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markota

12:35PM | 07/30/04
Member Since: 07/29/04
4 lifetime posts
Bvhvac
We're building a new 3400 sq. ft home. I desire to use a zoned HVAC and heating system since most of the time we will not be using the two bedrooms and only need heat and AC in the master at night. The rest of the house can sit static. The local HVAC dealer wants to put in three seperate systems. A 4 ton AC unit for the master bedroom and Study, a 5 ton system for the main part of the house that includes the kitchen, nook, great room, hallways and dining room, and a third 4 ton system for the other two bedrooms, full bath and garages. Know the ceiling are 12" in height. Trane states that this can all be accomplshed with one large 19+ seer system that is ducted properly and uses thermostatically controlled damper zones. What are your thoughts and suggestions about the zoned approach? The dealer initially recommended two 2 ton systems for the master and other two bedroom. They he bumped up the numbers? I understand that you really only want to up size by no more thean 15% our you'll run into the problem of short cycling the compressors, leading to higher energy costs, wear and tear and inadequate humidity removal. The local dealer is suggesting a total cost in the neighborhood of $30K which I feel is way out of line. Help me here before I go BROKE.

tomh

04:30PM | 07/30/04
Member Since: 07/01/03
550 lifetime posts
What is the climate where you live? Its really hard to second guess the HVAC estimates without knowing if you are in Phoenix or Seattle. Any HVAC contractor should base their bid on a heat load calculation. I have a similar sized house and use a 3.5 ton 15 SEER in the living areas and 2.5 ton for the bedrooms. We are in Sacramento. Obviously lots of variables. I responded earlier to a similar question on the BBS at this link. http://www.bobvila.com/BBS/Heating_and_Air/4398/4398/flat-page1.html More information is needed to answer your questions.

markota

09:44AM | 07/31/04
Member Since: 07/29/04
4 lifetime posts
We live in Ridgecrest, California, in the high desert, which varies from 110 degrees in the summer to 20 degrees in the winter. We have somewhat less humidity than Phoenix. Often it cools down to about 75 degrees at night in the summer. I'm a little confused. The insultion is R45 in the attic using TechShield for the roof and the walls are R22 with few south-facing windows. All other windows are under a covered patio. No one in this area uses boilers and chillers, though the idea is appealing; certainly less elaborate equipment. We are not interested in wall radiators/registers in the house. Another idea the contractor had was to run 3 separate systems to keep the ductwork runs at a minimum; I'm assuming this is to minimize air friction, making the air movement more efficient. I would like to consider a water-cooled condenser, like the FREUS unit or the RDS?

markota

06:54PM | 07/31/04
Member Since: 07/29/04
4 lifetime posts
We are planning two boilers (tankless water heaters) for general (bath, kitchen) hot water use. How much more effienct is it to heat water and pump it through the house to baseboard radiators? The high tech furnace I am considering is 96+% efficient. In this configuration I will need to add a humidifier. I assume in a looped boiler to baseboard radiator system there would be considerable heat loss through the tubing unless you insulated with a high R value insulation. It seems it would take more gas (BTUs) to heat water then air and pump it through ducts via a variable speed fan. We don't need a lot of heat. Usually just enough to get the get the house to 68 degress then its off the rest of the day until be get home at night. The thermostat is set to 58 at night. Certainly interested in state of the art here. Another thought about the boiler and baseboard configuration is the anticipated added cost of running copper pipe throughout the house. The installation costs might offset any initail cost savings. Another problem I see is the basebaord radiators will not match my slected baseboard. I know I won't be able to convince my wife on this configuration. I'd also need to run ceiling fans to move the heat around....another cost. How about a ceiling mounted radiator with a fan? Do you have an estimated cost for a chiller and boiler system supporting a 3400 square foot house? I am open to new ideas. I am suspect of the local dealer since they are comforatable selling and installing the same systems they have been installing for 30 years. I'd like to think outside the box here while saving some additional money for my grandchildren's college fund.

