GB2530911A

GB2530911A - Air ventilation unit

Info

Publication number: GB2530911A
Application number: GB1517224.0A
Authority: GB
Inventors: Colin Edward Broom
Original assignee: Eco Acoustics Ltd
Current assignee: Eco Acoustics Ltd
Priority date: 2014-10-03
Filing date: 2015-09-29
Publication date: 2016-04-06
Anticipated expiration: 2035-09-29
Also published as: GB201517224D0; GB2530911B; GB201417929D0

Abstract

An air-to-air heat recovery air ventilation unit 10 having a heat exchange unit 12, a fresh air flow path 14 and an extracted air flow path 16, both of the flow paths passing through the heat exchange unit whereby heat recovery can be effected. The air ventilation unit has a fresh air flow path obturator 18 (flap) and an extracted air flow path obturator 20; the obturators being operable to close the respective flow paths to a portion 12b of the heat exchange unit. The portion of the heat exchange unit can be in the range of twenty five percent to eighty percent of the whole heat exchange unit, preferably fifty percent. Preferably, each obturator is in the form of one or more plates, pivoted about the longitudinal centre line or a longitudinal edge. A method of air-to-air heat recovery air ventilation is disclosed. Heat exchange efficiency is maintained when a reduced level of ventilation is required. Reduction of the operating volume of the heat exchange unit results in reduced fan speed, power consumption and fan noise. The obturators can be controlled by a carbon dioxide sensor.

Description

Air Ventilation Unit The present invention relates to an air ventilation unit and in particular to an air-to-air heat recovery air ventilation unit. The invention also relates to a method of air-to-air heat recovery air ventilation.

Heat recovery air ventilation units and methods of heat recovery air ventilation are well known.

US patent publication 2013/0048267 Al discloses a ventilation unit having a supply air passage and a discharge air passage with a heat exchanger effecting heat recovery between air flowing in the two passages. The discharge air passage has a damper which is under the control of a temperature sensor and which operates so that discharge air can bypass the heat exchanger. Thus. the temperature of air supplied to a room can he controlled.

Similarly, International patent publication W02012/0l 1865 A2 discloses an air handling unit which is provided with a bypass damper. The damper is operated so that air bypasses the heat exchanger when Cull heat recovery is not required.

International patent publication WO 01/22021 Al is concerned with a method of defrosting a heat exchanger in an air ventilation unit. The fresh air supply to the heat exchanger is via two chambers, each supplying a respective one half of the fresh air supply side of the heat exchanger. Respective dampers are provided so that the chambers can he individually closed to the fresh air supply. Should defrosting be required, one of the dampers is operated to close the respective chamber. A full supply of heated fresh air to the room being ventilated is maintained by the fresh air supply via the other chamber. The air extracted from the room continues to flow through the whole heat exchanger; whereby the half of the heat exchanger associated with the closed chamber is defrosted.

None of the above mentioned patent publications are directed to the question of maintaining heat exchange efficiency when a reduced level ol ventilation is required. In conventional heat recovery ventilation units, airflow must be maintained at. or close to. 100% in order for the heat recovery to operate at maximum temperature efficiency. To meet latest energy saving Building Regulations ventilation units are required to operate on a trickle' speed mode, boosting to a higher speed when a signal from a room sensor, such as a CO2 transmitter is received. The speed/airflow change ratio is typically 50% on Trickle' to 90- 100% on Boost'. This precludes typical heat recovery units from being used as a normal heat exchanger will go into a laminar-flow' condition at the lower duty thus dis-enabling heat transfer to take place as this requires a turbulent-flow' condition to exist. Selecting a heat exchanger which could operate at the lower airflow and merely boosting the airflow upon a sensor signal is also not an option as the resistance through the exchanger would increase four-fold requiring an unacceptable increase in motor input power and fan noise. Obviously the temperature within (he room being ventilated is important in determining if heat recovery is required. However, a number of different circumstances can arise which result in a requirement for a reduced level of ventilation while maintaining heat exchange efficiency.

For example, the CO2 content of the air in the room can determine the level of ventilation required. The CO2 content of the air may he officially regulated, as is often the case for Classrooms. Thus, if the CO2 content is low only a reduced level of ventilation would be required but the heat exchange efficiency would certainly need to be maintained so that temperature of air being supplied to the room is maintained at a comfortable level. (One of the main reasons for providing air-to-air heat recovery is to ensure that cold air from outside is not supplied direct into the space served, thus causing unacceptable draughts). Other considerations include: lower fan speed to reduce noise; velocity of airflow within the room; and, of course, power consumption by the fans.

Heat exchangers in air-to-air heat recovery air ventilation units work within a very narrow air velocity bandwidth. Outside of this narrow bandwidth heat exchange is significantly reduced or fails completely, if the airflow velocity is too high the fans consume too much power. thus wasting energy. Indeed, in sonic countries (including the UK) the national regulations prohibit the use of air ventilation units in which the fan power consumption is too high. If the airflow velocity is too low a laminar airflow condition can arise within the heat exchanger which prevents effective heat recovery from taking place.

