Patent Application
20130045451
A known problem with a conventional gas-fired furnace, as well as with other types of gas-fired heating appliances, is that the furnace outputs considerably less heat (when using gas having the same heating value) when it is used at high altitudes. For example, above 5000 feet the heating capacity of a typical gas furnace will be reduced by about 20 percent compared to the heating capacity of the same furnace, using gas having the same heating value, at sea level (per the National Fuel-Gas Code Handbook; Section 8.1.2 High Altitude). Because of this, a consumer has heretofore been forced to buy a larger and thus more expensive furnace to obtain the same heating output at a high altitude location as a smaller furnace at a lower altitude. In view of this it would be desirable to provide a gas-fired furnace, or other type of gas-fired heating appliance, with the capability of increasing its heating output enough to compensate for a high altitude use of the furnace without having to upsize the furnace.
Schematically depicted in
The illustrative furnace 10 is of the draft-induced type, having an outer housing 14 within which a heat exchanger 16 is operatively disposed above a combustion chamber 18 having a gas burner 20 therein below the heat exchanger 16. Gas burner 20 is supplied with gas via a gas supply line 22 in which a modulating gas valve 24, operative to maintain a predetermined gas manifold pressure within the line 22, is connected. In common with conventional furnace gas valves, the illustrated gas valve 24 has a normal gas pressure control setting level of 3.5″ W.C. However, according to an aspect of the present invention, the gas valve is operable, in manners subsequently described herein, to enable its gas pressure control setting to be selectively increased to magnitudes greater than 3.5″ W.C. to thereby increase the high altitude heating capacity of the furnace.
During firing of the furnace 10, which is initiated and terminated under the control of a thermostat 26 disposed in a conditioned space served by the furnace 10 and operatively coupled to the furnace control 12 as shown, hot combustion gases 28 created by the burner flame 30 travel through the interior of the heat exchanger 16 into the interior of a vent structure 32 that is coupled to the upper side of the heat exchanger 16. Passage of the hot combustion gases 28 through the vent 32 is assisted by the operation of a variable speed combustion blower 34 operatively mounted in the vent 32. Also during firing of the furnace 10, return air 36a from the conditioned space served by the furnace 10 is forced by a variable speed indoor blower 38 exteriorly across the heat exchanger 16, for example through a duct structure 40, to receive combustion gas heat from the heat exchanger 16 and thereby create heated supply air 36b suitably conveyed to the conditioned space served by the furnace 10.
Turning now to
Referring now additionally to
User input of a desired elevation value responsively transmits identical selected elevation magnitude signals 44 to first and second lookup tables 46 and 48. Lookup table 46 charts indoor blower speeds against associated elevation values and is operative as shown to output to the furnace control 12 a desired indoor blower RPM signal 50 associated with the user selected elevation range value.
Lookup table 48 charts gas valve control pressure offsets (i.e., above the normal 3.5″ W.C. regulated gas pressure) against selected combinations of elevation range and gas heating values (or against only an elevation value as the case may be). When a user, via the touchpad 42, selects a desired elevation value and a desired gas heating value, the elevation magnitude signal 44 and a selected gas heating value signal 52 are transmitted to the lookup table 48 which responsively transmits to the furnace control 12 a desired pressure offset signal 54.
During firing of the furnace 10, the furnace control 12 regulates the operation and speed of the variable speed indoor blower 38 by outputting to the indoor blower 38 (1) 115 volt AC electrical power via lead 56 and (2) a speed control signal via lead 58. The speed control signal causes the indoor blower 38 to run at an increased speed corresponding to the magnitude of the lookup table signal 50 received by the furnace control 12, thereby causing the indoor blower 38 to deliver its designed-for CFM of air to the conditioned space despite the high altitude placement of the furnace 10 and the resulting ambient air density decrease. Alternatively, the indoor blower 38 could be a single speed blower and its speed control signal could be eliminated.
