GB2190738A - Heat pump system - Google Patents

Abstract

An all weather, year-round heat pump system for northern climates incorporates a containerless in-earth heat storage means comprising a compact nest of small bore pipes buried in a trench or pit. The heat circulation fluid comprises an anti- freeze mixture and is operated in winter, even under the most demanding circumstances within a few degrees of the freezing point of water. A solar energy collector, owing to the controlled temperature operates without ice build-up on the collector. The heat storage means builds an icy mass about the pipe nest as heat is extracted, so that a very large amount of heat is available from a relatively small installation requiring little ground area, due to the utilization of the latent heat of fusion. <IMAGE>

Description

SPECIFICATION Heating System This invention is directed to a heating system, and in particular to a heating system incorporating a heat pump in combination with a solar energy collector and an in-ground heat storage system.

Heating systems incorporating heat pumps are well known. Probably the most commonplace is the air source heat pump which extracts heat from ambient air outside the premises to be heated and transfers it at higher temperatures to a heat exchanger within the premises being heated. This type of heating system is of a very limited use in a cold climate, such as Canada, owing to the fact that the efficiency of the system diminishes with the decrease in ambient temperatures.

One of the major attractions in using a heat pump; is the capability of obtaining Co-efficients of Performance (COP) well in excess of unity, even to a COP value in the 3 to 4 range under suitable conditions. The COP may be defined as the ratio of useful heat available to the load, relative to the energy required to operate the system. However, the COP falls to a value close to unity at lower ambient temperatures, in the freezing range, thus equalling direct electric heating in heating value so that up to the present, simple heat pump systems using ambient air have not been adequate for general use in northern climates such as Canada, but are generally used in such climates only in a heat supplementary role to an established heating system.

Heating systems using a heat pump in combination with a solar collector are well known.

Similarly, heat pump systems using a body of water as the low temperature heat source are well known and can be quite successful when the water resource is available, and is adequate in temperature and volume to meet the heat load.

Of the many combined systems, a further one worth mentioning is the type wherein a heat collector is buried under the surface of the ground, having water or other suitable fluid circulated therethrough, to remove heat from the ground. This system relies upon the sun's heat to directly recuperate the collector, mainly during the off season. Such a system requires a large area of ground and the ground heat collector is large and expensive.

Other known solar heating systems operate by capturing heat at end-use temperature, storing it as sensible heat in rock beds and the like.

The following comments relate to certain of the prior art heating systems found in patent literature; U.S. 3,254,702 THOMASON (1); provides a rock bin, including a water tank and air ducts; U.S. 4,134,544 THOMASON (11); provides a solar heating system and a water tank including a back-up boiler; U.S. 4,040,566 CHIARETTI; provides a solar panel with a speciality shaped cover for heating water, with heat transfer to an air circulator within the building.

U.S. 2,529,154 HAMMOND et al; provides a solar collector and water circulation to heat the ground heat exchanger, from which a heat pump extracts useful heat, the system relying upon maintaining the ground at reasonably high temperature values, by control of the circulation of the water. The system does not operate with a fall in ground temperatures.

U.S. 4,295,415 SCHNEIDER; provides a prefabricated concrete building, with solar heat in outer walls circulated to, and stored in building-augmented mass.

U.S. 4,341,204 ECKER; provides a heat pump having heat release to the evaporator, to prevent ice formation.

U.S. 4,246,887 CHRISTENSEN; heat recovered from furnace exhaust and from solar energy is stored in a fluid tank.

The adoption of the foregoing systems to use in a cold climate present such practical problems as to render them economically nonfeasible.

