Refrigeration/Troubleshooting Manual

Transcription

1 Refrigeration/Troubleshooting Manual P.O. Box 245 Syracuse, NY P/N: Table of Contents: Section 1: Geothermal Refrigeration Circuits Overview... 2 Water-to-Air Refrigerant Circuit... 3 Refrig. Ckt. Component Operation... 3 Water-to-Water Refrigerant Circuit... 5 Heating Operation... 6 Cooling Operation... 6 Summary... 8 Guide Revision Table: Date By Page Note KT All First published Section 2: Heat of Extraction/Heat of Rejection Overview... 9 Performance Data... 9 Formulas Examples Section 3: Superheat/Subcooling Overview Definitions Checking Superheat and Subcooling Putting It All Together Pressure/Temperature Chart R-410A Pressure/Temperature Chart R Superheat/Subcooling Measurements Superheat/Subcooling Tables Examples Section 4: Desuperheater Operation Overview Desuperheater Cut-Away Appendix A: Troubleshooting Form

2 Section 1: Geothermal Refrigeration Circuits Overview Geothermal heat pumps are available in a variety of configurations to provide flexibility for installation in new construction or retrofit applications. Most common in North America are packaged water-to-air heat pumps, which provide forced air heating and cooling. Packaged units (see figure 1) have the compressor section and the air handler section in the same cabinet. There are also other types of geothermal heat pumps, such as water-to-water, which are used for radiant floor heating. exchanger (water-to-water and waterto-air units) is connected to the ground loop or open loop (well water) system. The load heat exchanger is connected to the hydronic load (for example, radiant floor heating) for water-to-water units. The load heat exchanger in a water-to-air unit is the air coil, which is connected to duct work. Water-to-water heat pumps heat or chill water instead of heating or cooling the air (see figure 5). The difference between a water-to-air and water-to-water heat pump is the load heat exchanger. A second water-to-refrigerant coil is substituted for the air to refrigerant coil. The source heat Figure 1: Water-to-Air Refrigeration Circuit Condenser (heating) Evaporator (cooling) 5 To suction line Heating Cooling Optional desuperheater installed in discharge line (always disconnect during troubleshooting) 1 3 Condenser (cooling) Evaporator (heating) 2 Refrigeration/Troubleshooting Guide,

3 Section 1: Geothermal Refrigeration Circuits Water-to-Air Refrigerant Circuit The water-to-air geothermal heat pump refrigerant circuit is very simple compared to air source heat pumps. Defrost cycle is not required, and all components are indoors in a single cabinet. The main components shown in figure 1 are the compressor (1), the air coil (2), the coaxial heat exchanger (3), the reversing valve (4), the or thermal expansion valve (5), and the filter drier (6). Compressor: The compressor (1) is the heart of the system. The compressor pumps refrigerant through the circuit, and increases the pressure of the refrigerant. Since pressure and temperature are directly related, when the pressure is increased, the temperature is also increased. When the temperature of the refrigerant is raised to a higher temperature than the temperature of the air flowing through the air coil (2) in heating, heat is released to the air to heat the building. Likewise, when the refrigerant temperature is raised to a higher temperature than the water flowing through the coaxial heat exchanger (3) in cooling, heat is released to the water. uses Copeland Scroll compressors. A scroll is an involute spiral which, when matched with a mating spiral scroll form as shown in figure 2, generates a series of crescent-shaped gas pockets between the two members. Scroll compressors work by moving one spiral element inside another stationary spiral to create a series of gas pockets that become smaller and increase the pressure of the gas. The largest openings are at the outside of the scroll where the gas enters on the suction side. As these gas pockets are closed off by the moving spiral they move towards the center of the spirals and become smaller and smaller. This increases the pressure on the gas until it reaches the center of the spiral and is discharged through a port near the center of the scroll. Both the suction process (outer portion of the scroll members) and the discharge process (inner portion) are continuous. The moving scroll moves in an orbiting path within the stationary (fixed) scroll as it creates the series of gas pockets. During compression, several pockets are being compressed simultaneously, resulting in Figure 2: Scroll Operation Compression in the scroll is created by the interaction of an orbiting spiral and a stationary spiral. Gas enters the outer openings as one of the spirals orbits. The open passages are sealed off as gas is drawn into the spiral. As the spiral continues to orbit, the gas is compressed into two increasingly smaller pockets. By the time the gas arrives at the center port, discharge pressure has been reached. Actually, during operation, all six gas passages are in various stages of compression at all times, resulting in nearly continuous suction and discharge. Refrigeration/Troubleshooting Guide 3

