CA1061773A - Ground heat exchanger - Google Patents

Abstract

A B S T R A C T
A ground heat exchanger adapted to be buried in the ground and to b used in association with a heat pump system for heating and cooling. The exchanger includes a heat conducting metal plate adapted to be vertically buried in the ground and carrying a fluid circulating coil adapted to be con-nected to the circuit of the heat pump system. The ends of the plate are each movably inserted into a corresponding slit of an upright tube filled with a heat conducting grease. Weights compress the grease within the tubes and cause its ejection through apertures of the tubes along both surfaces of the plate, so as to fill any voids between the plate and the ground and to also fill any new voids which may develop due to contraction of expansion of the plate with temperature variation and also due to ground movement.
The top ends of the tubes are accessible above ground surface, so that they may be refilled according to need. The elimination of air pockets or voids maintains the entire surface of the plate in contact with the ground, whereby the heat exchange efficiency is maintained even after a long period of use.
The thermal grease also prevents rusting of the plate surfaces which might impair its heat conductivity.

Description

Thc present inventlon relate~ to a ground h~at exchangkr acd~
more particularly, to such an exchang~r adapted to be used in comb~nation with a heat pump system ~or heatin~ and ¢oolinB o~ enclosed sp3ce~, Juch a~
homes and other bulldings.
The use of the earth as a subatantially constant temperature heat re~er~oir f~r heat exchange purposes is well kno~n. The use o~ the earth in heat exchange relstion with a heat pump system including a co~-pressor, a condenser, an expansion valve and an evQporator, ~ith the evaporator in the ~or~ o~ a heat exchanger buried in the ground, iJ al~o ~ no~n. Such a h0at pu~p 8yJte~ i~ des¢rlbed, ~or instance~ in ~.S.
Patent 2,513,373 dated July 4, 1950. ~ow~ver, in order to r~ain ~r~i-oient, a ground hest exchanger, obviously~ ~ust remain in constsnt and rine contact ~ith the ground ~o that the latter nay act as an orrlcient h~at dnt or a~ an ~t~icient source of heat. Rowe~er, u8ing the ~a~e heat eschaDger in ~inter-ti~e to coIlect heat ~ro~ the ground at 8 lo~ tomperature and a~ a heat dispoGal unit in ~ummer-t~ to di~per~e heat in tho gr wnd, re~ult~ in considerable variation~ in the operatlng temperature of the heat e~changer and, consequently, re~ult~ in e~pansion and contraction of the sa~e. Furthermoro, especially ln Northern cli~ates~ ground, upon rree~ing snd d~treosing, ~ores appreoiably ~ithin the span o~ ~ust one year.
Thereroro, a groQnd heat eschanger buried in the ground rapidly lo~es lt~
heat esch~nge e~ficiency due to the creation ot ~oid~ or air poc~et~ -betwoen the heat e~oheng~r surfaeoa and tho adJacent earth. Those heat 02ehang~r~ aro nor~ally ~sdo o~ ate d for low cost ana good heat conoucti~it~.
Howe~or~ ~to d ru~ts quito quio~l~ in the ground. Painti u Or the ate~l ~urraea~, naturally, docreases tho hoat condQcti~it~ at the int~rfae~ Yith the o~rth.
It i~ thereroro the geDeral obJect of the inrention to pro~de a eround heat exchslg~r o~ the eharacter described, whlch ~ill obriato the - -abovo-noted diaadr nt~ges in that it retain~ ita hoat conduct~ng rolatlo~shlp ~ith tho oarth in ~hich it iJ buriod ~or a very long time and despite ropsated contraction a~d ospan don and alQO ground ~cve~ont.
~nothor ob~oct ot tho invention is to provido a grou~d h~st

