Ground Heat Exchange Systems

1. Ground Heat Exchange Systems Paul Blain Senior Hydrogeologist MassDEP IGSHPA Accredited Installer

2. GSHP System Components • Delivery System (Heating and Cooling) • Radiant flooring • Air ducts • Heat Pump • Ground Heat Exchanger

5. What are the GROUND HEAT EXCHANGE OPTIONS ?

6. Ground Heat Exchange Options • Open Loop (Groundwater System) • Pump and Dump • Withdrawal/Recharge Wells • Standing Column Wells • Closed Loop (Ground Coupled System) • HDPE Pipe • Vertical • Horizontal • Concentric • Direct Exchange (DX) • Vertical • Diagonal

7. Open Loop Wells Sand and Gravel Bedrock Source: http://www.huemannonline.com/well_files/welldiagram.html http://www.capitalwell.com/wellDiagram.php

8. Open Loop Ground Heat Exchange Systems Advantages • Higher Heat Transfer Efficiency • Less Borehole Required Per Ton • Less Land Required • Less Site Disruption

9. Open Loop Heat Exchange Systems Disadvantages • Water Disposal Issues • Water Table/Well Yield May Change • Drought or Extended Periods of Dry Weather • Lowering of water table • Decrease in well yield • Water Quality Issues

10. Open Loop Heat Exchange Systems Three Primary Types: • Pump and Dump Wells • Withdrawal/Recharge Wells • Standing Column Wells (SCW)

11. Open Loop – Pump and Dump surface or diffusion well Advantages • High Heat Transfer Efficiency • Constant Water Temperature Disadvantages • Water Disposal Issues • Requires Sufficient Yield • Regulatory Issues • WMA/NPDES/GWDP

12. Withdrawal/Recharge Wells

13. Open Loop – Withdrawal/Recharge Wells Advantages • Higher Heat Transfer Efficiency • Less Borehole/Ton • Less Land Required

14. Open Loop - Withdrawal/Recharge Wells Disadvantages • Water Quality Issues • Requires Adequate Well Yield • Permitting Issues • Water Table/Well Output May Change • Injection Well Design Issues

15. Open Loop - Withdrawal/Recharge Wells Injection Well Design Issues - Clogging • Air Entrainment • Water Chemistry • Bacteria • Suspended Sediment – major reason for clogging Injection Well Criteria • Design for Lower Entrance Velocities – 0.05 ft/sec • Increase the Screen Length • Double Injection Well Screen Length

16. Standing Column Wells • Bedrock Well • Typically Several Hundred to 1,500 Feet Deep. • 60-100 ft/ton • 2-35 tons/well • Efficiency Increased with Bleed • Dual Use Option http://ocwelldrilling.com/OCWellDrilling/StandingColumn.html

17. A Standing Column Well Bridges the Efficiency Gap between the Closed Loop Systems and Open Loop Systems. Standing Column Wells Bleed Return Supply Closed Standing Column Open

18. Standing Column Wells Advantages • Higher Efficiency than Closed Loop • Requires Less Space • Drilling Contractor Widely Available • Dual Use Option • Conductive/ Advective Flow Bleed Return Supply

19. Standing Column Wells Disadvantages • Water Quality Issues • Regulatory Restrictions • Dual use Issues • May Require Fouling Precautions • Higher Pumping Energy May be Required • Deep aquifer withdrawals • Poorly designed systems • Dual Use Option Bleed Return Supply

20. Closed Loop Systems • High Density Polyethelene (HDPE) • Horizontal • Vertical • Pond/Lake • Concentric • Direct Exchange (DX)

21. HDPE Closed Loop Systems • “U” tube of High Density Polyethylene (HDPE) Piping • Piping filled with Antifreeze • Typically Propylene Glycol • Borehole is Grouted after Insertion of “U” tube • Heat Transfer is Conductive Bores are typically 300-500 feet

22. Typical Closed Loop Vertical Closed Loop Horizontal Closed Loop

23. Closed Loop – Vertical Advantages • Less Environmental Concerns • No Water Quantity Issues • No Water Quality Issues • Lower Maintenance

24. Closed Loop – Vertical Disadvantages • Lower Heat Transfer – Less Efficient • More Borehole/Ton • More Land Required • More Site Disruption • More Expensive To Install

25. North Shore Community College – Closed Loop Field • 50/500 ft. Wells • 10 by 5 grid • 100 ton System • 25,000 ft. of Borehole • Installed Summer 2010

26. Closed Loop HDPE Installation

29. Ten Circuit Concrete Vault – North Shore Community College

31. Horizontal “Slinky” Closed Loop System For a 3 Ton House • 3,000 ft. of Slinky • ~2,000 ft2 Area • 6 ft. Deep Trench

32. Closed Loop - Horizontal Advantages • Lower Installation Cost • Concentrate Heat Transfer Area Disadvantages • Lower Tonnage/ Borehole ft. • Significant Site Disruption http://www.idahogeothermal.com/2010/02/24/6-ton-water-source-heat-pump-and-closed-loop-system/

33. Closed Loop – Vertical Slinky System Advantages • Minimal Site Disruption • Less Land Area Required Disadvantages • Requires Deeper Installation than Horizontal Slinky Systems http://www.global-greenhouse-warming.com/ground-source-heat-pump.html

34. Closed Loop – Lake/Pond Advantages • High Efficiency • Low Installation Cost • Easy to Install/Repair Disadvantages • Limited Application • Regulatory Issues • Environmental Impacts

35. Concentric Systems • Pipe Within a Pipe • Flow Down Interior HDPE Ribbed Pipe • Flow Up Annular between HDPE and Fiberglass Exterior Pipe • Laminar Flow Down/ Turbulent Flow Up • HPGX System –Rygan http://www.thermonexus.com/hpgxtechnology.html

36. Closed Loop – Concentrix Advantages • High Heat Transfer • Smaller Wellfield/Less Site Disruption • Reduced Installation Time/Costs • Improved Heat Pump Performance Disadvantages • Lower Efficiency than Open Loop • Relatively New Technology

43. Installed HDPE Concentric System http://hpgxsystem.com/HPGXTech.aspx

44. DX Closed Loop Systems • Copper Tubing Loop Installed Vertically or Horizontally • Installed in Small Diameter/Shallow Borehole (>100 ft.) • Loops Filled with Refrigerant • Grouted After Copper Tubing is Installed Bores are typically <70 feet http://www.earthlinked.com/residential/how-it-works

45. Closed Loop - DX Advantages • High Heat Transfer Efficiency – Single Phase • Small Wellfield/Site Disruption • 8 foot diameter pit • Lower Energy Costs • No Water Pump/Water Heat Exchanger • Phase Exchange Occur in Ground • Potentially Lower Installation Costs • 15 -30% of Tubing/Less Bore Hole • Smaller Diameter/Shallower Bore Holes

46. Closed Loop - DX Disadvantages • Requires More Refrigerant • Environmental Concerns • Less Tolerant of Leaks (vapor phase) • Joints Must be Brazed • Corrosion Issues in Aggressive Soils • Requires Sacraficial Anode/Cathodic Protection • Maintain Temps. Within Certain Limits • High Material Costs (based on price of copper )