Tiny air conditioners? I found some! - (new info)

[Woody]

my mistake on the math at 12 volts, you are right. I was doing the conversion based on the 120 vac. I did find a formula to figure out btu's reqiured to cool a given space (volume) to be cooled (height x width x length ) to get volume then mutilply it by 15 btu's to get the total btu required. When I did the calculation on my teardrop it gave me a BTU required of 1980 btu's required to cool given space. I found that a 5200 btu A/C is a little overkill. It cools fine, but cycles fast. It takes awhile to remove humidity, it does cool down nice though. Insulated teardrop makes a difference as well. If two people are in the trailer the unit cycles longer to remove the extra heat generated. You should check out Larry Sorenson www.outbackteardrop.com site he spends alot of time in the desert and he built a mini swamp cooler and states it work well for him. He might be someone to talk to about his cooling system which he shows on his site

[bdosborn]

I don't know what the BTUH is of this unit but I've always thought you could use it for air conditioning somehow.
http://www.westmarine.com/webapp/wcs/st ... uctId=6290

Its a split unit and only uses 3.1 amps. It seems like you could put a different evaporator with a fan and blow cool air.
Bruce

[asianflava]

You could easily hook up a evaporator/blower assembly from a car. This system has a lot of potential. The only thing is, I don't have $600 to play with.

[fasttimes]

I don't know what the BTUH is of this unit...

The BTUs are probably way too low... like in the 100-200 BTU/h range. At least, that's what I've been told most small refrigeration units are able to do.

[fasttimes]

I did find a formula to figure out btu's reqiured to cool a given space...

That's OK, but these types of "formulas" are really just quick rules of thumb, and almost always wrong. For example, it does not take into account the amount of insulation, wall area (a square room has less area than a rectangular one, for the same total sq.ft), window area, average inside temp, orientation of house to sun, amount of shading, ect.

The best way to do this is either a "manual-J" which professional AC installers use in calculating the size needed, but I have never found Manual-J free on the Internet. You would have to buy the book ($100) or one of the software programs that use it ($50+).

The other way, is below. This is a reply I received long ago, when I asked about sizing an AC for a super-insulated house.:

You need to calculate the gains from conduction, air infiltration, solar
radiation, and internal heat sources. dT is the difference between the
temperature you want inside, and that outside. Note that roof temperatures
can be way above air temp, and southern & western walls will be warmer than
eastern walls. So perhaps use a temp of 130 for your ceiling, 120 for south
walls, 110 for west walls, and ambient (100?) for east walls. May have to go
even higher with all of these if your ambients get to 115. Have to guess the
summer earth temp for your floor, perhaps 70 degrees?

Floor conduction: perimeter in feet * 0.8 * dT (this may be a cooling
benefit, a negative dT, as the ground is cooling the floor). Insulate your
floor perimeter to help keep the earth below at a more stable and
comfortable temperature.
Wall conduction: (Area - window and door area) * dT / RValue (do this for
each wall and add together)
Window, door, and roof conduction is the same, just use appropriate areas
and R Values and add to above

Air Infiltration: This one is complicated depending on how much air change
you want, the outside humidity, and whether you have a heat exchanger or
not. I'd WAG 0.4 * cu ft / 60 * 4.5 * 12

Solar radiation: For each south and west window, calculate area * shading
coefficient * 125. The shading coefficient depends on shade sources --
trees, blinds, and LowE or not. Perhaps use 0.2 if you're using slat type
blinds, 0.4 if not.

Internal heat: Add all electrical power in the house used while you are
cooling -- the cooling fan, lights, appliances, computers, etc. Also count
people at 0.1 KW each. So add all of the kilowatts, and multiply by 3412 to
get BTUs generated.

All of the equations produce BTU, so add them all up to find a rough heat
gain. You need an A/C that is this big to keep you cool. There are HVAC book
much more detailed than this, but this should get you within about 25% if
you know the numbers. However, you'll have to guess with some of these
numbers, but you'll quickly see what matters and what does not. May give you
some ideas on where you need to improve or realocate money.