The present invention provides a system having a solar energy collector extracting useful heat from direct solar effect, also from air and from precipitation. The system employs a relatively low volume deep buried heat storage arrangement consisting of a nest of small bore pipes buried in earth without incorporating any container, and which does not rely upon direct solar recovery. In operation the system extracts heat from the solar energy collector, the heat circulating fluid functioning in winter, even under the most demanding circumstances at a temperature close to the freezing point of water, whereby the efficiency of the collector is significantly boosted owing to the extraction of useful heat energy from the total environmental contact with the collector, namely, solar heat, wind, rain and air moisture.The collected heat is upgraded by the heat pump and utilized to drive the heat load, in normal fashion. The heat pump would normally be located under cover within a conditioned space. Any excess available heat is circulated at collection temperature to the inground storage, ("storer") where, by utilizing the latent heat of fusion of water for producing a relatively small icy mass of saturated foreign soil within the ground, a large quantity of heat can be recovered, or in melting a portion of the icy mass by supplying the latent heat of fusion thereto, correspondingly stored.

Under adverse conditions when environmental heat is not available, e.g., for sub zero Calsius cold nights and cloudy days, some of the stored heat is removed and the volume of icy mass in the ground about the pipes of the pipe nest of the storer increases, as the latent heat is extracted from the saturated ground or body of water, if such is used.

It has been found that a small volume of ground, suitable to accept the build-up of a body of frozen soil and ice, can suffice to enable the working of the subject system in parts of Canada where previously reliance upon heat pump system other than for supplmental heating had not been feasible.

It has been found that with the in-ground storage system properly sized with respect to the solar energy collector that when these two components are operated as a permanent continuous source of thermal energy for the heat pump, a relatively small volume of ground can suffice to enable the heat pump to operate with a seasonable COP well in excess of unity and even in excess of 3 under Canadian climatic conditions, where the performance of other types of heat pumps whose source of thermal energy is environmental have not been able to obtain seasonal COP's of much greater value than unity, and where these other systems have in fact been forced to transfer to other heating means during severe weather when the requirement for heat was the greatest.

The present invention does not require a 100% back-up heating system but may reasonably be sized to supply total load required for the entire heating season.

Owing to the method adopted only a small volume of ground is required in which to locate a subject storer. In contrast, the prior art in-ground collector was a major undertaking involving a large area of ground and major earth moving and pipe laying equipment, with the need to use medium diameter pipe (e.g. 1 1/2 inches or greater). In the case of the present system it is possible to bury the nest of small bore pipes that comprise the storer quite deep in the ground, using means such as a back hoe to dig the necessary trench. It is also feasible to bury the storer many feet below the surface, and vertical burial in a suitable pit also is feasible and practical. In addition a water tank or a body of water such as a lake, well or pond can also be utilized.It has further been found that the subject storer can be fabricated from standard small bore pipe, namely 3/4 to 1 inch water piping, (usually plastic) in contrast to the prior art medium diameter arrangement, with consequent corresponding reductions in cost, and the sizing of associated mechanical equipment such as pumps.

Continuous in-ground storers operating at temperatures close to zero degrees Celsius (freezing) result in obtaining useful heat transfer to the storer from the ground. The most useful temperature range for the heat transfer for liquid comprises minus five degrees Celsius to plus ten degrees Celsius.

Certain further characteristics of the subject system and its method of operation are: 1) Operating the water-and-antifreeze heat circulating liquid medium during more severe weather at a temperature within a few degrees of the freezing point of water, such as within 4 degrees Celsius of freezing point.

(Higher media temperatures are possible during the milder periods of a typical heating season); 2) limiting the heat flux density in the storer to about 10 watts per meter of pipe length; 3) using in-ground pipe for the storer of approximately one inch internal diameter; 4) regulating the flow rate to maintain a temperature difference between the inlet and outlet of the storer at about 3 degrees Celsius.

As a consequence of operating the storer at a temperature close to freezing, the performance of a simple, unglazed collector is optimized, owing to the recovery of heat from; a) solar input; b) air and wind effect; c) latent heat of condensation of atmospheric moisture; d) sensible heat from rain; e) heat of fusion of atmospheric moisture without building up a layer of ice on the collector.

In operating the in-ground heat storer in the freezing range condition, thus causing the melting of the icy mass or the formation thereof by freezing of the earth surrounding the pipes of the pipe nest, both the volumetric and area heat storage requirement is minimized, in that heat is stored or collected as a function of the latent heat of fusion, and not the sensible heat of water. This leads to a very significant area reduction relative to a conventionai in-ground system.

