Methods and apparatuses for displaying energy savings from an HVAC system

A method and system of determining and displaying energy savings from an HVAC system operating in an energy saving mode. The HVAC system is operated to maintain a comfort mode temperature during a learning period. The energy consumed by the HVAC system at multiple outside ambient conditions during the learning period is determined. The correlation between a specific ambient condition and energy consumed by the HVAC system is determined. The HVAC system is run to maintain an energy saving setpoint temperature. The energy consumed by the HVAC system is determined at an ambient condition while maintaining the energy saving setpoint temperature. The energy savings are calculated as a function of the difference between the energy that would have been consumed by the HVAC system at the ambient condition based on the determined correlation and the energy consumed by the HVAC system while maintaining the energy saving setpoint temperature at the ambient condition.

FIELD OF THE INVENTION

The present invention relates generally to the determination of energy data and, in particular, to methods for estimating energy savings of an HVAC system.

BACKGROUND

As is well-known, thermostats control heating, ventilation, and air conditioning (“HVAC”) systems in buildings. A non-programmable thermostat allows a user, such as an occupant or building manager, to set one setpoint temperature for the heating season and one setpoint temperature for the cooling season to control the HVAC system. When the measured indoor temperature is below or above these setpoint temperatures, the HVAC system is activated. A programmable thermostat allows a user to program setpoint temperatures for different times of the day. For example, in the heating season, many users still set the thermostat to a lower set-back temperature at night. This temperature set-back reduces the amount of time that the HVAC system is activated in order to maintain the lower temperature and thus saves energy and money. However, the energy savings from such time-based programmed setpoint temperatures as compared to the comfort temperature that is set during the day is unknown to a user.

The Energy Star programmable thermostat specification has been in effect since April of 1995. The Energy Star specification states that a programmable thermostat is “a device that enables the user to set one or more time periods each day when a comfort setpoint temperature is maintained and one or more time periods each day when an energy-saving setpoint temperature is maintained.” The current specification defines comfort setpoint temperature as “the temperature setting in degrees Fahrenheit or degrees Celsius for the time period during which the building is expected to be occupied, e.g., the early morning and evening hours. The specification defines energy-saving setpoint temperature as “the setpoint temperature for the energy-saving periods usually specified for both the heating and cooling seasons. In the energy-saving mode, the thermostat setpoint may vary from the comfort setpoint temperature to the set-back temperature or the set-up temperature depending on the season. The set-back temperature is the setpoint temperature used during the heating season, normally at night or during unoccupied times of the day. This is a lower setpoint temperature than the comfort setpoint temperature. Similarly, the set-up temperature is a setpoint temperature used during the cooling season, normally at night or during unoccupied times of the day. This is a higher setpoint temperature than the comfort setpoint temperature. This specification has been confusing to users as to how to achieve energy savings from programmable thermostats. The EPA is considering issuing a new Energy Star specification in 2010. Even if the new specification is not finalized, the old Energy Star specification will be suspended due to the confusion to users.

Presently, users that invest in programmable thermostats to save energy and money do not have any ready means to determine how much energy and money is being truly saved. The programmable thermostats therefore are arbitrarily set at different temperatures, which may or may not save the user money and energy. Therefore, the present known programmable thermostats do not provide energy savings feedback to allow a user to adjust temperature setpoints and times based on how the building environment responds to changes in the internal and external environments.

BRIEF SUMMARY

According to at least some aspects of the present disclosure a method of determining energy savings from an HVAC system in a building operating in an energy saving mode is disclosed. The HVAC system is run to maintain a comfort mode temperature during a learning period. The energy consumed by the HVAC system at multiple outside ambient conditions during the learning period is determined. A correlation between a specific ambient condition and energy consumed by the HVAC system is determined. The HVAC system is run to maintain an energy saving setpoint temperature. The energy consumed by the HVAC system at an ambient condition while maintaining the energy saving setpoint temperature is determined. The energy savings is calculated as a function of the difference between the energy that would have been consumed by the HVAC system at the ambient condition based on the determined correlation and the energy consumed by the HVAC system while maintaining the energy saving setpoint temperature at the ambient condition.

