Steam system

Abstract

A steam system configured to heat water, the steam system comprising: a heat exchanger configured to receive steam and water, where the heat exchanger is configured to heat water with steam; a steam supply line configured to be connected to a steam source to supply steam to the heat exchanger; a condensate line configured to receive condensate from the condensed steam from the heat exchanger and to convey the condensate away from the heat exchanger; a water supply line configured to supply water to the heat exchanger; a water outlet line configured to receive the heated water from the heat exchanger and to deliver the heated water away from the heat exchanger; a steam valve disposed on the steam supply line and configured to control steam flow through the steam supply line; a condensate valve disposed on the condensate line and configured to control a flow of condensate through the condensate line; a first sensor disposed downstream of the steam valve and upstream of the condensate valve and configured to output a pressure signal indicative of a pressure in the steam system between the steam valve and the condensate valve, and / or a second sensor at the condensate outlet, a condensate temperature sensor configured to output a condensate temperature signal indicative of a temperature of condensate in a condensate line between the heat exchanger and the condensate valve; a third sensor disposed on the water outlet line and configured to output a water temperature signal indicative of a temperature of the hot water passing through the water outlet line; and a controller configured to control opening and closing of the steam valve and the condensate valve based on at least one of the pressure signal and the condensate temperature signal and the water temperature signal.

Description

TECHNICAL FIELD

[0001] The present invention relates to a steam system configured to heat water, a method of controlling a steam system, and a method of designing such a steam system. BACKGROUND

[0002] Steam systems are commonly used to heat water for use, for example in domestic hot water systems. Such steam systems can be controlled in various ways to control the water temperature. SUMMARY

[0003] According to a first aspect, a steam system configured to heat water is disclosed, the steam system comprising:

[0004] a heat exchanger configured to receive steam and water, wherein the heat exchanger is configured to heat the water with the steam;

[0005] a steam supply line configured to be connected to a steam source to supply steam to the heat exchanger;

[0006] a condensate line configured to receive condensate from condensed steam from the heat exchanger and to transport the condensate away from the heat exchanger;

[0007] a water supply line configured to supply water to the heat exchanger;

[0008] a water outlet line configured to receive heated water from the heat exchanger and to transport the heated water away from the heat exchanger;

[0009] a steam valve arranged on the steam supply line and configured to control a steam flow through the steam supply line;

[0010] a condensate valve arranged on the condensate line and configured to control a condensate flow through the condensate line;

[0011] a first sensor arranged downstream of the steam valve and upstream of the condensate valve and configured to output a pressure signal indicative of a pressure in the steam system between the steam valve and the condensate valve, and / or a second sensor at the condensate outlet and configured to output a condensate temperature signal indicative of a temperature of the condensate in the condensate line between the heat exchanger and the condensate valve;

[0012] a third sensor arranged on the water outlet line and configured to output a water temperature signal indicative of a temperature of the heated water through the water outlet line;

[0013] a controller configured to control opening and closing of the steam valve and the condensate valve based on at least one of the pressure signal and the condensate temperature signal and the water temperature signal.

[0014] Controlling the flow with the steam valve and the condensate valve based on at least one of the pressure signal and the condensate temperature signal and the water temperature signal enables the system to simultaneously: (i) ensure overcooling of the condensate, which means that more heat from the steam has been transferred to the water, which results in a more efficient heating process, (ii) deliver a stable outlet water temperature even under fast or dynamic demand load changes, and (iii) achieve a high regulation ratio of the system. When controlling the steam valve and the condensate valve simultaneously based on the water temperature signal and the pressure signal, the system can further: (iv) ensure that the system never runs at a stall condition. The double control (i.e. with both the steam valve and the condensate valve) also means that, when there is a fast demand load change from a high demand load to a low demand load, the overcooling of the condensate can be achieved faster, resulting in a faster more efficient operation compared to other ways.

[0015] The first sensor can be a pressure sensor. The first sensor can be arranged in the steam supply line between the steam valve and the heat exchanger to output a pressure signal indicative of a pressure in the steam supply line downstream of the steam valve. The second sensor can be a temperature sensor. The third sensor can be a temperature sensor.

[0016] The controller can be configured to control the steam valve based on the water temperature signal and to control the condensate valve based on the pressure signal.

[0017] The controller can be configured to control the condensate valve based on a comparison of the pressure signal to a set pressure. The set pressure can be a set point pressure or a set pressure range, wherein the set pressure range is a range of acceptable pressures.

[0018] The controller can be configured to operate in a feedback loop to control the condensate valve to at least partially close when the pressure signal indicates that the pressure in the steam supply line is below the set pressure and does not increase, and / or to at least partially open when the pressure signal indicates that the pressure in the steam supply line is above the set pressure and does not decrease.

[0019] When the set pressure is a set pressure range, the pressure signal can indicate a pressure below the set pressure range when the pressure signal indicates a pressure below a lower end of the set pressure range. The pressure signal can indicate a pressure above the set pressure range when the pressure signal indicates a pressure above an upper end of the set pressure range.

[0020] In other words, the controller can be a PID controller, which can be configured to control the condensate valve based on a comparison of the pressure signal to a set point pressure or a set pressure range.

[0021] The set pressure can be higher than the pressure in the condensate line downstream of the condensate valve plus the condensate pressure drop of the condensate valve to prevent stagnation of the steam system.

[0022] When the set pressure is a set pressure range, the lower end of the set pressure range can be higher than the pressure in the condensate line downstream of the condensate valve plus the condensate pressure drop.

[0023] The set pressure can be lower than the steam supply pressure upstream of the steam valve minus the critical pressure drop of the steam valve.

[0024] When the set pressure is a set pressure range, the upper end of the set pressure range can be lower than the pressure in the condensate line downstream of the condensate valve plus the condensate pressure drop.

