Will this work? - single plane roof with only air as insulation

[4myr]

As a newbie I'm in search of simplicity - in this case, is it possible to cut out on roof foil and insulation and replace this by air [see pic].

 

• house has steel pillars, beams and roof truss. Steel pillars are connected to concrete slab
• roofing is light coloured fiber cement [like Diamond Jatulon Platinum Gray]
• roof insulation for heat and sound is air and south wind airflow between the roof and the house deck
• house [ceiling] deck is on the outside plastered cement board. The deck is slightly tilted to let water drops by gravity
• the house is cross ventilated and has forced exhaust fans to get rid of humid air

 

Questions I have:

• will this air roof insulation works [heat and sound] as good as roof foil and foam insulation in a standard pitched roof?
• what type of house deck material is cost effective in terms of sound and moisture insulation. Is gypsum board and cement board enough or any other better material?
• is Thai workmanship capable enough in making strong concrete to steel pillar connections as well as roof attachment to the steel truss?
• is this roof solution simpler and more cost effective than an ordinary pitched roof?

[Kwasaki]

It would work but you need thick insulation on the ceiling. 

[Crossy]

A "flying-roof" (or solar panels) with lots of ventilation is certainly a good way of reducing heat gain, but your "inner roof" (the cement board in your diagram) will need to have some weather resistance for when the horizontal rain comes along.

 

[PatOngo]

No aircon?.................................Just sweat a little!   

[scubascuba3]

Many buildings in the Navy base have this overlap design, some open such as in the Ops question, must be a benefit when it rains

[Artisi]

Too many open ended questions, suggest you find an architect / engineer experienced in these areas  and pose the questions. 

[sometimewoodworker]

8 hours ago, 4myr said:

As a newbie I'm in search of simplicity - in this case, is it possible to cut out on roof foil and insulation and replace this by air [see pic].

No. But it will make the foil more effective as long as it doesn’t degrade.

[Laza 45]

The flying roof above will protect the ceiling from direct sun reducing heat buildup.. but  It seems to me that your cement board will act as a heat sink and heat to the ambient outside temperature and you will get radiated heat into the rooms below.  I think if your ceiling were constructed with low mass materials it would work better.. 

[Artisi]

4myr: don't think that because you have a "breeze" between your ceiling and roof it will be cooler, you might feel cooler because of air movement owing to the effect of evaporation from perspiration - but not your ceiling, sure it will overcome heat build-up but it will still be the ambient temp. and the ceiling will require insulating. 

[SomchaiCNX]

Just keep it simple ????

https://en.wikipedia.org/wiki/Bernoulli's_principle

https://www.youtube.com/watch?v=mgeIWXld9FU

 

Even with a closed roof and the necessary ventilation holes the hot air can be sucked out from under the roof. Similar like like the smoke is sucked out of the car while driving with an open window.

The problem you can encounter is that your roof want to take of similar like the wing of an airplane if there is to much wind coming from the right direction.

 

[Lt Frank Bullitt]

Try this roofing now available here, expanded foam sandwiched between the roof sheet and a ribbed or flat metal sheet in various thicknesses, you get the insulation and as a bonus noise reduction when raining, unfortunately for me i found it after already installing corrugated cement roofing. 

[Surelynot]

Much might depend on the temperature difference between the air as it flows through the upper and lower roofs and the air temperature in the room below.

 

Air is a good insulator if it is trapped, but can be an effective conductor of thermal energy when moving.

 

So this set up might tend to heat up your room during the day...... but help to cool it at night.........maybe have baffles to stop daytime airflow and open them at night to allow air flow and aid cooling.

 

[HarrySeaman]

What you are suggesting is going to help vs the typical corrugated concrete roof that reaches the tops of the walls.  There are several things you can do to make the typical roof even better than what you are planning.

 

Heat builds up inside the enclosed space between the ceiling and the roof when the sun shines on the roof.  Sun shining on a white roof heats the air under the roof less than the sun shining on a colored roof.  There are heat reflective white paints for those who already have a colored roof and a couple of layers does wonders.

