Patent Application
20080156891
1. Field of the Invention
The subject invention generally pertains to almost any type of HVAC refrigerant system but particularly to PTAC units such as those commonly used for hotel rooms. The invention more specifically pertains to a method of providing such systems with a dehumidification mode without using a reheat coil or relying on a humidistat.
2. Description of Related Art
Refrigerant systems are widely used for heating, cooling and dehumidification of a comfort zone such as a room or other area of a building. Dehumidifying air may simply involve cooling the air below its dew point. Cooling alone, however, can make a room uncomfortably cold. Thus, a heater is sometimes activated to offset the cooling effect, whereby the air can be dehumidified without changing the temperature of the room. The use of a heater while dehumidifying by cooling is known as a reheat process.
The reheat process is applicable to various refrigerant systems; however reheat is not always suitable for Packaged Terminal Air Conditioners/Heat Pumps, also known as PTAC units. PTACs are self-contained refrigerant systems often used for cooling and heating hotel rooms; however, they are also used in a variety of other commercial and residential applications such as apartments, hospitals, nursing homes, schools, and government buildings. Even though PTACs often include an electric heater for a heating mode, energizing a refrigerant compressor for cooling/dehumidifying while energizing an electric heater for reheat would draw a lot of electric current. Such current is not always available due to the often-limited current carrying capacity of the wiring leading to each PTAC unit. Although heavier wiring could be installed, the cost of the higher gage wires would need to be multiplied by the total number of PTAC units of a particular installation. For a hotel with numerous PTAC units, the total cost of the wiring is significant.
Another difficulty of providing a PTAC unit with a dehumidifying mode is that typical dehumidification methods involve the use of a humidity sensor. Examples of such systems are disclosed in U.S. Pat. Nos. 6,892,547; 6,843,068; 6,223,543; 6,070,110; 5,915,473; 5,303,561; 4,735,054; 4,003,729; 3,989,097 and 3,111,010. Although a single humidity sensor may not be that expensive, the total cost can be substantial for installations that include numerous PTAC units.
Other dehumidification schemes are disclosed in U.S. Pat. Nos. 5,743,100 and 4,850,198. The '100 patent provides a refrigerant system with additional dehumidification by continuing to operate the supply air fan for a while after the compressor has been de-energized. Although beneficial, the dehumidification that occurs during the extended but limited run time of the fan may not always be sufficient to meet the total dehumidification needs of the comfort zone. The '198 patent discloses a refrigerant system that reduces humidity by momentarily energizing the cooling system after extended off periods. Although such a system is particularly useful during the night when the cooling demand is low, the system is less valuable during periods of high cooling demand.
Due to the cost and various other drawbacks of current dehumidification methods, there exists a need a dehumidification process that is not only suited for PTAC units but is also applicable to other HVAC systems as well.
It is an object of the present invention is to provide a refrigerant system with a dehumidification mode without relying on a heater for reheat.
Another object of some embodiments is to provide a refrigerant system with a dehumidification mode without using a humidity sensor.
Another object of some embodiments is to prevent overloading a refrigerant system's electrical system by not running the system's compressor and electric heater concurrently.
Another object of some embodiments is to provide dehumidification by closing an outside air damper, decreasing the speed of the supply air fan, and effectively lowering the setpoint temperature.
Another object of some embodiments is to provide dehumidification by automatically closing an outside air damper and decreasing the speed of the supply air fan as the room temperature decreases below a setpoint temperature.
One or more of these and/or other objects of the invention are provided by a refrigerant system that dehumidifies air without relying on a humidistat and without reheating the air. To reduce the humidity, the system closes an outside air damper, decreases the speed of the supply air fan, and effectively lowers the setpoint temperature.
A refrigerant system 10, schematically shown in
In a currently preferred embodiment, system 10 can be installed at an opening 20 of a building's exterior wall 22. System 10 has an inlet 24 for receiving recirculated return air 30a from within room 12 and an outlet 26 for discharging conditioned supply air 30b back into room 12. A supply air fan 28 disposed within a housing 32 moves the air from inlet 24 to outlet 26. Housing 32 also contains an outdoor fan 34, a fresh air damper 36, and a refrigerant circuit 38. Refrigerant circuit 38 comprises compressor 16 for compressing refrigerant, an outdoor refrigerant heat exchanger 40, an expansion device 42 (e.g., thermal expansion valve, electronic expansion valve, orifice, capillary, etc.), and an indoor refrigerant heat exchanger 44.
