CA3066568A1 - An air-to-air heat and energy recovery ventilator that can be configured for portability - Google Patents

Abstract

ABSTRACT
An invention that alleviates the challenges associated with providing energy-efficient ventilation in air-tight buildings at a reasonable cost is presented. The invention is an air-to-air heat and energy recovery ventilator (H/ERV) that can be used to passively heat or cool and/or humidify or dehumidify air depending on the operating condition. Furthermore, the H/ERV
may be specially designed and operated as a portable ventilation system. The H/ERV is based on a modular design in which appropriate off-the-shelf parts can be tightly assembled to achieve leak-proof operation.
The critical component of the H/ERV is a polymer-based, compact, and efficient quasi-counter-flow shell-and-tube exchanger. The exchanger facilitates the transfer of heat or energy between two separate air streams that are at different temperatures and/or humidity.

Description

TITLE
An air-to-air heat and energy recovery ventilator that can be configured for portability BACKGROUND OF THE INVENTION
Field of the Invention This invention is related to the general field of energy efficiency and sustainability in buildings.
There is an acute demand for depleting non-renewable energy resources due to a continuous increase in global population and industrialization. Importantly, buildings now account for a significant section of the energy produced globally and are increasingly designed to be air-tight and thereby minimize energy wastage. However, air-tight buildings require some form of mechanical ventilation to expel indoor pollutants such as moisture, germs, air-bone particulates, volatile organic compounds, carbon dioxide, etc., and replace the outgoing (stale) air in buildings with incoming (fresh) air from the ambient environment.
The specific subject of this invention is the equipment that is used for mechanical ventilation in buildings, which is also called a heat/energy recovery ventilator (H/ERV).
Prior Art The prior art consists of several inventions of H/ERVs. The critical component of these H/ERVs is an exchanger where heat or energy (i.e., heat and moisture) is extracted from an air stream and released to another air stream either within the same or a different air plenum. The processes of heat/energy extraction and release occur within the same air plenum for regenerative exchangers and in different air plena for recuperative exchangers. Irrespective of the details of specific inventions, the exchangers that are used in H/ERVs can be broadly categorized into five groups.
A. Recuperative flat-plate heat/energy exchangers Recuperative flat-plate heat/energy exchangers are designed to have parallel plates where non-contacting air streams flow in alternative channels usually in cross-flow or counter-cross-flow configuration. In heat exchangers, the plates are constructed from impermeable materials (e.g., polymers or metals) and only sensible heat is transferred between the air streams. However, in energy exchangers, permeable plates (e.g., membranes) enable the transfer of heat and moisture between the air streams.

2 B. Regenerative flat-plate heat/energy exchangers Regenerative flat-plate heat/energy exchangers extract and store heat/energy from an air stream flowing in one direction within the matrix of an exchanger for a period of time. Afterwards, the direction of air flow is reversed and the stored heat/energy is released to a new air stream. These exchangers operate periodically and in pairs such that, at each point in time, a unit delivers fresh air to a space whereas another unit expels stale air from the space.
C. Regenerative heat/energy wheels Regenerative heat/energy wheels are similar to regenerative flat-plate heat/energy exchangers except that, instead of periodically reversing the direction of air flow, two regions of a rotating wheel (that houses an exchanger) are simultaneously exposed to two air streams that are flowing = in opposite directions.
D. Liquid loop heat/energy exchanger systems Liquid loop heat/energy exchanger systems typically consist of two exchangers in which a stream of liquid (e.g., desiccant solution) extracts heat/energy from an air stream in a liquid-to-air exchanger (LAE), flows through a loop, releases the heat/energy to another air stream in a different LAE, and continuously repeats the cycle.
E. Heat pipe heat exchangers Heat pipe heat exchangers are different from exchangers A ¨ D because heat transfer is mainly achieved through the phase change of a liquid that is enclosed in a chamber at vacuum pressure.
As air comes in contact with one end (evaporator) of the heat pipe heat exchanger, the liquid in the chamber absorbs heat from the air stream, vaporizes, and transports to the other end (condenser) of the heat pipe heat exchanger where it releases the heat to a different air stream and condenses to liquid state before it is transported back to the evaporator to repeat the cycle.
The aforementioned state-of-the-art exchanger technologies that are used in H/ERVs have key manufacturing and operational limitations.
Specialized machinery and machined components are often needed to manufacture existing exchangers (A ¨ E), and these result in a high production cost for the H/ERVs.
Due to the geometric structure of theses exchangers, H/ERVs are not designed based on a modular approach

