[Jonathan Flowers (OP)]

More: because the cold temperature leads to a greater level of heat loss

Less: because the surrounding air is cooler and a lower balloon temperature is required to achieve the requisite lower density of balloon air

The same: Actually, it's all about relative temperature, and so the same dynamics apply at all temperatures.

I can convince myself of all three answers.  Intellectually I would like it to be the last one above.

I am tempted to apply the common sense answer which says that I only see hot air balloons on sunny days so I suspect that hot days are more fuel-efficient, though of the course the even more common sense answer says that you wouldn't want to be sitting in a basket on a perishing cold day.

Is there a thermodynamicist in the house?

[yor_on]

colder temperatures are denser (less kinetic energy=more molecules per area) but when it comes to atmospheric layers there will be lesser and lesser molecules the higher you come.

If you look at high altitude balloons they seem very empty as they leave the ground, but it's necessary for them not to bust when they expand higher up due to the lessening pressure around them.

Not to high up (1000 meters three thousand feet sort of:) I would say that they will use more energy in cold weather as the atmosphere should be denser. But maybe I'm wrong? In hot weather you will have a lot of upwinds helping the balloon raise, I think, that is )

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Or maybe I'm thinking totally wrong here, as the atmosphere is denser you will spend a lesser amount of energy to get that buoyancy and become lighter than the air..

Now I'm really confused?
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No, thinking of it once more i think you will need to spend more energy the colder it gets to keep you afloat?

Or, awh..

[Madidus_Scientia]

How could they bust? There's a hole at the bottom.

It's a good question, I don't know how to calculate the answer.

[yor_on]

Ah

I was thinking of hydrogen Balloons

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No sh* not hydrogen (Hindenburg:)
What's the name in English?

what we use instead?

you know 'weather balloons'
(Helium, sorry, need to put my brain in for renovation)
Or Hydrogen, yep it's high time..
weather balloons
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Sort of dangerous those

[syhprum]

Have weather sound balloons gone over to using expensive Helium they always used to use Hydrogen ?

[Geezer]

It's a good question, I don't know how to calculate the answer.

Archimedes should be able to help out. The envelope will produce as much lift as the mass of air it displaces. The mass of the envelope, the mass of hot air in the envelope, the basket etc., and the occupants has to be subtracted to determine the net amount of lift.

From what I have seen, balloonists seem to prefer to take off early in the morning, so perhaps the colder, denser air is more critical than the heat loss through the envelope. However, perhaps they just prefer early mornings because there is likely to be less air movement. Beats me!

[litespeed]

syhprum - Helium balloons are only good to about 80,000 ft. This is because they expand much more then hydrogen, and stress the balloon to bursting at high levels.  Hydrogen balloons are good up to about 100,000 ft.

PS: Hot air balloons in cold weather. I doubt it makes much difference for the simple reason the lift has to do with temperature difference. A hot air balloon simply needs to be proportionately warmer then the outside air, whatever the actual outside temperature. Accordingly, heat loss would seem to be no different whatever the outside temp since lift is simply the difference between the two, which, I suspect, remains nearly constant.

Geezer: Balloonists prefer morning and evening ascents because surface winds are generally lower at those times.

[Geezer]

Okydoky. So, is anybody brave enough to actually put pen to paper and produce some calculations that might help to answer the question, or have we all joined the latest branch of science;

"Anecdotal Physics"

[litespeed]

Hi geezer

I have the mathematical skills of a red cabbage.

PS from Red Cabbage:

The chemical energy of the propane remains roughly the same in both cool and warm air. That energy is used to overcome the 'heat energy' of the surrounding air. Cool weather might be doing the balloonist a favor by reducing the heat energy of the surrounding air. If that is the case - and insulating capacity of the balloon material remains the same - then less heat energy might be needed to create the differential?

Of course my next scientific breakthrough is to simply ask a hot air balloonist. But how much fun would THAT be!

[Geezer]

Hi geezer

I have the mathematical skills of a red cabbage.

PS from Red Cabbage:

The chemical energy of the propane remains roughly the same in both cool and warm air. That energy is used to overcome the 'heat energy' of the surrounding air. Cool weather might be doing the balloonist a favor by reducing the heat energy of the surrounding air. If that is the case - and insulating capacity of the balloon material remains the same - then less heat energy might be needed to create the differential?

Of course my next scientific breakthrough is to simply ask a hot air balloonist. But how much fun would THAT be!

We could, but that might be considered "cheating". I suspect the density ratio between the external air and internal is important, and lower external temperatures might reduce the energy required to achieve the "liftoff" ratio. On the other hand, it may not make the slightest difference. If I get really bored, I might have to do some sums  []

[windhorse]

I realize this question has been up a long time. But, I'm going to go with "less energy needed in the cold".
On this link : newbielink:http://www.haveballoonwilltravel.com/q&a.html [nonactive] , someone representing HaveBalloonWillTravel ballooning company says the following:

HOW MUCH CAN A BALLOON LIFT? It depends on how cold the air is and the size of the balloon. Balloons lift better in cold air than in warm air. The larger the air volume of the balloon, the more it can lift.

.
Also, check out Temperature at the bottom of this page: newbielink:http://www.fun-flying.com/weather.htm [nonactive].