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Can I air condition my mechanical room? Answered

I have a mechanical room that houses my 2 HVAC units.  The room is not air conditioned and gets very hot in summer.  I'd like to use it for some storage since it's a good size, but would like the room to be cool.  Can I air condition the room by running a duct from the HVAC unit?  Seems like an obvious solution but then why did the builder not do it? 



Putting any kind of AC in there including a duct from the units themselves would be a complete waste of time & money & would certainly result in astronomical power bills.
Your best option would be to move the units outside, if this is not possible add a large extract fan to the room to help discharge the warm air preferably directly outside rather than into another room, if the hot air must be removed to the attic then a push pull set of extract fans on a ducted system would ensure you don't increase the heat load into the property, if you go for this option have them set via a simple thermostatic control in the room otherwise they could be running needlessly.
If you do decide to move the units seek professional advice, they will need to be properly purged of gas & recharged, also if the units are significantly further away from the air handlers than recommended by the manufacturer a little clever alteration to the gas pipe sizes many be necessary to ensure they run at their best.
Of course you may find that putting them outside is not an option for noise pollution reasons, A/C compressors can be noisy beasts especially at night when the noise carries so check with your landlord or planning office before you move them.

It might be worth the money to move the equipment to an outside shed if possible and money permits. It seems a very poor design to have all that heat inside a building you are trying to cool !!! If the mechanical room is on a lower floor or basement, that means all the heat in that room rises up into the upper floors that you are trying to cool ! Also, hopefully the vents "going into the attic" actually vent OUTSIDE and not into the attic, as that would further add a heat load ABOVE every room. It seems the reason the builder didn't do it is because they were too lazy to design a logical/efficient system. Moving it outside frees up a room for your use, and gets all that heat OUTSIDE where it belongs.

The room is on the second floor of the house. The house is in Florida so it gets very hot in summer. The room has a vent that allows heat to escape into the attic and the attic is vented outside. There is a bonus room located on the same floor which is air conditioned.

I would vent the room outside using a small fan at the top of one window (heat rises, so put the fan blowing OUT at the top of the window). If the room has a 2nd window, open it a little at the bottom so outside air comes in. Small fans dont use much electric. . That would at least get the room down to outside temps (and get that hot air OUTSIDE). Next I would cool the attic down from 145F down to about 110 degrees using styrofoam sheets up against the attic ceiling OR by painting the roof white with hydrated lime (whitewash). Check out "David's White Roof Experiment" on builditsolar.com If you cool the attic down to 110F, your indoor temperatures will go down 10F. My house went from about 93F down to 83F here in St. Louis. My house ALMOST doesn't need air conditioning. When we do run it... it runs a lot less often.

More air con takes more power. Where does the hot air from the aircon go to ?

There is a vent to the attic for the hot air to exit.

I'm suspicious about why the room should be "very hot" - is it hotter than a comparable room without the aircon unit in it. My concern for you would be that you could throw a lot of money into conditioning a room that wasn't designed to BE conditioned, because a lot of waste heat from the air con is actually heating the room in the first place.

Is the room ventilated at all ?

The room is vented into the attic to allow the heat to escape. The attic is vented to the outside. I'm not trying to make the room as comfortable as the rest of the house, just cooler so that it makes sense to store things in the room.

If the HVAC units are in the room, that means that the motors which drive them are in the room as well. As you can tell from your car, your vacuum cleaner, or your lawnmower, motors get hot when they are running.

So as long as the AC is active, that room is going to be warm. If you add extra AC and try to cool down that room, then you are hoisting yourself by your own petard.

One theoretical possibility would be to install a small "window" style AC unit for that room, with its motor housing outside the wall. But that unit itself is going to be running much more often, and driving up your electric bills much more, because the main HVAC motors are still going to be heating the room.