Thread: Is a mobile evaporative cooler in a tin shed a bad idea?

Originally Posted by 419

Thanks. That encourages me to carry out an experiment with ice blocks - the type sealed in plastic bottles - in front of my monster fan. Shouldn't be much of a humidity problem with that, apart from minor condensation on the blocks.

I should have made it clear if it wasn’t but it is a misting fan it doesn’t just blow across a bucket of water. It has a pressure pump feeding water to misting nozzles in front of the air stream. The phase change from liquid water to gas requires a large amount of energy which is drawn from the air, cooling it. I doubt your ice bottles will be anywhere near as efficient. It’s a relatively small surface area, it’s insulated by the plastic (edit and the phase change from ice to liquid water phase change reference is a furphy for melting)and cooling the air can only occur by conduction which is not terribly efficient.

Originally Posted by 419

We'll soon be getting to the same point with cooling and heating the house, especially after today's announcement that we'll be forced by our Victorian government to get rid of our gas hot water, gas heating and gas cooking and replace them with electrical appliances in the coming years.

I presume your shed is a steel structure. You say the walls in permanent shade are not a problem, and the roof is your main concern because you have the sun beating on it. Do as much as you can of what others have said, but also consider installing solar panels on the roof.

Normally, installers will want the solar panels to face the sun, which is north, and if the roof is flat they will want to set the angle using a frame to 'aim' them at the sun. That's fine in that at noon the panels will be taking the best advantage of the sun and as a bonus, your roof will be in the shade. At other times of the day the sun will get through the gaps on your panels and onto your roof. Though, there's a good argument for having panels installed east or west to take advantage of solar when you need it - at breakfast time and dinner time. But put those ideas aside for a second and consider something else.

So, here's an idea: Have panels installed to cover your entire roof, and here's the key, ignore notions of the ideal angle of the panel to sun type of thing, but have them installed parallel to the roof surface, covering the entire roof, perhaps even extending beyond the roof boundaries to ensure the entire roof is in the shade. If the roof is in the shade the shed will be cooler. If the panels generate electricity for you then you're ahead of the game when you're required to chuck your gas stove. In this orientation the panels' efficiency will drop, but maybe not too much to bother you.

Originally Posted by ErrolFlynn

So, here's an idea: Have panels installed to cover your entire roof, and here's the key, ignore notions of the ideal angle of the panel to sun type of thing, but have them installed parallel to the roof surface, covering the entire roof, perhaps even extending beyond the roof boundaries to ensure the entire roof is in the shade. If the roof is in the shade the shed will be cooler.

Absolutely brilliant suggestion.

Shade the entire roof area with solar panels, leave a nice gap under the panels, extend them to form eaves - even better. Its basically the tent fly principle. And you get electricity as a bonus.

Solar Shading.jpg

Originally Posted by ErrolFlynn

So, here's an idea: Have panels installed to cover your entire roof, and here's the key, ignore notions of the ideal angle of the panel to sun type of thing, but have them installed parallel to the roof surface, covering the entire roof, perhaps even extending beyond the roof boundaries to ensure the entire roof is in the shade. If the roof is in the shade the shed will be cooler. If the panels generate electricity for you then you're ahead of the game when you're required to chuck your gas stove. In this orientation the panels' efficiency will drop, but maybe not too much to bother you.

Alas, my idiot neighbour has a line of tall and still growing cypresses along my northern boundary, which will render solar panels useless for half the year.

I could probably achieve a similar result with a false roof above the existing shallow gable, but I'm not keen on the appearance or effort involved.

I'm looking into heat reflective paints to see how efficient they would be on the roof.

Originally Posted by GraemeCook

Its basically the tent fly principle.

Exactly so. I was thinking of something an uncle of mine did.

In the days before car conditioners were common he came up with an innovative idea. This was in SA (where it can get damn hot in summer). He had a station wagon and a large roof rack on top.

He fitted a large sheet of plywood to the underside of the roof rack. It covered a large area and helped keep (part of) the car in the shade all day. So, it wasn’t cool inside, but it was always cooler than most other cars that bake in the sun. It helped.

It seems as though insulation is your only hope, Obi-Wan.

Originally Posted by ErrolFlynn

He fitted a large sheet of plywood to the underside of the roof rack. It covered a large area and helped keep (part of) the car in the shade all day. So, it wasn’t cool inside, but it was always cooler than most other cars that bake in the sun. It helped.

