A small ground source heat pump system and a design method of an air conditioning terminal system thereof

Abstract

The present application belongs to the technical field of ground source heat pump system design, and particularly relates to a small ground source heat pump system and a design method of an air conditioning terminal system thereof. The system is provided with a water supply and return water header on the water inlet and outlet dry pipes of a heat pump unit to replace an external buffer water tank, and a method with heat capacity as a design control parameter is introduced, including three modules of heat capacity analysis and calculation, header parameter configuration and hydraulic check. The heat capacity analysis and calculation module determines the minimum water volume according to the rated refrigerating capacity, the minimum start and stop time of the compressor and the supply and return water temperature difference; the header parameter configuration module determines the inner diameter and length of the header with the minimum water volume as a constraint; and the hydraulic check module calculates the Reynolds number to judge the flow state, selects the corresponding friction resistance coefficient to calculate the most unfavorable loop resistance, and checks whether the loop resistance is not greater than the circulating pump head and the water pump works in the high efficiency interval. The present application realizes the suppression of the return water temperature fluctuation from the design source and the suppression of the frequent start and stop of the compressor.

Description

Technical Field

[0001] This invention belongs to the field of ground source heat pump system design technology, specifically relating to a design method for a small ground source heat pump system and its air conditioning terminal system. Background Technology

[0002] For small-scale ground source heat pump systems in rural residential buildings, the cooling / heating capacity of the heat pump unit is typically below 10kW. Due to initial investment limitations, a single compressor configuration is often used. These systems have small-diameter and short-length pipes, and the system water volume is usually less than 50L, resulting in extremely limited heat capacity. Because the user-side load fluctuates with day and night and the movement of people, the return water temperature fluctuates frequently, with measured fluctuations reaching 3-5℃. This leads to frequent compressor start-ups and shutdowns, sometimes as many as 15-20 times per hour. This not only causes indoor temperature fluctuations, affecting thermal comfort, but also increases system start-up and shutdown energy consumption and accelerates compressor mechanical wear. In severe cases, it can cause the system to shut down due to overheat protection.

[0003] To address the aforementioned problems, the main existing solution is to add an external buffer tank or phase change energy storage tank to the water system, thereby increasing the system's heat capacity and mitigating temperature fluctuations. However, this approach has inherent drawbacks for small systems: Adding extra hardware such as water tanks, valves, and pipe fittings significantly increases initial investment costs and requires additional installation space. New equipment also introduces leakage risks and necessitates regular maintenance and repair. Furthermore, traditional hydraulic calculation methods for end-point water systems only aim to balance pipe resistance and distribute flow, never considering the system's heat capacity as an independent design parameter. This leads to insufficient heat capacity in small systems being overlooked during the design phase, requiring the addition of external devices to compensate afterward. There is a persistent lack of an effective means to systematically address this issue at the design stage. Summary of the Invention

[0004] The purpose of this invention is to address the problem that traditional small ground source heat pump systems have small water volume and limited heat capacity, leading to frequent compressor start-stop due to return water temperature fluctuations caused by changes in user-side load. By improving the supply and return water manifolds in the inlet and outlet pipelines of the heat pump unit and introducing a design method that constrains the system's heat capacity parameters, this invention proposes a system configuration and terminal water system design method that does not require an external buffer water tank but increases the system's water storage capacity by setting up supply and return water manifolds to smooth out temperature fluctuations.

[0005] The present invention achieves the above objectives through the following technical solutions: Firstly, this invention proposes a small-scale ground source heat pump system, comprising a buried pipe underground heat exchange system, a ground source heat pump unit, and an air conditioning terminal system. The air conditioning terminal system includes terminal equipment, a circulating pump, and connecting pipes. Supply and return water manifolds are installed on the inlet and outlet water mains of the ground source heat pump unit. These supply and return water manifolds are used to store water to mitigate return water temperature fluctuations. The supply and return water manifolds include a supply water manifold and a return water manifold, with the supply water manifold and the return water manifold having the same inner diameter and length. The sum of the internal volume of the supply and return water manifolds and the internal volume of the terminal equipment is not less than the minimum water volume V. w,min The minimum water volume V w,min Determined according to the following formula: ,in, The rated cooling capacity of the ground source heat pump unit is [missing information]. Δt represents the minimum start-up and shutdown time of the compressor in the ground source heat pump unit, and Δt represents the supply and return water temperature difference of the air conditioning terminal system. The density of water, This is the specific heat capacity of water.

[0006] The ground source heat pump unit is connected to the air conditioning terminal system, and the compressor in the ground source heat pump unit is started and stopped based on the return water temperature of the air conditioning terminal system.

