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Saving Money on Air Conditioning

07/06/2011 3:20 PM

Does it actually save money/energy if one closes AC registers and doors in unused rooms.

We have several offices where I work that are not used. My office manager suggested that we shut the vents and doors to save money.

I'm somewhat skeptical that this will be worth the effort, but thought I'd ask.

It's a well insulated, single story building. In the heart of the desert.

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#1

Re: Saving Money on Air Conditioning

07/06/2011 4:02 PM

Yes, as long as there is adequate air flow from the supply registers to the return duct in the space where the thermostat is located, it should save money by allowing the occupied space to be maintained at desired temperature with less AC system run time. If your ducts have leaks this may not be the case as the amount of cooled air wasted would increase.

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#2

Re: Saving Money on Air Conditioning

07/06/2011 4:12 PM

I would say yes.

Probably not a substantial savings though, and only since you are in the desert. In areas of higher humidity I wouldn't recommend it..............it can screw up the cycling time of the unit and create cool, damp air.

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#3

Re: Saving Money on Air Conditioning

07/06/2011 4:47 PM

Photo: Associated Press

Just a little breezy last night. Everything had a coat of dirt on it this morning.

Didn't bother to check the pool.

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#4
In reply to #3

Re: Saving Money on Air Conditioning

07/06/2011 5:01 PM

I saw that on the news this morning.

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#5

Re: Saving Money on Air Conditioning

07/06/2011 5:21 PM

I do believe it would for two reasons.

1.) Depending on the location of the thermostat, the added "insulation" of the closed door would keep the cool air in the room, or connection of rooms, with the thermostat and away from less insulated materials such as windows. So the cool air should stay in the room with the thermostat longer, since it is dissipating to the outside environment more slowly, and so the AC would run less frequently.

2.) With closed vents it depends on the location of the vent on the ductwork. If you close vents to the room, the cooler air will be diverted to other rooms. If the rooms that the air is being diverted to are in some sort of connection with the thermostat, then yes, it will save money. If not then you will simply be getting more cool air to some rooms than others.

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#6

Re: Saving Money on Air Conditioning

07/06/2011 5:24 PM

Most certainly, as you would have 1 less room to lose cool air .

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#14
In reply to #6

Re: Saving Money on Air Conditioning

07/07/2011 8:23 AM

I agree completely.

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#7

Re: Saving Money on Air Conditioning

07/06/2011 5:35 PM

Where are the thermostats?

Zoned cooling?

Has the ZING! been delivered for testing yet?

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#8
In reply to #7

Re: Saving Money on Air Conditioning

07/06/2011 5:58 PM

The single thermostat is in a 40 foot hall, at the end of the AC run, about 30 feet from the air return at the other end. This bothers me, but it seems to cool OK now.

These rooms are all on the same system. There are 5 offices on one side of the hall, we would close off 4 of them. The room left open would be the next to last room at the far end of the run. The other side of the hall is used.

No Zing, yet. I check every day.

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#9
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Re: Saving Money on Air Conditioning

07/06/2011 6:09 PM

It sounds like the thermostat will not be a victim of an uncooled space or area, so that should not be an issue. I would agree with the others, it will probably help a little bit. I doubt it would hurt.

Rats! No ZING! Well, maybe he is getting the two seat 'Chick Magnet' version up to speed for us. Cool!

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#11
In reply to #9

Re: Saving Money on Air Conditioning

07/06/2011 11:45 PM

I have heard that an oversized AC unit is bad for a building as it will build too much moisture inside. I would think that shutting off some areas would have the same effect as an oversized system.

Are you crazy? Why would the Zing go to a desert to get sandblasted, when the

girls in the skimpy bikinis warm Florida breezes are so pleasant here.

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#12
In reply to #11

Re: Saving Money on Air Conditioning

07/07/2011 12:14 AM

Are you talking about an Air Conditioner or a swamp cooler?

An air conditioner, properly installed, has a drain to carry the moisture that is removed from the inside air and dump it outside. I've heard some people complain that Air Conditioned air is too dry, never too moist. Personally, I enjoy the dryness.

All machines, including air conditioners, are more efficient when properly sized for the task. If the A/C is too large, it may turn on and off more frequently, but I don't see how that would be bad for the building.

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#15
In reply to #11

Re: Saving Money on Air Conditioning

07/07/2011 8:32 AM

"Are you crazy? Why would the Zing go to a desert to get sandblasted, when the girls in the skimpy bikinis warm Florida breezes are so pleasant here."

Bob, you might be onto something here. These girls in the skimpy bikinis warm Florida breezes you speak of may just the environment for a valid test.

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#10

Re: Saving Money on Air Conditioning

07/06/2011 10:59 PM

Why would you be skeptical? An A/C is transferring heat. The more volume it transfers heat from, the more energy will be required. if you can reduce the volume from which you are extracting heat, then you will use less energy!

Others have addressed the thermostat location issue.

Another thing to consider is the condenser location. If the condenser is in direct sun, giving it some shade can make a significant difference. I've never understood why so many are mounted on the roof - about the worst possible place!

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#16
In reply to #10

Re: Saving Money on Air Conditioning

07/07/2011 10:43 AM

Good point. I just measured the surface temperature of the condenser, running. It's 104°F. Ambiant is 90° right now.

I'll measure it again this afternoon, when it gets up to 105 outside.

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#23
In reply to #10

Re: Saving Money on Air Conditioning

07/08/2011 7:24 PM

Compressor temp in the sun: 135°F.

I think some shade may help here.

I'm closing off 4 rooms on Monday.

