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UMASS AMHERST Continuing & Professional Education GeoScien ce Series Geothermal Heat Pumps: Concept to Completion Basic Review Basic Review Energy Budget Physics Behind Heat Pumps Definitions and Terminology 1

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  • Slide 1
  • Slide 2
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion Basic Review Energy Budget Physics Behind Heat Pumps Definitions and Terminology 1
  • Slide 3
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 2 The Energy Budget All bodies emit characteristic energy spectrum Energy Emitted Proportional to Temperature 4 Energy emitted drops as the square of the distance Emission governed by the Stefan-Boltzman Law I = T 4
  • Slide 4
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 3 Suns Emission Rate 6000K I = (5.67 x 10 -8 ). (6000 4 ) = 73.5 x 10 6 W/m 2 W = (energy per square meter) x (area of photosphere) = (73.5 x 10 6 ) x (4r 2 ); where r = 647 x 10 6 m = 3.865 x 10 26 W Energy Flux: Total Energy:
  • Slide 5
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 4 Energy Received by Earth W 1/r 2 r = 150 x 10 9 m A sphere = 4r 2 = 2.83 x 10 23 m 2 Energy Flux to Earth: W/m 2 = 3.865 x 10 26 Watts / 2.83 x 10 23 m 2 = 1367 W/m 2 Solar Constant (S o )
  • Slide 6
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 5 Energy Received by Earth
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  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 6 Earths Disk Energy Received By Earth W = (S o ) ( r 2 ),
  • Slide 8
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 7 Albedo 30% of incoming radiation is reflected
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  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 8 Energy Emitted by Earth Short Wave Radiation in Peak = 0.47 m Visible Light Heat Earth Long Wave Radiation out Peak = 10 m Infrared = heat 239 in = 239 out
  • Slide 10
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 9 Equilibrium Temperature of Earth
  • Slide 11
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 10 Effects of an Atmosphere
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  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 11 Effects of an Atmosphere
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  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 12 Effects of an Atmosphere Equivalent to Equilibrium T of 58C or 136F Too Hot!
  • Slide 14
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 13 Transfer Mechanisms Conduction - transfer of energy by neighboring molecules across a temperature gradient Convection - transfer of energy through larger scale motion of currents warm air rises, cool air sink convection Thermals and create weather Latent Heat transfer of energy through a change in state evapotranspiration (feeds our weather) Advection Same as convection but horizontal
  • Slide 15
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 14
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  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 15 Energy In = Energy Out The Energy Balance Top of Atmosphere W/m 2 Sunlight Absorbed + IR Back = IR emitted + Thermals + ET (163) (340) (398) (18) (86) Sunlight In = Sunlight reflected (atmos & land) + IR emission (340) (99.5) (239.7) At Earths Surface In Atmosphere Sunlight Absorbed + IR Absorb + Thermals + ET = IR space + IR ground (77) (358) (18) (86) (200) (340)
  • Slide 17
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 16 NASA
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  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 17 Earths Other Energy Source Radioactive decay of three elements 238 U, 232 Th and 40 K produce most of Earths internal heat Equivalent to 38 trillion Watts (U.S uses 0.3 trillion Watts) Spread over earths surface average heat flow to surface from radioactive decay produces 0.075 W/m 2 Enough to light a single 75 Watt bulb on 1000 m 2 lot (approximately an area = 100 x 100 ft) Energy absorbed from sun about 2200 times larger than heat flow Davies and Davies, 2010
  • Slide 19
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 18 The Real World - Insolation NASA
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  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 19 Long-Wave Radiation Out NASA
  • Slide 21
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 20 Absorbed Energy NASA
  • Slide 22
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 21 Average Surface Temperatures NASA
  • Slide 23
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 22 Temperature Variation with Depth TTeTemperature Variation in F VT Dept Mines, Mineral & Energy
  • Slide 24
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 23 Boutt et al., 2010
  • Slide 25
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 24 Mean Earth Temperatures in U.S. VT Dept Mines, Mineral & Energy
  • Slide 26
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 25 Energy absorbed by the earth is renewable It is stored by the soil, rock and water GSHP systems borrow this heat temporarily Summary
  • Slide 27
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 26 Physics of Heat Pumps 1060 Btu to evaporate 1 lb of water (at 60F) 1060 Btu is released when that 1 lb of water condenses
  • Slide 28
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 27 Closed system Heat Source (Ground) Heat Distribution (Structure) Expansion Valve Compressor Evaporator Hot Gas, High PressureCool Gas, Low Pressure Hot Liquid, High Pressure Condenser Cooler Liquid/Vapor Mix Low Pressure Heating
  • Slide 29
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion Ground Exchanger(GHEX) Interior Air Distribution 28 Coupling the Heat Pump Three main components to the System Heat Pump
  • Slide 30
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 29 GSHP Vocabulary BTU British Thermal Unit: energy required to raise 1 lb water 1 F Therm 1 Therm = 100,000 BTU Ton 12,000 BTU/h: the amount of heat required to melt 1 ton of ice in 24 hours So, 288,000 BTU to melt 1 ton of ice
  • Slide 31