4 Section 1: Geothermal Refrigeration Circuits a very smooth process. By maintaining an even number (six in a Copeland Scroll compressor) of balanced gas pockets on opposite sides, the compression forces inside the scroll work to balance each other and reduce vibration inside the compressor. Single speed and two-stage (UltraTech) scroll compressors are used in s product line. The two-stage scroll works exactly like the single speed scroll shown in figure 2, but it has additional components, a solenoid valve, and bypass ports in the scroll mechanism. When the solenoid valve opens the bypass ports as shown in figure 3, the capacity is reduced to 67%, since part of the scroll is bypassed. Figure 3: UltraTech Operation 67% - Ports Open 100% Ports Closed : The air coil (2), a refrigerant-to-air heat exchanger servers as the condenser in heating, and the evaporator in cooling. ial Heat Exchanger: The coaxial heat exchanger (3), a water-to-refrigerant heat exchanger, serves as the evaporator in heating, and the condenser in cooling. pump to switch from heating to cooling. The normal (non-energized) mode is heating. Therefore, the discharge gas from the compressor flows to the air coil in the non-energized mode. When the reversing valve solenoid is energized in cooling, the valve switches to allow the discharge gas from the compressor to flow to the coaxial heat exchanger. The reversing valve is a pilot-operated valve, which means that the solenoid opens a small port, connecting the copper tubing from the bottom port (discharge line from the compressor) to the valve chamber. The high pressure of the discharge line forces the valve to switch from one mode to the other. Thermal Expansion (): The (5) meters refrigerant to make sure that the proper amount of refrigerant is being fed to the heat exchangers in order to maximize the condensing and evaporating functions. The is also important in keeping liquid refrigerant from reaching the suction line of the compressor, which could damage the compressor. The is designed to operate bi-directionally in packaged water-to-air and water-to-water heat pumps. Figure 4: Operation Diaphram : The reversing valve (4) provides the ability to switch functions of the two heat exchangers, above. As shown in figure 1, the discharge line from the compressor is always connected to the bottom of the reversing valve. The center connection at the top is always connected to the suction line from the compressor. The other two connections allow the heat Seat Pin 4 4 = Liquid Pressure (opening force) 4 Refrigeration/Troubleshooting Guide,

5 Section 1: Geothermal Refrigeration Circuits Figure 4 shows the operation of the, and the four forces that affect the operation. The has two copper fittings for connection to the air coil and coaxial heat exchanger, as well as two smaller copper lines that are used for metering. One line is connected to a bulb that is attached to the suction line of the compressor. The bulb is filled with refrigerant. As the suction line temperature changes, the bulb pressure changes. The other line is connected directly to the suction line. The bulb pressure (force 1) pushes down on the diaphragm as the bulb pressure increases (suction line temperature increases). When the pressure pushes down on the diaphragm, the pin (which is attached to the diaphragm) is pushed away from the valve seat, which opens the valve. The other line, connected directly to the suction line uses suction pressure (force 2) to push up on the diaphragm as the pressure increases. As the diaphragm is pushed up, the pin is pushed into the valve seat, closing the valve. This relationship of temperature (bulb pressure) and pressure (suction line) creates a balancing effect, which causes the valve to meter at 0 superheat (see section 3 for explanation of superheat). Since it is important to make sure that liquid is not returning to the compressor, the valve spring (force 3) is adjusted to fool the valve into balancing at a higher superheat (usually 10 to 12). Force 4 (liquid pressure) is an opening force. : The filter drier (6) functions exactly as its name implies. It filters any particles from the refrigerant system, and it pulls moisture from the system. It is extremely important that the filter drier is changed any time the refrigerant circuit is open for a component replacement or repair, especially for systems with R-410A refrigerant. R-410A uses P.O.E. oil, which is hygroscopic (tendency of a material to absorb moisture from the air). Moisture contaminates the refrigerant circuit over time, and must be avoided. Figure 5: Water-to-Water Refrigerant Circuit Condenser (heating) Evaporator (cooling) To suction line Load Heating Load Load Cooling Optional desuperheater installed in discharge line (always disconnect during troubleshooting) Condenser (cooling) Evaporator (heating) Refrigeration/Troubleshooting Guide 5

