Air Cooling

Your proposed "cooling" method will only work when the outdoor air temperature is lower than the inside ambient air temperature; not, as you propose, when the outdoor temperature is very high. If it is 80 degrees indoors and you start an exhaust fan which moves, for example, 10,000 cfm to the outdoors, an equal amount of air must infiltrate into the house from the outside to makeup for the exhaust. If it is 100 degrees F outside and 80 F indoors, that exhaust fan will only work to warm up the inside of your home through the air exchange.

Now, if your home is located over a cooler underground cave system and is hermetically sealed above ground, you might end up in cooling your house with the exhaust fan, but then, you might as well just move into the cave and save on the electricity.

Thank you for the advice.I note that the proposed "cooling" method will only work when the outdoor air temperature is lower than the inside air temperature.

In fact, my requirement also happens to be the same.

Inside home gets very warm / hot, even when outdoor temperature is very cool. Most of the time,the ambient (outdoor) temperature is cooler than indoor.Therefore it is necessary to provide a system to draw the cool air from outside to replace the warm / hot air inside.

It is proposed to provide exhaust fan for this air exchange. Exhaust of indoor hot air to outside, through an exhaust fan, can bring cool air from outdoor to inside home through induced draft.

Help is needed how to practically implement the theory,that is how to size the exhaust fan,its location,installation etc.Shall be very grateful if information in those aspects also be given to me.

And, in certain locations and conditions, bringing in outside air, even when outside air has become cooler (e.g., at dusk and early nighttime) can actually make the inside more uncomfortable--because you'd have raised the inside humidity.

Can this be solved through any automatic control,to stop the fan automatically,whenever the humidity is raised beyond comfortable level?

Kindly advise.

The trick with using outside air is the know the ENTHALPY or energy content of the outside and inside air. For cooling if the outside air enthalpy is less than the inside air enthalpy then it's the way to go.

Have a look at this site it will give you some idea how to calculate the enthalpy of the air.

http://www.engineeringtoolbox.com/enthalpy-moist-air-d_683.html

There are systems that will do this automatically but it's a bit more complex and expensive than just putting in an exhaust fan. If you want to know more follow the links at the above site and read up on PSYCOMETRICS

Rather then rehash the comments made so far, Whole House Fans is the trades term for what you want.

http://www.atticfans.com/

It's clear, informative, and best of all - FREE (it outlines what parts do what and lists what you can expect to pay).

The site is vendor neutral. It's not a e-store and this is not a recommondation / sales ploy.

Best of luck in solvering your inquiry.

Mongo

Rule of thumb; One cfm per one square foot of building floor space should do the job. The exhaust fan should be placed at opposite ends of the structure for best results. Try to control the inlet air, ( a partially open window as opposed to a fully opened so you can control the exchange rate of inside air volume ). Humidity cannot really be controlled with out some way of condensing the air volume. Would advise reading up on evaporitive coolers. Refrigerated air conditioning is expensive by comparison, but provides dryer air. Hope I've helped.

What is your view, whether provision of exhaust fans can replace airconditioners?

I typically use a similar system (only opposite idea) when it gets too hot. We have a reasonably insulated house, so when the temp outside gets to be less than the temp inside, I set up a fan to suck the air in. This I typically run all nite. In the morning when outside temp begins to go up, I pull the fan and close up the windows, to save all the cold I stored the night before. Now of course you can suck the hot air out (exhaust) and also suck cooler air in (intake) at the same time. Of course both fans should be at opposite ends of the area to be cooled.

The method used by you depends on the stored cold in the night for use in the day.

Has it been cost effective? I mean whether cost for electricity consumed for running the fan whole night and cost of heat insulating the house are recovered by obtaining suuficient aircooling for whole of the day.

Also, please suggest materials normally used for heat insulation of house at ceiling,roof,side walls to minimise external heat (from sunlight) entering house?

There are typically two releated but different approaches: One type of attic fan pulls outside air through the attic alone: in other words its air inlet is located in the attic. These are thermostatically controlled, and the thermostat is usually set for 95f (35c) or so. They run in the hottest part of the day, when the attic temperature might otherwise rise to 130 - 140f. They significantly reduce the radiant heating of the airspace below.