[0025] The heat exchanger can be sized to ensure that the condensate is subcooled when the steam pressure between the steam valve and the heat exchanger is at the set pressure and when the flow of water is at the maximum demand.

[0026] The maximum demand can be related to the mass flow rate of water through the heat exchanger and / or the inlet temperature of the water. In other words, the maximum demand can correspond to a maximum mass flow rate of water through the heat exchanger and / or a minimum inlet water temperature.

[0027] The controller can be configured to control the steam valve based on the water temperature signal and to control the condensate valve based on the condensate temperature signal.

[0028] The controller can be configured to control the condensate valve based on a comparison of the condensate temperature signal to a condensate set temperature.

[0029] The condensate set temperature can be a set point temperature or a set temperature range.

[0030] The controller can be configured to operate in a feedback loop to control the condensate valve to at least partially close when the condensate temperature signal is above the condensate set temperature and does not decrease, and / or to at least partially open when the condensate temperature signal is below the condensate set temperature and does not increase.

[0031] When the set temperature is a set temperature range, the condensate temperature signal can indicate a temperature below the set temperature range when the condensate temperature signal indicates a temperature below the lower end of the set temperature range. The condensate temperature signal can indicate a temperature above the set temperature range when the condensate temperature signal indicates a temperature above the upper end of the set temperature range.

[0032] In other words, the controller can be a PID controller that can be configured to control the condensate valve based on a comparison of the temperature signal to a set point temperature or a set temperature range.

[0033] The controller can control the condensate valve to have a minimum opening degree which is not fully closed.

[0034] If the condensate valve is fully closed, the true condensate temperature cannot be measured, as the measurement is downstream of the heat exchanger.

[0035] The controller can be configured to control the steam valve based on a comparison of the water temperature signal to a set water temperature.

[0036] The set water temperature can be a water setpoint temperature or a set water temperature range.

[0037] The controller can be configured to operate in a feedback loop to control the steam valve to be at least partially open when the water temperature signal is below the water setpoint temperature and does not increase, and / or to be at least partially closed when the water temperature signal is above the water set temperature and does not decrease.

[0038] When the water set temperature is a set water temperature range, the water temperature signal can indicate a temperature below the set water temperature range when the water temperature signal indicates a temperature below the lower end of the set water temperature range. The water temperature signal can indicate a temperature above the set water temperature range when the water temperature signal indicates a temperature above the upper end of the set water temperature range.

[0039] In other words, the controller can be a PID controller which can be configured to control the steam valve based on a comparison of the water temperature signal to a water setpoint temperature or a set water temperature range.

[0040] According to a second aspect, there is disclosed a method of controlling a steam system according to any preceding claim, the method comprising:

[0041] receiving a pressure signal or a condensate temperature signal;

[0042] receiving a water temperature signal; and

[0043] controlling opening and closing of the steam valve and the condensate valve based on at least one of the pressure signal and the condensate temperature signal and the water temperature signal.

[0044] The method can comprise controlling the steam valve based on the water temperature signal, and controlling the condensate valve based on the pressure signal.

[0045] The method can comprise controlling the condensate valve based on a comparison of the pressure signal to a set pressure.

[0046] The method can comprise operating the control of the steam valve and the condensate valve in a feedback loop by controlling the condensate valve to be at least partially closed when the pressure signal indicates a pressure in the steam supply line below a setpoint pressure and does not increase, and / or to be at least partially open when the pressure signal indicates a pressure in the steam supply line above a setpoint pressure and does not decrease.

[0047] The set pressure can be higher than the pressure in the condensate line downstream of the condensate valve plus the condensate pressure drop of the condensate valve to prevent stagnation of the steam system. The set pressure can be lower than the steam supply pressure upstream of the steam valve minus the critical pressure drop of the steam valve.

[0048] The method can comprise controlling the steam valve based on the water temperature signal and controlling the condensate valve based on the condensate temperature signal.

[0049] The method can comprise controlling the condensate valve based on a comparison of the condensate temperature signal to a set condensate temperature.

[0050] The method can comprise operating in a feedback loop to control the condensate valve at least partially closed when the condensate temperature signal is higher than the set condensate temperature and does not decrease and / or at least partially open when the condensate temperature signal is lower than the set condensate temperature and does not increase.

[0051] The method can comprise controlling the condensate valve to have a minimum opening that is not fully closed.

[0052] The method can comprise controlling the steam valve based on a comparison of the water temperature signal to a water set temperature.

[0053] The method can comprise operating in a feedback loop to control the steam valve at least partially open when the water temperature signal is lower than the water set point temperature and does not increase and / or at least partially closed when the water temperature signal is higher than the water set point temperature and does not decrease.

[0054] According to a third aspect, a method of designing a steam system according to the first aspect is disclosed, the method comprising:

[0055] receiving a steam supply pressure in an environment in which the steam system is to be installed;

[0056] determining a steam critical pressure drop across the steam valve;

[0057] determining a maximum demand load of the heat exchanger; and

[0058] selecting a heat exchanger size based on the steam supply pressure, the steam critical pressure, and the maximum demand load.

[0059] The method can further comprise receiving a condensate return pressure in an environment in which the steam system is to be installed, determining a condensate pressure drop across the condensate valve, and selecting the heat exchanger size further based on the condensate return pressure and the condensate critical pressure.

[0060] The method may include: selecting a set pressure at the inlet of the heat exchanger based on the steam supply pressure and the steam critical pressure; wherein selecting the heat exchanger size includes determining the heat exchanger size for which the condensate is subcooled when the inlet pressure of the heat exchanger is the set pressure and when there is a maximum demand load.