3 with interconnecting components and can, therefore, not be manufactured by using off-the-shelf materials (e.g., regular polyvinylchloride or acrylonitrile-butadiene-styrene fittings).
H/ERVs that use regenerative-type exchangers (B and C) are susceptible to leakage and the cross-over of contaminants between the different air streams. Similarly, air streams can be contaminated with carry-over from liquid desiccants if direct-contact liquid-to-air exchangers are used in liquid loop heat/energy exchanger systems (D). Although liquid loop heat/energy exchanger systems can have incoming and outgoing air streams that are situated at different locations in a building (which makes them suitable for retrofits), they require complicated infrastructure and controls.
The exchangers used in most H/ERVs are typically designed with narrow channels or matrices (A ¨ C) or narrowly-spaced fins (E) to increase the heat transfer surface area. Corrugated surface structures are also used to create turbulence and improve heat transfer in the exchangers. These design approaches make the H/ERVs susceptible to frosting in cold climates which can significantly limit their performance.
Traditionally, H/ERVs are installed in buildings to access the ambient environment by means of a dedicated ductwork system or connection(s) to an existing ductwork. Certain so-called single-room H/ERVs have been developed for use in small spaces and can be directly installed through walls, windows, ceilings, and roofs without a complex ductwork system.
Nevertheless, none of these single-room H/ERVs can be defined as portable in terms of non-invasive installation and mobility.
SUMMARY OF THE INVENTION
The invention (henceforth called "the H/ERV") is designed to provide mechanical ventilation to buildings using a novel exchanger (henceforth called "the exchanger").
The H/ERV operates by using two fans to draw two separate air streams into a shell-and-tube exchanger. Fresh air from the outdoor (i.e., the outdoor air) is drawn into the exchanger and discharged into the interior of a building as the supply air. On the other hand, stale air from the building (i.e., the return air) is vented through the exchanger to the outdoor as the exhaust air.
The exchange of heat between the air streams in the exchanger ensures that ventilation is achieved in the conditioned space while reducing the required heating or cooling load. At winter

4 conditions, the return air is typically warmer than the outdoor air and heats up the outdoor air inside the exchanger. On the other hand, at summer conditions, the outdoor air is typically warmer and releases heat to the colder return air.
Figure 1 shows the main components of the H/ERV, i.e., the exchanger (4), fans (6), and accessories which include headers (1), caps (2), mechanical couplings (3), adapters (5), and a connector chamber (7). These components are found in two other embodiments of the H/ERV, i.e., Figures 2 and 3, although the connector chamber (7) in Figure 1 is replaced with a differently-shaped but similar chamber (8) in Figure 3.
The H/ERV presented herein possesses a superior exchanger and certain unique features that overcome the shortcomings of existing technologies.
First, unlike existing exchangers (A ¨ D) that are made of flat plate or matrix structures, a shell-and-tube structure is adopted for the exchanger of the H/ERV. Shell-and-tube exchangers are prevalent in the process industry but are not adopted for ventilation in buildings due to their supposedly complex manufacturing, bulky structure and susceptibility to leakage. The limitations of existing shell-and-tube exchangers are overcome in this invention by using a simple, inexpensive, and robust manufacturing technique. Furthermore, prefabricated off-the-shelf parts can be used to manufacture an embodiment of the exchanger to achieve excellent effectiveness, mechanical rigidity and compactness at a moderate cost.
Secondly, the H/ERV is designed using a stringent modular philosophy such that each of its components can be attached or detached without the need for adhesives or special fasteners.
Despite the modular design of the exchanger, preliminary testing does not indicate any detectable leakage between the shell and tube sides even at differential pressures of up to 400 Pa.
The modular design that is adopted in this H/ERV is not utilized in existing H/ERVs.
Thirdly, in an embodiment of the H/ERV, except for the fans (6), the components 1 ¨ 5, 7, and 8 are polymer-based to minimize the risk of corrosion that is associated with the use of metallic exchangers, casings and components in existing H/ERVs (A ¨ E). Additionally, the polymeric smooth-surfaced tubes of the exchanger can delay the onset of frost formation.
Importantly, the exchanger is configured in such a way that the air stream with the highest risk of frosting flows in a relatively large shell space which is less susceptible to blockage even if frosting occurs.