I noticed that the above calcs don't seem to take into account the effects of humidity level.

I found that a 5200 btu A/C is a little overkill. It cools fine, but cycles fast...

You mentiond it using 600 watts. I assume that is when the compressor is cycled on. What about when the compressor is off? Did you measure the 600 watts, or just look at the name-plate rating? How long is the on cycle, and the off cycle and at what outside and indoor temps?

You should check out Larry Sorenson www.outbackteardrop.com...

Larry's site, along with Dave & Louise's page are the ones that inspired my interest in TTT & TD.

[Woody]

I noticed that the above calcs don't seem to take into account the effects of humidity level.

The formula I found was one to basically simple caculation for figureing req. btus againist volume of area to be cooled (simple rule of thumb). There was no other variables in the formula. I was not to worried about humidity or heat gain considering it is a camper and the only time I would be in it was at night anyway.

You mentiond it using 600 watts. I assume that is when the compressor is cycled on. What about when the compressor is off? Did you measure the 600 watts, or just look at the name-plate rating? How long is the on cycle, and the off cycle and at what outside and indoor temps?

.

The A/C unit is rated at 4.5 amps @120 vac with the compressor running. The surge when compressor start is something different. I measured the amp load with compressor running and it was 4.9 - 5 amps. It was hard to get a reading on compressor start, but it appeared to be almost double to 9.8 - 11 amps. Now like I said it was hard to get a reading on start. Normal fan operation I had not thought about checking. I would assume that it would be less than half the normal run amps , but I do not know. I will have to check it out. I had thought in a pinch that the 1000 watt inverter I have might power the "fan only" function for some air movement atleast on cool nights when dry camping. The temps in Florida in the summer are in the mid to high 90's with 70 -100% humidity. The A/C on initial power on (set @ 75 degrees) would cycle like normal unit mounted any where in the beginning, but as the trailer cooled down it would cycle short(2 minutes or so) to maintain the temp and then it would wait(3 -5 minutes) and short cycle again probally due to insulation and the small volume it had to cool. When two people were in there, the heat load would make it run longer naturally.

Larry's site, along with Dave & Louise's page are the ones that inspired my interest in TTT & TD.

Larry's site was the first site I saw and I too got the bug

Btw we are still talking about campers right? The only formula that I really need is the one that keeps my beer cold and the fun of camping never to end

[fasttimes]

You should check out Larry Sorenson www.outbackteardrop.com site he spends alot of time in the desert and he built a mini swamp cooler and states it work well for him. He might be someone to talk to about his cooling system which he shows on his site

I thought I would expand the swamp cooler idea, just to help those that search for the info in the future. The info can be found on http://www.outbackteardrop.com/body8.html

He also wrote some additional info in his site guestbook:

"There's many questions on the 12v swamp cooler. It's just a box made to fit into our limited space. Everyone's would be different. Try to make it as tall as possible with the most pad surface area. Our cooler consumes about 1 quart per hour on a low humidity day (10-20%). The more humid it is, the less it cools. You can use any pad material available at all hardware stores but avoid the 'aspen' type because they will clog the tube holes. Experiment and see what works best for your application. The 100 cfm fan that blows into the trailer works ok but having two or a 200 cfm fan would be better."

I can also suggest a couple of extra things:

- Take a look at the Attwood V625 model pump instead of the V500 model he used. It uses 1.0 Amps max. vs the 1.4 Amps max for the V500 model.

- For fan and/or water pump speed control, put together your own PWM motor speed controller(s) for $2-$5 each. There are lots of different examples out there. The one I have built in the past is at http://vb3.forums.bit-tech.net/showthread.php?t=2298 and a few other examples include:
http://www.bit-tech.net/article/51/
http://www.nomad.ee/micros/pwm555.html
http://www.cpemma.co.uk/pwm.html
http://casemods.pointofnoreturn.org/pwm/index.html
http://www.overclockers.com/tips1127/
do a google search

[fasttimes]

The story is not over yet. I contacted the comapany, and have more info. Here is the reply I received:

Our DC1 is a window unit and SU600 is a split unit system. Please visit
our new web site for the latest information on our air conditioners at

http://www.thermocompressor.biz

We have a distributor in the USA. Please contact him to discuss your
requirements. He is
Dr Shaam P. Sundhar
President
Inventions Oasis, Inc
6, Tall Timbers Drive,
Princeton, NJ 08540
Phone: (609)921 0187
Fax: (609) 921 8193

Dr Sundhar should be able to sell you a sample unit of SU600. If you are
unable to contact him, please let me know.

