CA2827295A1 - Control for geothermal heating system - Google Patents

Abstract

A geothermal energy transfer system has a heat transfer loop associated with a heat pump and a heat absorption loop to circulate fluid through an energy source, such as the ground or body of water. The loops are connected through a reservoir and each loop has a circulating pump to circulate fluid through respective loops. The flow rates of the pumps are selected to optimise energy transfer in each loops and differences in the flow rates are absorbed in the reservoir.

Description

1 CONTROL, FOR GEOTHERMAL HEATING SYSTEM

4 [0001] The present invention relates to geothermal energy transfer systems.
SUMMARY OF THE INVENTION
6 100021 It is well known to use a heat pump to transfer energy between a consumer of 7 energy, such as a building, and a source of energy such as the surrounding environment. The 8 heat pump uses a closed cycle that passes a refrigerant through an expansion phase, that 9 requires the absorption of external energy, and a compression phase, which rejects energy to the building. In order to supply energy to a particular location, the rejected heat is transferred 11 in to the heating system of that location and the energy required to effect the expansion of the 12 refrigerant is absorbed from an external source. Similarly, when heat is to be extracted from 13 the location, the location acts as a source and supplies the energy for the expansion of the 14 refrigerant and the heat generated during compression is rejected to the surrounding environment that acts as a consumer.
16 100031 The environment may be the air itself. as is the case with traditional air 17 conditioning units or heat pumps. However, such an arrangement has a poor efficiency due 18 to fluctuations in the air temperature.
19 100041 A preferred external source has a substantially constant temperature and the ground or large body of water are typically used. It is therefore known to provide a heat 21 exchange loop between the heat pump and such a source so that heat may be absorbed in to 22 the loop to supply energy to the heat pump or may be rejected from the loop to remove 23 energy from the heat pump. The loops are typically an extensive run of pipe containing a 24 saline, glycol or ethyl alcohol based heat exchange fluid. The pipe is buried in a trench between one or two meters beiow the normal surface, At that depth, the earth is at a 26 substantially constant temperature and provides an energy source to either provide energy to 27 or absorb energy from the heat transfer fluid because of the temperature differential between 28 the heat exchange fluid and the surrounding.
29 100051 Where available, a large body of water may be used as the energy source. The heat transfer loop is placed in the water and heat transfer fluid circulated through the loop.

1 100061 The heat exchange loop is typically closed to isolate the heat transfer fluid from 2 the environment. To compensate for losses of fluid and changes in the condition of fluid, a 3 flow centre is placed in the heat exchange loop to subdivide the heat exchange loop in to a 4 heat transfer loop and a heat absorption loop.
100071 In a non-pressurized system, the flow centre acts as a reservoir for heat transfer 6 fluid. In a pressurized system, a dedicated reservoir is not provided as the system is typically 7 charged with air after tilling. In both applications, the flow center is usually placed between 8 the loop that passes fluid through the heat pump (the heat transfer loop) and the loop that 9 passes fluid through the ground or water loop (the heat absorption loop).
A pump circulates the heat transfer fluid through the heat transfer loop and returns it to a manifold from which 11 the heat absorption loop is supplied.
12 100081 These arrangements typically size the circulating pump to maintain a turbulent 13 flow through the heat transfer loop. However, such an arrangement has been found to 14 introduce a loss of efficiency in the overall performance of the energy transfer system.
100091 Tt is therefore an object of the present invention to obviate or mitigate the above [6 disadvantages.
17 100101 In general terms, an energy transfer system includes a first loop to circulate fluid 18 through a heat pump and a second loop to circulate fluid through a geothermal energy source.
19 Each of the loops is connected to a flow center to provide a reservoir of fluid for circulation.
A respective pump is connected in each of said loops to establish respective flow rates of 21 fluid in each of said loops, with balance flow being provided by the flow center.