[0007] Furthermore, the system also includes a heat capacity analysis and calculation module, a manifold parameter configuration module, and a hydraulic verification module; The heat capacity analysis and calculation module is used to obtain the rated cooling capacity and minimum start-stop time of the compressor of the ground source heat pump unit, and, in combination with the supply and return water temperature difference of the air conditioning terminal system, determine the minimum water volume required by the air conditioning terminal system. The manifold parameter configuration module is used to determine the inner diameter and length of the supply and return water manifold with the minimum water volume as a design constraint, so that the sum of the internal volume of the supply and return water manifold and the internal volume of the terminal equipment is not less than the minimum water volume. The hydraulic verification module is used to calculate the flow resistance of the most unfavorable loop of the air conditioning terminal system based on the inner diameter and the length, and to verify that the flow resistance is not greater than the head of the circulation pump and that the operating point of the circulation pump is in the high efficiency range, so as to determine the final values ​​of the inner diameter and the length.

[0008] Furthermore, the single-unit cooling or heating capacity of the ground source heat pump unit is no more than 10kW. Thus, the minimum water volume determined by the aforementioned minimum water volume calculation formula is kept within the range that can be met by using supply and return water manifolds with commonly used engineering pipe diameters, which matches the load characteristics of the small system targeted by this invention.

[0009] Furthermore, the nominal diameter of the supply and return water manifold is not less than DN40, so as to avoid the pipe length required to meet the minimum water volume exceeding the actual available space due to the pipe diameter being too small, or the flow velocity and flow resistance in the pipe being too high.

[0010] Furthermore, the supply and return water manifolds are laid underground to save system layout space and to coordinate with the underground construction method of the underground heat exchange system. The underground laying method can also buffer the disturbance of the water temperature inside the pipe caused by drastic changes in ambient temperature and reduce the risk of water freezing inside the pipe in winter under the condition of open-air laying.

[0011] Furthermore, the heat capacity analysis and calculation module determines the minimum water volume through the following steps: Based on the rated cooling capacity of the ground source heat pump unit The minimum start-stop time of the compressor and the supply and return water temperature difference of the air conditioning terminal system Calculate the minimum required heat capacity using the following formula. : ; According to the minimum heat capacity Specific heat capacity of water The density of water The minimum water volume is calculated according to the following formula. : .

[0012] Furthermore, the manifold parameter configuration module determines the inner diameter D and length L of the supply and return water manifolds according to the following volume constraint relationship: - ; in, Let be the internal volume of the terminal device; when solving, first calculate the pipe diameter with the pipe length fixed, and then adjust the pipe length if the requirements cannot be met.

[0013] Furthermore, the hydraulic verification module is used to perform hydraulic verification on the inner diameter and length determined by the manifold parameter configuration module, including: Calculate the Reynolds number of the fluid in the supply and return water manifold based on the inner diameter and volumetric flow rate, and determine the flow regime based on the Reynolds number; Based on the determined flow regime, a method for calculating the friction resistance coefficient corresponding to the flow regime is selected to calculate the flow resistance of the most unfavorable loop in the air conditioning terminal system. If the flow resistance is greater than the head of the circulating pump, or the operating point of the circulating pump deviates from the high-efficiency range, the system returns to the manifold parameter configuration module to re-determine the inner diameter and length of the supply and return water manifolds until the flow resistance is not greater than the head of the circulating pump and the circulating pump operates in the high-efficiency range.

[0014] Furthermore, in the hydraulic verification module, the Reynolds number Re is obtained according to the following formula: ; Where Q is the volumetric flow rate of the air conditioning terminal system, and D is the inner diameter of the supply and return water manifold. The kinematic viscosity of water; The criteria for determining the flow state are as follows: when Re < 2300, it is laminar flow; when 2300 ≤ Re ≤ 4000, it is a transition zone; and when Re > 4000, it is turbulent flow.

[0015] Furthermore, based on the determined flow regime, the method for calculating the corresponding frictional drag coefficient is selected, including: If the flow regime is laminar, the frictional resistance coefficient is calculated according to the following formula: ; If the flow regime is turbulent, then the friction drag coefficient is calculated according to the Colbrook equation: ; in, This is the equivalent roughness of the pipe's inner wall. If the flow regime is a transition region, the frictional resistance coefficient is determined by interpolation.

[0016] Furthermore, the flow resistance is calculated using the Darcy-Weisbach formula for pressure drop along the friction path, as follows: ; in, Where L is the friction resistance coefficient, L is the length of the supply and return water manifold, and D is the inner diameter of the supply and return water manifold. Let ρ be the density of water, and v be the average flow velocity across the pipe cross-section.

