QUOTE(dunsuntutmybuntut @ Jan 31 2009, 01:20 AM)
my thoughts about plywood usage... how long can it last... treated, painted and the sorts? it is a permanent structure... as long as the building stands with good management of the BH, the product remains. one reason why i refused the consultants design of including kolam in each floor or kolam overall is... if they can guarantee the waterproofing will last forever... then i'lll consider. i have seen with my own eyes how terrible a leaked water container's effect has on a BH... its a nightmare. imagine the uncle already had 500++ nests per 45 days ... the planks became moldy and the nests black... the birds flew away... it wasn't mine but i almost shed tears!!!
There are wood buildings that are still standing more than 50 years on. Plywood if it is treated and embedded I believe it will last. I was thinking of using plywood for the floor and laying on top of it cement board. On top of this will be another thin layer. In australia this method is used a lot even in toilets and kitchen.
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i strongly believe the usage of mist system is better (and a bit costlier) with pumps, specific valves and tubings. the reason why is it is 100% human controlled and humidity can be easily regulated. besides, if a leak did happen it wont be as damaging as a kolam.
I think misting system doesn't work well and often resulted in mould. Even with a hygrostat the control is very bad.
I am now designing my first BH and had considered a number of systems and misting system definitely, in my considered opinion, to be the worst approach to use. Let me explain a bit about the physics of relative humidity and from this we can get some understanding of the various systems that can be designed.
Humidity means basically the amount of water vapour in the air. At any one temperature the air can hold a certain maximum of such water vapour. As an eg. at 30 degC the air can hold AT MOST 30 g/m^3. If there is only 15 g/m^3 of water vapour than the relative humidity is 50%.
If this air is in an enclosed box and inside this box is a pool of water. The water in the enclosed box will evaporate until it reaches 30 g/m^3. The relative humidity now will be 100%.
If you now poke a hole in the box the relative humdity will start to drop until the amount of water vapour evaporated is equal to those lost through the hole. So in order to ensure that you get 80% relative humidity we could make the hole smaller or increase the rate of evaporation. Rate of evaporation can be achieved by increasing the surface area of the water exposed to the air.
Blowing water into the air will increase the relative humidity and often to saturation (100%) and even with a hygrostat it will always over compensate due to what engineers called transport lag. As the water vapour blown into the air is quite large droplets it will not remain in the air for long. If you want water vapour to remain much longer an ultrasonic misting/humidifier has to be used. This can be quite expensive.
I read in a indon book that what they do in indonesia was to lay on the floor jude cloth that is wet by pools of water. But as bird pooh will drop onto the jude, over time it can be a stinking mess that is almost impossible to clean. Finally I came up with a design, just completed the installation yesterday, where a small channel of water is placed along the wall (about 4 feet off the ground). I use the rain drainage channel to hold the water. And over the sides I will drape cheap dish washing cloth. The water will soak the cloth and the water will evaporate from the surface of the cloth. The water in the channel is controlled by a float valve.
I had tested the system in my kitchen and it worked. I recorded an evaporative rate of 200g of water over a 12 hour period(morning till evening) for a 2 sq.ft of cloth area.
We can control the surface area to control the relative humidity. Once this is established the relative humidity will remain quite stable over a temperature range. It is all natural and everything is self-adjusting. Environmentally friendly just like in natural caves.
Air entering into the BH is often quite dry and to ensure that the fluctuation is not too drastic I bought a water tank and placed it at the roving area.
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regarding turbulence and ventilation holes... i'm still a bit in the dark. what i do know is the accepted position is 2 feet below ceiling level. whether or not two sets (one near the floor, one near the ceiling) is recommended i do not know. someone mentioned that cool air enters the lower ones and hot air exits the higher one... but what about the inter floor holes? shouldn't that be enough for hot air to exit? even the location of the vent holes is debatable... some say most holes should be facing walls more exposed to wind and it is not necessary for each face of the building to have them... but how the hell do we control the wind??? its not like every day the wind hammers just one side of the building.
its stuff like this that needs transparent discussion. if everyone can pinch in ideas and opinion it sure would help us all build an almost perfect BH.
I notice and had seen a number of designs of ventilation holes and the reason for ventilation holes was for heat ventilation. If you have more holes than your relative humidity will drop. I think Harry often suggested closing those holes and he was actually right but I read in other places a lot of these consultants were insulting his advice. Actually what he adviced was correct.
If you are using these holes for getting rid of heat from WITHIN the BH than the strategy will not work. The solution will cause more problems than solve.
Heat MUST BE PREVENTED from reaching the BH at all cost - this means insulation.
Now if you have a double wall than the ventilation holes will reduce the heat from reaching into the BH and turbulence and lost of relative humidity will not be a problem.
A very strange design was to have a long pipe from the inside wall to the outside wall and the person explained to me it was to get rid of the heat inside. More often than not the heat outside is higher and it will flow inwards rather than outwards.
For maintaining temperature below 31 degC , HEAT MUST BE PREVENTED FROM ENTERING THE BH.
Air-conditioning etc. are a waste and in the long term expensive.
Jan 29 2009, 09:40 PM
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. I have a farm here in kuantan and I was thinking of having a joint venture with others but somehow that did not play out well. So I thought of building a cheap one with minimum capital input and let the BH expand on its own dictated by the success of the BH itself. So I had been thinking of ways to see how this could be done. The BH could also be an experimental and learning BH to try out different approaches. I presented it so that hopefully someone could critic it i.e. find fault with it. I already know some of weakness of the design such as termites eating the wood or plywood. Plywood can be made waterproof by painting it with a layer of fibre glass glue. This is used by those making speed boat with plywood. 
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