23 100111 Embodiments of the invention will now be described by way example only with 24 reference to the accompanying drawings in which:
100121 Figure 1 is a schematic representation of an energy transfer system;
26 100131 Figure 2 is a perspective view of a flow center;
27 100141 Figure 3 is a schematic representation of flow through the flow center of Figure 2;
28 100151 Figure 4 is a view, similar to Figure 2 of an alternative flow center;
29 10016] Figure 5 is a schematic representation of flow through the flow center of Figure 4:
[0017] Figure 6 is a further embodiment of the energy transfer system;
_ , _ 1 100181 .. Figure 7 is a side elevation of a further embodiment of flow centre:
2 [0019] Figure 8 is a section on the line VIII ¨ VIII of Figure 7:
3 100201 Figure 9 is a section on the line IX ¨ IX of Figure 8.
4 100211 Figure 10 is a flow chart showing a first control strategy Ibr operation of the heating system of figure 1, 6 100221 Figure 11 is a flow chart showing a second control strategy for operation of the 7 heating system of figure 1 in a heating mode, and 8 100231 Figure 12 is a flow chart showing the second control strategy for operation of the 9 heating system of figure 1 in a cooling mode.
DETAILED DESCRIPTION OF THE INVENTION
11 100241 Referring therefore to Figure 1. a building 10 has a heating and cooling system 12 12 to distribute heat through the building or to remove heat from the building. The heat 13 distribution system may be an air circulating system. or a water circulating system that 14 transfers heat between different areas of the building and a heat source. The heating and cooling system 12 includes a heat exchanger 14 that cooperates with a heat exchanger 16 to 16 transfer heat between a heat pump 18 and the building 10.
17 [00251 The heat pump 18 is of conventional construction and includes a heat exchanger 18 20 connected in a refrigerant loop 19 to the heat exchanger 16 through a throttle valve 22 and 19 a compressor 24. Expansion of a refrigerant through the throttle valve 22 causes heat to be absorbed in to the refrigerant and compression of the refrigerant through the pump 24 causes 21 heat to be rejected.
22 [0026] The heat exchangers 1 6 and 20 absorb or reject the heat depending upon the mode 23 of the operation of the refrigerant cycle. A reversing valve 23 reverses the flow direction to 24 allow the heat pump 18 to function in a heating mode to supply heat to the building, or a cooling mode in which heat is extracted from the building 10. .A thermostat 27 and controller 26 25 is incorporated in to the system 12 to control operation and maintain the required 27 temperature in the building 10, 28 [0027] The heat exchanger 20 cooperates with a further heat exchanger 26 to transfer heat 29 between the relhgerant loop 19 and a heat transfer loop indicated at 28.
The heat transfer loop 28 includes a pump 30 that circulates a heat transfer fluid, typically a saline, glycol or 31 ethyl alcohol based mixture. through a return pipe 32 and a supply pipe 34.
_ 1 100281 The pipes 32. 34 arc connected in series with a pair of header pipes 36, 38, one of 2 which, 36 acts as a supply and the other. 38 acts as a return. The header pipes 36, 38 that are 3 connected to opposite sides of a heat transfer unit 40 to provide a heat absorption loop 41.
4 The heat transfer unit 40 may be a loop or multiple loops connected in parallel, to the header pipes 36, 38. The loop is buried in the ground or under water, or. preferably.
is a self 6 contained heat transfer unit of the type more fully described in United States Patent 7 Application 61/367,166, and the contents of which are incorporated herein by reference. The 8 loops may also include loops to auxiliary heat consumers, such as a pool or spa, if required 9 and as shown in figure 6. with a suffix `13' for clarity. A pump 42 is connected in the header pipe 36 to circulate fluid through the heat absorption loop 41 defined by the pipes 36,38 and 11 the heat transfer unit 40.
12 100291 A flow center 44 is connected in parallel with the pipes 36, 38 and 32, 34 through 13 stub pipes 46. The flow center 44 is seen more fully in Figure 2 and, in its simplest form.
14 comprises a cylindrical housing 50 sealed at its lower end. A cap 52 with a vent valve 54 is fitted to the housing 50 to provide venting to accommodate expansion and contraction of 16 fluid in the fluid circulation loops 28,41. The stub pipes 46 are connected on diametrically 17 opposite sides of the housing 50. In the case of the pressurized configuration, the vent valve 18 54 is replaced with an air valve allowing the system to be pressurized.
The Cap 52 is 19 installed as to seal the system.