 

Thai corrugated cement roofs are rarely sealed at the bottom edges, allowing for air, bugs, and other critters to enter.   If you can find a way to screen the open area at the bottom of the roofing to allow only air to enter and by adding a rotating ventilator close to the peak of the roof you can move more air through this space and reduce the heat buildup from the sun shining on the roof.  This will give you the same effect as what you propose.

 

Adding a thick layer of fiberglass insulation on top the ceiling is the best way to help prevent heat from the enclosed space get into the living quarters.  NEVER put the insulation on the bottom of the roof because that won't prevent heat from air circulating between the ceiling and roof from heating the ceiling - the insulation needs to be between that air inside the roof and the ceiling. 

 

If critters get in you can expect problems from them making nests in the insulation.  Be sure to have an access opening in the ceiling so you can get into the area between the ceiling and the roof to get rid of any critters and repair any damaged insulation.

[natway09]

Mechanical ventilation will in no way change the humidity ,,,,just feel a bit cooler

[geworthomd]

21 hours ago, scubascuba3 said:

Many buildings in the Navy base have this overlap design, some open such as in the Ops question, must be a benefit when it rains

This style has five main benefits. 1. It is easy to construct and doesn't need trusses. 2. It catches water run off without the need for trough's on all sides. 3. The front overhang shades sun out on the hottest time of the day. 4. The greatest wall for windows to the sea is made larger.  5. It is cheap to construct out of a variety of materials.  There are no expensive dormers, lintels or gables.

 

Infrared radiation is the primary heat source.  The roof should try to keep the infrared from going into the occupancy area below.  Keeping your roof a distance away from your concrete board will allow this, the same as an attic.  As the other person said, the larger air space means that you will have to enclose the ends or the rain will flood your occupancy ceiling.  I say go for it and have fun!  I sure do like the idea that somehow you would be able to get the air to flow through from the ocean side to the land side under that space and without the rain getting through.  That should be easy to do and it would decrease your heat transfer into that dead space.  I would like to suggest that you put it on stilts off the ground a bit in order to gain ventilation.  I would not make it on the ground like this picture even though ground level looks nicer.  It is made of flat panels that are easy to assemble and tear down to move.  It has an air space that keeps infrared from heating the room below.  Ideal for the military in hot areas.  Insulation in the ceiling should keep some of the cold in, in theory, but it doesn't really contribute.  Ceiling insulation works better for keeping room heat in.  For cold insulation we would have to look at double pane windows, thicker doors and and insulation in the walls - hard to do when your walls are made from bricks.  Just adding ceiling insulation in this situation would be a wast of money.  Adding any type of blanket reflective insulation under the bottom side of the roof will add to the removal of infrared.  You could do this except now you have to worry about having to find a way to make that waterproof, creating a whole bunch of extra cost.  I've noticed that in most Thai buildings the rooms heat up rapidly after the air conditioning is off.  I guess this is just the trade off.  If you put the very smallest style air condition in that is of inverter style and a roof style evaporator cooler for days then you can get away with the cheaper energy system of this design?  Using solar panels on the roof was a great suggestion by one of the other authors.  I would certainly put money into the solar panels before I would put any money into insulation.  The roof should be made of a reflective color, normal galvanized look etc.  I wouldn't recommend it be of a dark color due to increased heat absorption.  What a fun project this could be.  If it was four feet off the ground your neighbors could all come to your house during the next Tsunami 

[khunPer]

Some level of heat insulation under the top roof plate is most important for reducing that heat radiates down on the cement bord, which as heavy concrete/material will store heat. You can have roof plates with just a simple heat reflection of the inner side, which has an remarkable effect compared to nothing; often it also reduce noise, but that's depending of thickness of the insulation layer.

 

The cement board is however a good noise reducer in itself – the heavier material, the more noise insulation – as long as it's not vibrating (low sound frequencies), which however would be fairly unlikely.

 

As @Crossy mentioned, almost horizontal rain, which can be very heavy during the monsoon period or just strong Cb-showers – is a factor to care about in Thailand, so if you place any insulation material on top of the cement deck, be aware of water and moisture don't build up in, or inside, the insulation material. Good ventilation of an attic is always advisable...????

[jensmann]

it works. we have slab board ceiling topped with 5 cm concrete. the medal sheet roof is on the side 50cm separated from the house. the air moves up and sucks the cooler air from the nearby forest.

perfect.

most important: make sure no sunlight touches neither wall nor windows !!! 

