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Did you know you can extract heat from chilly outside air and use it to heat your house? This feat is performed by the magic of a heat pump--an appliance that uses refrigeration technology rather than fuel combustion to provide warmth and cooling.
Heat pumps are not new-- they've been in use for more than thirty years. But upward-spiraling energy costs and technological breakthroughs have catapulted heat pumps into position as a popular, sensible alternative to conventional heating and cooling systems. Early heat pumps were something of a disappointment-- they were noisy and prone to breakdown, and they failed to provide ample warmth on really cold days. Advances have ushered in a new generation of energy-efficient, reliable systems that are winning over homeowners and builders alike.
How do heat pumps work?
Heat pumps transfer heat from one place to another--providing both heating and cooling. They work on the fundamental principle that heat exists in air even at extremely low temperatures--down to -460º F. In the winter, a heat pump extracts heat from outside air and delivers it indoors. To cool a house on hot summer days, it works in reverse, extracting heat from room air and pumping it outdoors. The process is a bit technical, but here's a brief look at how they work:
Air-source heat pumps. The most common type of heat pump is an "air-source" system. "Split" air-source systems have an outdoor unit which includes a compressor, outdoor coil, fan and reversing valve. That unit is connected with refrigerant-filled tubing to an indoor component. The indoor unit contains a fan, indoor coil and a supplemental resistance heating element. "Package" systems combine both components in a single unit that's typically placed on the roof.
Depending on whether the heat pump is in a cooling or heating mode, the refrigerant moving through the system makes the indoor coils either hot or cold. A blower draws room air in through a filter and pulls it across the indoor coil. An optional electric-resistance heating element can kick on when needed to supplement heat. As the air passes by the coils, it either gathers or gives off heat-- depending on whether the coils are hot or cold. Warm or cool air travels through ductwork and registers into your rooms.
Heat pumps give off less heat at one time than a conventional gas furnace. This means they offer a mellower type of heat, stay on longer and circulate more air throughout the house. They're controlled by the same type of thermostat used for forced-air systems.
On really cold days a heat pump must work especially hard to collect heat-- that's when the supplemental heater switches on to boost warmth.
Some heat pumps can heat your water, too. The Hydrotech 2000 Heat Pump by Carrier is a system that utilizes the warm air that a heat pump gives off to help heat your water. Adding to its performance is a built-in microprocessor that varies fan speeds and output depending on need. This greatly improves a heat pump's efficiency.
New thermal storage units even store heat and cold, collecting it during non-peak hours for peak-hour use. The Phoenix THP/3 stores both heat and cool in a large insulated water tank. It also supplements hot-water heat.
Ground-source and water-source heat pumps. Not all heat pumps extract heat from the air. Ground-source and ground-water source heat pumps circulate water mixed with antifreeze through a system of buried tubing to gather heat from the earth or ground water, which is much more consistent in temperature than air. Below-ground temperatures are normally warmer than outside air in the winter and cooler than the air in summer.
The ground-source system employs a closed loop of tubing that is buried below the frost line; the water-antifreeze mixture circulates through the tubing, gathering heat from the earth. A ground-water system typically involves pumping water from one well, transferring its heat to your house, then returning the water to another well.
WaterFurnace, from WaterFurnace International can be set up either as a ground-source, closed system or an open-loop ground-water system. It uses half the electricity of ordinary heat pumps. Though the pump is about the same price as most heat pumps, the excavation and the ground loop of piping can be quite expensive-- $2000 or more.
Is a heat pump right for your home?
Whether or not a heat pump will save you money on energy bills depends on a number of factors, including the type of fuel prevalent in your area, your climate, and the amount of insulation and other energy-efficient features built into your home.
According to Richard Jarvis, Technical Specialist with the National Appropriate Technology Assistance Service (NATAS), "If you have natural gas available, it probably makes sense for you to use it for heating and cooling with a conventional air-conditioning system." Natural gas is a more efficient, less expensive fuel than electricity, needed for heat pumps.
