Patent Publication Number: US-2007112694-A1

Title: Facility energy management system

Description:
FIELD OF THE INVENTION  
      This invention relates generally to managing energy usage in a facility.  
     BACKGROUND OF THE INVENTION  
      Energy for space heating, domestic hot water and recreation facilities such as swimming pools are some of the largest uses of energy in most facilities. Heating can be accomplished with electricity and/or any of a number of heating fuels. The most common heating fuels are petroleum based fuels such as heating oil, natural gas, or propane. Most facilities use a petroleum-based fuel for all their heating applications. Fuel costs can comprise a significant part of an energy bill for a facility located in colder climates wherein heating is required throughout the day and through multiple seasons of the year. Petroleum based fuel for heating is generally charged based on a commodity price plus a delivery charge, and does not change dramatically based on consumption during a billing period.  
      A facility&#39;s total electrical load comprises electricity used by devices and fixtures within the facility. The electrical load typically fluctuates throughout the day, with the lowest demand at night, and the highest demand in the late afternoon and early evening. Charges for electricity use are generally based on the amount of energy used over a billing period, plus a penalty for the maximum rate of use (billed kW demand charge). This structure penalizes a user for a high rate of use. Even though electricity demand through most of a day can be a small fraction of the peak electrical demand, the facility is charged a demand charge based on the peak usage.  
     SUMMARY  
      Recent changes in petroleum fuel costs and electricity rate structures have created opportunities to reduce energy costs by selecting the most efficient means of providing the required heat to a facility. It is thus an object of the invention to provide a system or method to take advantage of the different pricing structures of fuel and electricity to provide energy to the facility in a cost efficient manner.  
      According to one aspect of the invention, there is provided a method of managing energy supplied to a facility that requires electricity and heat. The method comprises monitoring a marginal cost of electricity from an electricity vendor and determining a facility current electrical load and a facility current heating load. The method also comprises obtaining fuel to supply energy to meet the heating load when the marginal cost of electricity is greater than a marginal cost of a fuel or the current electrical load is greater than a peak billed demand threshold. When the marginal cost of electricity is less than the marginal cost of the fuel and the current electrical load is less than the peak billed demand threshold, electricity is obtained from the electricity vendor up to the peak billed demand threshold to supply energy to the meet at least part of the current heating load, and fuel is obtained to supply energy to meet any current heating load not met by energy from the electricity. By using electricity to meet at least part of the current heat load when the current electrical load is less than the peak billed demand threshold, the facility&#39;s electricity consumption fluctuations are smoothed and the amount of fuel consumed over a given period is reduced; in other words, the method serves to fill the valleys in the facility&#39;s fluctuating current electrical load with electricity used to meet at least part of the heating load.  
      The method can further comprise monitoring energy prices of a power pool, and when the energy price of the power pool exceeds the collective cost of the electricity and the fuel, obtaining electricity from the electricity vendor and selling the obtained electricity to the power pool.  
      According to another aspect of the invention, a system can be provided that includes a controller programmed to carry out the above method, and sensors for determining a current heat load and a current electrical load of the facility. The controller is stored with or is communicative with electricity vendor electricity cost and fuel source fuel cost data. The system can include electric and fuel boilers communicative with the controller, and respectively operable to generate heat from the obtained electricity and fuel. The system can also include a control valve communicative with the controller and operable to control delivery of heat from the boilers to the facility. The system executes a reduced cost method of providing heat, from either electricity or fuel, or both. The system leverages the electricity rate structures to take advantage of low cost electricity that is available in off peak periods. The system reduces costs by displacing high cost fuel with low cost “off peak” electricity.  
      The peak billed demand threshold can be assigned a value equal to a historical peak billed demand threshold from a previous billing period. This is particularly useful when the electricity vendor charges a demand charge in each current billing period that is based on the peak billed demand over one or more previous billing periods. Should the current electrical load exceed the peak billed demand threshold, a new peak billed demand threshold value can be set that is equal to the current electrical load.  
      Alternatively, and to reduce the number of instances when the electricity vendor charges the facility a demand charge based on exceeding a demand charge threshold, the peak billed demand threshold can be assigned a value equal to the electricity vendor&#39;s demand charge threshold.  