[0061] Those skilled in the art will recognize that, in addition to mutual exclusion, any feature or parameter described with respect to any of the foregoing aspects can be applied to any other aspect. Furthermore, in addition to mutual exclusion, any feature or parameter described herein can be applied to any aspect and / or combined with any other feature or parameter described herein. Attached Figure Description

[0062] Various embodiments will now be described by way of example only with reference to the accompanying drawings, wherein:

[0063] Figure 1 A first exemplary steam system for heating water is schematically shown;

[0064] Figure 2 A second exemplary steam system for heating water is schematically shown;

[0065] Figure 3 This is a flowchart illustrating the steps of a basic method for heating water using an exemplary steam system;

[0066] Figure 4a and Figure 4b This is a flowchart illustrating the steps of a more detailed method for heating water using an exemplary steam system; and

[0067] Figure 5 It shows the design for, such as Figure 1 and Figure 2 A flowchart of the steps of an exemplary method for an exemplary steam system. Detailed Implementation

[0068] Figure 1 A first exemplary steam system 100 configured to heat water, for example, in a domestic hot water system, is shown. The first exemplary steam system 100 includes a heat exchanger 12 configured to receive steam on a supply side 14 and water on a demand side 16, and to heat the water with the steam. In this example, the steam and water remain separate.

[0069] In this example, the steam system 100 includes a steam supply line 18 configured to connect to a steam source 20. In this example, the steam supply line 18 connects to a supply side inlet 22 (also referred to as a steam inlet 22) of the heat exchanger 12 to supply steam to the heat exchanger 12 on the supply side 14. In this example, the steam source 20 can supply steam at a constant pressure (e.g., 400 kPa).

[0070] Steam supplied via the steam supply line 18 to the supply side 14 condenses as it passes through the supply side 14 and transfers heat to the demand side 16 of the heat exchanger 12.

[0071] In this example, the steam system 100 includes a condensate line 24 configured to connect to a condensate drain 26. The condensate line 24 connects to a supply side outlet 28 (also referred to as a condensate outlet 28) such that the condensate line 24 is configured to receive condensate (from the condensed steam) from the supply side 14 of the heat exchanger 12 and transport the condensate away from the heat exchanger 12 to the condensate drain 26.

[0072] In some examples, the condensate received in the condensate drain 26 can be heated in another system and can be connected to the steam source 20 to provide a closed loop system that provides steam for the steam source 20.

[0073] In this example, the steam system 100 includes a water supply line 30 configured to connect to a demand side inlet 34 (also referred to as a water inlet 34) of the heat exchanger 12 on the demand side 16. The water supply line 30 is configured to supply water to the demand side 16 of the heat exchanger 12. The water supplied to the water inlet 34 can be relatively cold water. In this example, the water supply line 30 is configured to connect to a water source 32, such as a domestic water system.

[0074] In the heat exchanger 12, the water received on the demand side 16 is heated with the steam received on the supply side 14 such that the steam condenses and exits the heat exchanger 12 as condensate, and the water is heated to exit the heat exchanger 12 as heated water.

[0075] In this example, the steam system 100 includes a water outlet line 36 connected to a demand side outlet 38 (also referred to as a water outlet 38) on the demand side 16 of the heat exchanger 12 to receive heated water from the demand side 16 of the heat exchanger 12 and transport the heated water away from the heat exchanger 12 toward a drain 37. When the heat exchanger is operating to receive steam at the steam inlet 22, the water at the water inlet 34 is relatively cold compared to the heated water at the water outlet 38.

[0076] In some examples, the drain 37 can be connected to the water source 32, e.g. by a closed loop of the domestic water system. Heated water from the drain 37 can lose heat through the domestic water system and reach the relatively cold water source 32.

[0077] In this example, a steam valve 40 is provided on the steam supply line 18 and is configured to control the flow of steam through the steam supply line 18. The steam valve 40 can be, for example, a ball valve. In other examples, the steam valve can be any suitable valve, for example a slide valve, piston valve or ball valve. In this example, the steam valve 40 is connected to the controller 50, which is configured to control the opening and closing of the steam valve 40. In other words, the steam valve 40 can be actively controlled by the controller 50 to control the flow of steam through the steam supply line 18. In this example, the steam valve 40 is a variable control valve, and by gradually opening the steam valve 40, the mass flow rate of steam through the steam valve 40 is increased to supply more steam to the supply side 14 of the heat exchanger 12, and by gradually closing the steam valve 40, the mass flow rate of steam through the steam valve 40 is decreased to supply less steam to the supply side 14 of the heat exchanger 12. In this example, the steam valve 40 can be sized based on the pressure of the steam supplied by the steam source 20, such that when it is fully opened, it will have at least a critical pressure drop across the steam valve 40 (i.e. any further pressure drop will not result in an increase in steam velocity). This will ensure that gradually closing the steam valve 40 from its maximum opening will decrease the mass flow rate through the steam valve 40, enabling the steam valve 40 to be used over its entire opening characteristic.

[0078] In this example, a condensate valve 42 is provided on the condensate line 24 and is configured to control the flow of condensate through the condensate line 24. In this example, the condensate valve 42 is connected to the controller 50, which is configured to control the opening and closing of the condensate valve 42 in a similar manner to the steam valve 40. In other examples, the condensate valve 42 and the steam valve 40 can be different types of valve, which are controlled differently.

[0079] In this example, a pressure sensor 44 is provided in the steam supply line 18 between the steam valve 40 and the steam inlet 22 of the heat exchanger 12. The pressure sensor 44 is configured to output a pressure signal indicative of the pressure in the steam supply line 18 downstream of the steam valve 40 (i.e. between the steam valve 40 and the heat exchanger 12). In some examples, the pressure sensor can be provided anywhere downstream of the steam valve 40 and upstream of the condensate valve 42 to output a pressure signal indicative of the pressure in the steam system on the supply side 14 between the steam valve 40 and the condensate valve 42. In other examples, the pressure sensor can be any type of sensor or combination of sensors that can be used to indicate the pressure in the steam system between the steam valve 40 and the condensate valve 42.

