Air conditioning question......thermo-dynamics and cost.....

[Will__]

I need to find an air conditioning solution for my shop in Barcelona. We simply don't have the money to install a big double (condenser & head unit) system, and thus we're going for a mobile one, with an out-tube that needs to go to the outside. (the vent is already there)

 

But I have some questions:

 

The shop is on two levels, ground floor 65 metres squared, upper mezannine level 45 m sq. I know best practise would be 2 x 3000 Watt machines, but that will be expensive as well, and the electric bills will kill us.

 

If we get a 1000 Watt or 1500 Watt machine, and also a seriously fast/powerful fan, to move the whole air system around, surely that would work? Yes, it would take longer to cool down, but it would make some difference, no? Would we need the big fan as well? Or would we get some difference with just the machine?

 

And should it go upstairs? Cold air descends, thus in theory the cold air would flow downstairs over the balcony (internal mezzanine one) and stairs, pushing the warm air upstairs where it could be cooled in turn. Or should the machine go downstairs, pushing the warm air upstairs to just chill for a while? (pun intended)

 

Also, how do I go about calculating what the machine will cost us? It's proving to be something of a headache to find out our kilo watt per hour cost from the electrical company. This country is unreal for customer service.

 

Once I know it, I would guess that if, for argument's sake, my cost is 3 cents per kilowatt hour, then if the machine we get is 1500 watts, and I use it at full power for one hour, then it costs us 4.5 cents per hour. Is that right? Or is that just too simple......and would using it at exactly 50% power cost us 2.25c per hour?

 

Many thanks for any help with any of the above.

 

Will

[Tim Baxter]

2 x 3KW @ 3c (approx?) / KWH = 6c/hr and you can't afford it?

You don't actually say what you're flogging.  If it's none heat producing, fine but if it's anything like cooking get rid of the heated air at source with good extractors.

Looking at your mean temperature variation you'll only need a.c. for 3 - 5 months of the year (dependent on humidity of course).  Instead of investing in permanent plant consider renting for the few months you'll need it.  If you go for a.c. remember that you must seal the building otherwise you're only going to cool air which is then going to be lost to the atmosphere.  Install the a.c. at the top of your building so that the cooler air sinks to the ground floor.  As the a.c. cools and dries the air, all of it will eventually come down to your required levels and then the a.c. can be reduced to a maintenance level.  A drawback now is that you will be recirculating stale air and because you're in it you won't notice the build up of smells etc.

Alternatively, look for natural airflow to shift the hot air.  Upstairs and downstairs doors/windows (security permitting) should be open to let thermal flow shift your air and bring cooler air in at the bottom.  If the hot air rising makes upstairs too hot then assist with exhaust fans to boost the natural airflow through the building.

Generally as long as the moving air is at a lower temperature than skin it will feel cooling (again dependent on the humidity).

Alternatively, issue all your customers with light, see-through garments (possibly silk), enjoy the fun and create a fashion!

Your running costs maths is spot on.