Patent Application
20070287111
The present invention relates controlling the thermal energy generated by a heating system.
In U.S. Pat. No. 5,112,217, Ripka et al. describe a radiant burner having (1) a constant flow of fuel, (2) a variable flow of air, (3) an ignition source, (4) a radiation sensor that measures the radiation or luminosity of the flame and transmits that measurement to a computer, and (5) the computer computes what the desired efficiency should be and transmits signals to the variable flow of air apparatus to control the amount of air that enters the radiant burner to obtain the alleged maximum flame efficiency.
In particular, Ripka et al. describe the control system as controlling the fuel-to air ratio by varying combustion air to the burner; controlling fuel gas is briefly noted as a possibility but not described in apparatus or method. The '217 method utilizes optic sensor technology to sense flame luminosity as an indication of fuel-to-air ratio. The control apparatus and method are described as being appropriate for surface combustion type radiant burners that can be inserted in heating appliances such as furnaces or water heaters which are of different use, construction and application than the low-intensity radiant tube heater described in the present invention which is commonly used for space heating. The present invention does not use optical sensors as a feedback device instead it uses a pressure transducer to directly measure and control combustion air and uses an electronic modulating gas valve to directly control fuel gas pressure.
Ripka et al. describe an apparatus and method that change the fuel-to-air ratio of a burner operating at a single input with the use of a constant supply fuel gas regulating valve and vary the combustion air supply with the use of a fan or blower having a variable speed motor to achieve a desired reference radiation intensity. Ripka et al. does not attempt to teach how to maintain or optimize fuel-to-air ratio while at the same time vary burner heating capacity (BTU/h) for the purpose of optimizing comfort and fuel efficiency of a low intensity radiant tube heater. The present invention demonstrates a control and method that will accept external user input thermostatically or otherwise that will vary the heating input (BTU/h) capacity and control fuel-to-air ratio by varying both the combustion air supply the fuel gas pressure.
Simple logic programming changes of Ripka's computer apparatus will not result in a burner as described in the present invention. A burner's optimum fuel-to-air ratio throughout a range of a burner's varying inputs is determined by individually tailoring a fuel-to-air ratio curve for each fuel type and each input range, i.e. a burner with an input range of 50,000 to 100,000 BTU/h operating on natural gas will possess a different fuel-to-air ratio curve from a burner with the same input range operating on propane gas. Likewise two burners operating on the same gas with different input ranges will have two individual fuel-to-air ratio curves. Individually testing and tailoring fuel-to-air ratio curves for each input range and fuel type of a burner allows each heater to obtain its greatest possible fuel efficiency and combustion safety characteristics. Sharing a common fuel-to-air ratio curve would require sacrifices in either fuel efficiency or combustion safety.
As previously stated, Ripka et al. also implied, not taught, the constant flow of fuel could be altered to a variable flow of fuel. We used the term “implied” because Ripka et al. failed to explain to one of ordinary skill in the art how to accomplish that objective.
Ripka et al. did, however, acknowledge that alternative methods to control the flow of fuel and/or the flow of air were known. Those alternative methods are, according to Ripka et al., impractical. In particular Ripka et al. wrote, “While it is possible to directly measure the flow ratio of the fuel gas and air supplies to a burner and to regulate one or both of the flows so as to produce a combustible gas mixture that is optimum, such a detection and control system would be complex and prohibitively expensive in many applications. The designs of some burner applications include pressure switches to detect air flow rate, but such switches are capable only of detecting gross departures from the optimum excess air value and not of regulating the excess air percentage. Still other designs employ sensors which detect the presence and concentration of constituents, such as oxygen, of the flue gases emanating from the burner. Those designs however are subject to sensor fouling and can be unreliable and inaccurate.” In other words, Ripka et al. clearly and unequivocally teaches (1) measuring flow ratios of fuel and air is possible but too expensive to be used for radiant burner devices, (2) measuring the pressure of the air, not fuel, through pressure switches but those pressure switches are unreliable, and (3) measuring the concentration of certain gases emitted from the flame. Ripka et al. clearly and unambiguously teach away from using flow ratio measurement devices, pressure measurement devices and concentration measurement devices.
