GB2381061A

GB2381061A - Dehumidifiers

Info

Publication number: GB2381061A
Application number: GB0125052A
Authority: GB
Inventors: John Edward Gough
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-10-18
Filing date: 2001-10-18
Publication date: 2003-04-23
Also published as: GB0125052D0

Abstract

A dehumidifier may be in the form of a plurality of hollow flat plates or a number of tubes (8,9) located in an air stream requiring moisture removal without the risk of freezing and preventing air flow. Frost formed on the flat plates is removed by a plurality of parallel scrapers (5) which are mechanically driven by a motor (6) vertically upwards and downwards between and in contact with the respective plates. Frost formed on the tubes (8,9) is removed by a similarly vertically movable plate (10) having scraper rings (11, Fig.6) surrounding the respective tubes (8,9). A second scraper (12) travels horizontally across the bottom of the dehumidifier within a drip tray (16) collecting frost from the scrapers (5) or plate (10). The scrapers (5) or plate (10) remain static at the bottom of their stroke until passed by the scraper (12). The scraper (12) is an inverted bucket scoop which at the end of its stroke comes into contact with a worm screw (14) which removes ice deposits from the scoop. The worm screw (14) pushes the ice into an insulated collection device (18, Fig.9). The collection device includes a level switch which is able to stop frost collection when liquid in the device reaches a predetermined level.

Description

THIS INVENTION RELATES TO LOW AIR TEMPERATURE DEHUMIDIFICATION. Dehumidifiers are available in two forms, the first utilising a desiccant and the second utilising the refrigerant vapour compression cycle.

With the first the desiccant is better suited to low temperatures but needs to be reactivated to remain operational i. e. dried and so a wet air stream is created in achieving this. This wet air requires discharging via a pipe or duct to a point outside of the controlled space. This is not practical in many situations and limits the potential of the dehumidifier in it not being portable. In addition air is required to replenish that exhausted by the reactivation process and such air could be higher in moisture content than that being dehumidified therefore increasing the work load.

With the second the evaporator comprising of tubes with fins mechanically bonded to them is not suitable in low air temperatures. This is because the fluid within the tubes needs to be at a temperature below the dew point of the air to condense the moisture within the air. When the moisture condenses it immediately freezes onto the coil surface unlike at higher air temperatures where it naturally drips out of the coil into a collection tray.

If the cycle is allowed to continue in low air temperature conditions the ice formed builds up until there is no airflow across the coil. When airflow ceases the process is non-operational, i. e. No further dehumidification takes place. In these situations liquid refrigerant can return to the compressor, which will result in equipment failure. Should a defrost cycle be incorporated the dehumidifier is not operational during this cycle and some moisture previously removed is allowed to evaporate back into the controlled space. The process should be continuous to maximise plant thermal efficiency in low air temperature conditions where the refrigeration performance is at its minimum.

With the present invention a dehumidification cooling coil provides operation without the need for defrost cycles even at low air temperature achieved by mechanically removing the ice formed on the coil surface in contact with the air being processed and a means for subsequent collection to minimise moisture migration back into the controlled space.

With this invention there are two forms of dehumidification coil, the first having hollow plates and the second having fin less tubes. Both forms utilise a refrigeration plant with refrigerant directly passing through them or with a secondary coolant such as brine, thermofluid or glycol solution passing through them.

Continuous operation is achieved by mechanically removing the ice formed on the dehumidification coil surface in contact with the air being processed. By regular removal of the ice the air path is kept clear and the need for defrost cycles eliminated.

For simplicity the dehumidification coil is referred to as an evaporator due to the fact that if refrigerant passes through it as a component of the refrigerant vapour compression cycle then it would be called an evaporator even though its function condenses moisture from the air it is processing.

Making reference to the following accompanying drawings the first form of this invention i. e. hollow plates is now described where: Figure 1 shows the vertical hollow panels, which form the evaporator.

Figure 2 shows an isometric view of the scraper assembly with one of the parallel motion guides not shown for clarity.

Figure 3 shows an isometric exploded view of part of the scraper and frame.

Figure 4 shows a section through the evaporator assembly and demonstrates the location of the scraper.

Referring to the drawings, for demonstration purposes twelve hollow panels (1) are shown.

These are positioned and bonded side by side to provide a common hollow vessel in which the liquid refrigerant enters each panel at the distributor connection (2) where it evaporates and exits at the common suction outlet (3). Depending upon the design duty required the size and quantity of panels (1) would vary to provide the required surface area. These panels would be brazed or metalurgically bonded in sequence to from the single evaporator. The clearance gap between the panels (1) allows the process air to pass in a single direction. It is within this gap where ice is formed and collects during dehumidification and where the scrapers (5) shown in figure 2 are accommodated. The scrapers (5) extend the depth of the evaporator panels (1) as shown in figure 4. To improve efficiency the panels (1) could be corrugated when viewed from above with the scraper (5) having the same profile, offset to interlock. This would increase the contact factor and minimise the volume of air not being processed.

For the demonstration with twelve panels (1) forming the evaporator assembly there are eleven scrapers (5), one located in each air gap. The quantity of scrapers (5) is dependent upon the number of panels (1). Each scraper (5) is connected to the adjoining scraper (5) if manufactured as individual items or may be manufactured as a single comb component. The cross section of each scraper (5) blade has a profile to encourage easy vertical upward motion within the air gap whilst in the downward motion the panels are cleared of ice deposits formed during the dehumidification process. The parallel scrapers (5) have a timed, temperature controlled, pressure controlled or continuous vertical motion upwards and downwards by means of a drive motor through worm screw (6), rack and pinion or similar device maintaining parallel motion of the scrapers (5) between the evaporator panels (1). A frame (7) sized to suit the face area of the evaporator, house the drive device and its components is used to locate and secure the scraper (5) assembly to the evaporator panels (1) assembly.

During operation the ice formed on the evaporator panels (1) is removed from the air gap by scrapers (5) during their downward motion, the ice is pushed out of the bottom gap where it is collected and removed. This part of the process is described for both forms of the device later within this document.

In figure I and figure 4, insulation (4) is shown on the external perimeter surfaces of the evaporator panels (1) and the suction header of the evaporator panels assembly where air is not passed across and the scrapers (5) do not operate. This is to enhance performance of the

evaporator assembly, eliminate ice formation to these surfaces and minimise risk of frost damage to other surrounding components.

And now by making reference to the following accompanying drawings the second form of this invention is now described where Figure 5 shows a section of the tube in tube evaporator and typical coolant circuiting diagram and Figure 6 shows a section of the ice removal plate (10) with scraper rings (11) together with the tube in tube evaporator and plug (22).

Referring to the drawings tubes (8), capped at the bottom by means of a plug (22) formed with a parallel shoulder to recess into tube (8) having a flat bottom and concave top to encourage fluid flow upwards. The overall diameter of plug (22) would equal that of tube (8) and be metalurgically bonded and finished to ensure the plug (22) and tube (8) are parallel on their external surface. These are positioned in a manner similar to a conventional fluid to air evaporator coil to maximise air contact however do not have fins, are vertical in orientation and have a tube (9) positioned within thus eliminating the need for return bends, common to a conventional coil. The outer surfaces of the tubes (8) are in contact with the process air and it is upon these surfaces that the moisture contained within the process air condenses and either drips off or condenses onto and freezes.

The first point of entry of the coolant is at the air off coil position of the evaporator assembly.

The coolant is delivered into the inner tube (9) where it moves downward, exits the open end of the inner tube (9) and enters the evaporator tube (8) travelling upwards. The coolant, no longer at its coldest condition, having been passed through the last row of evaporator tubes (8) is then delivered by pipes to the inner tube (9) of the second row nearest air off coil position of the evaporator where it extends downward to exit the open end of tube (9) and rise through the associated tube (8). Again at the top of evaporator tube (8) the coolant, slightly warmer than the previous, continues through the evaporator assembly in the same manner until it reaches the last row. At this point, the entry point of the process air, the coolant passes down through inner tube (9) and after absorbing heat from the process air exits by a pipe work header at the top connecting the several rows forming the evaporator where it is returned to the cooling plant.

The scraper plate (10) is formed from a stable plastic material either machined from sheet material or moulded prior machine finish. The horizontal plate (10) connects to a drive device (6) such as that of the first form evaporator to provide vertical upward and downward motion. The Plate (10) has a series of holes to suit the centres of the evaporator tubes (8), these holes having clearance and a rebate on the underside. A bonded type seal comprising Annulus and V-type ring forms the scraper ring (11) which is secured into the rebates of the scraper plate (10). The V-type ring permits unrestricted upward motion however grips the evaporator tube (8) on the downward motion of the scraper plate (10) thus forcing the ice formed to the bottom of the evaporator block where it is disposed of prior the return of the same scraper plate (10) to its uppermost position.

To complete the evaporator assembly, of both forms of this invention, by making reference to the following drawings the ice disposal is now described where: Figure 7 shows views of the drip tray, horizontal ice scraper and worm screw.

Figure 8 shows a section of the drip tray, horizontal ice scraper, worm screw and evaporator assembly, of the second form, with scraper plate, tubes and scraper rings.

For both forms the ice cleared from the evaporator surface is pushed to the bottom by the prongs (5) or the plate (10) and drive device (6). When the prongs (5) or the plate (10) reach the bottom of their stroke a second scraper (12) moves horizontally across the width of the prongs (5) or plates (10) by means of a parallel motion device (15) similar to drive device (6).

This scraper (12) is in contact with the bottom of the prongs (5) or plate (10) both of which remain static at the bottom of their stroke until the width has been passed by the scraper (12). This scraper (12) formed of a similar material to that of the prongs (5) or plate (10) is formed like an inverted bucket scoop as shown in figure (10) and when at the end of its stroke comes into contact with the worm screw (14) at which point the prongs (5) or plate (10) return to their top position. The bottom scraper (12) remains static for a period of time while the worm screw (14) removes the ice deposits from the scraper (12) following which the drive device (15) returns the scraper (12) back to its housing within the drip tray (16). The drip tray (16) moulded or formed from several mouldings, has insulation to assist performance and efficiency.

Figure 9 shows a section through the worm screw (14), drip tray (16), delivery tube (17), collection device (18), delivery tube airtight collar (19), air release valve (20), level switch (21) and location of heat source together with the second form of evaporator.

Making reference to figure 9 the worm screw (14) pushes the ice into a suitably sealed and insulated collection device (18) beneath the complete assembly via a tube (17) with air tight collar (19) preventing moisture migration back into the controlled space from the collection device. If the evaporator assembly is used within, for example a conventional packaged dehumidifier of the refrigeration compression cycle type, the evaporator collection device (18) could utilise some of the heat of rejection to melt the ice deposited into the collection device (18) allowing it to level off rather than collecting into a frozen heap. The level switch (21) is incorporated to stop the process when the collection device (18) reaches a predetermined liquid level. As the condensate fills the collection device (18) the air being displaced is allowed into the controlled space via the air release valve (20). The collection device (18) would comprise of a fixed top section and removable bottom section to allow manual removal when full. The bottom section of the collection device (18) would incorporate a gasket joint and means of securing to the fixed top section, this joint being located above the maximum condensate level. The drain could be piped to a suitable drainage point out of the conditioned space if this is desirable and practical.

The completed assembly, evaporator, scraper plate, drip tray etc. is tilted slightly backward at the top in the direction of air flow and side wards at the top towards the worm screw assembly (14) to encourage the ice or water to move down towards and into the worm screw assembly (14) and hence into the collection device (18). When incorporated within a conventional dehumidifier the casework design of the finished product would accommodate and conceal this design feature. Air being processed requires fan assistance in the normal manner, which connects to inlet and outlet spigots (23) secured to the evaporator case, these spigots being suitably sized for the air volume and coil face area.

Claims

CLAIMS 1. A dehumidification cooling coil providing operation without the need for defrost cycles even at low air temperature achieved by mechanically removing the ice formed on the coil surface in contact with the air being processed and subsequent collection to minimise moisture migration back into the controlled space.
2. A dehumidification cooling coil as in claim 1 where in the coil takes 2 forms, the first having hollow plates forming a single vessel vertically side by side with an air gap between each plate and the second having vertical tubes capped at the bottom and containing an internal tube providing coolant inlet. The vertical tubes supported and connected to one another by pipe work in an arrangement to maximise air contact.
3. A dehumidification cooling coil as in claim 1 or claim 2 where in ice removal from the coil surface in contact with the air being processed is provided by 2 forms of scraper positioned within the air gap and achieving contact with the coil surface. To satisfy coil form 1 the scraper takes the form of a comb having prongs extending into the air gap between the hollow plates and to satisfy coil form 2 the scraper takes the form of a horizontal plate with a series of holes to accommodate the vertical tubes. The scrapers are driven downwards to collect the ice deposited upon the coil and then return to their starting position at the top of the coil out of the air stream.
4. A dehumidification cooling coil as in claim lor claim 2 or claim 3 provided with a horizontal scraper located within a drip tray beneath the coil, mechanically engaged to remove the ice previously collected from the coil surface by the vertically moving scraper at its bottom stroke.
5. A dehumidification cooling coil as in claim 1 or claim 2 or claim 3 or claim 4 provided with a drip tray to accommodate a horizontal scraper beneath the coil and a rotating worm screw which is contacted by the horizontal scraper at the end of its stroke. The continuous rotation and direction of screw moves the ice deposit off the horizontal scraper and into a delivery tube leading into a collection device.
6. A dehumidification cooling coil as in claim 1 or claim 2 or claim 3 or claim 4 or claim 5 provided with an insulated casing complete with spigots providing effective coil face area, means of directing the air being processed and incorporate the guides and drive devices for the scrapers and worm screw.
7. A dehumidification cooling coil as in any preceding claim provided with a semi- detatchable collection device equipped with gasketed joint, level switch, air release valve and heat source to melt the ice collected.