6 Section 1: Geothermal Refrigeration Circuits Water-to-Water Refrigerant Circuit The water-to-water heat pump refrigerant circuit, as shown in figure 5, functions exactly the same as the the water-to-air refrigerant circuit with one exception. The air coil is replaced by a second coaxial heat exchanger. The source coax is the same as the water-to-air unit coax. However, the load coax heats or chills water instead of heating or cooling the air. Heating Operation For the purposes of discussing the refrigerant circuit operation in heating and cooling modes, the water-to-air circuit will be used. The other configurations directly apply with minor terminology/component changes. In heating mode (see figure 7), the reversing valve is not energized. The high temperature, high pressure refrigerant gas from the compressor flows to the air coil. As the air moves through the air coil, the cool (typically 70) air causes the hot refrigerant (typically 130 to 180) to condense into a liquid. Thus, the air coil is the condenser in the heating mode. After leaving the air coil (condenser), the refrigerant is approximately the temperature of the leaving air. The refrigerant is within a few of being at the same pressure as it was at the compressor discharge line. This is the heating liquid line. The liquid line of a packaged unit changes location, depending upon the mode of operation. It is always located between the and the condenser. However, since a geothermal unit is a heat pump, the condenser can either be the air coil (heating) or coaxial water coil (cooling). At the, the refrigerant is forced through a very small opening, which causes a large pressure drop. As mentioned earlier, pressure and temperature are directly related, so the temperature also drops after the. At this point, the refrigerant is a low temperature liquid (typically 15 to 50, depending upon loop temperature). The warm water (or water/antifreeze solution) flowing through the coaxial heat exchanger (typically 30 to 60) causes the cold refrigerant to boil off (evaporate) into a gas or vapor. Thus, the coax is the evaporator in heating. After leaving the coax (evaporator), the refrigerant is now approximately the same temperature as the water entering the heat pump. This low pressure gas enters the compressor, and the cycle starts all over again. Proper refrigerant metering will insure that no liquid is returned to the compressor. Section 3 discusses superheat and subcooling, which allow the technician to evaluate how well the condenser and evaporator are operating. Cooling Operation In cooling mode (see figure 8), the reversing valve must be energized. The high temperature, high pressure refrigerant gas from the compressor flows to the coaxial heat exchanger. As the water (or water/ antifreeze solution) flows through the coax, the cool (typically 50 to 100) water causes the hot refrigerant (typically 130 to 180) to condense into a liquid. Thus, the coax is the condenser in the cooling mode. After leaving the coax (condenser), the refrigerant is approximately the temperature of the water leaving the coax. The refrigerant is within a few of the compressor discharge line pressure. This is the cooling liquid line. The liquid line of a packaged unit changes location, 6 Refrigeration/Troubleshooting Guide,

7 Section 1: Geothermal Refrigeration Circuits Figure 7: Heating Condenser (heating) Evaporator (cooling) To suction line Optional desuperheater installed in discharge line (always disconnect during troubleshooting) Condenser (cooling) Evaporator (heating) Figure 8: Cooling Condenser (heating) Evaporator (cooling) To suction line Optional desuperheater installed in discharge line (always disconnect during troubleshooting) Condenser (cooling) Evaporator (heating) Refrigeration/Troubleshooting Guide 7

8 Section 1: Geothermal Refrigeration Circuits depending upon the mode of operation. It is always located between the and the condenser. However, since a geothermal unit is a heat pump, the condenser can either be the air coil (heating) or coaxial water coil (cooling). condenser in cooling and the evaporator in heating. Water-to-water units use a second coax instead of the air coil. The reversing valve is energized in the cooling mode. The non-energized mode is heating. At the, the refrigerant is forced through a very small opening, which causes a large pressure drop. Once again, since pressure and temperature are directly related, the temperature also drops after the. At this point, the refrigerant is a low temperature liquid (typically 35 to 45, depending upon return air temperature and air flow). The warm air flowing through the air coil (typically 70 to 80) causes the cold refrigerant to boil off (evaporate) into a gas or vapor. Thus, the air coil is the evaporator in cooling. After leaving the air coil (evaporator), the refrigerant is now approximately the same temperature as the air entering the heat pump. This low pressure gas enters the compressor, and the cycle starts all over again. Summary To summarize, refrigerant circuits in geothermal heat pumps can be configured for packaged water-to-air, water-to-water, split systems or combination water-to-air and water-to-water units. All circuits utilize a Copeland scroll (single or two-stage) compressor, one or two water-to-refrigerant coaxial coils, an air-to-refrigerant coil, a reversing valve, a bi-directional, and a filter drier. Combination units include a direction valve and a 3-way valve to switch condenser operation. The air coil operates as the condenser in heating, and the evaporator in cooling. The source (loop) coax operates as the 8 Refrigeration/Troubleshooting Guide,

