way more cooling for being at home for the same technique
 

Offline mengfeiTopic starter

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Re: TEC for for room cooling
« Reply #19 on: May 28, 2024, 09:18:16 am »
^wow! Cool Gadget  ;D

will check it out, thanks
 

Offline Berni

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Re: TEC for for room cooling
« Reply #20 on: May 28, 2024, 09:36:54 am »
Yes the simplest evaporation cooler is mist water over a room fan.

The problem with that is that it increases indoor humidity. Apart from mold issues, this makes the cooling effect less effective because high humidity makes hot temperatures more uncomfortable (sweat does not evaporate, so you end up sweaty and not getting cooling from said sweat). This can be improved by moving the evaporating cooler outside, then run cold water indoors. So you get the cooling effect but not increase indoor humidity.

These cooling panels are indeed a good idea, however one has to be careful with humidity there too. Reducing air temperature also causes a increase in %RH humidity because cold air is less capable of holding moisture. If you live in a dry area this is not a problem. But if you live in a more humid area, the %RH will get so high that water starts condensing on these panels. In those cases you need a recuperation ventilation system to exchange indoor/outdoor air to keep it dry enough, or in even more humid areas you need an AC somewhere in the house that works as a dehumidifier to keep the indoor air dry enough.

In most cases air conditioning is about managing humidity, not just temperature. In fact humidity management is the reason air conditioning was invented, it was first used in textile factories (because the textiles didn't run trough the machines properly if too wet/dry). They used liquid ammonia phase change powered by steam engines to get the cooling for drying the air. The factory workers being nice and cool inside was just a free bonus.
 

Online Siwastaja

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Re: TEC for for room cooling
« Reply #21 on: May 28, 2024, 09:41:35 am »
Human already has evaporative cooling system built-in. Problem is, external evaporative cooling competes with it. Even if temperature is reduced a bit, humidity is increased and it feels equally hot or even worse.

It does work well in really dry, almost desert-like conditions; say, when you can afford increasing near-0% RH to some modest 30-40% level. But it doesn't have to be specifically "moist" for it to stop working. For example in Finnish summer conditions, evaporative coolers basically never work, not even during dry seasons because our dry seasons are still not that dry. Maybe in once-in-50-years record drought they could work well.

But for certain areas, maybe Texas, they are fine, but usually not as the only cooling option, but a hybrid solution. Power consumption is less than on compressor based cooler.
 

Offline Marco

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Re: TEC for for room cooling
« Reply #22 on: May 28, 2024, 03:20:58 pm »
Unfortunately, in many countries split aircons are very hard to get for DIY installations. The only ones I see are for caravans and campers which are only 400-500W, from 12V DC, and still cost 600 euro.

The ones with prefilled hoses which need to be installed by professional nudge-nudge-wink-wink are available, though getting a vacuum pump set isn't that expensive either.

Some brands are switching to R290 (propane) to avoid F-gas requirements and legal DIY but those are not very common yet (legal in liberal nations like UK/Netherlands, I'm sure in Australia you need to hire someone with a 5 year education regardless).
 


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