[RocketDog]

6 hours ago, SomchaiCNX said:

Just keep it simple ????

https://en.wikipedia.org/wiki/Bernoulli's_principle

https://www.youtube.com/watch?v=mgeIWXld9FU

 

Even with a closed roof and the necessary ventilation holes the hot air can be sucked out from under the roof. Similar like like the smoke is sucked out of the car while driving with an open window.

The problem you can encounter is that your roof want to take of similar like the wing of an airplane if there is to much wind coming from the right direction.

 

The venturi effect is only effective with relatively fast mass flow. 

To illustrate this turn on your shower and watch the shower curtain deflect inward toward the water flow. Decrease the water flow and watch the curtain drift outward again. Jet pumps for shallow wells are another example as are carburetors for gas engines. High mass fluids like water display this property more strongly than low mass fluids such as air. 

 

Don't count on much effect from gentle breezes. 

[RocketDog]

18 hours ago, sometimewoodworker said:

No. But it will make the foil more effective as long as it doesn’t degrade.

 

3 hours ago, geworthomd said:

This style has five main benefits. 1. It is easy to construct and doesn't need trusses. 2. It catches water run off without the need for trough's on all sides. 3. The front overhang shades sun out on the hottest time of the day. 4. The greatest wall for windows to the sea is made larger.  5. It is cheap to construct out of a variety of materials.  There are no expensive dormers, lintels or gables.

 

Infrared radiation is the primary heat source.  The roof should try to keep the infrared from going into the occupancy area below.  Keeping your roof a distance away from your concrete board will allow this, the same as an attic.  As the other person said, the larger air space means that you will have to enclose the ends or the rain will flood your occupancy ceiling.  I say go for it and have fun!  I sure do like the idea that somehow you would be able to get the air to flow through from the ocean side to the land side under that space and without the rain getting through.  That should be easy to do and it would decrease your heat transfer into that dead space.  I would like to suggest that you put it on stilts off the ground a bit in order to gain ventilation.  I would not make it on the ground like this picture even though ground level looks nicer.  It is made of flat panels that are easy to assemble and tear down to move.  It has an air space that keeps infrared from heating the room below.  Ideal for the military in hot areas.  Insulation in the ceiling should keep some of the cold in, in theory, but it doesn't really contribute.  Ceiling insulation works better for keeping room heat in.  For cold insulation we would have to look at double pane windows, thicker doors and and insulation in the walls - hard to do when your walls are made from bricks.  Just adding ceiling insulation in this situation would be a wast of money.  Adding any type of blanket reflective insulation under the bottom side of the roof will add to the removal of infrared.  You could do this except now you have to worry about having to find a way to make that waterproof, creating a whole bunch of extra cost.  I've noticed that in most Thai buildings the rooms heat up rapidly after the air conditioning is off.  I guess this is just the trade off.  If you put the very smallest style air condition in that is of inverter style and a roof style evaporator cooler for days then you can get away with the cheaper energy system of this design?  Using solar panels on the roof was a great suggestion by one of the other authors.  I would certainly put money into the solar panels before I would put any money into insulation.  The roof should be made of a reflective color, normal galvanized look etc.  I wouldn't recommend it be of a dark color due to increased heat absorption.  What a fun project this could be.  If it was four feet off the ground your neighbors could all come to your house during the next Tsunami 

Insulation retards heat flow regardless of the heat source. In cold climates the walls are normally insulated so insulating the ceilings is obvious. But radiation, nominally blocked by foil, as you say, is only one form of heat flow. The foil is far from a perfect reflector however and still conducts heat itself. Convection and conduction are the other two ways heat is transferred.

 

Air inside a closed space will naturally set up currents that transfer heat from the source (the roof tiles) to the sink (your ceiling). Thermopane windows don't work unless there is a vacuum between the two panes; only radiation can pass a vacuum. 

 

The most cost-effective way to retard heat flow is fiberglass insulation with aluminized mylar film on both sides of it. That stops radiation as well as convection. Building supply houses sell a 1.5x4m rolls of the stuff with an R25 thermal resistance factor value for 200฿. It will pay for itself in electricity cost in two years, installs quickly and easily, and never wears out or requires maintenance.