    
    
     DRAWINGS  
      The present invention will be further understood from the following detailed description, with reference to the accompanying drawings, in which:  
       FIG. 1  is a functional block diagram of an energy management system for a facility in accordance with one embodiment of the present invention;  
       FIG. 2  is a block diagram of inputs and outputs to a processor of the system;  
       FIG. 3  is a graph of a sample of daily electrical energy consumption by a typical facility within a given time period;  
       FIG. 4  is a flowchart of the system&#39;s generalized operation undertaken by the system processor.  
       FIG. 5  is a screen print of an information display from the system in operation at the facility. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION  
      System Components  
      Referring to  FIG. 1  and according to one embodiment of the invention, an energy management system  10  is provided that manages electricity and fuel used by a facility  11 .  
      The facility  11  is a building that requires heat and electricity. The facility  11  uses electricity to power electrically-powered fixtures and devices found within the building. Collectively, these fixtures and devices impose an electrical load  12  on the facility  11 . The facility  11  also uses electricity and fuel to power respective electric and fuel heating assemblies  14 ,  16 . The electric and fuel heating assemblies  14 ,  16  heat one or more heatable fluids  18  for use in the facility  11 . Such fluids include water, air, and other heatable fluids known in the art for storing and transferring heat, e.g. refrigerants. Heating the collective heatable fluid(s) impose a heat load  20  on the facility A.  
      The electrical heating assembly  14  is comprised of an electrical heating element  22  and an electrical heat storage device  24 . The heating element  22  can be one or more electric furnaces to heat air and/or one or more electric boilers to heat water. Instead or in addition to the electric furnace, the electric boiler can be coupled to a heat exchanger to heat air. The electrical heat storage device  24  can be a container for storing heated water, such as the boiler&#39;s water tank or a swimming pool. Similarly, the fuel heating assembly  16  is comprised of a fuel heating element  26  and a fuel heat storage device  28 , wherein the fuel heating element  26  can be one or more fuel furnaces and/or fuel boilers, and the fuel heat storage device  28  can be a heated water storage container.  
      The facility  11  is electrically coupled to a conventional electrical power grid (not shown). Via the power grid, the facility purchases electricity from an electricity vendor A, which can be an electric utility, an independent power producer (IPP), or a trader in a power pool. The purchased electricity is used to meet the electrical load  12  and power the electric heating assembly  14  (collectively, “facility total electrical demand”).  
      The facility  11  has a fuel storage tank  29  for storing fuel for use by the fuel heating assembly  16 . The fuel can be natural gas, butane, propane, heating oil or any other heating fuel as is known in the art. Fuel is purchased from a fuel vendor (not shown) who sends a tanker (not shown) to replenish the tank  14  from time to time. Alternatively, the facility  11  can be coupled to a fuel line (not shown) and the fuel vendor can supply fuel directly to the facility  11  via the fuel line.  
      Fuel is typically purchased from the fuel vendor at a fixed rate. Electricity, however, is typically purchased from the electricity vendor A at a rate that can vary depending on a number of factors. For example, when purchasing electricity from an electric utility such as British Columbia Hydro and Power Authority (“BC Hydro”), these factors include a demand for electricity (i.e. electrical load), supply voltage, and geographical area of the facility. BC Hydro customers who have an electricity demand at or over a certain number of kilowatts (kW) are billed on a rate schedule that includes a basic charge, a charge for electricity consumption, and a charge for demand. The basic charge is a fixed price for the billing period. The energy charge charges a fee per kilowatt hours (kWh) consumed over the billing period; this per kWh fee may change when electricity consumed exceeds a certain kWh threshold (“energy charge threshold”). The demand charge charges a fee per kW when the electrical load exceeds a certain kW threshold (“demand charge threshold”) within the billing period; the demand charge may contain multiple demand charge thresholds each with different per kW fees. Other electricity utilities may impose a demand charge in a different manner; for example, for some utilities, a demand charge is charged each billing period (e.g. per month) and is a percentage of the peak electricity demanded over a number of billing periods (e.g. over the last calendar year).  
      In addition to electric utilities, electricity can be purchased from other electricity vendors A, such as an IPP and traders in a power pool. Electricity can typically be purchased from an IPP at a fixed rate. In contrast, electricity purchased from the power pool is typically priced hourly, and the purchaser is billed at the rate that is in effect for each hour. Prices in a power pool can be extremely volatile and can fluctuate from hour to hour; the prices are typically lower at night when there is lower demand and a surplus of energy is available. Some utilities have adopted a similar billing structure, and charge customers based on time of day usage wherein the charge rate is different through the day; these utilities may or may not have an additional demand charge.  
