Semi Passive Home Cooling.

[bbradsby]

There is nothing 'passive' about heat transfer. However, Passive Cooling, as used in relation to building design, refers not to a lack of action but to a moderation of climatic extremes with little or no use of external power, fuel, or mechanical refrigeration technology. It relies on designing with, not against, the local climate, environment, and the laws of thermodynamics - it requires a full analysis of those existing site/natural conditions so the design constraints and opportunities are identified before pencil or pixel are taken in hand to begin the design process.

A simple example of 'passive cooling' is the roof pond, which cools the rooms below - first via evaporative cooling of of the actual water at night, then via conduction of heat from the structure into the cooler water, and finally cooling the air in the rooms below via air convection current powered by the cooled structure above.

Passive cooling is design with nature, rather than against it.

[Naam]

There is nothing 'passive' about heat transfer.

any cooling is achieved by heat transfer from one medium to another one. period!

[necronx99]

There is nothing 'passive' about heat transfer.

any cooling is achieved by heat transfer from one medium to another one. period!

Oh Yeah? Explain this.

[Naam]

what part of "any cooling is achieved by heat transfer from one medium to another one" is it you don't understand?

[thaibeachlovers]

Thought you all might enjoy this song from Flanders and Swan.

First and Second Law

...................................

The First Law of Thermodymamics:

Heat is work and work is heat

Heat is work and work is heat

Very good!

The Second Law of Thermodymamics:

Heat cannot of itself pass from one body to a hotter body

(scat music starts)

Heat cannot of itself pass from one body to a hotter body

Heat won't pass from a cooler to a hotter

Heat won't pass from a cooler to a hotter

You can try it if you like but you far better notter

You can try it if you like but you far better notter

'Cos the cold in the cooler with get hotter as a ruler

'Cos the cold in the cooler with get hotter as a ruler

'Cos the hotter body's heat will pass to the cooler

'Cos the hotter body's heat will pass to the cooler

First Law:

Heat is work and work is heat and work is heat and heat is work

Heat will pass by conduction

Heat will pass by conduction

Heat will pass by convection

Heat will pass by convection

Heat will pass by radiation

Heat will pass by radiation

And that's a physical law

Heat is work and work's a curse

And all the heat in the Universe

Is gonna cooool down 'cos it can't increase

Then there'll be no more work and there'll be perfect peace

Really?

Yeah - that's entropy, man!

And all because of the Second Law of Thermodynamics, which lays down:

That you can't pass heat from the cooler to the hotter

Try it if you like but you far better notter

'Cos the cold in the cooler will get hotter as a ruler

'Cos the hotter body's heat will pass to the cooler

Oh, you can't pass heat from the cooler to the hotter

You can try it if you like but you'll only look a fooler

'Cos the cold in the cooler will get hotter as a ruler

That's a physical Law!

Oh, I'm hot!

Hot? That's because you've been working!

Oh, Beatles - nothing!

That's the First and Second Laws of Thermodynamics

[Naam]

Oh, you can't pass heat from the cooler to the hotter

yes, you can! what do you think a simple fridge is doing?

not sure about fridges in Flanders though

Edited April 12, 2012 by Naam

[bbradsby]

...so. back on topic:

Necro, your talking about something similar to geothermal cooling, in essence. Your air medium system won't work, and will be a boondoggle. Liquid medium systems are the way to go, and can work IF you have sufficiently large temperature change [Delta T] between pond bottom water temp and your inside air temp with best passive practices in-place already. Then think about how a car's liquid cooling system works and its components, and you'll have a clue where to start. I've read about glycol heat transfer medium systems. It requires deep wells, pumps, pipes, air handler boxes... expensive stuff. IF it works, your payback period will be in the decades perhaps.

Instead, do a deep green house with lots of shade & insulation, add some room fans and an inverter aircon as a backup for when it's just too bloody hot to stand.

[Naam]

...so. back on topic:

Necro, your talking about something similar to geothermal cooling, in essence. Your air medium system won't work, and will be a boondoggle. Liquid medium systems are the way to go, and can work IF you have sufficiently large temperature change [Delta T] between pond bottom water temp and your inside air temp with best passive practices in-place already. Then think about how a car's liquid cooling system works and its components, and you'll have a clue where to start. I've read about glycol heat transfer medium systems. It requires deep wells, pumps, pipes, air handler boxes... expensive stuff. IF it works, your payback period will be in the decades perhaps.

Instead, do a deep green house with lots of shade & insulation, add some room fans and an inverter aircon as a backup for when it's just too bloody hot to stand.

i beg to differ Bbradsby. if you have a deep well with ample water flow and a delta t >10ºC you don't even need a compressor/condenser chiller to use that water as direct cooling medium for the inside units. all what it takes is an adequately dimensioned pump to supply these units and of course insulated supply piping to the units. a system like this would mean tremendous savings of electric energy because the inside units consume ~90w and for let's say 6 units a 1½ hp (~1.1kWh) pump would suffice.

assuming a 30% overall loss this system would generate approximately 90,000 btu/h using only 1.64kWh whereas conventional units would use ~9kWh to generate the same cooling capacity.

initial capital cost (assuming the well exists) would be not more than one third of conventional units. unfortunately long term success is only guaranteed if the well produces a sufficient volume of water even during extended dry periods.

[bbradsby]

Yeah, these geothermal systems work all over the place for heating or cooling. But it's so site-specific - cost of bores in various strata, and at what depth, if any, one can get water with adequate Delta T and flow - and it requires a proper mechanical engineer. So unless you're offering your services, I thought it best to let sleeping dogs lie.

In the US, back when earth-sheltered structures were en vogue, that there was data developed on temperatures of the ground at various depths, so that passive cooling & heating could be calculated. Anybody know of any such data for LoS? Ground water would be the same temp as the adjacent stratum, it would be fair to assume. But flow data would assuredly require an expensive, deep bore.

[HPJ]

Have trees for shades and a fishpond with downward water flow before the wind enters the house with natural ventilation like the illustration enclosed will make you happier than finding answers for the geothermal heating/cooling solutions.

Sent from my iPhone using ThaiVisa app

[xthAi76s]

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.

Where can one find real, good spectrally-sensitive window films in Thailand/Bangkok? From my research, the best films all seem to be sold outside of Thailand. Thanks.

Actually, I just searched more thoroughly and found another of your posts re Southwall ()

Edited April 20, 2012 by xthAi76s