sprinkler on the roof instead of a/c

[sweatalot]

we've got a big room under the roof. No aircon. Gets quite hot now.

I am considering to put a sprinkler on the roof and spray water all day long. This wouldn't be too expensive because we have our own well and a big water container close to the house. All we need would be a pump and some hoses.

I just don't know how effective this would be.

Anyone experience or advice? I would be very grateful.

[IMHO]

It won't change the ambient air temp, thus, no substitute for AC that way I see it.

Edited March 6, 2015 by IMHO

[luk AJ]

We do this on the roof of our factory. It helps for sure. Evaporation = cooling

[2fishin2]

Doubt it would cool the room at all. And not to mention the big mess of water you would have all the time.

[luk AJ]

Nothing beats a good old law of physics. You don't have to wuestion this one, it is just a matter of fact.

[sweatalot]

It won't change the ambient air temp, thus, no substitute for AC that way I see it.

the temperature inside the room is much hotter than the outside temperature. (Same as in a car in the sunshine) Evaporation of water would cool for sure. The question is how much?

And it would not need a high volume flow of water.

[2fishin2]

If it was such a good idea....people all over the world would be doing it. Im not saying it wont cool, Im saying that is not the answer. Ventilate

[SpokaneAl]

In the desert we used a slightly similar system called a swamp cooler. It essentially sprayed small droplets of water into the house, which would evaporate, resulting in a nice cool room.

However it does not work at all in humid climates.

[sweatalot]

Doubt it would cool the room at all. And not to mention the big mess of water you would have all the time.

I don't expect a big mess of water - I would turn down the flow so that the roof is just wet and the water dropping on the soil would nurture the grass around the house as a welcome side effect.

[bankruatsteve]

Go for it. It's not going to help anything, but you will think it does and that's all that matters.

[luk AJ]

Go for it. It's not going to help anything, but you will think it does and that's all that matters.

did you try? At our factory we do this on hot sunny days and it does work. Why you try to convince people it doesn't? Painting the roof white would also work. Let's see what Mr Bankrupt has to say about this..

[IMHO]

It won't change the ambient air temp, thus, no substitute for AC that way I see it.

the temperature inside the room is much hotter than the outside temperature. (Same as in a car in the sunshine) Evaporation of water would cool for sure. The question is how much?

And it would not need a high volume flow of water.

Let's say the air temperature outside is 38c - doing this water idea, the best you can hope for is an indoors temp of err, 38c. OTOH, AC is going to give you whatever indoor temp you want, so long as it's sufficiently sized. Want it to be 24c inside when it's 38c outside? AC can do, water on a roof cannot

[IMHO]

Guys, it all depends on just how much the inside air temps are influenced by the roof surface temps, as to whether this idea will have an effect. You can't just blanket write it off - if you could, you should also blanket write-off every roof insulation technique there is too.

LIke I say though, there's just no way it's going to make indoor air temps that are lower than outdoor air temps. Which is what AC can do.

[billd766]

Doubt it would cool the room at all. And not to mention the big mess of water you would have all the time.

I don't expect a big mess of water - I would turn down the flow so that the roof is just wet and the water dropping on the soil would nurture the grass around the house as a welcome side effect.

The downside to your plan is that the grass will grow and you will have to cut it more often.

[IMHO]

Doubt it would cool the room at all. And not to mention the big mess of water you would have all the time.

I don't expect a big mess of water - I would turn down the flow so that the roof is just wet and the water dropping on the soil would nurture the grass around the house as a welcome side effect.

The downside to your plan is that the grass will grow and you will have to cut it more often.

Well, the other downside is that water isn't free, neither is pumping it, nor the pipework/nozzles to build the system

[SpokaneAl]

The only thing I have here is an opinion, so take my thoughts the applicable number of grains of salt.

When I look at our tile roof, there is, of course, a ceiling between the roof and our living space. So while I would think that lowering the temp of the roof would help, I can't see it helping very much, especially with the temp of the water, which could be fairly warm during the hot season.

Additionally, the main temp drop comes from rain, which cools everything and lowers the outside temp.

As for me, we will stick with plenty of fans during the day and the a/c for a couple or three hours each evening.

Edited March 7, 2015 by SpokaneAl

[Daffy D]

I think the sprinkler idea is only any good for an open spaced roofed area where an AC would be impractical.

