Heat Pump Connections and Interior Piping

Transcription

1 Job Sheet 3 Heat Pump Connections and Interior Piping OBJECTIVES In this job sheet, you will observe how the presence of air in the ground loop affects the geothermal heat pump performance. You will also characterize the pressure drop as a function of the flow rate in the heat exchanger of the geothermal heat pump, and observe the effect of the expansion tank in a pressurized system. PROCEDURE In the following steps, the system will be configured as a pressurized system without an expansion tank. The system will not be flushed or pressurized. On startup, you will observe air circulating in the loops. The presence of air in the loops reduces the liquid mass flow in the loops. If the amount of energy that needs to be transferred to the ground remains constant during the experiment, and remembering that this energy is equal to you will observe a difference in the loop temperature differential ( ) when this value is compared to the value obtained in a system without the presence of air. 1. Make sure that the main power switch is set to Off. Open the priming tank cap. Set the priming tank three-way valves as shown in this diagram. Wait for five minutes before proceeding with the next step. Festo Didactic

2 2. Perform the following settings on your training system: Main power switch... Off Thermostat... Cooling mode Temperature set point... 5 C (9 F) below room temperature Valve HV-1... Closed Valve HV-2... Open Valve HV-3... Open Valve HV-4... Open Valve HV-5... Closed Valve HV-6... Open Valve HV-7... Open Valve HV-8... Closed Valve HV-9... No adjustments required Valve HV Handle in horizontal position Valve HV Open Valve HV Open Valve HV Open Pressure gauge PI-1 selector switch... Right Pressure gauge PI-2 selector switch... Right Desuperheater On/Off switch... Off Priming tank three-way valves... Pumping station three-way valves... Priming tank cap... Closed Air distribution register... Open 3. Set the main power switch to On. a The position of the lower three-way valve on the priming tank has been chosen to avoid priming problems during this experiment. Normally, it should be set as the upper three-way valve. If there is too much air in the system, the circulating pump may stop pumping fluid and will need to be primed. Switching to a nonpressurized system configuration with a priming tank will solve the problem. 4. Take temperature measurements at start-up of the system and every five minutes once the compressor has started. Complete Table 11. Table 11. Temperature measurements with air in the system. Time At start up After 5 min After 10 min 72 Festo Didactic

3 5. Set the thermostat operating mode to Off. 6. Position the priming tank three-way valves as shown in this diagram. This will configure the system as a non-pressurized system with a priming tank. 7. Set the thermostat operating mode to cooling. Once the compressor has started, take temperature measurements every five minutes. Complete Table 12. Table 12. Temperature measurements without air in the system. Time After 5 min After 10 min 8. Set the thermostat operating mode to Off. 9. Using your results from Table 11 and Table 12, how was the ground loop temperature differential influenced by the presence of air? Festo Didactic

4 Pressure drop as a function of the flow rate In the next steps, you will observe the relationship between the ground loop heat carrier flow rate and the pressure drop across the geothermal heat pump heat exchanger. 10. Perform the following settings on your training system: Main power switch... Off Thermostat... Heating mode Temperature set point... 5 C (9 F) above room temperature Valve HV-1... Open Valve HV-2... Open Valve HV-3... Open Valve HV-4... Open Valve HV-5... Open Valve HV-6... Open Valve HV-7... Open Valve HV-8... Closed Valve HV-9... No adjustments required Valve HV Handle in horizontal position Valve HV Open Valve HV Open Valve HV Open Pressure gauge PI-1 selector switch... Right Pressure gauge PI-2 selector switch... Right Desuperheater On/Off switch... Off Priming tank three-way valves... Pumping station three-way valves... a Air distribution register... Open Pressure gauges PI-1 and PI-2 feature a selector valve. The position of this selector valve, left or right, determines the parameter being measured. For instance, the left position of pressure gauge PI-1 corresponds to the ground loop header return pressure; while the right position of pressure gauge PI-1 corresponds to the header supply pressure. Similarly for pressure gauge PI-2, the left position corresponds to the geothermal heat pump heat exchanger outlet pressure while the right position corresponds to its inlet pressure. 11. Turn the system on and wait until the ground loop is purged. 12. Close valves HV-3 and HV Use HV-1 to adjust the flow rate and complete Table Festo Didactic

5 a If you cannot reach 9.5 L/min (2.5 gal/min), simply note the value of the maximum flow obtained. Table 13. Pressure drop as a function of the flow rate. Flow [L/min (gal/min)] Inlet pressure (PI-2 right) Heat exchanger Outlet pressure (PI-2 left) Pressure differential (PI-2 right - PI-2 left) 0 (0) 2 (0.5) 4 (1.0) 6 (1.5) 8 (2.0) 9.5 (2.5) 12 (3.2) 14. Fully open valves HV-1, HV-2, HV-5, and HV-6. Record the flow rate indicated on FI-1 and FI-3. Calculate the total flow rate and complete the last row of Table 13. FI-1 flow rate: FI-3 flow rate: Total flow rate (FI-1 + FI-3): Festo Didactic