At the same time, the furnace control 10 regulates the operation and pressure regulation level of the modulating gas valve 24 by outputting to the gas valve 24 (1) 24 volt ac electrical power via electrical power lead 60, (2) a regulating pressure offset signal via lead 61, and (3) a gas flow regulating signal via lead 62. The regulating pressure offset signal elevates the maximum manifold pressure regulation magnitude of the valve (for example, beyond its normal 3.5″ WC level) to a level indicated by the magnitude of the signal 54 received by the furnace control 12. This upward valve pressure regulation level adjustment increases the heating capacity of the furnace 10 to compensate for its high altitude placement without the previous necessity of upsizing the furnace. The flow regulating signal modulates the gas flow to the burner 20 as required by the heating demand.
It should be noted that the regulating pressure offset signal (lead 61) and the gas flow regulating signal (lead 62) may be the same signal with compensation calculated and adjusted at the furnace control instead of the gas valve. Such a signal would have a predefined relationship to the output of the gas valve (e.g., a 50% PWM signal that corresponds to 50% of the valve's maximum capacity). In any case, the gas valve 24 would need to be pre-set during production to be capable of exceeding 3.5″ W.C. which is the current maximum value of gas valves commonly utilized on residential gas furnaces. While the gas valve 24 has been representatively illustrated as being a modulatable gas valve, it could alternatively be a single stage gas valve, in which case the gas flow regulating signal (lead 62) could be replaced with a simple “on/off” signal.
Operatively coupled to the furnace control 12 by the indicated electrical leads 64, 66 and 68 as shown in
The combustion air blower speed is changed, via a speed control signal output to the blower from the furnace control 12 via a lead 78, based on feedback from the pressure switches, the low pressure switch 70 being set to be just closed at the selected minimum blower speed (corresponding to the minimum heating capacity of the furnace), and the high pressure switch 72 being set to be just closed at the selected maximum blower speed (corresponding to the maximum heating capacity of the furnace). A lead 80 from the furnace control 12 transmits 115 AC electrical power to the combustion blower 34. In developing the present invention it has been found that this combustion blower control technique automatically provides altitude compensation for combustion blower flow capacity by increasing the speed of such blower at higher altitudes. As in the case of the indoor blower 38, the combustion blower 34 could be a single speed blower if desired.
Schematically depicted in
As can be seen, the present invention is operative to increase the manifold regulation pressure of a furnace gas valve beyond its normal 3.5″W.C. fixed setting, and to also correspondingly optionally increase the combustion and indoor blower flow rates (if these devices are variable on the system in question) to compensate for the placement of a furnace at a high altitude. In this manner, the same furnace can be used at varying altitudes without altering its heating output, thereby eliminating the previous necessity of upsizing the furnace. While this desirable and cost effective altitude compensation technique has been representatively described in conjunction with a furnace, it will be readily appreciated by those skilled in this particular art that principles of the present invention could also be advantageously employed in conjunction with other types of gas-fired heating appliances.
Additionally, while the present invention has been described as being implemented via an automatic heating capacity altitude compensation system, it will be appreciated that principles of the present invention could also be employed by the use of manual adjustment of gas valve and blower components of a gas-fired heating appliance. For example, the gas valve 24 could be provided with a manual high altitude adjustment structure permitting its pressure regulation setting to be manually increased above 3.5″ W.C. Additionally, altitude compensation for the furnace 10 could be achieved simply by replacing its standard gas valve (having a fixed 3.5″ W.C. gas pressure regulation setting) with a high altitude gas valve with a fixed gas pressure regulation setting greater than 3.5″ W.C.
The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.
The present application claims the benefit of the filing date of provisional U.S. patent application No. 61/524,383 filed Aug. 17, 2011. The entire disclosure of the provisional application is hereby incorporated herein by this reference.
| Number | Date | Country | |
|---|---|---|---|
| 61524383 | Aug 2011 | US |
