US20250251144A1

US20250251144A1 - Combi heating system and control method

Info

Publication number: US20250251144A1
Application number: US19/016,537
Authority: US
Inventors: Michael A. Garrabrant; Matthew C. Blaylock
Original assignee: STONE MOUNTAIN Tech Inc
Current assignee: STONE MOUNTAIN Tech Inc
Priority date: 2024-02-05
Filing date: 2025-01-10
Publication date: 2025-08-07
Also published as: WO2025170710A1

Abstract

A system that includes a hydronic heat pump; an indirect storage tank (IST) configured to heat potable water stored therein; an air handler unit (AHU) configured to heat an enclosure; a hydronic loop configured to direct hydronic flow between the hydronic heat pump, the IST and the AHU; a temperature control system comprising a space heating thermostat configured to control an air temperature in the enclosure and one or more IST thermostats configured to control a temperature of the potable water in the IST; and a control system comprising control logic configured to control operation of components of the combi heating system among a plurality of predetermined operating modes, in response to an operating call from the temperature control system.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Patent Application No. 63/549,719, filed Feb. 5, 2024, which is incorporated herein by reference in its entirety.

BACKGROUND

Heat pumps are known to provide heating and cooling at high efficiencies, and can be used in various applications such as, without being limited to, space heating and/or cooling (e.g., residential homes, commercial buildings and the like), potable water heating, swimming pool heating, snow melting, and industrial processes heating and/or cooling.
Using an input of work or thermal energy, a heat pump moves energy from a low temperature source to a high temperature sink. For vapor compression cycle heat pumps, the work input may be provided by a compressor driven by an electric motor. For sorption or heat engine type heat pumps, the thermal energy input can be provided by combustion of fuel, solar energy or waste heat.
Heat pumps are often described by the low temperature energy source and high temperature sink. For a conventional electric vapor compression heat pump utilized for residential space heating, the low temperature source is often outside ambient air, and the high temperature sink is the indoor air. In this case, the heat pump can be described as air-to-air (A-A). If the low temperature source is a heat exchange loop in the ground, the heat pump is often described as geothermal.
Some heat pumps are air-to-water (A-W), meaning the low temperature energy source is outdoor air and the high temperature sink is water, or more specifically a hydronic loop that circulates into the building or a tank of potable water, where heat energy is removed from the hydronic loop before returning to the heat pump to be re-heated. The low temperature energy source for such “water delivery” heat pumps can also be geothermal, water (e.g., lake or pond), or a waste heat stream. Water delivery heat pumps can be of the vapor compression, sorption or heat engine types.
The heated hydronic loop can be used to heat many different loads, such as (without being limited to) space heating in a building, a tank of potable water, a swimming pool, or an industrial process. When used for space heating in a building, the hydronic loop can transfer its energy to the indoor air via a heat exchanger coupled to an air moving device in, for example, an “air-handler” or “fan coil”, a radiant heat exchanger, or an under-floor piping system. The flexibility of the hydronic loop delivery allows a single heat pump to provide heating to one or more of the loads described above.
When a water delivery heat pump is used to provide space heating to a residential home, it is often also used to heat potable water. Residential space heating systems are often “forced-air”, meaning an air-moving device (air-handler or fan coil) is used to move indoor air from the indoor space via ducts, through a heat exchanger where the air is heated, and back to the indoor space via ducts. The heat exchanger is normally heated by the combustion of fossil fuel (e.g., a furnace), a hydronic loop (e.g., a boiler or a heat pump), or a condenser coil (e.g., a heat pump). Potable water heating using a water delivery heat pump is normally provided using an indirect storage tank (IST), where the hydronic loop flows through a heat exchanger inside a storage tank containing potable water, thereby heating the potable water. In some examples, storage tanks configured with the heat exchanger being external to the storage tank may also be utilized.
Due to higher complexity and mass compared to conventional heating technologies such as furnaces and boilers, heat pumps may become less effective and efficient when cycled on and off on a frequent basis. It is desirable for both the heating system and controls to be designed to minimize the frequency of on-off cycles, and maximize the length of the on periods. This is especially important for thermally driven heat pumps such as sorption and heat engines.
For water delivery heat pumps that provide both space and potable water heating (often called “combi” heating systems), opportunities exist for a control method to minimize on-off cycles and maximize the length of heat pump on periods.