Another example disclosed is an energy savings monitoring system having an HVAC system. A thermostat is coupled to the HVAC system to control the HVAC system. The thermostat includes a display and a controller. The controller is operative to run the HVAC system to maintain a comfort mode temperature during a learning period. The controller determines the energy consumed by the HVAC system at multiple outside ambient conditions during the learning period. The controller determines a correlation between a specific ambient condition and energy consumed by the HVAC system. The controller runs the HVAC system to maintain an energy saving setpoint temperature. The controller determines the energy consumed by the HVAC system at an ambient condition while maintaining the energy saving setpoint temperature. The controller calculates the energy savings as a function of the difference between the energy that would have been consumed by the HVAC system at the ambient condition based on the determined correlation and the energy consumed by the HVAC system while maintaining the energy saving setpoint temperature at the ambient condition. The display is operative to display the calculated energy savings.

Additional aspects will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments, which is made with reference to the drawings, a brief description of which is provided below.

DETAILED DESCRIPTION

Referring toFIG. 1, a programmable thermostat100is shown with a coverplate (not shown) removed. The thermostat100includes a display102that shows the current operation and status of the HVAC system. The display102shows the temperature104, the date and time106, and a status field108. The temperature104is the actual room or indoor temperature measured by the thermostat100. In this example, the temperature is expressed in Fahrenheit but other units of measurement such as Celsius can be used. The status field108includes different setpoints that may be programmed such as a Wake setpoint, a Leave setpoint, a Return setpoint, and a Sleep setpoint. The display102also includes an “on” indicator110with an appropriate set of icons such as a fan icon112, a heat icon114, and a cooling icon116that indicate the mode of the HVAC system that is currently activated. In this example, the heat icon114is highlighted indicating that the heating system of the HVAC system is on providing heat. The cooling icon116indicates that the cooling system of the HVAC system is on providing cooling while the fan icon112indicates that the fan of the HVAC system is on. A mode field120indicates whether the HVAC system is in heating mode or cooling mode. A savings method field122indicates the mode of the savings method employed. As will be explained, an option is a learn mode in which the thermostat determines a base amount of energy consumption and another option is a save or savings option, which calculates energy savings based on the current energy savings setpoint temperature. Finally, a savings percentage124shows the percentage of energy saved by running the HVAC system to maintain the current setpoint temperature.

The thermostat100also includes a control panel130that includes programming keys such as a set time key132, a set program key134, a run key136, an up key138, and a down key140that allow a user to change the setpoint temperatures and program the times that the setpoint temperatures are maintained by the HVAC system controlled by the thermostat100. The control panel130also includes a fan switch142to activate the fan of the HVAC system, a mode switch144that allows activation of the heating and cooling functions of the HVAC system and an energy savings switch146. The energy savings switch146has a learn position, a save position, and an off position for the process of implementing the energy savings display feature as will be explained below.

In this example, the energy savings percentage124on the display102can be expressed as a percentage of the energy saved by placing the thermostat100at a set-back (in the case of heating) or set-up (in the case of cooling) setpoint temperatures versus a comfort setpoint temperature for normal operation of the HVAC system. Alternatively, other energy savings metrics like currency saved or carbon footprint reduction can be used to show the energy savings. These metrics can be derived from the energy measurements by the thermostat100. Another device such as an off-site computer can be used to calculate the energy savings as will be explained.

