Evaporative cooler question

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If the house is airtight, once you reach 60% RH you won't be able to evap any more water (if you want to mainintain 60%) , so how will you cool it.
Evap cooling and airtight are not compatible.
Even though it is an open system, evap is mych more energy efficient compared to AC.
Mark
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Please note the exhaust fan in series with the 54% humidistat.
Nick
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You are just not getting it. The air out of a roof mount is often already near the 54% level. Wasting more electric trying to squeeze a little more cooling out of a given volume of air is not cost effective.
Then there is a question of what type of pads are you suggesting. The traditional Aspen shaving or other synthetic pads that are one or two inches thick? Or the more efficient (and expensive types) that are 4 to 8 inches thick?
The beauty of an evaporative cooler is being able to live differently than living with refrigeration You can leave your windows open and operative devices such as ovens as much as you like. Regardless the humidity level is often regarded as too high.
Anyway, any savings in minimal. Are you suggesting changing life style to save two or three gallons of water a day so we can keep our pool full and pour a couple thousand gallons a day on the lawn to keep it looking nice?
Refrigeration is still the preferred method of cooling.
How to improve refrigeration efficiency is where your efforts should be applied. One way is to use an evaporative cooled air to cool the condenser coils. One that has been around for a long time used copper condenser coils and sprayed water directly on the coils. Commercial users often use pools with cooling towers for cooling their freon.
And the building industry is looking hard at ways to make homes energy efficient in the SW:
http://www.eere.energy.gov/buildings/info/documents/pdfs/35316.pdf
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I'd say the same.

Indoor evaporation is equivalent, with improvements.

None whatsoever.

Nonono. That is ugly.

Would you have any evidence for this article of faith?
Nick
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If you have never lived in a house with an evap cooler, then you have no idea what you are talking aobut.
Mark
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That is what I am trying to get through to him. Reminds me of a brilliant engineer we once hired. He could solve the most difficult differential equations. Problem was he could not build anything.
For comfort I myself would prefer refrigeration but for our lifestyle the cooler is preferable. We like to have our windows open and like the air movement. The significantly lower cost is another advantage. The malls and other stores have refrigeration but I note that the big box stores like Lowes, Home Depot, SAMS, and COSTCO all use evaporative coolers. Can you imagine the complaints they would get from their customers if they let the humidity get up to the 54% level?
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No. Cooling only at night cuts water use by about half, 4.3 vs 8.0 gallons for this small well-insulated house.
20 GH'house conductance (Btu/h-F) 30 TAM6'max air temp (F) 40 TAA.1'average air temp (F) 50 WA=.00384'average humidity ratio 60 TC'comfort temp (F) 70 WC=.012'comfort humidity ratio 80 PC`*.075*(WC-WA) 90 FOR H=0 TO 23 STEP 2 100 TA=TAA+(TAM-TAA)*SIN(2*PI*H/24)'outdoor temp (F) 110 CFM=GH*(TA-80)/(1000*PC-(TA-80))'exhaust airflow (cfm) 120 IF CFM<0 THEN CFM=0 130 P=2*PC*CFM'water use (lb/2h) 140 PRINT 500+H;"'";H;TAB(11);INT(TA+.5);TAB(18);CFM;TAB(32);P 150 GPD=GPD+P/8.33'water use (gpd) 160 FANENERGYNENERGY+2*CFM/2470*90/1000'fan energy (kWh/day) 170 NEXT H 180 PRINT GPD,FANENERGY
hour outdoor cfm water temp (F) use (lb)
0 91 42.459 3.118189 2 99 100.0495 7.347639 4 104 184.9898 13.58565 6 106 237.6865 17.4557 8 104 184.9896 13.58564 10 99 100.0495 7.347633 12 91 42.45896 3.118186 14 84 10.81643 .7943586 16 78 0 0 18 76 0 0 20 78 0 0 22 84 10.81645 .7943604
gal/day kWh/day
8.060906 6.663029E-02

http://www.eere.energy.gov/buildings/info/documents/pdfs/35316.pdf
Pay no attention to the gas furnace and the $75K PV array on the roof :-) Some honest "zero-energy houses" (eg Rose in Portland OR) have heat pumps vs gas furnaces, but the PV part is still very expensive.
Nick
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So what? That is a piddling savings. Families use much more than that just flushing the toilets not to talk about watering the lawns and keeping swimming pools, golf courses, football fields etc. etc. You are going to be running the inside cooler more and use more electric. Running a fan all night is more wastefull than using 4 gallons of water.
Now if you want to really save you should set your home thermostat at 62 for the winter.
And again the main reason we even use evaporative cooling is because we can keep the windows open. Refrigeration is so much more comfortable. The people of Phoenix have both. They use the swamp cooler until the humidity gets too high. Faith has nothing to do with it. It is living in comfort. Anytime the humidity gets more than 30% we get uncomfortable as we are not used to it. Since it is so hot outside we get used to heat and tend to set our thermostats higher than people from the east find comfortable. The same goes for humidity. We are used to the hot dry outside air and humid is not comfortable.
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For this small well-insulated house.

Keep up. In this model, the fan only runs 0.65 hours per night.

