Optimizer for two staged refrigeration systems

An optimizer for modulating the speed of an indoor fan and first and second stage compressors of a two staged refrigeration system with a plurality of relays and an already existing power source. The optimizer is comprised of a speed modulation device, a supply air temperature sensor, and a controller. The speed modulation device is located in proximity to the existing power source and configured to collect current and power related information from the refrigeration system and power source to send to the controller. The supply air temperature sensor is linked to the indoor fan of the two staged refrigeration system and operable to obtain supply air temperature values. The controller is linked in communication with the speed modulation device and supply air temperature sensor and is operable to generate a system mode based on the power, current, and supply air temperature information. Speed commands are then sent to the speed modulation device to modulate the speed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. 12/653,382 entitled “Optimizer for Single Staged Refrigeration Systems”.

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BACKGROUND OF THE INVENTION

1. Technical Field

Embodiments are generally related to two staged refrigeration systems, and more particularly to two staged refrigeration systems used in but not limited to residential air conditioning systems, roof top units, residential and commercial air source heat pumps, and water source heat pumps.

2. Discussion of Prior Art

Two staged refrigeration systems are widely used in both residential and commercial buildings. Typical systems maintain single zone room temperatures by staging one or more compressors on and off in two stages. Two staged refrigeration systems operate so that a first group of compressors activate during low load conditions or lower room temperature bias of the set-point. At a high system load, high bias of the room temperature set point, or after the first group of compressors have been active for an extended time period, another group of compressors activate. Compressor groups deactivate in stages when the building load decreases. Typical two staged refrigeration systems are comprised of compressors, a thermostat, a condensing unit, and a supply air fan with ON and AUTO modes of operation. The fan ON mode allows the supply air fan to run continuously regardless of the compressor status. In AUTO mode, the fan status is controlled so that both the compressor and supply air fan turn on and off simultaneously. A circulation fan (also called an indoor fan) supplies air to the conditioned space.

Over the years, engineers have worked to improve two staged refrigeration systems. Particular inventive emphasis has focused on minimizing over-sizing during the equipment selection process. Yet because cooling loads and heating loads vary substantially over the operative spectrum, these measures did not solve the excessive indoor humidity and noise levels, high energy consumption rates, and the high cost of compressor replacements and other necessary repairs often associated with the refrigeration systems.

Further development of the variable capacity compressor resulted in a more energy efficient refrigeration system with greater indoor comfort control. In this system, the compressor could modulate the cooling capacity to within a range of 15 to 100 percent.

The above mentioned development in turn led to the creation of a system comprising both a variable capacity compressor and variable frequency drive. In this new system, the fan speed and compressor capacity could be modulated to maintain the zone temperature set point and discharge air temperatures, respectively. Due to high retrofit costs, however, this system is not implemented in the millions of already existing refrigeration systems. Noise levels are still high under partial load conditions as well. US patent application 20090255278 to Lifson and Taras (2005), proposes a single integrated modulation device that controls a condenser fan, compressor, and indoor fan or, alternatively, three separate modulation devices that each control one of the three previously stated devices (condenser fan, compressor, and indoor fan) at the same speed. Results from lab experiments conducted by the inventor of the proposed application suggests that modulating the condenser fan at the same speed as the compressor and indoor fan will result in a 20+ energy penalty under most operating conditions. The optimizer proposed in the following application also utilizes a single modulation device, however since it controls only the compressor and indoor fan, is more energy efficient than the device proposed by Lifson and Taras.

SUMMARY OF THE INVENTION

Accordingly, it is one aspect of an embodiment of the present invention to integrate the modulation and control devices for the indoor fan and compressor into a single, more cost efficient optimizer that can be readily implemented in new and existing two staged refrigeration systems in settings including but not limited to residential air conditioning systems, residential and commercial heat pump systems, water source heat pump systems, and roof top units.

It is another aspect of an embodiment of the present invention to resolve humidity and noise problems in buildings that have single and two staged refrigeration systems currently in use.

It is a further aspect of an embodiment of the present invention to prevent liquid sludge related compressor damage as well as minimize motor failure.

It is yet a further aspect of an embodiment of the present invention to maintain adequate humidity control, thermal comfort levels, maintenance and repairs, and eliminate short cycling in both new and existing refrigeration systems.

