IGSHPA Tech. Conference & Expo

Size: px
Start display at page:

Download "IGSHPA Tech. Conference & Expo"

Transcription

1 IGSHPA Tech. Conference & Expo Horizontally-Bored GHEX Design Presented by: Ryan Carda Geo-Connections, Inc.

2 Learning Objectives Overview of horizontal directional drilling (HDD) Understanding the installation process Design implications Accounting for the variables Ensure that design/drawings are easy to comply with Calculation example using LoopLink PRO

3 HDD Equipment Originally used for utilities Great when excavation not an option Relatively new method for geo Image courtesy of A-One Geothermal

4 Benefits of HDD Provides access to areas otherwise can t Minimal disturbance Install under buildings, parking lots, lake beds, etc. o Area can still be used, unlike excavated (horizontallytrenched) loops Excavation costs are generally lower Drilling costs usually comparable to vertical (in unconsolidated soils)

5 HDD Example #1 Senior Apts (IN) 22 bores x 300 ft long

6 HDD Example #2 H.S. (IA) 150 bores x 600 ft long

7 Steering & Tracking

8 Loop Installation Steps

9 Closed-Loop GHEX Design Bldg loads, NRG usage, schedule, etc. GSHP schedule, capacity, COP/EER, etc. Soil/Rock Formation Properties Borehole Considerations Borehole diameter Grout Thermal Conductivity Pipe Flow Considerations Pipe diameter Number of parallel flow paths (bores) Maximum borehole length

10 Borehole Heat Transfer Model Vertical Bore Horizontal Bore Thermal Circuit:

11 Similarities Bore definition is the same: Single loop configuration o Avg. shank spacing o U-bend size vs. bore length & gpm Full length grouting o Bore length vs. grout TC value o Heat transfer required - don t rely on bore collapse! Heat transfer not a function of direction o e.g. vertical vs. horizontal

12 Measurement of Soil Properties Soil property measurement same as vertical FTC test recommended for commercial projects > 25 tons Images courtesy of GRTI

13 Key Differences Soil type Unconsolidated only Installation depth Ground load imbalance vs. ambient effects o Deep earth temp (1) or mean earth temp (2)?? o Max depth ~40-50 ft. (sonde limitations) Drilling offset & entry angle Fixed u-bend configuration No mechanical spacers or alternative loop options

14 Installation Depth Matters Horiz. trench: installed close to surface (<10 ft.) Calculate temp swing at depth/time of year o Kusudah-Achenbach Ground energy naturally rebalances Vert. bore: installed below level of ambient influence (>15 ft.) Deep earth temp Ground load imbalance must be accounted for Horiz. bore: - need definitions for both sets of data to properly calculate

15 Mean Earth Temp: Kusudah-Achenbach Soil temp vs. depth/day - Louisville, KY T O T O Temperature (F) T M A S Depth 0 ft 6 ft 8 ft 16 ft January 75 March May July September November Februar y Apr il June August October December 257

16 Fig 5.11: Mean Earth Temp. Data

17 Soil Temperature Funnel Various soil diffusivity values (ft2/day) (T d -T M )/A S = 0.26 ft 2 /day Soil Depth (ft) = 0.60 ft 2 /day = 0.96 ft 2 /day 24 30

18 Soil/Bore Definition

19 Account for Entry Angle Drilling starts at surface Entry angle depends on manufacturer o Typically 8-18 o 3:1 common (18.4 ) For deep HDD bores, large % of bore is installed in entry portion o To reach 45 ft. depth takes 135 ft. run

20 Drilling Offset for Multiple Rows Bore rows typically offset from one another Keeps header trench width to a minimum Entry angle & drilling offset affect avg. spacing

21 Layout Definition

22 Example 100-ton commercial building in K.C. Two zones - cooling dominant system Combined design day load profile: Assumed soil properties: Deep earth temp = 58.5 F Formation TC = 1.20 Btu/hr-ft- F Formation diffusivity = 0.85 ft 2 /day

23 Starting Point for GHEX Layout Nominal GSHP Flow = 3 gpm per ton ¾ Loops à 1Ton per flowpath (3 gpm) > 3 gpm for turbulence < 3.8 gpm for head loss 1 Loops à 1.5 Tons per flowpath (4.5 gpm) > 4 gpm for turbulence < 6 gpm for head loss 1-1/4 Loops à 2-3 Tons per flowpath (6-9 gpm) > 5 gpm for turbulence < 12 gpm for head loss

24 Figure 5.5. Optional ground loop layouts for a nominal 3-Ton GSHP.

25 Selection of Loop Pipe Size Flow Rate (gpm) / /4 Nominal D R-1 1 Pipe Siz e (in.) } Maximum Flow for 4' H L f p er 10 0' of pip e 40 F FP = 32 F 12.5% 25 F FP = 16.2 F } Minimum Flow for 20% P 25 F FP = 18.7 F 20% E 25 F FP = 18.5 F Turbulence (Re=2,500) Figure 5.4. Flow rate range bands for selected circulating fluids.

26 Questions? Contact Info: Ryan Carda