Reminds me; a school friend became a trainee cameraman with the ABC in the early 1960's. The ABC used 16 mm film cameras then - big, bulky things. The camera crew used a Holden panel van with a full length roof rack - bumper to bumper - with a 25 mm plywood floor so that they could use it as a filming platform.

He also insisted that that van was much more comfortable in summer than other vehicles.

Don't knock it until you've tried it! If I didn't have a 'swampy' I wouldn't be able to do anything for 6 months of the year. I've been using them in my sheds for over 20 years and if you use them wisely there are no rust issues - just need to have somewhere for the air to flow through.
As for the insulation, I painted the roof of my last shed with a thermal paint and never looked back - went from barely being able to stand in there on a sunny day to being able to hold my hand against the underside of the iron. Was fully intending to do the same to the new shed but the 'Surfmist' colorbond roof had pretty much the same effect and combined with a solar-exhaust fan, it never gets any hotter in the shed than it is outside. Bliss!

Hi humidity in the environment will increase the likelyhood of corrosion on ferrous materials. How much over a time period is a bit of a guess...but it will!!!!.

Evaporative coolers increase humidity in the space in which it is used.

I gotta agree with Vern (TTiT) especially when it comes to hard-mounted installations.

I spent a few years installing the damned things (I was the poor sucker who called around in the ceiling cavity while "the boss" walked around below, tapping the ceiling with a broom where he wanted the vents... ) and, IMHO, they work exceptionally well when used correctly.

Problems with high humidity almost always come from people using 'em like refrigeratives.

They work on pumping high cpm through your house (or shed) and as such really need a few open windows. If correctly rated, they'll exchange the air in the house a couple of times every few minutes. They do not recycle the air in the house, nor do they work well when 'pressurising' your house.

It's also recommended that when you're done with them you turn the water OFF (with the remote) and let the fan run for another 5 or 10 minutes. This should expel any existing high humidity (or higher than outside ambient) air to the outside.

Simple rules, but it's amazing how many complaints we got about "bad installations" when the owners just locked up the house and switched 'em on expecting 'em to be a cheap refrigerative.

No matter how carefully we explained it during the install or despite the fact that (gasp) it's stated clearly in the owner's manual.

Portable swampy's are subject to the same conditions but often cause issues because very few of 'em actually duct in air from outside and as such are rarely vented back to the outside. They work by increasing the internal humidity of the house, not by increasing the humidity of outside ambient and passing that through the house. On a muggy day they'll often bring the humidity up past dew point, leading to condensation where you don't want it.

Yeah, but refrigerated AC doesn't need any brain power at all

Originally Posted by Skew ChiDAMN!!

Problems with high humidity almost always come from people using 'em like refrigeratives.

When you try and cool air with water (direct evaporative cooling) you must increase humidity . All one needs to do is look at a psychometric chart to verify this FACT!!
Most people today do NOT use them like refrigerated unit.

Originally Posted by Skew ChiDAMN!!

They work on pumping high cpm through your house (or shed) and as such really need a few open windows. If correctly rated, they'll exchange the air in the house a couple of times every few minutes. They do not recycle the air in the house, nor do they work well when 'pressurising' your house.

That is true. You must get rid of the hot air which is replaced with cooled moisture laden air. If selected correctly the best temperature drop they can achieve is 10C...if 40C ambient the house will be around 30C assuming ambient humidity is low...if its high expect higher room temps! They dont work in the tropics!

Originally Posted by eskimo

When you try and cool air with water (direct evaporative cooling) you must increase humidity . All one needs to do is look at a psychometric chart to verify this FACT!!
Most people today do NOT use them like refrigerated unit.

I've no argument that with that fact. My point was that the problems with high humidity generally occur when people misuse the cooler.

Nor did I say that "most people" use them like refrigerative, I said "most people with humidity problems" have, in the sense that they've shut windows & doors before turning 'em on. The exact opposite of what they should be doing.

That is true. You must get rid of the hot air which is replaced with cooled moisture laden air. If selected correctly the best temperature drop they can achieve is 10C...if 40C ambient the house will be around 30C assuming ambient humidity is low...if its high expect higher room temps! They dont work in the tropics!

Correct, except for the last statement. They do work in the Tropics, just not as efficiently. Where they don't work is when the ambient humidity is close to dew point. Admittedly, in the Tropics such high humidity is more common than down south; even in Melbourne I've seen the odd day where they cool better by turning the water off and just using 'em as a household-wide fan.

That's one of the cons of the system, but to many people it's balanced by one of the pros: at scale, they're cheaper to run.