      In practice, the demand charge makes up a significant portion of the total electric cost when the facility&#39;s total electrical demand exceeds the demand charge threshold at any time within the billing period, or if the customer&#39;s peak demand in one month is particularly higher than in other months. Electricity costs can be lowered by reducing the relative size of the demand charge to the energy charge. This can be achieved, for example, by reducing the peak electrical load (peak shaving) and/or increasing electricity consumption during low demand periods (valley filling).  
      Referring now to  FIG. 2 , the system  10  includes a system processor  30  that is programmed to manage the use of electricity and fuel by the facility  11  to reduce the total energy costs to the facility  11 . The system processor  30  can be a direct digital controller (DDC), a PID controller, a programmable logic controller (PLC), an application specific integrated circuit (ASIC), a general purpose computer, or any type of programmable controller as is known in the art.  
      The processor  30  has a random access memory unit (not shown) that stores data relating to the price of electricity and the price of fuel. An input/output device such as an electronic display and keyboard (not shown) is coupled to the processor  30  and can be used to manually input new electricity and fuel pricing data into the processor  30 . The processor  30  is also coupled to an external communications network  31  to automatically receive and store new electricity and pricing data; for example, a modem or network card (not shown) can be connected to the Internet to automatically update electricity and fuel pricing data from the electricity and fuel vendors. The electricity pricing data includes the current market rate of electricity available for purchase by the system  10 , priced in units of kilowatthour (kWh). In addition, depending on the jurisdiction, the opportunity may exist to purchase or sell electricity through a power pool or purchase power contracts from an IPP. The electricity pricing data will also include information relating to, but not limited to, current power pool prices at the power pool, such as contracts entered into by the operating environment and current pool prices. Fuel pricing date includes the current market rate for the fuel available for purchase by the system  10 . The market rate for the fuel will depend on the fuel being utilised. Fuels such as natural gas, propane and butane are typically priced in units of gigajoule (gJ).  
      The system  10  includes sensors communicative with the processor  30  that provide the processor  30  with data relating to the current energy load demanded by the facility  11  as well as the operational condition of the electric and fuel heating assemblies  14 ,  16 . The system  10  also includes actuators communicative with the processor  30  which are used to control operation of the electric and fuel heating assemblies  14 ,  16  as well as the distribution of heated fluids throughout the facility  11 . The sensors and actuators include: 
      Electrical heating system sensors  33 : these sensors  33  are installed in the electrical heating assembly  14  and include temperature sensors  33  for monitoring the temperature of the heatable fluids at the outlet of the electrical heating element  22  (to confirm the heating element  22  is operational) and in the heat storage device  24  (to measure the amount of energy available for heating), as well as meters  33  for measuring the electrical power consumed by the electrical heating assembly  14 .     Fuel heating system sensors  34 : these sensors  34  are installed in the fuel heating assembly  16  and include temperature sensors  34  for monitoring the temperature of the heatable fluid(s) at the outlet of the fuel heating element  26  (to confirm the heating element  26  is operational), and in the heat storage device  28  (to measure the amount of energy available for heating) and may include meters for measuring the fuel consumed by the fuel heating assembly  16 .     Current electrical load sensors  35 : these sensors  35  collectively measure the facility&#39;s total current electrical load, i.e. the instantaneous net electrical power demanded by all electrical facilities in the facility  11 , including the power required by the electrical and fuel heating assemblies  14 ,  16 . Such sensors  35  may include voltage and current transformers connected to a wattmeter capable of calculating the power consumption and providing a signal to the processor  30 . The current electrical load  12  can be determined by subtracting the total electrical load measured by sensors  35  from the electrical heating system electrical load measured by sensors  33 .     Current heat load sensors  36 : these sensors  36  collectively measure the temperature of the current heat load  20  at facility  11 . Such sensors include temperature sensors for measuring the temperature of a hot water tank for supplying domestic hot water, rooms requiring space heating, heated swimming pools, hot tubs, etc.     Electrical heating assembly actuators  37 : these actuators  37  control operation of the electric heating assembly  14  and include a switch that controls flow of electricity to the heating element  22 , and valves for controlling the flow of heated fluid to and from the heat storage device  24 .     Fuel heating assembly actuators  38 : these actuators  38  control operation of the fuel heating assembly  16  and include a valve that controls fuel flow to the heating element  26 , spark ignitor for igniting the fuel, and may include valves for controlling the flow of heated fluid to and from the heat storage device  28 .     Main fluid control valve(s)  39 : a main fluid control valve  39  is provided for each heatable fluid to control the flow of the heatable fluid from the electrical and fuel heating assemblies  14 ,  16  to the rest of the facility  11 . As shown in  FIG. 1 , the main control valve  39  is fluidly coupled to a conduit that receives unheated fluid  18  directly from a fluid source, a conduit that receives heated fluid from the electric heating assembly  14 , a conduit that feeds fluid  18  directly to the heat loads  20  within the facility  11 , and a conduit that feeds fluid through the fuel heating assembly  16  and to the heat loads  20 . 