[0017] Secondly, this invention proposes a design method for an air conditioning terminal system of the aforementioned small-scale ground source heat pump system, comprising the following steps: S1: Determine the minimum heat capacity required by the air conditioning terminal system based on the rated cooling capacity of the ground source heat pump unit, the minimum start-stop time of the compressor, and the supply and return water temperature difference of the air conditioning terminal system. S2: Determine the required minimum water volume based on the minimum heat capacity, specific heat capacity of water, and density of water; S3: Using the minimum water volume as a design constraint, configure the inner diameter and length of the supply and return water manifolds in the air conditioning terminal system so that the sum of the internal volume of the supply and return water manifolds and the internal volume of the terminal equipment is not less than the minimum water volume; S4: Calculate the Reynolds number of the fluid in the supply and return water manifold after configuration, determine the flow state based on the Reynolds number, and select the corresponding friction resistance coefficient calculation method based on the determined flow state to calculate the flow resistance of the most unfavorable loop of the air conditioning terminal system. S5: Compare the flow resistance with the head of the circulating pump, and check whether the operating point of the circulating pump is in the high-efficiency range. If the flow resistance is not greater than the head of the circulating pump and the circulating pump is operating in the high-efficiency range, then determine the final values ​​of the inner diameter and length of the supply and return water manifold; otherwise, return to step S3 to reconfigure the inner diameter and length of the supply and return water manifold until the requirements are met.

[0018] The beneficial effects of this invention are as follows: 1. This invention uses a heat capacity analysis and calculation module to convert the rated cooling capacity and minimum start-stop time of the heat pump unit into the minimum water volume required by the air conditioning terminal system. This provides a clear heat capacity constraint target for pipeline design, ensuring from the design stage that the system's own water volume is sufficient to mitigate return water temperature fluctuations, eliminating the need for any external buffer tanks or phase change energy storage devices. Compared to existing technologies that require adding external water tanks to compensate for insufficient heat capacity, this invention directly eliminates the initial investment in additional hardware such as water tanks, valves, and pipe fittings, avoiding the installation space occupation and leakage risks associated with new equipment. It is particularly suitable for rural residential buildings with limited installation space and maintenance conditions.

[0019] 2. This invention uses a hydraulic verification module to calculate the Reynolds number of the fluid in the pipe and determine the flow regime after the diameter and length of the supply and return water manifolds are determined. It then employs different methods depending on whether the flow is laminar, in a transition zone, or turbulent. The method of calculating friction resistance coefficient using interpolation or the Colbrook equation fills the gap in the application of traditional HVAC design codes, which only consider turbulent flow and do not cover laminar flow conditions. This ensures the accuracy of resistance calculation under large-diameter design conditions. Simultaneously, the hydraulic verification module configures the flow resistance of the most unfavorable loop to be no greater than the head of the circulating pump and that the pump's operating point is within its high-efficiency range. This ensures that the decrease in resistance per unit length due to increased pipe diameter offsets the increase in total resistance due to increased pipe length, maintaining the original high-efficiency operating point of the circulating pump. This achieves heat capacity enhancement without replacing the circulating pump or adjusting the system flow rate, making the design scheme highly feasible in practical engineering. Attached Figure Description

[0020] Figure 1 This is an overall structural block diagram of a small ground source heat pump system provided in an embodiment of the present invention; Figure 2 A flowchart illustrating the design method of an air conditioning terminal system provided in an embodiment of the present invention; Figure 3 A schematic diagram of a traditional solution that uses an external buffer water tank to prevent frequent compressor start-stop. Figure 4 This is a schematic diagram of the system principle of the present invention, in which a water supply and return manifold is used to replace an external buffer water tank; Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above application content.

[0022] First Embodiment like Figure 1 As shown, this embodiment provides a small-scale ground source heat pump system, including a buried pipe underground heat exchange system, a ground source heat pump unit, and an air conditioning terminal system. The buried pipe underground heat exchange system is used for heat exchange with underground soil and rock. The heat pump unit includes a compressor, condenser, throttling device, and evaporator to complete the refrigerant's cooling / heating cycle. The air conditioning terminal system includes air conditioning terminals, a terminal circulation pump, and connecting pipes to form a user-side water circulation system; the air conditioning terminals may include fan coil units or underfloor heating coils.

[0023] For small ground source heat pump systems, due to initial investment limitations, a single compressor configuration is often used. The overall cooling / heating capacity is usually below 10kW. The pipe diameter is small, the pipe length is short, the heat capacity of the terminal system is small, and there is basically no energy storage capacity.

[0024] Figure 3 The diagram illustrates the design principle of a traditional solution that uses an external buffer tank to prevent frequent compressor start-stop cycles. This external buffer tank is connected in series or parallel in the terminal water circulation loop, increasing the total system water volume to mitigate return water temperature fluctuations. However, this solution requires additional hardware such as tanks, valves, and pipes, increasing initial investment costs, occupying extra installation space, and introducing leakage risks and regular maintenance requirements.

