Figure run cost and AC size?

[oldgoat]

I have a 22 x 26 garage with insulated walls, ceiling, doors and window. The west side is completely shaded by the house so it doesn't catch the evening sun. Wanting to put a air conditioner of some kind out there, but would like to figure out the cost of running the different options and also what would be a decent size top there. The only window is a slider and the biggest I found was a 12000 btu which I think would be the min. that I might get by with. Was thinking about a Soleus 18000 split or package system but confused about how to figure the run cost of it. One split I looked at is a 230V and 8.1 amps. The conersion chart I have says to take volts x amps to get watts and then take watts x cost per kwh and divide by 1000 to get the cost per hour to run. The way I understand it the 8.1 amps to per leg so wouldn't I need to take 16.2 x the volts to get the watts? Would it be realistic to expect a 12000 btu to cool this size of shop or just wishfull thinking.

 

[mike944]

To answer your direct question, it's 8.1 x 230

Each "leg" is only 115V, not 230. You could also calculate the wattage as 8.1 x 115 x 2 legs. you get the same answer.

However, That won't give you your cost of operating. That will only give you your cost to run. It won't run the entire time.

For example, lets say you had a HUGE unit that drew, lets say 30 amps. It could probably cool your garage in a few minutes. Lets say it runs for 10 minutes per hour. 6.9KW on for 10 minutes = 1.15KW used per hour.

For our other example, lets say you had a very small unit, 5 amps, but in order to cool your garage, it has to run continuiously. 1.15KW on continuiously = 1.15 KWH. Same cost.

That's a very simplified answer, and the actual cost is probably not the same, but the point i'm trying to make is you also need to look at how often a particular unit will run. Large units will run less. Small units will run more. Your cost to operate really has to do with how many BTU's of heat are soaking into the room, that the air conditioner needs to absorb, as well as the "SEER" efficiency rating of the unit. That's your primary driver of operating cost, not the amperage rating of the unit.

Here's an explanation of "SEER" (starts about halfway down the page) http://www.bankrate.com/brm/news/pf/20050810b1.asp
I would encourage you to do some additional research on SEER ratings, what they mean, and the SEER rating of the units you are considering.

In addition, the air circulator fan has a current draw as well, but it's much smaller than the compressor. All AC's have 2 sources of current draw. The air circulator fan, and the compressor unit (which includes the outdoor fan, if it's a split system) The compressor unit is your primary power consumer. The run time of the compressor is 100% dependent on the amount of BTU's that your room needs, and the SEER rating. The circulator fan can either run continuiously, or can be set to "auto" and will operate only when the compressor runs.
________
Honda VT800

 

[oldgoat]

Actually I have looked into the SEER issue. One place that I read at had a chart of savings for different SEER's from a 10 SEER. Another contractor had a piece about SEER not being the only thing to look at and the largest SEER isn't always the best because of the price difference between different levels and the amount of time each year that it would really come into play. He says that a 18 in the midwest isn't really cost effective unless you get a really good deal, but in AZ it would be more than worth it. For me where I would only be out in the garage part of the time going more than 13 probably isn't going to be cost effective either, but I'm trying to see whether first a 12000 btu casement AC would be reasonable to try to use or spend at least double to go to a mini split system. Actually I am thinking more along the lines of a backup system for the home in case something would happen to it I would be able to go to the garage for a few days if need be until a AC guy could come out. Also with the conversion from R22 is it practical to stay with a R22 system or go to the puron system or get by with a basic system for the short term and then go to the new in a few years.

 

[Three Stooges Racing]

What do you use for heat? Would a heat pump be usefull for you. My suggestion is to go with 13 SEER split system. Good bang for the buck. 1.5 to 2 tons would likely be a gracious plenty. Will you keep it conditioned all the time or only when you are out there? If all the time go with a smaller system. If only at times go with a larger system. A good rule of thumb is 30% run time for average conditions.

 

[vrrmm]

Hey Guys

As of the first of the year the smallest size that can be manufactured is 13 seer. Here is a link to a costs savings chart.
CHART here

A window a/c although cheaper up front will cost more to run every year. Another solution is a ductless unit. A little more upfront but will last longer and be cheaper to run(can be bought on the internet).

Some 10 seer are still around but not many.

But living in MA I would not suggest a 18 seer but in Florida it is common sense.

 

[oldgoat]

I probably won't keep it conditioned unless I plan on being out there. It runs N and S so I can open the window and the door and get a decent breeze through there. I have a ventless heater that I plan on using in the winter, but the heat pump idea is probably good. I don't know anything about them, but understand that they have improved a lot over the years. I have a through the wall 17,800 BTU with a heat pump that I was looking at and found a couple of min split systems, one of them a 13 SEER. I don't like the idea of cutting a hole in the wall for the window unit, but the split units are a few hundred more also. Have already shot the budget to heck and kind of hate to slit my throat going for more. Helps to justify it with having a separate unit in case the house unit goes bad though or if the kids cars go down and we need it to try to revive one. Do the heat pumps work very good when the temps get down in the single or teens?

 

[Three Stooges Racing]

Het pumps are very efficent to about 35deg,then the back up heat kicks in. In Va. heat strips are generally used,but many kinds can be tied it. Boilers,oil furnaces etc.

 

[mike944]

Conventional heat pump efficiency in heating mode does drop off significantly when it's very cold outside. "Ground-source" heat pumps, also known as geothermal heat pumps are the most efficient heating/cooling system out there. But, they're one of the more expensive ones to install, so if you've already blown your budget, that's probably not an option for you. Just figured i'd mention it as a possible option for others though.
________
vaporgenie