# What's solar augmented air conditioning?

You say, "Help!  I have a high heat load.  I run a 4-ton unit for my house.  It works fine, but it's only 10 SEER and my wife likes it cold in her upstairs office.  The unit's running constantly, it seems, to meet the 71-degree setpoint for up there.  Meanwhile, I'm cold in the living room."  Well, for normal ducted units, you could try closing some of the vents downstairs for your own comfort, but the fact is the unit still is going to need to be hammering away to meet the upstairs setpoint of 71.

Airspool's solution is to install a 1-ton solar-powered DC hybrid air conditioner upstairs.  Then, during the day, the power for office cooling is normally coming from the sun (weather depending).  The savings are substantial.  Here's an estimate...

percentage of projected savings =  (1 - old unit system tons/(old unit system tons + new unit system tons) + (.025 x degrees you can now increase your main unit's setpoint))  x 100

An example is in order.  Let's assume, again, that your main unit 4 tons, and you're adding a 1-ton Airspool unit.  Let's say that once you do this, you can now set back your main unit by 5 degrees, meaning that you can have the thermostat at 76 degrees while the upstairs unit is set to 71 degrees.  According to the Arizona Public Service Company and other, you'll saving around 2.5% per degree for making this switch. Your main load is upstairs.  A bit of that 71-degree air will make it downstairs, but we're not actually taking that into account.  We're assuming that, to keep from freezing (as stated above,) you're good for it to be 5 degrees warmer.

Then...

percentage of projected daytime savings = [(1 - 4/(4+1) +(.025 x 5))] 100 = (1 - .8 +.125)100 = 32.5%.

So, potentially, you can save more money by installing a smaller solar unit.  Notice that nothing was taken into account for the run cost of the solar unit.  And, in sunny environs, that's usually true during the day. To include nighttime, assume that solar can run 8 hours/day and that the solar unit is 22 SEER using grid power since it's a plug-in hybrid.  Assume that the runtime is 50% less at nighttime since it's (theoretically) a bit cooler.  Then, the formula is...

Percentage of projected savings = [daytime hours x (daytime hours + nighttime hours) x (1 - old unit system tons/(old unit system tons + new unit system tons) + (.025 x degrees you can now increase your main unit's setpoint))  x 100] + (run time ratio of nighttime:daytime) x nighttime hours x ((daytime hours + nighttime hours) [ (1 - old unit system tons/(old unit system tons + new unit system tons)) + (.025 x degrees you can now increase your main unit's setpoint))  - (old unit seer/new unit seer) x (new unit tons/(new unit ton + old unit tons)] x 100

The last part above decreases the percentage of savings by the amount needed to run the new unit at nighttime.

So, a lot of plugging and chugging for this formula using the stated coefficients...

= {8/(8 + 16) x (.325 (known from above for the daytime)) + (.5) x (16/(8 + 16)) [(1 - 4/(4+1) +(.025 x 5) - (10/22)(1/5)]} x 100

={8/24 x .325 + .5 (16/24) [(1 - .8) + .125 - .09]}100= {.108 + .5 x .666 x [.2 + .125 + .09]}100= .108 + .333 [.2 + .125 -.09]}100

= {.108 + .333[.235]}100 = {.108 + .108}100 = 21.6%

So, overall, by only adding a 1-ton Airspool unit to your home, your cooling savings would be around 32.5% for daytime hours and 21.6% for a 24-hour cycle.  Not bad.