 
 Processor Programming and System Operation 
   

      The processor  30  is programmed to monitor the electricity and fuel pricing and current electrical and heat loads  12 ,  20 , and to execute a strategy for using electricity and fuel in a manner that reduces the total energy costs to the facility  11 .  
      Referring to  FIG. 3  the processor  30  is programmed with a “valley filling” strategy that makes use of electrical power in non-peak periods. This strategy operates under the constraint that the current electrical load  12  of the facility  11  will never exceed a specified peak billed demand threshold  40 . The peak billed demand threshold  40  is a maximum allowable net electrical power, as measured for the peak demand measurement, demanded by all electrical devices in the facility  11  other than the electrical heating assembly  14  that is expected in the current demand billing period. Typically this value is assigned to be the peak billed demand recorded and billed during the same month in previous year or years; however, the value may be based on any historical period of time and dynamically updated to account for unexpected electrical power consumption conditions. The vertical axis  42  in  FIG. 3  represents electrical load in kW, while the horizontal axis  44  represents the time of day in hours, beginning at midnight and ending 24 hours later at midnight. The function  46  illustrates the electrical load  12  of the facility  11  over a typical day (i.e. the electrical load of all devices and fixtures not including the electrical and fuel heating assemblies  14 ,  16 ). The area  48  below the function  46  is the total electrical energy in kWh consumed by the facility  11  over a typical day in kWh excluding the electricity consumed by the electrical and fuel heating assemblies  14 ,  16 . The area  50  above the function  46  and constrained by the peak billed demand threshold  40  line is the electrical energy in kWh available for valley filling.  
      When the facility  11  purchases electricity from an electricity vendor A that charges an additional demand charge that is triggered when the current electrical load  12  exceeds the current billed demand charge threshold, the processor  30  can assign the peak billed demand threshold  40  to be a value that is less than or equal to the demand threshold. In such case, the area  50  represents the electrical energy in kWh available for use by the facility that will not be subject to a demand charge.  
      Referring now to  FIG. 4  the processor  30  program executes the valley filing strategy by continuously iterating through the following process steps:  
      At a first stage shown as block  60 , the processor  30  compares the marginal cost of the fuel to the marginal cost of electricity by accessing this information stored in the memory unit, or externally via the communications network  31 . The marginal cost of the fuel is calculated by taking the price of fuel, converting it to units of $/gJ, and accounting for the efficiency of the fuel heating assembly  16 . Similarly, the marginal cost of electricity is calculated by taking the price of electricity, converting it to units of $/gJ, and accounting for the efficiency of the electrical heating assembly  14 .  
      When the marginal cost of electricity is greater than the marginal cost of the fuel, the processor  30  is programmed to advance to stage  63  wherein the electrical heating assembly  14  is turned off and the fuel heating assembly  16  is set to generate sufficient heat energy to satisfy the heating load  20 . Operation of the electric and fuel heating elements  22 ,  26  such as electric and fuel boilers and electric and gas furnaces are well known in the art and thus not described in detail. In addition, the main fluid control valve  39  is set to deliver unheated heating fluid to the fuel heating assembly  16  for heating.  
      When the marginal cost of electricity is less than the marginal cost of fuel then the processor  30  is programmed to advance to block  62  wherein the peak billed demand threshold  40  is compared to the current electrical load  12  as measured by the current electric load sensors  33 . When the peak billed demand threshold  40  is less than the current electrical load  12 , the processor  30  is programmed to advance to block  63 . At this stage, the electrical heating assembly  14  is turned off and the fuel heating assembly  16  is set to generate sufficient heat energy to satisfy the heating load  20 . In addition, the main fluid control valve  39  is set to deliver unheated heating fluid to the fuel heating assembly  16  for heating.  