Anonymous

07:10AM | 08/01/04
Efficiency is a ratio of how much heat energy you put in to how much heat you get out the other end. The loss of efficiency occurs in the transfer. The question you want to ask in comparing ducted systems is how much heat will be lost from the square inches of surface of the duct vs the square inches of surface of the pipe.

A hot water pipe that is 1-inch in diameter has about 4 square inches of surface or about 1 square foot of surface per 36 running feet of pipe.

A duct to carry the same amount of heat in air handles 1400 cfm of air through a cross-section of abut 300 square inches; however, the same duct to carry the 5-ton air conditioning has to have a cross-section of 500 square inches to carry 2000 cfm. The square root of 500 is about 22 inches on a side or 4 times 22= 88 inches per linear inch of duct. Thirty-six running feet of that duct would have 36x12x88=38,000 square inches or / 144 = 264 square feet of surface.

There would be 264 times more surface of a duct than a pipe to carry the same heat. The emissive output of a square foot of surface at 120F (let us say that the medium is 120F) might be 100 btuh per square foot, then the pipe would 'lose' 100 btuh in 36 feet and the duct 26,400 btuh in 36 feet. This means the duct is 264 times more costly than the pipe for the same length. NOT using ducts as often as possible is a money-saver, thus the increase in number of ductless-split cooling units.

Warm air heat grew rapidly in the 1960's because people didn't know and didn't care about the cost of heat (being cheap gas and oil at the time) and very few people understand this efficiency loss from the surface of a duct. (If each joint of the duct is not masticked and taped to assure no air loss the actual efficiency is about 50%).

Whether air or radiators, as soon as the heat leaves, they are 100 percent efficient. However, air heat is less efficient AND less effective because convecting air tends to rise so you will need ceiling fans to move the heat downward as the warm air rises to the ceiling as it is blown into the room. Unless you put air registers below the windows the cold air will cross the room at the floor making a chill. To think about it, cooling partially involves creating a 'wind chill', so warm air heat continues that while warming. Heat pump owners are very familiar with the cold feeling while the heat is on.

Baseboard heat warms the walls and windows BEFORE they become cold. As the heat rises up the walls the heat is expended, some of the heat is sent through the air directly to the occupants as radiation (that is why they are called radiators. There are no warm air radiators.) That is why baseboard heated people in the northeast continent still have radiators after 100 years and baseboard after 60 years if they can afford it. They typically keep their thermostat at 68F, while warm air people put their thermostat at 74F, and heat pump people wear a sweater most of the winter.

As to two-stage or other burners, Weil McLain makes a modulating-input gas boiler called the Ultra that can be installed at 250,000 btuh input, but modulates down to about 60,000 btuh and between that for any demand. It runs at about 94% efficiency and can handle all of your house heat - and hot water needs through an indirect water heater tank. One long-lasting burner for all is a lot easier to service than a few short-lived heaters.

You can do a Google search for Freus prices and others. The best way to get a quote is through the estimators of the companies that will do the work. You might get some sharp installers by calling the companies whose equipment you might use. Some of the manufacturing majors will even lay out the installation for you so you have engineered plans for the installation to be done by tradesman subcontractors and there might be some possibility of 'marketing' opportunities for them in showcasing the installation.

tomh

10:14AM | 08/01/04
Member Since: 07/01/03
550 lifetime posts
Harold, your answers are a real education for me. One thing I still don't understand is the use of a radiant system in an AC application. In our part of the country, winter lasts from December to February. We can heat the house with 40,000 BTU units, but we tremendously upsize this in order to have the air-handling capacity to use forced air central AC. One solution to deal with this is to use variable speed fans and variable output furnaces. The ability to chill a house during the long and hot summer is the key issue.

We have the option to use evaporative cooling, but with daytime temps over 100 degrees, the air just doesn't cool enough, and has the drawback of humidity. We have not seen chiller units installed in residential applications here, but homes are larger now and can approximate the demand of a commercial building.

What is the footprint of these chiller systems? What wold the drawback be in residential applications as you see it? Is this commonly done where you live in NJ?
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