I'm typing naked at the keyboard in a 39.5 F room.
Nick
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So? With water at about $2 a thousand you are saving at least 25 cents a month!!

So? In the SW water costs an average of about $2 a thousand. Power costs over 8 cents per KW. Using your numbers, running the fan, you will save about 0.8 cents worth of water per night and the fan must be 100 watts or less just to break even. Water is more plentiful than electric power.
Can you bring it around to using more water and less electric? Preferably with refrigeraton cooling.

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That may increase a lot when present interstate agreements expire.

Your arguments might be a lot more persuasive if you were to learn the difference between power and energy.

Keep up. The 90 watt fan would use 32 Wh/night, ie about 8 cents/month for this small well-insulated house.
Nick
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Rich wrote: ...

That's a false economy...water is <far> less plentiful in actual terms, <particularly> in the West.
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Should have said cheaper. Point is that the little used by coolers is insignificant compared by that used for irrigation. The fountains of Las Vegas do not present a conservation theme either. I have not checked lately but for quite some time the government was paying farmers and supplying water to irrigate land and raise cotton in AZ and paying farmers in the east not to raise it.
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Rich wrote:

My point is that under present policies, water costs are artificially low in much of the West, which you have just reinforced... :)
And, it's absolutely impossible to justify all of US ag policy, just as it is any other area of US policy owing (in large part) to the conflicting interests that compete to build it...so it's futile to even start <that> discussion.
I wasn't arguing, just pointing out a situation as one who lives where long-term water is a major issue...
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Me too (for the past 45 years watching the population grow and grow), presently on the upper end of the Colorado river. The CO reservoirs might even get full this year. But Mead and Powell is something else.
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Rich wrote:

We (as in KS) has been fight w/ CO (and, to a <slightly> lesser degree, NE) over the Arkansas, N Platte, and Republican Rivers for about that long....KS won a Supreme Court decision about two or three years ago regarding how much upstream states could (legally) siphon off prior to the crossing of state lines...CO has yet to even come close to meeting the mandates so that the Arkansas (closest river of any size to us) is now (and has been for ~20 years or so) dry most of the time at the CO/KS border and the Cimarron hasn't flowed out of NM for about twice that. Although it was always a case where there may not have been surface water all the time, until about the mid-60's there was always enough that a simple hand hole scooped in the bed would raise water--now it's bone dry and grown over until about 100 miles east of us...
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Yeah, I know. However, the Arkansas drainage area has been the deepest drought area of the state and unfortunately being on the eastern slope it is not an area that ever gets a lot of moisture. This year I think they are well above normal so it should start to flow again. And NM is the same. Those streams can not be depended on to continuously supply significant water. Sooner or later farm irrigation is going to have to end or the country is going to have to get rid of a lot of people.
The Aquifers in NE are being pumped dry but the farms continue to drill deeper and deeper.
The Colorado river is something else. That is the area with the heaviest snow but is a major supply for many states but it too can not be considered much more as a source of water for agricultural irrigation.
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I did live in Phoenix, and I much preffered the evap except when it was humid outside. With the evap, you can (you have to in fact) leave the windows open. we kept the window by the stove open, and the hot humid air from cooking would exhaust right out the window.
We had to use AC during monsoon season when it is humid outside, and the house was stuffy.
To to OP, you should visit someone with an evap cooler and see if you like it. Some people do, some don't. I loved it. People in the esat don't know anything about evap coolers. Go see someone that has one.
P.S I had mine set up with a small bleed that I fed to the garden. The bleed water reduces the buildup of scale so you don't have to change the pads as often.
Mark
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The post is so long maybe I missed fenestration being factored in there. As expected the amount of glazing being assumed is 'frugally' less than 10 percent of the wall area.
People don't live in an average,they want to be cool at the 'peak'.
If they are trying to maintain 80F in the space, you need a different approach to calculate air flow.
Assuming an ambient of 106F db and 65 wb. You could saturate this air to 65, but typically the temperature depression would possibly be 80% of the difference between the wet bulb and dry bulb 106-.8x(106-65)s.2F
If you want to maintain 80 then the temperature differential is only going to be 80-73.2= 6.8F.
So for 'a ton' of sensible cooling you would need over 1600 CFM of evaporative cooling for the ambient. An ambient condition where there is less difference between the dry bulb and wet bulb temperatures will need even more air flow.
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Sure... 96 ft^2 of (shaded) windows is 8% of the floor area.

OTOH, averages are good for estimating water and energy consumption, and a house with a long time constant can average day and night temps.

Maybe not.

Why would you think that's important in this case?

Why would you think that's important in this case?

But the house above only needs (105.9-80)128 = 3315 Btu/h of peak cooling and (91.1-80)128 = 1421 Btu/h of average cooling. With a 78 hour time constant, it can cool itself more efficiently at night...
And it wouldn't be hard to add a few earthtubes on the north side and sprinkle the ground above them to make 108 cfm of dry cool air, then add moisture to that.
Nick
It's a snap to save energy in this country. As soon as more people become involved in the basic math of heat transfer and get a gut-level, as well as intellectual, grasp on how a house works, solution after solution will appear. Tom Smith, 1980
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