GB2447948A - Gas compression heat extraction system - Google Patents

Abstract

A system is provided for extracting heat from ambient air, or another gas, by compressing the air and extracting heat using a heat exchanger. Air is drawn into the system from the atmosphere via an inlet 6 and into a compressor 1. The air is compressed in the compressor, increasing its temperature, and transferred via piping 9 to a heat exchanger 2 where heat is transferred to air, or another fluid, to be heated. The air or fluid to be heated is supplied to the heat exchanger through a duct 10, and having been heated, leaves the heat exchanger through a duct 11. A drain 3 may be provided to remove accumulated condensation in the heat exchanger. Preferably, the pressure in the system is maintained by an expansion device 4, such as a valve or turbine, adjusted to provide the desired back pressure. The compressed air leaves the heat exchanger via piping 13 and passes through the expansion device before being exhausted to the atmosphere. The reduced temperature exhaust gas may be used to provide a source of cooling. Preferably, the turbine can provide a source of energy, such as electricity from a generator (G, fig.4) to power an electric motor (M, fig.4), to assist in driving the compressor.

Description

Heating/Cooling System It is well known that useful heat can bc

extracted from even low temperature ambient air by means of a conventional refrigeration cycle. The method is not as widely used as might he expected. The authors believe that practical problems (such as icing) mean that net energy gains are low and equipment costs high so that installation may be uneconomical.

The system described in this document provides an alternative approach by compressing ambient air to raise its temperature. A heat exchanger is used to transfer heat to air for space heating-or to any other suitable fluid for alternative applications.

The depleted air is exhausted to atmosphere. Prior to exhaust to atmosphere the depleted exhaust air may be used to provide cooling. It may be that the same or a similar process can he applied to other fluids to advantage in certain circumstances.

Efficiency of the system can be increased by introducing a turbine or other device into the outgoing stream. Such a device serves a dual purpose in providing energy to contribute to compression of the air (or for other use) and in maintaining necessary back pressure.

In cases where there is an available supply of air (or other gas) at above ambient temperature (such as air from an extraction system) such gas can be introduced into the inlet to the compressor. This will increase the effectiveness of the system. It may be used to provide a method of heat recovery from extracted air.

Provision may be made for draining condensation from the heat exchanger.

Some applications will (in addition to the turbine or other device mentioned above) be able further to benefit from the outgoing air stream by exploiting the difference in temperature between the air stream and ambient air.

Figure 1 shows the basic system of gaining heat from ambient air.

Figure 2 shows an example of the system in Figure I where the outgoing air stream is used to assist in driving the system.

Figure 3 shows the system in Figure 1 where waste gas is introduced into the air inlet.

Figure 4 shows the system in Figure 1 incorporating the features of Figures 2 and 3.

Figure 5 shows a system of space heating incorporating the features of Figures 1, 2 and 3.

Figure 6 shows the system in Figure 1 incorporating the features of Figures 2 and 3 used to heat a swimming pool.

The fundamental details of the system are shown in Figure 1. Air is drawn from atmosphere via inlet 6 into compressor 1. It is compressed thus increasing its temperature and transferred via suitable piping 9 to heat exchanger 2 where the useful heat is transferred across the heat exchanger to the air or other fluid to be heated. The air or other fluid is supplied through duct 10 and having been heated leaves the heat exchanger through duct 11 to use.

In many applications condensation will accumulate in the heat exchanger. In such applications a drain 3 may be provided at a suitable location.

Compressed air depleted of heat leaves the heat exchanger at 13 Pressure in the system is maintained by an expansion device 4, such as a valve, designed or adjusted to provide the desired back pressure. Ilaving passed through the expansion valve the air is exhausted to atmosphere.

The instant system is capable of functioning through a wide range of pressures/temperatures according to the requirements of a particular application.

Potentially, useful heat can be extracted from pressures less than twice atmospheric up to many atmospheres. System design will vary. Factors will include the volume of air required, its pressure/temperature and whether heat is to be transferred to air or any other gas or liquid.

Compressors can be driven by any suitable power source. In many cases electrically driven compressors will be most appropriate but other external power sources such as steam, hydraulic or air power could be used. Internal combustion engines or gas turbines may sometimes be a way to maximise effectiveness.

Irrespective of motive power used -the compressor, its motor and any cooling circuit could be housed within a duct or cowl such that the air entering the system is drawn over these prior to compression. The waste heat emitted by the compressor, its motor and any cooling circuit is drawn into the instant process and exploited. The exhaust from an internal combustion engine could be fed directly into the ingoing airflow and the heat used in the instant system. Likewise exhausted steam could be condensed in this way.

To minimise heat loss the pipe from compressor to heat exchanger could be as short as possible. It may also benefit from being lagged.

In some applications an open drain may suffice to clear condensation from the heat exchanger but a design which includes means of separately discharging condensed liquids may be preferred.

In simple installations the expansion valve may be preset to maintain the approximate desired pressure in conjunction with the chosen compressor (which may have a variable speed control). An alternative approach preferable in many cases would be to use a pressure control valve.

