Sand Storms and 140 Degrees F

Can you keep dust out of the enclosures? If so, maybe small window units would work.

Flat white paint, combined with an enclosed water jacket?

I'm hesitant to suggest this, but it could be worth a shot. Maybe contact halskinner and obtain some samples of his magic paint. It may be enough to keep the insides of the enclosures well below 130°.

How's this for a plug?

The enclosures will be gasketed and dust tight. I will have to provide small window type AC units but am concerned about the dust storm affect on them.

Can you wrap the exhaust side of the AC units with galvanized duct and vent them into a breathable box?

Combined with your gasketed enclosures, this should keep all sand out of your system.

I'm not sure if this would be necessary, but you could even vent a small amount of exhaust air back into the enclosure. This would serve to create a very slight positive pressure inside.

What do you mean by a breathable box ?

Do what we did in the Saudi & Iraqi deserts during Desert Shield and Desert Storm.....we protected air intakes on our equipment by wrapping them brand new nylon stockings....change then often! Works great protecting the barrel on M-16 rifles etc etc too!

Not much else will filter out sand and desert dust blown about by those dust storms. I don't miss those storms whatsoever!

Just so happens these are for a power plant fire protection system in Saudi. I don't think the King wants us using panty hose on his power plant.

I think CaptMoosie is on to something.

What if you contact a panty hose manufacturer and obtain a roll of the material and fashion some type of a frame on the cooling unit and some type of a filter frame for the panty hose material?

This way nobody gets their panties in a bunch over the use of panty hose

Thanks KJK.

"Takes Bow...."

That's a great idea you have there contacting an USA-based pantie hose manufacturer to build special filters for those AC units....at least the Petro Dollars will be flowing back here for once! BUY AMERICAN!!!!!!!!!! ***GRINZ*** As long as Jennifer Lopez models the pantie hose first!!!

CM, would a standard HVAC filter stop the sand?

Also, you guys had AC over there, how did you attend to or protect the outside unit?

Then I think his Royal Hinnyness King Abdullah bin Abdul-Aziz bin Abdul-Rahman bin Faisal bin Turki bin Abdullah needs to get a reality check and get a life, unless he wants to spend mega Petro Dollars with an elaborate and costly system where a simple and inexpensive one will suffice.

See what the Air Farce "Weenies" are using to protect their air conditioned condos in Riyadh, Dharhan, King Khalid Military City and other Royal Saudi AF bases. They use to comfort, unlike the US Army's Grunts sweating it out in the middle of the desert.

Hey, don't 'sweat it'!! LOL

KJ and CM...I am not feeling any love here.......but I can't help but smile in spite of my problem. CM...you were there...what did you all do regarding AC units ?

WJMFIRE, I was a CO of an US Army Reinforced Engineering Company there. We were in-country nearly 8 months and never saw a building or field tent that had AC units. Initially, after stepping off the plane at Al Kardj Royal Saudi AF Base and later marshaling our equipment off the USN's RO/RO vehicle cargo ship the USS Altair at the ort of Dharhan, we live in "Tent City" north of the base for a few weeks. After that we lived in our equipment as we road-marched north up to the Tapline Road which parallels the Saud-Iraqi border and a major oil pipeline.....we never saw AC units like the USAF Weenies, the USA medical units and the higher brass. We considerd ourselves very lucky to get a very limited field shower every 2 weeks...sometimes longer. After a week, no one noticed the BO because everyone stunk! LOL Water there is as precious as gold and not wasted on hygiene (unfortunately!).

Wow. I was in the Navy and that's how I paid for college. I never had to live like that though.

Thank you very much for your service. You guys are showing/have showed unbelievable bravery over there and we all owe a great deal of gratitude.

Do you have parameters on the duration of the storms?

They can last for days, sometimes up to a week. That's my experience with them. Nothing is safe. Everything gets a good "sandblasting".

Ah, that changes my reply right there!

Okay I'll take a stab. First make you sure you run "tee" vents on each cylinder so should they blow they wont turn into rockets. One good rocket in a room can ruin your entire day.

Second I'd run a tube and shell heat exchanger between the chiller and evaporator. I'd plumb the exchanger so that if the chiller rolls snake eyes you'd have an emergency back up. You could run "building water" into the chiller and just after a single pass dump that water with the heat it picked up. So the water that circulates in the room you're conditioning stays the same water all the time. The water that would be used for emergencies would occupy the space normally used by the chiller itself.

