Patent Application
20130220589
Not Applicable
Not Applicable
1. Technical Field
Embodiments are generally related to packaged multiple zone heating and cooling systems with compression refrigeration systems, and more particularly but not limited to use in residential air conditioning systems, roof top units, water source heat pumps, and air source heat pumps for both residential and commercial buildings.
2. Discussion of Prior Art
Packaged multiple zone heating and cooling systems with compression refrigeration systems are widely used in both commercial and industrial settings. Typical applications include but are not limited to commercial air source heat pump units, commercial water source heat pumps, and roof top units.
Packaged multiple zone heating and cooling systems with compression refrigeration systems typically are comprised of one or more constant speed compressors, an indoor fan, a return air fan, and a plurality of terminal boxes. Compressors are staged on and off in stages in order to maintain the required supply air temperature values.
Speed modulation devices, such as variable speed drives, are often installed on supply air fans for the purpose of controlling the fan speed. Controlling the fan speed maintains building or plenum static pressures as well as at least one terminal box damper in the fully open position. Variable speed drives are generally installed on return air fans for the purpose of maintaining building or plenum static pressures and tracking the supply air fan speed. A minimum fan speed is often specified for the supply air fan to prevent system coils from freezing.
A terminal box is often installed for each thermally controlled zone. This terminal box maintains the zone temperature by either modulating the reheat (constant terminal box), the airflow (variable air volume terminal box), or both the airflow and reheat (variable volume with reheat terminal box).
Multiple zone heating and cooling systems that are currently available are in many ways energy inefficient. When constant speed supply and return fans are employed in multiple zone heating and cooling systems, near constant fan power is used regardless of the building load. A substantial amount of energy is wasted as a result. Constant air volume terminal boxes incorporated in the packaged heating and cooling systems consume reheat energy at a rate three times greater than-necessary. When variable volume terminal boxes are installed, the constant speed fan over-pressurizes the terminal control box damper. This may potentially lead to a stuck damper, excessive airflow through the damper, or airflow leakage through the ductwork.
Another problem with multiple zone heating and cooling systems is that short cycling of the compressor is a common occurrence. During compressor short cycling, both untreated humid outside air and water that has condensed on the coils are carried into the conditioned space. As a result, humidity within the space reaches excessively high levels and tends to make it susceptible to the accumulation of mold or other damage. Short cycling also substantially reduces the life-span of the compressor and lowers the energy performance of the overall system.
In an effort to lessen the problems associated with short cycling, engineers have installed hot gas by-pass systems in some units of multiple stage refrigeration systems. In these systems, a by-pass valve allows compressed gas from the discharge to flow directly back to the suction side of the compressor when the compressor capacity is higher than the load. While this method has proven to decrease the occurrence of short cycling, unreliable system performance has led engineers to disable the control option in practice. A substantial energy penalty also results from the use of the hot gas by-pass system.
Engineers have recently introduced but not yet implemented variable capacity compressor technologies as another way to try to eliminate short cycling problems. Even with this improved control, however, the system is still burdened by cost and energy penalties.
Short cycling is also a major problem associated with multiple stage units. Due to large incremental capacity changes when one or more stages are turned on or off, the system capacity does not always match the actual load. The consequent frequent on/off loading or on/off cycling substantially increases system failure rates associated with the compressors, contactors, and motor windings. This shortens the overall lifespan of the system.
By far the most energy inefficient aspect of packaged multiple stage cooling systems is the current method for keeping system coils from freezing. Since there is currently a lack of reliable measuring devices, keeping coils from freezing is only accomplished utilizing a minimum fan speed. The fan speed is set as high as 70% with a minimum terminal box airflow of 60%. When both the minimum fan and minimum terminal box airflow are set on high, the system functions like a constant air volume system. As such, the fan power and thermal energy may be two or three times higher than needed.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to an embodiment of the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
Accordingly, it is one aspect of an embodiment of the proposed invention to solve current system problems in packaged multiple zone heating and cooling systems by eliminating compressor short cycling, preventing the coils from freezing, and minimizing excessive indoor humidity and reheat.
It is another aspect of an embodiment of the proposed invention to lower the frequency of short cycling and minimum airflow rates in order to reduce the rate of energy consumption by 20% to 40% and increase the system life span by 30% to 70%.
It is a further aspect of an embodiment of the proposed invention to substantially lower compressor failure rates and O & M costs by reducing the rate of on and off cycling.
It is yet a further aspect of an embodiment of the proposed invention to provide a feasible solution for retrofitting existing systems.
In one embodiment, a method of dynamically controlling heaters and compressors of multiple zone heating and cooling systems that operate in a plurality of stages and require the use of a supply air temperature sensor is provided. The method includes providing a controller in communication with the supply air temperature sensor and operable to receive supply air temperature values. The method also comprises obtaining a plurality of system status conditions, and based on at least some of the system status conditions stage the heaters and compressors in a plurality of stages to modulate the supply air temperature values to within a predetermined range.
In another embodiment, an optimizer for dynamically controlling heaters and compressors of multiple zone heating and cooling systems to modulate supply air temperature values to within a predetermined range is provided. The optimizer includes a supply air temperature sensor operable to determine the supply air temperature values. A controller is linked in communication with the supply air temperature sensor and configured to determine a plurality of system status conditions. The controller activates and inactivates the heaters and compressors in a plurality of stages based on at least some of the system status conditions.
The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate an example of at least one embodiment of the present invention and are not intended to limit the scope of the invention. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected to,” “linked to”, “attached to,” and variations thereof are used broadly to encompass both direct and indirect mountings, connections, and supports.