9 Section 2: Heat of Extraction/Heat of Rejection Overview As mentioned in section 1, most geothermal heat pumps are packaged water-to-air heat pumps. Therefore, the refrigerant circuit is evacuated and charged at the factory, and there is no need to connect refrigerant gauges unless the technician has verified that there is a refrigerant circuit problem. Since connecting gauges can cause a loss of charge and affect performance, recommends against connecting refrigerant gauges at startup. There are a number of checks that can be made at startup to verify performance without connecting refrigerant gauges. Heat of extraction is a calculation of the amount of heat that is being extracted or absorbed from the water or water/antifreeze solution by the evaporator (coaxial heat exchanger) in the heating mode. Heat of rejection is the amount of heat that is being rejected to the water by the condenser (coaxial heat exchanger) in the cooling mode. In addition to measuring the temperature rise or drop across the air coil, calculating heat of extraction or heat of rejection allows the technician to verify that the heat pump is performing according to specifications. If the calculation shows that the heat pump is performing poorly, then refrigeration gauges may be required to further troubleshoot the problem. Performance Data Before discussing heat of extraction (HE) / heat of rejection (HR) calculations, the technician should understand how to use the performance data in the catalog to compare the unit specifications to actual calculations. Figures 9 and 10 show performance data for a typical 3 ton geothermal water-toair heat pump. the highlighted columns indicate HE and HR. In figure 9, HE is the amount of heat that is being extracted from the water (for example, ground loop) by the refrigerant circuit. The compressor and fan power (kw column) is used to operate the refrigerant circuit. The heat delivered to the space (HC column) equals the HE from the water plus the waste heat of the power used for compressor and fan. If the kw is converted to Btuh, and added to the HE, the sum should equal HC. For example, in figure 9, at 30 EWT, 9.0 and 70 EAT, the heating capacity is 30,700 Btuh. HE is 21,800 Btuh. If the kw (2.63) is converted to Btuh (2.63 x = 8.97 MBtuh or 8,970 Btuh), and added to HE, the result is HC. Therefore, if HE is within, 10-15% of catalog performance, HC should also be within specifications. There is no need to connect refrigerant gauges if HE is within specifications. In figure 10, HR is the amount of heat that is being rejected to the water (for example, ground loop) by the refrigerant circuit. The compressor and fan power (kw column) is used to operate the refrigerant circuit. The heat rejected from the space (HR column) equals the heat from the air (TC column -- amount of cooling) plus the waste heat of the power used for compressor and fan. If the kw is converted to Btuh, and added to the TC, the sum should equal HR. For example, in figure 10, at 90 EWT, 9.0 and 75 DB/63 WB (50% RH), HR is 43,400 Btuh. TC is 34,400 Btuh. If the kw (2.73) is converted to Btuh (2.73 x = 9.31 MBtuh or 9310 Btuh), and added to TC, the result is HR. Thefore, if HR is within, 10-15% of catalog performance, TC should also be within specifications. There is no need to connect refrigerant gauges if HR is within specifications. Refrigeration/Troubleshooting Guide 9