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e~ahanger Or the chsracter de~¢ribed having meun~ to auto~aticall~ fill ~ith a heat conducting medium an~ voids or air pocketa dsveloping bet~bon the ground and he~t exchanger surraces.
Another ob~ect of the inventlon iJ to provlde a ground heat exchanger of the character de cribed, ha ing meanJ ror the ~l~pl~ rqpl~D-ishing o~ the heat condlcting ~ediu~.
~ nother ob~ect of the inrention is the pro~is~on Or a h~at e~changer o~ the character d cribed, in ~hich the ~oid ~illing heat condlcting ~ediu~ i~ a thermal gres~e wh~ch ooat~ the heat e~ahangor ~ur~ace~ snd pre~enta lts rustln2.
The ~oregoing and other ob~ecta of the in~ention ~ill beco~o more appsrent durlng the ~ollo~lng disclo~ure and br referring to the drs~ngs, in ~hlchs Figure 1 ia a perspocti~e ~le~ Or the s~s~mbly o~ the heat e~ohangsr unit Or the i~vention;
Figure 2 i8 a partlal cross-Jection, takon along lino 2-2 Or Figure 1 Figuro 3 i~ a partial plan ~ection, tak~n along line 3-3 Or Figure 2 Flgure~ 4, 5, nd 6 re partial cro~-soctlons Or the he~t ox~haDger plato and coil in accordanco ~ith throe di~rerent ~bodi~e~toJ
snd Figure ? ~8 8 pl n ~iew Or a prorsrred rr ngo~ent of the nuld circulating coil ~hich i~ part o~ the heat oxchangcr pl~te ot tho ~n~ention.
In the dr~lng~, like rereronce ch~racters lndic~to liko el~o~t~
throughout.
Tho ground heat e~chaDger in accordan¢e ~ith the in~entlon i8 generallr indicated at 1 and co~pri~eJ an elongated reotsn~lar ~lat ~et l platb 2 and a pair o~ upright end tube~ 3, oa¢h ha~ing a verti¢ lly oxtending sllt 4 in the region ot it~ lo~er end portion The sllt 4 ba~ ~ubatantially tho hoight o~ the plate 2 and recei~es the end of the plato~ ~o that the latter o~tend~ ~ithin the tubo 3, ~9 ~ho~n i~ ~igure 3.
Sllt ~ h J at inter~al~ a plurality o~ in~ard}y o~tending ~ingcrs 5 equally spaced ~long the longth o~ each edge o~ the slit aDd slidsbl~

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3l~3~ f~
engaging tho oppo~lte sur~aces of the plato 2, Slit 4 between the fingers 5 de~lnes aperture~ 6 on sach side of the plate 2, th~ ~pcrtol~
being in c~mmmication with the inslde of the tube 3. The plate 2 bet~een tubes 3 carries a fluid circulating coil 7 e~tending over the entire ~r-face of the nlate and connected at its ends 8, into the circuit o~ a heat pu~p used as a heating and/or oooling ~y~tem for a house or the like.
3ach tube 3 is filled with a ~lowable heat conauctlng mediu~ 9, whlch i~
maintained under constant pressure within the tube 3 by ~eans o¢ a ~eight 10 freely slidable ~ithin the tube 3 and restinB on top of ~ho ~odiu~ 9.
The pre~sure exorted by the weight 10 ia Ju~lclent to e~trudb the ~ediu~ 9 through ap~rtures 6 aloDg the plate ~urface~. Plate 2 i~
adapted to be burlod in the ground a in a ver~lcal plane ~ith the upri3ht tube~ 3 e~teDding above the top ~dge o~ the plato to ter~inato at tho grou~d Jurrace. ItJ open end i~ normally olosed by a r~o~ablo cap 11 to ~hi¢h a rope, or ¢able 12, i~ attached and loo~ly e~toDds ~ithin tho tube 3 to be attached at lt~ lower end to the welght 10. ThuJ, the ~eight can be removed ~rom the tube and the tube rerilled with the tharaal ~ediu~
9, wheDo~er deaired. The bottom ena ar each t~be 3 is closed.
Nediu~ 9 18 prererably a greaso, such a~ lubricating greasa used in car~, cont d ning a heat-conducting ~otal in powdored for~. Tho grealo ~ay bo ~ Jilicone grease, su¢h a~ the sillcone greaJo ~snu~actured b~ Do~ Ch~elcsl~ Iimited, and containing copper o~ide in powdered ~or~
diaper~od tbrou8hout the grease. This is a so-called th~r~al ereaso or heat-conducting grease~ which ha~ a coefrlcient Or heat conaucti~i~y X ot .43, a~ co~pared to tbe nor~al oarth conauctivi~y of .oe to 1.4. The X
~actcr ~bo~e ~entionod is de~igned in ter~ Or BT~ trans~itted per ~q~are foot surface area per inch thickness.
Rerore burying the plate 2, both its surrace~ are entlrely coated with the ther~al grease and, once buried, the tubes 3 are rilled with a ther~Ql grease. During use, any air pocket which de~elopJ betw~o~
the plate and the earth i~ quiokly rilled wlth the pressurized ther~al greaJe being estruded through the apertureJ 6 of the tube~ 3 and the greaJe noving ~long both ~sces of ths plate to rill the void~ or ~r : '