Ripka et al. distinctly teach away from measuring the pressure of both the fuel and the air. More importantly, Ripka et al. suggest that there is no radiant burner device that measures the pressure of the fuel and the pressure of the air to obtain the desired maximum flame efficiency.
Presently, radiant heaters and radiant heating systems most commonly operate at a single preset input and space temperature is controlled by a thermostat by turning the heater or heating system on or off. In the early to mid 1990's, radiant heaters have been developed to operate at either of two distinct preset inputs by varying the fuel pressure communicated to the burner via a two-stage fuel regulator. One radiant burner with a two-stage operation is described in U.S. Pat. No. 5,353,986 titled “Demand Radiant Heating System” by Joseph B. Wortman. In the '986 patent, Wortman describes a radiant heater with a single fuel control capable of dual regulation. The dual regulation is limited to only providing a high or low input rate to respond to a high or low heat demand.
Further advances in radiant burner input control are described in U.S. Pat. No. 5,989,011 titled “Burner Control System” by Caruso et al. Caruso et al. in the '011 patent disclose a control system. Caruso et al. describe the control system as being capable of altering the fuel pressure to the burner by varying air pressure from a blower to the fuel regulator via an air regulator. By continuously varying the air pressure communicated to the fuel regulator, the discharge gas pressure to the burner is also varied allowing a continuously variable input.
However, in neither cited patent (U.S. Pat. No. 5,353,986 and U.S. Pat. No. 5,989,011) is air pressure (volume) to the burner's fuel/air mixing apparatus varied.
Since heater inputs are sized to satisfy building heat loss based on an outdoor design temperature that occurs approximately 1-5% of the time during the entire heating season. In other words, heating systems that conform with the above-cited references normally operate at an input that exceeds the demand. It is favorable to have the option of varying the heater input based on the heating demand to decrease the number of heater on/off cycles and to increase occupant comfort in the heated space.
Two-stage burners are alternative options to the heaters that conform to the cited references. Such two-stage burners are limited to only two distinct operating rates offering only coarse control of varying demands and do not match the heat demand for the majority of the time. Continuously variable modulating control allows fine control of heater input to match the heat demand closely, operating at any percentage of the heater's full rated input, within a predetermined range.
In both patents mentioned (U.S. Pat. No. 5,353,986 and U.S. Pat. No. 5,989,011), there are disadvantages to varying gas volume (or pressure) to the burner mixing apparatus without also varying combustion air volume (or pressure) to the burner's mixing means. Without variation of the air flow to the burner simultaneously with variation of fuel flow, sacrifices are made in terms of heater performance and efficiency as well as combustion quality and efficiency. It is desirable to vary the heater's input not only by controlling the gas flow to the burner, but also the combustion air flow. By varying both the combustion air and gas flow (pressure or volume); combustion efficiency, combustion quality, heater efficiencies and flue emissions can be more closely regulated for optimum infrared heater performance.
In commonly assigned U.S. Pat. No. 5,211,331 entitled “Control in Combination with Thermostatically Responsive Assembly”, Timothy Seel describes a variable rate system of infrared burners-in-series. The infrared system of burners possesses the ability to vary fuel and combustion air to achieve modulating system input. Seel does not disclose, teach or suggest any ability to control a single “unitary” style infrared heater with associated burner modulating controls and blower mounted internal to the burner housing.
A version of the control that can be used in the present invention is manufactured by Varidigm Corporation of Plymouth, Minn. That control has the capability of controlling a modulating gas valve and varying the speed of a single-phase shaded-pole motor. That control, however, cannot be merely inserted into the present invention without tailoring certain parameters to obtain the desired results.
Fractional horsepower DC motors are readily available in the market and can easily be controlled to vary their speed, but a DC motor is more expensive than a shaded pole motor of similar size. In addition to the DC motor costing more, a controller is needed to send a control signal to the DC motor to vary its speed; a controller would also need to send a separate control signal to vary the gas valve, adding more cost. The ability to vary the speed of a shaded pole motor allows a cost savings by eliminating the need to use a more expensive DC motor as well as incorporating motor control, gas valve control and burner ignition and sequencing.