5 Finally, the H/ERV may be specially designed to access the ambient environment (i.e., draw in the outdoor air and vent the exhaust air) such that it overcomes the challenges of invasive installation and lack of mobility that is associated with single-room H/ERVs.
There may be other superior features of the H/ERV (as compared to existing H/ERVs) which might not have been discussed in this patent but would be obvious to anyone that is skilled in the field of heat and energy recovery technologies.
LIST OF FIGURES
Figure 1 Schematic representation of an embodiment of the air-to-air heat and energy recovery ventilator (i.e., the H/ERV).
Figure 2 Schematic representation of a second embodiment of the H/ERV.
Figure 3 Schematic representation of a third embodiment of the H/ERV.
Figure 4 Schematic representation of the side-view cross-section of the exchanger.
Figure 5 An embodiment of the arrangement of tubes in the shell of the exchanger.
Figure 6 A second embodiment of the arrangement of tubes in the shell of the exchanger.
Figure 7 A third embodiment of the arrangement of tubes in the shell of the exchanger.

6 DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION
An embodiment of the H/ERV in Figure 1 is hereby described concisely. The outdoor air is drawn using a fan (6) and supplied through an adapter (5) and a connector chamber (7) to the header (1) of the tube side of the exchanger. The header (1) fits into the tube cap (2) which is attached to the shell of the exchanger using a mechanical coupling (3). The outdoor air is conditioned in the exchanger (4) and discharged to the interior of a building as the supply air through another mechanical coupling (3) which is connected to a tube cap (2) and header (1).
Similarly, in an opposite direction, the return air from the building flows through a header (1) into the exchanger (4) where it is conditioned and further flows through another header (1) at the outlet of the shell. A fan (6) that is connected to the header (1) at the outlet of the shell through an adapter (5) is used to vent the conditioned air in the shell as the exhaust air.
The exchanger (4) is a quasi-counter-flow shell-and-tube heat exchanger. As shown in Figure 4, the tube side of the exchanger consists of several rows of tubes whereas the shell side is the space cavity that encloses the tubes. The geometric dimensions of the shell and tubes are determined through the use of a simplified effectiveness¨NTU (number of heat transfer units) model. A simple mathematical ratio, which accounts for the external diameter of the tube and internal diameter of the tube cap, is used to calculate the maximum number of tubes that can fit into the shell. Holes of exacting specifications are drilled into the tube cap (2) to provide for a leak-proof and rigid connection with the tubes. Figures 5 ¨ 7 depict the arrangement of the tubes in a staggered pattern to limit stress concentration in the tube cap (2).
In a special embodiment, the H/ERV may be non-invasively installed (e.g., using short ducts and special kits) to an opening in a building (e.g., window or door) to access the ambient environment. Furthermore, the H/ERV may be subsequently decommissioned and transported to a different location without altering or damaging the structural integrity of the building. Such an embodiment of the H/ERV constitutes a portable heat and energy recovery ventilator.
The alternative embodiments of the H/ERV on holistic and component levels are described accordingly.
The embodiments of the H/ERV are not restricted to what is presented herein (i.e., Figures 1 ¨ 3) but may include other embodiments that may be developed hereafter.