[0080] In this example, the water temperature sensor 46 is disposed on the outlet water line 36 and is configured to output a water temperature signal indicative of the temperature of the heated water in the outlet water line 36. In other examples, the temperature sensor can be any type of sensor or combination of sensors that can be used to indicate the temperature of the water in the outlet water line 36.

[0081] In this example, the controller 50 is configured to control the opening and closing of the steam valve 40 and the condensate valve 42 based on the water temperature signal and the pressure signal. Controlling the steam valve 40 and the condensate valve 42 simultaneously can control the level (or height) of the condensate in the heat exchanger 12. For example, if the steam valve 40 is open while the condensate valve 42 is closed, or the steam valve 40 is open more than the condensate valve 42, such that the mass flow rate of steam through the steam valve 40 (and thus into the steam inlet 22) is greater than the mass flow rate of condensate through the condensate valve 42 (and thus out of the condensate outlet 28), the level of condensate in the heat exchanger will rise. Conversely, if the steam valve 40 is closed while the condensate valve 42 is open, or the steam valve 40 is open less than the condensate valve 42, such that the mass flow rate of steam through the steam valve 40 (and thus into the steam inlet 22) is less than the mass flow rate of condensate through the condensate valve 42 (and thus out of the condensate outlet 28), the level of condensate in the heat exchanger will fall.

[0082] Controlling the level of condensate in the heat exchanger 12 helps control the amount of heat conducted through the heat exchanger 12 by changing the area of the heated surface that is exposed to the steam. By controlling the level of condensate, the steam system 100 can ensure that the condensate is subcooled in the heat exchanger before being discharged. This can significantly reduce the amount of flash steam downstream, which can improve the performance of the system and also reduce heat loss. It also helps prevent stalling of the steam system 100 (as increasing the condensate level decreases heat transfer, which increases the pressure of the steam in the heat exchanger), providing enough pressure to discharge the condensate through the condensate valve 42.

[0083] The size of the heat exchanger can typically be designed to operate at a predetermined steam inlet pressure at which the heat exchanger is configured to subcool the condensate when the water is at maximum demand. For some applications, maximum demand corresponds to maximum water flow rate through the heat exchanger 12. In other applications, maximum demand can correspond to minimum inlet water temperature. In further applications, maximum demand can be related to both the mass flow rate of water through the heat exchanger 12 and the minimum inlet temperature of the water. In this example, the size of the heat exchanger 12 can be designed to operate at a predetermined steam inlet 22 pressure, where the predetermined steam inlet 22 pressure is equal to or lower than the supply pressure of steam upstream of the steam valve 40 minus the critical pressure drop of the steam valve 40, where the heat exchanger 12 is configured to subcool the condensate when receiving steam at or below the predetermined steam inlet 22 pressure. This maximizes the efficiency of the steam system 100 as it ensures that the condensate will always be subcooled if the inlet pressure is maintained at or below the predetermined steam inlet pressure. As a result, this will enable the steam system 100 to subcool the condensate at all load conditions.

[0084] In this example, there is a set pressure for steam between the steam valve 40 and the condensate valve 42. In this example, the set pressure is a setpoint pressure, for example X kPa. The setpoint pressure can be set to the predetermined steam inlet 22 pressure at which the heat exchanger 12 is sized for.

[0085] To ensure that the steam system 100 does not stall at any point (i.e. to ensure that the pressure in the condensate line upstream of the condensate valve is always high enough to drive steam through the condensate valve to the condensate drain), in this example, the set pressure is set to be higher than the pressure in the condensate line downstream of the condensate valve plus the condensate pressure drop of the condensate valve.

[0086] Setting the set pressure to be higher than the pressure in the condensate line downstream of the condensate valve plus the condensate pressure drop of the condensate valve, and lower than or equal to the steam supply pressure upstream of the steam valve minus the critical pressure drop of the steam valve, ensures that the steam system 100 does not stall at any point and that the condensate will always be subcooled, thereby improving the reliability and efficiency of the system.

[0087] Thus, as will be referred to with reference to the following figures, Figure 3As explained in more detail by the flowchart in Figure 4, based on the water temperature signal and the pressure signal, simultaneous control of the inflow and outflow of the heat exchanger 12 at the supply side 14 with the steam valve 40 and the condensate valve 42 enables the system to simultaneously: (i) ensure cooling of the condensate, which means that more heat from the steam has been transferred to the water, which leads to a more efficient heating process, (ii) provide a stable outlet temperature even under fast or dynamic demand load changes, (iii) achieve a high regulation ratio of the system, and (iv) ensure that the system does not stagnate under any conditions. The dual control (i.e. control with both the steam valve 40 and the condensate valve 42) also means that, when there is a fast demand load change from a high demand load to a low demand load, subcooling of the condensate can be achieved faster, thus enabling a more efficient operation faster than other ways.

[0088] In this example, the controller 50 is configured to control the condensate valve 42 based on a comparison of the pressure signal with a setpoint pressure. In this example, the controller 50 operates in a feedback loop to control the condensate valve 42 to control the pressure at the pressure sensor to be at the setpoint pressure. In other words, when the pressure signal indicates that the pressure should be increased, the controller 50 can control the condensate valve 42 to be at least partially closed, and when the pressure signal indicates that the pressure should be decreased, the controller 50 can control the condensate valve 42 to be at least partially open.