6 15. Set the thermostat operating mode to Off. 16. Using the data in Table 13, plot a graph of the pressure drop as a function of the flow rate in Figure 52. Pressure drop Flow rate Figure 52. Pressure drop as a function of the flow rate. 17. Is the pressure drop in the heat exchanger increasing or decreasing with a flow increase? 18. When a flow indicator is not installed on the ground loop, the flow in the geothermal heat pump can be evaluated by measuring the pressure drop across the heat pump water inlet and outlet ports using the heat pump manufacturer's fluid pressure drop table. Using Table 10, " Relationship between the fluid flow and the pressure drop in the geothermal heat pump of your training system." on page 1, what would be the flow equivalent to a pressure drop of 20 kpa (3 psig)? Flow equivalent to a pressure drop of 20 kpa (3 psig): 76 Festo Didactic

7 Effect of the expansion tank in a pressurized system In the following steps, you we will demonstrate how the expansion tank is able to compensate for the pressure loss due to a volume change in the ground loop. Since the geothermal trainer has a small piping volume compared to an actual system, the variation of volume caused by a temperature change may not be clearly detectable. To simulate a variation in volume in a ground loop, you will store a mixture of water and air in the trainer before you pressurize the system. Once the system is pressurized, you will isolate the expansion tank from the loop by closing the hand valves at its inlet and outlet. The mixture of air and water will then be released resulting in a pressure drop similar to the expansion of a ground loop volume. When the two hand valves of the expansion tank are later opened, the resulting pressure increase will compensate for the pressure drop previously observed. 19. Make sure that the main power switch is set to Off. Open the priming tank cap. Set the priming tank three-way valves as shown in this diagram step.. Wait for five minutes before proceeding with the next Festo Didactic

8 20. Perform the following settings on your training system: Main power switch... Off Thermostat... Cooling mode Temperature set point... 5 C (9 F) below room temperature Valve HV-1... Open Valve HV-2... Open Valve HV-3... Open Valve HV-4... Open Valve HV-5... Open Valve HV-6... Open Valve HV-7... Open Valve HV-8... Closed Valve HV-9... No adjustments required Valve HV Handle in horizontal position Valve HV Open Valve HV Open Valve HV Open PI-1 Selector... Right PI-2 Selector... Right Desuperheater switch... Off Priming tank valves... Pumping station valves... Priming tank cap... Open a Air distribution register... Open Air should be present in the system piping. Once the trainer has run for a few minutes, the second ground loop will be isolated from the rest of the system. Water in this loop is non-pressurized and is a mixture of air and water. The addition of this loop simulates the expansion of the ground loop tubing due to a variation of ground temperature in an actual system. 21. Set the main power switch to On. Allow the system to work for four minutes or until you can see a white fluid circulating in the pipes. 22. Close valves HV-3 and HV-4 to isolate the second ground loop from the system. The system will now be purged using the priming tank. Once completed, the priming tank will be bypassed and the system pressurized. It is important to note that in this configuration the expansion tank is part of the circuit, as it would be in a standard pressurized system. 78 Festo Didactic

9 23. Position the priming tank's three-way valves as shown in this diagram in order to purge the system. Allow the system to run for four minutes or until you can see an air-free flow in the transparent pipes. 24. To pressurize your training system, start by turning the priming tank's upper valve as shown in this diagram. 25. Observe how the pressure increases on the pressure gauge PI-1 with the selector in the left position. Wait for two minutes to let the pressure stabilize. Record the pressure reached after two minutes. Ground loop pressure: 26. Turn the priming tank's lower valve clockwise as shown in this diagram. 27. Turn the priming tank's upper valve clockwise as shown in this diagram. The system is now pressurized. 28. Close HV-12 and HV-13 to isolate the expansion tank from the circuit. Record the ground loop pressure at PI-1 left and PI-1 right. Ground loop pressure at PI-1 left: Ground loop pressure at PI-1 right: 29. In the next steps, the second ground loop will be added to the circuit. This loop has not been pressurized and is a mix of water and air. With the addition of this loop, do you think the ground loop pressure will increase, decrease, or remain the same? 30. Open valves HV-3 and HV-4 to add the second ground loop to the circuit. Record the ground loop pressure at PI-1 left and PI-1 right. Ground loop pressure at PI-1 left: Ground loop pressure at PI-1 right: Festo Didactic

10 31. Did the system pressure behaved as you predicted? Yes No 32. In the following steps, you will add the expansion tank back onto the system and observe its effect on the ground loop pressure. Open valves HV-12 and HV-13. Record the ground loop pressure at PI-1 left and PI-1 right. Ground loop pressure at PI-1 left: Ground loop pressure at PI-1 right: 33. Did the pressure rise? Yes No 34. Do you think that a fully pressurized expansion tank will be able to absorb a contraction of the piping in the ground loop? 35. Would you recommend the installation of an expansion tank in a system with a priming tank? 36. Turn the priming tank's valves as shown in this diagram to purge the system. Allow the system to run for four minutes or until you can see an airfree flow in the transparent pipes. 37. Set the thermostat operating mode to Off, then set the main power switch to Off. Name: Date: Instructor's approval: 80 Festo Didactic