GB2491849A - Ventilation system with heat exchanger bypass and a mixing space - Google Patents

Abstract

A passive ventilation system for a ventilated space or structure 14 has a heat exchanger 12, a by-pass path 8,9 and a mixing space 11 for mixing air 16 from the outside environment with ambient air 18 from the ventilated space, the heat exchanger 12 heating external environmental air 16 with ambient air 15, the system being controlled to exchange heat (fig 1a) below a desired maximum temperature for the space 14, or to by-pass the heat exchanger 12 if above. The desired maximum temperature can be higher than an ideal operative temperature (fig 3). An embodiment omits by-pass path 9, and has an outlet (22, fig 2a & 2b) for excess heated air from mixing space 11. A controller may also account for seasons, weekends, and time of day.

Description

A Ventilation System and Method of Operating a Ventilation System The present invention relates generally to ventilation systems and in particular to ventilation systems used in ventilated structures such as school classrooms, meeting rooms and similar places where some warm ambient air is mixed with external environmental air for thermal as well as air quality control.

It will be understood there are a large number of buildings which provide ventilated structures for commercial, industrial and domestic purposes. In order to provide thermal efficiency these structures tend to be relatively well-sealed with high levels of thermal insulation so means for controlled ventilation are important to maintain air quality. One approach is to provide forced air systems with relatively powerful fans to draw air from or force air into the relatively closed structure to ventilate it but such an approach will consume energy and may be noisy along with having on-going maintenance costs. The forced air system may also provide air conditioning (e.g. supply of heating or cooling) with further costs and energy usage. Simple ventilation vents or open apertures can cause drafts which are not desirable. Recently passive ventilation systems have been providedwhich include an intermediatemixing space between the interior and exterior with apertures at each end. Due to the relative sizes of the apertures, their spacing, and the size/volume of the mixing space, there is mixing of incoming external environmental air and some internal ambient air, with the combination then falling into a ventilated structure such as a room in a building for air quality control. Some fresh air enters the ventilated structure whilst draughts are avoided, heat within the ambient air is transferred to the incoming environmental air and, possibly other than for generating mild mixing turbulence, the ventilation system does not need a fan to drive airflow so needs little energy usage.

As buildings, and so ventilated structures, become more thermally insulated it will be understood that the heatgenerated naturally or incidentally in a room or structure may exceed heat losses at least during occupancy. It will be understood that natural heating may be from the body heat of the occupants and solar heating through glazing whilst incidental heating may be from computers, overhead displays, lighting, vending machines, kettles etc. In such circumstances the actual operation of dedicated heating systems may be limited to times of no occupancy or in readiness for expected occupation mostly during periods of cold weather. Such an approach may not be the most thermally efficient.

in accordance with aspects of the present invention there is provided a ventilation system for a ventilated space or structure, the system comprising a heat exchanger, a by-pass path and a mixing space for mixing in use ventilation external environmental air and incident internal ambient air from the ventilated space, the heat exchanger having an ambient path and an environmental path whereby in use heat exchange is provided between incident outilowing ambient air and inflowing external environmental air to provide ventilation environmental air for the ventilated space until in use a maximum desired temperature for the ventilated space is achieved above which the external environmental air flow switches fully or partially to the by-pass path to the mixing space.

The heat exchanger may be configured by its structure, fabrication materials and/or shape to limit heat exchange between the incident ambient air and the external environmental air flow or when the ambient air within and/or the ventilated space or structure reaches the desired maximum temperature.

The heat exchanger may have a valve arrangement associated with a controller and a temperature sensor for ambient air and/or the ventilated structure or space in use whereby an operative valve in the valve arrangement is fully or partially closed or opened dependent upon whether the ambient air and/or the ventilated space or structure has reached the desired temperature. The operative valve may be in an environmental path and/or an ambient path to or within the heat exchanger or an operative valve in the valve arrangement provided for each path.

In the mixing space the external environmental air may pass through a first aperture inlet and the incident internal ambient air may pass through a second aperture inlet, the first and the second aperture inlets sized, spaced from each other and configured in a shape of the mixing space to provide desired mixing.