[0089] In some examples, the controller 50 can be a PID (proportional-integral-derivative) controller configured to operate in a feedback loop to control the condensate valve to be at least partially closed when the pressure signal indicates that the pressure in the steam supply line 18 is below the set pressure and not rising, and to control the condensate valve to be at least partially open when the pressure signal indicates that the pressure in the steam supply line is above the set pressure and not falling. This takes into account the lag time in changing the condensate valve 42 and observing the change. The PID controller can control the amount of partial opening or closing of the condensate valve 42 based on the distance of the steam pressure from the set pressure and the rate of change of the steam pressure.

[0090] In other examples, the set pressure can be a set pressure range, which can include an acceptable pressure range, e.g. Y-Z kPa, and the condensate valve 42 can be controlled to ensure that the pressure between the steam valve 40 and the condensate valve 42 is within the set pressure range. When the set pressure is a set pressure range, the pressure signal can indicate a pressure below the set pressure range when the pressure signal indicates a pressure below the lower end of the set pressure range. The pressure signal can indicate a pressure above the set pressure range when the pressure signal indicates a pressure above the upper end of the set pressure range.

[0091] When the set pressure is a set pressure range, the lower end of the set pressure range can be set to be higher than the pressure of the condensate line 24 downstream of the condensate valve 42 plus the condensate pressure drop. In these examples, the upper end of the set pressure range can be lower than or equal to the steam supply pressure upstream of the steam valve 40 minus the critical pressure drop of the steam valve 40.

[0092] In this example, the controller 50 is also configured to control the steam valve 40 based on a comparison of the water temperature signal to a water set temperature. In this example, the water set temperature is a water setpoint temperature, for example 60 degrees Celsius.

[0093] In this example, the controller 50 operates in a feedback loop to control the steam valve 40 so as to control the temperature at the water temperature sensor 46 (in the hot water line 36) to be at the water setpoint temperature. In other words, when the water temperature signal indicates that the water temperature should be increased (i.e. the water temperature is lower than the water setpoint temperature), the controller 50 can control the steam valve 40 to be at least partially open, and when the water temperature signal indicates that the water temperature should be decreased (i.e. the water temperature is higher than the water setpoint temperature), the controller 50 can control the steam valve 40 to be at least partially closed.

[0094] In this example, the controller 50 is a PID (proportional-integral-derivative) controller configured to operate in a feedback loop to control the steam valve 40 to be at least partially closed when the water temperature signal indicates that the water temperature in the water line 36 is higher than the water setpoint temperature and not decreasing, and to be at least partially open when the water temperature signal indicates that the water temperature in the water line 36 is lower than the water setpoint temperature and not increasing. This takes into account the lag time to make a change to the steam valve 40 and observe the change. The PID controller can control the amount of opening and closing of the steam valve 40 based on how far the water temperature is from the water setpoint temperature and the rate of change of the water temperature.

[0095] In some examples, the water set temperature can be a set water temperature range, which can include an acceptable temperature range, for example 55-65 degrees Celsius. In such examples, when the water temperature signal indicates a temperature lower than the lower end of the set water temperature range, the water temperature signal can indicate a temperature lower than the set water temperature range. When the water temperature signal indicates a temperature higher than the upper end of the set water temperature range, the water temperature signal can indicate a temperature higher than the set water temperature range.

[0096] Figure 2A second example steam system 200 is shown. The second example steam system 200 is similar to the first example steam system 100, with like reference numerals indicating like features. The second example steam system 200 differs from the first example steam system 100 in that it does not include a pressure sensor, but instead includes a condensate temperature sensor 48 disposed at the condensate outlet 28 on the condensate line 24 (i.e., between the condensate outlet 28 and the condensate valve 42), and configured to output a condensate temperature signal indicative of the temperature of the condensate in the condensate line between the heat exchanger 12 and the condensate valve 42. In other examples, the condensate temperature sensor can be any type of sensor or combination of sensors that can be used to indicate the temperature in the condensate line 24.

[0097] In yet other examples, a steam system can include a pressure sensor as in the first example steam system 100 and a condensate temperature sensor as in the second example steam system 200.

[0098] In this example, the controller 50 is configured to control the opening and closing of the steam valve 40 and the condensate valve 42 based on the water temperature signal and the condensate temperature signal. Controlling the steam valve 40 and the condensate valve 42 based on the condensate temperature signal enables the steam system 200 to ensure that the condensate is subcooled by directly controlling the temperature of the condensate. Controlling the steam valve 40 and the condensate valve 42 based on the water temperature signal also enables a stable outlet water temperature to be delivered even under rapid or dynamic demand load changes, and achieves a high turndown ratio for the system 200 in a similar manner to the first example steam system 100. The second example steam system 200 is more prone to flow starvation than the first example steam system 100, as it does not directly control the pressure in the supply side 14.

[0099] In this example, the controller 50 can be configured to operate in a feedback loop in the same manner as in the first example steam system 100 to control the steam valve 40 to control the temperature at the temperature sensor (in the outlet water line 36) to be at the water setpoint temperature.

[0100] The controller 50 in the second example steam system 200 differs from the controller in the first example steam system 100 in that it is configured to control the condensate valve 42 based on a comparison of the condensate temperature signal to a condensate set temperature.

[0101] In this example, the condensate set temperature is a condensate setpoint temperature, for example 90 degrees Celsius. Ideally, the condensate set value temperature is below 100 degrees Celsius to ensure sub-cooling of the condensate. In this example, the controller 50 operates in a feedback loop to control the condensate valve 42 so as to control the condensate temperature at the condensate temperature sensor 48 to be at the condensate setpoint temperature. In other words, when the condensate temperature signal indicates that the condensate temperature should be reduced (i.e. the condensate temperature is determined to be above the condensate setpoint temperature based on the condensate temperature signal), the controller 50 can control the condensate valve 42 to be at least partially closed, and when the condensate temperature signal indicates that the condensate temperature should be increased (i.e. the condensate temperature is determined to be below the condensate setpoint temperature based on the condensate temperature signal), the controller 50 can control the condensate valve 42 to be at least partially open.

