Swamp Cooler
Last Post 28 Mar 2015 01:55 PM by hogsmen. 13 Replies.
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desertlifeUser is Offline
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18 Sep 2014 09:23 PM
I live near Phoenix and I am trying to size a swamp cooler for my house to replace an old AC system so as to reduce electrical footprint…become more green! I have plenty of water, so no problem there. The old AC system is 2.5 tons. How would I go about sizing a new swap cooler since they are rated in CFM and not in tons?
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18 Sep 2014 09:39 PM
Well, not sure an evaporative cooler (AKA swamp cooler) will make you more "green" as they can use a significant amount of water! However, it is true that they may provide equivalent AC cooling capacity for less than half the electrical power as AC.

You may also want to consider that evaporative coolers, or at least direct (open circuit) evaporative coolers, bring cool air having a relative humidity that is typically between 70-90% into the building. This may be desirable in extremely dry climates, however, this high humidity could also cause damage to unprotected metal or cause other undesirable issues.

The effective cooling capacity of an evaporative cooler depends on the elevation, design indoor dry bulb temp, design outdoor dry bulb temp, design outdoor relative humidity (or really the dry bulb temp coincident wet bulb temp), cooler design efficiency (typically between 80-90%) and the air flow rate (CFM) through the cooler evaporative media pads. At 100% efficiency (which isn't possible), the cooler leaving dry bulb temp would in fact be the outdoor wet bulb temp.

For example, at an elevation of 1117 feet, design indoor dry bulb temp of 75F, design outdoor temp of 110F, design outdoor relative humidity of 10%, cooler design efficiency of 90% and cooler design cooling capacity of 2.5 tons, the required air flow rate would be 10,276 CFM. The cooler leaving dry bulb temp will be 72.2F. The water evaporation rate would be 44.7 GPH and the water bleed-off rate would be 10.3 GPH, making the total water makeup rate be 55.0 GPH.

If you increase the design indoor dry bulb temp to 78F, the required air flow rate would decrease to 5,030 CFM. The cooler leaving dry bulb temp would still be 72.2F. The water evaporation rate would decrease to 21.9 GPH and the water bleed-off rate would decrease to 5.0 GPH, decreasing the total water makeup rate to 26.9 GPH. This illustrates how dependent and sensitive evaporative cooler performance can be to the aforementioned parameters.  As the outdoor relative humidity increases, the performance of an evaporative cooler quickly descreases.  This is why evaporative coolers are only highly effective and commonly used in areas having very hot and dry climates.

We have free DIY evaporative cooler performance software on our website if you want to play with the numbers to better assess performance in your climate:

Borst Evaporative Cooler Performance Software
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
desertlifeUser is Offline
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19 Sep 2014 08:47 AM
Thank you for the quick response and great info sailawayrb. I was aware of the high water requirements but I didn’t realize how much the cooling and CFM depends on the outdoor humidity. It now makes perfect sense and the calculator works great. I don’t think having the extra humidity in the house will be a problem here.
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19 Sep 2014 09:36 AM
Sure thing and happy to help :-)
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hogsmenUser is Offline
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24 Mar 2015 03:13 PM
I have DIY built one these for my barn. The actual performance appears to match the calculator performance very well. However, could you please explain the equations and assumptions that were used for the calculator water rates? I am wondering if I can downsize the requirements some for another project. Thank you in advance for your kind assistance!
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24 Mar 2015 09:22 PM
Hogsmen, Borst has not been active on this forum for several weeks. I suggest that you PM them or contact them directly by going to their website. They always seem more than willing to help DIY people.
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hogsmenUser is Offline
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25 Mar 2015 02:32 PM
Thank you Icfbound. I submitted my questions to the Borst Engineering website and will hopefully get answers.
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26 Mar 2015 09:36 AM
Their website promised a 48 hour response, but received this in less than 24 hours:

Hi Ron,

We are happy that you found our evaporative cooler calculator to be useful! Now please allow me to answer your specific questions.