Thus a suitable airflow velocity needs to he determined and maintained: low enough to meet the power consumption requirements imposed on the fans (often referred to as specific fan power) but high enough to prevent a laminar airflow condition within the heat exchanger. It is lound that (lie difference between the highest permitted speci lie fan power and the lowest airflow velocity for effective heat exchange is typically 10-20%. That is. from the highest specific fan power the system can only be turned down by 10-20% before effective heat transfer ceases. This severely limits the amount by which the level of ventilation can be reduced while maintaining effective heat exchange.

A problem thus exists in maintaining heat exchange efficiency when a reduced level of ventilation is required. The present invention seeks to mitigate this problem.

According to a first aspect of the present invention there is provided an air-to-air heat recovery air ventilation unit having a heat exchange unit, a fresh air flow path and an extracted air flow path. both of the flow paths passing through the heat exchange unit whereby heat recovery can be effected, wherein the air ventilation unit has a fresh air flow path obturator and an extracted air flow path obturator with the obturators being operable to close the respective flow path to a portion of the heat exchange unit.

According to a second aspect of the present invention there is provided a method of air-to-air heat recovery air ventilation wherein a fresh air flow path and an extracted air flow path both pass through a heat exchange unit whereby heat recovery can be effected, the method comprising the step of closing both flow paths to a portion of the heat exchange unit when reduced ventilation is required.

Preferably, the said portion of the heat exchange unit is in the range of twenty five percent to eighty percent of the whole of the heat exchange unit.

Beneficially, the said portion of the heat exchange unit is fifty percent of the whole of the heat exchange unit.

Preferably, each obturator is in the form of one or more plates.

More preferably, at least one of the obturators comprises a rectangular plate pivoted about the longitudinal centre line thereof.

Again more preferably. at least one of the obturators comprises a rectangular plate pivoted about a longitudinal edge thereof A preferred embodiment of the present invention will now be described, by way of example only and with reference to the accompanying drawings, in which:-Figure 1 is a diagrammatic plan view illustrating typical air paths in an air-to-air heat recovery air ventilation unit.

Figure 2 is a diagrammatic longitudinal cross-section illustrating part of the unit shown in figure 1 with a fresh air balancing flap in an open position, Figure 3 is the same view as in figure 2 but with the balancing flap in the closed position, Figure 4 is a diagrammatic lateral cross-section illustrating part of a unit similar to that shown in figure 1 with a fresh air balancing flap and an extracted air balancing flap both in an open position, and Figure 5 is the same view as in figure 4 hut with the balancing flaps in the closed position.

Referring to the diagrammatic plan view of figure 1, there is shown an air-to-air heat recovery air ventilation unit 10 having a heat exchange unit 12. a fresh air flow path 14 and an extracted air flow path 16. The flow paths 14, 16 pass through the heat exchange unit 12 whereby heat recovery can be effected. The air ventilation unit has a fresh air flow path obturator 18 and an extracted air flow path obturator 20. The obturators 18, 20 are operable to close the respective flow path 14, 16 to a portion of the heat exchange unit 12. Air flows in the air paths due to (he operation of fans 22.

As illustrated in figure 1. the ohturators 18, 20 are in the form of one or more rectangular plates or balancing flaps. The fresh air balancing flap 18 is shown as being pivoted along it's longitudinal centre line. The extracted air balancing flap 20 is shown as two plates pivoted along a longitudinal edge of each plate. The pivot position of each plate can be varied, with the arrangement as shown being a preferred option for ease of manufacture of the unit 10. In this embodiment, the pivot spindles of the balancing flaps are rotated by small electric motors.

Figure 2 is a diagrammatic longitudinal cross-section illustrating part of the ventilation unit 10 shown in figure 1 with a fresh air balancing flap 18 in an open position. With the fresh air balancing flap 18 in the open position, as illustrated, the fresh air intake fans 22 are run at, or close to, 100% of their operational maximum. A maximum volume of fresh air per unit ti me thus passes through the full extent of the heat exchange unit 12.