[0102] In some examples, the controller 50 can be a PID controller configured to operate in a feedback loop to control the condensate valve 42 to be at least partially open when the condensate temperature signal indicates that the condensate temperature is below the set condensate temperature and not to increase, and to control the condensate valve 42 to be at least partially closed when the condensate temperature signal indicates that the condensate temperature is above the condensate setpoint temperature and not to decrease. This takes into account the lag time in changing the condensate valve 42 and observing the change. The PID controller can control the amount of partial opening or closing of the condensate valve 42 based on how far the condensate temperature is from the set condensate temperature and the rate of change of the condensate temperature.

[0103] In other examples, the set condensate temperature can be a set condensate temperature range, which can comprise an acceptable temperature range, for example 85-90 degrees Celsius, and the condensate valve 42 can be controlled to ensure that the condensate temperature between the heat exchanger 12 and the condensate valve 42 is within the set condensate temperature range. When the set condensate temperature is a set condensate temperature range, the condensate temperature signal can indicate that the condensate temperature is below the set condensate temperature range when the condensate temperature signal indicates that the condensate temperature is below the lower end of the set condensate temperature range. The condensate temperature signal can indicate that the condensate temperature is above the set condensate temperature range when the condensate temperature signal indicates that the condensate temperature is above the upper end of the set condensate temperature range.

[0104] In this example, with the condensate temperature being monitored with the condensate temperature sensor 48, the controller 50 can be configured to control the condensate valve 42 so that it has a minimum opening that is not fully closed. If the condensate valve 42 is fully closed, then the true condensate temperature cannot be measured as the measurement is downstream of the heat exchanger 12 and closing the condensate valve 42 would prevent the condensate from flowing out of the heat exchanger 12.

[0105] Figure 3is a flowchart showing basic steps of a method 300 of controlling a steam system such as the first example steam system 100 or the second example steam system 200.

[0106] In block 302, the method 300 includes the controller 50 receiving a pressure signal in the first example steam system 100 or a condensate temperature signal in the second example steam system 200. In some examples combining the first example steam system 100 and the second example steam system 200, the controller 50 can receive both a pressure signal and a condensate temperature signal.

[0107] In block 304, the method 300 includes the controller 50 receiving a water temperature signal. Block 302 and block 304 can occur simultaneously or one after the other in any order.

[0108] In block 306, the method 300 includes the controller 50 controlling opening and closing of the steam valve 40 and the condensate valve 42 based on the received water temperature signal and at least one of the received pressure signal and the condensate temperature signal.

[0109] Figure 4a and Figure 4b is a flowchart showing a more detailed example method 400 of controlling a steam system 100, 200. Figure 4a and Figure 4b are configured to run simultaneously and concurrently, although they can also run sequentially. Figure 4a From block 302 of Figure 3 From block 304 of Figure 4b From block 304 of Figure 3 From block 304 of

[0110] From block 302, the method 400 in this example is configured to control the condensate valve 42 based on the pressure signal and / or the condensate temperature signal. From block 304, the method 400 in this example is configured to control the steam valve 40 based on the water temperature signal.

[0111] From block 302, the method 400 controls the condensate valve 42 based on a comparison of the pressure signal to a set pressure or a comparison of the condensate temperature signal to a set condensate temperature. In this example, from block 302, the method 400 proceeds to block 402 in which it is determined whether the pressure needs to be raised or the condensate temperature needs to be lowered. In other words, in the presence of a set pressure, block 402 determines whether the pressure signal indicates that the pressure is below the set pressure, and in the presence of a set condensate temperature, block 402 determines whether the condensate temperature signal indicates that the condensate temperature is above the set condensate temperature.

[0112] If it is determined that the pressure is below the set pressure or that the condensate temperature is above the set condensate temperature, the method proceeds to block 404, in which the condensate valve 42 is controlled to close (e.g., gradually close), and then returns to block 302 in the feedback loop. If the controller 50 is a PID controller, determining whether the pressure needs to be increased can involve determining whether the pressure signal indicates that the pressure in the steam supply line is below the set point pressure and is not increasing (i.e., the derivative of the pressure signal with respect to time indicates a negative trend), and determining whether the condensate temperature needs to be decreased can involve determining whether the condensate temperature signal indicates that the condensate temperature is above the set condensate temperature and is not decreasing (i.e., the derivative of the pressure signal with respect to time indicates a positive trend).

[0113] If it is determined that the pressure does not need to be increased or that the condensate temperature does not need to be decreased, the method 400 proceeds to block 406. In block 406, the method includes determining whether the pressure needs to be decreased or the condensate temperature needs to be increased. If it is determined that the pressure needs to be decreased or that the condensate temperature needs to be increased, the method proceeds to block 408, in which the condensate valve 42 is controlled to open (e.g., gradually open), and then returns to block 302 in the feedback loop. If the controller 50 is a PID controller, determining whether the pressure needs to be decreased can involve determining whether the pressure signal indicates that the pressure in the steam supply line is above the set point pressure and is not decreasing (i.e., the derivative of the pressure signal with respect to time indicates a positive trend), and determining whether the condensate temperature needs to be increased can involve determining whether the condensate temperature signal indicates that the condensate temperature is below the set condensate temperature and is not increasing (i.e., the derivative of the pressure signal with respect to time indicates a negative trend).

