Job Sheet 2. The Ground Loop OBJECTIVE PROCEDURE. Introduction

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1 Jo Sheet 2 The Ground Loop OBJECTIVE In this jo sheet, you will learn how to determine the numer of oreholes using the testing well approach and the information provided y the manufacturer of the heat pump. PROCEDURE Introduction The Geothermal HVAC project simulates a situation where a house needs to exchange 4392 W (15000 Btu/h) to fulfill its energy needs during the summer. To design a geothermal heat pump for the project, the numer of oreholes that will allow the ground to asor the amount of energy that the house needs to release must e determined. To calculate the numer of oreholes, it is necessary to measure the ground temperature and the heat flow sent to the ground loop. The shape factor and the thermal conductivity of the well must also e determined. In this procedure, you will measure the ground temperature and calculate the energy dissipated y the ground. The ground temperature would normally e otained y evaluating the steady-state average of the temperature measurement at the inlet and outlet of the test loop. However, on the Geothermal Training System, this temperature can readily e measured y TC-7 (simulated earth ground). The testing well setup will e simulated using ground loop 2 as the test loop and the geothermal heat pump as the heat source. For the purpose of this experiment, you will assume that the geothermal heat pump is equivalent to a 3.2 kw (10918 Btu/h) water heater. The geothermal trainer pump will e set in cooling mode to reject heat in the ground. Festo Didactic

2 1. Perform the following settings on your training system: Main power switch... Off Thermostat... Cooling mode Temperature set point...5 C (9 F) aove room temperature Valve HV-1... Closed Valve HV-2... Closed Valve HV-3... Open Valve HV-4... Open Valve HV-5... Closed Valve HV-6... Closed 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... Air distriution register... Open 2. Set the main power switch to On Using a digital thermometer, measure the ground temperature at TC-7 (simulated earth). : 3. Set the thermostat 5 C (9 F) elow room temperature and adjust valve HV-4 to otain a flow of 8 L/min (2 gal/min). Complete Tale 8. is the average of temperatures and. is the difference etween the temperature of the well inlet and outlet,. 46 Festo Didactic

3 Tale 8. TC-3 and TC-4 temperatures. Time (min) The difference etween the temperature measured at TC-3 and TC-4 should stailize after aout 12 minutes. 4. Plot the graph of as a function of time Time (min) Figure 33. as a function of time. 5. What is the temperature of the well (once the plateau is reached)? : 6. Use the following equation to calculate the heat loss in the orehole. Use the results from the previous step to do so. where is the heat flow rate in W (Btu/h) going into the ground is the mass flow rate of the heat carrier fluid in kg/s (l/h) is the constant pressure specific heat of the fluid in J/kg C (Btu/l F). It is equal to 4.18 kj/kg C (1.01 Btu/l F) for water at room temperature is the temperature difference in C ( F) etween and (or, equivalently, ) Festo Didactic

4 1 L of water = 1 kg, 1 W = 1J/s, Water density = 62.3 l/ft³, 1 ft³ = gal Heat loss in the orehole: 7. Is similar to the calculated in step 6? Yes No 8. Assume a vertical cylinder with = 15 m (49.2 ft) and = 0.20 m (0.65 ft), and find the value of " " using the following equation: 9. The thermal conductivity of the testing well ( ) can now e determined with the information gathered so far (refer to Equation (2-4)). where is the thermal conductivity of the ground in W/m C (Btu/h ft F) according to energy conservation law. 10. Assume the geothermal heat pump used in the project has a capacity of W (15000 Btu/h) in cooling mode for a temperature drop in the water loop of 8.33 C (15 F). How many wells identical to the testing well should e used to meet the requirements of the project? Be careful with units Btu/h = 1 W. Use 1 C = 1.8 F in the case of a temperature drop. 48 Festo Didactic

5 Note that: where is the numer of oreholes is the heat from the heat pump to e dissipated y the ground in W (Btu/h) is the thermal conductivity of the ground in W/m C (Btu/h ft F) is the shape factor of the orehole in m (ft) is the specified drop in temperature in C ( F) 11. Set the thermostat operating mode to Off, then set the main power switch to Off. Name: Date: Instructor's approval: Festo Didactic