100301 In operation, the heat transfer loop 28 and the heat absorption loop 41 are filled 21 with fluid through filling the housing 50. The vent 54 allows for venting of air from the 22 system and a cap 52 for adding/replenishing fluid during/after initial installation. The pumps 23 30 and 42 operate to circulate fluid through the heat exchanger 26 and through the heat 24 exchanger 40. The pump 30 is sized to provide a turbulent now through the heat transfer loop 28 at a rate that maximizes heat transfer between the heat exchangers 26 and 20. The 26 rate required to attain optimum heat transfer will vary in different design conditions but for a 27 supply of fluid at a particular temperature an optimum rate can be determined. from operating 28 characteristics of the heat pump 18.
29 [0031] For a given heat transfer rate into the building 10. and with a design temperature of the heat transfer fluid and the known characteristics of the heat exchanger 26, an 31 appropriate flow rate of the fluid passing through the heat exchanger 26 can be determined.
32 Frequently. the design temperature and flow rates are specified by the manufacturer of the 33 heat pump. For example. with a Geostar Model GT064. a nominal heat transfer o127100 Btu/hr is specified with a flow rate of 16 US gpm and an assumed entering water temperature 2 of 20 F. Correction tables are provided to compensate for different entry water temperatures 3 (EMI
4 [0032] Similarly, the pump 42 is sized to provide a circulation through the heat absorption loop at a rate that optimizes the transfer of energy between the heat exchanger 40 6 and the surroundings. Again this will depend upon the particular design conditions but an 7 optimum flow rate can be attained, taking into account the temperature of the heat source, the 8 thermodynamic properties of the fluid and the heat transfer characteristics of the heat transfer 9 unit 40.
100331 For the same thermal load, the heat absorption rate from the surroundings through I the heat exchanger 40 may require a different flow rate through the heat absorption loop 41 to 12 that in the heat transfer loop, 28.
13 [0034] The pumps 30, 42 can then be sized to provide those respective flow rates.
14 Preferably, each of the pumps 30, 42 are variable flow rate pumps that can be adjusted to increase or decrease the flow rate to suit particular control strategies.
Alternatively, one of the 16 pumps 30, 42 may be a fixed capacity and the other variable to permit adjustment of the 17 respective flow rates. If a steady condition is anticipated then both pumps may be of fixed 18 flow rating for the anticipated conditions in the respective loop.
However, as will be 19 explained more fully below, the ability to adjust the flow rates may be used advantageously in the operation and control of the heating and cooling system 12.
21 100351 As illustrated in Figure 3, the flow center 44 operates as a reservoir to receive 22 excess fluid from the heat absorption loop 41 and supply a balancing fluid back into that loop 23 through respective ones of the stub pipes 46. Typically, it is found that the flow rate through 24 the heat absorption loop 41 is greater than that required in the heat transfer loop and so the flow center 44 receives fluid from, and delivers fluid to. the heat absorption loop 41. In 26 Figure 3. the flow required through the heat transfer loop 28 is denoted by Y and the flow 27 rate required in the heat absorption loop 41 is X + Y. The flow center 44 thus receives X
28 gallons per minute from the heat absorption loop 41 through one of the stub pipes 46 acting 29 as an inlet and similarly delivers X gallons per minute to that loop 41 from the other stub pipes 56 acting as an outlet to supply the pump 42. In one installation with an eighteen 31 kilowatt heat load, it has been found that a flow rate through the heat absorption loop 41 in _ 5 _ I the order of 23 gallons per minute is optimum with a flow rate through the heat transfer loop 2 28 of 16 gallons per minute.
3 100361 Those flow rates will of course depend upon the nature of the heat exchanger 40 4 and the temperature of the environment T in which the heat exchanger 40 operates.
100371 Fluid circulation in the heat absorption loop 41 may also enable a selective 6 precooling or preheating of the fluid in the flow center 44. For example, when heating a 7 dwelling, the fluid can be preheated in the flow center 44 from fluid circulation in the heat 8 absorption loop 41 and when cooling a dwelling, the fluid can be precooled in the flow center 9 from fluid circulation in the heat absorption loop 41.
100381 A further embodiment of flow center is shown in Figures 4 and Sin which like 11 components will be denoted with like reference numerals with the suffix a added for clarity.
12 Referring there-I-bre to Figure 4. the flow center 44a includes a pair of cylindrical housings 13 50a1 50a2. Each of the housings has a cap 52a and vent valve 54a. A
balancing tube 60 14 interconnects the upper end of the housings 50a to allow for fluid to flow between the housing.