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 30 Thermal Conductivity Thermal Conductivity equivalent to Hydraulic Conductivity D constant head reservoir L Sand Darcys Experiment (1857) Q h Q L Q A h Q Q ( h/L) A
  • Slide 32
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 31 Q/A gradient slope = K = Hydraulic Conductivity Rewrite, Q = Darcys Law K h/L) A For heat flow: Q = heat flow in Btu/hr h/L = temperature gradient = T/L (F/ft) A = cross sectional area of flow = L 2 (ft 2 ) K = thermal conductivity = (Btu/hr/F/ft)
  • Slide 33
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 32 Pulling terms together, Q = (T/L) A = QL/TA Units are: Btu/hr/F/ft 1 Unit Volume 1 1 Conceptually, Temperature Gradient = 1 1 1 = Heat Flow in Btu/hr through a unit length of material per unit area under a unit temperature gradient
  • Slide 34
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 33 Specific Heat Capacity c p - Specific heat capacity is the amount heat energy a unit mass of material takes into storage or releases from storage per unit change in T 1Btu/lb/F This is equivalent to specific storage in hydrogeology
  • Slide 35
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 34 Conceptual Meaning of Specific Heat Capacity 1 unit Mass Earth Heat Out or In 1 unit in T
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  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 35 Volumetric Heat Capacity is also equivalent to specific storage s is the amount of heat energy a unit volume of material takes into storage or releases from storage per unit change in T. s has units of Btu/ft 3 /F s = c p Volumetric Heat Capacity Specific and Volumetric Heat Capacity are related by
  • Slide 37
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 36 Conceptual Meaning of Volumetric Heat Capacity Heat Capacity 1 unit Volume earth Heat Out or In 1 unit in T
  • Slide 38
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 37 Heat Capacity Heat Capacity is equivalent to Storage used in hydrogeology C = Q/ T C = Heat Capacity in Btu/F Q = heat energy in Btu T = temperature in F
  • Slide 39
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 38 Heat Capacity and Specific Heat Capacity Two important relationships: C = c p x total mass of material being heated C = s x total volume of material being heated
  • Slide 40
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 39 Thermal Diffusivity Thermal Diffusivity equivalent to Transmissivity D = / c p D is a measure of the rate at which a temperature disturbance at one point in a body travels to another point in the body similar to transmissivity English Units are: ft 2 /hr Thermal conductivity / volumetric heat capacity
  • Slide 41
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 40 GSHP Efficiency Terminology Coefficient of Performance COP energy in or energy output (Btu/h) electrical energy needed (Btu/h) at a specific T Energy Efficiency Ratio EER (steady state cooling eff.) cooling capacity (BTU/h) electrical energy input (Btu/h) at a specific T Seasonal Energy Efficiency Ratio (SEER) total cooling over entire cooling season (BTU/h) electrical energy used over cooling season (Btu/h) EER = 0.875 x SEER
  • Slide 42
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 41 GSHP Acronyms EAT Entering Air Temperature EWTEntering Water Temperature LWTLeaving Water Temperature HCTotal Heating Capacity TCTotal Cooling Capacity CFMCubic Feet per Minute GPMGallons per Minute GSHPGround Source Heat Pump
  • Slide 43
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 42 Important Conversions & Calculations 1 Watt = 1 Joule/sec 1 Watt = 3.412 BTU/hr 1 Btu = heat to raise 1 lb of water 1 degree Farenheit 12,000 Btus per hour = 1 ton
  • Slide 44
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion 43 A Useful Calculation Flow (gpm) x T difference (F) x 500 = Q (Btu/hr) Eg., ((1 gpm x 60 min/hr)/7.481 gal/ft 3 ) x 62.4 lbs/ft 3 = 498 lbs water/hr (~500 lbs/hr) In a closed loop system: for a 10 degree temperature difference 1 gpm x 500 lbs/hr x 10 F temp diff. = 5000 Btu/hr Therefore, 1 gpm adds 5000 Btus of heat per hour 5000 Btu/hr / 12,000 Btu/hr/ton = 0.42 tons or 1 gpm flow needed per 0.42 tons or 2.4 gpm required per ton of heating or cooling when you have a 10 temp. diff.
  • Slide 45
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion The Thermodynamics of it All: Do GSHPs Work in Cold Climates? Coefficient of Performance (COP) = Heat Energy Output Electric Energy Input Industry claims COP ranging from 3 to 6 From the Second Law of Thermodynamics and the Carnot cycle: COP theoretical limit = Indoor Temperature (Indoor Temperature - Temperature of Heat Source/Sink) 44
  • Slide 46
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion Thermodynamics (continued) Degrees Farenheit to degrees Kelvin conversion: K = 5/9 (F - 32) + 273 Example: Heat a dwelling to 70 F ~ 294 K Ambient groundwater temperature in Massachusetts is typically about 54 F ~ 285 K From the Carnot cycle: COP theoretical limit = 294 K = 33 294 K 285 K 45
  • Slide 47
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion Thermodynamics (continued) What happens to the theoretical efficiency toward the end of the heating season if the entering water temperature has dropped to 35 F? 35 F ~ 275 K COP theoretical limit = 294 K = 15 294 K 275 K 46
  • Slide 48
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion Thermodynamics (continued) Why is the theoretical heat pump efficiency many times greater than the actual COP? No heat pump is 100% efficient - Not all of the energy put into the heat pump is converted into the work of pumping heat some energy lost as waste heat It takes energy to pump the heat transfer fluid through the ground coupled part of the system and the air or water through the buildings heating ducts 47
  • Slide 49
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion Ground Exchange vs. Air Exchange Heating season Cooling season FF
  • Slide 50
  • UMASS AMHERST Continuing & Professional Education GeoScience Series Geothermal Heat Pumps: Concept to Completion Entering Heat Pump Temperature vs. Theoretical Maximum COP Entering Temperature F Theoretical Coefficient of Performance