The other alternative pulls outside air into the living space. Even if it is very warm out, these will help keep you cooler, as long as the outside air is not much greater than your body temp. (Even if it is equal, the air motion promotes evaporative cooling of your skin.)

The common terms for the two types are Attic Fan and Whole House Fan. If you google electric company sites you can find calculators for such things. But in general, both types are more efficient that compressor-driven airconditioners, and can be used in conjunction with aircon.

Electric company sites can also provide advice on insulation. Generally, more is better -- in other words you have to put in a very large quantity of insulation for it not to pay back in 10 years or less: although that depends on relative costs where you live.

Hello, I live in a very dry desert area, the humidity is on average less the 25% with temperatures up in the 95* to 115* during the summer months. We use what is commonly known as an evaporative cooling system. Basically, it consist of a box with a waterfall system on three sides and on the fourth side is the blower. Which in turn draws air in from the outside, through the waterfall filtration pads, and then on into the dwelling. For a more reliable unit in temps over 100*, it is best to build a shage box over and around the evaporative cooler. A box with in a box. Thus, as temps. increase, your ambient temp in the box will actually allow for the air temp to be less then the outside air and as you draw this air into the cooler, it will help sustain temps below 100*F. After your input air above 100*F, the swamp cooler is no longer efficient and your water temp is at equal temp as the out side air. One could possibly create a dual duty system, cooling the air before it is actually used in the cooling of the structure. Then you have created an actual air conditioning system. Which is commonly known in the industrial world as a HVAC, or otherwise, "high volume air conditioning" system. The use of a cold water chiller and evaporative coil system.

This is common information from the major suppliers such as ThermoKing, Train, Carrier, Lennox and so forth. Good luck in your quest.

Lord MAximo

Based on my living experience, the hot air will float attop the room (i.e near roof), since hotter air will have less density than colder air (you may prove it yourself by moving toward the ceiling in the full housed room).

So it is reasonable to put the exhaust fan, in the wall near roof or in the ceiling to exhaust the hot air, meanwhile let the air intake opened at lower side, such as near the floor. The inflow air will also push the hotter air toward the outlet.

Seems too simple explanation, but it works! I enjoy being in my own room. In the worst case of equal temperature at outdoor with the indoor, I still take the benefit of flowing air that take my calor away, letting me stay cool.

Take what ever valuable from above, throw away what you think as garbage. Meanwhile I still stay cool. Again again and again

Thank you for the message,taken from your own live experience,which almost answers / rather confirms the theory of provision of exhaust fan, for the purpose outlined in the origin of the discussion, under this topic.

What remains to be addressed is the basis of design,selection - sizing of exhaust fan,installation of the system, to practically realise the benefit expected out of the theory.Shall also be grateful to receive any mathematical calculations,standard specifications etc.

Just an after thought:

Although it is certainly possible to cool a residence using the exhaust fan as discussed previously, it is not a preferred method. One reason for this is that the negative air pressure in the dwelling produced by the exhaust fan will result in uncontrolled and unfiltered infiltration of make-up air from the outside. The makeup air will be drawn from the source of least resistance. This results in high levels of dust and other particulate matter indoors. A preferred method would be to mount a filtered supply fan on one wall of the dwelling, with a corresponding exhaust vent on an opposite wall to provide for a good mixing of air inside the building. The filter media would help keep the inside air cleaner and as a side benefit, the positive pressure in the dwelling would help keep out unwanted flying insects.

The positive pressure with filtered makeup is one method used on industrial control rooms, where personnel habitability concerns due to potential infiltration of chemical, biological or radiological contaminants are at issue.

Exactly right. You would be turning your house into a giant vacuum cleaner, somewhat like a PC and you know how much dust they collect.

You can however use wind driven exhaust fans in the ceiling cavity to get rid of the hot air there and this will cool you house down. You can buy these fans over the counter for less than $100

Is the conclusion, NOT to install exhaust fan?

In a nutshell it's probably not a good idea for a house that is fairly well insulated. The roof cavity on the other hand is a different matter and in hot climates like Australia the heat build up can be extreme. In this situation they work well by getting rid of this and hence reducing the heat being radiated downwards from the roof cavity. As I stated earlier you can get wind powered fans to do this over the counter.