The first and the second aperture inlets may be adjustable in terms of size absolutely or relative to each other. The first and the second aperture inlets may be adjustable in terms of spacing between each other. The first and the second aperture inlets may be adjustable manually and settable to a manual adjustment. The first and the second aperture inlets may be adjustable automatically and adjusted under the control of a controller dependent upon desired requirements. The desired requirements may be time of day, the desired temperature, expected environmental conditions, previous environmental conditions and similar factors.

Also in accordance with aspects of the present invention there is provided a ventilated structure or space in a building including a ventilation system as described above.

A damper or closure for the mixing space may be provided whereby the mixing space can be substantially closed to effectively prevent ventilation of the ventilated structure or space through the mixing space at least by external environmental air flow.

The ventilated structure or space may have a direct ventilation aperture which may be opened when required. The direct ventilation aperture may be closed by a flap. The direct ventilation aperture may be thermally below the mixing space in terms of convection or driven air flows within the ventilated structure or space. There may be a plurality of direct ventilation apertures. The plurality of direct ventilation apertures may be collectively or individually or be grouped to open when required together or in a sequence. The sequence may be a timed sequence or a temperature dependent sequence or an objective dependent sequence.

Additionally in accordance with aspects of the present invention there is provided a method of controlling ventilation in a ventilation system comprising:-A) Configuring a heat exchanger to provide heat exchange between an external environmental air flow and an outilowing ambient air flow from a ventilated space to adjust the temperature of the external environmental air flow to a ventilated space and/or a mixing space; B) Configuring the mixing space to receive environmental air from the heat exchanger and/or directly for mixing with re-circulated ambient air from the ventilated space and return to the ventilated space; C) Monitoring the temperature of the ventilated space to adjust the flow of external environmental air from the heat exchanger or from the bypass as a proportion with the internal ambient air in the mixing space until a desired maximum temperature is achieved in the ventilated space.

D) Monitoring the temperature of the inlet ventilation air to the space to ensure this is above the threshold associated with cold draughts.

Once the desired maximum temperature in the ventilated space is achieved the heat exchanger may be by-passed so that all environmental air directly flows to the mixing space through a by-pass path to the ventilated space.

Other features and aspects of the present invention are defined in the description and/or claims below.

Embodiments of the invention of aspects of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic illustration of a first embodiment of aspects of the present invention; Figure 2 is schematic illustration of a second embodiment of aspects of the present invention; and, Figure 3 is graphic pictorially illustrating possible temperature profile changes over a day within a ventilated structure or space.

In accordance with aspects of the present invention there is provided a system for the ventilation of a building mostly in winter using heat recovery and mixing ventilation. The system aims to use thestored heat and to enhance the storage of internal heat gains in the thermal mass, that is to say the building fabric and internal structure from which a ventilated structure is formed, and soreduce dedicated heating requirements for either maintenance of the interior temperature or pre-heating of cold incoming ventilationair whilst also minimising fan power usage.

Buildings comprise of ventilated structures and spaces, such as a school classroom, which have a number of modes of heat loss including (i) heat loss through the fabric of the building and (ii) heat loss associated with the ventilation air which primarily occurs during occupied conditions. The losses need to be compensated by the addition of heating, and sometimes cooling, in order to maintain a comfortabletemperature. if the insulation in a building is sufficiently good, then the heat gains within the buildingwhile occupied (emitted from people, lighting and electrical equipment) are often higher than those lost by the modes (i) and (ii) above and the building has excess heat available. However, overnight or when the building is not occupied it continues to lose heat at least by mode (i) above and the building may require heating the following morning to compensate for this and any environmental ventilation air to remove any stale air feeling in the building.

Aspects of the present invention relate to provisionof a low energy ventilation system to retain and use the excess heat generated while the building is occupied to buffer the heat losses when unoccupied. The system provides:-; 1) the control of the interior temperature to adjust and typically maximise the ambient temperature within the building but within acceptable limits during pad of the occupied day, as this will lead to a higher interior temperature the following morning and hence a reduction in the amount of heating required; 2) the means to supply fresh air above the temperature associated with cold draughts; 3)the ability to minimise the use of fan power in terms of motor energy usage by using a combination of mechanical/natural ventilation and heat recovery (MVHR) and mixing ventilation.