The evaporation rate in GPH is the air flow rate in CFM times the wet bulb depression (which is the difference between the outdoor dry and wet bulb temps) times the design saturation efficiency (in decimal form) divided by 8700.

The water bleed off rate in GPH is the air flow rate in CFM divided by 1000 and is limited to no more than 50% of the evaporation rate.

The water makeup rate in GPH is the sum of the evaporation rate and the water bleed off rate.

The water recirculation rate in GPM is three times the evaporation rate in GPH divided by 60.

These equations are from Principals of Evaporative Cooling Systems, A. Bhatia. And for completeness, here is the actual evaporative cooler calculator code:

'Cooler Performance Calculations'

'Design Efficiency'
de=deper/100;

'Density Ratio'
dr=17.6808*bpinhg/(didbtdegf+459.67);

'Wet Bulb Depression'
wbddegf=dodbtdegf-wbtdegf;

'Leaving Dry Bulb Temp'
ldbtdegf=dodbtdegf-(wbddegf*de);

'Heat Transfer Temp Differential'
deltatdegf=didbtdegf-ldbtdegf;

'Air Flow Rate'
afrcfm=dafrcfm;
if ((deltatdegf>0) && (dcct>0) && (dafrcfm==0)){
afrcfm=(12000*dcct)/(1.08*dr*deltatdegf);
}

'Cooling Capacity'
cct=dcct;
if ((deltatdegf>0) && (dafrcfm>0) && (dcct==0)){
cct=dafrcfm*(1.08*dr*deltatdegf)/12000;
}

'Evaporation Rate'
ergph=afrcfm*wbddegf*de/8700;

'Water Bleed Off Rate'
wborgph=afrcfm/1000;
if (wborgph>0.5*ergph){
wborgph=0.5*ergph;
}

'Makeup Water Rate'
mwrgph=ergph+wborgph;

'Water Recirculation Rate'
wrrgph=3*ergph;
wrrgpm=wrrgph/60;

We hope this response adequately addresses your questions. Please don’t hesitate to contact us if you have any further questions or if we may be of any further assistance.

Sincerely,
Erick Borst

When I replied back to thank Erick for this assistance and mentioned the firestorm on the Radiant site I received another response that they were dealing with a family death and had lost a son.
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26 Mar 2015 03:44 PM
Thanks for sharing. I feared it might be something like that.
CONservative: The first three letters are all you need to know to fully understand this Republican.
<br /> <br />
Racist: A person who believes their race is superior to another race.
<br /> <br />
Religion: The deception of suckers who fear nonexistence to believe in a nonexistent supreme being and to adhere to false doctrine to control and exploit them.
<br /> <br />
Republican: A greedy, racist, sexist person who skillfully uses deception, hate, fear and religion to control and exploit suckers to gain personal wealth and power to benefit themselves while using government to limit the freedoms, safety and pursuit of happiness of others.
<br /> <br />
Sexist: A person who assaults, discriminates, intimidates or stereotypes the opposite sex.
<br /> <br />
Sucker: A weak minded person who has been brain washed and who usually lacks education and critical thinking skills allowing them to be easily deceived. <a href="https://www.youtube.com/watch?v=vGAqYNFQdZ4">Watch...Don't Be a Sucker!</a>
<br /> <br />
Trumpian: A narcissistic and skilled con artist Republican who is highly attractive to suckers and uses Fascist and Nazi tactics and commits traitorous acts to undermine democracy to gain personal wealth and power.
sailawayrbUser is Offline
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27 Mar 2015 10:32 AM
Hey, NO tragedy here! My forum absence has been the consequence of very limited personal time. We have place in Maui that we visit every year for a couple weeks during the prime whale watching season (early-February). Spring is also our busiest time completing our various project designs and project fabrications and then beginning our various construction projects for clients. This year we had an uncle pass way, but this was expected for some time and not a surprise. And finally, we have been assisting one of our sons, who had been a great asset to our company, transition to his new career as a police officer when he graduates from the WA State Police Academy in May:

Dietrich

I expect to have more time in the coming weeks. However, you may always PM me or send your questions directly to us by using our website:

Contact Borst Engineering & Construction LLC
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
icfboundUser is Offline
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27 Mar 2015 11:02 PM
I am very happy to hear all is mostly well sailawayrb! Congratulations on your son being a policeman and eagle scout before that. Thanks again for everything you contribute to this forum too.
CONservative: The first three letters are all you need to know to fully understand this Republican.
<br /> <br />
Racist: A person who believes their race is superior to another race.
<br /> <br />
Religion: The deception of suckers who fear nonexistence to believe in a nonexistent supreme being and to adhere to false doctrine to control and exploit them.
<br /> <br />
Republican: A greedy, racist, sexist person who skillfully uses deception, hate, fear and religion to control and exploit suckers to gain personal wealth and power to benefit themselves while using government to limit the freedoms, safety and pursuit of happiness of others.
<br /> <br />
Sexist: A person who assaults, discriminates, intimidates or stereotypes the opposite sex.
<br /> <br />
Sucker: A weak minded person who has been brain washed and who usually lacks education and critical thinking skills allowing them to be easily deceived. <a href="https://www.youtube.com/watch?v=vGAqYNFQdZ4">Watch...Don't Be a Sucker!</a>
<br /> <br />
Trumpian: A narcissistic and skilled con artist Republican who is highly attractive to suckers and uses Fascist and Nazi tactics and commits traitorous acts to undermine democracy to gain personal wealth and power.
icfboundUser is Offline
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27 Mar 2015 11:03 PM
I am very happy to hear all is mostly well sailawayrb! Congratulations on your son being a policeman and eagle scout before that. Thanks again for everything you contribute to this forum too.
CONservative: The first three letters are all you need to know to fully understand this Republican.
<br /> <br />
Racist: A person who believes their race is superior to another race.
<br /> <br />
Religion: The deception of suckers who fear nonexistence to believe in a nonexistent supreme being and to adhere to false doctrine to control and exploit them.
<br /> <br />
Republican: A greedy, racist, sexist person who skillfully uses deception, hate, fear and religion to control and exploit suckers to gain personal wealth and power to benefit themselves while using government to limit the freedoms, safety and pursuit of happiness of others.
<br /> <br />
Sexist: A person who assaults, discriminates, intimidates or stereotypes the opposite sex.
<br /> <br />
Sucker: A weak minded person who has been brain washed and who usually lacks education and critical thinking skills allowing them to be easily deceived. <a href="https://www.youtube.com/watch?v=vGAqYNFQdZ4">Watch...Don't Be a Sucker!</a>
<br /> <br />
Trumpian: A narcissistic and skilled con artist Republican who is highly attractive to suckers and uses Fascist and Nazi tactics and commits traitorous acts to undermine democracy to gain personal wealth and power.
LbearUser is Offline
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28 Mar 2015 01:31 PM
The problem with "swamp coolers" in Phoenix is during monsoon season From July - September . During these wet and very hot and VERY HUMID months the swamp coolers are quite useless in removing the humidity out of the air. So when it is 110F and humid, you got some pretty miserable conditions.

Why not just get a ductless mini split? Mitsubishi now makes 30 SEER 13.5 HSPF  heat pump units in 12,000 Btu - 24,000 Btu. For around $3k installed you would be all set.

These will not only be very energy efficient but they will also remove the moisture out of the air which a swamp cooler will not do.

Phoenix is probably one of the worst places to be during July - September. The heat and humidity is atrocious. It's a "dry" heat the rest of the year but man those 3 - 4 months during summer monsoon is pure misery.


hogsmenUser is Offline
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28 Mar 2015 01:55 PM
Sorry, I am bad. I misconstrued and miscommunicated what Erick wrote. Very glad all is okay. Congratulations regarding Dietrich too. Truly a very good bunch of guys and gals at Borst. Their customer support for free assistance was impressive.

Lbear, I am not in AZ. I am in SW TX. I have infinite water but limited power. We use these for barns which works very well here. I raise pigs and shoot wild hogs. However, I wouldn’t use one in my home for exactly the reasons Borst and you mentioned.
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