I watch my dashboard for searches. There have been a few looking for duct size designs.

Supply air duct sizes are determined by how much air (cfm) is to be delivered to a specific area of a civil structure (home). If a bedroom is 12 x 12 feet, or 144 square feet, and the ceiling is 8 feet, the volume is 1152 cubic feet. The velocity of the air, going through the ceiling grill, or floor grille, will affect the amount of air noise in the room. I prefer the more acceptable velocity of 500 feet per minute (fpm). Therefore, if you wish to exchange the volume of air in the room 5 times per hour, at 500 fpm, the diameter of the branch duct feeding the ceiling, or floor grille, would be 9 inches. That’s a little faster (tiny), at .06 friction per 100 foot of duct, but that depends on whether you use round metal, or flexible duct materials. A rectangular branch duct would include sizes from 8 x 9 inches to 4 x 20, and 6 1/4 x 12. Transitioning from round ducts to rectangular ducts, and back, is an acceptable way of adapting to structural elements, and maintaining correct air distribution throughout the air distribution system (ductwork). Since the furnace, or air handler is probably rectangular the first transition might be a plenum, on the furnace, or air handler to round ductwork. The plenum is where most air distribution mistakes occur.

From the ceiling, or floor grill, the main, and other branch, duct sizing back to the furnace, or air handler, is proportionally sized to include volumes of air to be delivered to other spaces along the way back.

I used a Trane Ductulator, I have had for 30 years, to find the numbers above. In the past, I used the equal pressure method for designing air distribution ductwork systems. That’s where the friction per 100 foot of duct comes in. However, it’s quicker to use velocity, and volume to do the designing because of air exchanges between rooms (spaces), and it all seems to balance out ok.

Another example could be; when deciding between a 14 inch and a 16 inch return air duct, choose the 16 inch. The furnace, or air handler generally won’t take in any more air than it can deliver, and won’t deliver any more air than it takes in, and it will slow down the air velocity through air filters located in a return air grille. Filters located in the furnace, or air handler are exposed to higher velocities.

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The borehole cost is different between drillers.  Each driller has a variety of costs, and overhead, that must be figured in the “price per foot” bid price.

Like other trades, finding the lowest price per foot may not be the best deal.  If the driller charges less it may be because of post-drilling cleanup, or insurance and bonding issues.

Call around and get some bids, and have the driller tell you what is to be done, On Paper.

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I cut back on my articles for a couple days. All of a sudden there were many people searching for things like the following:

cost “about geothermal energy”.
negative things about geothermal energy.
5 positive and 5 negative things of a Geoexchange.
geothermal electric bill.
how is heat transferred from on thing to.
geothermal energy (negative things).
geothermal cooling household.
geothermal borehole pipes.

The negative things about geothermal system for homes is not the drilling, unless you need 25, or 30 boreholes. It is, however, the digging up of the entire property to bury a slinky, or series of pipes just below the surface. It seems that the amount, or total length, of the pipes can also cause an increase in the horsepower needed to pump an adequate amount of water through the heat pump, allowing it to operate under its factory specified volume of water.

In spit of that, the Geoexchange system is the most cost effective, energy efficient air conditioning, and refrigeration method available today.

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Addendum:

Someone asked “Why geothermal energy negatives”? Well I guess I should have clarified that, a little. Its not the concept of Geothermal, its the current methods used to employ the technology. Current methods used to couple high efficiency heat pumps, and other equipment, to the unlimited energy resources provided by Mother Earth are not very efficient. There is, however, a new High Performance Geoexchange Sysem being made available as we speak.

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Once properly developed, the Geoexchange technology can save a lot of energy, and money, for everyone.

If even a small part of Americans changed over to Geoexchange air conditioning systems, that change would reduce utility bills for them, and the rest of the country.

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Addendum:

Probably one of the most creditable benefit is the adaptation of digital control circuits, and how more efficiently they cause the Geoexchange system to function because of the inherent redundancy found in volumes of water contained in the ground source heat exchanger.

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Here’s a neat blog. http://thisnewhouse.wordpress.com/

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I could add to the Return air for geothermal systems by adding that in a vaulted ceiling, or second story, it is best to have what is called a high return air intake for two story homes with only one air conditioning system. The high return air will capture, and return for conditioning, warmer air trapped in the upper levels of the structure. This allows the centralized thermostat control to more effectively control the overall temperature of the entire structure.

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Addendum:

There have been a lot of questions about Return Air. The amount of return air in terms of cubic feet per minute (CFM), or dimentionally (length x width, or diameter), of the return air duct, is generally determined by the amount of static air pressure designed into the air handler fan by the manufacturer. Most furnaces used to be designed around one inch water column air pressure, or more, delivering air at around 1000 feet per minute (FPM). The return air is usually designed around .01 to .05 inches water column, more or less. In order to Reduce the amount of design static air pressure the duct has to be made larger. Smaller ducts have more static pressure losses than larger ducts. The static air pressure is related to the velocity, (FPM), and the volume (CFM). Increase the static pressure cause a smaller duct with higher velocities, which can cause air noises in the ductwork. A return air cannot be too large because the air handler (furnace) cannot deliver anymore air than it takes in, and it cannot take in more air than it delivers. Its called a balanced system. I talked about negative, and positive air pressures in a structure, here before. There are high pressure systems that do not follow the above design characteristics.

Don’t forget the air filter. It causes static pressure losses also. To much filter, or a dirty filter can cause the refrigeration system suction pressures to drop below freezing. That can cause the condensate contain in the cooling coil area to freeze, and, enough ice can cause even more restriction to the air flowing over the cooling coil, which cause a loss in capacity, causing the house to get very hot, and humid. This condition is called a “Snow Ball”.

Change, or clean those filters!

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I have some friends who built an outdoor fireplace on their patio. They invited my wife, and me over for a bar-B-Q. The food was great, but the outdoor fireplace was a special treat. It was late in the evening, and the fireplace was burning with only a few logs on the fire. We roasted hot dogs, and marshmallows, over the open fire. The evening was a little cool out and the heat from the fireplace was a pleasant, comforting element of the evening.

I think we are going to build one on our patio, now.

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