Heat recovery is an effective way of reducing the heat losses associated with ventilation. The heat recovered will be retained in the interior leading to a gradual increase in the temperature of the space as the thermal mass of the building and its spaces (i.e. the walls, furniture etc) heats up. However, owing to fluctuations in the internal heat gains, solar gains and exterior temperatures, there are likely to be conditions for which such a heat recovery system can recover so much heat that the ambient temperature of the interior space wouldrise to a temperature above that which the occupants may consider comfortable and acceptable at least in the long term.lf this occurs, the ventilation airflow normally taken from the building should bypass the heat exchanger in order to vent the excess heat gains and prevent overheating in a low energy manner. An alternative would be to increase the flow rate through the building in terms of ventilated structures and spaces and the heat exchanger, but this results in increased fan power consumption so is less efficient.

In many situations such as in winter, the exterior temperature may still be relatively cold at the point at which this requirement for bypass is reached. As a result, the incoming ventilation air still requires pre-heating as otherwise this would cause localised cold draughts, even though there are excess heat gains within the building. In such a situation, it would be possible for the incoming air to be pre-heated by either:- (a) an external heat source and/or, (b) having only a fraction of the outilowing air by-passing the heat exchanger and mixing this air which is directly flowing into the building with a second stream of inflowing air which passes through the heat exchanger.

However, both of these solutions will incur an energy penalty associated with the supply of heat or the fan work in driving air through the heat exchanger.

In accordance with aspects of the present ventilation system there is pre-heating of the incoming external environment air by mixing with the interior warm ambient air, in such proportion that the mixture reaches a comfortable temperature prior to reaching the occupants. The interior warm air itself is heated by the natural actions of the occupant's own body heat and inherent heating from such sources as lighting, electrical equipment and solar action as well as dedicated heating sources when active. This approach will require much less energy, since air does not need to flow through the heat exchange system nor is additional heat required in the building if the internal heat gains exceed the total heat loss.

Once the occupants have left the building, typically at night, ventilation will cease and the building will lose heat to the exterior through the fabric (walls, roof, and windows). The heat which has been captured during the previous day in the thermal mass of the build ingprovides a source to balance this heat loss or to go some way to maintain a base level air temperature in the building if used in accordance with aspects of the present invention. Thus, only if a significant proportion of the previous day's heat build-up is lost overnight will operation of an external heating system be required to add some thermal energy prior to the occupants arriving on the following day. In this way, the use of the building as a store of the thermal energy produced by the occupants provides a means of minimizing or reducing the overall heating load of the building. A higher temperature is set initially when the occupants leave for example at night so that a higher like-for-like temperature remains when the occupants return in the morning. Figure 1 and Figure 2 illustrate respectively first and second embodiments of aspects of the present invention as schematic illustrations. The main differences between the embodiments relate to how a mixing space 11, 21 respectively deals with ventilation flows in the system and exhausting of excess heat. Other parts of the ventilation systems have been give consistent reference numbers for comparison. Thus, each embodiment provides a respective ventilation system 10, 20 in which a heat exchanger 12 is provided alongside the mixing space II, 21. The heat exchanger 12 can be of a direct action type with ambient air from within a ventilated space or structure 14 in a flow shown by arrowhead 15 exchanging heat with an external environmental air flow shown by arrowhead 16 all within the heat exchanger or possibly a secondary heat exchanger type where a carrier fluid is provided in a tertiary possibly pumped circuit to facilitate heat exchange efficiency in comparison with simple plate heat transfer functionality. In any event the heat exchanger 12 essentially extracts heat energy from ambient air flows from the ventilated space or structure 14 to heat incoming external environmental air flows for the space or structure 14. Thus, the normal inherent heat displacement, hot or cold, of addition of the external ventilation air flows into the space or structure 14 can be checked so that the temperature of the space or structure 14 can increase through natural heating (occupants' body heat) and inherent heating (lighting, electrical equipment etc.) if the heat losses are controlled by insulation.