SUMMARY

Aspects of the present disclosure relate to combi heating systems and methods for controlling combi heating systems. A combi heating system includes a hydronic heat pump; an indirect storage tank (IST) configured to heat potable water stored therein; an air handler unit (AHU) configured to heat an enclosure; a hydronic loop configured to direct hydronic flow between the hydronic heat pump, the IST and the AHU; a temperature control system comprising a space heating thermostat configured to control an air temperature in the enclosure and one or more IST thermostats configured to control a temperature of the potable water in the IST; and a control system comprising control logic configured to control operation of components of the combi heating system among a plurality of predetermined operating modes, in response to an operating call from the temperature control system. The plurality of predetermined operating modes include a space heating (SH) mode, a water heating (WH) mode and a combination (combi) mode configured to provide a combination of space heating and water heating. In response to the operating call, the control system is configured to (i) select a mode among the plurality of predetermined operating modes, (ii) activate the hydronic heat pump, (iii) control operation of one or more of the AHU and IST and (iv) control operation of the hydronic loop in accordance with the selected mode. Responsive to receiving a termination of the operating call from the temperature control system, the control system is configured to at least one of, after the termination: a) continue operation of the hydronic heat pump after the termination until a predetermined condition is met, b) redirect any heat energy remaining in the hydronic loop after the termination to one of the AHU and the IST, and c) continue operating the AHU to output any heat energy remaining in the hydronic loop after the termination.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an example combi heating system according to an aspect of the present disclosure.

FIG. 2 is a functional block diagram of an example control system of a combi heating system according to an aspect of the present disclosure.

FIG. 3 is a flowchart diagram illustrating an example operation of a combi heating system in a space heating mode, according to an aspect of the present disclosure.

FIG. 4 is a flowchart diagram illustrating an example operation of a combi heating system in a water heating mode, according to an aspect of the present disclosure.

FIG. 5 is a flowchart diagram illustrating an example operation of a combi heating system in a combi mode, according to an aspect of the present disclosure.

