Semi Passive Home Cooling.

[necronx99]

Background

My intended build area is lower Nakhon Sawan where it is, quite frankly, bloody hot all year round (3 days below 30 degrees in the last year).

The house will be a low stilt house with a high roof and plenty of both natural and mechanical ventilation and shade. Only the bedroom will be wall insulated and airconned. The roof will be white or silver and will have an internal radiant barrier on top of the ceiling.

The objective is to add cheap green cooling.

Please note I have little idea of the mechanics of heat interchange and air, nor materials science.

The Idea.

Reading up on passive cooling systems, I have started to think about the adjoining fish pond which at 3 meters or so is pretty cool down the bottom.

How to leaverage this naturally cooling source?

The Plan.

Build an array of pipes with several inlets and outlets and sink it to the bottom of the fishpond. Use solar powered fans to draw air through this array, where it is hopefully cooled by the surrounding water and expell it into the house through several vents.

The bits I have no idea about.

Pipe material.

The standard blue plastic plumbing pipe, will this allow sufficent heat exchange between the water and air? Is there something better?

The length of Run.

How long will the air need to be in this pipe under water to cool it to the maximum?

How to stop Condensation

From filing up the pipes and keep them clean. Will these pipes just turn into a giant germ factory pumping poison into the house?

Could some sort of wick system extract unwanted water buildup?

Net Result.

Could this process inject enough cool air into the building to noticably cool it.

Costs.

Somes hundred (?) meteres of blue pipe.

Some glue.

One or 2 solar powered fans

Some Somchai time.

It is worth the effort or am I a clueless loon?

Naam, your vote has been noted. I would appreciate your technical knowledge however.

[Crossy]

Have a look here http://www.builditsolar.com/Projects/Cooling/passive_cooling.htm lots of information on passive cooling many of which can be applied here.

I'm not sure about sourcing cooling from a pond mind, unless it is very large.

[bankruatsteve]

Well, since you posed a question with a choice of two answers, I have to go with "insane". Definitely and out-of-box idea though. But there's no way you could efficiently cool air in that manner. Ceiling fans are probably the cheapest way to stay "cool" in this climate.

[necronx99]

Have a look here http://www.builditso...ive_cooling.htm lots of information on passive cooling many of which can be applied here.

I'm not sure about sourcing cooling from a pond mind, unless it is very large.

It's been suggested I will cook the fish.

[Crossy]

It's been suggested I will cook the fish.

Now there's a marketing idea, ready cooked fish straight from the pond. All we have to do now is work out how to grow chips and we have instant fish-n-chips

Seriously, unless you use an actual water-source heat pump I doubt the fish will even notice.

[onionluke]

You incorporate a glass floor to allow you observe the fishes underfoot .. Great idea though .

[klikster]

I'm not expert on heat transfer, but I used to sell fans for large cooling towers and process air-cooled heat exchangers so I picked up on come of the basics. It sounds like you might end up with a relatively expensive big mess that doesn't do very much good.

PVC is not a good heat conductor. If you really want to recirculate water from the pond, pipe it through a metal radiator of come sort and blow ambient air across it. But that really won't do much. One of the more effective (IMO) methods is cooling the space above the ceiling using a forced draft fan at one end of the attic and drawing air at other openings. Think in therms of a fan diameter of 1 mt or more.

As far as cooking the fish, not likely to happen. As I understand things, the entire surface area of the pond is continually being cooled by evaporation. (latent heat of evaporation?).

Naam, *knock* *knock*, Naam?

[necronx99]

I'm not expert on heat transfer, but I used to sell fans for large cooling towers and process air-cooled heat exchangers so I picked up on come of the basics. It sounds like you might end up with a relatively expensive big mess that doesn't do very much good.

PVC is not a good heat conductor. If you really want to recirculate water from the pond, pipe it through a metal radiator of come sort and blow ambient air across it. But that really won't do much. One of the more effective (IMO) methods is cooling the space above the ceiling using a forced draft fan at one end of the attic and drawing air at other openings. Think in therms of a fan diameter of 1 mt or more.

As far as cooking the fish, not likely to happen. As I understand things, the entire surface area of the pond is continually being cooled by evaporation. (latent heat of evaporation?).

Naam, *knock* *knock*, Naam?

I'm not pumping water, but am blowing air through the system. This has been experimented with in a process called earth pipes typically buried underground. From a link from Crossy, a test in India produced the following figures from a 50 meter 4 inch pipe, albeit with a 300 watt motor doing the pushing. In the tests the ambient was 40c with an pipe temp of 26c and an output temp of 27c

Cooling = (weight flow)(specific heat of air)(dTemp)

= (2145 ft/min)(0.083 ft^2)(0.065 lb/ft^3) (105.4F- 81F) (0.22 BTU/lb-F) = 62.1 BTU/min or 3427 BTU/hr or 0.31 ton of AC

the reviewer seemed to think this was a good outcome, I have no idea what a ton of A/C is so can't compare.

