Integrated micro combined heat and power system

#The present invention generally relates to a cogeneration system for the supply of electrical power, space heating (SH) water and domestic hot water (DHW), and more particularly to a small scale Rankine-type cogeneration system that utilizes a scroll expander and an organic working fluid.

#The concept of cogeneration, or combined heat and power (CHP), has been known for some time as a way to improve overall efficiency in energy production systems. With a typical CHP system, heat (usually in the form of hot air or water) and electricity are the two forms of energy that are generated. In such a system, the heat produced from a combustion process can drive an electric generator, as well as heat up water, often turning it into steam for dwelling or process heat. Most present-day CHP systems tend to be rather large, producing heat and power for either a vast number of consumers or large industrial concerns. Traditionally, the economies of scale have prevented such an approach from being extrapolated down to a single or discreet number of users. However, increases in fuel costs have diminished the benefits of centrally-generated power. Accordingly, there is a potentially great market where large numbers of relatively autonomous, distributed producers of heat and electricity can be utilized. For example, in older, existing heat transport infrastructure, where the presence of fluid-carrying pipes is pervasive, the inclusion of a system that can provide CHP would be especially promising, as no disturbance of the adjacent building structure to insert new piping is required. Similarly, a CHP system's inherent multifunction capability can reduce structural redundancy.

#The market for localized heat generation capability in Europe and the United Kingdom (UK), as well as certain parts of the United States, dictates that a single unit for single-family residential and small commercial sites provide heat for both SH (such as a hydronic system with radiator), and DHW (such as a shower head or faucet in a sink or bathtub), via demand or instantaneous system. Existing combination units are sometimes used, where heat for DHW is accumulated in a combination storage tank and boiler coil. In one configuration, SH water circulates through the boiler coil, which acts as the heating element for the water in the storage tank. By way of example, since the storage capacity required for instantaneous DHW supplying one to two showers in a single family residence (such as a detached house or a large apartment) is approximately 120 to 180 liters (roughly 30 to 50 gallons), it follows that the size of the storage tank needs to be fairly large, sometimes prohibitively so to satisfy thermal requirements of up to 25 kilowatts thermal (kWt) for stored hot water to meet such a peak shower demand. However, in newer and smaller homes there is often inadequate room to accommodate such storage tank volume. In addition to the need for instantaneous DHW capacity of up to 25 kWt, up to 10 kWt for SH is seasonally needed to heat an average-sized dwelling.

#The following detailed description of the preferred embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

#FIG. 1 shows a schematic diagram of an integrated micro-CHP system according to an embodiment of the present invention showing an indirectly-fired configuration with a storage tank and both SH and DHW capability;

#FIG. 2 shows a schematic diagram of an integrated micro-CHP showing an indirectly-fired configuration with no storage tank and both SH and DHW capability;

#Referring initially to FIG. 1, one embodiment of the micro-CHP system 1 is an indirectly-heated, dual-loop system that includes a first (or primary) circuit 100 and a second circuit 150. An advantage of the indirectly fired system is that first circuit boiler (or evaporator) conduit overheating and subsequent burn-out is avoided. First circuit 100 includes a expander 101, a condenser 102, a pump 103 and one portion of interloop heat exchanger 104. An organic working fluid (such as naturally-occurring hydrocarbons or halocarbon refrigerants, not shown) circulates through the loop defined by the fluidly-connected expander 101, condenser 102, pump 103 and interloop heat exchanger 104. Piping 110 is used to connect the various components of first circuit 100, whereas the pump 103 provides the pressure to supply the organic working fluid to the interloop heat exchanger 104, thereby completing the first circuit 100. A generator 105 (preferably induction type) is coupled to expander 101 such that motion imparted to it by expander 101 generates electricity. While the expander 101 can be any type, it is preferable that it be a scroll device. The scroll expander can be a conventional single scroll device, as is known in the art. An oil pump 108 is used to provide lubricant to the scroll. The presence of oil helps to establish a seal between the intermeshed stationary and orbiting wraps that make up the scroll's crescent-shaped chambers (not shown). A level indicator switch 120 with level high 120A and level low 120B indicators is placed at the discharge of condenser 103. Controller 130 is used to regulate system operation. It senses parameters, such as organic working fluid temperatures, at various points within the first circuit and level information taken from the level indicator switch 120. Through appropriate program logic, it can be used to open and close valves (not presently shown) in response to predetermined conditions, such as an electric grid outage. The generator 105 is preferably an asynchronous device, thereby promoting simple, low-cost operation of the system 1, as complex generator speed controls and related grid interconnections are not required. An asynchronous generator always supplies maximum possible power without controls, as its torque requirement increases rapidly when generator 105 exceeds system frequency. The generator 105 can be designed to provide commercial frequency power, 50 or 60 Hz, while staying within close approximation (often 150 or fewer revolutions per minute (rpm)) of synchronous speed (3000 or 3600 rpm).