Two-stage and modulating infrared heaters with fixed combustion air flow set the combustion air flow for the maximum input rate. In laboratory testing in accordance with the European Standard prEN 416-2 “Single Burner Gas-Fired Overhead Radiant Tube Heaters For Non-Domestic Use”, it has been shown that two stage heaters exhibit 9-10% lower radiant efficiency at low input due to the blower delivering an excess of combustion air, which is fixed to deliver a volume and pressure of air that is optimum only at maximum input rate. Besides a reduction in radiant efficiency, two-stage infrared heaters show an approximate 2% decrease in thermal efficiency at low input versus high input. By reducing the combustion air and fuel when input is reduced, a modulation infrared heater will maintain its optimum radiant efficiency at all firing rates. That results in an exhibition of radiant efficiency at low fire that is 9-10% higher than a two-stage heater. That capability is not possible in current modulating or two stage infrared heater design with single speed blowers. In addition, by maintaining heat exchanger temperature through varying fuel and combustion air flow with respect to burner pressure, the radiant efficiency of the heater can be maintained throughout the entire input modulation range. Not only is radiant efficiency improved, but also thermal efficiency increases as input rate decreases, thermal efficiency increases 3-4% at minimum input versus maximum input. Two stage infrared heaters typically allow for a 30-35% input turndown from high input to low input, an air and fuel modulating heater can exhibit input turndowns up to 70% from maximum input to minimum input, doubling the turndown capability of a two-stage infrared heater.
The present invention relates to the use of apparatus for continuously varying the input of radiant gas heaters that respond to heat demand. The variable input radiant heater apparatus consists of a burner housing having a combustion air and fuel inlet and a burner assembly for mixing the fuel and air and conveying the mixture into a heat exchanger for combustion. Combustion takes place inside the heat exchanger and resulting hot products of combustion are moved to through the heat exchanger to the exhaust end due to air pressure from a combustion air blower providing either positive air pressure from the burner end of the heater or negative pressure from the exhaust end of the heater. At the exhaust end of the heat exchanger, the combustion gasses are vented from the heater. A signal is conveyed to a controller mounted in the burner housing from a heat demand control device. Based on the signal, the controller varies the input of the heater to satisfy the heat demand. The input of the burner is varied by changes in the combustion air (via blower speed changes) and fuel (via modulating gas valve) supplied to the burner assembly.
Generically, the present invention is directed to a single radiant heater or multi-burner radiant heating system. In particular, the present invention is directed to a single radiant heater or multi-burner radiant heating system that modulates the burner input by varying fuel and combustion air supply to the burner's mixing apparatus. The apparatus continuously varies the input of radiant gas heaters that respond to heat demand. The variable input radiant heater apparatus have a burner housing with a combustion air and fuel inlet and a burner assembly for mixing the fuel and air, and conveying the mixture into a heat exchanger for combustion. Combustion takes place inside the heat exchanger and resulting hot products of combustion are moved to through the heat exchanger to the exhaust end due to air pressure from a combustion air blower providing either positive air pressure from the burner end of the heater or negative pressure from the exhaust end of the heater. At the exhaust end of the heat exchanger, the combustion gasses are vented from the heater. A signal is conveyed to a controller mounted in the burner housing from a heat demand control device. Based on the signal, the controller varies the input of the heater to satisfy the heat demand. The input of the burner is varied by changes in the combustion air (via blower speed changes) and fuel (via modulating gas valve) supplied to the burner assembly.
1. Objectives of the Present Invention
It is an object of the present invention to combine patented burner control technology and detailed laboratory analysis of infrared heaters specifically, to customize the operation and settings of the control for the purpose of optimization of performance, efficiencies and safety unique to an infrared heater.
It is an object of the present invention that a modulating gas valve controls fuel supply. The gas valve may have either pneumatic or electronic modulation. The fuel volume and pressure issued from the outlet of the gas valve to the burner can either be controlled by an electronic signal from the controller or a pneumatic (air pressure) signal from the blower. An advantage of the present invention using an electronic modulating gas valve is that the control of the gas valve is independent of the air pressure generated by the blower allowing for customization of the fuel to combustion air ratio. An advantage of the ability to customize this ratio is that heater performance, efficiencies and safety can be maximized for various burner fuel types and inputs.