This reduction in size requirement has enabled the storer to be sized together with the solar collector to provide a sensibly permanent continuous source of thermal energy for the heat pump to enable it to operate with seasonal COP's well in excess of 1 and even as high as 3 or more.

In addition to the foregoing summarized benefits, it is usually feasible to bury the subject heat storer below the frost level, in which case there is recovery of useful heat from the earth.

Certain embodiments of the invention are described with reference to the accompanying drawings, wherein: Figure 1 is a schematic arrangement of a solar storage heat pump system in accordance with the present invention; Figure 2 is a diagrammatic side view of a heat storage in-ground accumulator, and Figure 3 is a schematic side section view of the Fig. 2 accumulator.

Referring to Fig. 1, the system 10 has a solar collector 12, which may be of unglazed plastic, for purposes of economy. An inground storage means 14 comprising a nest of small bore pipes is connected by pipes 16, 18 to a circulation system 20 having a pair of circulator pumps 22, 24 and a heat exchanger 26.

The heat exchanger 26 provides low grade heat to a heat pump 28 for providing useful heat to a load such as a residence, (not shown).

Fig. 2 shows a diagrammatic arrangement of a deep buried heat storage means 14 comprising a nest arrangement of small diameter plastic pipe buried in a narrow trench 30 (Fig.

3). Typically, the trench may be seven to ten fee deep, to locate the storage means 14 below the frost line, to thereby receive useful heat input by direct transfer from the adjacent ground, and to enable the latent heat of fusion of the water within the soil in the region of the storer pipe nest to be available to the system, by the creation of a progressively increasing icy mass as heat is extracted.

The primary circulation system 20 utilizes a water based anti-freeze mixture.

In operation, under mild conditions, the heat storage 14 need not come into play, and the heat transfer liquid suffices to transfer heated liquid from the solar collector 12 to the heat exchanger 26 which serves heat pump 28, to supply useful heat to the load.

Under favourable weather conditions excess heat from the collector 12 is transferred to the storage means 14, to defrost and convert some of the icy mass present about the nest of pipes of the storer to water, whilst circulating heat transfer liquid from the storage means 14 to the collector 12. The low temperature of the heat transfer liquid produces relatively high performance of the collector 12, which collects large quantities of environmental heat, including solar, wind, precipitation and latent heat from air humidity and rain without building up a significant mass of ice on the surface of the collector. The build-up of ice on the collector surface is generally precluded, owing to the selected operating temperature range of the transfer liquid.

Owing to the deep buried location of the storage means 14 at low temperatures of the heat transfer liquid, useful heat is received from the surrounding ground.

At certain phases of heat depletion, the moisture in the ground around the pipes of the storage means 14 becomes frozen, such as during long cold cloudy periods. During daylight hours, with heat available from collectr 12 to the storage 14, the icy mass in the trench 30 and the ground is progressively diminished as the added heat supplies the heat of fusion, and progressively defrosts the icy mess. Owing to the low temperature at which storage means 14 operates there is little or no tendency for its heat to dissipate.

Usually the tendency is the reverse, and heat is received from the surrounding ground. Also, in view of the containerless nature of the storage means 14 moisture tends to migrate to the ice and frozen soil mass, in known fashion, to increase its mass within and adjacent the trench, as latent heat is withdrawn to serve the heat load.

Thus, due to the adopted low temperature heat transfer and collection system, losses from the system are very low. Also the efficiency of the collector 12 is very high, often exceeding 100% of its theoretical capacity with respect to available solar energy quite significantly, owing to the acquisition of heat from all aspects of the environment.

By providing the input of low grade heat to the heat pump at close to freezing, its COP is maintained at a value in excess of one, and more usually in excess of three throughout the heating season. Owing to the utilization of the latent heat of fusion of water, the volume of exchanger 14 and the size of trench 30 can be greatly restricted. Vertical burial of the nest of pipes of storage means 14 in a pit is also feasible.