The normal objective of a ventilation system is to provide a comfortable environment so temperature is maintained at an acceptable level for the activity expected, so higher for sedentary activities (office or classroom) in comparison with more strenuous pursuits or simply where there is more movement (corridors) or a higher occupant density (an assembly hall) or more incidental/natural heating (dining area or highly glazed conservatory). Where the background natural or incidental heating means that there would be a temperature increase, as such heating will be greater than heat losses, the tendency is to normally use cooler external environmental air to cool and regulate the temperature within the ventilated space or structure within reason. It will be appreciated that if the external environmental temperature is higherthan such cooling will not be possible. The approach of aspects of the present invention is to suspend such temperature increase control for a period before expected higher heat losses at night or during holiday periods or most importantly when there is no or reduced occupancy so less natural/inherent heating to offset heat losses. In such circumstances the temperature of the building in terms of the fabric (walls etc), fixtures and fittings, furniture as well as the air will be higher than normally desired. The building acts a heat store which is at a higher temperature so on a like-for-like basis will cool from that higher temperature so when normal' occupancy returns the residual temperature will be higher. In such circumstances there will be less need for operation of the dedicated heating system to rapidly increase the ventilated space temperature to an acceptable level and/or a shorter timeperiod till natural/incidental inherent heating in the highly thermally insulated building elevates the temperature.

In the first embodiment depicted in figure Ia and figure lb as indicated the heat exchanger 12 receives relatively hot ambient air from the ventilated structure 14 in a schematic flow 15. External ventilation air 16 is pre-heated or warmed by flow 15 so that a heat adjusted environmental ventilation flow depicted by arrowhead 17 enters the ventilated space 14 or possibly the mixing space 11 to mix with ambient air 18 to be returned ona ventilation flow 19 into the space or structure 14. The process of pre-heating the air quality refreshing ventilation flow 17 continues until the temperature of the ambient air 18A and/or the space/structure 14 reaches a desired maximum value. This can be referred to as a heat exchange mode depicted in Figure 1 a. Once the desired temperature value is reached further heating is unacceptable although the space will continue to require ventilating to maintain air quality. In this case, ambient air within the space/structurel4 is dumped as shown by arrowhead 9 without passing through the heat exchanger 12 and external environmental ventilation airl 6 will pass along a by-pass path 8 to the mixing space 11 without pre-heating. This temperature stable phase can be referred to as a mixing mode depicted in figure lb. The flow 15 is diverted away from the heat exchanger 12 through path 9 by a valve 7 whilst the external environmental flow 16 rather than passing through the heat exchanger 12 is diverted to the by-pass path 8 by a valve 6 in a suitably controlled valve arrangement. Typically, the ventilation system will have a number of temperature and possibly other sensors coupled to a controller (not shown) whereby operation of valves in the valve arrangement will be coordinated dependent upon temperature at least in the ventilated structure or space 14.

In a second embodiment as depicted in Figure 2a and Figure 2b a ventilation system operates in a similar fashion to that described with regard to the first embodiment depicted in Figure 1 but with no bypass path 9 for ambient air as depicted in figure 1 and the mixing space 21 providing an outlet 22 for excess heated air. Thus, as before the heat exchanger 12 receives relatively hot ambient air from the space 14 for heat exchange with external environmental air 16 in order to pre-heat that air 16 to provide a ventilation airflow 17 into the space 14. Once a desired maximum temperature has been reached in the space 14 and/or the ambient air in that space 14 then a valve 7 acts to stop further relatively hot ambient airflow 15 into the heat exchanger 12 and a valve 6 acts to divert the external environmental air flow 16 into a by-pass path 8 to the mixing space 21 in order to mix with ambient air 18 to provide a ventilation flow 19.