You'd have to take some temp readings underground to see how deep you need to be to get a constant annual temp reading. Run the underground line very similar to a geothermal set up. So the heat of the building water would be stripped down several degrees, returning that heat to mother Earth. It isn't high tech but it would buy you time if the chiller goes down and you need to keep your vessels from going critical.

See crude drawing..I swear I haven't opened the Cabernet...yet.

Fredski...really!!! Cmon guys I have a real design issue here that is stumping me. And by the way Fredski I think you are in the Cab,

Bury the tanks 18" in the sand, and pipe the gas.

Lower the surface temperature of the building. Titanium dioxide pigment is very cool. Use several coats, so the sand doesn't remove all of it. THEN worry about further cooling. Don't cool until you absolutely need to. Is this gas stored, or in operation, because losing gas cools the container. If the average temperature is less than 130., heavily insulate the tanks with hot water heater jackets. They'll stay closer to average that way.

Does this need to be failsafe? What happens in a power cut or when the air-con fails, do the cylinders become unsafe?

Power is not a problem because the place makes it's own...it's a power plant. The cylinders have a relief valve that pops if temperature gets too high, but then the gas is gone. The gas (compressed to liquid) will not be circulated, but just sits there until a fire occurs. The enclosures are approximately 6'H x 5'W x 3'D and mounted outside on a slab. They are 12 gauge steel and we will insulate them, but as those with experience know, metal in Saudi gets too hot to touch. I am considering mounting a sun shield over them.

I understand the relief valve provides a backstop protection, however I would challenge the assumption that a power station can rely on its own output for safety systems - events in Japan would suggest this is a dangerous assumption. All power stations need a dark start capability which would be compromised in this case if the fire suppression system had cooked off during the outage.

Yup, agreed. Just look at how many nuke plants in the USA have been cited by the NRC for backup generation equipment failure to start during tests and inspections.....

In light of the Japanese nuke fiasco, this is indeed a scary proposition.

On Navy ships, heat shields are placed all around ammo storage lockers located in the weather. The lockers also have a relief valve to release pressure if the temperature goes too high.

Wjmfire,

A different approach: Cylinders are made for storing compressed gases at pressures up to 6000PSI, instead of the normal 2000PSI. Similarly, regulators can be obtained for these higher input pressures. You have not mentioned what the chemical is, but that it is a liquid in the cylinders. Depending on the temperature/pressure curves for the material, perhaps instead of air conditioning and all that, use of a higher-rated cylinder and regulator would solve your problem in a simpler way.

--John M.

Heptafluoropropane is the chemical. Unfortunately, the cylinders are specifically UL Listed and FM approved for the chemical. Also we have to perform hydraulic flow (discharge) calculations specific to the flow data from the valve and dip tube. Therefore we have to use these cylinders.

Correct me if I'm wrong but I think that on a decent desert the night temperature falls VERY low comparing to day time. You'll need of course air/water and water/air heat exchangers, heat isolated water storage tank and surely dealing with sand, but no A/C. By the way if Amir has a cultural issue with panties, you can always use burka fabric. It should filter sand just fine. S.M.

You are correct about the temperature extremes. We have designed in heaters as well. I am thinking about a standard 5000 BTU window air conditioner with an enclosure over the outside, with a fan and HVAC filter.

If you use a window shaker (I can't believe you're actually considering this) I can guarantee you it will allow sand/dirt to pass from the outer coil to the inside space. Use a split system and seal the wall penetration.

Have to agree, burial is the best for temperature extremes. Why throw energy at both hot and cold. GA to Jerry

Also definitely a split system AC, and put the outside bit as high as possible, as most abrasion is at ground level. GA to Fredski

GA to you

_{Fair throwing them about, must be Christmas}

How about mounting these cylinders inside a refrigerator and forget air conditioning. Make your own thermostats and set the on /off temps for what you think is best. Then who cares is there are sandstorms or how long they last. Rescue

Somewhere you mentioned this is an adjunct to a power plant. That being the case I would assume there is cooling water available. A selfcontained unit with a water cooled condenser installed inside the structure could solve your problem. Heavy insulation with a highly reflective exterior will help. You will have to size the AC unit to maintain normal comfort indoor temperatures otherwise the unit will kick off on overload if the air entering the cooling coil is too high, ie, 90F or higher. A more expensive option would be an engineered "built up" system designed to handle a much higher room temperature than the standard packaged unit is designed to handle for comfort cooling.

If cooling water is not available a geothermal system might solve your problem with the condenser coil buried very deep in the sand. It will require some astute engineering to determine the size of the condening coil and the depth it will have to be buried. Good luck.

Lou Bindner

A thought from a non-engineer. Can you get the pressure tanks that are rated for a higher temerature? Otherwise the consequences of a failure in the AC system might be explosive, no?