In my version i would replace deep earth with the pond which should give a better exchange and power the fans with PV.

[Crossy]

I have no idea what a ton of A/C is so can't compare.

1 Ton is 12,000 BTU

[necronx99]

I have no idea what a ton of A/C is so can't compare.

1 Ton is 12,000 BTU

So in a beautiful world 4 of these pipes would be equv to a 1 hp ac?

[prefabs]

Interesting thread but could end up long and anywhere

[Pseudolus]

If the pipes break in the pool, would that be like a jacuzzi then? Also why only insulate one room? Surely insulation all over would be the ticket

[Pacificperson]

The bottom line is how many BTUs of cooling do you get per Kwh of electricity consumed. Is this system going to be more efficient than a standard AC? The other issue is that most fish ponds are fairly shallow and can get fairly warm all the way to the bottom.

[klikster]

I'm not pumping water, but am blowing air through the system. This has been experimented with in a process called earth pipes typically buried underground. From a link from Crossy, a test in India produced the following figures from a 50 meter 4 inch pipe, albeit with a 300 watt motor doing the pushing. In the tests the ambient was 40c with an pipe temp of 26c and an output temp of 27c

Ah, sorry, my bad, necronx99. One of the first things would be to decide how many cfm of air you want to move, then the pressure drop through those pipes. You would likely be talking "blowers" not axial flow fans in order to overcome the static pressure of each duct. You might be able to find a site that has formulas or calculators for the pressure drop. Then there are those nasty bends.

Edited March 29, 2012 by klikster

[T_Dog]

Attached is a paper on the concept the OP is asking about and it is quite viable. The Greeks of the olden days had a system where the sunny side of the house was made into a large chimney. Air would get hot and rise inside pulling air out the bottom of the chimney which as connected to the house. On the other side of the house, the only way air could get in was through long earth tubes that went to a filter house quite a way from the house. Air was cooled in the earth tubes before being pulled into the house and then out the chimney. Condensation is the the big problem with these systems but they do indeed work well for cooling and can be completely passive.

earth tubes.pdf

[extexthai]

A few things to consider...if you aren't locked into a design you can't live without, try incorporating a breezeway, orientated north and south (the direction of the monsoonal air movements) and think of a radiator core. Then use ACC block on the exterior and red brick on the interior with a dead air space in between. I did this with our house and even though I pre-wired for AC in two parts of the house, I have not yet bought any for cooling purposes. We open the house up early in the morning and turn on the exhaust fans that were put in at ceiling heigth to get rid of any warm air that has found its way to the ceiling, thus drawing in the cool air. Before the sun gets to cooking, we close all windows and doors and it stays just as lovely as can be, all day long. You will notice the loss of cool air in the evening as the sun is setting, but by this time it is already cooling outside, down again. This breezeway makes for three wings of the house, the east side (office and guest room with an adjoining bathroom) that only gets morning sun, the west side that is the kitchen, living room and dining room with only three windows to cover, and the MBR and related bath, up over the breezeway. We have a terrace opening from the bed room and a balcony opening on the other end to get unrestricted airflow and it works like a champ. I did go with large gable louver vents for more than adequate air exchange in the attic and it makes a huge difference compared to those wimpy, so called louver vents I see available here. I think we accidentally hit the jack pot with this design and I am so pleased with it. By the way, the breezeway itself it probably the most used room of the house during the day. Good luck. ett

[nocturn]

A few things to consider...if you aren't locked into a design you can't live without, try incorporating a breezeway, orientated north and south (the direction of the monsoonal air movements) and think of a radiator core. Then use ACC block on the exterior and red brick on the interior with a dead air space in between. I did this with our house and even though I pre-wired for AC in two parts of the house, I have not yet bought any for cooling purposes. We open the house up early in the morning and turn on the exhaust fans that were put in at ceiling heigth to get rid of any warm air that has found its way to the ceiling, thus drawing in the cool air. Before the sun gets to cooking, we close all windows and doors and it stays just as lovely as can be, all day long. You will notice the loss of cool air in the evening as the sun is setting, but by this time it is already cooling outside, down again. This breezeway makes for three wings of the house, the east side (office and guest room with an adjoining bathroom) that only gets morning sun, the west side that is the kitchen, living room and dining room with only three windows to cover, and the MBR and related bath, up over the breezeway. We have a terrace opening from the bed room and a balcony opening on the other end to get unrestricted airflow and it works like a champ. I did go with large gable louver vents for more than adequate air exchange in the attic and it makes a huge difference compared to those wimpy, so called louver vents I see available here. I think we accidentally hit the jack pot with this design and I am so pleased with it. By the way, the breezeway itself it probably the most used room of the house during the day. Good luck. ett

love to see a drawing or pics

[klikster]