#An external heating loop 140 (shown preferably as an SH loop) can be coupled to first circuit 100 via connectors (not shown) on condenser 102. As an option, a preheat coil 145 can be inserted into the external heating loop 140 such that the hydronic fluid (typically water) flowing therethrough can receive an additional temperature increase by virtue of its heat exchange relationship with heat exchange fluid flowing through second circuit 150 (discussed in more detail below). The hydronic fluid flowing through external heating loop 140, is circulated with a conventional pump 141, and is supplied as space heat via radiator 148 or related device. As an example, hydronic fluid could exit the condenser 102 at about 50° Celsius and return to it as low as 30° Celsius. The capacity of the system 1 is up to 60 kWt; however, it is within the scope of the present invention that larger or smaller capacity units could be utilized as needed. Inherent in a micro-CHP (cogeneration) system is the ability to provide heat in addition to electricity. Excess heat, from both the heat source and the expanded working fluid, can be transferred to external DHW and SH loops. The nature of the heat exchange process is preferably through either counterflow heat exchangers (for either or both the DHW and SH loops), or through a conventional hot water storage tank (for a DHW loop). It will be appreciated by those of ordinary skill in the art that while the embodiments depicted in the figures show DHW and SH heat exchangers in parallel (and in some circumstances being supplied from the same heat exchange device, shown later), it is within the spirit of the present disclosure that series or sequential heat exchange configurations could be used.

#Second circuit 150 includes two parallel sub-loops 150A, 150B. Heat to the two parallel sub-loops 150A, 150B is provided by a burner 151, which is supplied with fuel by a gas train 152 and variable flow gas valve 153. Piping 160 (which makes up the parallel sub-loops) passes through a combustion chamber 154, which is where the heat from the combustion of fuel at burner 151 is given up to the heat exchange fluid (not shown) that flows through piping 160. Piping 160, which includes a finned tube portion 161 disposed inside the combustion chamber 154, branches out into the first parallel sub-loop 150A, which transports the heat exchange fluid that has been heated in combustion chamber 154 to interloop heat exchanger 104 in order to give up the heat to organic working fluid flowing through first circuit 100. Block valves (not shown) could be used to regulate flow between the sub-loops; however, by idling the pump of the inactive sub-loop, significant flow in that sub-loop is prevented without the need for additional valving. The second parallel sub-loop 150B transports the heat exchange fluid to DHW heat exchanger 180 in order to heat up domestic hot water. One side of domestic hot water heat exchanger 180 (which can be a water storage tank) includes coil 180A configured to transport the heat exchange fluid, and another side, the shell 180B, to transport domestic hot water (not shown) from a cold water inlet 191A, past coil 180A and to DHW outlet 191B. Typically, the cold water comes from either a well or a city/municipal water supply. Similarly, temperature sensor 171B can detect the temperature of the DHW coming out of the DHW heat exchanger 180. This sensor can also be linked to a controller 130 (discussed in more detail below). Combustion chamber 154 includes an exhaust duct 155, an exhaust gas recirculation device 156 with exhaust duct heat exchanger 157, and fan 158. It will be appreciated by those skilled in the art that although the fan 158 is preferably shown as an induced-draft fan, it could also be a forced-draft fan, if properly located relative to the combustion chamber 154. Temperature sensor 171A is placed at the combustion chamber 154 outlet for the second circuit 150 to measure the temperature conditions of the heat exchange fluid, in a manner similar to that of temperature sensor 171B. Second circuit pumps 185A, 185B are used to circulate heat exchange fluid through the second circuit 150, with pump 185B circulating heat exchange fluid through DHW heater 180 and pump 185A circulating heat exchange fluid through interloop heat exchanger 104. The exhaust duct heat exchanger 157 and an exhaust gas recirculation (EGR) device 156 accept hot exhaust gas from the burner 151 and recirculate it in an internal heat exchange process, thereby lowering the temperature of the exhaust gas that is pulled away and vented to the atmosphere by fan 158. The heat given up by the exhaust gas in the exhaust gas heat exchanger 157 is used to provide additional heat to other parts of the system 1. In the present figure, this additional heat is used to increase the temperature of the heat exchange fluid flowing in second circuit 150.