The mixing space 21 typically has a shape with apertures on opposite sides such that the spacing of the apertures and their relative sizes provides a means whereby some of the ventilation flow 19a passes into the space 14 whilst dependent upon temperature/turbulence some of the ventilation flow I 9b may be released through the outlet 22. In some embodiments the relative sizing and spacing may be manually adjustable and set as required or automatically adjustable dependent upon requirements by a controller (not shown) associated with sensors. Figure 2a provides a heating or heat exchange mode till the desired maximum temperature is achieved whilst figure 2b provides a mixing mode when the desired temperature has been reached so the objective is to ensure that the addition of ventilation air does not overly disturb that temperature whilst avoiding cold draughts.

It will be appreciated that the ventilation systems in accordance with aspects of the present invention can switch between the heat exchange mode and the mixing mode as required. The heat exchange mode increasing the temperature in the ventilation space 14 to reach the desired temperature whilst the mixing mode using ventilation air to maintain and if necessary cool the ambient air in the spacel4 if the natural/inherent heating in the space 14 should escalate ambient temperature in the space beyond that acceptable to occupants. If the conditions should fall below that desired in terms of temperature or if a high pulse of ventilation air is required with possibly shock heating then the system will switch back to the heat exchange mode for at least a short time.

The present invention uses the ventilation system to elevate the building temperature beyond that normally acceptable prior to periods of reduced natural/incidental heating. The actual desired temperature to be reached will depend on a number of factors and may be variable dependent upon experience and projection/prediction. For example it will be understood that a meeting room may be arranged to accommodate a relatively wide range of numbers of people so the desired temperature may be altered between when there are a few tens of occupants to when there are a hundred or more as well as between a physical activity such as line-dancing compared to an audience for a play. Furthermore the period to elevate the temperature will generally be much quicker for a large number of occupants compared to a smaller number so the strategy towards the desired temperature may be adjusted in terms of small incremental steps and time spacing along with the period at the elevated desired temperature dependent upon requirements.ln such circumstances the ventilation system can vary in terms of performance dependent upon changing use of the ventilated structure or space in a building along with heat retaining content such as furniture levels. A controller can be used to coordinate such variables for active determination of desired or maximum temperature when required from actual or predicted conditions, changes to the building and previous results/responses by the building to pre-heating. For illustration purposes figure 3 provides a basic consideration of temperature changes in a building over a twenty-four hour period in winter but it will be appreciated that in reality there will be a wider range of variables including Seasons, weekends, timetabled changes in use and changes in working patterns. As can be seen there is a comfort temperature C which is the temperature agreed as best for a ventilated space in terms of occupancy/activity. It will be understood that it is an objective to maintain the temperature C during the working day 30, and certainly between limits F and D, but early in the morning the building may have cooled at least in the Winter to such an extent that dedicated heating maybe required to reach the temperature C in a reasonable time and probably before the start of the working day 30. The natural occupant heating and inherent heating by electrical apparatus/lighting would take too long but once at temperature such natural/inherent heating will maintain the comfort temperature and may even mean that some cooling or heat dumping is required in well insulated buildings. The present invention aims to maximise the temperature at the end of the day or beginning of reduced occupancy/inherent heating period to a higher desired temperature so that the temperature by implication at the start of the working day or period of use/occupancy is higher so reducing the need for as much dedicated heating to attain the comfort temperature C during that period 30.

In the above circumstances line 31 schematically depicts a typical temperature profile for a day whilst broken line 32 shows the new profile with a ventilation system in accordance with aspects of the present invention, the temperature being elevated to a maximum temperature D as described above. Thus, the initial temperature is higher so in a well insulated building the early morning temperature Da is higher than the normal temperature N expected and the difference Z will mean less energy is needed by the dedicated heating system to reach the comfort temperature C for the building.

In ventilation systems in accordance with aspects of the present invention it will be noted that (i) without the heat exchanger the ventilation flow will lead to much more loss of heat when occupied so that in very cold conditions, it may not be possible toheat up the interior space to a minimum comfort temperature value using the excess internal heat gains, so that there would be a need for the addition of external heating during the occupied day (ii) without the heat exchanger in less severe but still cold conditions it may not be possible to heat up the interior space or ventilated structure towards a maximum comfort temperature value for sufficiently long periods during the occupied day using the excess natural/inherent internal heat gains, so that there would be a need for the addition of external heating prior to occupation the following day (iii) without the mixing space the environmental incoming air for air quality which bypasses the heat exchanger once the building has reached a maximum air temperature in terms of thermal comfort, will require heating either by supplying additional external heating or by passing additional air through the heat exchanger, both of which incur additional energy costs.