The low operating temperature of the collector enables the energy recovery efficiency to be maintained even during winter weather when the ambient temperature is 10 or 15 degrees Celsius below freezing. The collector efficiency is enhanced, even optimized by the operating temperature of the storage system which enables the collector to operate more efficiently all year, including winter. The operation of the collector is at a maximum under these conditions. Theoretically, operation of a system other than that of the present invention at an even lower temperature for the heat transfer liquid might appear to boost thermal efficiency, but the collector surface will become contaminated with ice.The apparent synergism provided by operating the heat transfer liquid at close to the freezing point of water reduces the volume and area requirement of the storage system to a minimum and also minimizes the required size of the solar collector. The collector and the storage system co-operate as a system.

The phase "permanent continuous energy source" is meant to convey that the system is capable of sustaining a predetermined load during even the most adverse weather conditions normally experienced from year to year.

The adoption of a containerless icy mass forming heat storer having a nest of small bore pipes provides a high capacity, low cost, flexible heat storage means that is effectively self regulating, within limits, for meeting system needs; while the operation thereof close to the freezing point of water permits the system to operate, in large measure, substantially independently of ambient temperature.

Claims (15)

1. The process of operating a heating system incorporating system components comprising a heat pump, environmental heat col lector means, heat load means to receive useful heat from the heat pump, in-ground low temperature containerless heat storage means and a low temprature circulation circuit for displacing liquid in heat transfer relation between respective one of said system components, comprising the steps of; operating said heat storage means at a temperature close to the freezing point of water, whereby the ongoing withdrawal of heat therefrom produces the formation of a compact, progressively increasing icy mass, and the addition of heat thereto produces progressive central melting of the icy mass; circulating non-freezing heat transfer liquid to said collector means at said close-tofreezing temperature and utilizing collected heat upon upgrading by said heat pump, to said heat load so that said system operates substantially independently of short term ambient temperature.

2. The process as set forth in claim 1 where the efficiency of said collector means is optimized.

3. The process as set forth in claim 1 wherein said heat collector means collects solar heat, wind heat, precipitation heat, and on occasion, precipitate change-of-state latent heat without sensible accumulation of ice on the collector surface of said collector means.

4. The process as set forth in claim 1 wherein the value of the co-efficient of performance (COP) of said heat pump is maintained in excess of unity up to a value of about 3 on a year by year basis.

5. The process as set forth in claim 1 wherein said system heat transfer liquid is operated within the range of plus 10 to minus 5 degrees Celsius, of zero Celsius.

6. In a thermal energy supply system a low temperature containerless heat storage means for in-ground buried installation, comprising a nest of small bore pipes, extending in mutuaily spaced apart parallel relation between at least two headers, to provide a pipe assembly of slim cross-section suitable for burial directly in the earth within an elongated trench suitably for burial directly in the earth within an elongated trench as a back hoe.

7. The system as set forth in claim 6 wherein said pipes are plastic.

8. The storage means as set forth in claim 6 having a heat transfer capacity of up to 10 watts per meter of pipe length, in transferring the latent heat of fusion of water locally entrained about the buried pipe.

9. The thermal energy supply system as set forth in claim 6, in combination with solar collection means connected in liquid circulating relation with said fluid storage means, said solar collection means being sized in relation to the capacity of the system to operate down to minus five degrees Celsius.

10. The thermal energy supply system as set forth in claim 6, the size thereof being related to a predetermined heat capacity as a function of the latent heat of fusion of water.

11. The thermal energy supply system as set forth in claim 8, further including pump means for circulating heat transfer liquid through the system, and heat pump means for raising the temperatures of heat received from said solar collection means and recovered from said storage means to a predermined minimum exchange temperature.

12. The thermal energy supply system as set forth in Claim 10, having said in-ground nest of small bore pipes buried in outwardly extending relation within a pit.

13. The system as set forth in claim 1 or claim 6, said system comprising a permanent continuous thermal energy source.

14. A process of operating a heating system substantially as described herein with reference to the accompanying drawings.

15. A thermal energy supply system substantially as described herein with reference to the accompanying drawings.