FIG. 2is a view of the back plate200of the thermostat100. The back plate200includes a remote sensor input panel202, a pulse input panel204, and an HVAC control output panel206. The remote sensor input panel202receives input signals from a remote sensor or sensors (not shown) which can measure various factors that are used to determine an ambient condition. In this example, one or more of the remote sensors are used to determine outside ambient conditions, which may be used to determine energy savings. Outside ambient conditions include conditions of an outdoor environment or an environment exterior to the room in which the thermostat100is installed or an environment that is indicative of outdoors. The pulse input panel204in this example has two sets of pulse inputs210and212. The pulse inputs210and212can be connected to different pulse inputs from the remote sensor or the HVAC system. The HVAC control output panel206includes a power output220, a fan output222, two heating system control outputs224and226, two cooling system control outputs228and230, and a reversing valve output232. The outputs220,222,224,226,228,230, and232are coupled via wires to the HVAC system. The inputs can be used by the thermostat100to activate various components on the HVAC system. In this example, the HVAC system can have two cooling and heating stage units that are individual controlled by the heat control outputs224and226and the cooling system control outputs228and230respectively. The reversing value output232can be used to control an HVAC system that has a heat pump to alternate from heating and cooling modes. As is well known, in most heat pump systems the basic operation of heating and cooling is accomplished in the same manner. However, below a certain temperature, the outside air does not provide sufficient heat, so a backup heating element that can be either gas or electric is employed. In the case where the HVAC system includes a heat pump, the energy from a compressor and a fan blower are required for both heating and cooling.

FIG. 3is a block diagram of the internal components of the thermostat100. The thermostat100includes a controller300, a programming control interface302, an inside temperature sensor304, a compressor relay output306, a heater relay output308, and a blower fan relay output310. In this example, the thermostat100includes an RF module312that wirelessly receives data communicated from a remote RF module316that is coupled to an outside temperature sensor318to determine ambient conditions. Other sensors such as a solar sensor or a humidity sensor can also be coupled to the remote RF module316to measure data to determine the ambient conditions. It is to be understood that the outside temperature sensor318can be directly coupled to the thermostat100rather than sending data via a wireless interface. The controller300is also coupled to a storage device320that stores correlations found during the learning period, programs to control the HVAC system and programming determined from the control panel130.

As shown inFIG. 3, the controller300controls what is displayed on the display102. The controller300receives programming inputs from the control panel130inFIG. 1via the programming control interface302. The controller300receives temperature data from the indoor temperature sensor304representing the temperature inside the building. The various components of the HVAC system330may include sensors that are coupled to the pulse inputs210and212inFIG. 2. Such sensors send pulse inputs that reflect energy consumed by various components of an HVAC system330. Of course other interfaces may be included in the thermostat100to receive additional data from the operation of the HVAC system330.

In this example, the HVAC system330can include a compressor332, a gas furnace334, and a blower fan336. Of course, other heating systems such as an electric furnace or a heat pump may be used instead of the gas furnace334. The compressor332is coupled to a compressor relay342, which is in turn coupled to the compressor output306that allows the thermostat100to activate the compressor332. The furnace334is coupled to a heater relay342, which is in turn coupled to the heater output308that allows the thermostat100to activate the furnace334. The fan blower336is coupled to a fan blower relay346, which is in turn coupled to the fan blower output310that allows the thermostat100to activate the fan blower336. The HVAC system300has a cooling mode that requires electrical energy to operate the compressor332to produce cool air and the fan blower336to circulate the cool air. The energy consumed in the cooling mode is determined by data from a sensor on the compressor input332and a sensor on the fan blower336. In this example, the HVAC system300has a heating mode that requires gas to operate the furnace334to produce hot air and electrical power to operate the fan blower336to circulate the hot air. The energy consumed in the heating mode includes the gas energy determined by data from the furnace334and electrical energy consumed by the fan blower336as determined from data from a sensor on the fan blower336. Alternatively, if the furnace is an electrical furnace, the energy consumed in the heating mode includes electrical energy from the furnace and electrical energy consumed by the fan blower336. If the furnace is a heat pump, the energy may include energy from the compressor332, the fan blower336and in some cases of colder temperature, the energy from a back up heating system.