[0025] Figure 4 This is a schematic diagram illustrating the design principle of using a supply and return water manifold to replace an external buffer water tank in this invention. Figure 3 The core difference is that this invention does not add any external water tank or phase change energy storage device. Instead, it sets up supply and return water manifolds on the inlet and outlet water mains of the heat pump unit, increases the diameter and length of the manifolds, and allows the manifolds themselves to store enough water, using the water volume of the manifolds themselves to replace the function of an external buffer water tank. Figure 4 The location and route of the supply and return water manifolds are marked with thick solid lines, and compared with the original design to visually demonstrate the changes in physical configuration of this invention. The larger diameter and longer supply and return water manifolds significantly increase the internal water storage capacity, thus replacing the traditional manifold design. Figure 3 The internal and external water tanks have a heat capacity buffering function.

[0026] Example: A small ground source heat pump system has a rated cooling capacity of 10kW, a minimum compressor start-stop time of 300s, a supply and return water temperature difference of 5℃ in the original system's air conditioning terminal system, a flow rate of 1.72m³ / h, a main pipe diameter of DN40, a specific friction resistance of 51.72Pa / m, a most unfavorable loop resistance of 30kPa, an evaporator resistance of 50kPa, a fan coil unit resistance of 30kPa, a water pump head of 120kPa, and an efficiency of 80%.

[0027] Minimum heat capacity: =10×300 / 5=600kJ / ℃; Specific heat capacity of water The minimum water volume required by the system is: .

[0028] Understandably, this value is the lower limit constraint of the system design. The actual total water volume of the system must reach or exceed this value in order to meet the heat capacity buffering requirements.

[0029] In this embodiment, the system also includes a heat capacity analysis and calculation module, a manifold parameter configuration module, and a hydraulic verification module.

[0030] Specifically, the heat capacity analysis and calculation module is used to obtain the rated cooling capacity and minimum start-stop time of the compressor of the ground source heat pump unit, and, in combination with the supply and return water temperature difference of the air conditioning terminal system, to determine the minimum water volume required by the air conditioning terminal system.

[0031] It should be noted that the root cause of the frequent compressor starts and stops is insufficient total water volume in the terminal water system, causing the return water temperature to rapidly exceed the compressor's start-stop control threshold when the user-side load changes. Therefore, to solve this problem at its source, it is first necessary to quantify exactly how much water volume the system needs to effectively buffer temperature fluctuations.

[0032] This embodiment establishes a quantitative relationship between compressor operating constraints and system water heat capacity through a heat capacity analysis and calculation module. The minimum allowable operating time of the compressor and the temperature difference between the system supply and return water are used as design inputs to deduce the minimum heat capacity that the system must achieve.

[0033] Understandably, this design approach is fundamentally different from existing technologies. In traditional design methods, heat capacity has never been used as a constraint in pipeline design. This embodiment, however, is the first to incorporate this parameter as an independent design variable into the calculation system.

[0034] Furthermore, the heat capacity analysis and calculation module determines the minimum water volume through the following steps: Based on the rated cooling capacity of the ground source heat pump unit The minimum start-stop time of the compressor and the supply and return water temperature difference of the air conditioning terminal system Calculate the minimum required heat capacity using the following formula. : ; According to the minimum heat capacity Specific heat capacity of water The density of water The minimum water volume is calculated according to the following formula. : .

[0035] Among them, the rated cooling capacity of the heat pump unit As specified in the compressor manufacturer's specifications, the unit is kW or W; minimum start-stop time of the compressor. The minimum interval between two compressor starts is given in the compressor specifications and is usually not less than 180 seconds. All the above parameters should be calculated using a consistent unit system. For example, if the rated cooling capacity is in kW, the minimum start-stop time is in seconds, and the specific heat capacity of water is in kJ / (kg·℃), then the calculated minimum water volume should be in cubic meters (m³). 3 .

[0036] As an example, for a small 10kW ground source heat pump unit, take... =300s, =5℃, then the minimum required heat capacity =10×300 / 5=600kJ / ℃.

[0037] Continuing with the previous example, This value represents the minimum total water volume required by the terminal water system. It can be understood that this value is a lower limit constraint for system design; the actual total water volume of the system must reach or exceed this value to meet the heat buffering requirements.

[0038] The minimum heat capacity required by the terminal water system is positively correlated with the system scale (cooling / heating capacity). The larger the system load, the greater the cooling capacity of the heat pump unit, and the greater the minimum heat capacity required under the same minimum operating time and supply / return water temperature difference. Based on this, designers can directly estimate the required minimum heat capacity according to the aforementioned formula based on the system scale, and use it as input for the manifold parameter configuration module.