Persons skilled in the technology will understand it is possible to vary the details of the operation of the system, perhaps by using a smaller heat exchanger to raise the temperature of very cold external environmental air to a more temperate value, and then pass this air on to the mixing system or space which will raise the temperature to a thermally acceptable value, or by use of a bypass in which some air passes through the heat exchanger and some bypasses the heat exchanger, and the mixture is then mixed with air in the space -the details of such variations in the operation of the system would depend in detail on balancing the simplicity of the system (as described above) with the potential incremental energy benefits and would depend amongst other factors upon:- (a) the fraction of the net internal heat gains which can be stored in the thermal mass of the building prior to reaching the maximum acceptable temperature of the air and/or, (b) the relative energy consumption of running a very efficient heat exchanger for a short time or a less efficient heat exchanger for a longer time and/or, (c) the variation in the external temperature during the winter season which may lead to different optimal operation on different days.

Aspects of the present invention provide the benefits of a combined strategy of using heat exchange and mixing ventilation to regulate the temperature of the thermal mass in a building in which the internal heat gains (when occupied) exceed the heat loss from the building to ensure:- (i) heat recovery will enable the internal heat gains generated during the occupied time to be retained in the building by heating up the interior thermal mass, until reaching a maximum comfort temperature. This heat store provides a source for the heat loss from the building during unoccupied conditions, e.g. at night, and hence minimises the overall heating load of the building (ii) mixing ventilation, which is used once the air of the building has heated up to a maximum comfortable temperature, provides a means of pre-heating the (cold) incoming ventilation air to a comfortable temperature while minimising the energy required to do this, since it draws on the internal heat gains in the space and it uses zero or very low power to achieve this pre-heating by using either natural mixing or mixing with a low power fan.

It will also be understood with aspects of the present ventilation system, when the system operates in conditions when the exterior temperature is below the maximum thermal comfort temperature of the space but at or above the temperature at which air can be brought directly into the building without causing cold draughts at occupant level, the building ventilation would run in upward displacement mode (natural). In this operating mode, there will be a series of dampers/openings at low level in the space and an opening at high level, to allow for direct in and out flow of air. If the external temperature fluctuations over a 24 hour period still involve conditions for which the exterior is cold, and there is a possibility that heating is required, then, when the external conditions are cold, the system will run using the heat exchange system to heat the building to a pre-defined comfort temperature, and then it will evolve to mixing ventilation. However, as the duration of the period of warm external temperatures increases, the specific temperature to which the heat exchange system will pre-heat the interior will decrease, and the system will then run in mixing mode until ultimately changing to natural displacement ventilation as the exterior warms up. Eventually, as the mean external temperature warms up, there may be a shift to use of night-time cooling of the thermal mass, to a temperature which is sufficiently warm to prevent the need for morning pre-heating but so that the thermal mass is able to buffer the heating of the building during the day and prevent overheating.

Ultimately, if the exterior temperature rises to values above the maximum thermal comfort value, then the system will switch to run in heat exchange mode whilst the thermal mass is sufficiently cold that it can absorb the internal heat gains, so that the incoming air is cooled to a value close to the interior temperature. This will limit further ingress of heat flux associated with the ventilation. In the absence of mechanical cooling, the only means of maintaining the interior space below a maximum comfort temperature is through the absorption of the heat gains by the thermal mass of the building. Since the night time temperature typically falls to low values, in such a situation the operation would involve a period of night cooling to remove the thermal energy which accumulates in the day and thereby recharge the cooling capacity for the following day. Note that during the occupied day, once the thermal mass has heated up and lost its ability to absorb the heat gains in the space and maintain an interior temperature lower than the exterior, the ventilation strategy will revert to natural upflow displacement.

It will be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.