10 Formulas The formula is the same for HE and HR. The amount of heat being extracted or rejected can be calculated if the temperature difference between water entering and leaving the coaxial heat exchanger (TD) is known, and the water flow () is measured. The only other item needed is the type of antifreeze. A fluid factor is used to represent the specific heat of the water/antifreeze solution, as well as to convert the units ( and ) to Btuh. HE or HR (Btuh) = x TD x Fluid Factor Where: = Flow rate in U.S. gallons per minute TD = Temp. diff. (between water in & out) Fluid Factor = 500 for water; 485 for most antifreezes Figures 11 and 12 show the tools required for checking HE and HR. All technicians installing and servicing geothermal heat pumps should have at least one set of these tools. Flow rate can be determined by measuring the pressure drop across the coaxial heat exchanger. The pressure gauge and adapter should be inserted into the P/T (pressure/ temperature) port of the Water IN connection. Record the reading. Next, insert the gauge into the Water OUT port, and record the reading. The difference between the IN and OUT is the pressure drop. Once the pressure drop of the heat exchanger is known, the flow rate can be determined by consulting the performance data for the particular unit. Example: In heating mode, model 036 has EWT of 50, water pressure IN of 40, and water pressure OUT of 35. The pressure drop, therefore is 5. Figure 10 shows three water pressure drop values and three water flow rates. At 50, if the pressure drop is 1.7, the flow rate would be 5.0 ; if the pressure drop is 3.1, the flow rate would be 7.0 ; and if the pressure drop is 5.0, the flow rate would be 9.0. The flow rate in this example is 9.0. Rarely are the temperature and pressure drop exactly as shown in the tables, so there will be some interpolation required (for example, 52 EWT and 4.7 pressure drop). NOTE: A large gauge face is preferred, since it will be easier to read pressures to the nearest 0.5. ALWAYS use the same gauge in the IN and OUT connections. The use of two gauges could cause false readings, since they could both be out of calibration in opposite directions. Never force the gauge adapter into the P/T port. The gauge adapter could break off in the P/T port, or the force could cause the ring holding the P/T port bladder to become dislodged, potentially ending up in a pump impeller. Once the flow rate is determined, the pocket thermometer can be used to obtain TD. Insert the thermometer into the Water IN P/T port. Record the temperature. Insert the thermometer into the Water OUT port, and record the temperature. The difference between the IN and OUT is the TD. In heating, EWT (entering water temperature) will be warmer than LWT (leaving water temperature); in cooling it will be just the opposite. The last item needed is the type of fluid circulating through the heat pump. As mentioned earlier, 500 should be used for pure water (open loop/well water systems). Use 485 for most antifreeze solutions (see Flow Center and Loop Application Manual for details on antifreeze solutions). 10 Refrigeration/Troubleshooting Guide,

11 Section 2: Heat of Extraction/Heat of Rejection Figure 9: Typical Performance Data - Heating 036 Performance Data: 3.0 Ton, 1200 CFM, Heating EWT Entering Water Temp () Flow Rate (U.S. ) Water Press. Drop (PSI & Ft. of Head) Entering Air Temp () Heating Capacity (MBtuh) Heat of Extraction (MBtuh) Leaving Air Temp () Input Power (kw) Coefficient of Performance Desuperheater Capacity (MBtuh) WPD Heating Heating with Desuperheater PSI FT EAT HC HE LAT KW COP HC HE LAT KW DH COP Figure 10: Typical Performance Data - Cooling Total Cooling, (MBtuh) = SC + LC (Latent Cap) Sensible Cooling (MBtuh) 036 Performance Data: 3.0 Ton, 1200 CFM, Cooling Heat of Rejection (MBtuh) Input Power (kw) Energy Efficiency Ratio EWT WPD EAT Cooling Cooling with Desuperheater DB/ PSI FT WB TC SC HR KW EER TC SC HR KW DH EER 75/ / / / / / / / / / / / / / / / / / Refrigeration/Troubleshooting Guide 11

12 Section 2: Heat of Extraction/Heat of Rejection Figure 13 includes an example water-to-air performing better than specifications. heat pump in heating mode; figure 14 shows the same heat pump in cooling. Following Example 2: l 036, ground loop system are two examples based upon these figures, with ProCool (ethanol) antifreeze solution, which are shown on the next page. cooling mode. Example 1: l 036, ground loop system with ProCool (ethanol) antifreeze solution, heating mode. 1) Fluid factor = 485 2) EWT = 30.0 LWT = 23.5 TD = 6.5 3) Pressure IN = 40 Pressure OUT = 36.6 Pressure drop = 3.4 From performance data, = 7.0 4) HE = x TD x Fluid Factor HE = 7.0 x 6.5 x 485 = 22,067 Btuh Catalog HE = 21,300 Btuh. Therefore, unit is 1) Fluid factor = 485 2) EWT = 90.0 LWT = TD = ) Pressure IN = 40 Pressure OUT = 36.3 Pressure drop = 3.7 From performance data, = 8.0 4) HR = x TD x Fluid Factor HR = 8.0 x 11.2 x 485 = 43,456 Btuh Catalog HR = 43,400 Btuh. Therefore, unit is performing better than specifications. NOTE: HE and HR should be within 10-15% of catalog values. Figure 11: Pressure Gauge with Adapter Gauge Adapter (P/N TSPTN) Adapter Protector Pressure Gauge (P/N TSPG-GC or equivalent) Figure 12: Pocket Thermometer Pocket Thermometer P/N TSDT or equivalent 12 Refrigeration/Troubleshooting Guide,