[0039] Furthermore, as a preferred embodiment, the single-unit cooling or heating capacity of the ground source heat pump unit is no greater than 10kW; the nominal diameter of the supply and return water manifold is no less than DN40. For small systems with limited layout space, to meet the heat capacity requirements within a reasonable pipe length range, it is preferable to use supply and return water manifolds with a diameter no less than DN50 to reduce the required pipe length and lower pipe resistance. By setting the lower limit of the pipe diameter, it can be ensured that the manifold has sufficient flow and water storage capacity, avoiding the need for a pipe length exceeding the actual available space or causing excessive system resistance due to an excessively small pipe diameter.

[0040] Specifically, the manifold parameter configuration module is used to determine the inner diameter and length of the supply and return water manifolds based on the minimum water volume as a design constraint, so that the sum of the internal volume of the supply and return water manifolds and the internal volume of the terminal equipment is not less than the minimum water volume.

[0041] The manifold parameter configuration module determines the feasible design region within the parameter space formed by the inner diameter D and length L of the supply and return water manifolds. This region is defined by both thermal capacity constraints and hydraulic constraints. Combinations of D and L that satisfy the thermal capacity constraints constitute a family of feasible solutions. Among them, the combination that simultaneously ensures that the total flow resistance of the most unfavorable loop is not greater than the head of the circulating pump and that the pump operates in the high-efficiency range is the feasible design space that simultaneously satisfies both thermal capacity constraints and hydraulic constraints. This ensures that the sum of the internal volume of the manifold and the internal volume of the terminal equipment is not less than the required minimum water volume, and also ensures the hydraulic compatibility of the adjusted system with the original circulating pump.

[0042] Specifically, the water volume of the air conditioning terminal system consists of two parts: one is the volume of the supply and return water manifold, which is a design variable and is the main body of the energy storage of this invention; the other is the volume of the terminal equipment, that is, the internal water volume of each fixed component in the air conditioning terminal system other than the manifold. It is understood that the internal volume of the terminal equipment is determined by the structure of the selected equipment itself, and is used as a known constant in the heat capacity check during design calculations, remaining unchanged regardless of adjustments to the piping design parameters in this invention. Therefore, the total water volume of the system can be expressed as: The portion that can be actively adjusted by designers to increase water volume is mainly the volume of the supply and return water manifolds. .

[0043] Furthermore, the manifold parameter configuration module determines the inner diameter D and length L of the supply and return water manifolds according to the following volumetric constraints: - ; The supply and return water manifolds consist of two pipes: a supply water manifold and a return water manifold. This refers to the existing water volume in the terminal equipment, including at least one of the following: the volume of the fan coil unit, the volume of the underfloor heating coil, and the volume of the connecting pipes. When solving this problem, first calculate the pipe diameter with a fixed pipe length based on the available space for the manifold layout; adjust the pipe length if the requirements are not met.

[0044] As a conservative engineering design, it is advisable to adopt... =0, that is, according to π / 2 × D 2 × L ≥ V w,min The calculations below will be performed using this conservative approach.

[0045] According to the above formula: m 3 If the total length of the supply and return water manifolds is L = 10m, then the pipe diameter of the supply and return water manifolds that meets the minimum water volume requirement is: The value is DN100.

[0046] If we want to reduce the manifold diameter to DN80, the manifold length required to meet the minimum water volume requirement is: .

[0047] As can be seen, the manifold parameter configuration module uses the minimum water volume as a design constraint to determine the diameter and length of the supply and return water manifolds.

[0048] The water volume of the air conditioning terminal system consists of two parts: one is the water volume of the supply and return water manifold, which is a design variable; the other is the water volume of the connecting pipes between the manifold and the terminal equipment. The latter is generally smaller and can be considered as a safety margin. Therefore, the minimum water volume of the system that meets the minimum heat capacity constraint can be approximately replaced by the supply and return water manifold volume.

[0049] According to the above embodiments, the manifold parameter configuration module, while meeting the minimum heat capacity constraint, also needs to reserve adjustment space for subsequent hydraulic verification. It is understood that different combinations of pipe diameter and length may produce the same water volume but correspond to different flow resistances. Therefore, this embodiment does not determine a set of D and L in isolation, but rather determines the optimal combination of D and L through feedback iteration of the subsequent hydraulic verification module.

[0050] Specifically, the hydraulic verification module is used to analyze the total flow resistance of the most unfavorable loop of the air conditioning terminal system based on the inner diameter and length, configure the total flow resistance to be no greater than the head of the circulating pump, and verify that the circulating pump is operating in the high-efficiency range, so as to determine the final value of the inner diameter and length and maintain the rated operating point of the circulating pump in the terminal water circulation loop.

