BTU to WATT -- What am I missing?

[CosmickGold]

I'm trying to decide if a mini 5,000 BTU air conditioner would be practical in my van without using a generator.  But I'm stuck on the conversion between Watts and BTUs.   The specs page for this Frigidaire mini air-conditioner, in the Specifications panel, states "Watts (cool): 450".  Great! But when I look up "Watts to BTU" on Google, I always get "BTUs/hour to Watts", and that 5,000 BTUs = 1,465 Watts.  (Not exactly 450.) What gives?

 

[B and C]

Don't forget there is a startup surge on air conditioners. There has been a few post or threads where they recommended an energy efficient model (maybe the one you are looking at). They were running it off a 1000 watt peak inverter generator though as far as I can remember. Jim in Denver (member here) is one of the few to actually run an air conditioner off solar that I know of.

Edit: It states that it draws 450 watts while running (startup a lot more). Why are you trying to convert BTU's? I'm confused (not hard to do)

 

[XERTYX]

I believe I remember a conversation I read or maybe from one of Jim's videos that he has over 1kw of solar on the roof and he uses a very specific Maytag I believe aircon that surges up to probably 1kw and runs at 450w I believe. Maybe 320w on eco mode. (I've watched a few videos on this I wanted to determine how difficult it would be to refrigerate a meat locker for instance or to preserve an above ground root cellar dugout)

During shaded times it's a huge draw but if its during the day with a full battery and 500w or so (more is better) on the roof its doable to use surplus from the panels to run one. The startup spike will be 1kw or better so a 500w inverter most likely wont work unless it has a surge of 1kw or more.

BTUs I think are usually measured in watts for heating and not cooling. Like for instance a space heaters element.

 

[tx2sturgis]

You swerved into the actual way that Air Conditioning efficiency is rated. 

Read up on the physics involved by googling SEER, EER, and COP.

(Seasonal Energy Efficiency Rating, Energy Efficiency rating, and Coefficient of Performance)

In other words, how many BTU are you getting per watt? Or how many watts does it take to provide a certain number of BTU?

You asked is it practical without a generator...you mean solar power from the panels on the roof of a van...right?  Well, it can be done...it is possible...but is it cheap? Nope. 

Your definition of 'practical' might be different than others, but essentially your budget needs to be fairly high and your expectations fairly low.

 

[XERTYX]

If anyone has a better explanation, I would love to hear it.

I certainly dont.

 

[CosmickGold]

You are trying to compare BTUs to Watts. That's apples and oranges. ... So you have energy units, and heat units.

Eureka!  I think you've indirectly given me the answer.  I thought BTUs came directly from the Watts provided.  But since BTU's measure heat and cold, the outside air absorbing heat from the inside air has A LOT to do with the BTU's blowing out those front vents!  ... perhaps far more than the watts of electricity flowing through the wires.  So the 450 watts really is just 450 watts, while BTUs are what's being exchanged between inside and outside air.   Thank you so much for pointing out Apples and Oranges!

 

[CosmickGold]

.... You asked is it practical without a generator...you mean solar power from the panels on the roof of a van...right?  Well, it can be done...it is possible...but is it cheap? Nope. ....

My concept is to run the little air-conditioner only during the high heat of the day while the sun is beating down.  For that, I have 400 watts of solar on the roof, and another 400 watts of battery power inside.  Plus my inverter is 1000 watts (2000 watts peak).  So it sounds doable.  (You're right about that setup having been expensive the acquire.)

But my inverter is NOT true sine wave.  Motors buzz while running from it.  Will my inverter work with an air-conditioner?  Pure sine wave inverters waste energy in the process of waveshaping, so might draw too much extra power for my concept to work well.

 

[XERTYX]

From my early experiences with inverters and the corresponding sage council I recieved at the time (without having such a valuable resource as this forum) was that things like armature magnetic motors found in old black and decker type power drill (the ones you can see blue sparks inside the fan while its running) do well on modified sine wave. Anything with sensitive electronic components it is far far wiser to run on pure sine wave inverters. The only possible exceptions being devices like laptop chargers that further rectify the electricity back into another form such as DC but even still it's wise to use pure sine to prevent "noise" in the rectifier circuit and possibly send the equipment to an early grave. 

My 2 cents, if it's a cheap pos piece of equipment that can be easily and cheaply replaced maybe take the chance on modified. But an expensive aircon unit I'd only want to run on pure sine.

 

[jimindenver]

I do run a small 5000 BTU air conditioner off of my solar. Actually two of them at the peak of the day off of 1185 watts of solar. A 800 watt/ 1000 watt peak inverter generator will start and run one of them. They are the Frigidaire energy star units that are rated at 410 watts running and have a soft start which is what lets the little generator to run them. You pay for that efficiency but on solar it is worth it.

It takes between 750 and 800 watts to fully power one of the A/C's. Most of my van designs carry that much and so the people enjoy using much of the equipment that I do. (a/c, electric stove, etc.)

My inverter is not Pure sine wave. It is a industrial Modified sine way made to handle the starting surge of motors. Starting the A/C's is nothing compared to starting a circular saw that will stall out a Honda 2000i. Rated at 1250 watts it can handle 2500 watts for 10 minutes. It is also cleaner than most MSW inverters.

 

[Weight]

My 6000 btu would run on my 2000W generator. Your 450 watt rating is based on drawing 4 amps at 115 volts. If you ever plan on using inverter, that would be some where around 40 12 volt amperes. Estimated. That is only while on cooling. Less while just fan. More during compressor start-up.

 

[future_vandweller]

Eureka!  I think you've indirectly given me the answer.  I thought BTUs came directly from the Watts provided.  But since BTU's measure heat and cold, the outside air absorbing heat from the inside air has A LOT to do with the BTU's blowing out those front vents!  ... perhaps far more than the watts of electricity flowing through the wires.  So the 450 watts really is just 450 watts, while BTUs are what's being exchanged between inside and outside air.   Thank you so much for pointing out Apples and Oranges!

Heat and energy are one and the same, with heat being one of many forms of energy.  The fault lies with the US heating & cooling industry.  Instead of accurately describing an AC system as X BTU/hr, they say X BTU's.  The AC unit of your example is capable of removing 5000 BTU of heat each hour from the room that is being cooled; in metric units, this works out to 1465 Watt-hours or 5.3 million Joules[font=Tahoma, Verdana, Arial, sans-serif] of heat/energy.

[/font]The 450 Watt electrical specification refers to the power (energy per unit time or work) required for the task of moving 5000 BTU/hr from one side to the other.  So, in one hour, the (electrical) energy consumed by the AC unit is 450 Watt-hrs or 1.6 million Joules.  For historical reasons, the US has used a combination Imperial & metric units to describe heating & cooling systems.  In the US the efficiency # CoP (coefficient of performance) is the heat removed in BTU/hr divided by electrical energy required in Watts - a mix-up of measurements units.

Since energy can't be created or destroyed, the heat being removed from the cooled space and the electrical energy required to run the machine are dumped on the hot side of the AC.  This amounts to 1465 Watt-hrs plus 450 Watt-hrs (1915 Watt-hrs) or about 6500 BTU/hr.

 

[Weight]

Wow. just. wow.