Overview of Geothermal Heat Pumps

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					Overview of
Geothermal Heat Pumps

SURE Workshop
January 13, 2006


Hugh I. Henderson, Jr., P.E.
CDH Energy Corp
Cazenovia, NY
www.cdhenergy.com
                     What is it?


• Couples the building to the earth, a lake, or river
   – Uses “constant temperature” heat source/sink
• It’s a heat pump system that:
   – Rejects heat to the ground for cooling
   – Extracts heat from the ground for heating
   – Moves heat within the building
• Energy efficiency is its first attraction
• Simplicity in operation and maintenance
                       It’s at Heat Pump
• A Machine that transfers heat from a
  lower temperature to higher
  temperature
                                                                                                Hot
• A refrigerator or air conditioner that                                                  Refrigerant Gas
                                                                                           (e.g. 130 F)
  runs “backwards”
                                                                              Hot Side


• COP = Heat Out
                                        Room Air
        Power In                        (e.g. 70 F)                                                          Supply Air
                                                                                                            (e.g. 110 F)



• Heating COPs: ~2-5
                                               Warm
                                         Refrigerant Liquid
                                           (e.g. 110 F)
• Seasonal Avg COP: ~3                                                                                          Compressor moves
                                                                                                                refrigerant from cold
                                  Flow restriction                                                                zone to hot zone
                               maintains pressure
                             difference between the
                               hot and cold zones
                                                                Cold
                                                          Refrigerant Vapor
                                                             (e.g. 30 F)
                           To Ground Loop                                     Cold Side                             From Ground
                             (e.g. 35 F)                                                                           Loop (e.g. 40 F)
           And a Ground Heat Exchanger
              Vertical Bores (holes in the ground)

Bore Field Circuiting

                         Bentonite fill

                          6 inch dia.



138 ft




         15 ft spacing
Or a Pond Loop Heat Exchanger
      Other Types of Heat Pumps
                         All Heat Pumps extract
                         low grade from a low
Heat Pump Water Heater
                         temperature source

                               Air-Source Heat Pump
              Is it Renewable?
• Pulls heat from the earth (or body of water)
   – Uses “seasonally” stored solar energy
   – 70% of energy for space heating comes from ground
• Uses “constant” ground temperature to achieve
  high efficiency
• Is that the right question?
• Real questions:
   – NET amount of energy savings
   – What local and power plant emission reductions result
     from energy savings
   – What is its embodied energy content and system life

       My Thesis: kWhsaved = kWhfrom renewable source
Doesn’t Matter: “It’s good”
•   Low Operating Cost
•   Low Energy Use and Environmental Impact
•   Level Seasonal Electric Demand
•   Simplicity
•   Low Maintenance
•   No Exposed Outdoor Equipment Required
     It’s a System
     Includes ground loop, piping, pumps, HPs, building loads


                                                                  Cold
                                                                  Water
Pilings     Bores                                                 Inlet
                                                                          Hot Water Recirc.

                         50 hp
                      Loop pumps,                          4           3,200 gal
                                      HP         HP      10 ton          H.W.
                        variable
                         speed                            HPs           storage




   Ground HX                Space Conditioning                    Water Heating



    •     Can be applied to meet space heating loads, cooling loads, and water heating
          loads
    •     The normal HVAC design details matter
A Close Cousin
The Water Loop Heat Pump System

• Many of the same “inside
  the building” issues                                                        Heat
                                                                                                 HP

                                                                                                 HP
                                                                            Pumps
• Commonly used HVAC                                                                             HP

                                                                                                 HP

  system
             Fluid
             Cooler
             (Cooling Tower)
                               Outlet                                                      Loop
                               Damper                                                     Pumps




                                                          Boiler               Boiler                    Loop Supply
                                                          Pump                 Pump                      Temperature

                                 2-Speed                                                              Boilers
                                 Fan
                                                Outdoor
                Spray                           Air
                Pump                                               Boiler               Boiler
                                                                     #1                   #2
                                           Inlet
                                           Damper
      Loop Temperatures à Efficiency
          – Heating COPS: 3-5
          – Cooling EERs: 10-20

                   Performance
      7                                      30
      6                                      25
      5                                      20
             COP
      4




                                                  EER
COP




                                       EER   15
      3
                                             10
      2
      1                                      5
      0                                      0
          20 30 40 50 60 70 80 90 100 110
                    Loop Temperature
                                                Ground Loop Loads
                                                         Daily Ground Loop Heat Transfer
                                 10000
                                                           Heat Rejection to Ground Loop


                                  8000                       Cooling
Daily Heat Transfer (MBtu/day)




                                  6000



                                  4000



                                  2000



                                    0



                                 -2000                                                       Heating

                                                          Heat Extraction from Ground Loop
                                 -4000
                                         1998     1999           2000             2001           2002
                                        Ground Loop Loads
Ground Loop Loading (million BTU)
                                    1,000

                                     800       Heat Rejection
                                               Heat Absorption
                                     600

                                     400

                                     200

                                       0

                                    -200

                                    -400
                                                7        7         8    8   8        8
                                        -97 ul-9 p-97 v-9 n-98 ar-9 y-9 ul-9 p-98 v-9 n-99 ar-99
                                      ay J Se No Ja M                 a   J Se No Ja M
                                     M                               M
“Ground Temperature is Constant Year-round”
   …until you reject and extract heat into it
                                                            Daily Average Temperature
                  100
                                                    Outdoor Air
                                                    Ground Loop Supply
                                                    Ground Loop Return
                  80