13 Section 2: Heat of Extraction/Heat of Rejection Figure 13: Heating Operation Example Load IN To suction line Load For water-to-water units substitute a second coaxial heat exchanger for the air coil. Load OUT Return Air Heating Supply Air Cooling Optional desuperheater installed in discharge line (always disconnect during troubleshooting) Line (saturation) temp Line (saturation) (loop) IN Figure 14: Cooling Operation Example (loop) OUT Load IN To suction line Load For water-to-water units substitute a second coaxial heat exchanger for the air coil. Load OUT Return Air Heating Supply Air Cooling Optional desuperheater installed in discharge line (always disconnect during troubleshooting) Line (saturation) temp Line (saturation) (loop) IN (loop) OUT Refrigeration/Troubleshooting Guide 13

14 Section 3: Superheat/Subcooling Overview Superheat and subcooling are used to determine if the heat pump has the proper refrigerant charge, as well as for verifying that the condenser and evaporator are performing properly. Superheat and subcooling can even be used to troubleshoot refrigerant circuit blockages or a bad. Definitions Saturation Temperature: Saturation temperature, sometimes called boiling point, is the temperature at which a refrigerant changes state. For example, Table 1 shows that refrigerant R-410A has a saturation temperature of 32 at 100. Therefore, the refrigerant at 100 is a liquid if it is below 32, and a gas (vapor) if it is above 32. Superheat: Superheat is defined as the number of degrees above the saturation temperature of a refrigerant. For example, if the temperature of refrigerant R-410A is 40 at 100, it has 8 of superheat, since the saturation temperature is 32. Subcooling: Subcooling is defined as the number of degrees below the saturation temperature of a refrigerant. For example, if the temperature of refrigerant R-410A is 28 at 100, it has 4 of subcooling, since the saturation temperature is 32. Checking Superheat and Subcooling Superheat and subcooling should only be checked after the heat of extraction or heat of rejection calculations (see section 2) indicate that the unit is performing poorly. Connecting refrigerant gauges should be done as a last resort. Checking superheat and subcooling requires a refrigeration gauge set with manifold and hoses, plus a digital thermocouple type thermometer. Heat pumps produced by have two schrader ports for service connections, one at the discharge line of the compressor, and one at the suction line of the compressor. When these pressures are used in conjunction with the suction line temperature and liquid line temperature, superheat and subcooling can be calculated. Insulation should be removed from the suction line and liquid line, and the copper should be free from insulation glue, so that the thermocouple makes a good connection at the copper line. Figures 15a and 15b illustrate the locations for taking pressure and temperature measurements. Notice that the two areas for temperature measurement are suction line and liquid line. In order to check superheat and subcooling, the saturation temperature must be determined, which requires the pressure of the refrigerant and the actual temperature of the refrigerant at the same location. However, the only location where both temperature and pressure are easily obtained is at the suction line. In section 1, temperatures and pressures were discussed in relation to components, both before and after the components. It was also mentioned that the discharge pressure and the liquid line pressure are within a few of each other. Most manufacturers of packaged equipment adjust their service data to allow the technician to use the discharge pressure as the liquid line pressure. Therefore, for checking superheat and subcooling, use discharge pressure with liquid line temperature, and suction pressure with suction temperature. Although superheat and subcooling can be calculated anywhere in the refrigeration 14 Refrigeration/Troubleshooting Guide,