[0051] Understandably, after determining the pipe diameter and length combination under the premise of meeting heat capacity constraints, the manifold parameter configuration module needs to further verify whether the hydraulic characteristics of this combination are compatible with the original system. Specifically, when the pipe diameter increases, the pipe cross-sectional area increases, the flow velocity decreases at the same volumetric flow rate, and the frictional resistance per unit length decreases significantly; however, increasing the pipe length will lead to an increase in total frictional resistance. This invention utilizes the offsetting relationship between the decrease in resistance per unit length caused by increasing the pipe diameter and the increase in total resistance caused by increasing the pipe length, ensuring that the total flow resistance of the most unfavorable loop after adjustment is not greater than the head of the circulating pump and that the pump operates in the high-efficiency range. Thus, while increasing the system's heat capacity, it maintains the rated operating point of the original circulating pump, achieving the technical effect of not replacing the circulating pump and not adjusting the system flow rate.

[0052] Furthermore, the hydraulic verification module performs hydraulic verification on the inner diameter and length determined by the manifold parameter configuration module, including: The Reynolds number of the fluid in the supply and return water manifold is calculated based on the inner diameter and volumetric flow rate, and the flow regime is determined based on the Reynolds number.

[0053] Specifically, in step S4 (i.e., step S4 in the second embodiment), the Reynolds number... We obtain it according to the following formula: ; Where Q is the volumetric flow rate of the terminal water circulation loop, and D is the inner diameter of the pipe. The kinematic viscosity of water; The criteria for determining the flow regime are: laminar flow when Re < 2300, transition zone when 2300 ≤ Re ≤ 4000, and turbulent flow when Re > 4000.

[0054] In a preferred embodiment, the method for calculating the frictional resistance coefficient is selected based on the determined flow regime, including: If the flow is laminar, the friction drag coefficient is calculated using the following formula: ; If the flow is turbulent, the friction drag coefficient is calculated according to the Colbrook equation: ; in, This is the equivalent roughness (m) of the inner wall of the pipe, which can be obtained from a table for commonly used pipe materials.

[0055] If the flow regime is a transition zone, the frictional resistance coefficient is determined by interpolation, that is, linear or nonlinear interpolation is performed between laminar and turbulent flow to ensure the continuity of resistance calculation.

[0056] Understandably, traditional HVAC design codes assume turbulent flow in their hydraulic calculations, neglecting methods for handling laminar or transitional flow states. This embodiment explicitly specifies the verification of the Reynolds number after pipe diameter adjustment and selects the corresponding friction coefficient calculation method based on the actual flow regime. This fills the application gap of traditional design codes in small-system, large-diameter design scenarios, ensuring the accuracy of hydraulic calculations.

[0057] In a preferred embodiment, the total flow resistance is calculated using the Darcy-Weisbach formula for pressure drop along the friction path, as follows: ; in, Where L is the friction resistance coefficient, L is the pipe length, and D is the pipe inner diameter. Let ρ be the density of water, and v be the average flow velocity across the pipe cross-section.

[0058] Step S5: Resistance Verification and Parameter Determination The total flow resistance ΔP new The flow resistance is compared with the head of the circulating pump, and it is checked whether the operating point of the circulating pump is in the high-efficiency range. If the total flow resistance is not greater than the head of the circulating pump and the circulating pump is operating in the high-efficiency range, the final values ​​of the inner diameter and length of the pipe are determined; otherwise, the process returns to step S3 (i.e. step S3 in the second embodiment) to reconfigure the inner diameter and length of the pipe until the requirements are met.

[0059] Specifically, if ΔP new If the pipe diameter and length are not greater than the head of the circulating pump (120 kPa in this example) and the circulating pump operates in its high-efficiency range, it means that the hydraulic characteristics of the currently configured pipe are matched with the circulating pump, provided that the heat capacity requirements are met. The circulating pump can operate at high efficiency near its rated operating point, and the design is complete. If ΔP new If the resistance is greater than the head of the circulating pump, it indicates that the resistance of the current pipeline configuration is too high, exceeding the driving capacity of the circulating pump. It is necessary to return to step S3 and reselect the combination of pipe diameter and length. During reconfiguration, the pipe diameter can be further increased or the pipe length appropriately shortened to reduce the total resistance, but the volume constraint π / 2 × D must be ensured simultaneously. 2 × L ≥ V w,min - V terminal The condition still holds true. Through several iterations, it can converge to the optimal solution that simultaneously satisfies the thermal capacity constraint and the hydraulic constraint.