I personally don't mind the heat so much it's the humidity that makes me feel all hot and sweaty.

A sprinkler system will only add to general humidity.

Give me AC every time.

Till the electric bill comes in then we have a couple of days frantically turning everything off

[luk AJ]

The only thing I have here is an opinion, so take my thoughts the applicable number of grains of salt.

When I look at our tile roof, there is, of course, a ceiling between the roof and our living space. So while I would think that lowering the temp of the roof would help, I can't see it helping very much, especially with the temp of the water, which could be fairly warm during the hot season.

Additionally, the main temp drop comes from rain, which cools everything and lowers the outside temp.

As for me, we will stick with plenty of fans during the day and the a/c for a couple or three hours each evening.

i hope you find a suitable solution, just to make my point clear, the cooling effect is not because of the water temperature but because of evaporation. As such it is possible to enjoy a cold beer in the desert if you wrap it with a wet towel. Cheers!

[GinBoy2]

This would be a swamp cooler on an epic scale. That being said, the water (especially since we are in a drought) and the electricity, and I have to say the probable marginal cooling is not in my estimation a good bet.

Buy yourself a cheap AC and be done with it. You'll be cooler and without a what I can only imagine a whole lot of mess of water cascading from your roof 24/7

[sweatalot]

Thanks for your input - I am still waiting if somebody has experience with a construction like this.

It is for sure that this water cooling would have an effect. The question is only how much?

Why will it have an effect?

Some posters mentioned the evaporation effect. Water comes on a hot roof. It uses the heat energy to evaporate.

(means changing fluid water into steam) For evaporating energy is needed which is taken from the hot roof which lowers the temperature.

So far physical facts.

It could be calculated but this would be difficult because you would need a lot of facts like conductivity of the roof material, the windows, heat capacity of the walls etc. So experimenting will be easier.

Inside temperature will not be lower than outside temperature. Agreed. But have you ever come into a car which has been parked in the sunshine? You would be lucky if the inside temperature would be like outside.

If you use A/C to get the temperature under outside temperature your electric bill would be significantly lower.

Our room size is about 60 sqm with a pitched area and 6 Thai windows with as much as no isolation. The ceiling is about 3,50 m

Airconditioning would be quite expensive and not very effective unless we get new windows.

Water bill? I mentioned that we have our own well (130 m deep) So costs would be only for the electricity used for pumping

Edited March 7, 2015 by sweatalot

[MaeJoMTB]

It won't change the ambient air temp, thus, no substitute for AC that way I see it.

the temperature inside the room is much hotter than the outside temperature. (Same as in a car in the sunshine) Evaporation of water would cool for sure. The question is how much?

And it would not need a high volume flow of water.

Let's say the air temperature outside is 38c - doing this water idea, the best you can hope for is an indoors temp of err, 38c. OTOH, AC is going to give you whatever indoor temp you want, so long as it's sufficiently sized. Want it to be 24c inside when it's 38c outside? AC can do, water on a roof cannot

You clearly don't understand the physics of this.

Evaporation CAN reduce the temperature to below ambient.

(it's all about the most excited molecules being blown away)

https://answers.yahoo.com/question/index?qid=20080225194135AAgFquW

Edited March 7, 2015 by MaeJoMTB

[96tehtarp]

Thanks for your input - I am still waiting if somebody has experience with a construction like this.

It is for sure that this water cooling would have an effect. The question is only how much?

Why will it have an effect?

Where I live this is a very popular technique especially among people whose homes have corrugated steel roofing. It's most effective on roofs with no ceiling, fx. a carport roof if you spend a lot of time sitting outside in the shade under the carport or porch roof. It definitely makes a difference on the hottest days.

The OP should try it low tech style by simply spraying water from a garden hose on the roof section in question during the hottest period during a hot day. I does help but it's no substitute for A/C. If the OP is satisfied with the results he can install PVC pipes and sprinklers on the roof for next to no money at all. I wouldn't recommend spraying water all day. That might be overkill.

[Sophon]

It won't change the ambient air temp, thus, no substitute for AC that way I see it.

the temperature inside the room is much hotter than the outside temperature. (Same as in a car in the sunshine) Evaporation of water would cool for sure. The question is how much?

And it would not need a high volume flow of water.