FIG. 6 is a flowchart diagram illustrating an example operation of a combi heating system in an indirect storage tank top off mode, according to an aspect of the present disclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure relate to a combi heating system and a method of controlling a combi heating system for an enclosure (e.g., a building). In some examples, the combi heating system may include a water (hydronic) delivery heat pump, a hydronic loop, an air-handler or fan coil (collectively AHU), an indirect storage tank (IST), at least one thermostat measuring the indoor air temperature (indoor thermostat) of the building, and a control system. The combi heating system may also include at least one control valve to direct the hydronic loop flow to either the AHU or the IST. In some examples, the hydronic loop may include a circulating pump. In some examples, the AHU may include an air-to-water heat exchanger (heat exchanger).
In a non-limiting example, the water delivery heat pump may be configured to modulate its heating output, either in discrete steps or infinitely variable, and the hydronic output temperature from the heat pump may be configured to be controlled based on the outdoor air temperature (outdoor reset) or other input parameter. In a non-limiting example, the AHU may utilize a multi-speed (such as low-medium-high) or variable speed blower or fan (collectively, blower). The hydronic loop may include at least one temperature sensor measuring the hydronic temperature, which is preferably located in or near the AHU.
In a non-limiting example, the IST may include a primary thermostat or temperature sensor (aquastat) located at a first position on the tank (e.g., at the approximate mid-point of the tank), and a second thermostat or temperature sensor (LTT) located at a second position on the tank (e.g., near the bottom of the tank). The indoor thermostat may be configured to control the temperature of the indoor air of the building being heated. In a non-limiting example, the indoor thermostat may include a stage 1 call for heat, a stage 2 call for heat, and, optionally, an emergency call for heat. In some examples, the indoor thermostat may include a single stage call for heat (and an optional emergency call). In some examples, the indoor thermostat may include multiple stage calls for heat (e.g., two stages or greater) and an optional emergency call.
When a call for space heating is received from the indoor thermostat, the control system acts to turn on the water delivery heat pump in space heating mode and to turn on the hydronic pump (of the hydronic loop), which causes the hydronic loop temperature to rise. When the temperature of the hydronic loop reaches a pre-determined temperature (such as 90° F. for example, to prevent cool air from exiting the AHU), the AHU blower turns on, moving indoor air across the heat exchanger, thereby causing the indoor air to be heated. If the AHU blower is configured for multi—or variable—speed, the AHU blower may initially operate at low speed (unless the indoor thermostat is calling for stage 2 or emergency heating, where the AHU blower may initially operate at a higher speed). The heat pump may be configured to modulate its heating output to maintain a target hydronic output temperature, based on the outdoor ambient temperature (typically, the lower the outdoor temperature, the higher the target heat pump outlet temperature target), or other input. If the indoor thermostat has not removed the call for space heating within a pre-determined time, the control system acts to increase the AHU blower speed and/or instructs the heat pump to increase the target hydronic supply temperature.
After the indoor thermostat removes the call for space heating (space heating mode), the control system determines if the temperature sensor located near the bottom of the indirect storage tank is below a predetermined value (such as 90° F. for example, indicating the water in the bottom of the IST has cooled off). If the temperature is below the predetermined value, the control system acts to divert the hydronic flow from the AHU to the IST, instructs the heat pump to operate in water heating mode, and turns the AHU blower off. The control system then monitors the temperature sensor near the bottom of the IST until it increases to a predetermined level, at which point the control system acts to divert the hydronic flow from the IST to the AHU, turns the AHU blower on (in some examples at the lowest speed), and instructs the heat pump to shut off. The AHU blower may remain on until the hydronic supply temperature falls below a predetermined value. This “hot water top off” control method permits the heat pump to continue to operate for a longer period of time after the call for space heating is removed, and reduces the chances that the heat pump may need to turn back on later for a water heating only call, both of which increase the overall heating system efficiency. The control method also dumps the heat energy out of the hot hydronic loop after the IST top off cycle is completed, causing the heat energy available in the hot hydronic loop to not be wasted.
If, after the indoor thermostat removes the call for space heating, the control system determines that the temperature sensor located near the bottom of the IST is above the predetermined value (e.g., water in the bottom of the IST is still hot, so no water heating required), the control system acts to reduce the AHU blower speed to its lowest setting (if multi or variable speed) and tells the heat pump to reduce the target hydronic supply temperature to a low temperature that is hot enough to provide space heating (100° F. for example), for a predetermined period of time (10 minutes for example). This “over-shoot” control method permits the heat pump to continue to operate for a longer period of time after the call for space heating is removed, at a low hydronic output temperature that allows the heat pump to operate at a high efficiency, without overshooting the indoor air temperature inside the building.
If the primary thermostat (or temperature sensor) on the IST calls for a water heating cycle at the same time the indoor air thermostat is calling for space heating (combi mode), the control system may direct the heat pump to operate in combi mode, direct the hydronic loop to the IST, and turn off the AHU blower (unless the space heating call is Stage 2, in which the control system may keep the system in space heating mode for a pre-determined time). Ideally, the heat pump may target a high hydronic output temperature when in combi mode so that the water in the IST is heated quickly (since there is a dual call for space heating). The control system then monitors the temperature near the bottom of the IST. After the temperature rises to a predetermined value (110° F. for example), the control system directs the hydronic loop to the AHU, turns the AHU blower on (for example at a middle or high speed to increase the rate of space heating), and starts a timer. After the timer expires, or if the temperature at the bottom of the IST falls below a predetermined value (whichever condition occurs first), the control system acts to direct the hydronic loop to the IST and turns the AHU blower off. The control system then monitors the temperature near the bottom of the IST. After the temperature rises to a predetermined value, the control system directs the hydronic loop to the AHU, turns the AHU blower on, and starts a timer. This control loop repeats until either the call for space or water heating is satisfied, at which point the control system will put the heating system into space or water heating only mode.
When a call for water heating is received from the primary IST thermostat (or temperature sensor), the control system tells the heat pump (in water heating mode) and hydronic pump to turn on. After the hydronic supply temperature reaches a predetermined level (80° F. for example), the control system directs the hydronic loop to the IST, where it acts to heat the water in the IST. If, during the water heating cycle a call for space heating is received, the control system acts to put the system in combi mode (described above). Else, once the primary IST thermostat (or temperature sensor) is satisfied, the control system will check to see if a space heating call has been received within a prior period of time (2 hours for example). If yes, the control system will tell the heat pump to turn off, direct the hydronic flow from the IST to the AHU, and turn the AHU blower on. This control logic allows the heat energy in the hot hydronic loop after the water heating cycle is completed to heat the building instead of being wasted. If no, the control system tells the heat pump to turn off and turns the hydronic pump off after a period of time (3 minutes for example, to allow the heat pump time to cool down).