But in the Northeast or other regions where fuel-oil or resistance-electrical heat is more the norm, a heat pump can realize substantial savings. Although electrical-resistance heating is much less expensive to install than a heat pump, the heat pump can deliver 1 1/2 to 2 1/2 times more heat with the same amount of energy, depending on climate, the house, and the particular system.
Heat pumps are most effective at saving energy when in the heating mode. The problem with an air-source heat pump in a cold climate, however, is that your household needs more heat as the temperature outside goes down-- but the heat pump works less efficiently at lower outdoor temperatures. Below a temperature known as the "balance point," normally from 30 to 45º F, supplementary heat is required--and that means expensive electrical-resistance heating kicks in.
The right way to decide the most appropriate form of heating and cooling for your home is to do an economic analysis, based on a system's purchase cost and efficiency, the cost of your fuel and your home's heating/cooling load requirements. For more information about appropriate fuels, check out the Department of Energy's fact sheet, "Comparing Energy Sources," at the Energy Efficiency and Renewable Energy Network (EREN) on the web.
Energy efficiency
All heating and cooling appliances carry a federal "Energyguide" label that rates a unit's energy efficiency for both cooling and heating modes. These ratings are based on a relative scale; they let you know how a particular model compares to other low- and high-efficiency models.
Manufacturers commonly use two indexes for measuring-- Seasonal Energy Efficiency Rating (SEER) for cooling and Heating Seasonal Performance Factor (HSPF) for heating. Both are arrived at through sophisticated testing and reflect performance over an entire season.
Government regulations now require that all newly-manufactured models have a cooling SEER of at least 10.0 and a heating HSPF of 6.85. These regulations do not guarantee that a new unit you buy will comply; many dealers still have older, less-efficient models in inventory.
Carrier's Infinity 2000 rates high marks with an SEER of 15.5 compared to high-efficiency models at 13.05 and low-efficiency models at 7.25. Trane's high-efficiency, variable-capacity unit tops the industry with an SEER of 16.9.
In the heating mode, Carrier's HSPF of 10. is very high compared to low-efficiency models at 5.3 and high-efficiency models at 8.9.
Buyers' options
Most heat pump manufacturers make products in several sizes, measured by the amount of air they move. Units are designated by "tons"-- a measurement that originally referred to the amount of ice needed to cool an equivalent amount of air. Typical home sizes range from 1 1/2- to 5-ton capacity.
Though sizing a system should be handled by a professional, Eric Eilar of Air Conditioning Exchange in Glendale, California says, "You can get a rough idea of size by figuring about 400 square feet of living space per ton in older houses; a 1600-square foot house would normally require about a 4-ton system. Newer houses with double-paned windows and more insulation can get by with smaller systems."
Prices for materials run from just under $2000 for small, low efficiency models to top-of-the-line, high-efficiency units at $7500. As Eilar points out, "Price goes up dramatically when you get into the high-efficiency models."
The most efficient heat pumps have variable-capacity controls. Rather than running the system at full-capacity all of the time, these controls coordinate the compressor and blower to adjust to your house's heating/cooling load requirements. Because they seldom run at full speed, they're quieter and they save you money over the long haul.
Zoned Heating & CoolingZoned heating and cooling is one of the hottest new concepts in efficient energy usage. With a zoned system, you can independently control the air flow sent to various rooms or zones in you home, directing heating or cooling where you want it at various times of the day. To make this possible, a system needs a special, multi-zone programmable thermostat and a few motorized dampers. For best results, the air handler's output should be variable. In fact, it's best if it can be controlled over an infinite range of speeds, automatically adjusting the amount of heating or cooling delivered throughout the house according to the need.
Do You Really Need a New Heat Pump?A new heat pump can save you money in the long run. But does your furnace or heat pump need replacement? Do you want a new heat pump because your present one isn't heating or cooling properly or is making too much noise? You may find that simple repairs are all that's needed. If you're considering a new heating appliance to eliminate problems with an older one, first read through these common problems and their fixes --this information just might save you a bundle.