16 100391 Each of the housings 50a receives the return from one loop and the supply to 17 another of the loops. Thus, the housing 50a1 receives fluid returned from the heat absorption 18 loop 41a through the pipe 38a and supplies fluid to the heat transfer loop 28a. Similarly, the 19 housing 50a2 receives the return through pipe 38a from the heat transfer loop 28a and supplies fluid through the pipe 34, 36a to the heat absorption loop 41a.
21 100401 The interconnection of the units is shown in Figure 5, from which it will be 22 appreciated that the differential fluid returned from the heat absorption loop 41a through the 23 pipe 38a may flow from the housing 50a1 through the bridge 60 to the housing 50a2 to 24 supplement supply to the pump 42a. Again, the pumps 30a and 42a will be sized to accommodate the optimum flow rates through the respective transfer loops.
26 100411 A further embodiment of flow centre is shown in Figures 7 through 9 in which 27 like reference numerals will be used for like components with a suffix added for clarity.
28 Flow centre 44c can be used interchangeably with the flow centres 44.
44a, 44b shown in the 29 previous embodiments. The flow centre 44c has a cylindrical housing 50e which is encompassed in an insulating foam 70 and encased in an outer easing 72. A cap 52c is 31 secured to the housing 50e and has an upstanding square boss 76. A
retaining bracket 78 is 32 fitted over the cap and has a square hole 80 that fits around the boss 76. The bracket 78 is I secured to the easing 72 by bolts 82 and thereby tamper proofs the cap by preventing 2 unauthorized removal. The bracket 78 may also be used.. after release of the bolts 82 and 3 inversion of the bracket 78. as a wrench to remove the cap 52c, 4 100421 A pair of cross tubes 90, 92 extend diametrically through the housing 50c and are sealed at the intersection oldie tubes with the housing 50c. Each end of the tubes 90, 92 is 6 threaded to provide a connection with respective ones of the pipes 32c.
34c, 36c, 38c, as will 7 be described in more detail below. Each of the cross tubes 90, 92 has an array of holes 94 at 8 its midpoint. The holes 94 are evenly distributed, around the circumference of the tube 90, 92 9 and in the embodiment shown there are four holes 94 equally spaced about the circumference. A greater or lesser number of holes 94 may be provided depending upon the 11 particular circumstances, The aggregated cross section of the holes 94 is the same as or 12 slightly greater than the cross section of the corresponding tube 90.
92.
13 10043j As can be seen in Figure 7, a sight glass 96 is provided on the exterior of the flow 14 centre 44c to provide an indication of the level of fluid contained within the flow centre 44c.
Conveniently, a spectrum indicating different colors of fluid corresponding to the 16 approximate composition of thesolution being circulated through the flow centre is provided 17 alongside the sight level for easy reference and routine maintenance.
18 100441 The tube 90 is connected between the return pipe 38c of the heat absorption loop 19 41c and the supply pipe 340 of the heat transfer loop 28c so that one end acts as an inlet from loop 41c and the other as an outlet to loop 28. The tube 92 is similarly connected between 21 the return pipe 32e of heat transfer loop 28c and the supply pipe 36c of the heat absorption 22 loop 41c to provide respective inlets and outlets.
23 100451 In operation, fluid from the heat absorption loop 41c is delivered by the pump 42c 24 to the tube 90 where it flows from the return pipe 38c to the supply pipe 34c. Similarly, flow in the heat transfer loop 28c from the pump 30e is delivered to the tube 92 from the return 26 pipe 32c to the supply pipe 36c. of the heat absorption loop 41c. The pumps 30c. 42c have a 27 differential flow rate so that typically the flow delivered to the tube 90 from the absorption 28 loop 41c is greater than the flow rate extracted from the tube 90 by the transfer loop 28c. The 29 balance of the flow is discharged through the holes 94 in to the reservoir provided by the interior of the housing 50c.
31 100461 Similarly, the flow required from the tube 92 to supply the absorption loop 41c is 32 greater than that delivered by the return pipe 32c of the transfer loop 28c and therefore 7 _ 1 makeup fluid is provided through the holes 94 in the tube 92 from the housing 50c. The 2 holes 94 therefore provide for a cross flow between the heat transfer loop and absorption loop 3 to maintain the desired flow rates as determined by the respective pumps.
4 109471 The effect of the delivery of the fluid in the return pipe 38c to the tube 90 is to supply it directly to the inlet to the pump 30c, effectively supercharging the inlet to pump 30c 6 to a positive pressure, to ensure that it is operating under optimum conditions. The pump 30c 7 is not required to operate at a reduced inlet suction pressure, but at the same time ensures that 8 the required flow rates between the two loops is maintained to provide optimum efficiencies.