[0060] Specifically, in traditional terminal water system piping design, due to the small pipe diameter and high flow velocity, the fluid Reynolds number is typically greater than 4000, indicating a turbulent flow state. In this state, the frictional resistance coefficient is determined by the Colbrook equation. However, this invention, by increasing the pipe diameter while maintaining a relatively constant flow rate, significantly reduces the fluid velocity, leading to a decrease in the Reynolds number and potentially causing the fluid to enter a laminar flow state (Re < 2300). In laminar flow, the calculation method for the frictional resistance coefficient is completely different from that in turbulent flow. Therefore, in this embodiment, the hydraulic verification module first calculates the Reynolds number of the fluid in the adjusted manifold to determine the flow regime.

[0061] Continuing with the previous example, the total resistance of the original system = 30 + 50 + 30 = 110 kPa. The improved supply and return water manifold has a diameter of DN80, a length of 14.3m, and a flow velocity of 0.1m / s.

[0062] While maintaining a constant flow rate, increasing the pipe diameter causes the flow velocity and Reynolds number to decrease synchronously, potentially leading to a flow pattern that transitions from the turbulent region to the laminar region via the transition zone. When Re < 2300, the flow is in the laminar region, where the friction coefficient decreases linearly according to λ = 64 / Re, independent of pipe wall roughness. When 2300 ≤ Re ≤ 4000, the flow is in the transition zone, where the flow is unstable, and the friction coefficient can be determined by interpolation. When Re > 4000, the flow is in the turbulent region, where the friction coefficient is determined by the Colbrook equation and is related to both pipe wall roughness and the Reynolds number, with the effect of roughness increasing with increasing Re.

[0063] Continuing the previous example, the improved supply and return water manifold has a diameter of DN80, a length of L=14.3m, a flow velocity of 0.1m / s, and a kinematic viscosity of... ,but: In the turbulent region, the frictional resistance coefficient should be calculated according to the Colbrook equation.

[0064] Despite the increased pipe diameter and decreased flow velocity, the flow in the manifold remains in the turbulent region (Re≈7.6×10). 3 However, the resistance decreased significantly, with a specific friction resistance of 1.71 Pa / m, which is much lower than that of the original system. To reduce the initial investment, the manifold diameter was appropriately reduced and the pipe length was increased according to the configuration module of the manifold parameters.

[0065] In contrast, we examine the case where the manifold enters the laminar flow region. Using the Reynolds number formula Re = 4Q / (πDν) and taking the upper limit of laminar flow Re = 2300, at the rated flow rate Q = 1.72 m³ / s... 3 / h、ν=1.004×10 -6 m 2 Under the condition of / s, the minimum pipe diameter D required to enter laminar flow can be obtained. min≈263 mm (between DN250 and DN300): When the pipe diameter is smaller than this value (e.g., standard pipe DN250, Re≈2424), the flow is still in the transition / turbulent region; when the pipe diameter is increased to the standard pipe DN300 (D=0.30 m, pipe length still taken as 14.3 m), the flow velocity drops to about 0.0068 m / s, Re≈2.0×10 3 When the flow temperature is below 2300°, the flow enters the laminar flow region. At this point, the frictional resistance coefficient must be calculated strictly according to the laminar flow formula λ=64 / Re≈0.032 (independent of pipe wall roughness), with a specific frictional resistance of only about 0.0024 Pa / m, far lower than the 1.71 Pa / m in the turbulent flow condition after enlarging the pipe diameter mentioned earlier. This condition is precisely the blind spot ignored by traditional HVAC design, which only assumes turbulence: if empirical formulas such as those from Colbrook are directly applied in this region, results inconsistent with the actual laminar flow resistance will be obtained. The hydraulic verification module of this invention ensures the accuracy of resistance calculation throughout the entire process from turbulent to laminar flow by first determining the flow regime of Re and then selecting the corresponding calculation formula.

[0066] The iterative process of configuration, verification, feedback, and reconfiguration described above is the key guarantee for achieving the dual goals of heat capacity improvement and hydraulic compatibility in this invention. Through this design logic, the final determined pipe diameter and length satisfy both the heat capacity sufficiency condition and the hydraulic equivalence condition, thus possessing good feasibility in practical engineering.

[0067] In summary, this invention achieves the same heat capacity buffering effect with extremely low incremental cost by storing heat in the supply and return water manifolds themselves, without adding any additional equipment or maintenance requirements, thus possessing significant economic and practical advantages.

[0068] This embodiment achieves thermal capacity adequacy verification and hydraulic equivalence verification during the system design phase through the collaborative work of the heat capacity analysis and calculation module, the manifold parameter configuration module, and the hydraulic verification module. This ensures that the final system does not require any external buffer tank or phase change energy storage device. It can effectively suppress return water temperature fluctuations by relying solely on the water stored in the terminal pipes. This suppresses frequent compressor start-stop from the design source and significantly improves the system's operational reliability and energy efficiency.