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pockets. ~ t~
It has been calculated that an air space of only 1/8 of ar inch separating the plate surface from the eartl~ wlll reduce the heat exchange efficiency of the heat exchanger at least five times For instance, a heat exchanger normally designed to exchange 100,000 BTUs will thus only have 20,000 BTUs per hour.
It has been found that, even after only six months' operation, such air pockets are formed over substantially the entire plate surfaces. This is due to ground movement with freezi and defreezing and with the variation in the operating temperature of the heat exchanger which is as much as 100F. between winter snd summer operation. Under this temperature variation, the plate 2 can expand and contract to a total amount of ~" over a length of about 24', whlch is the length necessary for this plate to have supposlng a 3' width, to handle the heat exchange load of a heating pump designed to heat and cool a normal size house. This contraction and expansion is simply taken care of by the plate moving out into the end upright tubes 3.
The thermal grease, naturally, also protects the plate against oxidation and eliminates another heat exchange barrier, th plate being normally made of copper or an alloy of aluminum and zinc.
In summer-time, heat dries the earth and, thus, lt may be necessary, as i8 known, to wet the earth surface in the region Of the heat exchanger, for instance by means of a perforated water spinkler tube 1~ connected to a water supply by a pipe 14, in turn provided with an electro valve 15 automatically controlled by a humidity responsive transducer 16 buried in the ground.
Whenever the earth is too dry, the pipe 14 will discharge water to wet the earth around the heat exchanger 1. In winter-time, the humidlty of the earth migrates towsrds the plate 2 ant no such watering is neeted.

-5-- . : :. , The fluid medium circulatlng coil 7, the fluid medium being for instance Freon, as commonly used in refrigerstlng 8y8t~

can take different forms, as shown in Figures 4, 5, and 6. The coil 7 may consiRt simply in a pipe 17, of copper, alumlnum or the like, or steel, directly welded to one side of the plate 2 a~
by weldlng 18.
As an alternative, a pipe 17', formed as a coil, can be sandwiched between two half plates 2' spot-welded together betwe~

the pipes and bent to form a corrugated cross-section, as shown in Figure 5.

As another alternative, the pipes could have helicoi!dal flns lnside the tube, to increase the heat transfer between the fluit and the plate.
As a further alternatlve, the pipes 17 or 17' are completely ellmlnated and two half plates 2", of corrugated cros~
sectlon, are ~uxtaposed and spot-welded together, leaving pa~sage 20 for the heat exchange fluid 21.
The coil can have any desired path, for instance a simple zlgzag path, as shown in Figure l; but it is preferred to design the coil 90 aR to have the path shown in Pigure 7, including two sets o~ parallel paths, so connected that substantially equal fluld flow wlll occur in each set and also in each leg of the set the system being 80 arranged that substantially the same length :
of flow in each path and, consequently, the same resistance to flow is encountered in each path.
More speciflcably, there are two sets of parallel tubes 2 and 24 respectlvely, disposed side by side, along the length of the plate 2. The tubes of both sets are of equal length. The common inlet tube 25 is bent back at 26 into a U to form a leg 27 which acts as a manifold for the tubes 23 of the first set.
The8e tubes discharge in a common outlet manifold 28, which forms a branch parallel to the outlet common tube 29 and communicates therewith at 30.