FIG. 1 shows the primary components of an example water-delivery heat pump, space and domestic water heating system, according to an aspect of the present disclosure. Water-delivery heat pump [101] sits outside of the building to be heated and delivers heat energy to the building space or domestic hot water tank via a hydronic loop that includes hydronic supply line [117], and hydronic return line [116]. The heating control system may be located, for example, within the air-handler (AHU) (as shown in FIG. 1 ), within the heat pump, or any suitable location depending on preference. AHU includes a blower and hydronic heat exchanger [104]. The AHU blower [103] moves indoor air to be heated (return air) into the AHU and through the hydronic heat exchanger [104]. AHU blower [103] may be single speed, multi-speed, or variable-speed. In a non-limiting example, AHU blower [103] may be multi-or variable-speed. Heated indoor air [113] then exits the AHU. The indoor air temperature is monitored and controlled by the indoor thermostat [121].
Domestic water is heated in an indirect storage tank (IST) [105], which includes cold water inlet [114], hot water exit [115], hydronic heat exchanger [106], primary temperature sensor (aquastat) [107], and a lower tank temperature (LTT) sensor [108]. In a non-limiting example, LTT [108] is located so that 5 to 15 gallons of water are stored in the IST below the LTT. The hydronic loop includes circulating pump [109], control valve [118], and one or more temperature sensors (for example, temperature sensors [110, hydronic supply] and [111, hydronic return]) that measure the temperature of the hydronic fluid circulating in the hydronic loop. Circulating pump [109] may be single speed, multi-speed, or variable-speed. Control valve [118] acts to direct the hydronic loop flow to either heat exchanger [104] in the AHU [102] for space heating, or to the heat exchanger [106] in the IST [105] for water heating.
FIG. 2 shows heating control system [220] is connected to, and communicates with, indoor space heating thermostat [221], Heat Pump [201], AHU blower [203], hydronic loop control valve [218], hydronic loop temperature sensors [210 and 211], hydronic loop circulating pump [209], lower IST temperature sensor (LTT) [208], and primary IST temperature sensor (aquastat) [207].
FIG. 3 describes the basic control logic when in space heating (SH) mode. Upon a call for space heating from the indoor thermostat, the control system acts to turn on the hydronic pump, directs the hydronic loop to flow to the AHU, and instructs the heat pump to turn on in SH mode (e.g., stage 1 if multiple stages are available). The control system then waits until the hydronic loop temperature increases to a pre-determined value before turning the AHU blower on (e.g., at low speed if AHU is multi—or variable—speed), and starting Timer 1. The control system then monitors Timer 1, the indoor thermostat, and the IST aquastat. If Timer 1 expires, the control system acts to increase the speed of the AHU blower (to medium for example) and starts Timer 2. If a Stage 2 space heating call is received from the indoor thermostat, the control system may instruct the heat pump to operating in Stage 2 Space Heating Mode, and may increase the AHU blower speed to high. Typically, a Stage 2 space heating call indicates the indoor temperature has decreased below the indoor thermostat set-point (differential) by a pre-determined value that is greater than a Stage 1 differential, meaning additional space heating input is needed. Typically, the heat pump will act to increase the hydronic loop temperature when in the Stage 2 Space Heating Mode, which increases the amount of heat energy provided to the building, in combination with the higher AHU blower speed.
If a call for WH is received from the IST aquastat, the control system may switch to Combi Mode (FIG. 5 ). If Timer 2 expires, the control system may initiate Stage 2 Space Heating mode (described above), if not already in this mode. If the call for SH from the indoor thermostat is removed, the control system may start Timer 3, instruct the heat pump to operate in Stage 1 Space Heating mode, and reduce the AHU blower speed to low. After Timer 3 expires, the control system checks the LTT to determine if it is below a pre-determined value. If yes, the control system switches to IST top off mode. If no, the control system instructs the heat pump to turn off, waits for the hydronic loop temperature to decrease below a pre-determined value, and then turns the AHU blower and the hydronic pump off.
FIG. 4 describes the basic control logic when operating in water heating (WH) mode. Upon a call for water heating, the control system acts to turn on the hydronic pump, directs the hydronic loop to flow to the IST, and instructs the heat pump to turn on in WH mode. The control system then monitors the indoor thermostat and IST aquastat. If a SH call is received from the indoor thermostat, the control system may switch to Combi mode (FIG. 5 ). After the IST aquastat is satisfied (e.g., the IST is re-heated and the call for WH is removed), the control system may instruct the heat pump to turn off. If the heating system has previously operated in SH mode within a pre-determined period of time (2 hours for example), the control system directs the hydronic flow to the AHU and turns the AHU blower on low speed. After the hydronic loop temperature decreases below a pre-determined value (90° F. for example), the control system acts to turn the AHU blower and hydronic pump off. If the heating system has not previously operated in SH mode within the pre-determined period of time, the control system starts Timer 4 and after Timer 4 expires, may turn the hydronic pump off.
FIG. 5 describes the basic control logic when operating when there is a call for SH and WH at the same time (Combi mode). After Combi mode is initiated, the control system records the lower IST temperature (LTT). If the indoor thermostat is calling for Stage 2 SH, the control system may act to direct the hydronic flow to the AHU, turn the AHU blower on high speed, and start Timer 5. The control system then monitors Timer 5, the IST aquastat, the SH thermostat, and LTT. If the IST aquastat is satisfied (e.g., the IST is re-heated and the call for WH is removed), the control system may act to switch to SH mode. If the call for SH from the indoor thermostat is removed, the control system acts to switch to WH mode.
If Timer 5 expires, or the LTT decreases below a pre-determined value (105° F. for example), the control system may direct the hydronic flow to the IST and then monitor the IST aquastat, SH thermostat, and LTT. If the IST aquastat is satisfied (e.g., the IST is re-heated and the call for WH is removed), the control system may act to switch to SH mode. If the call for SH from the indoor thermostat is removed, the control system may act to switch to WH mode. If the LTT increases above a pre-determined value, the control system may record LTT, direct the hydronic flow to the AHU, turn the AHU blower on high, and start Timer 5. The control logic described above repeats (e.g., the system switches back and forth between SH and WH) until either the SH thermostat or WH aquastat is satisfied and the system moves into SH only mode or WH only mode.
FIG. 6 describes the basic control logic when operating in IST top off mode. The control system may directs the hydronic flow to the IST and instruct the heat pump to operate in water heating mode. The control then monitors LTT, the indoor space heating thermostat, and the IST aquastat. If a call for SH is received, the control system may switch to SH mode. If a call for WH is received, the control system may switch to WH mode. If the LTT increases above a pre-determined value (e.g., indicating the domestic water in the IST has been re-heated), the control system may direct the hydronic flow to the AHU, turn the AHU blower on low speed, and instruct the heat pump to turn off. After the hydronic loop temperature decreases below a pre-determined value, the control system may turn the hydronic pump and AHU blower off, and may return to an idle state.
While the present disclosure has been discussed in terms of certain embodiments, it should be appreciated that the present disclosure is not so limited. The embodiments are explained herein by way of example, and there are numerous modifications, variations and other embodiments that may be employed that would still be with the scope of the present disclosure.

