Refrigerator Troubleshooting Diagram

Archive for the ‘Air Conditioning’ Category

Heat Pump Usage

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In the last fifty years, several large office buildings and small college campuses have been constructed using water-to-water heat pumps. Their capacities were up to several hundred tons. These systems usually use well water. That means two wells are used. One is used for supply and one for disposal. A possible arrangement is shown in Fig. 17-23.

The supply and disposal wells are manually selected. Well water and return water are mixed, for both evaporator and condenser. This is done on a temperature basis. Under some conditions, this system can become an internal source heat pump. That is, when the exterior-zone heating and interior-zone cooling loads are in balance, or nearly so, little or no well water is needed.

Internal source heat pumps without wells are used where there is sufficient internal cooling load to supply the net heating requirements under all conditions. Excess heat can be disposed of through cooling towers.

A problem with these systems is related to a high electrical load for the pumping system. A variety of variable-flow piping schemes have been devised to overcome this problem.

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February 7th, 2011 at 1:54 pm

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Special Requirements of Heat Pump Systems

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The installation, maintenance, and operating efficiency of the heat pump system are like those of no other comfort system. A heat pump system requires the same air quantity for heating and cooling. Because of this, the air moving capability of an existing furnace is extremely important. It should be carefully checked before a heat pump is added. Heating and load calculations must be accurate. System design and installation must be precise.

The air-distribution system and diffuser location are equally important. Supply ducts must be properly sized and insulated. Adequate return air is also a must.

Heating supply air is cooler than with other systems. This is quite noticeable to homeowners accustomed to gas or oil heat. This makes diffuser location and system balancing critical. Typical installations of heat pumps are shown in Fig. 17-22.

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February 7th, 2011 at 1:51 pm

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Heat Pump Outdoor Thermostat

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In a straight heat pump or supplementary electric heater application, at least one outdoor thermostat is required to cycle the heaters as the outdoor temperature drops. In the Fuelmaster system, the indoor thermostat controls the supplemental heat source (furnace). The outdoor thermostat is not required. Since the furnace is serving as the secondary heat source, the Fuelmaster system does not require the home rewiring usually associated with supplemental electric strip heating.

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February 7th, 2011 at 1:49 pm

Heat Pump Defrost

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During a defrost cycle, the heat pump switches from heating to cooling. To prevent cool air from being circulated when heating is needed, the control automatically turns on the furnace to compensate for the heat pump defrost cycle. (Most modern heat pump systems do the same thing with strip heating.) When supply air temperature climbs above 110 to 120°F (43.3 to 48.9°C), the defrost limit control turns off the furnace and keeps indoor air from getting too warm.

After a defrost cycle, the air temperature downstream of the coil may go above the 115°F (46.1°C) closing point of the heat pump delay. Then, the compressor will stop until the heat exchanger has cooled to 90 to 100°F (32.2 to 37.8°C), as it does during normal cycling operation between furnace and heat pump.

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February 7th, 2011 at 1:48 pm

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Heat Pump Operation

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On mild temperature heating days, the heat pump handles all heating needs. When the outdoor temperature reaches the “balance point” of the home (heat loss equals heat pump heating capacity), the two-stage indoor thermostat activates the furnace (secondary heat source). When the furnace fires, a heat relay deenergizes the heat pump.

When the second stage (furnace) need is satisfied and plenum temperature has cooled to 90 to 100°F (32.2 to 37.8°C), the heat pump delay turns the heat pump back on. It controls the conditioned space until the second stage (full heat) operation is required again.

When outdoor temperature drops below the setting of the low-temperature compressor monitor (field installed option) the control shuts out the heat pump. The furnace handles all of the heating need. The low temperature compressor monitor is standard on models dated 1974 and after.

During the cooling season the heat pump operates in its normal cooling mode. It uses the furnace blower as the primary air mover. See Fig. 17-21.

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February 7th, 2011 at 1:47 pm

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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.

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February 7th, 2011 at 1:44 pm

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Absorption Operation Cycle

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Figure 17-8 is a schematic diagram of an absorption cold generator. Note that the evaporator, absorber, concentrator, and condenser are enclosed in a single casing. The heat exchanger is located externally below the main shell.

• Evaporator. The evaporator pump circulates the refrigerant (water) from the refrigerant pump into the spray trees. To utilize the maximum surface for evaporation, the refrigerant is sprayed over the evaporator tubes. As the spray contacts the relatively warm surface of the tubes carrying the water to be chilled, a vapor is created. In this manner heat is extracted from the tube surface, chilling the fluid in the tubes. The vapor created in this process passes through eliminators to the absorber.

• Absorber. The lithium-bromide solution (under proper conditions) keeps the pressure in the absorber section low enough to pull the refrigerant vapor from the high-pressure evaporator. As the vapor flows into the absorber, it mixes with the absorbent solution being sprayed over the tube bundle.

• Heat exchanger. The heat exchanger is used only asan economizer. The cool diluted solution from theconcentrator pump is heated by the hotter concentratedsolution moving from the concentrator to theabsorber steam or hot water (heating medium) is conserved. The heat transfer in the heat exchanger brings the temperature of the diluted solution closer to the boiling point. It also brings the concentrated solution temperature closer to the absorber temperature.

• Concentrator. Steam or high-temperature water entering the concentrator is controlled to boil off the same quantity of refrigerant picked up by the absorber. The refrigerant vapor is given up by boiling the solution in the concentrator. The vapor passes through eliminators to the tube surface of the condenser.

• Condenser. The refrigerant vapor from the concentrator is condensed on the tube surface of the condenser and falls into the pan below the tube bundle.

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February 7th, 2011 at 8:47 am

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Changeover Sequence for Hot Water Operation

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When the thermostat is set for heating, the chilled water pump is off. The pressure from the hot water pump moves the check ball to seal off the water in the chiller tank. See Fig. 17-5. Now the water in the chiller system is dormant. The hot water pump circulates the water from the hot water generator through the air handler and back to the generator through the water reservoir. During the heating cycle the reservoir also serves as a place to relieve air from the system. The tube from the top of the reservoir passes through the chiller tank and runs up to the distribution pan, which is open to atmospheric pressure.

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February 7th, 2011 at 8:44 am

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Changeover Sequence for Chilled Water Operation

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When the thermostat calls for cooling, the hot water pump is off. The chilled water pump moves water from the chiller tank and pumps it up a “candy cane” shaped loop and out to the air handler. See Fig. 17-4. As the water returns to the chiller tank to be cooled again, it passes through the water reservoir.

The water does not flow through the tubes of the hot water generator as it returns to the chiller tank. The water in the generator is dormant because it is plugged by a check ball. This is held in place by the pressure from the discharge side of the chilled water pump.

Written by sam

February 7th, 2011 at 8:41 am

Chiller Heater

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Some gas-fired units furnish cooling for the summer and heat for the winter. The user changes the functions simply by changing the settings of a room thermostat. The “all-year” units are designed for outdoor installation. They operate on either natural or propane gas.

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February 7th, 2011 at 8:39 am

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