Rigid HVAC Micro DC AirCon
- Thread starter jmnielsen
- Start date
IIRC, 12,000 BTU is a ton, derived from the calculation: melting a one ton block of ice (metric tonne or short ton?) releases a given amount of thermal energy or has a given cooling capacity.
If the aforementioned 1500 BTU were to be correct, you are looking at a unit that is one-eighth of one ton.
If the aforementioned 1500 BTU were to be correct, you are looking at a unit that is one-eighth of one ton.
Grassland
Well-known member
12000 BTU per hour is "1 ton of cooling"
While most cooling systems in homes are oversized, even poorly built homes tend to be better insulated that the typical camper. You also need to factor in internal loads like lighting, chargers, transformers/converters and of course living creatures like humans and pets.
As mentioned, doing load calculations is the best bet. Save money on purchases by doing the math on paper (or software since it's 2021) and when the math says you have a load of 8600 BTU per hour,.you know the magic BS 1500 BTU micro AC does nothing but cost money.
Insulation is the gift that keeps on giving long after some high end mechanical HVAC system has reached end of life.
I try to explain this to people every day at work
While most cooling systems in homes are oversized, even poorly built homes tend to be better insulated that the typical camper. You also need to factor in internal loads like lighting, chargers, transformers/converters and of course living creatures like humans and pets.
As mentioned, doing load calculations is the best bet. Save money on purchases by doing the math on paper (or software since it's 2021) and when the math says you have a load of 8600 BTU per hour,.you know the magic BS 1500 BTU micro AC does nothing but cost money.
Insulation is the gift that keeps on giving long after some high end mechanical HVAC system has reached end of life.
I try to explain this to people every day at work
vintageracer
To Infinity and Beyond!
There ya go!
A simple explanation of what appears to be a complex subject for most folks.
luthj
Engineer In Residence
Its really hard to get a good load calculations for a van/vehicle. Things like air exchange due to body vents or the cab AC system, thermal conduction through the body, and solar gain are tough to estimate. There is a good reason that even well insulated 5th wheel trailers need 30k+ BTUs in the southern full sun summer.
I believe most pop up forced air furnaces are around 30k btu’s. Seems like AC and heating should have roughly equal power
luthj
Engineer In Residence
Not necessarily true in a vehicle. Solar gain and dehumidification of air intrusion play a large role. In cold weather air leakage and cold air from exposed sheetmetal pools on the floor, where it doesn't affect comfort as much. In how weather it pools on the ceiling, which significantly impacts comfort.
That being said, very cold weather, say near zero, is 60F from comfort. Vs hot weather, which is 20-35F from comfort. So heating loads can get you in the ballpark for cooling needs. Really the only good solution for most is to either compare performance of a very similar or identical setup, or to actually test. Buying a cheap window unit off craigslist, and testing it through a window/door is a good start. You will know for certain what kind of cooling is needed for various conditions.
Hi - any update on the unit and how it performs?
VDBAZFJ
Adventurer
Hello! Yes. Unfortunately it was a waste of money. My trailer cabin is just under 2 cubic meter which this unit is supposed to be able to cool. And it does cool. But not enough to make it worth the cost and install.
I had trailer in my garage out of sun, turned on the A/C and let it run for 12 hours over night and it dropped the inside temp 5 degrees. You could also tell that the air was dehumidified/cooled. I continued to let it run the rest of that day while I was at work, when I got home, the temp had gone up inside but was still 5 degrees cooler than outside temp. Granted, this was Tucson in July. But it was not in sun. Ambient temp in garage was 93 during the day. 87 in trailer. I suspect, if you put two living bodies inside with A/C on, it would be even less effective. I removed it from my trailer.
It’s a nice unit for what it is! But honestly, I don’t know what purpose it would be used for. Any ideas?
First, thanks for the report and for trying it out. Two cubic meters is indeed pretty small. You're right - if all it could handle in the shade was a five degree drop it'll be useless in the sun. I'm curious how you had it mounted and plumbed? Was the main unit outside with hoses run in? I saw only one video where someone was using one of the units in a van. He said it basically worked as a spot cooler. Apparently the air coming out of the thing is cool.
