Refrigerator Troubleshooting Diagram

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Heat Pumps

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A heat pump is a mechanical refrigeration system. It is arranged and controlled to utilize the condenser heat. The condenser heat is wasted or dissipated into the air when a condenser-compressor are mounted outside a building being air conditioned. By utilizing the heat generated by the condenser can be used for some useful purpose. This useful purpose is in most instances, space heating. Heat-pump systems may be classified as:

• Package, or built-up
• Air-to-air
• Water-to-air
• Water-to-water

Earth coupled systems are also used as a variation of the water-to-water concept. Keep in mind that the heat pump is primarily a central air conditioner. It can also act as a heating system. During the cooling season the heat pump performs exactly like a central air conditioner. It removes heat from the indoor air and discharges it outside. See Fig. 17-17.

During the heating season, the heat pump reverses its function. It changes from a cooling system to a heating system. It then removes the available heat from the outdoor air and discharges it inside the house. See Fig. 17-18.

There is heat in outdoor air, even at 0°F (−17.8°C). In fact, heat is available in outdoor air down to −460°F (−273°C).

Since the heat pump is a refrigeration machine, it needs only enough electrical power to run a compressor, an outdoor fan, and an indoor blower. The result is a heating system with a seasonal efficiency of better than 150 percent. This means that for every kilowatt of electric power used, the heat pump will produce more than 1.5 kW of heat energy. Only the heat pump can give this level of efficiency.

Heat pumps are available in all sizes for apartments, homes, and commercial applications. Heat pumps are not new. General Electric has been selling them since 1952. There are now various types of units on the market.

One unit, the Fuel master, works with a heat pump. It can be used with gas, oil, and electric furnaces. See Fig. 17-19. As can be seen from the illustration, the heat pump resembles a compressor-condenser unit. However, the control box is different. See Fig. 17-20. The control box has relays and terminal strips factory installed and wired. The heat pump delay and defrost limit control are included in the unit.

Written by sam

February 7th, 2011 at 1:44 pm

Posted in Air Conditioning

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Ground to Water and Ground to Air Heat Pumps

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In these systems, coil A in Figure 4.2 is buried underground and heat is extracted from the ground. These heat pump systems have limited use. Practical applications are limited to space heating where the total heating or cooling effect is small, and the ground coil size is equally small. This system requires the burial of several meters of pipe per ton of refrigeration, thus requiring a large amount of land.

Figure 4.2 Types of heat pumps (here, the first part refers to the heat source for the outdoor coil during the heating process and the second part indicates the medium treated by the refrigerant in the indoor coil).

Figure 4.2 Types of heat pumps (here, the first part refers to the heat source for the outdoor coil during the heating process and the second part indicates the medium treated by the refrigerant in the indoor coil).

 

Written by sam

January 30th, 2010 at 6:43 pm

Air to Water Heat Pumps

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In Figure 4.2, these systems work in reverse of the water-to-air heat pumps: they extract heat from ambient or exhaust air to heat or preheat water used for space or process heating. The system is simply reversed. Heat is extracted from the air inside the home and transferred to water and put back in the ground. All the householder is select the temperature that makes their as cool as they wish.

Figure 4.2 Types of heat pumps (here, the first part refers to the heat source for the outdoor coil during the heating process and the second part indicates the medium treated by the refrigerant in the indoor coil).

Figure 4.2 Types of heat pumps (here, the first part refers to the heat source for the outdoor coil during the heating process and the second part indicates the medium treated by the refrigerant in the indoor coil).

 

Written by sam

January 30th, 2010 at 6:42 pm

Air to Air Heat Pumps

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These systems use air on both sides (on coils) and provide heating or cooling. In the cooling mode, heat is removed from the air in the space and discharged to the outside air. In the heating mode, heat is removed from the outside air and discharged to air in the space. In these units, it is necessary to provide defrost controls and periods to maintain maximum efficiency. These are the most popular systems for residential and commercial applications because of easy economical installation and lower maintenance cost.