Claims (20)

1. Claims 1. A ventilation system for a ventilated space or structure, the system comprising a heat exchanger, a by-pass path and a mixing space for mixing in use ventilation external S environmental air and incident ambient air from the ventilated space, the heat exchanger having an ambient path and an environmental path whereby in use heat exchange is provided between incident ambient air and an external environmental air flow to provide ventilation environmental air to aventilated space until in use a desired maximum temperature for a ventilated space is achieved where above the external environmental air flow switches fully or partially to the by-pass path to the mixing space.
2. 2. A ventilation system as claimed in claim I wherein the heat exchanger is configured by its structure, fabrication materials and/or shape to limit heat exchange between the incident ambient air and the external environmental air flow or when the ambient air within and/or the ventilated space or structure reaches the desired maximum temperature.
3. 3. A ventilation system as claim 1 or claim 2 wherein the heat exchanger has a valve arrangement associated with a controller and a temperature sensor for ambient air and/or the ventilated structure or space in use whereby an operative valve in the valve arrangement is fully or partially closed dependent upon the ambient air and/or the ventilated space or structure has reached the desired maximum temperature.
4. 4. A ventilation system as claimed in claim 3 wherein the operative valve is in the environmental path and/or the ambient path to or within the heat exchanger or an operative valve in the valve arrangement is provided for each path.
5. 5. A ventilation system as claimed in any preceding claim wherein in the mixing space the ventilation environmental air passes through a first aperture inlet and the incident ambient air passes through a second aperture inlet, the first and the second aperture inlets sized, spaced from each other and configured in a shape of the mixing space to provide desired mixing.
6. 6. A ventilation system as claimed in claim 5 wherein the first and the second aperture inlets are adjustable in terms of size absolutely or relative to each other.
7. 7. A ventilation system as claimed in claim 5 or claim 6 wherein the first and the second aperture inlets are adjustable in terms of spacing between each other.
8. 8. A ventilated structure or space in a building including a ventilation system as claimed in any preceding claim.
9. 9. A ventilated structure as claimed in claim 8 wherein a damper or closure for the mixing space is provided whereby the mixing space can be substantially closed to effectively prevent ventilation of the ventilated structure or space through the mixing space at least by external environmental airflow.
10. 10. A ventilated structure as claimed in claim 8 or claim 9 wherein the ventilated structure or space has a direct ventilation aperture which may be opened when required.
11. 11. A ventilated structure as claimed in claim l0wherein the direct ventilation aperture may be closed by flap.
12. 12. A ventilated structure as claimed in claim 10 or claim 11 wherein the direct ventilation aperture is thermally below the mixing space in terms of convection or driven air flows within the ventilated structure or space.
13. 13.A ventilated structure as claimed in any of claims 10 to 12 wherein there are a plurality of direct ventilation apertures.
14. 14.A ventilated structure as claimed in claim 13 wherein the plurality of direct ventilation apertures may be collectively or individually or be grouped to open when required together or in a sequence.
15. 15. A ventilated structure as claimed in claim 14 wherein the sequence may be a timed sequence ora temperature dependent sequence or an objective dependent sequence.
16. 16. A method of controlling ventilation in a ventilation system comprising:-A) Configuring a heat exchanger to provide heat exchange between an external environmental air flow and an ambient air flow from a ventilated space to adjust the temperature of the external environmental air flow to a mixing space; B) Configuring the mixing space to receive environmental air from the heat exchanger and/or directly for mixing with re-circulated ambient air from the ventilated space and return to the ventilated space; C) Monitoring the temperature of the ventilated space to adjust the flow of environmental air from the heat exchanger as a proportion with the ambient air in the mixing space until a desired maximum temperature is achieved in the ventilated space.
17. 17. A method as claimed in claim 16 whereinonce the desired maximum temperature in the ventilated space is achieved the heat exchanger may be by-passed so that all environmental air directly flows to the mixing space thorough a by-pass path to the ventilated space.
18. 18. A ventilation system substantially ashereinbefore described with reference to the accompanying drawings.
19. 19. A ventilated structure or space substantially as hereby described with reference to the accompanying drawings.
20. 20. A method of controlling ventilation in a ventilation system substantially as hereinbefore described with reference to the accompanying drawings.