In one embodiment, an optimizer for modulating the speed of an indoor fan and first and second stage compressors of a two staged refrigeration system with a plurality of relays and an already existing power source is provided. The optimizer is comprised of a speed modulation device, a supply air temperature sensor, and a controller. The speed modulation device is located in proximity to the existing power source and configured to collect current and power related information from the refrigeration system and power source and send that information to the controller. The supply air temperature sensor is linked to the indoor fan of the two staged refrigeration system and operable to obtain supply air temperature values. The controller is linked in communication with the speed modulation device and supply air temperature sensor. This controller is operable to generate a system mode based on the power and current values and supply air temperature information and send speed commands to the speed modulation device. System modes include heating, cooling, ventilation/cycling, and auxiliary heating modes. Cooling and heating loads are identified based on the fan speed and supply air temperature patterns. The controller sends load information to the speed modulation device to modulate the speed of the indoor fan and first and second stage compressors.

The controller identifies possible faults including (but not limited to) issues involving low charge in the compressor, compressor leakage, dirty coils, and fan belt loss. Since system faults are reported and detected, there is a reduction in compressor and fan failure rates, on and off cycling rates, and O&M costs. Starting the compressor at a low speed maintains a stable motor winding temperature and reduces the inrush current by more than half. Further, motor failure is minimized and liquid sludge related compressor damage prevented. The optimizer applies (but is not limited) to rotary, scroll, screw, and reciprocating compressors. Compressor noise is also reduced under partial load conditions.

Notably, the method and system disclosed herein provides a feasible solution for retrofitting existing systems or those systems that are currently implemented in approximately over 50% of building spaces. However, the optimizer can also be implemented in new systems as well. Due to an energy penalty when moisture is removed from a building, the higher the already existing relative humidity levels, the lower the expected percent energy savings. The optimizer can help reduce peak demand by approximately 30% to 70% depending on the sizing and over-sizing of existing systems. It may also increase system energy by approximately 50%, and reduce energy consumption rates by approximately 20% to 50% according to the seasonal load profile and existing room humidity conditions.

The above-described features and advantages of the present disclosure thus improve upon aspects of those systems and methods in the prior art designed to provide cooling and heating to a single zone using a two staged refrigeration system.

DRAWINGS REFERENCE NUMERALS

DESCRIPTION OF THE PREFERRED EMBODIMENT

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,” “attached to,” and variations thereof are used broadly to encompass both direct and indirect mountings, connections, and supports.

FIG. 1shown below illustrates an embodiment of an optimizer for use in a two staged refrigeration system. Power for running the optimizer is derived from existing power source101, which can be either single or three phase depending on the voltage and frequency. Examples of possible voltages and frequencies are 110, 208, and 480 volts at frequencies of 50 and/or 60 Hz. Speed modulation device102converts the source power to the frequency required to modulate the speed of first stage compressor106, second stage compressor107, and indoor fan108. Speed modulation device102powers compressors106,107, and fan108by way of power lines111,114, and116.

Existing relays103,104, and105are interconnected along power lines111,114, and116between first stage compressor106,second stage compressor107, indoor fan108, and speed modulation device102. Relays103,104, and105start and stop indoor fan108and compressors106and107based on the control schedule of the existing refrigeration system. As an option, an existing room thermostat not illustrated in the figure may also be used to start and stop indoor fan108, first stage compressor106, and second stage compressor107using the control sequence installed in the thermostat or in controller110. The thermostat may also determine the system mode based on a predetermined room temperature set point. As an example, if the room temperature is higher than the predetermined set point, then indoor fan108, first stage compressor106, and second stage compressor107will activate.

Controller110generates the speed modulation command and relays that command to speed modulation device102. Supply air temperature signals are received by controller110from supply air temperature sensor109. Temperature sensor109can be attached to indoor fan108by supply duct work112and to controller110by way of power line115. Power related data including (but not limited to) the power factor, output torque, input and output currents, voltages, and frequencies are sent to controller110by speed modulation device102. Controller110also records historical data, identifies the system mode, building loads, and system faults, and may be linked to and communicate with upper level controllers. Power line113may be used to connect controller110to other devices.

FIG. 2shown below illustrates the decision making processes of controller110. Controller110is comprised of mode identification module201, control module202, and fault detection module203.