Depending on climate, air-source heat pumps (including their supplementary resistance heat) are about 1.5 to 3 times more efficient than resistance heating alone. Operating efficiency has improved since the 1970s, making their operating cost generally competitive with combustion-based systems, depending on local fuel prices. With their outdoor unit subject to weathering, some maintenance should be expected.

The most popular heat pump is the air-source type (air-to-air) which operates in two basic modes:

• As an air-conditioner, a heat pump’s indoor coil (heat exchanger) extracts heat from the interior of a structure and pumps it to the coil in the unit outside where it is discharged to the air outside (hence the term air-to-air heat pump), and
• As a heating device the heat pump’s outdoor coil (heat exchanger) extracts heat from the air outside and pumps it indoors where it is discharged to the air inside.

Written by sam

January 30th, 2010 at 6:39 pm

Water to Air Heat Pumps

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Some heat pumps have been designed to operate utilizing a water source instead of an air source simply by designing the outdoor heat exchanger to operate between the heat pump working fluid and water instead of between the working fluid and air. These so-called water-to-air heat pumps have advantages over the air-to-air type if a relatively warm source of water is available which does not require an excessively large amount of pumping power. In particular, industrial waste heat might be used.

In this case, the difference from the water-to-water heat pump is in the method of treating the air. This system provides heating and cooling of air with water as the heat sink or source. The same sources of water can be used in these systems. These systems are less efficient than the water-to-water systems because of the much lower heat transfer coefficient of air. These systems are commonly used in large buildings and sometimes in industrial applications to provide hot or cold water.

The water-to-air heat pumps removes heat from water and converts it to hot air in exactly the same way that a cold water drinking fountain removes the heat from the water and discharges the heat from the side or back of the drinking fountain.

Written by sam

January 30th, 2010 at 6:25 pm

Water to Water Heat Pumps

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In these heat pump systems, the heat source and the heat sink are water. The heat pump system takes heat from a water source (by coil A) while simultaneously rejecting it to a water heat sink (by coil B) and either heats or cools a space or a process. In practice, there are many sources of water, e.g. waste water, single or double well, lake, pool, and cooling tower. These heat pumps use less electricity than other heat pumps when they are properly maintained. However, without proper maintenance the operating costs increase dramatically.

Table 4.5 shows typical COPs for a water-to-water heat pump operating in various heat distribution systems. The temperature of the heat source is 5°C, and the heat pump Carnot efficiency is 50%.

Table 4.5 Example of how the COP of a water-to-water heat pump varies with the distribution/return temperature.

Table 4.5 Example of how the COP of a water-to-water heat pump varies with the distribution/return temperature.

 

Written by sam

January 30th, 2010 at 6:16 pm

Classification of Heat Pumps

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A systematic classification of the different types of heat pumps is difficult because the classification can be made from numerous points of view, e.g. purpose of application, output, type of heat source, type of heat pump process, etc. If the heat is distributed via a mass flow, e.g. warm air or warm water, this mass flow is called the heat carrier.

Customarily, in the USA heat pumps are classified for the heating of buildings according to the type of heat source (first place) and type of heat carrier (second place). A distinction can be made between the terms:

• heat pump, covering only the refrigeration machine aspect, and
• heat pump plant which besides the heat pump itself also contains the heat source.

This differentiation is due to heat from the heat source being transferred to the cold side of the heat pump by an intermediate circuit, the cold carrier.

Another usual classification differentiates between

• primary heat pumps which utilize a natural heat source present in the environment, such as external air, soil, ground water, and surface water,
• secondary heat pumps which reuse waste heat as heat source, i.e. already used heat, such as extract air, waste water, waste heat from rooms to be cooled, and
• tertiary heat pumps which are in series with a primary or secondary heat pump in order to raise the achieved, but still relatively low temperature further, e.g. for hot water preparation.

Furthermore, heat pumps are generally classified by their respective heat sources and sinks. Depending on cooling requirements, various heat source and heat sink arrangements are possible in practical applications. The six basic types of heat pump are as follows:

• water-to-water,
• water-to-air,
• air-to-air,
• air-to-water,
• ground-to-water and
• ground-to-air.