The price of USA474 for DC1 is no longer valid.

If your camping trailer is about 300 cu ft in volume, then our SU600 is
very suitable for your application. DC1 is for space of 150 cu ft.
Currently our SU600 and DC1 can only operate on 12VDC.

There is a good news, we are in the process of manufacturing our own
rotary compressor, and the future operating voltages will start from
12V, 24V, 36V and 48V. However, this will take another 6 to 12 months.

If you got to the web site, they have two AC units of interest. The DC1, now called the DC 300, is a 300 watt/1020BTU window unit (I thought it wat a split unit!) that weighs in at only 35 lbs.:

Compressor: 12V DC compressor
Cooling capacity: 300 watts (1020 Btu/h)
Cooling space: 6ft x 4 ft x 6 ft (144 ft3) at R-value (heat resistance) of about 5
Electricity: DC 12V @ 10A
Refrigerant: HFC-134a
Ambient air temperature: 24 to 330 C
Room temperature: 230 to 250 C
Thermostat: remote wireless control, +16 to +30 deg C
Dimension Length x Height x Depth: 315mm x 453mm x 340mm (12.5 in x 17.75 in x 13.4 in)
Casing: 0.7mm steel panel
Weight (approximately): 16 kg


For you guys saying the 300 watt unit is too small, they also have the new (to me) SU600. This (really) is a split unit (meaining quite in the trailer) and built for D-I-Y install. The unit has a little over double the cooling capacity, at 630 watts/2150 Btu.:

Compressor: 12V DC compressor
Cooling capacity: 630 watts (2150 Btu/h)
Cooling space: 6ft x 8 ft x 6 ft (288 ft3) at R-value (heat resistance) of about 5
Electricity: DC 12V @ 23A with low voltage cut-out system.
Refrigerant: HFC-134a
Ambient air temperature: 24 to 330 C
Room temperature: 230 to 250 C
Thermostat: remote wireless control, +16 to +30 deg C
Dimension Length x Height x Depth:
Evaporator (cooling unit) 26.75 in x 9.75 in x 7.10 in (680mm x 250mm x 180mm)
Condenser assembly (with compressor): 18.25 in x 8.75 in x 13.25 in (465 mm x 220 mm x 335 mm)
Casing: 0.7mm stainless steel
Weight (approximately): 28.5 kg (indoor unit weighs 10kg & outdoor unit weighs 18.5 kg)

So, anyone intersted now?

[steve wolverton]

fasttimes - Neat stuff. I wish they had a split 110 unit that size. Any ideas on the weight?

The only thing that makes me nervous about that unit is finding parts/service.

I want a 110 unit, and so far the Petcool is looking like the way to go. $400 is a big pop, but I imagine well worth it in Texas in July.

Steve

[RAYVILLIAN]

I've thought about trying to split a cheap 110 AC. Talked to my best friends son who does heating and cooling and he thought that it wouldn't be to hard to make something like a car AC with compresser condenser outside and cooling coils inside but it would have to be charged after it was put together. I might try it on the new tear and post info.
Gary

[James (tinbender)]

we put split systems in all the time and we put in little one that are not split.they are made for wine rooms inside houses.the wine rooms that are under the house we can vent the one piece under the house if we don't have that choice we use a split system.I'm not sure where we buy them but i can find out when i go back to work because they have all sizes and shapes avalable.I don't have aneed for one because when we go camping in the summer up in the sierra's it still stay cool most of the day.
http://www.geocities.com/august95664/mycubby.html

[Arne]

I looked into the wine coolers a while back. If I remember correctly, they were expensive and not light...