Heat Pump Maintenance
According to the DOE, regular maintenance is the key to an efficient heating system. Dirty filters, clogged burner ports and improper settings can drastically reduce furnace efficiency. They recommend a yearly inspection by a qualified service technician and replacing or cleaning filters on a monthly basis. A permanent air screen or electronic air filter should be cleaned according to manufacturer's recommendations. Properly maintaining your heating system-- whether it's a conventional system or a high-efficiency one-- is the best way to ensure years of problem-free, economical, comfortable heating.
Most heating systems operate reliably for a long time if they are well-maintained. Before you call a furnace technician for a repair or roll up your sleeves to do the work yourself, call your utility or check their Web site—in many areas, the utility company will send a technician to your home to check minor furnace problems for free.
If you smell gas in your home or near your furnace, particularly if the odor is strong, immediately evacuate the house, leave the door open, and call your gas utility or the fire department from your neighbor's house or a cell phone. (Don’t use the phone in the house or turn light switches off or on.)
Sometimes a furnace may not seem to be generating any heat. In this situation, check the master switch and circuit breaker or fuse. The electrical system may have overloaded. If you don’t find a tripped circuit breaker or blown fuse, your thermostat may be faulty.
Filter Care
Clean or replace a disposable furnace filter periodically during the winter—check the filter monthly. Brush and vacuum the heat exchanger surfaces every year, if recommended by your owner's manual. Before the heating season, clean the blower blades and seal any air leaks in ducts with several wraps of duct tape.
A little maintenance goes a long way toward keeping your forced-air equipment working properly. Start by cleaning or replacing the filter. With forced-air furnace systems, air returning to the furnace’s blower first passes through an air filter designed to catch dust and debris and help clean the air before it’s recycled to your home.
A good furnace filter can help reduce allergens but isn’t designed to significantly improve air quality in your home. For that, you’ll need a special air filter (talk to a heating specialist about this).
When typical filters become clogged with debris, they cut down on a furnace’s efficiency and, over time, can cause parts to wear out faster. Change filters quarterly or sooner if they look dirty. Pleated fabric filters are a good, inexpensive choice for reducing dust and allergens.
Here's how to change a replaceable filter:
1) Turn off the power to the unit.
2) Look for the door or panel that conceals the blower; sometimes this is marked "Filter." Lift this door or panel off of its holding hooks or unscrew its retaining screws to remove it.
3) Standard filters are mounted next to or under the blower motor. Slide the filter out along its tracks. Check to see whether it is a disposable filter or intended to be cleaned and replaced--this should be marked on the filter's edge, along with directions for cleaning if applicable. If it's a disposable filter, its size will probably be printed on the frame's edge also. Make a note of its size.
4) Buy a replacement and slide it back into place, noting that arrows stamped on the side indicate the proper direction of airflow; be sure you face these in the proper direction.
Motor Care
Some fan motors and fans need oiling; some have sealed bearings. If recommended by your maintenance manual, oil the bearings according to the manufacturer’s directions.
If the motor runs but the blower doesn’t move air, the belt that connects the two probably has broken. Replacing it is an easy fix. First, turn off all power to the unit and turn off the gas at the gas valve that serves the furnace. Remove the door on the front of the furnace cabinet to give you access to the blower. (It may be on a slide-out drawer or the blower pulley and motor will be easily accessible.) Check the number stamped on the belt and get an exact replacement from a home center or heating supply outlet.
You can usually slip the belt on the motor’s (smaller) pulley first, then start it on the blower pulley. Rotate the blower pulley by hand, holding the belt in place but keeping your fingers from being caught between the belt and the pulley. The belt should slip right into place. If it seems to be too tight or difficult using this method, it may be necessary to adjust the motor mount to provide more slack. Then re-tighten the tension once the belt is in place. Check the manufacturer’s specifications for proper tension—in most cases, the belt should deflect about an inch when you press down on it.
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