As should also be apparent to one of ordinary skill in the art, the systems shown in the figures are models of what actual systems might be like. Many of the modules and logical structures described are capable of being implemented in software executed by a microprocessor or a similar device or of being implemented in hardware using a variety of components including, for example, application specific integrated circuits (“ASICs”). Terms like “controller” may include or refer to both hardware and/or software.
Embodiments of the invention provide an optimizer for multiple zone heating and cooling systems and methods that can be retrofitted in existing systems or incorporated into new systems. Embodiments may apply but are not limited to rotary, scroll, screw, and reciprocating compressors.
In some embodiments, controller 112 can also be linked to optional supervisory controller 103. Supervisory controller 103 sends system information to controller 112 including but not limited to information on the supply air temperature set point and operating mode. Controller 112 is linked in communication with heater relays 104,105,106, and 107, and compressor relays 108, 109, 110, and 111 of existing compressor system 114. The relays are turned on and off by controller 112 based on the system information. The type and design of the relay is not limited to that illustrated in
Further, in some embodiments, optional outside air temperature sensor 101 can be linked in communication with controller 112. Outside air temperature sensor 101 is configured to send outside air temperature values to controller 112.
Existing packaged multiple zone heat pump with a compression refrigeration system 214 is comprised of heater relays 204, 205, and 206 for activating and inactivating heating stages and compressor relays 208, 209, 210, and 211 for activating and inactivating cooling stages. As in the embodiment shown in
Interface module 302 functions as an interface between the system operator and controller 112 and/or between supervisory controller 103 and controller 112. Through such communication, controller 112 obtains information on the system status. Supervisory controller 103 can be linked in communication with controller 112 to send status information including but not limited to data on the minimum and maximum supply air temperatures for cooling, maximum heating supply air temperature, number of stages, rotation time period, and the minimum time interval needed between system activation and inactivation. As an alternative, the previously stated status information may be updated and programmed by system operators using human interface methods such as a human operated computer and/or keypad.
Sequence module 303 is configured to periodically change the order of the compressors according to a rotation time interval.
When the optimizer is incorporated in a heat pump system, mode identification module 301 determines the system mode information based on any one of the methods detailed below.
In a first method, system mode information is received directly from supervisory controller 103.
In a second method, the system mode is determined based on outside air temperature values. Heating mode is assigned when the outside air temperature is lower than a predetermined value (for example, approximately 40° F.). Cooling mode is assigned when the outside air temperature is higher than a predetermined value (for example, approximately 65° F.). If the outside air temperature does not satisfy either of the previously stated conditions, it is assigned to the circulation/ventilation or free cooling mode.
In a third method, the system mode is determined based on the supply air temperature values and compressor stages. Circulation/ventilation mode is assigned when the supply air temperature values lie between predefined minimum and maximum cooling set points and the heating and cooling stage is not activated. Heating mode is assigned when one or more heater stages are activated, or when neither the heater nor the compressor stages are activated and the supply air temperature values are higher than a predefined minimum heating supply air temperature value. Cooling mode is assigned when one or more compressor stages is activated or neither the heater nor the compressor stage is activated and the supply air temperature is lower than the maximum cooling supply air temperature set point.
Control module 304 controls the activity of the compressor and heater stages based on a set of operating conditions that differ depending on the application setting. Compressor stages are sequenced on and off to maintain supply air temperature values in relation to predefined minimum and maximum supply air temperature limits. Staging of the compressors and heaters ensures adequate building humidity and temperature control. The following gives the specific conditions under which control module 304 activates or inactivates the relays for the compressor and heater stages.
When the heater and compressor stage relays are deactivated and the supply air temperature is lower than a predetermined minimum temperature for heating, or the system is transitioning from the circulation mode to the cooling mode, a first stage heater relay should be activated.
When the optimizer is applied to roof top or air conditioning units as seen in
When the optimizer is applied to a heat pump unit as seen in the embodiment shown in
If the heater and compressor relays are deactivated and the supply air temperature is above a predetermined maximum cooling temperature set point, or the system is transitioning from cooling mode to circulation mode, switch valve 207 can be set to cooling mode. This will activate first stage compressor relay 208.
If supply air temperature values drop below a predetermined minimum cooling temperature (for example approximately 45° F.), first stage compressor relay 208 is deactivated. If supply air temperature values rise to a temperature over the predetermined maximum cooling temperature (for example approximately 65° F.) in a predetermined time period (for example, approximately two minutes), an additional compressor stage relay is activated.
The following gives the specific conditions for different settings under which control module 304 activates or inactivates compressor stages (if two or more compressor stages are already active).
When the optimizer is applied to roof top units or heat pumps in the cooling mode, an additional compressor stage relay is activated if supply air temperature values are above a predetermined maximum temperature. If supply air temperature values are below a predetermined minimum temperature, one compressor stage relay is deactivated.
When the optimizer is applied to heat pumps in the heating mode, an additional compressor stage relay is deactivated if the supply air temperature is above a predetermined maximum temperature. If supply air temperature values are lower than a predetermined minimum temperature value, additional compressor stage relays are activated.
The optimizer proposed in this application identifies both the compressor and fan faults using patented technologies developed in the past. The programming of controller 112 is not detailed in this disclosure but is known to a person of ordinary skill in the art.
Various features and advantages of the invention are set forth in the following claims.
This application is related to U.S. patent application Ser. No. 12/653,382,121,409 filed on Dec. 14, 2009 and entitled “Optimizer for Single Staged Refrigeration Systems”.
