Tuesday, June 14, 2016

Air Conditioning

We liked our new portable air conditioner so much, we got a second one:

Here's the story:

The HVAC pros we called in to get quotes for a replacement furnace (ours is 23 years into its 20 year expected lifespan) and brand new central air conditioning all had a similar ball park:
  • The furnace would have to be replaced to install central air conditioning.
  • Our house would need about 2.5 to 3 tons of air conditioning capacity.
  • The job would cost $11,000, minimum.
Since the furnace was still running fine, we opted to get the new portable AC unit for the master bedroom, and see how much life we could squeeze out of the furnace. A little online shopping revealed the 13,500 BTU/hr Haier model to be the best bang for the buck right now. That prompted Brianna to ask me (since I'm the mechanical engineer and should know these things) what the difference between "tons" and "BTU/hr" was in air conditioning.

I had to look it up, and it's actually pretty interesting: "Ton" was a slang term that later became standardized. It turns out that one ton of ice melting over the course of one day (24 hours) will remove (absorb) almost exactly 12,000 BTU/hr (for all 24 hours). So "one ton" of air conditioning means a unit that can remove 12,000 BTU per hour.

Our new portable air conditioner is rated at 13,500 BTU/hr. We were practically halfway to the 2.5 tons required for our whole house!

So, we ordered a second one while the price was still good. It won't be quite as efficient or effective as a properly sized central air conditioner, but it ought to keep the house below 75F, and the two units cost less than $800 total - a twelfth the cost of a whole new installation. When the furnace gives up the ghost, we'll probably install central AC. But until then, we'll hang on to our money. Or spend it on other things. Probably we'll spend it on other things.


Once we had the second AC unit on order, we got rid of the old evaporative cooler in the great room, which really had not handled the winter well (tons of rust, and all my fault since I did a poor job of winterizing it).

I installed this one a little differently: I removed the castors and placed the unit on top of an old IKEA table we had kicking around. I had to cut off 4.5" from the table leg to get it the right height (Actually, cutting off 4.625" probably would have been better, but oh well).

This height adjustment prevents the surrounding furniture from blocking air flow, and allowed me to set up the air ducts as the minimum possible length, which did require me to do some cutting:

(That's the radon mitigation system outside the window, not a part of the new AC unit). I also had to "adjust" one of the connection brackets with my dremel (Thanks Dad!).

Finally, since this is a ground-level window, and it can no longer lock while the ducts are in place, I added a locking pin:

And the best part is: the times the AC units have to work the hardest are also the times we'll have the greatest amount of solar energy production! We get to cool the house without heating up the planet!

Update: Brianna had the good idea to put a filter on the air intake. I'm very glad we did!

Update 2: One AC unit on the main floor wasn't cutting it. I set up a price alert, and a week later we were able to snag a third unit (the second for the main floor) for the same price. It is set up the same was in the opposite corner of the house, near the kitchen. We've been able to come home to a 72-degree house on days that hit 95+ degrees!

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