[0114] If it is determined in block 406 that the pressure does not need to be decreased or that the condensate temperature does not need to be increased, the method 400 proceeds to block 410, in which the condensate valve 42 is not controlled to change its opening, and then returns to block 302 in the feedback loop. If the controller is a PID controller, the condensate valve 42 cannot be controlled to open or close even if the pressure is below or above the set pressure or the condensate temperature is below or above the set condensate temperature, because previous control can have already increased or decreased the pressure or the condensate temperature. Thus, a PID controller that monitors the derivative of the pressure signal and / or the condensate signal can be used to account for a lag time between implementing control of the condensate valve 42 and observing changes in conditions in the steam system. The PID controller can control the amount of opening and closing of the condensate valve 42 based on how far the condensate temperature is from the set condensate temperature and the rate of change of the condensate temperature.

[0115] In the case where the controller 50 receives a condensate temperature signal (e.g. in the second exemplary steam system 200), there can be an additional block between block 402 and block 404 that determines whether the gradual closing of the condensate valve 42 is to further close the condensate valve 42 completely, or determines whether the condensate valve is at a minimum opening. If it is determined that the condensate valve 42 is to be closed completely or is already at a minimum opening, the method can proceed directly to block 410 to avoid controlling the condensate valve to close completely or beyond the minimum opening. This ensures that the condensate temperature can continue to be accurately measured as it is not blocked from flowing out of the heat exchanger 12.

[0116] From block 304, the method 400 proceeds to control the steam valve 40 based on a comparison of the water temperature signal to the set water temperature. In this example, from block 304, the method 400 proceeds to block 412 in which it is determined whether the water temperature needs to be raised. In other words, block 412 determines whether the water temperature signal indicates that the water temperature is below the set water temperature.

[0117] If it is determined that the water temperature is below the set water temperature, the method proceeds to block 414 in which the steam valve 40 is controlled to open (e.g. gradually open) and then returns to block 304 in the feedback loop. If the controller 50 is a PID controller, determining whether the water temperature needs to be raised can involve determining whether the water temperature signal indicates that the water temperature is below the setpoint water temperature and is not rising (i.e. the derivative of the water temperature signal with respect to time indicates a negative trend).

[0118] If it is determined that the water temperature does not need to be raised, the method 400 proceeds to block 416. In block 416, the method includes determining whether the water temperature needs to be lowered. If it is determined that the water temperature needs to be lowered, the method proceeds to block 418 in which the steam valve 40 is controlled to close (e.g. gradually close) and then returns to block 304 in the feedback loop. If the controller 50 is a PID controller, determining whether the water temperature needs to be lowered can involve determining whether the water temperature signal indicates that the water temperature in the water line 36 is above the setpoint water temperature and is not falling (i.e. the derivative of the water temperature signal with respect to time indicates a positive trend).

[0119] If it is determined in block 416 that the water temperature does not need to be lowered, the method 400 proceeds to block 420 in which the steam valve 40 is not controlled to change its opening size and then returns to block 304 in the feedback loop. If the controller is a PID controller, the steam valve 40 can not be controlled to open or close even if the water temperature is below or above the set water temperature as previous controls can have already been raising or lowering the water temperature. Thus, a PID controller that monitors the derivative of the water temperature signal can be used to account for a lag time between implementing control of the steam valve 40 and observing changes in conditions in the steam system. The PID controller can control the amount of opening and closing of the steam valve 40 based on how far the water temperature is from the setpoint water temperature and the rate of change of the water temperature.

[0120] Figure 5 FIG. 5 is a flowchart illustrating steps of a method 500 of designing a vapor system, such as the first example vapor system 100 or the second example vapor system 200.

[0121] In block 502, the method includes receiving a vapor supply pressure of an environment in which the vapor system is to be installed. In block 504, the method includes determining a critical pressure drop across the vapor valve 40.

[0122] In block 506, the method can include receiving a condensate return pressure of the environment in which the vapor system is to be installed. In block 508, the method can include determining a condensate pressure drop across the condensate valve 42. In some examples, blocks 506-508 can be omitted.

[0123] In block 510, the method includes determining a maximum demand load of the heat exchanger. This can be based on a maximum mass flow rate of water through the system and / or a maximum temperature difference between the inlet water 34 and a set water temperature at the heat exchanger 12.

[0124] In block 512, the method includes selecting a heat exchanger size based at least on the vapor supply pressure, the vapor critical pressure drop, and the maximum demand load, and optionally also based on the condensate return pressure and the condensate pressure drop. For example, the size of the heat exchanger can be set to ensure subcooling of the condensate at the maximum demand load, and with an inlet vapor pressure equal to or less than a set pressure that is equal to the vapor supply pressure minus the critical pressure drop. The set pressure can also be based on the condensate return pressure and the condensate pressure drop. For example, the set pressure can be greater than the condensate return pressure plus the condensate pressure drop.

[0125] It will be appreciated that the application is not limited to the above-described embodiments, and that various modifications and improvements can be made without departing from the concepts described herein. Any feature can be used alone, or in combination with any other feature or combination of other features, except where such combination is mutually exclusive. This disclosure is also directed to any of the individual features described herein.

Claims

1. A steam system configured to heat water, the steam system comprising: a heat exchanger configured to receive steam and water, wherein the heat exchanger is configured to heat water with the steam; a steam supply line configured to be connected to a steam source to supply steam to the heat exchanger; a condensate line configured to receive condensate from condensed steam from the heat exchanger and to transport the condensate away from the heat exchanger; a water supply line configured to supply water to the heat exchanger; a heated water line configured to receive heated water from the heat exchanger and to transport the heated water away from the heat exchanger; a steam valve disposed on the steam supply line and configured to control steam flow through the steam supply line; a condensate valve disposed on the condensate line and configured to control condensate flow through the condensate line; a first sensor disposed downstream of the steam valve and upstream of the condensate valve and configured to output a pressure signal indicative of pressure in the steam system between the steam valve and the condensate valve, and / or a second sensor at a condensate outlet and configured to output a condensate temperature signal indicative of temperature of the condensate in the condensate line between the heat exchanger and the condensate valve; a third sensor disposed on the heated water line and configured to output a water temperature signal indicative of temperature of the heated water through the heated water line; a controller configured to control opening and closing of the steam valve and the condensate valve based on at least one of the pressure signal and the condensate temperature signal and the water temperature signal.

