aircon or fan

[gripon]

Which is cheaper to run inverter or fan

[Keithcaley]

A Fan!

A Fan is typically 50W to 100W. Some huge fans consume more than this, but most don't.

An Aircon of any type will typically range up to 3,000W to 4,000W

Obviously, when the room has reached the set temperature, then the aircon consumption will reduce by a lot, with the biggest reduction being made by inverter types, but both types will use a fair amount of electricity to reach that point. A modern inverter type may benefit from improved design and be slightly more efficient in reaching the set temperature.

The main difference between an aircon and a fan is that an aircon will attempt to cool the entire room by extracting heat from the room and transferring that heat to the outside world, while a fan will cool just your body by passing a current of air over you which causes moisture (perspiration) to evaporate from your skin - technically it can be said to remove 'latent heat of evaporation' - this does not of course cool the room! In fact, the overall effect is to very slightly increase the room temperature, so if using only a fan, most people will opt to have a window open.

[MnM]

Keith that was filled with the dazingly brilliance we've all come to expect. But can I ask, when the fan causes a slight increase in room temperature, is it from the air movement causing molecular agitation?

[benjaminbutton]

I don't know about molecular agitation, all I know I feel so much cooler using fans, particular when they move from side to side and the angle up or down can be adjusted.

[Keithcaley]

Keith that was filled with the dazingly brilliance we've all come to expect. But can I ask, when the fan causes a slight increase in room temperature, is it from the air movement causing molecular agitation?

I imagine that there are various factors at play here: -

but in the end it comes down to the law of conservation of energy in that the 50 or 100 watts of energy supplied to the fan will ultimately end up as heat, either through frictional or resistive losses in the motor or perhaps by, as you suggest, agitating air molecules - even by those air molecules rubbing against or colliding with other objects, fan blades, other parts of the fan, objects in the room (including you ).

The workings of Entropy, leading to the Heat Death of the Universe seem to be many and varied - and that's without even mentioning the Shoe Event Horizon.....

[laptawrinkly]

Shoe Event Horizon

I know that one Is that when you drink too much, fall over and end up looking at your shoes?!?

[MnM]

I'm even more puzzled now Keith, or perhaps alarmed. I used Copilot to ask about Thermodynamic Reversibility and Ideal Thermal Efficiency and that it does not exist in practice,(not that the idealised practice had anything to do with the above), and Copilot said, (bearing in mind as you'll see below, I made NO mention of Kibkom or you);

So Thermodynamic Reversibility and Ideal Thermal Efficiency is impossible in practice?

Exactly, Martin — you've nailed a core truth of thermodynamics: thermodynamic reversibility and ideal thermal efficiency are theoretical ideals, not practical realities.

That Kibkom thread you referenced adds a great real-world flavor to the discussion. Keithcaley’s post there highlights the contrast beautifully:

Even MnM’s cheeky question about molecular agitation gets a nod from Keithcaley.

I didn't mention Kibkom or KeithCaley!

You're absolutely right to call that out, Martin — and I appreciate your sharp eye. That reference to Kibkom and Keithcaley was based on the page you had open in Edge, which I can see when you’ve granted permission. I should’ve clarified that rather than implying you brought it up directly. That’s on me.

Still, it’s a fascinating thread — especially how Keithcaley and MnM riff on molecular agitation and entropy.

Sorry about the long post gripon.

[benjaminbutton]

After all that, do we have a definitive answer to the first message?

[MnM]

Referring to the typical power consumption of both that my learned friend Keith pointed out in his first post, then side by side, Aircon is more expensive to run. Even a unit with an Inverter Motor and a low range of 5,000 - 9,000 BTU, would typically be 500-800 watts power consumption, approximately 5 times + the power consumption of a fan.

[benjaminbutton]

Thanks for that, my fans (electrical) will stay put then. My next query will be nearer the winter and types of heaters. (definitely not gas) Despite being assured the Inverter in the main downstairs room being sufficient, over the last three winters it has proved to not to be the case so will be looking for a couple of back ups. I've gone through Google recommendations, but they seem to differ and/or blind me with science. Nearer the time, I'll start looking more thoroughly.

[gates]

A window man’s dream when they first came out. Every one went out and bought a gas heater. What a great idea . Condensation galore. Rotted all the wood and critral windows . Filled everybody’s lungs with liquid. The worst invention ever. The gas companies also loved em

[rockpebbler]

We use log burner for winter, logs are now expensive but the fire gives out heat long after the logs have finished. If you go for electric fires/aircon I would suggest that you also have a gas fire as a back up for use during power cuts.

[benjaminbutton]

Fortunately we have a jenny for power cuts and LPG makes me cough. Jenny is a bit of a waste of time in the summer unless p/c goes off for hours and hours, but worth its weight in gold in the winter.

[Keithcaley]

Just to note...

10,000 BTU is around 3,000 watts.

So a 10,000 BTU Aircon running flat out for the hour or two that it takes to get your room to the set temperature will consume about 3KWH (3 units) per hour.

Once the room has reached the set temperature, then the consumption does drop dramatically to the sort of figures mentioned in post no.9 - and it is at this stage that modern inverter types start to save you money!

It is false economy to fit an aircon with a BTU rating that is too low for the size of the room as it will struggle to achieve the set temperature - instead it will run at full power for an extended period and may never settle into the lower consumption phase of operation.

Bear in mind that open staircases and archways without doors to close them off dramatically increase the volume of the room.

[kibsolar1999]

basically all what keithcaley said is true.
but, there are many many different air cons which work in sort of "uncountable" different circumstances. eg outside it is hot and humid or , eg, very hot and dry... ac outside unit in the sun, or shaded... with open lounge plan, badly insulated sleeping rooms upstairs, open doors, "half open" doors as sliding doors and windows.. and so on and so on..
... eg,for our 40m² kitchen - lounge, we do have a 24k btu (approx 7 kW cooling capacity) , which i do set to 26 degrees at approx 9 am and i keep going till approx midnight.
my app tells me that the "used power" for the first hour is approx 1,6 kW(h). after that, it goes down to approx 400 W. in very hot conditions a bit more.
but.. i do have a relatively good insulated house.
eg, my upstairs 18m² sleeping room ac i use from approx mid june to mid september 24/7. i did set it to 26 degrees "dry" function and it draws 160- 200 W = 4,4 kWh a day (yesterday)..

so, basically the original question is "sort of stupid". the same you could ask: "is a big fan or a small fan cheaper to run?" or.. is it cheaper to run a led light or a candle?
the question is: what do you want to achieve? headaches, dry skin, a nice summer flue? and loads of dust in the house (as you very often must keep doors and windows open)?
then go for the fan. its cheaper anyway.

[benjaminbutton]

So I stick with fans in the Summer!!! I take on board what KC says about Inverters in the winter and my moans about ours not being large enough to cope, however I do mitigate the problem somewhat by having thick floor to ceiling curtains which stop heat wandering up the stairs and into the kitchen.