Let's say the air temperature outside is 38c - doing this water idea, the best you can hope for is an indoors temp of err, 38c. OTOH, AC is going to give you whatever indoor temp you want, so long as it's sufficiently sized. Want it to be 24c inside when it's 38c outside? AC can do, water on a roof cannot

You clearly don't understand the physics of this.

Evaporation CAN reduce the temperature to below ambient.

(it's all about the most excited molecules being blown away)

https://answers.yahoo.com/question/index?qid=20080225194135AAgFquW

While you are right in theory, in practical terms there is no way that putting a sprinkler system on the roof (with a large attic space between the roof and the living area) will be enough to lower the temperature in the living area to below ambient temperature. Sure it will have an effect in reducing the heat transferred down from the roof, but the effect is probably only going to be marginal. And as others have mentioned the humidity will be increased possibly negating any positive effect (not to mention the risk of mould build up)

In our village there are actually a couple of businesses (a shop and a restaurant) that used sprinklers on their metal roofs in the last hot season to keep the temperature down. In both cases we are talking about mostly open areas, and to me the effect was negligible.

'

Sophon

[Neeranam]

was in a large restaurant today which had this - it was much cooler than outside and no water on the floor.

[bankruatsteve]

So, do you have a ceiling under this roof that you might want to water? If so, there is no way you would notice any significant delta in comfort unless you just BELIEVE. It sounds like your construction is a hot box and that's just the way it's going to be. Even A/C might not help that much. Suggest you try shading and fans instead.

Where's Dr. physics Naam for things like this?

[2fishin2]

If this sprinkler on roof was such a good deal, the system would be in use all over the world. When is the last time you've ever seen such a system? Ill answer that Ive never seen one in my life. Doesnt work no matter what Dr Physics says....

[sweatalot]

It won't change the ambient air temp, thus, no substitute for AC that way I see it.

the temperature inside the room is much hotter than the outside temperature. (Same as in a car in the sunshine) Evaporation of water would cool for sure. The question is how much?

And it would not need a high volume flow of water.

Let's say the air temperature outside is 38c - doing this water idea, the best you can hope for is an indoors temp of err, 38c. OTOH, AC is going to give you whatever indoor temp you want, so long as it's sufficiently sized. Want it to be 24c inside when it's 38c outside? AC can do, water on a roof cannot

You clearly don't understand the physics of this.

Evaporation CAN reduce the temperature to below ambient.

(it's all about the most excited molecules being blown away)

https://answers.yahoo.com/question/index?qid=20080225194135AAgFquW

"Evaporation CAN reduce the temperature to below ambient. "

got me, you are right. The problem is the evaporating temperature for water is 100 C, so if the temperature is above 100 C you can reduce the temperature below 100 C. But this effect will "evaporate" if the temperature goes below 40 C

Edited March 7, 2015 by sweatalot

[Farma]

2fishin2 Just because you haven't see it doesn't mean it won't work.

It's common in parts of Thailand with little humidity. I normally see it used on open sided tin roof restaurant areas and on river boat restaurants. In my experience it makes a difference and does cool down the area underneath.

Edited March 7, 2015 by Farma

[bankruatsteve]

Uhm - the boiling temp for water is 100C at sea level. The evaporation temp is somewhat above the dew point and varies depending on RH and temp. Evaporation is what makes cooling things cool. But, water on a tin roof is probably the least efficient way to do that.

[sweatalot]

Thanks for your input - I am still waiting if somebody has experience with a construction like this.

It is for sure that this water cooling would have an effect. The question is only how much?

Why will it have an effect?

Where I live this is a very popular technique especially among people whose homes have corrugated steel roofing. It's most effective on roofs with no ceiling, fx. a carport roof if you spend a lot of time sitting outside in the shade under the carport or porch roof. It definitely makes a difference on the hottest days.

The OP should try it low tech style by simply spraying water from a garden hose on the roof section in question during the hottest period during a hot day. I does help but it's no substitute for A/C. If the OP is satisfied with the results he can install PVC pipes and sprinklers on the roof for next to no money at all. I wouldn't recommend spraying water all day. That might be overkill.

try it low tech style by simply spraying water from a garden hose

That's exactly what I am going to start tomorrow as a pilot project. Just using a sprinkler that I have anyway with a garden hose that I have anyway fixed on a bamboo stick.

I will adjust the water flow so that the roof is just wet with not much water running down. The watering time will be between 10 a.m. and about 5 or 6 pm

Edited March 7, 2015 by sweatalot