2. The steam system of claim 1, wherein, The controller is configured to control the steam valve based on the water temperature signal and to control the condensate valve based on the pressure signal.

3. The steam system of claim 2, wherein, The controller is configured to control the condensate valve based on a comparison of the pressure signal to a set pressure.

4. The steam system of claim 3, wherein, The controller is configured to operate in a feedback loop to control the condensate valve to at least partially close when the pressure signal indicates pressure in the steam supply line is below the set pressure and does not increase, and / or to control the condensate valve to at least partially open when the pressure signal indicates pressure in the steam supply line is above the set pressure and does not decrease.

5. The steam system of claim 3 or 4, wherein, The set pressure is higher than pressure in the condensate line downstream of the condensate valve plus a condensate pressure drop of the condensate valve to prevent stagnation of the steam system.

6. The steam system of any one of claims 3-5, wherein, The set pressure is lower than steam supply pressure upstream of the steam valve minus a critical pressure drop of the steam valve.

7. The steam system of any one of claims 3-6, wherein, The heat exchanger is sized to ensure that the condensate is subcooled when pressure of steam between the steam valve and the heat exchanger is at the set pressure and when flow of the water is at maximum demand.

8. The steam system of claim 1, wherein, The controller is configured to control the steam valve based on the water temperature signal and to control the condensate valve based on the condensate temperature signal.

9. The steam system of claim 8, wherein, The controller is configured to control the condensate valve based on a comparison of the condensate temperature signal to a condensate set temperature.

10. The steam system of claim 9, wherein, The controller is configured to operate in a feedback loop to control the condensate valve to at least partially close when the condensate temperature signal is above the condensate set temperature and not decreasing, and / or to at least partially open when the condensate temperature signal is below the condensate set temperature and not increasing.

11. The steam system of claim 10, wherein, The controller controls the condensate valve to have a minimum opening that is not fully closed.

12. The steam system of any one of claims 2-11, wherein, The controller is configured to control the steam valve based on a comparison of the water temperature signal to a set water temperature.

13. The steam system of claim 12, wherein, The controller is configured to operate in a feedback loop to control the steam valve to at least partially open when the water temperature signal is below a water set point temperature and not increasing, and / or to at least partially close when the water temperature signal is above the water set point temperature and not decreasing.

14. A method of controlling a steam system according to any preceding claim, the method comprising: receiving the pressure signal or the condensate temperature signal; receiving the water temperature signal; and controlling the steam valve and the condensate valve based on at least one of the pressure signal and the condensate temperature signal and the water temperature signal.

15. The method of claim 14, comprising: controlling the steam valve based on the water temperature signal, and controlling the condensate valve based on the pressure signal.

16. The method of claim 15, comprising: controlling the condensate valve based on a comparison of the pressure signal to a set pressure.

17. The method of claim 16, comprising: controlling the steam valve and the condensate valve in a feedback loop by controlling the condensate valve to at least partially close when the pressure signal indicates that the pressure in the steam supply line is below a set point pressure and not increasing, and / or to at least partially open when the pressure signal indicates that the pressure in the steam supply line is above a set point pressure and not decreasing.

18. The method of claim 16 or 17, wherein, the set pressure is above the pressure in the condensate line downstream of the condensate valve plus a condensate pressure drop across the condensate valve to prevent stalling of the steam system.

19. The method of any one of claims 16-18, wherein, the set pressure is below the steam supply pressure upstream of the steam valve minus a critical pressure drop across the steam valve.

20. The method of claim 14, comprising: controlling the steam valve based on the water temperature signal, and controlling the condensate valve based on the condensate temperature signal.

21. The method of claim 20, comprising: controlling the condensate valve based on a comparison of the condensate temperature signal to a set condensate temperature.

22. The method of claim 21, comprising: operating in a feedback loop to control the condensate valve to at least partially close when the condensate temperature signal is above the set condensate temperature and not decreasing, and / or to at least partially open when the condensate temperature signal is below the set condensate temperature and not increasing.

23. The method of claim 22, comprising: controlling the condensate valve to have a minimum opening that is not fully closed.

24. The method of any of claims 15 to 23, comprising: controlling the steam valve based on a comparison of the water temperature signal to a water set temperature.

25. The method of claim 24, comprising: operating in a feedback loop to control the steam valve to at least partially open when the water temperature signal is below the water set point temperature and not increasing, and / or to at least partially close when the water temperature signal is above the water set point temperature and not decreasing.

26. A method of designing a steam system according to claim 1, the method comprising: receiving a steam supply pressure in an environment in which the steam system is to be installed; determining a steam critical pressure drop across a steam valve; determining a maximum demand load of a heat exchanger; and selecting a heat exchanger size based on the steam supply pressure, the steam critical pressure, and the maximum demand load.

27. The method of claim 26, further comprising: receiving a condensate return pressure in an environment in which the steam system is to be installed; determining a condensate pressure drop across a condensate valve; and selecting the heat exchanger size further based on the condensate return pressure and the condensate critical pressure.

28. The method of claim 26 or 27, comprising: selecting a set pressure at an inlet of the heat exchanger based on the steam supply pressure and the steam critical pressure; wherein selecting the heat exchanger size comprises determining the heat exchanger size at which condensate is subcooled when the inlet pressure of the heat exchanger is the set pressure and when there is a maximum demand load.

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