9 109481 The controller 25 is used to control operation of the heating system 10 and may be a simple thermostat interacting with the heat pump 18 to switch pumps 30, 42 on or off.
11 I Iowever, as explained in greater detail below, the controller 25 may also be used to modulate 12 operation of the pumps 30, 42. The pumps 30,42 may be fixed flow rate pumps, or one 13 pump may be variable and the other fixed. In the preferred implementation. each of the 14 pumps 30, 42 is a variable flow pump to provide differing flow rates in the respective loops 28, 41. An example of such a pump and a suitable controller is a Danfoss VLT
micro drive ¨
16 FC51. The controller 25 provides a variable reference fiequeney to the motor of the pump 17 which adjusts the rotational speed of the motor to match the reference frequency. Variable 18 flow rates may also be provided by using a pair of pumps connected in series and selectively 19 switching one of the pumps on or off.
100491 The controller 25 in a preferred embodiment, is a programmable controller havin.g, 21 outputs, namely Y1. Y2, and 0. Outputs Y1. Y2 control operation of the compressor 24 with 27 Y1 calling for a first intermediate load, typically 67% of compressor capacity, and Yl calling 23 for a full, 100% load. The output 0 controls reversing valve 23 to switch between heating 24 mode and cooling mode.
[0050] In general terms, the output Y! is used to provide a reference frequency that sets 26 the pump 30 at an intermediate flow rate, to match the required flow rate through the loop 28 27 when the compressor 24 has an intermediate load. and to maintain the pump 42 at a 28 corresponding predetermined flow rate in excess of pump 32. Upon an output Y2 being 29 received, when the compressor is conditioned to full load, the output of each pump 30, 42 is correspondingly increased to match the flow rates to the full load operating condition of the 31 system.
- s -1 100511 The flow centre 44c of Figure 9 facilitates initial setup of the relative flow rates in 2 the heating and cooling system 12, which, in turn, enhances control of the system 12 after the 3 initial setup.
4 100521 During initial setup. assuming a single. variable flow pump 30c is used in the heat transfer loop 28c. the pump 30c is set to an initial intermediate flow rate, typically that 6 specified by the manufacturer of the heat pump 18. The flow rate is determined by 7 measuring the pressure drop across the heat exchanger 26c, after applying a correction factor 8 to accommodate for varying temperatures of the fluid in the loop 28c. A
first set point xl of 9 the reference frequency is established for the required flow rate of pump 30c. With the flow rate in loop 28c established, the flow rate of the pump 42c is adjusted to match that of the 11 pump 30c. This is facilitated in the flow centre 44c by reducing the level of fluid through the 12 drain port provided on the sight glass. so that the fluid is level with the upper cross tube 90.
13 At this level, the relative flow rates in the loops 28c, 41c, can be observed from the flow 14 through the cross ports 94. When the flows are equal. there is no net flow across the ports 94 and the flow rates arc balanced.
16 10053] Upon attaining a balanced flow, the pump 42c is adjusted to increase the flow in 17 the loop 41c to achieve a nominally increased flow rate. It has been found that an increased 18 flow rate of 5% - 10% is satisfactory for typical installations. A first set point zi of the 19 reference frequency is established for the pump 42c, [00541 The demands of the heat pump 18 with the compressor 24 operating at full load 21 require an increased flow rate in the loop 28c. Accordingly, a second set point, x/. is 22 established lbr the increased flow rate required from pump 30e, either empirically or by 23 measuring the pressure drop across the heat exchanger 26c as specified for a full load, and a 24 corresponding set point zi established for the pump 42e. This may be done by observing net flows in the flow centre 44 or by extrapolation from the previous settings.
26 100551 With the initial conditions established, the fluid is replaced in the flow centre 44.
27 The controller 25 may then be used to control the pumps 30, 42 in normal use.
28 100561 In one embodiment of the control strategy, as shown in Figure 10, the outputs of 29 controller 25 are used to adjust the flow rates from the pumps 30c. 42c, in the required ratio, to meet the demands of the system 12.
31 [0057] The output 0 determines the mode, heating or cooling, and upon the thermostat 32 calling for an increase in temperature (in the heating mode), or a reduction of temperature (in .5.