Claims

What is claimed is:

1. A combi heating system comprising:

a hydronic heat pump;

an indirect storage tank (IST) configured to heat potable water stored therein;

an air handler unit (AHU) configured to heat an enclosure;

a hydronic loop configured to direct hydronic flow between the hydronic heat pump, the IST and the AHU;

a temperature control system comprising a space heating thermostat configured to control an air temperature in the enclosure and one or more IST thermostats configured to control a temperature of the potable water in the IST; and

a control system comprising control logic configured to control operation of components of the combi heating system among a plurality of predetermined operating modes, in response to an operating call from the temperature control system, the plurality of predetermined operating modes comprising a space heating (SH) mode, a water heating (WH) mode and a combination (combi) mode configured to provide a combination of space heating and water heating,

wherein, in response to the operating call, the control system is configured to (i) select a mode among the plurality of predetermined operating modes, (ii) activate the hydronic heat pump, (iii) control operation of one or more of the AHU and IST and (iv) control operation of the hydronic loop in accordance with the selected mode; and

responsive to receive a termination of the operating call from the temperature control system, the control system is configured to at least one of, after said termination:

a) continue operation of the hydronic heat pump after said termination until a predetermined condition is met,

b) redirect any heat energy remaining in the hydronic loop after said termination to one of the AHU and the IST, and

c) continue operating the AHU to output any heat energy remaining in the hydronic loop after said termination.

2. The system of claim 1, wherein the control system is configured to minimize on-off cycles of the hydronic heat pump and maximize a length of on periods of the hydronic heat pump.