Heating, ventilation, air conditioning, and refrigeration (HVAC/R) systems generally have components including a compressor, a condenser fan, and a blower, which each operate according to power received from one or more power sources. Each of these components are powered with either an AC power source or with a DC power source. Compressors powered with DC power are generally power inefficient. Accordingly, an HVAC/R system with a DC powered compressor is generally power inefficient.
Described herein is a DC compressor, configured to be powered with a DC power source. The DC compressor comprises an AC compressor configured to be powered with an AC power source, and a DC/AC inverter configured to receive power from a DC power source and to provide the power to the AC compressor.
In some embodiments, an HVAC/R system comprises a compressor configured to be powered with an AC power source, and a power supply configured to receive power from a DC power source and to provide the power to the compressor. In some embodiments, the compressor comprises a DC/AC inverter configured to receive power from a DC power source and to provide the power to the compressor.
The power supply 110 is configured to provide power to each of the components and the control module 150 according to the needs of the components and the control module 150. In addition, the control module 150 is configured to provide control signals to the components according to the type of signal (AC or DC) needed by the components.
Use of a VFD to power the compressor 125 allows for speed control, removing the limitation on the system to be either fully on or off. For example, an HVAC/R system with a VFD can operate the compressor at a speed corresponding to the cooling requirements of the environment having its temperature controlled. For example, if the controlled environment generates 500 watts of power, the compressor can be operated at a speed that corresponds to the heat generated by the 500 watts. This allows for improved power efficiency in the system because power inefficiencies experienced with repeatedly starting and stopping the compressor is avoided.
Furthermore, in some controlled environments, such as well insulated spaces, the heat generated is relatively constant. Accordingly, the energy to be removed is relatively constant. For such environments, the compressor motor may be designed for operation according to the load corresponding to the relatively constant energy to be removed. Such limited range of load allows for the compressor to be efficiently operated.
Another benefit to speed control is that the range of temperatures in controlled environment is dramatically reduced when compared to conventional HVAC/R systems in which the compressor is either fully on or off. In conventional HVAC/R systems, in order to prevent frequent state changes between off and on, the control system works with a hysteresis characteristic. In such systems, temperature excursions correspond to the hysteresis. For example, in some systems the hysteresis of the system is 3 degrees. If the temperature is set to −5 C, once the temperature of the environment is −5 C, the compressor is turned off. However, because of the 3 degrees of hysteresis, the compressor will not be turned on again until the temperature of the environment is −2 C. In contrast, in an HVAC/R system with a VFD controlling the compressor, the active control system incrementally increases and decreases the speed of the compressor to provide precise control of the temperature in the environment. As a result, there is no hysteresis, and, accordingly, significantly reduced trade-off between consistency of temperature and power consumption.
The about 24V DC signal can be provided by any DC source. In some embodiments, the about 24V DC signal is provided by two about 12V batteries.
The two inverters 84 and 85 are each configured to receive a 12V DC input and output a 120V rms AC signal. In some embodiments, the DC power source 60, the inverters 84 and 85 are serially connected across the 24-volt DC input. Accordingly, the inverters 84 and 85 each receive an about 12V input. In response to the 12V input, the inverters 84 and 85 each produce an AC signal of about 120V rms.
The 120V rms AC signal of inverter 84 is provided to rectifier 87, and the 120V rms AC signal of inverter 85 is provided to rectifier 86. The rectifiers 86 and 87 rectify the respective AC signals producing substantially DC outputs of about 165V each. The rectifiers 86 and 87 are connected in series, and therefore collectively produce a substantially summed DC signal of about 330V. In the embodiment shown in
The filter 88 is connected across the serially connected rectifiers 86 and 87. The filter is configured to improve the quality of the DC output signal by filtering non-DC components of the signal produced by the rectifiers 86 and 87. As shown in
In
In another embodiment, an HVAC/R system as described above incorporates a pulsed operation control valve to control refrigerant flow to the evaporator from the condenser. The VFD powered HVAC/R system yields varying compressor-speeds resulting in variable refrigerant flows to the condenser and to the evaporator. However, conventional expansion devices such as capillary tubes or expansion valves (AEV or TEV) cannot handle or take advantage of varying refrigerant flows and hunt or flood, thereby reducing evaporator efficiency and system performance. In order to achieve desired advantages of such variable refrigerant flows, according to this embodiment, a pulsing refrigerant control valve is used to produce a full range of evaporator superheat control at all refrigerant flows without starving or flooding the evaporator. Such refrigerant control is especially important at lower refrigerant flow rates resulting from variable compressor speeds. Conventional expansion devices are designed to operate at full flow and are inefficient at lower flows, and fluctuating flows, again, starving and/or flooding the evaporator. The pulsing valve may be a mechanical valve such as described in U.S. Pat. Nos. 5,675,982 and 6,843,064 or an electrically operated valve of the type described in U.S. Pat. No. 5,718,125, the descriptions of which are incorporated herein by reference in their entireties. Such valves operate to control refrigerant-flow to the evaporator throughout the variable refrigerant flow ranges from the compressor and condenser.
While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices and processes illustrated may be made by those skilled in the art without departing from the spirit of the invention. For example, inputs, outputs, and signals are given by example only. As will be recognized, the present invention may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others. Moreover, it is to be understood that the HVAC/R systems described herein may be configured as air conditioners, chillers, heat pumps and refrigeration systems.