It is an object of the present invention that the combustion air pressure and volume supplied to the burner is variable and is controlled by varying the speed of the blower motor. An advantage of the present invention is that the motor may be DC, permanent split capacitor (AC, single phase) or shaded pole (AC, single phase). The option allows for the most economical choice as the motor market dictates. The controller varies the speed of the motor by electronic signal. Currently there is no other control readily available that can vary the speed of a fractional horsepower shaded-pole motor.
It is an object of the present invention to be able to control motor speed of a standard single-phase shaded pole motor that is commonly used in single and two-stage infrared heaters. Achieving motor speed control by purchasing a more expensive DC motor is not required.
It is an object of the present invention to incorporate the burner control into infrared burner design such that the compact, lightweight control allows mounting of the control inside the burner housing and also allows optional mounting of the blower inside the burner housing without the need to increase the housing size.
It is an object of the present invention to control the input to any point within a predetermined range of input rates. The burner may operate at any input between and including full rated input to 30% of full rated input. The input range may be narrowed by reprogramming of the control's logic chip(s) if desired.
It is an object of the present invention to vary the burner input based on any one of various demand control devices.
It is an object of the present invention to detect heated area conditions with a traditional mechanical thermostat. By recording input rates and duration of past heating cycles, a programmed algorithm can pre-determine the initial heater input of a new heating cycle. During a new heating cycle the controller can adjust this pre-determined heater input based on timing of the new heating cycle and/or additional limit sensors or thermostats.
It is an object of the present invention to detect heated area conditions with a temperature sensor in the space. By calculating the difference between a set point temperature and an actual air temperature the controller can vary the heater input to respond to sensed heat demand.
It is an object of the present invention to detect user-controlled settings from a manually operated potentiometer to select heater input based on user demands.
It is an object of the present invention to control the combustion characteristics at the continuously varying input rates by continuously varying the fuel flow and combustion air flow to the burner's mixing means. Continuously changing condition inputs communicated to the burner control dictate the desired heat input. Combustion air flow and fuel flow are continuously varied to achieve changing input requirements to satisfy the desired heat demand.
It is an object of the present invention to monitor burner pressure and correct fuel flow and/or combustion air flow to maintain proper combustion under varying burner pressure conditions and to control blower speed and gas valve position independent of each other. The controller is pre-programmed with the required gas valve positions for every burner pressure. In response to changing demands, blower speed adjusts first to achieve a desired burner pressure, as correct burner pressure is sensed the fuel is immediately adjusted for desired combustion based on the pre-programmed settings. If adequate burner pressure cannot be achieved by changing blower speed, the fuel supplied will adjust according to the burner pressure that is achieved. If burner pressure decreases during a heating cycle, the controller senses the pressure drop and the controller will adjust the gas valve to supply the fuel necessary for correct combustion at the lower burner pressure.
2. Heater
The heater or multi-burner heating system 10 in this invention includes a burner housing 12 to which a heat exchanger 14 is connected. The heat exchanger's 14 length and shape may be various. Examples of shapes include and is not limited to straight, U-shaped, J-shaped, L-shaped, and polygonal shaped. The heat exchanger 14 is of conventional construction and will typically be mounted below a reflector 16 covering the length of the heat exchanger 14. The entire heater 10 including burner housing 12, heat exchanger 14 and reflector 16 is typically suspended (with conventional suspension instruments like cables, rods, cords and the like 102) from and/or attached (screws, bolts, nails and the like) to a ceiling 100 of a structure (not identified).
In accordance with this invention, the housing 12 is provided with a single fuel delivery system 120 including (1) a modulating gas valve 121, (2) a gas manifold 122 whose inlet side 122a is connected to the outlet side 121a of the gas valve 121 and (3) a burner assembly 123 whose inlet side 123a is connected to the outlet side 121a of the manifold 121.