When there is a requirement for a reduced level of ventilation, both the fresh air and extracted air balancing flaps are closed. For example. a CO2 sensor (not shown) may detect that the CO2 level in the room being ventilated is relatively low and that consequently only a reduced level of ventilation is required. The balancing flaps 18 and 20 are thus closed, preferably by an electronic control system (not shown) linked to the sensor. Figure 3 corresponds to figure 2 but shows the fresh air balancing flap 18 in the closed position. As depicted in figure 3, this closes off 50% of the heat exchange unit 12. The fresh air 14 flows only through part 12a of the heat exchange unit while a portion l2b is closed off. As the heat exchanger plates of the heat exchange unit 12 are disposed horizontally, fresh air 14 flows through portion I 2a of the heat exchange unit but cannot enter the portion I 2h. The extracted air balancing flaps 20 are operated correspondingly so as also to close off the portion 12b to the flow of extracted air 16. With airflow through the heat exchange unit 12 thus limited to 50% of the whole of (he heat exchange unit, the fans 22 can be "turned down" or reduced in speed by approximately 50% and still maintain the same relative airflow per volume of heat exchanger per unit time as if the fans were running at full speed with all the balancing flaps open. Thus, despite the substantially reduced fan speed, the airflow in the "open" portion 12a of the heat exchange unit 12 remains turbulent and thus effective heat transfer is maintained.

In this condition, airflow into and out of the room is substantially reduced. Of course, the power being consumed by the fans is reduced and in most eases there will be a reduction in noise from the fans etc. There has been described a 50% reduction of operating volume of the heat exchange unit with a corresponding 50% reduction of fan speed awl/or power consumption. This is for case of description. There is not necessarily an exact linear relationship between the two, hut the general concept of substantially lowering the fan speed and/or power consumption while maintaining effective heat recovery has been explained. Similarly, while a 50% reduction of operating volume of the heat exchange has been described and illustrated; the invention is not limited to this percentage reduction. There are no precise limits to the percentage reduction in the operating volume of the heat exchange. However, in practice it is considered that the most useful range would be twenty five percent to eighty percent of the whole of the heat exchange unit. That is, the common portion I 2h of the heat exchanger unit 12 which is closed off can be in the range twenty five percent to eighty percent of the whole of the heat exchange unit. The portion 12a which remains open is, of course. correspondingly in the range seventy live percent to twenty percent of the whole of the heat exchange unit. For the closed olT portion 12h, much below 25% and one starts to approach the same position as the 10-20% reduction of airflow which may just about be achieved without any reduction in the effective volume of the heat exchange unit. Much above 80% is considered to be such a massive reduction in ventilation as not to he of any great practical application.

Figure 4 is a diagrammatic lateral cross-section illustrating part of a ventilation unit similar to that shown in figure 1 with a fresh air balancing flap 18 and an extracted air balancing flap 20 both in an open position. In the arrangement of figure 4 the fresh air balancing flap 18 is pivoted along it's lower longitudinal edge, in contrast to the centre line pivot shown in figure 2. hi figure 4, the extracted air balancing flap 20 is pivoted along it's lower longitudinal edge; the same as is the case in figure 2. The pivot points are determined according to laclors such as ease of manufacturing the unit 10. Figure 5 is the same view as in figure 4 but with the balancing llaps 18 and 20 in the closed position. Operation of the ventilation unit illustrated in figures 4 and 5 is the same as described above in relation to figures 2 and 3.

Thus, there has also been described a method of air-to-air heat recovery air ventilation wherein a fresh air flow path 14 and an extracted air flow path 16 both pass through a heat exchange unit 12 whereby heat recovery can be effected, the method comprising the step of closing both flow paths 14, 16 to a portion of the heat exchange unit 12 when reduced ventilation is required.

Claims

Claims 1. An air-to-air heat recovery aft ventilation unit having a heat exchange unit, a fresh air flow path and an extracted air flow path, both of the how paths passing through the heat exchange unit whereby heat recovery can he effected, wherein the air ventilation unit has a fresh air flow path obturator and an extracted air flow path obturator with the obturators being operable to close the respective flow path to a portion of the heat exchange unit.
2. An air ventilation unit as claimed in claim 1. said portion of the heat exchange unit is in the range of twenty five percent to eighty percent of the whole of the heat exchange unit.
3. An air ventilation unit as claimed in claim I, said portion of die heat exchange unit is fifty percent of the whole of the heat exchange unit.
4. An air ventilation unit as claimed in any preceding claim, wherein each obturator is in the form of one or more plates.
5. An air ventilation unit as claimed in claim 4, wherein at least one of the ohturators comprises a rectangular plate pivoted about the longitudinal centre line thereof.
6. An air ventilation unit as claimed in claim 4 or claim 5, wherein at least. one of the obturators comprises a rectangifiar plate pivoted about a longitudinal edge thereof.
7. An air-to-air heat recovery air ventilation unit substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
8. A method of air-to-air heat recovery air ventilation wherein a fresh air flow path and an extracted air flow path both pass through a heat exchange unit whereby heat recovery can be effected, the method compnsing the step of closing both flow paths to a portion of the heat exchange unit when reduced ventilation is required.
9. A method as claimed in claim 8. wherein the step of closing both flow paths consists of closing the flow paths to a portion of the heat exchange unit which is in the range of twenty five percent to eighty percent of the whole of the heat exchange unit.I (1 A method as claimed in claim 8, wherein the step of closing both flow paths consists of closing the flow paths to fifty percent of the heat exchange unit.