Any icing can be dealt with by localised heaters or other means.

Cycling of the equipment can be thermostatically controlled.

The system according to Figure 2 follows Figure 1. But pressure is maintained by an expansion device 4 which in addition to providing the back pressure necessary for the operation of the instant system at the same time draws energy from the compressed air as it expands. The energy thus gained can be used to help drive the compression stage of the instant system.

It is not an essential feature of any expander device which may be provided that its output should be used to assist the instant system. The output can be used in any appropriate way.

Figure 3 shows the system in Figure 1 where a supply of gas at or above ambient air temperature is introduced in addition to or in place of ambient air. The supply of this potentially warmer gas enters inlet 5. Any necessary incoming ambient air enters inlet 6.Both supplies mingle at junction 7 before continuing according to the process illustrated in Figure 1 or Figure 2.

Any such supply of gas will usually be forced by fans or similar. In consequence that supply will take preference over ambient air. If there is a surplus of forced air the excess can leave the system via the ambient air inlet/duct 6. If there is insufficient forced air then the balance required by the compressor will be drawn from ambient air through the ambient air inlet. Thus the mix of forced and ambient air will be self regulating. It may be possible to increase the efficiency of this process by means of flap valves.

Different methods of regulating the flow of one or both of the streams may be employed in other cases.

Such a system provides the opportunity for automatic recovery of waste heat from an air extraction system. Because the temperature of waste air is raised by the compression process recovery of heat is more efficient and more effective than if the waste air supply is used simply to pre-heat incoming air.

A version of the system in Figure 1 incorporating the features in Figures 2 & 3 is described in Figure 4. Forced air supply enters inlet 5. Any further air needed enters inlet 6 and the two airstreams mingle inside casing 8. On occasion if a surplus of air is forced through inlet 5 it leaves via inlet 6. If there is a precise balance between forced supply and compressor demand air flows through inlet 5 alone. In all cases the air demanded by the compressor flows through casing 8 around compressor 1 with its driving electric motor M (which are housed in the casing 8). The air is then drawn into the compressor where it is compressed and forced along lagged pipe 9 to heat exchanger 2.

Air to be heated is fanned across the low pressure side of the heat exchanger via duct 10. It then leaves the heat exchanger and is transferred to use by duct 11.

Condensation collects in sump 12 where it is drained via drain 3 to waste or other use.

The compressed air then enters pipe 13 which transfers it to expansion device 4. The expansion device includes a turbine impellor which is connected to gearbox and generator G. The expanding air drives the impellor which in turn drives the gearbox and generator. The air then passes through any necessary further restriction before passing to the external atmosphere. Electricity generated is then fed into the supply to the compressor motor to assist in driving the compressor.

Figure 5 shows an integrated space heating system which includes supply of fresh air into the relevant enclosed space. The heating process follows that described by Figure 4.

Fresh air introduced via duct 10 is heated as it passes through heat exchanger 2 and transferred by duct II to the space to be heated. The air is circulated by fans 14 and/or 15. The warmed air passes through the space to be heated 16 according to the heating and ventilation requirements of the designers. An equivalent amount is extracted and transferred by duct 5 and casing 8 to the compressor (fanned if required). Additional air may be supplied at inlet 6 to casing 8 if operating conditions require.

Figure 6 shows the system in Figure 1 incorporating the features in Figures 2 & 3 where an air to liquid heat exchanger is used to transfer heat from compressed air directly to swimming pool water. Cold water leaves the pooi 17 via pipe 18 including pump 19 which circulates the cold water through the heat exchanger to be heated and returned via pipe 20 to the pool.

As with other applications the temperature limits can be controlled thermostatically.

An alternative approach is to use an intermediate heat exchanger so that heat is transferred from the air to liquid heat exchanger by a non corrosive fluid. Thereafter the heat is transferred to the pool water via a liquid to liquid heat exchanger.

The cold stream output from the above described systems can be used as a means of cooling or air conditioning' -either directly or by means of suitable heat exchanging equipment. In such cases the heat output at heat exchanger 2 can either be put to use (as suggested above) or sent to waste.

Claims (6)

1. Claims I A system for extracting useful heat from ambient air (or other

   gas) by means of compressing such gas and extracting heat using any of a variety of heat exchangers.
2. 2 The system in Claim I where the flow of the exhaust stream is exploited to provide a source of energy which can be used to contribute to the driving of the instant system and/or elsewhere.
3. 3 The system in Claim 1 where the exhaust gas provides a heat sink which can be exploited (for example to provide refrigeration or as part of a process contributing to compressing the inlet air).
4. 4 The system in Claim I where a supply of waste gas at or above ambient temperature (such as air extracted by a ventilation system) is used to provide a partial or total supply fbr the instant system.
5. The system in Claim I used to heat and/or cool any fluid either as an end in itself and/or as a method of heat transfer.
6. 6 A system of space heating and ventilation according to claims 1, 2, 3, 4 and as appropriate where provision is made for replacement/recycling of air with integrated recovery of heat from replaced air and heat transfer to recycled air.