                  60
Temperature (F)




                  40




                                                                                                                             Loop Flow (1e5 gallons)
                                                                                                                        10
                  20                                                                                                    8
                                                                                                                        6
                                                                                                                        4
                                                                                                                        2
                    0                                                                                                   0
                        J   J   A   S   O   N   D   J   F    M   A   M J   J   A   S    O   N   D   J   F   M   A   M
                        1997                        1998                                            1999
GHPs Reduce Electric Demand
Ground Loop Heat
   Exchangers
 Closed Loop Options
                                     Horizontal Slinky Loop
                Horizontal Loop
Pond Loop
            Point of heat
            exchange with
            heat pump




                       Loop Piping
                                         Vertical Bores
Open Loop Options
Standing-Column Well
                  Supply
                  Return

                 Casing
                           Open Loop Well

                 Outflow




 Inflow




          Well
What is a Good Building Application?
• Should have “balanced” Heating and
  Cooling Loads
  – Though cooling loads have more impact that
    cooling loads:
     Qrejection = Cooling Load + HP Power
     Qextraction = Heating Load - HP Power in
• Modest seasonal cooling loads (200-600 full
  load hours)
• More energy savings from Heating than
  Cooling
• Buildings with “diverse” or “highly-zoned”
  loads
Schools!
Fond du Lac, Wisconsin
                      Ramada Inn
                      Geneva , New York

149 rooms
       100,000 sq. ft.
• All-Electric GX
   – 294 tons space
   – 40 tons water
       • Rooms
       • Restaurant
       • Laundry
   – Variable speed loop pumping
• Ground HX length of 34,000 ft in pilings and bore field
  (105 bore ft / ton)
 “Good” and “Bad” Applications
• Successful Applications (small loops)
  – Schools, hotels, office buildings
  – Diverse loads (i.e., lots of zones)
  – Cooling “full load hours” are modest
• Less Successful Applications (big loops)
  – Fast food restaurants, box box retail, heat
    rejection loads, etc.
  – High cooling loads à more seasonal heat
    rejection
KEY: Use Energy Recovery to
Mitigate Heating Loads
Heat fresh air with exhaust air
            KEY: Variable Speed Pumping

         • Savings up to 90% from variable speed
           pumping
                       Ramada Hotel - Geneva, NY

                         Heat Pumps




            Constant Speed Pumping




MEASURED Variable Speed Pumping                    12% of Constant Speed


Best Practice/Improved Variable Speed
               Pumping


                                        -   50   100   150   200   250   300   350   400
                                                 Annual Energy Use (MWh)
Fond du Lac High School
20% reduction in annual energy cost ($40,000+)
15% reduction in source energy use (8,400 MMBTU)
 Evansville HS Geothermal Impact




                     Electricity   Demand   Natural Gas
Option                 [kWh]        [kW]      [therms]
 Standard Practice     1,222,714      673        82,580
 Enhanced Design       1,362,959      479         9,700
Savings                (140,245)      194        72,880
Energy cost reduction = 36%
Source energy reduction = 28%.
                                          Results - Cost
                               Wisconsin School Energy Cost Survey 1998
                             918 Schools, 69.8 million sq ft, $0.622/sq ft avg.

                                                  $0.54/sq ft District w/cooling
                     250
                             $0.48/sq ft GX           $0.59/sq ft VAV
 Number of Schools




                     200

                     150

                     100

                      50

                      0
                           0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
                                                 Energy Cost ($/sq ft)


$0.45/therm, $0.029/kWh, $7.24/kW on peak, $0.020/kWh off-peak ~ $0.07/kWh average
                                          Residential Costs Look Better…
                                          But will this electric/gas cost ratio last?
                                                                                                                                                                                        Space
                                                              Electric Gas Use     Oil Use     Total                                                                                   Heating
                                                                (kWh) (therms) (gallons)      Costs                                                                                    Savings
                                 Geothermal HP (COP=3)         9,769                        $ 1,270
                                 Gas Furmace (90%)                600     1,111             $ 1,967 $                                                                                        697
                                 Oil Furnace (85%)                600                 846 $ 2,025 $                                                                                          755
                                 Notes: $0.13/kWh, $1.70/therm, $2.30/gal, Heating Load = 100 MMBtu
                                                  GHP Savings vs. Gas Costs                                                                           GHP Savings vs. Oil Costs
                               $1,400                                                                                          $1,400


                               $1,200                                                                                          $1,200
Annual Space Heating Savings




                                                                                                Annual Space Heating Savings
                               $1,000                                                                                          $1,000


                                $800                                                                                            $800


                                $600                                                                                            $600


                                $400                                                                                            $400


                                $200                                                                                            $200


                                 $-                                                                                              $-
                                        0.00   0.50        1.00           1.50    2.00   2.50                                           0.00   0.50     1.00     1.50        2.00     2.50   3.00   3.50
                                                          Cost of Gas ($/therm)                                                                                 Cost of Oil ($/gal)
                Summary
• Geothermal saves costs and energy in the
  right applications (e.g., schools, hotels)
• Traditional HVAC design details mater
• Four-hour session in March will cover:
  – Design issues (ground loop, pumping,
    ventilation)
  – Case study examples of good and bad building
    applications