Air conditioning feed

SimpleSimon · Oct 23, 2011

Been asked ti design a circuit for two 7Kw air con units. Both in a school, both quite high off the ground. Going to go as fat as the isolator than ait con guy can put his in from there.
never done air con circuits before so my question is, would the two units share a compressor or would they have their own? Was thinking of two seperate circuits. 6mm SWA clipped direct to an isolator protected by a C32.
But unsure about the compressor....

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Engineer54 · Oct 24, 2011

I take it your talking about ''Split Unit AC's. So as they have quoted to you ''2 X 7KW AC units' ...then you take them as being 2 separate systems, as it's the compressor that is rated, and not the internal fan control units. You can however have 2 fan control units fed by 1 compressor unit ....

the pict · Oct 24, 2011

Are you installing the units also, or just the cabling and islolaters, also the 7KW may be the refrigeration duty and not the current demand
Pict

Engineer54 · Oct 24, 2011

Further to my earlier reply, it is normal for the supply isolators to be positioned next to the compressor units that will always be located on the ''outside of the building. These will be either high mounted on purpose made wall brackets, or sitting on the floor. Floor mounted) The fan coil units (FCU's) take little in the way (unless they have actual electrical heating elements incorporated) of power, basically just being a fan /evaporation unit.... Most modern AC unit's work on heat pump/compressor technology for heating mode these days!!!

SimpleSimon · Oct 24, 2011

So i need to ask the air con guy if his units will be fed by one compressor or two seperate ones. Did yiu say these are usually housed outside?

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TheatreSparks · Oct 24, 2011

I have just been involved in the install of two 10kw air con units, they had a 32a supply to each of the outside units and the internal fan units are normally fed off the outside units as the cable also doubles up as the control line between the units. The manufacturers will almost certain spec'd a minimum fuse size. The outside units are the ones that have the compressors located in them, they are outside as they use the external air to either dump the heat from inside (cooling) or to pull heat in (heating). The fan units inside draw very little current (2~3 amps) but the external units can pull a fair bit more.

Engineer54 · Oct 24, 2011

SimpleSimon said:
So i need to ask the air con guy if his units will be fed by one compressor or two seperate ones. Did yiu say these are usually housed outside?

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Yes, the compressor units are always located outside!! The isolators feeding these units also double as the means of local isolation... Only special compressor unit models supply 2 FCU, so i would imagine your installation are 2 separate AC systems Simon.

SimpleSimon · Oct 24, 2011

Thanks as always 54. So if im just installing the feed would i be providing it up to the isolator that i provide?
dont think my company have given me enough info about how far im supposed to go.

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SimpleSimon · Oct 24, 2011

Engineer54 said:
Further to my earlier reply, it is normal for the supply isolators to be positioned next to the compressor units that will always be located on the ''outside of the building. These will be either high mounted on purpose made wall brackets, or sitting on the floor. Floor mounted) The fan coil units (FCU's) take little in the way (unless they have actual electrical heating elements incorporated) of power, basically just being a fan /evaporation unit.... Most modern AC unit's work on heat pump/compressor technology for heating mode these days!!!

And if they are high on brackets would i not be best to provide local isolation at ground level.

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Engineer54 · Oct 24, 2011

SimpleSimon said:
Thanks as always 54. So if im just installing the feed would i be providing it up to the isolator that i provide?
dont think my company have given me enough info about how far im supposed to go.

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Yes, just to the isolator, the AC guy will do the connections from there...

SimpleSimon said:
And if they are high on brackets would i not be best to provide local isolation at ground level.

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More often than not, the isolator is actually fitted to the compressor itself. If in your case the compressor unit isn't installed yet then i would position it relatively close to the AC position. Installing at low level wouldn't be thanked by the AC guy ..lol!!