Rich256 wrote:

Abby Normal wrote:

The indoor scheme is not an improvement on evap cooling, it makes it worse.

Wrong.

I just can't see how the indoor fans and water he talks about could do
any better.

With no house mass, an indoor scheme would do no better than a swamp
cooler with perfect controls (more than an on/off switch :-) But swamp
coolers don't have those controls, and indoor schemes don't need
big blowers and boxes :-)

Just checking weatherbase on Yuma:

Average High July: 107
Average Low : 81
Precip: Nil
Days above 90: 31

We also need the humidity ratio. With wo pounds of water per pound of
dry air outdoors, we could keep a house with 400 Btu/h-F of thermal
conductance to 107 F outdoor air and no internal heat gains 82.9 F
with wi = 0.0121 indoors (an efficient corner of an ASHRAE 55-2004
extended comfort zone with clo = 0.5 and vel = 0.5 m/s) with a swamp
cooler with perfect controls or indoor evaporation by evaporating
P pounds per hour of water with C cfm of airflow if (107-82.9)(400+C)
= 1000P, since C cfm of airflow has an effective conductance of about
C Btu/h-F and it takes about 1000 Btu to evaporate a pound of water.
So P = 0.0241C + 9.64 pounds per hour.

And a cubic foot of air weighs about 0.075 pounds and there are
60 minutes in 1 hour (you guys might want to argue about that :-),
so P = 0.075x60C(0.0121-wo), which makes C = 2.14/(0.00674-wo), so
a perfect swamp cooler or indoor scheme would only work with 107 F
outdoor air if wo were less than 0.00674, which seems unlikely.
NREL's nearest weather stations are San Diego and Tucson, with
wo = 0.0116 and 0.0109 in July. Phoenix has wo = 0.0105 in July.

With 81 F dry ventilation at night, the house would be comfortable
if wo 0.0121. With LOTS of night ventilation and thermal mass and
insulation, it would stay comfortable all day. An underground house
might also be comfortable.

If the average outdoor temp in Yuma is (107+81)/2 = 94 F, the house
needs 24h(94-82.9)400 = 106.6K Btu/day of cooling. That might come
from a floorslab with C = 4"/12x40'x60'x25Btu/F-ft^3 = 20K Btu/F
warming about 5 F over the day. We might cool a slab over a layer of
hollow blocks with a perfect swamp cooler and an underfloor blower,
or cool a plain slab with a soaker hose. (The soaker hose or blower
could also make an AC more efficient with cooler night air, if wo
were too high for evaporative cooling.)

If the average outdoor temp is 85 for 6 hours at night and the average
slab temp is 78, we can remove 106.6K Btu from the slab in 6 hours
(at 17.8K Btu/h) if (85-78)(400+C)+17.8K = 1000P, ie P = 0.007C+20.6
= 4.5C(0.0121-wo), which makes C = 4.58/(0.0105-wo), so we can do perfect
swamp or indoor evaporative cooling if wo 0.0105, which might happen
50% of the time, if wo = 0.0105. With C = 2470 cfm (a $55 90 W 16"
Lasko 2155A window fan), wo = 0.00592 max, and P = 37.9, ie 4.5 gph.

But wo 0.00592 may be unlikely in July, and water costs money, esp
with "Precip: Nil," so we might decide to use AC during most of July.

Nick