A few things to consider...if you aren't locked into a design you can't live without, try incorporating a breezeway, orientated north and south (the direction of the monsoonal air movements) and think of a radiator core. Then use ACC block on the exterior and red brick on the interior with a dead air space in between. I did this with our house and even though I pre-wired for AC in two parts of the house, I have not yet bought any for cooling purposes. We open the house up early in the morning and turn on the exhaust fans that were put in at ceiling heigth to get rid of any warm air that has found its way to the ceiling, thus drawing in the cool air. Before the sun gets to cooking, we close all windows and doors and it stays just as lovely as can be, all day long. You will notice the loss of cool air in the evening as the sun is setting, but by this time it is already cooling outside, down again. This breezeway makes for three wings of the house, the east side (office and guest room with an adjoining bathroom) that only gets morning sun, the west side that is the kitchen, living room and dining room with only three windows to cover, and the MBR and related bath, up over the breezeway. We have a terrace opening from the bed room and a balcony opening on the other end to get unrestricted airflow and it works like a champ. I did go with large gable louver vents for more than adequate air exchange in the attic and it makes a huge difference compared to those wimpy, so called louver vents I see available here. I think we accidentally hit the jack pot with this design and I am so pleased with it. By the way, the breezeway itself it probably the most used room of the house during the day. Good luck. ett

love to see a drawing or pics

+1

[BeastOfBodmin]

Certainly is a good site.

One of the first links is to

http://www.oikos.com/esb/51/passivecooling.html

which asks for

average maximum temperature

average minimum temperature

average maximum relative humidity

average minimum relative humidity

I have not been able to find the latter numbers for Thailand, just the average relative humidity. Any ideas?

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[bbradsby]

The oikos site is a good one. But there is no singular Thailand Climate - inland parts of Thailand are not in Humid Tropical climate zones and the dryer portions of the year can be more of a Sahel climate - with hot and dry seasons, even if periodic, heavy rains occur. So evap cooling can be made to work, along with thermal mass and air movement. In the humid, Coastal Tropics, passive cooling is more difficult. No matter your location, one is well advised to carefully analyze the actual onsite climate and wind patterns. Then use this info as design criteria. Here are some strategies:

Shade sitework & exterior walls from ever seeing the sun- planting, external shading devices, louvers, overhangs...

Use light colors for roof and exterior walls, and use radiant paint on walls that do get direct sun,

Keep window glass completely out of direct sun, and use a real spectrally-selective window film if you can't.

Go Big, R-30, on attic insulation w/ radiant barrier, and highly ventilate attics,

Roof ponds cool even in humid tropics, but are expensive & tech challenges, but there ya go,

Shut your house up when outside temp begins to warm up, and let your inside, cooler air & masses buffer it til late in the day,

Weatherstrip all openings so your cooler inside air is not blown out & replaced by hot outside air- this occurs quickly even in a light breeze;

Use shaded, insulated thermal mass on the inside walls & floor slabs, and

Use low-level air movement to maximize thermal comfort without disturbing hotter air near the ceiling.

One thing people look past as they focus on building tech only, is sitework design: bodies of water cool by evaporation, and shaded gardens up-windstream of your house or in a courtyard cool the air by evapo-transpiration before wafting into your house - the plants breathing out water vapor cools the air as well as cleans & oxygenates it. Locating sitework paving, car storage or your kitchen upstream does the opposite!

Internal heatloads can have a large effect as well, with refr's & freezers being the worst, plasma TVs & lighting being factors as well. Manage your internal heatloads carefully so you have less to fight. LED lighting, Thai [exterior] Kitchen, or at least use a chimney/stack effect to get your refr/freezer loads away from occupied zones. But this only works if cool air replaces that exhausted.

A house that is finely attuned to its site micro-climate, as well as to the larger climate zone, is a work of art created by someone who is willing and able to dig a bit deeper.

Edited April 8, 2012 by bbradsby

[BeastOfBodmin]

Thanks for the tips.

When I last spent time looking hard I found data for my region of interest. Knowledge of prevailing wind direction is a good point.

Also the idea of shutting up the house when it gets hot.

Could avoid roof ponds via geo cooling or other heat dumping but that also introduces other challenges.