 

I just insulated the entire ceiling space in my house with a double layer, >R50 for less than $600 including installation labor. The effect was immediate and tangible;  by far the most bang for your buck. The labor crew boss noticed and determined on the spot to insulate his mother's house. I have clay tile roofing backed by the laughably thin layer of foil which is useless in the face of the constant radiation pressure of the clay tiles in the hot sun, which also store the heat until well after sunset. 

 

Evaporative coolers, working on the latent heat of vaporization effect, are useless in humidity environment greater than 50%. I have no aircon at all in my house in Colorado. A single large evaporative cooler works for my entire 3000 Sq ft bi-level house with thick ceiling insulation. Amazingly they sell the silly things in stores here and the first thing people using them notice is that they don't cool the air. The second thing they notice is that the water reservoir doesn't empty very fast because the water really isn't evaporating and taking heat out of the incoming air. There may be a few places in Thailand where they will help some a few months a year, but very damn few. 

 

Inverter aircon have nothing to do with airconditioner operation except as concerns the compressor motor. The compressor/evaporator part of the aircon is the same as in all airconditioners. An Inverter stage simply takes a variable voltage AC mains input (common here), converts it to DC voltage and then  chops it and converts it into three-phase power for brushless DC compressor motors. These BLDC motors operate well on square wave current so the converter itself is also more efficient. That means the aircon can operate on widely varying voltages, withstand power surges and brownouts better, and the brushless motor is more efficient than the AC induction motor which is more prevalent (now) and cheaper. Brushless DC motors are slowly replacing AC induction motors in higher hp ratings every year since they use less copper (the rotor is a permanent magnet) and are lighter and more energy efficient as well. 

 

Honda makes portable generators using the power inverter concept so the shaft speed of the engine does not have to be 3600rpm to produce 60Hz power. No fancy speed regulators are needed for the engine. The DC voltage from the generator can be chopped to any frequency square wave and the low-pass filtered to produce clean quasi-sinewave AC power at any frequency desired. 

 

So if the OP wants a simple solution he should use the sloped roof he desires but enclose it enough to prevent water ingress, vent it as needed, then insulate the hell out of the ceiling. A small aircon will then work well for him. Airflow is a vastly over-rated, but admittedly cheap, cooling method unless you sweat buckets and the humidity is low. Fans don't work at all for cooling unless some form of evaporation is employed. Fans just blow hot air from one place to another. 

[Artisi]

56 minutes ago, RocketDog said:

 

Insulation retards heat flow regardless of the heat source. In cold climates the walls are normally insulated so insulating the ceilings is obvious. But radiation, nominally blocked by foil, as you say, is only one form of heat flow. The foil is far from a perfect reflector however and still conducts heat itself. Convection and conduction are the other two ways heat is transferred.

 

Air inside a closed space will naturally set up currents that transfer heat from the source (the roof tiles) to the sink (your ceiling). Thermopane windows don't work unless there is a vacuum between the two panes; only radiation can pass a vacuum. 

 

The most cost-effective way to retard heat flow is fiberglass insulation with aluminized mylar film on both sides of it. That stops radiation as well as convection. Building supply houses sell a 1.5x4m rolls of the stuff with an R25 thermal resistance factor value for 200฿. It will pay for itself in electricity cost in two years, installs quickly and easily, and never wears out or requires maintenance.

 

I just insulated the entire ceiling space in my house with a double layer, >R50 for less than $600 including installation labor. The effect was immediate and tangible;  by far the most bang for your buck. The labor crew boss noticed and determined on the spot to insulate his mother's house. I have clay tile roofing backed by the laughably thin layer of foil which is useless in the face of the constant radiation pressure of the clay tiles in the hot sun, which also store the heat until well after sunset. 

 

Evaporative coolers, working on the latent heat of vaporization effect, are useless in humidity environment greater than 50%. I have no aircon at all in my house in Colorado. A single large evaporative cooler works for my entire 3000 Sq ft bi-level house with thick ceiling insulation. Amazingly they sell the silly things in stores here and the first thing people using them notice is that they don't cool the air. The second thing they notice is that the water reservoir doesn't empty very fast because the water really isn't evaporating and taking heat out of the incoming air. There may be a few places in Thailand where they will help some a few months a year, but very damn few. 