15 Section 3: Superheat/Subcooling circuit, there are two points that are most useful for troubleshooting purposes. First of all, it is imperative that liquid is not returned to the compressor. Liquid refrigerant will wash some of the compressor oil away from critical internal parts, causing premature compressor failure. Plus, the compressor is designed to pump gas, not liquid, and will be operating under adverse conditions. Checking for superheat at the suction line of the compressor insures that the state of the refrigerant at this point is a gas (vapor). The amount of superheat at the suction line determines how well the evaporator (coax in heating, air coil in cooling) is working. Superheat is normally in the 8 to 12 range, but the installation manual will provide specific information for the unit being serviced. NOTE: Check the temperature of the suction line near the bulb, especially on split systems. is overcharged. If subcooling is measured, the high value would indicate that there is a problem with the refrigeration charge. Table 3 lists the conditions associated with high or low superheat and subcooling. Table 4 is an example of typical data found in the installation manual. Figures 16 through 18 illustrate examples of a normally charged system, an undercharged system, and an overcharged system. The other location to check is the liquid line. Since the liquid line is located after the condenser (air coil in heating, coax in heating), the amount of subcooling determines how well the condenser is working. In most cases subcooling is in the 4 to 10 range, but the installation manual will provide specific information for the unit being serviced. Putting It All Together In section 1, operation was discussed. Since the spring has been adjusted to maintain 8 to 12 of superheat, it will close down when necessary to maintain the predetermined superheat setting. Therefore, subcooling plays a crucial part in evaluating the unit s refrigeration charge. In other words, if the unit is overcharged, the will close down to maintain superheat, backing up liquid refrigerant in the condenser. If only superheat is measured, the technician would not know that the unit Refrigeration/Troubleshooting Guide 15

16 Section 3: Superheat/Subcooling Table 1: Pressure/Temperature Chart, R-410A Refrigerant Saturation Saturation Saturation Pressure Temp () Pressure Temp () Pressure Temp () PSIG R-410A PSIG R-410A PSIG R-410A Refrigeration/Troubleshooting Guide,

17 Section 3: Superheat/Subcooling Table 2: Pressure/Temperature Chart, R-22 Refrigerant Saturation Saturation Saturation Pressure Temp () Pressure Temp () Pressure Temp () PSIG R-22 PSIG R-22 PSIG R Refrigeration/Troubleshooting Guide 17

18 Section 3: Superheat/Subcooling Figure 15a: Superheat/Subcooling Measurement - Heating Load IN Load 1 To suction line 2 R-410A Manifold/Gauge Set For water-to-water units substitute a second coaxial heat exchanger for the air coil. Load OUT Return Air Supply Air Optional desuperheater installed in discharge line (always disconnect during troubleshooting) Line (saturation) temp Line (saturation) (loop) IN Thermometer 1 2 (loop) OUT Figure 15b: Superheat/Subcooling Measurement - Cooling Load IN To suction line 1 R-410A Manifold/Gauge Set Load 2 For water-to-water units substitute a second coaxial heat exchanger for the air coil. Load OUT Return Air Supply Air Optional desuperheater installed in discharge line (always disconnect during troubleshooting) Line (saturation) temp Line (saturation) (loop) IN Thermometer 1 2 (loop) OUT 18 Refrigeration/Troubleshooting Guide,

19 Section 3: Superheat/Subcooling Table 3: Superheat/Subcooling Conditions Superheat Subcooling Condition Normal Normal Normal operation Normal High Overcharged High Low Undercharged High High Restriction or is stuck almost closed Low Low is stuck open Table 4: Typical R-410A Unit Superheat/Subcooling Values EWT Per Ton Pressure (PSIG) Pressure (PSIG) Heating - Without Desuperheater Super Heat Sub Cooling Air Temperature Rise (-DB) Water Temperature Drop () EWT Per Ton Pressure (PSIG) Pressure (PSIG) Cooling - Without Desuperheater Super Heat Sub Cooling Air Temperature Drop (-DB) Water Temperature Rise () Refrigeration/Troubleshooting Guide 19

20 Section 3: Superheat/Subcooling Figure 16: Normally-Charged System, Heating Load IN 90.0 Load For water-to-water units substitute a second coaxial heat exchanger for the air coil. Load OUT 70.0 Return Air Heating Supply Air Cooling To suction line Optional desuperheater installed in discharge line (always disconnect during troubleshooting) Line (saturation) 29 temp 300 Line (saturation) Superheat = = 10 Subcooling = = (loop) IN (loop) OUT Figure 17: Under-Charged System, Heating Load IN 87.0 Load For water-to-water units substitute a second coaxial heat exchanger for the air coil. Load OUT Return Air Heating Supply Air Cooling To suction line Optional desuperheater installed in discharge line (always disconnect during troubleshooting) Line (saturation) 29 temp Line (saturation) Superheat = = 15 Subcooling = = (loop) IN (loop) OUT 20 Refrigeration/Troubleshooting Guide,

