- Layout, Fabrication, and Installation of SLINKY Ground Heat Exchangers

INTERNATIONAL GROUND SOURCE HEAT PUMP ASSOCIATION I OKLAHOMA STATE UNIVERSITY

Acknowledgements C

The foIIowing individuals have conkibubed in the Rlnancial support for the project came from the +-

development ofthe materials and i d ~ ~ reported in Elsctric POIRBT R8138arCh In&-, the National thisdocument: Rural E l b c Coopmtive Amchkiom, Phillips

Pete Everhart, Phil Mbmbm, Come% Drhmpipe, Charles Machine Works (manufbhm Lynn Vick, Ron Webber, Joe Hamph, Iany dDibch Wibh trenching and horizontal boring Eitehnan, Heather and Bin Van Astine, Jaam Bone, equipment), and the Oklahoma Council for the Eked Jms, Ran& Pmy, June Rteh and Bobi Advancement of Scisne and Technolo#. Stepheniion.

I. Introduction A b a number of years of testing multiple-pipe when using the equivalent of 4 fmt of pipe per foot of

ground heat exchangers, sufficient research and trench and 80 feet of b n c h length when using the experimental test results &st &at will allow equivalent of 12 foot of pipe per foot of trench. significant reductions in trench length. These new Table 1 summarizes the new designs that have been pipe configurations reduce heat exchangers trench tested and proved successll. length to 125 feet per nominal ton of cooling capacity

Table I : Systems tested

Description Pipe (feet) Trench (feet)

SLINKY 1,000 feet 80 feet Extended SLINKY 500 feet 125 feet Four Pipe 500 feet 125 feet

Note: P@e size is W4 inch.

Figure 1 illustrates the pipe configurations of the two coils, SLJNKY and Extended SLINKY, that are under development and demonstration at this time. Coil pitch (distance htween mils) for both coil types is shown on the drawing.

These types of ground heat exchanger^ have a numkr of advankges that should lower the insbl- lation first cost.

1. These heat exchangers can be fabricated off si fe.

2. By rolling or foIding, the heat exchangers can

be transported to the job site thus minimizing field labor.

3. The heat exchanger is a unit type construction which simplifies field placement in the trench without the use of special placement equip- ment.

A fixture (figure 2) can be consbted to hold the pipe in place while the loops are being tied bgether. Plastic wire tie wraps with metal catches, nylon rope, duct t ~ p e or any other low cost method of faskning the pipe together for transportation and placement is acceptable.

II. Pipe Material Selection The International Ground Source Heat Pump shall k

Association CIGSKPA) recommends the following for 1. Either Class B (general purpose and dielectric, polyethylene and polybtylene pipe makerials (See in colors) or Class C (weather resistant, black Appendix C of the IGSHPA's the Closed-hop/ in color mnbining not less than 2% c h n GroundSource Heat Pump Systems: Installation black) Guide): 2. I1 (density, 0.91 to 0.92 glem3)

3. Grade 1 (flow i t e 0.25 to 0.75 dlO min)

The minimum cell classiiication numbr accept- T h e cell classification shall be printed on the pipe abb for poIyethylene pipe is PE355434C or . for positive identification. If the pipe cannot be PE345434C when tested under ASTM 3350. identified by ceU classitication number, then other

means of identification must be established. Labels P O L ~ ~ such as PE3408, high density, ete., are not sufficient

Polybutylene shall be manufactured in accor- and cannot be used to satisfy the intent of the dance with ASTM Standard D-258 1. The material IGSHfA recommended minimum standards.

4 It-- 10 inches between coils $ 3fi*

S L m

k- 80R

Coil Diameter = 3 ft.

EXTENDED S L r n K P

NOTES: I. Emh type of heat exchanger is fabn'cuted from a 314 in, HDPE pipe. 2. Trench depths are 5ft.

FIGURE 1: Multiple pipe ground heat exchangers

I FIGURE 2: Fabrication fixture I

III. Coil Configuration Circular coiled heat exchangers can be configured

in a number of different ways. The two types fabrimted and tested at Oklahoma State University are: 1) a SLINKY mgure 3) in which the individual circular ails overlap and 2) a Extended SLINKY (Figure 4) where individual coils are separated and do not overlap.

Zn addition to the two heat exchangers described in Figures 3 and 4, conhetors have developed other configurations that are specifically designed ta meet their installation needs. TWQ of these methds axe given here.

Lynn Vick Method The Extended SLINKY can be fabricated in a flat

configuration Figure 5) for transporhtion to the field by tying the return pipe to the base of the coil.

Before the coil is placed in the trench, the return pipe is cut free from the bottom of the heat ex- changer and is installed at the tap of the ground heat exchanger.

Bill VanAIstine Method Coils are 30 b 32 inches in diameter and are

spaced 30 to 32 inches apart from the point where they me tied. A 30- ta 32-inch circle is used since it is easier to shape while the person fabricating is standing up. The 30- to 32inch spacing places the loops against each other but not overlapping (see Figure 6). This spacing is an average man's sbp or arm length hence no special measuring devices are needed, The trench length (approximately 150 feet) will vary depending on how much lead in pipe is needed at the header pit. Seven hundred feet of pipe is required for this configuration.

FIGURE 3: SLINKY Coil

FIGURE 4: Extended SLINKY

Note: During transporfafivn, the return @pe is taped to the coil botfom which allows the ground beat exchawr tu be foldedover to fit on a flat bed trailer.

FIGURE 5: Extended SLINKY (Lynn Vick)

Note: 700 feet of pipe

FIGURE 6: Extended SLINKY (Bill Van Alstine)

N. Pipe Sizes Circular heat exchanger pipe sizes have been Pipe sizing will be selected on system flow rate, fluid

formed fmm V2,3/4, 1, and 1-l/4 inch pipe sizes. type, operating *mperatwes and pumping energy.

V. Forming the Circular Heat Exchanger Forming the SLINKY coil from a pipe roll consists the pipe roll, as shown in Figure 7. This end should

of allowing the pipe roll to remain in the same be the closest to the f ixkue when unrolling it. circular configuration it was coiled during rnanufac- Figure 8 illustrates how the individual pipe coils are turing. The trick is to r a y off individual coils from pulled from the roll to and through the coil fixture. the pipe coil roll. A common mistake is to uncoil the I t works much in the same way as you would unroll pipe as if it were to placed in a straight line. Laying a newly purchased garden hose. OR of the pipe should begin with the outside coil of

I FIGURE 7: "Laying off" pipe coils

( FIGURE 8: Pulling pipe coils through fixture

VI. Coil m g Tie T j p e

The tie wrap must be sufficiently strong t o held the coil in posikion during fabricakion, transportation and placement in t h e trench. After pIacement and bacMlling, the t ies are of no value and therefore cam deteriorate with no consequence.

Plastic wire tie wraps with metal catches are recommended. These type of ties have sufficient

strength to allow a SLINKY coil to be rolIed into a doughnut shape (see Figure 9). Figure 10 illustrates how the tie is made. Wire ties with suffdent strength to hold the coil in place are expensive.

Duct tape has been successhlly used by a number of contractors. If the coil is carefully Lied with a sufficient number of tape wraps the coil can be successfully transported and installed in the trench.