GB2072321A - Heat pump system - Google Patents

Abstract

A heat pump (15) for heating a building (3) is connected to the volume of air in a duct system, more particularly the sewage system (1, 2). The earth around the duct system serves as heat source and heat accumulator while the air flowing through the duct system serves mainly as a heat transfer medium. Outside the heating season the earth accumulator is recharged by warm sewage and storm water without additional installations being required. <IMAGE>

Description

SPECIFICATION Heat pump system The invention relates to a heat pump system for heating buildings and/or for a hot water service, the earth being used as a low-temperature heat source.

The earth can be used as a low-temperature heat source as well as other heat sources, such as air and/or water, for the earth can also serve as a seasonal heat accumulator. A particular difficulty arising in using the earth as a heat accumulator in built-up areas is the preparation of adequate underground heat exchange surfaces via which the heat to be removed from the earth can be transferred to a heat vehicle medium. Other problems arise because the "spent" heat accumulator must be recharged during the summer and it may even be necessary in some cases to provide special installations for this purpose, for instance, based on solar collectors.

It is the object of the invention to provide a heat pump system in which the earth is used as heat source and heat accumulator and in which the conveyance of heat from and to the earth is achieved quite simply.

Accordingly the present invention provides a heat pump system for heating buildings and/or for a hot water service, the earth being used as a lowtemperature heat source, in which the evaporator of the heat pump is arranged to take up heat from a volume of air in an underground service duct.

A necessary precondition for this invention is, therefore, the existence of an underground service such as is commonly found, at least in industrialised countries, e.g. for drinking water distribution, the removal of sewage and/or other supply and discharge systems, e.g. in the form of cable ducts. The temperature of the air in such services is substantially unaffected by seasonal temperature variations and remains somewhere between from 8 to 1 50C. It can therefore be used as a heat vehicle during the winter without any risk of the heat pump evaporator icing up.Heat pump operation throughout the year is therefore possible and makes it unnecessary to install additional fossil fuel heating systems; the relatively high and fairly constant air temperature leads to heat pump operation of relatively high efficiency, so that the driving energy required for the compressor of the heat pump is reduced. In association with an appropriate accumulator- again because the air temperature remains substantially the same both in the daytime and at night - the novel system is particularly suitable for operating exclusively during low-tariff electricity periods.

Depending upon the season, the air used by the system either removes heat from the earth around it or yields heat thereto, the duct system, which is usually fairly extensive, absorbing the heat of a relatively large volume of the earth as heat source.

Preferably the heat pump is connected to the volume of air in the ducting of a sewage system; the volume of air and the earth are heated additionally by the sewage flowing in the ducting, and the seasonal topping-up of the heat accumulator formed by the earth is greatly simplified, the heat of the sewage being used.

Also, sewage air is usually at least substantially moisture saturated and can therefor yield not only its sensible heat but a further considerable amount of latent heat.

One convenient embodiment comprises an open-end air circuit including an air line which has a fan disposed therein and which extends from a main sewer of the sewage network via the evaporator of the heat pump to the atmosphere.

Unpleasant odours from sewage air can be reduced or obviated if a stench trap is provided in the air line and/or the exit end thereof is disposed in the atmosphere above the roof of the building.

As a rule, every building connected to a sewage line has a vent pipe associated therewith.

Advantageously, to prevent a direct short circuit between the vent line and the heat pump air line of the same building, a restrictor is provided in the vent pipe of the sewage system of the building.

In order to promote a fuller understanding of the above and other aspects of the present invention, an embodiment will now be described, by way of example only, with reference to the accompanying drawing which is a view in diagrammatic form showing part of a sewage network to which a number of buildings are connected; and in the case of one building showing an embodiment of the invention.

By way of lines 2, a number of buildings 3 are connected to a collecting duct 1 of a sewage service; the sewage-producing elements of the buildings 3 are indicated in very schematic form and have the reference 4.

Also a gulley 6 of the street service extends into the duct 1, a gas-tight separation between gulley 6 and duct 1 being provided by means of a water seal 7. The drawing also shows on one of the buildings 3 a storm water drain 8 for storm water discharging from a drain gulley 9 and a roof gutter 10; drain 8 is connected by way of another water seal 12 and a line 11 to line 2. Each building 3 has a vent pipe 13 which branches off its sewage system and extends to atmosphere above the roof 14.

The gulleys or lines 6, 8, the lines 9, 2, and the duct 1 are (as is also a manhole 16 which is connected to the duct 1 and which will be described hereinafter) disposed at least to some extent below ground level, although this feature is not expressly shown in the drawing.

One of the buildings 3 has a heat pump 15 embodying the invention. An air line 17 extends to the building 3 concerned, from manhole 1 6 of duct 1. Disposed along the line 1 7 is a housing 1 8 in which are disposed an evaporator 1 9 of heat pump 1 5 and a fan 20 which maintains a flow of air from the manhole 1 6 into the casing 18 and through a continuation 21 of air line 17 to the atmosphere.

To prevent a direct short circuit of the air flow by way of vent pipe 1 3 and line 2, the building having the heat pump system has a restrictor 22, shown in the form of a cover over the exit to atmosphere of the vent pipe 13. The reason for making every effort to obviate a direct short circuit of the air flow is that the dwell time of the short circuit air flow in the sewage system would be too short for it to be heated adequately and thus remove sufficient heat from the accumulator formed by the earth.

When the heat pump 15 is in operation, the fan 20 runs and takes air from manhole 16 and duct 1; the intaken air is replaced by air flowing in mainly through the vent pipes 13 and the lines 2 of the other buildings 3 into the duct 1. The distance travelled by the air in the sewage service is so long that sufficient heat is transferred to the air from the earth around the sewage system so hat the air reaches the evaporator 1 9 approximately at the temperatures mentioned. In other words, the air from the duct system is not primarily the or a heat source for the heat pump 15 but serves mainly as a heat vehicle medium for conveying the heat stored in the earth around the duct system.

The earth around the duct system is therefore discharged as an accumulator or store during the heating season. The accumulator is charged at periods when little, if any, heat is required for the heat pump 1 5 and the sewage and storm waters are at a temperature above that of the "spent" earth. No additional installations are needed for this recharging of the earth accumulator.

Claims (6)

1. A heat pump system for heating buildings and/or for a hot water service, the earth being used as a low-temperature heat source, in which the evaporator of the heat pump is arranged to take up heat from a volume of air in an underground service duct.

2. A system as claimed in Claim 1, in which the' evaporator is arranged to take up heat from a volume of air in the ducting of a sewage system.

3. A system as claimed in Claim 2, comprising an open-ended air circuit including an air line which has a fan disposed therein and which extends from a main sewer of the sewage network via the evaporator of the heat pump to the atmosphere.

4. A system as claimed in Claim 3, in which a stench trap is provided in the air line.

5. A system as claimed in Claim 3, in which the vent pipe of the sewage system of the building is provided with an air flow restrictor.

6. A heat pump system substantially as herein described with reference to the accompanying drawing.