Greenhouse Heat Sink / evaporative cooler / humidifer
Came up with this design, anybody using anything similar? Did it work?
No apologies for kiddy drawing, best i can do in the jungle on an IPad
Forget the pc fan, it will have to be a ducted fan, speed controlled, as used in hydroponics
I don't use anything of the sort, but counter current heat exchange is more efficient. If you could reverse the circuit somehow so the cold air was coming from the main tank and the cool water ran anti-parallel to the hot air, you might see better exchange.
All that being said, evaporative cooling in the regular misting sense would probably be just as efficient and less complex.
It is countercurrent and the main purpose is a heat sink to heat the greehouse at night.
If the arrows on the above diagram are correct, the air and water travel in the same direction. A countercurrent system would have them travelling in opposite directions so there was always a strong temperature differential between the two.
I think what manders is saying is that the air is blowing upwards from tthe bottom of the tank from a 'dip pipe' duct or similar.
I think that Physalaemus is right in his supposition that a simple evaporative coling system (either misting or wet media type) would be easier to construct and so long as you have sufficient water circulation give you a heat resevoir aswell. Watch out for Legionaires desiese if you get atomisation or small droplets.
Ok back out of the jungle so can respond in a clearer manner, Steve you right i was intending to put a pipe down the center, although more recently i was thinking to just feed it in directly at the bottom to save space in vertical vessel.
Good point about legionaires and droplets.
Not sure a standard evaporative cooler would either transfer or store enough heat to be usefull but i'll look into it. Seems to me you have the same number of moving parts and the complexity is rather similar but less efficient at heat storage.
Of course the tradional heat sink idea is to use gravel, but you need an awfull lot of gravel to have a significant effect, using water would be much more effective, 3 X by volume, if you can get good enough heat transfer.
Anyway still open to ideas until i've finalised the design.
Last edited by manders; 10-12-2011 at 06:54 AM.
Back out of the jungle? sounds exotic!
For the heat sink you could use a gravel and water base I suppose. The gravel (from memory) would be about 1250 kg/metre cubed and when mixed with water (1000kg/metre cubed) to eradicate air spaces would give you a higher thermal mass than with water alone.
Evaporative cooling may work well depends on what your 'on' conditions, temperature and humidity are as to what you can get out of it, a quick look at a psychrometric chart should tell you, but if you are in a jungle with high humidity you are right, you wont get a lot, but it will be no less effective than that of your layout as the cooling effect can only follow a wet bulb temperature line.
You may well need a method of topping up the water level automatically,depending on teh water usage rate, unless you can do it manually as required.
Not sure what your primary purpose is, cooling or a heat sink, or both, or just to minimise the temperature swings in a temperate or tropical climate.
Hope that helps a bit.
Steve, i'm based in the uk, just been out hiking in thailand for a while.
Original purpose was to save nightime heating as a normal heat sink, later i realised it could also usefully reduce the peak summer temp and maintain some humdity (ideally id like to do away with the autovents as they cause the humidity to plummet when they open).
So yeah if it can reduce the temperature swings and maybe save some heating in spring and autumn then it be worth constructing.
Sorry dont see the point of mixing gravel and water, water stores 5.2 X more heat than gravel on a mass basis. When i did the calcs **** strawbridges 1m3 (1.8 te) of gravel effort could barely store 2kWhrs of heat which is useless. Can get the same effect from only 300 kgs of water.
See what you are doing now, in which case what you propose will work, i've never used a system like it but there are people (I think even in this forum, but cant find the link) who have created evaporative coolers with pumps and wetted media but not gone the extra stage and used a large reservoir of water as a heat sink. The exchanger design and air volumes will need thinking about. I presume you intending to speed control the fan on humidity rather than temperature, just allowing the heat sink to dissipate its heat by conduction to the surroundings.
Take your point on the gravel mix, I was just thinking of the mass rather than the thermal properties, apologies.
Put warm water into the lower tank and get cool water out? How that?
Originally Posted by manders
If the lower tank is placed in a refrigerator you can put warm water into it and take cool water out.
Otherwise you put lukewarm water into the lower tank and take lukewarm water out. I cannot detect a big cooling effect in the outlined design.