VDBAZFJ
Adventurer
I did have it mounted outside with hoses going into cabin are for outtake and intake. When this unit is on a table and turned on, the air does indeed get cold and feels like a strong flow. But once you have 4 feet of hose connect to both sides, the air flow is nil. I even went so far as to install a bilge pump inline on intake side but it did little to help.
The laws of thermodynamics are quite simple. You need a given amount of energy to raise a given amount of air by 1 degree Fahrenheit in a given period of time. There are no short cuts, e.g. $230 Chinese air conditioner to cool your camper in five minutes, using 12 volts and 20 amps of power.
I understand the desire to have this type of system in your van or tear drop, but it simply does not work, I am sorry to say. There are online calculators that you can use to figure out how much power is required to cool or heat a given space in a given amount of time. You also need to, at least approximate, the heat lost through your walls and ceilings, in order to have an idea what is required to keep you comfortable in varying conditions.
I understand the desire to have this type of system in your van or tear drop, but it simply does not work, I am sorry to say. There are online calculators that you can use to figure out how much power is required to cool or heat a given space in a given amount of time. You also need to, at least approximate, the heat lost through your walls and ceilings, in order to have an idea what is required to keep you comfortable in varying conditions.
@VDBAZFJ Thanks for the info.
@DzlToy I hear you; everything has its limits. In my case the squaredrop I'm using is exactly the size of a queen size bed, so 34 sq ft. Depending on the temperature drop desired online calculators put the needed BTU at somewhere between 1,600 and 3,300 BTU. That lines up with experience as I've got a 5000BTU window unit cooling it now and it's just way way overkill. It'll freeze me out during Houston summer nights and keeps it cold in there during Houston summer days. So based on experience with my trailer a unit smaller than 5000 BTU is of interest.
@DzlToy I hear you; everything has its limits. In my case the squaredrop I'm using is exactly the size of a queen size bed, so 34 sq ft. Depending on the temperature drop desired online calculators put the needed BTU at somewhere between 1,600 and 3,300 BTU. That lines up with experience as I've got a 5000BTU window unit cooling it now and it's just way way overkill. It'll freeze me out during Houston summer nights and keeps it cold in there during Houston summer days. So based on experience with my trailer a unit smaller than 5000 BTU is of interest.
Consider a 2000 BTU rack mount AC from a company like Tripp Lite or if you are up for a DIY project, take a sealed, high-efficiency reefer unit from a company like TechNautic, add a sound deadening enclosure and a fan and you are in good shape. These products are infinitely more reliable and durable than $100 window units or RV-grade products. Rich Boren owns CruiseRO, Technautic and LaPaz Cruise Supply and Yacht Management. Coming out of the marine world, he believes in quality products and doing things right the first time. IIRC, the highest output Technautics unit extracts 4,000 BTU of heat per hour. Mabru Power Systems may offer another option.
34 square feet with a 4 foot high ceiling = 136 cubic feet of air. Discounting heat loss through walls, doors and windows, which you can't actually do, you need 49 BTU to make 90F air into 70F air. To make 20F air into 70F air, you only need 123 BTU.
Thus, insulation, or resistance to thermal transfer, is the solution. With R-5 insulation, a rectangular box comprised of 188 square feet of paneling and a 20F temperature delta, you need 752 BTU to maintain 70F. With a 50F delta, you need 1880 BTU. This does not account for heat loss through fans, windows, door seals or heat produced by two humans, who each output 100W per hour.
34 square feet with a 4 foot high ceiling = 136 cubic feet of air. Discounting heat loss through walls, doors and windows, which you can't actually do, you need 49 BTU to make 90F air into 70F air. To make 20F air into 70F air, you only need 123 BTU.
Thus, insulation, or resistance to thermal transfer, is the solution. With R-5 insulation, a rectangular box comprised of 188 square feet of paneling and a 20F temperature delta, you need 752 BTU to maintain 70F. With a 50F delta, you need 1880 BTU. This does not account for heat loss through fans, windows, door seals or heat produced by two humans, who each output 100W per hour.