Can't remember all the details, but other than being a bit smaller in size, I don't recall their being any weight or cost advantage.......

[fasttimes]

fasttimes - Neat stuff. I wish they had a split 110 unit that size. Any ideas on the weight?

It's listed in the above message. 28.5 kg = about 63 lbs. Is your trailer gong to have a 12V battery? Run off the 12V and keep the battery topped off with a standard RV 120VAC-to-12VDC converter (or PC power supply, as mentioned in another thread.)

The only thing that makes me nervous about that unit is finding parts/service.

AFAIK, they are currently using Danfoss compressors and control electronics. These can be found easy. I would think that the "balance-of-system" items are also probably off-the-shelf items, or at least sutible replaments could be found if the company went under. A service manual would be nice. I'll have to ask, next time I contact the company.

I want a 110 unit, and so far the Petcool is looking like the way to go. $400 is a big pop, but I imagine well worth it in Texas in July.

The 2000BTUs of the Petcool AC is close to ideal, especally if you want an AC model. I'm not a fan of the hose method of supplying the cooled air/return air, but it could be worse (a window unit-- yuck.)

I'm not worried about price. This is a small market, and we will never see small ACs in the same price-point as a mass-produced 5000BTU window unit.

[Arne]

The down side of a petcool,as i understand it, is it determines temp like an old car a/c (no thermostat)... you set it to be comfortable, but when the outside climate changes, you have to manually adjust the temp setting on the petcool (which is outside).... to maintain comfort...

[MarkP]

The energy efficiency ratio (EER) of this unit appears comparable to that of the typical small window A/C unit. If everything else were equal, the 120 VAC unit would consume the same amount of energy on average as the smaller capacity 12 VDC unit only it would cycle on and off frequently whereas the smaller capacity unit would run more continuously. However, everything else is not equal. What is necessary to control humidity is that you cool the air low enough to cause condensation. You therefore don't want to cool alot of air all at once. You want to cool a little bit of air then mix it with the warm air in the room. An oversized a/c unit results in the system putting out a lot of cool clammy air making the whole room cool and clammy(humid). An oversized unit typically will continue to blow air the whole time but will cycle the compressor on and off just enough to keep the room air at the temperature setpoint, the evaporator coil never gets down to the dew point and the system removes no humidity. A smaller unit handles less air but it gets it good and cold and wrings out at least some moisture.

To run either system at night you would have to have batteries anyway and an inverter doesn't cost that much so on the face of it there is much less incentive to go with the fancy little 12 VDC unit. The 120 VAC unit is capable of getting the trailer cooler overall because it is larger but it is assumed that you will be exercising some restraint and limiting the target temperature to something that either system could reach, otherwise it is not possible to make a comparison. The oversized 120 VAC unit (and it would be oversized for the small well insulated trailers) would have trouble dealing with the humidity. There are a couple of things that could be done. First is to make sure that you set the a/c so that the fan shuts off when the compressor does. Second, take off the cover and block off about half of the evaporator coil with plastic or sheet metal. Something with holes in it that uniformly reduces airflow would be the best but just slapping foil over one side of the coil would also work. This reduces airflow and cools the air deeper, past the dew point so that more humidity is removed.

I am sure that the properly sized, purpose built unit would be the better choice particularly if money were no object, but the energy savings are not what they first appear since the smaller capacity unit will be running longer. If you can't afford to run the big 5,000 btu/h unit continuously you also can't afford to run the five smaller 1,000 btu/h units that you would need to run to get the same capacity, and if you can live with only 1,000 btu/h cooling then you may be able to live with the oversized unit if you can control the humidity. As long as both units are approximately equal in efficiency the decision won't be made on the basis of energy use because they will both use equal amounts of energy over the course of a day. A different strategy would help such as turning a/c off whenever you leave, letting the trailer get hot, then turning it on and blasting it for a while when you get in. Off again, on again: not the best strategy for comfort but it will get you close to the same energy use.