21 Section 3: Superheat/Subcooling Figure 18: Over-Charged System, Heating Load IN 85.0 Load For water-to-water units substitute a second coaxial heat exchanger for the air coil. Load OUT Return Air Heating Supply Air Cooling To suction line Optional desuperheater installed in discharge line (always disconnect during troubleshooting) Line (saturation) 34 temp Line (saturation) Superheat = = 10 Subcooling = = (loop) IN (loop) OUT Figure 19: Water-to-Air Refrigerant Circuit with Desuperheater Load IN To suction line Load For water-to-water units substitute a second coaxial heat exchanger for the air coil. Load OUT Return Air Supply Air Line (saturation) temp Line (saturation) (loop) IN Heating Cooling Desuperheater (loop) OUT Refrigeration/Troubleshooting Guide 21

22 Section 4: Desuperheater Operation The desuperheater option includes a waterto-refrigerant coaxial heat exchanger installed between the compressor discharge line and reversing valve, which is connected to the condenser (air coil in heating, coax in cooling) as shown in figure 19. Unlike the source coax in all geothermal heat pumps, the desuperheater coax is a doublewall, vented water-to-refrigeration heat exchanger. Figure 20 illustrates a cut-away of the desuperheater coax. The operation of the desuperheater takes advantage of the superheat at the discharge line. For example, in figure 16, the discharge pressure is 300. The saturation temperature at 300 is 96. The discharge line at these conditions would typically be around 160. Therefore, the superheat (actual temperature saturation temperature) is 64. As domestic hot water flows through the desuperheater heat exchanger, some of the superheat at the discharge line is used to heat domestic water, which lowers the superheat at the discharge line, thus the term desuperheater. Water flow rate through the desuperheater coax must be very low to avoid turning the desuperheater into a condensor, and robbing too much heat from the main condenser. Typically, about 0.4 per ton is used for desuperheater flow rate. The desuperheater pump operates anytime the compressor is operating (unless the one of the temperature limits is open). In heating, the desuperheater takes some of the heat that would have been used to heat the space via the condenser (air coil), and uses it to make domestic hot water. Even though the desuperheater is robbing some of the heat from the space, it is a very small amount, and the system is heating water at a very high C.O.P. (3.0 to 4.0, depending upon loop temperature), compared to an electric water heater at a C.O.P. of 1.0. Some geothermal heat pumps turn off the desuperheater pump when back up heat is energized. However, studies show that on an annual basis, the system is more energy efficient when the desuperheater is utilized any time the compressor is running. When the hot water tank is already heated, a thermal switch turns off the desuperheater pump. The pump may also be turned off if the compressor discharge line is too cool. Figure 20: Desuperheater coax cut-away Smooth Wall Inner Tube Rifled Copper Tube Steel Outer Wall Refrigerant Air Gap Water In cooling, the desuperheater takes some of the heat that would have been rejected to the ground loop via the condenser (coax), and uses it to make domestic hot water. Therefore, the desuperheater produces nearly free hot water (other than the fractional horsepower circulating pump) in the cooling mode. 22 Refrigeration/Troubleshooting Guide,

23 Troubleshooting Form Please make copies of this form. Customer/Job Name: Date: l #: Serial #: Antifreeze Type: Diagram: Water-to-Air and Water-to-Water Units Load IN Load For water-to-water units substitute a second coaxial heat exchanger for the air coil. Load OUT Return Air Heating Supply Air Cooling To suction line Optional desuperheater installed in discharge line (always disconnect during troubleshooting) Line (saturation) temp Line (saturation) (loop) IN Note: DO NOT connect refrigerant gauges until Heat of Extraction or Rejection has been checked. Note: Disconnect desuperheater before proceeding (loop) OUT HE or HR = x TD x Fluid Factor (Use 500 for water; 485 for antifreeze) SH = Temp. - Sat. SC = Disch. Sat. - Liq. Line Temp. Refrigeration/Troubleshooting Guide 23

24 P.O. Box 245 Syracuse, NY US CAN FAX * ** *** * AHRI certification is shown as the brand under the Enertech Manufacturing certification reference number ** Industries geothermal heat pumps are shown as a multiple listing of Enertech Manufacturing s ETL certification *** geothermal heat pumps are listed as a brand under Enertech Manufacturing s Energy Star ratings