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1~611r~;~
The arrangem-n~ o~ the ~econd ~et of tube~ 24 1~ rever~ed namely: the inlet manifold 31 forms a slde branch of the common inlet tube 25 and i8 parallel to the leg 27 thereof and communlc~
therewith at 32 at one end of the inlet manifold 31, while the pipes 24 have their outlet in direct communication with the common outlet tube 29.
The arrangement is such that the path through anyone of t~
tubes 23 and 24 is equal, starting from the common inlet point 32 to the common outlet point 30. Obviously, the diameters of the tubes 23 and 24 are the same and the diameter of the leg 27, outlet tube 29, outlet manifold 28 and inlet manifo~d 31 is also the same.
From the foregoing arrangement, a parallel path system i~
obt8ined for lncreased fluid flow and, at the same time, the ~ :
flow rate in each tube 23 and 24 is substantially the same for ::
uniform heat exchange efficiency over the entire surfaces of the plate 2.

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1- A ground heat exchanger operatively comprising a plate of heat-conducting material having a pair of opposite lateral edges and carrying a fluid circulating coil arranged in the plane of said plate and in heat-conducting relation therewith, said coil adapted to be connected at its ends to a circuit con-taining a fluid which is to be in heat exchange relationship with the ground, a pair of tubes each having a longitudinal slit extending through the wall thereof, and each having one of said opposite lateral edges of the plate slidably engaged therein, the walls of said tubes providing apertures communica-ting the interior of said tubes with the opposite outer sur-faces of the plate, and a flowable heat-conducting material operatively contained in said tubes and outwardly flowable under pressure through said apertures against the opposite outer surfaces of said plate and filling spaces and gaps eventually occurring between said plate and the surrounding ground.

2- A ground heat exchanger as claimed in claim 1, wherein pressure means are provided to maintain said flowable heat conducting material under pressure.

3- A ground heat exchanger as claimed in claim 2, wherein said pressure means include a weight freely resting on top of said material within said tube.

4- A heat exchanger as claimed in claim 1, wherein said tubes extend as substantially right angles to and have one end located above one of the longitudinal edges of said plate, said tubes being open at one end.

5- A heat exchanger as claimed in claim 4, wherein said tubes are upright and open at their top end, further including a weight in each tube, freely resting on top of the material in the tube, a cap removably closing said top and rope means attaching said cap to said weight.

6- A ground heat exchanger as claimed in claim 1, wherein each slit is wider than the thickness of said plate at the end portion of said plate entering said tube, the slit edges forming inwardly and oppositely directed fingers slidably engaging said plate end portion, said apertures being defined by the portions of said slit between said fingers.

7- A ground heat exchanger operatively comprising an elongated heat exchanger plate adapted to be disposed in a vertical plane within the ground, a pair of upright tubes each having an upper end portion outwardly extending relative to the ground and a lower end portion provided with a longitudinal lateral slit extending through the wall thereof, slidably re-ceiving an associated end of the plate, and allowing shifting of the plate in the corresponding slit with respect to the tubes upon contraction and expansion of the plate, each slit forming apertures communicating the inside of the tube with the opposite outer surfaces of said plate, a fluid circulating coil carried by said plate in the plane thereof and extending substantially coextensive and in heat-conducting relation with said plate, said coil adapted to be connected at its ends to a circuit containing fluid which is to be in heat exchange relationship with the ground, a thermally conducting and flow-able grease-like material contained in said upright tubes, and pressure means in the upper end portion of said upright tubes urging the material in said tubes toward outward flow through said apertures against said opposite outer surfaces to fill spaces and gaps eventually produced at the interfaces of said plate and ground upon contraction and expansion of the plate.