The thermostat100allows the display of energy savings based on data inputs on the display102inFIG. 1. The energy savings are based on a learn mode where the thermostat100learns the correlations for energy usage from different ambient conditions to estimate and display energy savings from operating the HVAC system330at an energy saving setpoint temperature at any particular ambient condition in comparison to operating the HVAC system at a comfort temperature.

In this example, there are three different methods of learning the correlation between ambient conditions and energy use by the HVAC system330to determine energy savings. A first method requires instruments on the HVAC system330to monitor electrical power and/or gas consumption and a sensor such as the outdoor temperature sensor318to measure outdoor ambient conditions. A second method estimates energy savings by monitoring the on and off times of the HVAC system330. The second method requires a sensor such as the outdoor temperature sensor318to measure outdoor ambient condition. Since the on-time of the HAVC system330will trend the power and gas consumption of the HVAC system330, additional instruments on the HVAC system330are not required. A third method estimates energy savings by reviewing the heat loss of the building and the on and off times of the HVAC system300, therefore not requiring any additional instruments.

The first method estimates energy savings by measuring the outdoor ambient conditions, electrical power and/or gas consumption during comfort setpoint operation and during set-back or set-up operation and therefore uses a variety of the inputs for the thermostat100shown inFIGS. 2-3. The electrical power can be measured on the branch breakers of the load center or on the individual HVAC equipment such as the blower fan relay346inFIG. 3. The gas consumption can be measured on the feeder line to the gas furnace334via the heater relay344to produce electrical impulses reflecting gas consumption. The outdoor ambient conditions can be measured by the outdoor temperature sensor318mounted exterior to the building, such as on the sunniest exterior wall of the building, or mounted inside the building in an environment that is indicative of the temperature of the outdoor environment. Other sensors can measure humidity and solar exposure that contribute to the outdoor ambient conditions. The measurement devices communicate their read data via wired or wireless connection to the thermostat100. After installation of the thermostat100, a learning mode is initiated where the thermostat100is set to run at a comfort setpoint temperature. During the learning period, the energy consumption of the HVAC system300and the outdoor ambient conditions are recorded at fixed time intervals. The outdoor ambient conditions can be determined via temperature, solar radiation, humidity, and other data factors.FIG. 4is graph400including measurement points402of the energy consumed by the HVAC system300operating to maintain the comfort setpoint temperature. In the graph400, the vertical axis is a scale of the ambient conditions expressed in terms of temperature while the horizontal axis is the energy consumption of the HVAC system300. The slope of a curve406is derived from the measurement points402and represents the correlation between the energy consumption (En) of the HVAC system330and the ambient conditions.

At the end of the learning period, an equation is developed that provides the energy consumed by the HVAC system300for any given outdoor ambient condition (such as temperature). As shown inFIG. 4, the equation is a linear curve or slope406or some other form that adequately fits the measured data points402. In this example, the learning period can be several days or the time necessary for a 20% variation in ambient conditions. The user can switch the thermostat into an energy savings mode after the learning period ends.

In this example, the energy savings during set-back operation can be estimated by first estimating the HVAC energy consumption for the comfort setpoint temperature using the equation developed in the learning mode and the measured outside ambient conditions during set-back operation. This equation is:
En=(1/m)*(Outdoor Ambient Condition−b)

In this equation, m is the slope that is calculated during the learning period based on the measured data points402, the outdoor ambient condition is based on data such as temperature measured from the outdoor sensor318and b is a constant determined from the learning period. The HVAC energy consumption (Es) is measured for the set-back (set-up) setpoint temperature and the savings are estimated according to the following equation:
Percentage Savings=[(En−Es)/En]*100

The percentage is therefore the difference between the energy consumption for the comfort setpoint temperature and the energy consumption for the set-back setpoint temperature used during the heating mode of the HVAC system330. A different curve can be derived in the same manner for the set-up temperature used during the cooling mode of the HVAC system330.