      When the peak billed demand threshold  40  is greater than the current electrical load  12  then the processor  30  is programmed to advance to block  64  wherein the difference between the peak billed demand threshold  40  and the current electrical load  12  is compared to the heating load  20  as measured by the current heat load sensors  36 . When the heating load  20  can be satisfied by the electrical heating assembly  14  without increasing the total electrical demand beyond the peak billed demand threshold  40  then the processor  30  is programmed to advance to block  65  wherein the electrical heating assembly  14  generates sufficient heat energy to satisfy the heating load  20  and the fuel heating assembly  16  is turned off. In addition, the main fluid control valve  39  is set to deliver the heated fluid from the electrical heating assembly  14  directly to the heating load  20 .  
      When the heating load  20  cannot be satisfied by the electrical heating assembly  14  without increasing the total electrical demand beyond the peak billed demand threshold  40  then the processor  30  is programmed to advance to block  66  wherein the electrical heating assembly  14  is set to generate sufficient heat energy to raise the total electrical demand to the peak billed demand threshold  40 , without exceeding the peak billed demand threshold  40 . The main fluid control valve  39  is also set to deliver the heated fluid from the electrical heating assembly  14  to the fuel heating assembly  16 . The fuel heating assembly  16  is set to generate the remaining heat energy required to satisfy the heating load  20 .  
      According to a second embodiment of the invention, the processor  30  is further programmed with a second energy management strategy that monitors the price difference between the electricity vendor A and the power pool, and sells electricity purchased from the electricity vendor A under cost-advantageous circumstances. Depending on the jurisdiction, an opportunity may exist to purchase or sell electricity through a power pool or purchase power contracts from an IPP. Power purchased from an IPP is generally carried out under a fixed price contract. In contrast, power purchased from the power pool is typically priced hourly and the purchaser is billed at the rate that is in effect for each hour. Power pool prices may be extremely volatile and fluctuate significantly from hour to hour. For example, the price may be very low at night when there is surplus energy available, but in the event of a significant problem with one or more sources of supply, the night price can spike to 10 to 15 times the normal price. This generally lasts for 1 to 2 hours before the price falls back to normal levels.  
      When the facility  11  contracts with an IPP for the purchase of a fixed amount of power, the facility  11  cannot typically control exactly how much power it consumes. A customer with an IPP contract that uses either more or less power than the contracted amount is deemed to have purchased or sold the difference from the power pool at the price that is in effect during the hour of interest. The system  10  takes advantage of these factors by selling power to the power pool when the power pool price spikes significantly and relying solely on the fuel heating assembly  16  to satisfy the heating load  20 . In particular, the processor  30  is programmed to monitor the prices of the power pool via an external communications network (not shown). When the difference between the marginal cost of the fuel and the power pool price is greater than the marginal cost of electricity, it is more cost effective to sell electricity to the power pool, and the processor  30  stops operation of the electrical heating system  14 , activates the fuel heating system  16 , and then purchases electricity from the IPP up to the maximum contracted amount and sells this electricity to the power pool.  
      The processor  30  is programmed to ensure that the facility has sufficient energy to meet its energy demands, sufficient purchased electricity is reserved to meet the current electrical load  12 . Backup generators (not shown) can be provided in the system  10  to alleviate energy shortages caused by unexpected current electrical load spikes.  
     EXAMPLE  
      The system  10  can be installed at a facility having a gas heating system used to provide heat for an outdoor swimming pool, two outdoor spa pools, a snow melting system and some building space heating. The pool and spa facilities operate on a year round basis. The resort heating system initially consists of two 2.9 M BTUH boilers, operating at approximately 70% efficiency. Either boiler is capable of providing all required heat to meet the facility heat load. The output from the two boilers is directed to the individual heating loads using an electrically controlled mixing valve and a heat exchanger for each load.  
      Installing the system  10  involves replacing one of the two boilers with a 300 kW Caloritech electric boiler. A Delta Controls Direct Digital Control (DDC) system can be installed to control both the existing and the new boiler, as well as the mixing valves used to manage the heat directed to each of the heating loads.  FIG. 5  shows a schematic of a completed installation.  
      The control system monitors temperatures on each of the heating loops and controls both the boilers and the mixing valves. Selection of the electric or propane boilers as a heat source is completed automatically by the DDC control as programmed in the above description.  
      After the system is installed and operating, propane costs are expected to be reduced for the entire facility by approximately 50%, while electricity costs increased by less than 20%. Monthly net savings of up to $6,000 are expected.  
      While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the scope and spirit of the invention.