 

Inverter aircon have nothing to do with airconditioner operation except as concerns the compressor motor. The compressor/evaporator part of the aircon is the same as in all airconditioners. An Inverter stage simply takes a variable voltage AC mains input (common here), converts it to DC voltage and then  chops it and converts it into three-phase power for brushless DC compressor motors. These BLDC motors operate well on square wave current so the converter itself is also more efficient. That means the aircon can operate on widely varying voltages, withstand power surges and brownouts better, and the brushless motor is more efficient than the AC induction motor which is more prevalent (now) and cheaper. Brushless DC motors are slowly replacing AC induction motors in higher hp ratings every year since they use less copper (the rotor is a permanent magnet) and are lighter and more energy efficient as well. 

 

Honda makes portable generators using the power inverter concept so the shaft speed of the engine does not have to be 3600rpm to produce 60Hz power. No fancy speed regulators are needed for the engine. The DC voltage from the generator can be chopped to any frequency square wave and the low-pass filtered to produce clean quasi-sinewave AC power at any frequency desired. 

 

So if the OP wants a simple solution he should use the sloped roof he desires but enclose it enough to prevent water ingress, vent it as needed, then insulate the hell out of the ceiling. A small aircon will then work well for him. Airflow is a vastly over-rated, but admittedly cheap, cooling method unless you sweat buckets and the humidity is low. Fans don't work at all for cooling unless some form of evaporation is employed. Fans just blow hot air from one place to another. 

Great post.

"Fans just blow hot air from one place to another." exactly the same as opening all the windows on a hot day to cool the house. 

[Enoon]

 

Thatch the metal roof and it won't get hot enough to have an effect on the cement board (which will still need waterproofing).

 

It will also deaden the sound when the rains come.

 

But your wife will probably not like it.

 

 

[ICECOOL]

On 10/9/2020 at 3:26 PM, scubascuba3 said:

Many buildings in the Navy base have this overlap design, some open such as in the Ops question, must be a benefit when it rains

I note the rather large air-conditioning units

[SomchaiCNX]

7 hours ago, Lt Frank Bullitt said:

Try this roofing now available here, expanded foam sandwiched between the roof sheet and a ribbed or flat metal sheet in various thicknesses, you get the insulation and as a bonus noise reduction when raining, unfortunately for me i found it after already installing corrugated cement roofing. 

Only available in BKK I assume?

Any link?

 

[SomchaiCNX]

1 hour ago, RocketDog said:

 

 

The most cost-effective way to retard heat flow is fiberglass insulation with aluminized mylar film on both sides of it. That stops radiation as well as convection. Building supply houses sell a 1.5x4m rolls of the stuff with an R25 thermal resistance factor value for 200฿. It will pay for itself in electricity cost in two years, installs quickly and easily, and never wears out or requires maintenance.

 

I just insulated the entire ceiling space in my house with a double layer, >R50 for less than $600 including installation labor. The effect was immediate and tangible;  by far the most bang for your buck. The labor crew boss noticed and determined on the spot to insulate his mother's house. I have clay tile roofing backed by the laughably thin layer of foil which is useless in the face of the constant radiation pressure of the clay tiles in the hot sun, which also store the heat until well after sunset. 

 

Evaporative coolers, working on the latent heat of vaporization effect, are useless in humidity environment greater than 50%. I have no aircon at all in my house in Colorado. A single large evaporative cooler works for my entire 3000 Sq ft bi-level house with thick ceiling insulation. Amazingly they sell the silly things in stores here and the first thing people using them notice is that they don't cool the air. The second thing they notice is that the water reservoir doesn't empty very fast because the water really isn't evaporating and taking heat out of the incoming air. There may be a few places in Thailand where they will help some a few months a year, but very damn few. 