Not explosive, they are equipped with over pressurization devices that once ruptured will empty the contents to avoid an explosion. I have to use the tanks as designed. Switching to other tanks would cost many thousands of dollars in UL Laboratory costs, and take months to do.

I like the "cooling water" idea. That would be cheap and effective. Although placing the cylinders underground would also work, I don't believe it will be allowed.

Are you designing any redundancy in the system? Or just hoping when it hits 140 everything will stay online?

Nothing will actually become damaged at 140F or even 160F. The problem with 140F is that the system may no longer perform as intended due to being outside the Listed range of 32F - 130F. I design "wiggle room" into my calculations, and fully believe the system will work fine, but unless I can maintain the temperature range for which the system is Listed, I cannot certify the system at the time of plant commissioning.

If that's the deal, that listed range is your problem, and not overpressure, it's one of those rare cases that regulations live in their own universe. During actual use the 'hi' temp will drop within seconds, possibly to lower than optimum values. Got to obey though! S.M.

A further thought - Since you deem it unlikely that you will be permitted to bury the tanks, what about installing them in the coolest part of the structure - the floor -

I assume that these enclosures will be in the form of a container or similar with a metal floor.

attach the tanks to the floor, add insulation over them, add a false floor above.

Then externally add a metal skin with air separation from the outer walls and roof of the enclosure and design it to have good convective airflow between the skin and the walls. with the walls proper completely shaded by the skin from direct sunlight.

Do some small scale test, but I believe that this will gain you quite a few degrees passive cooling of the enclosure.

Sorry if someone already mentioned this.

How about a few small misters inside? Evaporative cooling.

All it would take is one small pressurized water line to feed them. To prevent wasting water, they could be controlled with a thermostatically controlled valve, that only opens at a certain temp...........say, 120°F.

They keep the entire old downtown section of Vegas cool with misters, should work for your application.

They wouldn't even need to be inside the structure. They could lightly mist the exterior.

Good idea, also @ wawa. I think I am going to experiment with a few of these. Thanks all.

In addition to my previous suggestion and adding a variation on Kramarat's

have a look at <http://en.wikipedia.org/wiki/Coolgardie_safe>

Rather than spray the water, use a moistened fabric covering over the enclosure proper behind the shading panels - the the moisture could 'wick' - by capillary action through the fabric from one or more reservoirs and be evaporated by the airflow between the shading panel and the enclosure - making the enclosure into a big coolgardie safe.

The only power required is to periodically top up the water reservoirs.

I'm not sure 'sandstorm' and the ventilation requirement for evaporative cooling are compatible - but you raise the thought of simply putting them in a tank of water.

The thermal mass should average the daily extremes, possibly also be advantageous with the internal thermal cycle.

Hi 34point5,

I think you misunderstand my concept, there would be no 'cooling' ventilation into the enclosure.

The fabric is on the outside of the walls and protected from sandstorm's sandblasting effect by the metal sunshield placed 50 -100 mm (2-4 inches) away (like the fly on a tent). the enclosure is cooled by conduction through its walls.

The sunshield (or metal tent fly) would have openings at ground level and centrally above the enclosure and create a chimney effect between it and the enclosure walls as the sunshield warms up this draws airflow over the damp fabric drawing the latent heat of vapourization (to evaporate the water) from the metal enclosure wall behind it, thus cooling the entire enclosure.

And with the tanks mounted under the false floor and in intimate contact with the metal floor of the enclosure, which presumably is sitting on the ground in the densest shade around (under the container) there is additional cooling by conduction into the ground.

Yes I did misunderstand. External would work.

But still, why not just put the tanks in the water mass?

I do have plant air available and you just solved my problem ! Thanks for the link; I will be using a lot of these.

Hi WJMFIRE,

What a result, brilliant, it's a shame you won't be ordering them through me but what the hell "If I can help somebody" (don't know how to show there words from a song).

Check out there other other products you never know!

Best regards,

John

Well, finally! I have seen those in ads in "Machine Design" magazine (if memory serves) and the concept seems sound though I've never tried them.

As I was reading all the other replies, these didn't come to my mind.

GA!

It seems to me, thermodynamically, that the net effect is that of expanding pre-cooled compressed air in the enclosure.

Strikes me as an 'open circuit' form of air conditioning, but highly inefficient, given the hp to compress air. But if the air, for some reason, is going to waste - why not?

_{I still fail to understand why any extra energy should be applied to this problem when passive thermal mass will solve all the issues 24/7.}

I agree with you