1 the cooling mode). an output Y1 is applied to the compressor 24 and each of the pumps 30, 4"2.
3 [0058] The compressor 24 operates at the intermediate load (e.g.
67%) and the pumps 30.
4 42 circulate fluid at the rates determined by the set points x1. z[
respectively.
100591 If after a set period. 30 minutes to 120 minutes, the thermostat has not attained its 6 required temperature, or if the thermostat calls for an immediate increase in temperature 7 greater than 2 C. the controller 25 provides outputs Y, to the compressor 24 and each of the 8 pumps 30c, 42c.
9 100601 The compressor 24 increases to full load and the output of pumps 30c, 42c. is increased to set points x7). z.:2 respectively. The system 12 operates at these conditions until 11 the required temperature is reached, or a further time limit is reached and the auxiliary heat is 12 switched on by output W.
13 100611 Upon attainment of the required temperature, the controller 25 removes the l4 outputs Y1 Y2 and W. and the system returns to an at rest condition.
with the compressor and the pumps 30c, 42c switched off.
16 [0062] By matching the flow rates of the pumps 30c, 42c, to the demands of the 17 compressor, the operation of the overall system may be optimized with the flow rates in the 18 respective loops maintained in the required ratio.
19 [0063] It will be appreciated that the relative flow rates of the pumps 30c, 42c may be adjusted to suit a particular installation and system configuration with the set points for each 21 pump chosen to provide the optimum flow rates.
22 [00641 The flexibility provided by the controller 25 and the use of a pump in each ofthe 23 loops 28c, 41e. may be utilized to further optimize the operation of the system 12.
24 [0065] As shown in the schematic of Figure 11 and 12, different operating conditions are attained depending on the mode of operation.
26 100661 In a heating mode. i.e. one in which heat is transferred in to the building 10, the 27 set points z1. z, are selected so that the relative flow rate of the pump 42c is increased beyond 28 that needed to balance the flows in each loop. Typically a flow rate of 110% of that of the 29 pump 30c is found satisfactory. although flows in the range 105% to 125%
may be used. .rhe increased flow from pump 42c is transferred through the flow centre 44c between the cross 31 tubes 90, 92, and is used to heat the fluid returning from the loop 28e as it enters the loop 41.
- I-1 100671 .[he fluid delivered through loop 41c to the loop 28c will have a temperature 2 approaching that of the ground source.
3 100681 The fluid is transferred at that temperature to the inlet 34c. of the loop 28c and 4 delivered to the heat exchanger 26c. Heat is extracted from the fluid for delivery to the building, resulting in a significant reduction of the temperature of the fluid. The fluid is 6 returned at that temperature to the flow centre 44c. where it is delivered through the cross 7 tube 92 to the supply header 36c.
8 10069] Because of the reduced temperature, there is a risk, in some operating conditions, 9 that localized freezing may occur. particularly on the surface of the header 36c and heat exchanger 40c, that impairs heat. transfer. This is mitigated by the admixture of the excess 11 flow from the pump 42c with the return flow from the loop 28, which elevates the 12 temperature of the fluid in the loop 41c. With a flow rate of the pump 42 at 110% of pump 13 32õ and a fluid temperature at around -5 C, it has been found that the overflow and admixture 14 can elevate the fluid temperature by 2 C. sufficient to mitigate the surface freezing.
100701 When operating in a cooling mode, i.e. when heat is rejected to the ground source.