 

Inverter aircon have nothing to do with airconditioner operation except as concerns the compressor motor. The compressor/evaporator part of the aircon is the same as in all airconditioners. An Inverter stage simply takes a variable voltage AC mains input (common here), converts it to DC voltage and then  chops it and converts it into three-phase power for brushless DC compressor motors. These BLDC motors operate well on square wave current so the converter itself is also more efficient. That means the aircon can operate on widely varying voltages, withstand power surges and brownouts better, and the brushless motor is more efficient than the AC induction motor which is more prevalent (now) and cheaper. Brushless DC motors are slowly replacing AC induction motors in higher hp ratings every year since they use less copper (the rotor is a permanent magnet) and are lighter and more energy efficient as well. 

 

Honda makes portable generators using the power inverter concept so the shaft speed of the engine does not have to be 3600rpm to produce 60Hz power. No fancy speed regulators are needed for the engine. The DC voltage from the generator can be chopped to any frequency square wave and the low-pass filtered to produce clean quasi-sinewave AC power at any frequency desired. 

 

So if the OP wants a simple solution he should use the sloped roof he desires but enclose it enough to prevent water ingress, vent it as needed, then insulate the hell out of the ceiling. A small aircon will then work well for him. Airflow is a vastly over-rated, but admittedly cheap, cooling method unless you sweat buckets and the humidity is low. Fans don't work at all for cooling unless some form of evaporation is employed. Fans just blow hot air from one place to another. 

Under what brand name is your 25 R material available in THailand? Any link?

 

[The Theory]

On 10/9/2020 at 1:18 PM, 4myr said:

will this air roof insulation works [heat and sound] as good as roof foil and foam insulation in a standard pitched roof?

About heat: with this type of roof you will receive heat more than outside in shade temperature(and depends on the roof metal sheets type the heat could be even higher) but never less than in shade outside temperature) could be even more because the ceiling receives heat radiation from the roof). Unless you cover the ceiling by insulation. 
about noise: if you use smart cement boards, they will work like drums and you don't want that(vibrates by low frequency just like Gipson boards. IMO if you use thick (2 inch) cement panels that are used for upper floors, works better. But is need more strength structurally to hold those heavy panels. 
and you need cavity walls to reduce noise ass well (but cavity walls as noise reducer could be a bit tricky around joints rather than regular cavity walls if your purpose is sound proofing). 
 

[RocketDog]

46 minutes ago, Artisi said:

Great post.

"Fans just blow hot air from one place to another." exactly the same as opening all the windows on a hot day to cool the house. 

Thanks, and true.

 

But technically I should have said they just move air. If the air itself is cooler than what it touches that object will become cooler. 

Most days the air here is so near body temperature that unless we sweated it wouldn't cool us much at all. 

[Farma]

28 minutes ago, SomchaiCNX said:

Only available in BKK I assume?

Any link?

 

I think that's what our builder is using and Its available up country. Our initial roofing was PE but on advice from the builder we upgraded to PU. Ask for PU roof.

 

Not someone were dealing with but will give you a link with details. Try facebook or dot com psspuroof

[RocketDog]

6 minutes ago, SomchaiCNX said:

Under what brand name is your 25 R material available in THailand? Any link?

 

I don't remember the brand but I bought it at Global House. I also comparison shopped it at Thai Watsadu and I wouldn't be surprised if Homepro carried it. 

I'm sure it's available at several places at competitive prices since it's a commodity item. Any large home improvement store will have a selection. Shop strictly by R value and forget thickness figures. 

 

The roll size area seems to be a standard but thickness is a function of the R value. I did notice that if you compare R value for various brands/prices you will find that you can get a higher final R value at lower cost by using two layers of lower R than one of a higher R. The R value advantage is not linear so much over R50 becomes less effective per $. 

 

This may hypothetically increase your installation labor somewhat, but the mylar film is also doubled as well, so worth any marginal labor cost. 

I never bothered to cut any of it. I just rolled it out and if there was an extra foot or so at one end I just doubled it over to fit the area. So the only real labor is getting the rolls into the attic and rolling them out. I also criss-crossed the second layer to cover where edges met on the first layer. 

 

If you have recessed lighting of any significant power you should pull the insulation around it since it will: you guessed it, trap the heat! The insulation itself is fireproof but it might shorten bulb life or even melt plastic fixtures. 

 

Farang friends who have visited my house have become true believers and plan to insulate their own houses. They wonder why they didn't do it years ago.

