Types of HVAC Systems
Split systems, mini-splits, furnaces and boilers are just a few of the choices for your home.
BY: Steven Castle and Jim Wheeler
According to the U.S. Department of Energy, modern conventional heating systems can achieve efficiencies as high as 97 percent, converting nearly all the fuel to useful heat for your home.
Heating units can be categorized into furnaces that provide heated air through ductwork, which is a popular type of heating system in the United States such as boilers that heat water for steam radiators or forced-water systems with baseboard radiators, electric heat and heat pumps. Furnaces generally use natural gas or propane for fuel, while boilers can use gas or oil.
Seek Annual Fuel Utilization Efficiency (AFUE) ratings (efficiency percentage) in the 80s and 90s. The national minimum for furnaces in the United States is 78 percent. Look for Energy Star-certified systems that are more energy-efficient, and consider sealed and combustion units that bring outside air directly into the burner and exhaust directly to the outside. These are the most efficient systems and do not pose a risk of backdrafting combustion gases.
All-electric furnaces have AFUE ratings of 95 percent to 100 percent, but they are not economical is many parts of the country. You can also consider electric heat pumps to heat or cool parts or all of your home. Some heat pumps can be added onto furnaces as well, to help use less gas or propane.
Radiant floors, or hydronic heating systems, often use piping under a floor. Flexible tubes are filled with water or a glycol solution to heat a concrete or other floor. These can be quite efficient and require either a boiler or heat pump. And they can be retrofitted, if carefully installed beneath wooden floor sheathing. Though radiant systems are much more effective if built into a concrete floor, which will retain the heat and release it slowly.
Air conditioning systems today come in several different sizes and types, and what you decide to add or upgrade in your home depends on the systems you already have, as well as the climate.
An air conditioning system’s output is measured in tons, a term derived from the amount of heat needed to melt one ton of ice in 24 hours. One ton of refrigeration can remove 12,000 British thermal units (Btu) of heat in one hour. An average, 2,000-square-foot home requires about 3 tons of cooling.
Today's best air conditioners use 30 percent to 50 percent less energy to produce the same amount of cooling as air conditioners made in the mid-1970s. Even if your air conditioner is only 10 years old, you may save 20 percent to 40 percent of your cooling energy costs by replacing it with a newer, more efficient model.
The most generally known efficiency rating is Seasonal Energy Efficiency Rating (SEER). SEER 13 is the minimum efficiency you should consider, but higher efficiencies are likely to be cost effective. Some central air systems have SEERs of 16. In hot, dry climates you should look at the Energy Efficiency Rating (EER), which denotes how well the system will work at peak conditions. Also look for Energy Star-rated systems for the best energy efficiency.
Air conditioners have three important parts that include a compressor, a condenser, and an evaporator. The compressor and condenser are normally located on the outside part of the air conditioner while the evaporator is located on the inside. Most central air conditioning systems in homes are split systems.
Many today use for ductless mini-split systems, which can be installed by do-it-yourselfers, though it is a moderately difficult project, as interior and exterior units must be installed and both refrigerant and condensation lines must be run between the two elements. These systems can run $1,500 to $2,000 per ton, according to the U.S. Department of Energy.
Some in hot but non-humid climates like the southwest use evaporative coolers, also called swamp coolers, that cool outdoor air by passing it over water-saturated pads, causing the water to evaporate into it. The cooler air is then directed into the home, and pushes warmer air out through open windows.Room air conditioners that fit into windows or can be installed in walls are good options for cooling selected spaces.
* Proper sizing of a home's heating and cooling systems is a key calculation.* Proper sizing is very important for efficient air conditioning. A bigger unit is not necessarily better because a unit that is too large will not cool an area uniformly. A small unit running for an extended period operates more efficiently and is more effective at dehumidifying than a large unit that cycles on and off too frequently.* Based on size alone, an air conditioner generally needs 20 British thermal units (Btu) for each square foot of living space. Other important factors to consider when selecting an air conditioner are room height, local climate, shading, and window size. Also look for a filter that slides out easily for regular cleaning, logically arranged controls, a digital readout for the thermostat setting, a built-in timer, and an Energy Star-rating for efficiency. Replacing an older unit with an EER rating.
10 Key Features of HVAC Systems
The following is a checklist of the most important features of an HVAC system for a new home. If it saves you even one callback, it's be worth the time to read it and remember its points:
(1) The design and type of ductwork. If the ducts aren’t sized and balanced properly, the home will never be comfortable. Externally insulated round ducts are the most efficient; long runs of flexible duct are the worst.
(2) The refrigerant. Federal law requires R-22 to be phased out in 2015; what little that remains available for servicing after that will be very expensive. I recommend systems that use the environmentally friendly R-410A.
(3) Balance dampers in the ductwork. The worst and noisiest place to adjust the amount of heating and cooling coming into a room is at the diffuser grille. Balance dampers should be installed some distance from the diffusers and be balanced by a qualified technician with the proper tools.
(4) Location of the indoor unit. Attic-mounted furnaces will eventually leak and cause ceiling damage, unless you take special design precautions, such as a secondary condensate pan and drain line to the exterior. Furnaces mounted in closets at floor level are less prone to cause leaks and water damage, and they are much easier to service.
(5) Location of the outdoor unit. The worst places to locate outdoor (condensing) units are where they can be seen and heard, such as outside a bedroom window; where they can be easily damaged; or under the edge of an un-guttered roof.
(6) Efficiency. As of January 2006, the minimum allowable efficiency for new air conditioners will be 13-SEER. (The minimum limit in 2005 is 10-SEER.) Think of it as miles per gallon: the higher the SEER, the lower the utility bill. In fact, some air conditioners (those rated close to 20-SEER) can cost half as much to run as those with the current minimum limits.
(7) A filter dryer. Installing a filter-dryer in an air-conditioner liquid line (the smaller one) always extends the compressor life by removing damaging moisture and any grit.
(8) The condenser (outside) coil type. Coils that are made of a single metal (such as aluminum coil and aluminum fins or a copper coil and copper fins) last longer and hold their efficiency better. This becomes especially critical in mildly corrosive environments; specially coated coils should be used where salt spray is encountered.
(9) Return-air considerations. Remember that in order for conditioned air to enter a room, an equal amount of air must be able to leave the room. Otherwise, there'd be no space for the conditioned air to occupy. The ideal condition here is for each room to have an entering-air diffuser and a return-air diffuser. However, this extra expense can be eliminated if you add transfer grilles or jump ducts sized at 300-400 fpm.
(10) Air-filter location. Air filters should be located where they are easy for the homeowner to reach. Since the filters should be replaced about every three to four months, the homeowner should be able to find the location and replace the filter with minimum effort and searching.
If you need assistance in sizing your HVAC sysytem or need Mechanical Designs for CalGreeen compliance, please call us 209-538-2879.