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#24
In reply to #23

Re: Saving Money on Air Conditioning

07/08/2011 7:53 PM

I think so.

I mounted a big garden umbrella on the sunny side of ours, with it tilted so the hot exhaust is directed away from the building. Ours is one of those round Carrier units that blows the exhaust air straight up. Fortunately, the unit is mounted on the ENE side of the house, so the tilt works both to provide better shade and to direct the air flow.

I've never made any scientific measurements to prove it., but its got to help... Actually I have an arbor with jasmine and grapes that shades it for the morning, and it's in the shade of the house after 4PM or so, so the umbrella is only needed for a few hours, but I still think it's worth it.

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#13

Re: Saving Money on Air Conditioning

07/07/2011 3:36 AM

Hi Lyn

Some saving methods - tried and tested in desert conditions - Namib and Khalahari Southern Africa:

  1. Fit zoned temp controllers that work by regulating the flow to each room via a variable damper in each supply duct.
  2. Check if the compressor pump motor will allow for the fitting of a variable speed drive connected to controller (1) above.
  3. Fit Whirlybirds (Roof turbine ventilators) to the roof to drain off excess heat load on the ceilings (Had up to 30% savings with this on on its own)Fit soffit vents all around the perimeter of the roof. Fit a ceiling vent above heat sources in the rooms, like photo copiers. It will also reduce the heat load on the ducting.
  4. Check if you have cavities in the outer walls. If yes, add vents at about a foot above ground and ensure they vent into the ceiling cavity where the Whirlybirds will extract it. Reduces heat load from the walls. Reduced density of hot air sorts out the flow up the walls.
  5. Paint the roof white to reflect heat.
  6. If you are not too tight on water you could add a 4" thick evaporative cooler panel (from Munters) to the outdoor (condenser) air-con panel. Tie the pump(12VDC solar powered from a boat shop) to an outside air temp. thermostat set at 75'F. This will also filter some /most of the dust preventing fowling of the condenser panels. Up to 50% savings on a hot day >75'F.
  7. Mothball the refridgerative aircon in the summer months and use Evaporative coolers. >80% saving on power.
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#17
In reply to #13

Re: Saving Money on Air Conditioning

07/07/2011 10:55 AM

1. Can't do.

2. Can't do.

3. There is no way to vent any rooms without excess expense.

4. The walls are 10" thick adobe.

5. As I type they are completing a re-foam/Re-roofing job. The roof is flat. There is now 1" of foam sheet over the base roof with a foam over-coat over that with bright white top coat.

6. Can't do.

7. Can't do.

So, I probably will construct a cover over the ground mounted condenser and close some of the rooms off.

By the way, we don't own the building.

Thanks!

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#20
In reply to #17

Re: Saving Money on Air Conditioning

07/07/2011 11:45 AM

On #3, it's not to vent the room, rather to vent the space between the ceiling and the roof. The cooler this space, the less heat is transferred into the rooms below. Since you say it's a flat roof, there may be little space. Of course there must be vents where cooler outside air can get in for this to work. In California, such vents are required by law. Attics can get up into the 130-150°f range, so 105° ambient air is cooler.

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#22
In reply to #20

Re: Saving Money on Air Conditioning

07/07/2011 7:59 PM

135°F at 2:00PM.

To modify the building in any way, I would have to file a request for a building permit, submit plans, etc.

It's a city owned building and when we moved in I had a 20x30 foot pad and wall constructed for equipment storage. The permitting process is arduous and I wouldn't want to go through that for a few hundred $ a year savings.

I'll block some vent off and see what happens.

Cheers.

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#18

Re: Saving Money on Air Conditioning

07/07/2011 11:09 AM

The effort would be minimal but if it's a constant volume system you'll have to be careful not to pinch the total air to the cooling coil to the point that you run into icing of the coil.

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#19
In reply to #18

Re: Saving Money on Air Conditioning

07/07/2011 11:12 AM

Lou,

This is Arizona. There is no moisture in our air.

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#21

Re: Saving Money on Air Conditioning

07/07/2011 7:33 PM

Closing the registers in those unused spaces will at least reduce the electric power demand of the air handler, which typically uses a centrifugal ("squirrel-cage") blower. Unlike axial (propeller) fans, the power required by a centrifugal fan diminishes with reduced or restricted airflow.

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#25

Re: Saving Money on Air Conditioning

07/12/2011 2:17 PM

Guys,

I have closed the vents in three rooms and will keep the doors closed in those rooms. That should help a little.

Thanks for all the input.

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#26
In reply to #25

Re: Saving Money on Air Conditioning

07/12/2011 2:46 PM

New thought.

With all of the cool condensate that is being dumped, could that cool water be misted onto the condenser coils to aid the cooling effect? Dump the condensate into a pan, and use a small pump to spray the condenser. Add a float switch to prevent running the pump dry. All thoughts welcome.

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#27
In reply to #26

Re: Saving Money on Air Conditioning

07/12/2011 3:10 PM

Two reasons.

1. I'm lazy and don't want to have to think.

2. When the humidity is high, it's never over 20% or so.

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#28
In reply to #27

Re: Saving Money on Air Conditioning

07/13/2011 7:38 AM

The last time I had to do some work to the A/C drain system, I let it dump into an office type waste pail. In about an hour, I had about 2.5 gallons. I'll send it to you.

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#29
In reply to #28

Re: Saving Money on Air Conditioning

07/13/2011 10:02 AM

Can you send it frozen? It's slightly less dense that way.

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#30
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Re: Saving Money on Air Conditioning

07/13/2011 10:06 AM

WHO THE HELL ARE YOU CALLING DENSE?

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