Mode identification module201indentifies the system operating mode based on the output of speed modulation device102, current and power values (either the actual current or actual power), and supply air temperature values. The operating mode is comprised of “off”, “circulation”, “first stage cooling”, “second stage cooling”, “first stage heating”, “second stage heating” or “auxiliary heating” modes of operation. Mode identification module201also supplies the supply air temperature values and indicates whether true power or current is in use. Minimum current and power values for indoor fan108and compressors106and107are determined using differing frequencies. The operating mode is determined based on the relationship between the power and/or current values for indoor fan108, compressors106and107, and the output of speed modulation device102as detailed in the following.

In “off” mode, actual current and/or power values are less than the predetermined current and/or power values for indoor fan108. In “circulation” mode, the actual current and/or power values are closest in value to the current and/or power values of indoor fan108as predicted using the current output of speed modulation device102. At the same time, supply air temperature values must lie within a predetermined range (for example between approximately 67° F. to 83° F.).

In “first stage cooling” mode, the actual current and/or power values are closest to the sum of the power/current values of fan108and those of compressor107. The supply air temperature must also lie below a predetermined value (for example 65° F.).

In “second stage cooling” mode, the actual current and/or power values are closest to the sum of the power/current values of indoor fan108and those of first and second stage compressors106and107. The supply air temperature must also be below a predefined value (below approximately 65° F., for example).

In “first stage heating” mode for a heat pump system, the actual current and/or power is closest to the sum of the power/current values for indoor fan108and the power/current values of first stage compressor106. The supply air temperature is also above a predetermined value (for example approximately 85° F.).

In “second stage heating” mode for a heat pump system, the actual current and/or power is closest to the sum of the power/current values of indoor fan108and the power/current values of first stage compressor106and second stage compressor107. The supply air temperature must lie above a predefined value (for example approximately 65° F.).

In “auxiliary heating” mode, actual current/power values are closest to the power/current values of indoor fan108as predicted by the current speed modulation output. The supply air temperature must be above a predetermined value (for example approximately 90° F.). In this mode, control module202modulates speed modulation device102at a maximum speed when the optimizer is, applied to a heat pump system. When the optimizer is applied to roof top units, control module202modulates speed modulation device102to maintain the supply air temperature below a predetermined value. This predetermined value may be a function of the fan speed. If the supply air temperature is higher than the predetermined value, the output speed must be increased. Likewise, if the supply air temperature is lower than the predetermined value, the output speed must be decreased.

Control module202determines the speeds of indoor fan108and first and second stage compressors106and107based on the supply air temperature values and system mode. In the “off” mode, the actual fan speed is zero. This is because relay105keeps indoor fan108inactive regardless of the output of speed modulation device102.

For both the “first stage cooling” and “first stage heating” modes, control module202′ commands the output of speed modulation device102at a minimum compressor speed (for example, at 50% of the maximum output). Relay104keeps compressors associated with second stage cooling or heating inactive. Once the system has transitioned from “first stage heating” and “first stage cooling” modes to “second stage heating” and “second stage cooling” modes, control module202commands the output of speed modulation device102at the minimum compressor speed for a predetermined period of time (approx. 5 min. for example). In other words, control module202commands the output of speed modulation device102at a minimum compressor speed in the “first stage cooling” mode, the “first stage heating mode”, and at the start of the “second stage cooling mode”.

The following details the procedure for finding the output of speed modulation device102. Upon activation of the compressor, the supply air temperature (SAT) may be taken in intervals of approximately a few seconds or shorter. Data is smoothed using a moving average (for example, 10 data can be used). Record the average supply air temperature at the first half time (Tsa1) as well as the average supply air temperature at the second half (5) time (Tsa2). The output of speed modulation device102may then be determined using the equation:
Spd=min(spdMax, max(spdMin,(currentSpd−β(Tsa1−Tsa2)))wherein Spd represents the percent speed assigned to speed modulation device102,currentSpeed represents the speed of speed modulation device102at its current rate.spdMin represents the lowest compressor speed limit.spdMax represents the highest speed limit of the speed modulation device.The β-modulation ratio ranges from 1 to 10 (4 is recommended).

Control module202modulates speed modulation device102to maintain the supply air temperature below a predetermined value. This predetermined value may be a function of the fan speed. If the supply air temperature is higher than the predetermined value, the output speed must be increased. Likewise, if the supply air temperature is lower than the predetermined value, the output speed must be decreased.

The optimizer identifies the compressor and fan faults using patented technologies already claimed in other patents. The programming of control device110is not detailed in this disclosure but is known to a person of ordinary skill in the art.