 

The energy savings are one thing but the sheer comfort of the room/house is impressive. That's what will convince you that you really made an improvement you can feel every single day. I just insulated the three bedrooms initially, but after a month I did the whole house since I was sold at that point. Hell, even the ceiling fans worked better since they weren't pulling hot air down from the ceiling.

 

Get a thermometer and watch how much faster your aircon cools the room and then pay attention to how much less often you hear the compressor cycling. We now keep all the windows in the house closed because even without aircon on the house stays cooler and less humid than outside. 

 

 

Good luck. 

[SomchaiCNX]

5 hours ago, RocketDog said:

The venturi effect is only effective with relatively fast mass flow. 

To illustrate this turn on your shower and watch the shower curtain deflect inward toward the water flow. Decrease the water flow and watch the curtain drift outward again. Jet pumps for shallow wells are another example as are carburetors for gas engines. High mass fluids like water display this property more strongly than low mass fluids such as air. 

 

Don't count on much effect from gentle breezes. 

Correct, but my house is just the last one in the row and there is a gap of about 10 m with the next one. Depending on the season I get a lot of airflow through that gap. 

[sometimewoodworker]

4 hours ago, RocketDog said:

 

Insulation retards heat flow regardless of the heat source. In cold climates the walls are normally insulated so insulating the ceilings is obvious. But radiation, nominally blocked by foil, as you say, is only one form of heat flow. The foil is far from a perfect reflector however and still conducts heat itself. Convection and conduction are the other two ways heat is transferred.

 

Air inside a closed space will naturally set up currents that transfer heat from the source (the roof tiles) to the sink (your ceiling). Thermopane windows don't work unless there is a vacuum between the two panes; only radiation can pass a vacuum. 

 

The most cost-effective way to retard heat flow is fiberglass insulation with aluminized mylar film on both sides of it. That stops radiation as well as convection. Building supply houses sell a 1.5x4m rolls of the stuff with an R25 thermal resistance factor value for 200฿. It will pay for itself in electricity cost in two years, installs quickly and easily, and never wears out or requires maintenance.

 

I just insulated the entire ceiling space in my house with a double layer, >R50 for less than $600 including installation labor. The effect was immediate and tangible;  by far the most bang for your buck. The labor crew boss noticed and determined on the spot to insulate his mother's house. I have clay tile roofing backed by the laughably thin layer of foil which is useless in the face of the constant radiation pressure of the clay tiles in the hot sun, which also store the heat until well after sunset. 

 

. 

Humm.

 

First the foil installed just under or touching the underside of the roof doesn’t act as a reflector, it acts as an extremely poor radiator, about 5% to 7%.

 

In the floating roof design the main heat transfer method between the 2 roofs is radiant and since you have cut that down by 93%~95% that is better than most other methods.

 

The foil gives the most cost effective reduction in radiant heat transfer at a vastly lower cost than fibreglass.

 

The foil on the top surface of the fibre glass will quickly loose its effectiveness as dust builds up so reducing it’s reflective properties.

 

The foil is able to reduce the effective heat from  my steel roof from 63^oC to 37^oC so as to laughing yes I am, all the way to the bank.

 

You do have to install the foil shiny side down for it to be effective.

 

Of course the film is only one part of the insulation but it’s so cheap to install when building you would be a fool not to include it at about 14~28 Baht per square metre

3 hours ago, SomchaiCNX said:

An Inverter stage simply takes a variable voltage AC mains input (common here), converts it to DC voltage and then  chops it and converts it into three-phase power for brushless DC compressor motors.

Sorry that’s total BS. DC is not, can never be 3 phase. The phases are related to the sign wave of AC current.

2 hours ago, RocketDog said:

Get a thermometer and watch how much faster your aircon cools the room and then pay attention to how much less often you hear the compressor cycling. We now keep all the windows in the house closed because even without aircon on the house stays cooler and less humid than outside. 

 

True, though with good design we never hear the outside units, the inverter cassette in the living room, when on doesn’t vary its fan speed and our bedroom AC has a silent mode so can’t be heard.

 

even better are the MrKen fans that on low speed move plenty of air and are virtually silent.

 

so with double AAC walls & high quality laminated IGUs we drop about 25db and between 20%~30% humidity. We also don’t have a storage heater for our roof material.