16 as shown in Figure 12, the temperature of returning fluid is elevated.
In this situation, 17 admixture with the excess flow will reduce the temperature and reduce the rate of dissipation 18 across the heat exchanger. which is undesirable. Accordingly, the pump 42 is controlled so 19 that the flow differential is reduced and pump 42 is set to operate at a slightly greater flow rate. i.e. 2% greater than pump 32. In this case, the set points zi are selected to minimize 21 the cross over flow in the flow centre.
22 100711 The control strategy. therefore, operates the pump 42e to over supply the loop 28c 23 during heating mode to permit admixture, whereas in cooling mode the admixture is 24 minimized by matching the outputs of pumps 42c and 28c.
10072! During transient conditions, the variability of the flow rates may also he used to 26 advantage and coordinated with the operation of the heat pump 18. as also shown in the 27 schematics of Figures 11 and 12.
28 100731 Assuming the building 10 is at the required temperature. the controller 25 29 maintains the heat pump 18 inactive and both pumps 32. 42 off, i.e. no flow.
10074] When the controller 25 calls for heating, initially the fan and heat. pump 31 compressor associated with the building 10 is switched on as indicated as -C. on at 1_1". After _11 _ 1 a pre set delay. e.g. 5 seconds, a control signal Y1 is sent to the pump 30c to initiate flow in 2 the loop 28c at the rate determined by the set point xi. After a further delay. e.g. 20 seconds, 3 the control signal Y.) is applied to the pump 42 to operate it at its maximum flow rate, i.e. at 4 set point z2 and the pump 30 is maintained operating at the interinediate speed xi. The increased flow rate is accommodated in the flow centre 41 and is maintained for an initial 6 purge period, typically a period sufficient to provide a complete circulation of fluid in the 7 loop 41, in the order of 300 seconds. .A flow ramp up period of 30 seconds is provided to 8 avoid sudden changes. If preferred. a higher flow rate than the set point z, may he used for 9 purging. but it is convenient to use the set point 22.
100751 After the initial purge period, the control signal to the pump 42 reverts to Y1 and 1 I the output of the pump 42 will be ramped down over a period of 30 seconds, to set point zii 12 The pump 30 is switched on at set point x1 as the heating mode is selected, the set point zi 13 provides an over capacity providing admixture with fluid returning from loop 28.
14 100761 If the required temperature is attained, the control signal Yi is removed. The controller 25 asserts an output Y2 to the pump 42 for a shut down period.
typically 300 16 seconds, to maintain circulation in the heat transfer loop 41.
Thereafter, the flow rate is 17 ramped down and the pump 42 switched off.
18 10077] When the required temperature has not been attained after a preset interval, i.e. 30 19 ¨ 120 minutes. the output Y, is asserted to each of the pumps 32,42 and both operate at their maximum respective rates, as determined by set points x2 and Once the temperature is 21 attained, the pumps 32, 42 are shut down as described above.
22 10078] A similar sequence is implemented in the cooling mode. with the set point z.? of 23 pump 42 being the lower value that matches the maximum capacity of the pump 32.
24 100791 The independent operation of the two pumps 32. 42, may therefore be used to establish optimum flow rates in each loop for steady state and transient conditions. without 26 impacting on the design conditions for the heat pump 18.
27 100801 It will he appreciated that the examples above are exemplary and other 28 combinations may be used to meet the particular design parameters of the system 12.
-