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[thaibeachlovers]

I have no idea about the merits or otherwise of your system, but one would not go amiss investigating as to how the Thais cooled their houses before the advent of electricity.

[passingas]

TBL,

From what I have been observing, at least up in the northern part of the country, is that they are underneath the house, in the shade that is afforded by the rest of the house that is up on stilts. I have also noticed in all the kinfolks houses, that they are all compartmentalized, allowing absolutely none to very little breeze to facilitate in helping cool things, inside. It's like something that they don't even think about. I notice the roofs....most of them hip, but the few gable roofs I see, there is minimal venting to get the oven like temps from over ones head. I lived in such a place while we were building our house. pg

[thaibeachlovers]

TBL,

From what I have been observing, at least up in the northern part of the country, is that they are underneath the house, in the shade that is afforded by the rest of the house that is up on stilts. I have also noticed in all the kinfolks houses, that they are all compartmentalized, allowing absolutely none to very little breeze to facilitate in helping cool things, inside. It's like something that they don't even think about. I notice the roofs....most of them hip, but the few gable roofs I see, there is minimal venting to get the oven like temps from over ones head. I lived in such a place while we were building our house. pg

Sorry, I may have been unclear, but I meant how they used to do it a couple hundred years ago. I don't know, but I'd imagine it involved vents at the ends of the high roofs and the direction the house was built in.

My MIL in the village lives in a very old wooden house, that is basically a large empty space with a high unlined roof space. Unfortunately, they added some small rooms and corrugated iron roofing more recently, so they too basically live outside. I had to sleep in a sort of porch with no walls to be cool enough.

[HPJ]

Plants surround the house, a good heat insulation on the roof and extended height roof top ventilation fans (2 meters from the roof top) can help cooling down the house for more than 5 degrees Celsius without engaging electricity.

Natural convection, shading and evaporation are both involved in this cooling.

If enough rooftop fans are installed, you don't even need a electric fan.

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[Naam]

I have no idea about the merits or otherwise of your system, but one would not go amiss investigating as to how the Thais cooled their houses before the advent of electricity.

the Thais didn't cool their houses. that in olden times and now houses built on stilts are cooled by the airflow under the bottom of the first floor is a fairy tale spread even now by people who possess a wealth of no idea. stilt houses get some cooling action because of a better airflow when designed for cross ventilation.

[Naam]

Pipe material.

The standard blue plastic plumbing pipe, will this allow sufficent heat exchange between the water and air? Is there something better?

there is something better than PVC and that copper and silver. there's no need to point out that both materials are too expensive to be used.

as far as the system itself is concerned... Klikster and another participant have correctly drawn the attention to the fact that the planned piping has quite an airflow resistance. there's talk about "hundreds" of meters but no diameter mentioned that a calculation (necessary air pressure) can be carried out. shooting from the hip i'd say "solar powered fans = no way!"

next info needed, just for the heck of it, depth, bottom area and water temperature of pond to prove that the idea is based on theoretical logic but in practice a stillborn baby.

"The roof will be white or silver and will have an internal radiant barrier on top of the ceiling."

go for it! we lived several years in the african bush in a house that hat a polished aluminium (aluminum for our American and Canadian friends) roof, no insulation in the attic, ceiling made of multi-ply cardboard, attic naturally ventilated. my first estimate for the living and attached dining room (total ~75-80m²) was 48,000 btu/h, nothing doing below! little did i know and i underestimated the experience of the local "bushman builders". ambient temperature ~35ºC / 95ºF, comfortable living room temperature of 26-27ºC achieved with one a/c unit of 12,000 btu/h.

rest of the house was energy efficient too. big roof overhang, windows recessed, positioning of the house and arrangement of rooms according to sun moving directions.

[Naam]

can't resist giving a small smartàss lecture

there is no such thing like "passive cooling". any cooling is "active". what is commonly called "passive cooling" is nothing but avoiding heat transfer by various means.

[klikster]

can't resist giving a small smartàss lecture

there is no such thing like "passive cooling". any cooling is "active". what is commonly called "passive cooling" is nothing but avoiding heat transfer by various means.

I think that goes along with the static vs. dynamic concept.

Too often we see posts and hear arguments that rely on static conditions. Almost any system related to housing has to be considered/operate dynamically.

Ex: Water or liquids: how much, how fast, how far, how high, what depth, conduit size are just a few. Same goes for dynamic loads vs static loads on structure, roof, etc.

Projects undertaken based on assumptions drawn from static thinking usually end up ranging from worthless to overly expensive.

[Naam]

Projects undertaken based on assumptions drawn from static thinking usually end up ranging from worthless to overly expensive.

bingo!