Evaporative Cooling question.......

[alex242]

Hi,

Can any of you guys pass on any info/knowlage on Evaporative Cooling as a customer of mine is looking at fitting it in a bakery as air conditioning. The bakery, well baking area is hot as expected due to ovens and so on...maybe as hot as 30-38degrees. I think this type of Evaporative Cooling pulls air in from outside through a sort of swampcooler as far as I can work out????

Q. I think the humidity is a major factor and is about all I know. Here in the UK is our climate to humid for these units to work well enough??

I would be grateful for any other suggestions for cooling this enviroment....

Thanks

[Pol]

Hi Alex,

As you suppose, humidity is the key factor indeed.

Dry, hot outside air is pulled in through a thin 'film' of water. Part of the water evaporates into the fresh air, thus cooling (and humidifying) the air going into the building.

With high outside humidity levels - rather common in the uk as far as I'm concerned - the water can not evaporate, hence no cooling.

With a heavy internal cooling load, and moderate outside temps all year round, I would suggest you consider a free cooling system to start with. You could top that up with a DX evap in the duct that only runs when the outside temp is too high.

[Abby Normal]

You can take outside air and humdifiy it. Sensible heat from the air is used to evaporate water. This works best if you use 100% outside air to cool. You blow cooled outside air into the space and let it displace inside air out through dedicated openings. This will prevent humidity from building up.


I only have some limited data for the UK, and a little rusty at SI but perhaps consider an outside air condition of 28C db and 18.6C wb.

We have a sensible internal heat gain of 10 Kw. We want to try and keep an area at 26C.

We want to cool the outside air down but not quite saturate it. A rule of thimb is to evaporatively cool the outdoor dry bulb down by " 80% of the differential between the outdoor dry bulb and wet bulb"

We want to depress the dry bulb temperature of the outside air by 0.8 x ( 28-18.6)= 7.5C. We are going to add water to the outside air then to cool it down from 28C to 28-7.5=20.5C

To determine your airflow to maintain 26C, use the 10 kW and the temperature differential of (26 - 20.5)=6.5 C. It will be high airflow per unit cooling.

You would blow in this cooled, humidified outside air at 20.5C db and 18.6C wb into the space and constantly displacing indoor air to prevent the humidity from building up too much. You also get burned on the cooling a bit with reheat from the fan and motor. Could end up with 60% RH inside at a cooler temperature if there was not a big internal latent gain inside.

If i was not so rusty on SI, I would plot it up and work it out, but it would just plot as a line right along the constant wet bulb temperature

You use the pyschrometric chart to figure out how much water you need based on the airflow and the change in the humidity ratio of the outside air and the supply air. Maybe its about 33 litres every hour in my example.

You blow in this air into the space and displace an equal volume of hotter air out of the space. The lower the outdoor wetbulb, the better it works.

[Abby Normal]

humidity is relative indeed, i have a wet bulb temperature of 28C to deal with all the time down here.

[Samarjit Sen]

Hi Alex242,

Evaporative Cooling is very prominent in our country and we have done a number of such projects for various applications. I will be able to provide you with all the details, but for that you will please have to wait for some time. I am at present outstation at one of my projects and hope to back to my office by the end of this week. I will give you the design details and the equipment details. Only thing that you need to provide me is with the physical dimension of the area to be cooled and the maximum ambient DBT and the WBT.

[Argus]

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Sound idea, but as this is a food preparation area and no doubt inhabited by bakery workers, I’d recommend professional advice on water contamination, especially legionella and pseudomonas, if you are considering open-water based cooling systems or sprays.

Check it out with the local environmental health department first - they might not like it.

.

[Ravi]

You can cool air upto 75 to 80% wet bulb depression using direct evaporative coolers but you may have problems as indicated by Argus. Indirect evaporative coolers can be an option in your case.

If you can tell us the nearest weather station to you, it is possible to estimate the reduction in DBT. For example, London has a DBT of 26.1C and MCWB of 17.8 (corresponding to 1% exceeding values). So, you can pull down the air temperature to 19.87C.

Coolarado has a different type of evaporative cooler. This was discussed in various forums and I personally communicated with Coolarado guy. They could answer all of my questions but I have some doubts that I couldn't express. They have working models available. You can give it a try.

[Samarjit Sen]

Evaporative Cooling could be applied in different ways. The so called Desert Coolers is also an Evaporative Cooling. For larger units, Spray Type units are more suitable. Water contamination can be easily treated.

I had used the principle of Evaporative System for various application. In some cases we had installed a small refrigeration water chilling plant so that the temperature of water is lowered. The effect has been good.

[Abby Normal]

.


Sound idea, but as this is a food preparation area and no doubt inhabited by bakery workers, I’d recommend professional advice on water contamination, especially legionella and pseudomonas, if you are considering open-water based cooling systems or sprays.

Check it out with the local environmental health department first - they might not like it.

.

Sounds like you are being respectfully cautious of the unkown argus. In dry climates it is a very common way of cooling the make up air in commercial kitchens

[Argus]

.

Whatever else the UK environment is, dry it aint!


.

[Abby Normal]

I doubt it is a heat wave when it is pouring rain there. He could just ventilate the place during a pouring rain and it would be more comfortable than that 38C.

[Abby Normal]

.

Whatever else the UK environment is, dry it aint!


.

If my dry bulbs and wet bulbs are reasonable it would work fine.

You don't need AC there unless it is a big internal heat gain anyways, easy climate too cool, keep the drapes drawn and windows closed in the day and open a window at night

[alex242]

Would just like to say a big thankyou for all your replys and as I thought it does not seem suitable for our climate.

I think it would maybe feel cooler but I dont think it would really bring down the temp much.

The first step would be to remove the warm air with a decent extract fan .

Thanks again.

[Abby Normal]

Would just like to say a big thankyou for all your replys and as I thought it does not seem suitable for our climate.

I think it would maybe feel cooler but I dont think it would really bring down the temp much.

The first step would be to remove the warm air with a decent extract fan .

Thanks again.

Lol, yes exhaust the heat out.

Swamp cooler does that and repalces it with cooler than ambient air. Your ambient is not bad to begin with.

[Darshi]

Lol, yes exhaust the heat out.

Swamp cooler does that and repalces it with cooler than ambient air. Your ambient is not bad to begin with.

I agree with you Abby Normal . The given outdoor design conditions can offer better relief with evaporative cooling than simple exhaust ventilation.

With indirect evaporative cooling and suitable air quantity , you can virtually air condition the place at 20 % operating cost.You get excellent indoor air quality to boot.