Claims (23)

1. A geothermal energy transfer system to transfer thermal energy between an enemy source and an energy consumer, said system comprising a first loop to circulate heat transfer fluid through said source, a second loop to circulate heat transfer fluid through said consumer, a fluid reservoir connected to each of said loops to receive fluid from and deliver fluid to each of said loops, a first pump to circulate fluid in. said first loop and a second pump to circulate fluid in said second loop.

2. The system of claim 1 wherein at least one of said pumps has a variable flow rate.

3.'The system of claim 2 wherein both of said pumps have a variable flow rate.

4. The system of claim 2 including a controller to control the flow rate of said pumps.

5. The system of claim 4 wherein said controller controls a heat pump thermally connected to one of said loops and, said flow rates are coordinated with the operation of said heat pump.

6. The system of claim 1 wherein each of said loops has a supply and a return and the supply of one of said loops is connected to the return of the other said loops.

7. The system of claim 6 wherein said reservoir is connected between the supply and returns of each loop to accommodate differing flow rates therein.

8. The system of claim 7 wherein the supply and returns are connected to respective inlets and outlets of said reservoir.

9. The system of claim 8 wherein said reservoir has a pair of inlets and a pair of outlets and said pumps are connected to respective pairs of said inlets and outlets.

10. The system of claim 9 wherein an inlet connected to one of said loops is connected to an outlet connected to the other of said loops.

11. The system of claim 10 wherein each of said inlets and outlets is in communication with said reservoir.

12. The system or claim 1 wherein the flow rates of said first and second pumps are different and said reservoir accommodates the differential in flow.

13. The system of claim 12 wherein at least one of said first and second pumps is adjustable for flow rate.

14. The system of claim 13 wherein both of said pumps are adjustable for flow rate.

15. The system of claim 14 wherein operation of said first and second pumps is controlled by a controller.

16. The system of claim 15 wherein said controller adjusts said first and second pumps between a first condition in which both pumps have an intermediate flow rate and a second condition in which both pumps have a flow rate greater than said intermediate flow rate.

17. The system of claim 16 wherein said flow rates are maintained in a predetermined ratio in both said first and second conditions.

18. The system of claim 17 wherein said rates may be varied depending on the operational mode of said energy transfer system_

19. A flow centre fig use in a geothermal energy transfer system. said flow centre comprising a reservoir to contain fluid, a first inlet for connection to a return of one loop and a supply of another to receive a differential flow through said loops, and an outlet for connection to a supply of said one loop and a return of said other loop to supply fluid to make up for a difference in flows in said loops.

20. A flow centre according to claim 19 wherein a pair of tubes extend through said reservoir to permit connection at opposite ends of said respective supply and return, said tubes having an aperture therein to provide respective ones of inlet and said outlet.

21. A flow centre according to claim 19 wherein a pair of reservoirs are provided and a conduit is provided to transfer fluid between said reservoirs.

22. A flow centre comprising a body defining a reservoir, a pair of tubes extending.
through said reservoir and having opposite ends for connection to respective pipes, and an aperture intermediate said ends to allow fluid communication between said tube and said reservoir.

23. The flow centre to claim 22 where said aperture is provided by a plurality of holes disposed about the circumference of said tube.