The second method of determining energy consumption savings estimates energy savings by monitoring the on and off times of the HVAC system330. The on time of the HVAC system330will reflect the power and gas consumption of the HVAC system330during the heating and cooling modes. The on times of the HVAC system330are controlled by the thermostat100, which stores the times that the HVAC system330are activated while maintaining the setpoint temperature in order to determine the on-time intervals and the intervals between the on-times. This method does not require any additional instruments on the HVAC system330but requires an outside sensor such as the sensor318to measure data such as temperature to determine the outdoor ambient conditions. As with the example above, the outside sensor318is preferably mounted on the sunniest wall of the building.

After installation of the thermostat100, a learning mode is initiated. The thermostat100is run at the comfort setpoint temperature during the learning period. During the learning period, the on and off times of the HVAC system330and the outdoor ambient conditions derived from factors such as temperature are recorded at fixed intervals as shown in a graph500inFIG. 5. The graph500is a plot of the recorded measured data points502for the second method. The graph500has a vertical axis representing the outdoor ambient condition while a horizontal axis represents the fraction of on time (Fn) of the HVAC system330. A curve504is interpolated based on the measured data points502. The curve504is mapped from the measurement points502and the slope variable, m, and the constant value, b, are determined and stored for future use. In this example, the learning period may be several days or the time necessary for a 20% variation in ambient conditions.

At the end of the learning period, an equation is developed that determines the energy consumed by the HVAC system300for any given outdoor ambient condition. As shown inFIG. 5, the equation is determined from the linear curve or slope504or some other form that adequately fits the measured data points502. The user may switch the thermostat100into an energy savings mode after the learning period ends.

During the set-back or the set-up operation at the respective setpoint temperatures, the outside ambient condition derived from the temperature and the on and off times of the HVAC system330will be recorded at fixed intervals.FIG. 6is a timing diagram600that shows an interval of on times602during the learning period at the comfort setpoint temperature and an interval of on times604during the operation of the HVAC system330at the energy saving setpoint temperature.FIG. 6shows the longer intervals between on times at set-back operation of the thermostat100as compared to the intervals between on times at comfort setpoint temperature therefore resulting in energy savings from the more infrequent use of the HVAC system330.

The energy savings during set-back operation may be estimated by first estimating the fraction of on-times for the HVAC system300maintaining the comfort setpoint temperature using the equation determined during learning mode and outside ambient conditions during the set-back operation. This fraction may be determined using the following equation:
Fn=(1/m)*(Outdoor Ambient Condition−b)

In this equation, m is the slope derived from the learning mode, the outdoor ambient condition is determined from the temperature measured from the outdoor sensor318and b is a constant determined from the learning period. The energy savings are estimated according to the following equation:
Percentage Savings=[(FnTs−ts)/(FnTs)]*100

As shown inFIG. 6, tnis the on time of the HVAC system330, while Tnis the measurement interval between the on-times (tn) during the comfort setpoint temperature operation. Correspondingly, tsis the on-time of the HVAC system300to maintain the set-back setpoint temperature during the period of set-back operation, while Tsis the measurement interval between the on-times (ts) during the set-back operation.

The percentage is therefore the difference between the energy consumption for the comfort setpoint temperature and the energy consumption for the set-back setpoint temperature as reflected in the percentage of time the HVAC system330is on at a certain ambient condition.

The third method estimates energy savings by examining the energy loss to the building and the on and off times of the HVAC system330. This method does not require any additional instruments on the HVAC system330. Over a period of time, the energy lost from the building will be compensated by the energy gained from the HVAC system330in order to maintain a fixed indoor ambient temperature. The energy gained from the HVAC system330is proportional to the energy used by the HVAC system330. For example, for 1 kWh of energy used in an electric heat pump, 3 kWh of energy from the outdoor ambient environment is obtained in the building for heating. The energy savings can be written as:
Savings=ΔE/E=(En−Es)/En=[(Pn−Ps)*t]/(Pn−*t)=(Pn−Ps)/(Pn).