The burner assembly 123 includes suitable apertures 123b, and an apertured stem 123c connected to the manifold 122 outlet 122b fitted with a suitable gas orifice 124. Mounted either downstream of the burner 123 or inside the burner 123 is a flame igniter 123d and flame sensor 123e.
The burner assembly 123 is positioned at the inlet end 141 of the heat exchanger 14.
3. Blower
A blower 18 is provided for causing a draft through (1) the combustion air inlet 125 of the burner housing 12, (2) the burner assembly 123, and (3) then the heat exchanger 14. The blower 18 may be positioned between the combustion air inlet 125 of the burner housing 12 and the burner assembly 123, forcing air through the burner housing 12 and heat exchanger 14. Alternately, the blower (draft inducer) may be positioned at the outlet end 142 of the heat exchanger 14, providing vacuum to pull air through the combustion air inlet 125 of the burner housing 12, through the burner assembly 123 then through the heat exchanger 14. An air restriction plate 20 is placed before or after the blower 18 to meter the combustion air delivered from the blower 18 to the burner assembly 123. Obviously, the blower 18 can be any conventional blower capable of providing the above-described attributes for conventional heating systems.
4. Controller
In accordance with this invention, a single controller 22 (control board) controls the operation and sequencing of the modulating gas valve 121, the blower 18 and the igniter 123d. The circuit board 22, manufactured by Varidigm Corporation of Plymouth, Minn., is powered both from a line voltage source 220 and from a 24V transformer 221 mounted in the burner housing 12 connected to line voltage 220. A pressure (or vacuum) switch 222 being sensitive to burner pressure via pressure lines 223 is electrically connected to the control board 22. The control board 22 monitors the opening and closing of the pressure switch circuit 222 to verify proper operation and calibration of a pressure transducer 224 on the control board 22. The pressure transducer 224 is also sensitive to burner pressure communicated via pressure lines 223, and that allows the controller 22 to alter blower 18 and gas valve operation 123 according to the current burner pressure.
A conventional thermostatically controlled relay 225 can be used to communicate heat demand to the controller 22. The control board 22 can collect data relating to a thermostat circuit 226 closing and opening cycle timing. Based on this timing the controller 22 can command ignition, modulation or shutting off of the burner 123. Alternately, an air temperature sensor or group of such sensors 227 can be used to communicate heat demand. The controller 22 can process the sensed temperature to command ignition, modulation or shutting off of the burner 123. Alternately, the user can initiate ignition and shut down the heater 10 as well as set the input rate during operation that can manipulate a manual potentiometer.
By using the modulating burner control 22 and making modifications for application on an infrared heater 10, fuel and combustion air can be varied in correct proportions for optimum safety, performance and efficiency. The compact size allows for mounting in the burner housing 12 of the heater 123. By tailoring the controller's 22 fuel and combustion air settings specifically for infrared heaters through performing detailed laboratory analysis of burner performance characteristics individual to infrared heaters, burner efficiencies and safety can be maximized as never before.
At minimum input, the present invention achieves a thermal efficiency 5-6% higher than a two-stage infrared heater at low input. In addition, the controller 22 allows for a greater range of modulation between high and low input rates than a two-stage heater.
The burner controller 22 has pressure-sensing capability that greatly improves the safety and reliability of an infrared heater. Since the controller 22 has independent control of the combustion air and fuel supplies, it can adjust the blower speed to compensate for additional flue lengths or for partial flue or inlet blockage in an effort to optimize combustion quality. If proper combustion is not achievable by increasing blower 18 speed, the controller 22 will command the gas valve to reduce gas flow maintaining proper burner combustion. This ability maintains the quality of emissions for the modulating infrared heater and corrects situations that would otherwise result in elevated heat exchanger temperatures of infrared heaters. Not only does this increase the overall safety of the heater, but also potentially increases the service life of the heat exchanger 14.