When system 10 operates in a cooling mode, compressor 16 forces refrigerant sequentially through outdoor heat exchanger 40 functioning as a condenser to cool the refrigerant with outdoor air 30c moved by fan 34, through expansion device 42 to cool the refrigerant by expansion, and through indoor heat exchanger 44 functioning as an evaporator to absorb heat from air 30 moved by fan 44. As can be seen in
If refrigerant circuit 38 is a heat pump system operating in a heating mode, the refrigerant's direction of flow through heat exchanger 40, expansion device 42 and heat exchanger 44 is generally reversed so that indoor heat exchanger 44 functions as a condenser to heat air 30, and outdoor heat exchanger 40 functions as an evaporator to absorb heat from outdoor air 30c. If additional heat is needed or refrigerant circuit 38 is only operable in a cooling mode, heater 18 can be energized for heating air 30 while compressor 16 is de-energized. In the heating mode, damper 36 can be open or closed.
To control system 10 for regulating the air temperature of room 12, a temperature sensor 46 can provide controller 14 with a temperature feedback signal 48 that varies with the room's temperature. Such temperature sensors are well known to those of ordinary skill in the art. Sensor 46 can be installed in housing 32 to sense return air 30a as the air enters inlet 24, or sensor 46 can be a conventional wall-mounted thermostat that provides controller 14 with feedback signal 48 via wires or a wireless communication link.
In addition to feedback signal 48, controller 14 also has an input 50 for receiving a plurality of commands 52, such as a cooling setpoint temperature, a heating setpoint temperature, a heating command, a cooling command and a dehumidify command (or dehumidification offset temperature). Input 50 can be in the form of a keyboard, touch pad, selector switch, push buttons, and various combinations thereof. The cooling setpoint temperature can be a user-inputted desired target temperature for room 12 when the room generally needs cooling. The heating setpoint temperature can be a desired target temperature for room 12 when the room generally needs heating. In some embodiments, the cooling setpoint temperature and the heating setpoint temperature are the same, i.e., there is only one user-adjustable temperature setpoint for both heating and cooling. The heating, cooling and dehumidify commands can also be manually inputted and used for determining whether system 10 operates in a heating mode, cooling mode, or dehumidifying mode.
In the cooling mode, controller 14 provides outputs 54, 56, 58 and 60 for controlling the operation of compressor 16, damper 36, and fans 58 and 60 such that the room temperature is kept within a certain range of the cooling setpoint temperature. The graph of
For the user-selected dehumidifying mode, the dehumidify command entered into input 50 effectively lowers the cooling setpoint temperature by a certain offset amount, and commands controller 14 to operate system 10 differently than during the cooling mode. Controller 14 in the dehumidifying mode regulates the room temperature 62 between upper temperature limit 82 (e.g., 72.5° F.) and a predetermined subcooling temperature limit 86 (e.g., 70.5° F.), as shown in the graph of
As with the cooling cycle, the dehumidifying cycle also has an on-period 88 and an off-period 90 in which compressor 16 is respectively energized and de-energized. Unlike the cooling cycle, however, the dehumidifying cycle's on-period 88 has a first period 92 and a second period 94 in which system 10 operates differently. Upon going from first period 92 to second period 94, controller 14 decreases the speed of fan 28 and ensures that damper 36 is closed. Damper 36 may or may not be open during first period 92. A typical operating sequence for the dehumidifying mode could be as follows:
During first period 92, compressor 16 is energized and fan 28 is operating at full speed or at some other desired speed to cool room 12. At the same time, damper 36 is preferably open (partially or fully) to provide at least some ventilation. After the room temperature decreases to a setpoint temperature (e.g., 72° F. or an offset temperature of 71° F.), second period 94 begins, at which time controller 14 decreases the speed of fan 28 and closes damper 36. The setpoint temperature between periods 92 and 94 can be the previously set cooling setpoint temperature 64 or an offset thereof. Regardless, the slower fan speed during second period 94 lowers the surface temperature of heat exchanger 44, which makes the heat exchanger more effective at removing moisture from the air. Keeping damper 36 closed during second period 94 avoids introducing moist outside air 30a into room 12. Allowing the room temperature to decrease below lower temperature limit 84 to subcooling temperature limit 86 prolongs the dehumidifying process that occurs during second period 94.
After the room temperature reaches subcooling temperature limit 86, controller 14 de-energizes compressor 16 to begin off-period 90. During off-period 90, room temperature 62 may begin rising until the room temperature once again reaches upper temperature limit 82 to repeat the cycle.
In the heating mode, as shown in
. Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those of ordinary skill in the art. Fan 28, for instance, can be two-speed or infinitely variable. It should be noted that controller 14 could include any appropriate microprocessor or circuitry that can provide the control scheme just described. The scope of the invention, therefore, is to be determined by reference to the following claims.