In this equation, Enis the energy consumed by the HVAC system330at normal operation (comfort setpoint temperature), and Esis the energy consumed by the HVAC system330at set-back operation. Correspondingly, Pnis the power consumed by the HVAC system330at normal operation, and Psis the power consumed by the HVAC system at set-back operation. For a given indoor temperature and outdoor ambient condition, the equivalent power of the HVAC system330, Pnmay be written as:
Pn=P0*(tn/Tn)=P0*Fn.

In this equation, Fnis the ratio of on-time during measurement time period or the fraction of on-time of the HVAC system330at normal operation to maintain the comfort setpoint temperature as shown inFIG. 6. P0is the maximum power of the HVAC system330. If the set-back point is lowered, then the equivalent power of the HVAC system, Psat the set-back point will also be lowered:
Ps=P0*(ts/Ts)=P0*Fs.

In this equation, Fs is the ratio of on-time to measurement time period or the fraction of on-time during set-back operation as shown inFIG. 6.FIG. 6shows that during operation at a comfort setpoint temperatures, the intervals between on-times602is relatively less while the intervals between on-times during the set-back operation604are relatively greater, resulting in energy savings. As explained above, the amount of energy savings is proportional to the difference in the calculated energy for the HVAC system330based on the on-time intervals to maintain the energy saving set-back setpoint temperature to the calculated energy that the HVAC system330based on the on-time intervals assuming operation to maintain the comfort setpoint temperature.

Further, changes in outdoor ambient conditions change the equivalent power at the two setpoint temperatures as shown inFIG. 7, which is a plot of the ambient conditions702in comparison to the power plots of the HVAC system330at the two setpoint temperatures704and706. The energy therefore leaves the building at a rate proportional to the indoor and outdoor temperature difference. This heat loss rate, Q, may be expressed as:
Q=κ(Tindoor−Toutdoor)

In this equation, the variable, κ, is a type of heat loss coefficient that depends on the construction of the building. Changing the indoor setpoint temperature will change the power supplied and the heat lost. The change in power supplied by the HVAC system330can be written as:
ΔP=Pn−Ps=P0*Fn−P0*Fs

In this equation, the change in power ΔP is derived from the maximum power of the HVAC system330multiplied by the ratio of the on-time, Fn, during the comfort setpoint temperature operation and the maximum power of the HVAC system330multiplied by the ratio of the on-time, Fs, during the energy saving setpoint temperature. The change of heat leaving the building may be written as:
ΔQ=Qn−Qs=κ(Tindoor n−Toutdoor s)

Equating the change in power and the change in heat loss provides an equation for saved power to consumed power for a lower setpoint temperature at any time, tx, during the operation of the thermostat100at a lower setpoint temperature.

The learning mode is used to determine the coefficient, cc. In this mode, the thermostat100examines the transition period from the HVAC system330maintaining one setpoint temperature to the HVAC system330maintaining another setpoint temperature. It is assumed that during the transition the outdoor ambient conditions are fairly constant and if the fraction of on-time just before (Fa) and just after (Fb) the transition is measured, the α coefficient may be estimated with the following:
α=(Fa−Fb)/(Ta−Tb)

At the end of the learning period the user can switch the thermostat100into an energy savings mode. During the energy savings mode the coefficient, α may be checked and refined with further setpoint temperature changes. To calculate the saved power to consumed power without operating at the setback temperature, the controller300determines the following:

Although an example of the controller300is described and illustrated herein in connection withFIG. 3, this component can be implemented on any suitable computer system or computing device. It is to be understood that the example controller300inFIG. 3are for exemplary purposes, as many variations of the specific hardware and software used are possible, as will be appreciated by those skilled in the relevant art(s).

Furthermore, each of the devices can be conveniently implemented using one or more general purpose computer systems, microprocessors, digital signal processors, micro-controllers, application specific integrated circuits (ASIC), programmable logic devices (PLD), field programmable logic devices (FPLD), field programmable gate arrays (FPGA), and the like, programmed according to the teachings as described and illustrated herein, as will be appreciated by those skilled in the computer, software, and networking arts.

In addition, two or more computing systems or devices can be substituted for the controller300inFIG. 3. Accordingly, principles and advantages of distributed processing, such as redundancy, replication, and the like, also can be implemented, as desired, to increase the robustness and performance of the controller300inFIG. 3. The controller300inFIG. 3can also be implemented on a computer system or systems that extend(s) across any network environment using any suitable interface mechanisms and communications technologies including, for example, telecommunications in any suitable form (e.g., voice, modem, and the like), Public Switched Telephone Network (PSTNs), Packet Data Networks (PDNs), the Internet, intranets, a combination thereof, and the like.

The operation of the example process to estimate and display energy savings shown inFIGS. 1-7, which can be run on the controller300, will now be described with reference toFIGS. 1-3in conjunction with the flow diagram shown inFIG. 8. The flow diagram inFIG. 8is representative of example machine-readable instructions for implementing the processes described above to calculate and display energy savings of the operation of HVAC system330at an energy savings setpoint temperature inFIG. 3. In this example, the machine readable instructions comprise an algorithm for execution by: (a) a processor, (b) a controller, and/or (c) one or more other suitable processing device(s). The algorithm can be embodied in software stored on tangible media such as, for example, a flash memory, a CD-ROM, a floppy disk, a hard drive, a digital video (versatile) disk (DVD), or other memory devices, but persons of ordinary skill in the art will readily appreciate that the entire algorithm and/or parts thereof could alternatively be executed by a device other than a processor and/or embodied in firmware or dedicated hardware in a well-known manner (e.g., it may be implemented by an application specific integrated circuit (ASIC), a programmable logic device (PLD), a field programmable logic device (FPLD), a field programmable gate array (FPGA), discrete logic, etc.). For example, any or all of the components of the controller300inFIG. 3could be implemented by software, hardware, and/or firmware. Also, some or all of the machine readable instructions represented by the flowchart ofFIG. 8can be implemented manually. Further, although the example algorithm is described with reference to the flowchart illustrated inFIG. 8, persons of ordinary skill in the art will readily appreciate that many other methods of implementing the example machine readable instructions can alternatively be used. For example, the order of execution of the blocks can be changed, and/or some of the blocks described can be changed, eliminated, or combined.

The controller300begins the learning period by setting the HVAC system330to maintain a comfort setpoint temperature (800). The controller300measures the outdoor ambient condition via a sensor or sensors external to the building and applicable energy data for the HVAC system330(802). The controller300correlates that outdoor ambient condition with the energy of the HVAC system330(804). As detailed above, the energy of the HVAC system330can be a direct measurement such as gas and electrical power or it can be an estimate based on the time intervals between each time the HVAC system330is activated to maintain the comfort setpoint temperature. The exact data gathered by the controller300depends on which of the three above described methods the controller300is using. The measured data is stored in the storage device320inFIG. 3by the controller300(806). The controller300determines whether there are sufficient data points for the learning period (808). The number of data points can be collected during a set period of time or with sufficient variation of the outdoor ambient conditions. If there are insufficient data points, the controller300loops back and measures another outdoor ambient condition and HVAC system data (802).

If there are sufficient data points, the controller300determines the correlation between the ambient conditions and the energy to maintain the comfort setpoint temperature such as by determining the slope of a curve as inFIGS. 4 and 5(810). The thermostat100is programmed with an energy saving setpoint temperature and the thermostat100controls the HVAC system330to maintain the building at the energy saving setpoint temperature (812). The controller300determines the energy savings based on the difference between the energy that would have been consumed by the HVAC system330at the ambient condition based on the determined correlation from the learning mode and the energy consumed by the HVAC system330while maintaining the energy saving setpoint temperature at the ambient condition (814). The exact determination made by the controller300depends on which of the three above described methods the controller300is using. The energy saving data is displayed on the display102(816).

While the present invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes can be made thereto without departing from the spirit and scope of the present invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the claimed invention, which is set forth in the following claims.