7 In an embodiment of the H/ERV, an inline axial fan is used for the shell side whereas an inline mixed-flow fan is used for the tube side due to the greater resistance of the tube side to air flow.
In addition, the shell-side fan is used to push air into the exchanger to ensure adequate mixing and reduce the possibility of frost buildup whereas the exhaust air fan is used to pull air out of the exchanger (see Figures 1 ¨ 3). However, depending on fan characteristics and exchanger tube/shell side resistances, other types of fans or fan combinations may be used to provide air flow in either push or pull directions.
Sound attenuation devices may be installed in the H/ERV to limit the noise produced by the fan(s).
The H/ERV may be equipped with flow and pressure control devices to prevent over-pressurization and/or equalize the air flow rates in the shell and tube sides of the exchanger.
The H/ERV may be designed to operate as an integral component of other heating, ventilating and air-conditioning systems.
The H/ERV may be adapted for non-building applications such as mines or process systems.
The exchanger may be designed as a regenerative flat-plate heat/energy exchanger (B) such that the shell side components and fan are excluded and only the tube side components and fan are retained. The exchanger may then be operated in pairs such that, for example, in one cycle at winter conditions, the outdoor air is drawn in to extract heat from the tubes in one exchanger while the return air releases heat to the tubes in a second exchanger. The air flows may be reversed in a subsequent cycle and the operation of the exchanger may be continuously repeated.
In an embodiment of the exchanger, the shell is polymer-based, designed with a cylindrical shape, and neither includes baffles nor a moisture trap for condensates.
However, the shell can be made of alternative materials (e.g., metal) and/or shapes (e.g., square).
Furthermore, single or multiple baffles may be installed in the shell to create turbulence and enhance heat transfer.
Moisture traps may also be added to the shell to eliminate the buildup of condensates.

8 In an embodiment of the exchanger, the tubes are polymer-based and impermeable. To enhance the effectiveness of the exchanger, the tubes may be selected from materials that have higher thermal conductivities than polymers. In addition, permeable tubes may enable energy transfer between the air streams in the shell and tube sides of the exchanger.
The arrangement of tubes in the shell is not limited to Figures 5 ¨ 7 but may include other simpler or more complex arrangements that are not presented herein.
The exchanger may be designed using other flow configurations such as cross-flow, counter-flow, co-current flow or a combination of different configurations that are not presented herein.
The aforementioned alternative embodiments of the H/ERV and its components are non-exhaustive and may include other items, designs, and strategies that may improve the form and function of the H/ERV. Furthermore, all forms of alternative embodiments that are presented herein or elsewhere may be adapted individually or at different levels of individual combinations to improve the form and function of the H/ERV.

Claims (8)

9The claims of certain embodiments of a heat and energy recovery ventilator which:

1. Consists of a quasi-counter-flow shell-and-tube exchanger wherein several rows of tubes are enclosed within a shell to transfer heat or energy between two separate air streams having different temperatures and/or humidity such that one air stream flows inside the tubes and the other air stream flows in the shell for the purposes of passively heating, cooling, humidifying or dehumidifying air depending on the boundary conditions of the exchanger at the ports (1) and fans (6);

2. Is designed and developed/manufactured modularly by using components of reasonable tolerances to achieve seamless integration and mechanical rigidity;

3. Is designed and developed/manufactured such that the components consist completely of off-the-shelf parts such as polyvinylchloride- or acrylonitrile-butadiene-styrene-based pipes (suitable but not limited to 1, 4, 7, 8) and fittings (suitable but not limited to 1, 2, 4, 7, 8) and polymer mechanical couplings (suitable but not limited to 3 and 5);

4. Is designed and developed/manufactured such that the components consist partially or wholly of other suitable off-the-shelf or machined parts;

5. Is designed and developed/manufactured such that the ports (1) of the shell and tube sides of the exchanger are modularly connected to fans (6) directly or indirectly by means of other components (i.e., 1, 5, 7 and 8);

6. Uses an arrangement that maximizes the number of tubes in the shell of the exchanger while limiting stress concentration in the tube cap (2);

7. Uses an adhesive-free attachment of tubes to the tube cap (2) to prevent leakage and maintain the mechanical integrity of the exchanger;

8. Constitutes a portable heat and energy recovery ventilator that can be non-invasively installed to access the ambient environment from the interior of a building and subsequently decommissioned while also being mobile either before or after installation.