The VBC (Variable Burner Control) 22 is designed to provide cost-effective modulation. It will provide up to 5:1 turndown, depending on burner characteristics, for unitary infrared burner characteristics, probably closer to 2:1 turndown. The VBC 22 controls standard induced or forced draft blowers 18, which are linked to a valve that delivers the proper fuel/air ratio at every input. Modulation provides a closer relationship between burner input and demand, improving temperature control. Pressure sensing by pressure transducer and adjustment of combustion air blower motor speed allows combustion air compensation for added inlet flue or vent as well as blocked vent, ensuring optimal burner operation for various installation scenarios. The VBC 22 also controls sequencing and ignition functions.
5. Operation
In operation, the heater 10 is operated in a similar fashion to other thermostatically controlled heating appliances. A thermostat 226 or other temperature sensing 225, 227 or control device 22 initiates the operation. Upon activation the blower 18 is energized and will operate at full speed. Once the pressure switch 222 proves flow of air through the burner and the pressure transducer 224 senses adequate pressure, the controller 22 allows an air purge period prior to ignition. After the purge period, the controller 22 energizes the igniter 123d then opens the gas valve 121. Gas flows through the gas valve 121, manifold 122 and orifice 124 then into the burner 123 where it mixes with the combustion air and the mixture is ignited by the igniter 123d. Ignition is detected by the flame sensor 123e, which signals the controller 22 to keep the gas valve 121 in an open position. If the flame is extinguished at any time during operation, the flame sensor 123e will signal the controller 22 to close the gas valve 121 and stop the flow of gas to the manifold 122. Upon ignition, initial input rate is 100% of full rated input or maximum input allowed as dictated by achieved burner pressure. The burner 123 will continue to operate at maximum input for a predetermined duration for heat exchanger warm-up. Following the warm-up period, the heater will modulate based on achieved burner pressure and/or signals from demand control devices. At all times during the operation of the heater 123, the burner pressure is monitored. Burner pressure, as realized by the blower operating speed, will dictate the appropriate gas pressure and volume as pre-determined by detailed laboratory testing for maximum safety, performance, efficiency and combustion and emissions quality. The heat and fire and associated flue gasses are pushed or drawn downstream through the heat exchanger 14, away from the burner 123 towards the exhaust end 142 of the heat exchanger 14. The fire and hot flue gasses heat up the heat exchanger 14. The heat exchanger 14 releases this energy through convective and radiant heat transfer from the tubes outer surface in all directions. The reflector 16 over the heat exchanger helps contain the convective heat to maintain desired tube temperature, it also reflects and directs the radiant energy down toward the heated space below the heater 10.
The heater described could also be grouped into a multi-burner heating system. In such a configuration, the exhaust ends 142 of multiple heat exchangers 14 are coupled together through a common draft inducer that is located at the exhaust end of the coupled heat exchanger. In this configuration, the draft inducer creates negative pressure through heating system drawing the flame and heated gasses toward the end of the coupled heat exchanger. All burners would modulate simultaneously as a result of connection to the same draft inducer.
In particular, the Varidigm control device incorporates a pressure transducer device to monitor the available combustion air pressure provided by the combustion air blower/inducer. The control then will modulate the gas valve pressure output to match the combustion air flow. Testing must be performed for each heater in the specified input ranges. Measurements were recorded along the full modulation range to obtain optimum combustion characteristics. Safety margins were also calculated then the data points are programmed into the logic of the Varidigm control.
In operation, this control compares the programmed pressure points with the actual pressure provided by the pressure transducer and will provide the corresponding gas pressure for the given combustion air pressure. If there are system variances that may cause increased or decreased pressure such as a partially blocked flue, the control compensates for the pressure variances. This is accomplished by the control increasing or decreasing the speed of the blower/inducer. By doing so, the control is always attempting to maintain the engineered combustion conditions under varying application conditions that are commonly found.
While a preferred form of this invention has been described above and shown in the accompanying drawings. It should be understood that the applicant does not intend to be limited to the particular details described above and illustrated, but intends to be limited only by the scope of the invention as defined by the following claims.
This application claims priority as a continuation-in-part application to U.S. patent application Ser. No. 10/858,244, filed on Jun. 1, 2004.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10858244 | Jun 2004 | US |
| Child | 11728464 | Mar 2007 | US |
