How much do I save with a portable AC unit versus Central AC?


  #1  
Old 07-09-12, 02:53 PM
S
Member
Thread Starter
Join Date: Jan 2006
Location: USA
Posts: 82
Upvotes: 0
Received 0 Upvotes on 0 Posts
How much do I save with a portable AC unit versus Central AC?

I live in Hawaii, where we have the highest energy costs in the country -- $0.44 per KWH

Although the outside temperature is perfect year-round, 75-78 degrees daytime, 68-72 degrees at night, I have to sleep with the windows shut and air-conditioning in my house because of the "vog" (volcanic smog, sulfur dioxide). The vog causes burning and itching throat, eyes, and massive headaches for me, especially if I sleep with the windows open.

I have central AC in my house. It's a Rheem model RAND-048JAZ, which is 13 SEER, 230 volts, 45 Amps and keep the programmable thermostat set to 77 daytime, 74 nighttime.

I need watch my energy costs because of our high rates, so I'm thinking of putting in a portable AC unit in just my bedroom and switching off the central AC. It's a 980 Watt portable AC unit which I would set to 74 degrees and run only at night when I sleep.

The pros with central AC are that it cools the whole house and helps the most with vog, and it only runs when the thermostat turns it on.

I'm sure the portable AC unit uses less energy, but it runs continuously. I would probably have it running 10 hours per day in my bedroom.

So, I'm trying to figure out really how much do I save with using the portable AC versus central AC, considering the portable AC is running continuously and the central AC runs only as-needed. If it's not that much difference, I'd prefer to use the central AC.
 
  #2  
Old 07-09-12, 03:02 PM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 9,498
Received 66 Upvotes on 61 Posts
You would save quite a bit of money with what you propose.
Portable units and all other a/c types use a thermostat to cycle the unit on/off as needed.
In fact they use electronic controls that can give you very good temperature control, many having timers to control when they cool.

Just be sure to get a two hose model as a single hose is less efficient and will create a negative pressure in the house, drawing in outside air.
 
  #3  
Old 07-09-12, 03:49 PM
S
Member
Thread Starter
Join Date: Jan 2006
Location: USA
Posts: 82
Upvotes: 0
Received 0 Upvotes on 0 Posts
Thanks for the reply. I already have a LG 9,000 BTU portable AC unit. Wish I knew about the single vs. dual hose. I understand what you're saying about it, and will get a dual hose the next time I get a portable AC.

I have a Kill-A-Watt energy meter and just hooked it up to the LG portable AC right now and am waiting to see what it reports.

Based on when I run central AC and when I don't, I figure the central AC is costing me about $140-$170 per month. My electric bill when I don't run central AC is around $280 per month, and around $420-$450 per month with central AC.
 
  #4  
Old 07-10-12, 03:25 PM
S
Member
Thread Starter
Join Date: Jan 2006
Location: USA
Posts: 82
Upvotes: 0
Received 0 Upvotes on 0 Posts
I had my portable AC unit plugged into a Kill-A-Watt meter for the last 24 hours. I ran the portable AC for a total of 10 hours (10pm-8am) during the last 24 hours. Based on the last 24 hours, Kill-A-Watt says my monthly cost is $138 per month!

This is very close to the same cost for me to run the whole-house central AC!

I'm not sure why the costs are so close, except that the central AC only runs intermittently as-needed, while the portable AC ran continuously for 10 hours straight (even if most of the time it was just the blower).

I have 2 large solar attic fans which supposedly lower the inside temperature of the house around 5 degrees so that the central AC doesn't have to run as often. Plus the outside temperature is only around 75-78 degrees (I close the windows and run AC because of the "vog" in the air). Perhaps the central AC just doesn't run that often. Maybe at much higher outside temperatures, the central AC would run more often and cost significantly more than the portable AC. At this point, there's no financial cost difference.

Just seems odd that whole-house central AC would cost me the same energy as a single portable AC unit. Weird.
 
  #5  
Old 07-10-12, 06:17 PM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 9,498
Received 66 Upvotes on 61 Posts
Well, you said....... "I would probably have it running 10 hours per day in my bedroom."

When you say that the portable cost as much as a central unit to operate you have the portable in a bedroom with the door closed right???
If you checked the kwh consumption with the portable in the main part of the house then no wonder your power consumption is high.
In a closed bedroom set at a modest temperature you should use less power.
 
  #6  
Old 07-10-12, 07:53 PM
S
Member
Thread Starter
Join Date: Jan 2006
Location: USA
Posts: 82
Upvotes: 0
Received 0 Upvotes on 0 Posts
Yep, bedroom door was closed. The bedroom is about 11 x 15. All windows closed and blinds pulled shut. I had the 9,000 BTU portable AC set to 72 degrees and the fan set to Low. I had the timer set to run it for 10 hours from 10pm-8am. It was the only thing plugged into the Kill-A-Watt meter. The Kill-A-Watt meter said it used 10.24 kWh in the past 24 hours.

At $0.436 per kWh, that cost me $4.46 to run the portable AC for 10 hours last night! Yikes
 
  #7  
Old 07-11-12, 03:52 AM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 9,498
Received 66 Upvotes on 61 Posts
It is possible that the costs were so high because the single pipe was causing warm air from the rest of the house to be drawn into the room.
 
  #8  
Old 07-11-12, 08:34 AM
HVAC RETIRED's Avatar
Member
Join Date: May 2008
Location: Wisconsin USA
Posts: 664
Upvotes: 0
Received 0 Upvotes on 0 Posts
I have central AC in my house. It's a Rheem model RAND-048JAZ, which is 13 SEER, 230 volts, 45 Amps and keep the programmable thermostat set to 77 daytime, 74 nighttime.
A 4-Ton 13-SEER condenser should pull around 15.2 amps, not 45-amps; look for the RLA amps.

Then you have to add the indoor blower motor which will be probably over 800-watts.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: