Refrigeration – Utilizing solar energy
Reexamination Certificate
2001-05-22
2004-08-17
Tanner, Harry B. (Department: 3744)
Refrigeration
Utilizing solar energy
C237S00200B, C126S690000
Reexamination Certificate
active
06775999
ABSTRACT:
FIELD OF THE INVENTION
The invention claimed and disclosed herein pertains to heat pumps, and more particularly to methods and apparatus to improve the efficiency of an evaporator in a heat pump.
BACKGROUND OF THE INVENTION
A heat pump can be a useful apparatus for heating or cooling an indoor environmental space, such as a home or an office building. The great majority of heat pumps work on an air-to-air-basis. That is, the heat pump moves thermal energy from one mass of air to another mass of air. The two masses of air typically are air in the indoor environmental space, and outdoor atmospheric air. In essence, the heat pump is configured as a reversible refrigeration unit. That is, the heat pump can be operated so as to cool the indoor environmental air, or it can be operated to cool the outdoor environmental air (in which case the thermal energy from the outdoor atmospheric air is transferred to the indoor environmental space, thereby effectively heating the indoor air).
FIG. 1
depicts a prior art refrigeration system
1
. This system can be considered as essentially “half” of a heat pump. (A heat pump actually includes two thermal expansion valves versus just the one valve
4
depicted in the figure, as well as a reversing valve to reverse the direction of flow of refrigerant in the system. The simplified system
1
of
FIG. 1
is shown for illustrative purposes only.) In
FIG. 1
, when the heat pump is operating to warm the indoor environmental space (and conversely cool the outdoor atmospheric air), the condenser
3
is located in the indoor space, and the evaporator is located in an outdoor environment. The system
1
circulates a refrigerant in a closed loop, as indicated by the flow direction arrows in the figure. Refrigerant in a vapor form is discharged from the compressor
2
(or “K”), and is directed to the condenser
3
. As the refrigerant passes through the condenser, heat is extracted from the refrigerant by passing the indoor air over a series of coils through which the refrigerant passes. As heat Q
B
is extracted from the refrigerant (and passed to the indoor environmental space), the refrigerant condenses from a vapor form to a liquid form. The liquid refrigerant then passes through a thermal expansion valve
4
where it flashes from a liquid to a vapor. The heat of vaporization causes a significant drop in the temperature of the refrigerant. The refrigerant is then passed through the evaporator
5
, where it absorbs energy Q
B
from the outdoor atmospheric air. The evaporator
5
comprises a series of tubing coils through which the refrigerant is passed. The refrigerant coils are typically in thermal energy communication with a series of heat transfer plates (or fins) which provide a larger surface area over which the heat transfer process can occur. The outdoor atmospheric air is forcibly moved over the heat transfer plates by a fan, and thus energy from the outdoor air is transferred to the refrigerant so that it can be subsequently transferred to the indoor air in the manner just described.
FIG. 2
depicts a typical installation for a heat pump evaporator. The setting is a residential house “H”. The heat pump evaporator
10
(also known as the outdoor heat exchanger) is typically located proximate to one side of the house. Refrigerant inlet and outlet lines
12
and
14
connect the heat pump evaporator to the other the components of the heat pump, which can be located in the house “H”. The heat pump is commonly supported by a slab or a platform
11
. The evaporator
10
is provided with a fan
16
which causes air to be drawn in from the sides of the evaporator and exhausted from the top of the evaporator. As the air is drawn through the evaporator, it passes over heat transfer plates
18
in the manner described above.
It should be appreciated that when the heat pump is operating to heat the indoor air, the outdoor heat exchanger operates as an evaporator. However, when the heat pump is operated to cool the indoor air, then the outdoor heat exchanger operates as a condenser. Since the present invention pertains to a heat pump operating in a mode to heat indoor air, I will refer to the outdoor heat exchanger as an “evaporator”.
Under the right conditions, a heat pump can be a very effective and efficient device for heating (and cooling) an indoor environmental space. However, in locations where the outdoor temperature can be very cold, or where the average temperature in winter months is relatively low, then the heat pump becomes less efficient since the thermal gradient between the refrigerant in the evaporator and the outdoor air can be low. That is, the higher the thermal gradient between the refrigerant in the evaporator and the outdoor air, the more effective the heat pump will be at heating the indoor space.
What is needed then is a heat pump which achieves the benefits to be derived from similar prior art devices, but which avoids the shortcomings and detriments individually associated therewith.
SUMMARY OF THE INVENTION
The present invention provides for methods and apparatus to increase the performance of an evaporator in a heat pump system when the heat pump system is being used to heat an indoor environmental space. The invention allows the performance of the heat pump evaporator to be increased by directing solar radiation to heat transfer plates within the evaporator. Generally, the evaporator is located in an outdoor environment.
A first embodiment of the present invention provides for a solar reflector for the evaporator described in the previous paragraph. The solar reflector includes a curved surface configured to reflect solar radiation to the heat transfer plates of the evaporator. The curved can be in the shape of a truncated parabola. That is, the curved surface is formed like a parabolic dish, but the bottom of the dish is “cut off”. This results in an opening in the curved surface which can accommodate the evaporator so that the curved surface can be placed around the evaporator by lowering it over the evaporator from the top. Further, the curved surface can be a dish-like shape (not necessarily parabolic) such that the curved surface defines an upper perimeter and a lower perimeter. The lower perimeter then defines a bottom opening which accommodate the evaporator. In this way the solar reflector can be placed around (at least part of) the evaporator to focus reflected solar radiation towards the heat transfer surfaces of the evaporator. This solar radiation warms the heat transfer surfaces, thus providing more energy which can be used to heat the indoor environmental space.
Since the evaporator can be provided with a refrigerant supply line and a refrigerant return line (as well as an electrical power line), these service lines can interfere with a solar reflector which is configured to completely surround the evaporator. Accordingly, the upper and lower perimeters of the curved surface can be configured to each form a partial circle, rather than a full circle. The “gaps” in each of the perimeters can then be aligned to thusly define a gap in the curved surface. The gap can then receive one of more of the service lines to allow the curved surface to be fit around the evaporator.
Also, in some instances the evaporator is located close to a building or a structure, and so it is not possible to completely surround the evaporator with a dish-type solar reflector. In this case the upper perimeter of the solar reflector can form a partial circle, and the lower perimeter can define three sides of a rectangular opening (or a partial circular opening). The rectangular opening (or the partial circular opening) is configured to receive the evaporator. In this case, rather than drop the solar reflector over the evaporator from the top, the solar reflector can be “slid” into place from the side of the evaporator.
To further improve the performance of the solar reflector, the inner surface (i.e., the surface facing the evaporator) of the curved surface can be a highly reflective surface. For example, the curved surface can be fabricated f
Reid John S.
Reidlaw, L.L.C.
Tanner Harry B.
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