In each of these types the first term represents a heat source for heating or a heat sink for cooling applications. Schematics of the common types of heat pumps are also shown in Figure 4.2.

Figure 4.2 Types of heat pumps (here, the first part refers to the heat source for the outdoor coil during the heating process and the second part indicates the medium treated by the refrigerant in the indoor coil).

Figure 4.2 Types of heat pumps (here, the first part refers to the heat source for the outdoor coil during the heating process and the second part indicates the medium treated by the refrigerant in the indoor coil).

 

Written by sam

January 30th, 2010 at 6:14 pm

Heat Pumps Heat Sources

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To understand the basic principle of the heat pump, one must realize that heat is a form of energy, the quantity of which is quite independent of the temperature which happens to exist at the time. In air, soil and water, in air extracted from buildings, and in waste water of any kind, there are enormous quantities of heat which are useless only because the temperature is too low. From all these sources, heat can be extracted, and with a small expenditure of additional, high-grade energy a heat pump can upgrade the waste heat to a temperature suitable for room heating.

The primary heat sources include air, water and soil. In practice, air is the most common source for heat pumps while water- and soil-source systems are less commonly applicable. In general, air, soil and ground water are considered practicable as heat sources for small heat pump systems while surface water, sea water and geothermal are more suited to larger heat pump systems. As far as low-temperature sources is concerned, ground or surface water, air and soil are most commonly used.

The technical and economic performance of a heat pump is closely related to the characteristics of the heat source. An ideal heat source for heat pumps in buildings has a high and stable temperature during the heating season, is abundantly available, is not corrosive or polluted, has favorable thermophysical properties, and requires low investment and operational costs. In most cases, however, the availability of the heat source is the key factor determining its use. Table 4.4 presents commonly used heat sources. Ambient and exhaust air, soil and ground water are practical heat sources for small heat pump systems, while sea/lake/river water, rock (geothermal) and waste water are used for large heat pump systems.

Several heat pump configurations can be visualized utilizing a seemingly inexhaustible number of energy sources. Some of these energy sources are outside air, sensible heat from stream or well water, latent heat diffusion from water (ice formation), warm discharge effluents from industry, fireplace waste heat, and heat generation in sewage. Most of these energy sources are not widely available to the general public. Four types of heat pump systems are in common use in practice:

• single-package heat pumps using an air source,
• split-system heat pumps using an air source,
• single-package heat pumps using a water source, and
• split-system heat pumps using a water source.

Single-package heat pumps have all the essential components contained within a single unit while split-system heat pumps house the essential components in two separate units (i.e. one unit outdoors and one unit indoors).

Written by sam

January 27th, 2010 at 8:17 pm

Large Heat Pumps for District Heating and Cooling

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Many large electrically driven heat pumps are running all over the world today and even more are ordered and planned for the future. Large heat pumps are defined as equipment with an output of about 500 kW or more. These are particularly used for district heating and cooling applications.

The point has often been made that the heat pump is competitive and is well established in markets where cooling is required, too. These markets are:

• simultaneous production of cold and heat (double utilization) such as in more recent HVAC applications or in the classical commercial cases of skating rink plus swimming pool, or refrigeration plus hot tap water production; and

• consecutive production of cold and heat in HVAC plants with the same equipment, known as the heating/cooling heat pump (air cooling and dehumidifying in the summer season and heating and possibly humidifying during the winter season).

The large heat pump for district heating and cooling use proves to be well-suited:

• for base load coverage in systems without combined heat and power generation (CHP),
• for low load, low temperature summer operation for domestic hot water production,
• where supply and/or return temperatures are low,
• where water is available as a heat source, for instance cleared sewage water, industrial waste water, lake or sea water. (There are also plants with a heat capacity up to 2.5 MW using ambient air as a heat source.)

Written by sam

December 8th, 2009 at 10:22 am

Posted in Refrigerator Heat Pumps

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