[0069] Second Embodiment like Figure 2 As shown, this embodiment provides a design method for an air conditioning terminal system in a small ground source heat pump system, used to construct an air conditioning terminal system for a small ground source heat pump system as described in the first embodiment. The method includes the following steps S1 to S5.

[0070] Step S1: Determine the minimum heat capacity required by the air conditioning terminal system based on the rated cooling capacity of the ground source heat pump unit, the minimum start-stop time of the compressor, and the supply and return water temperature difference of the air conditioning terminal system.

[0071] Step S2: Calculate the minimum required water volume The required minimum water volume is determined based on the minimum heat capacity, the specific heat capacity of water, and the density of water.

[0072] Step S3: Configure supply and return water manifold parameters based on heat capacity constraints With minimum water volume To constrain design requirements, determine the diameter D and length L of the supply and return water manifolds for the air conditioning terminal system. Ensure that the sum of the internal volume of the supply and return water manifolds and the internal volume of the terminal equipment is not less than the required minimum water volume.

[0073] Step S4: Flow regime verification and drag calculation Calculate the Reynolds number of the fluid in the supply and return water manifolds after configuration, determine the flow regime based on the Reynolds number, and select the corresponding friction resistance coefficient calculation method based on the determined flow regime to calculate the total flow resistance of the most unfavorable loop of the air conditioning terminal system.

[0074] Step S5: Hydraulic verification The flow resistance is compared with the head of the circulating pump, and it is checked whether the operating point of the circulating pump is in the high-efficiency range. If the flow resistance is not greater than the head of the circulating pump and the circulating pump is operating in the high-efficiency range, the final values ​​of the inner diameter and length of the supply and return water manifold are determined; otherwise, return to step S3 to reconfigure the inner diameter and length of the supply and return water manifold until the requirements are met.

[0075] Continuing with the previous example, the total resistance of the original system is 30 + 50 + 30 = 110 kPa. The original main pipe diameter is DN40. After the improvement, the supply and return water manifold diameter is DN80, the flow velocity is 0.1 m / s, the specific friction is 1.7 Pa / m, and the manifold resistance is 1.7 × 14.3 × 1.5 = 36.47 Pa, which is much smaller than the resistance of the original system.

[0076] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated.

Claims

1. A small-scale ground source heat pump system, comprising a buried pipe underground heat exchange system, a ground source heat pump unit, and an air conditioning terminal system, wherein the air conditioning terminal system includes terminal equipment, a circulating pump, and connecting pipes, characterized in that: A supply and return water manifold is installed on the inlet and outlet water mains of the ground source heat pump unit. The supply and return water manifold is used to store water to stabilize return water temperature fluctuations. The supply and return water manifold includes a supply water manifold and a return water manifold. The supply water manifold and the return water manifold have the same inner diameter and length. The sum of the internal volume of the supply and return water manifold and the internal volume of the terminal equipment is not less than the minimum water volume V. w,min The minimum water volume V w,min Determined according to the following formula: ,in, The rated cooling capacity of the ground source heat pump unit is [missing information]. Δt represents the minimum start-up and shutdown time of the compressor in the ground source heat pump unit, and Δt represents the supply and return water temperature difference of the air conditioning terminal system. The density of water, This is the specific heat capacity of water; The ground source heat pump unit is connected to the air conditioning terminal system, and the compressor in the ground source heat pump unit is started and stopped based on the return water temperature of the air conditioning terminal system.

2. The small ground source heat pump system according to claim 1, characterized in that, The system also includes a heat capacity analysis and calculation module, a manifold parameter configuration module, and a hydraulic verification module; The heat capacity analysis and calculation module is used to obtain the rated cooling capacity and minimum start-stop time of the compressor of the ground source heat pump unit, and, in combination with the supply and return water temperature difference of the air conditioning terminal system, determine the minimum water volume required by the air conditioning terminal system. The manifold parameter configuration module is used to determine the inner diameter and length of the supply and return water manifold with the minimum water volume as a design constraint, so that the sum of the internal volume of the supply and return water manifold and the internal volume of the terminal equipment is not less than the minimum water volume. The hydraulic verification module is used to calculate the flow resistance of the most unfavorable loop of the air conditioning terminal system based on the inner diameter and the length, and to verify that the flow resistance is not greater than the head of the circulation pump and that the operating point of the circulation pump is in the high efficiency range, so as to determine the final values ​​of the inner diameter and the length.

3. The small ground source heat pump system according to claim 1, characterized in that, The single-unit cooling or heating capacity of the ground source heat pump unit shall not exceed 10kW.

4. The small ground source heat pump system according to claim 1, characterized in that, The nominal diameter of the supply and return water manifold is not less than DN40.

5. The small ground source heat pump system according to claim 1, characterized in that, The supply and return water manifolds are laid underground.

6. The small ground source heat pump system according to claim 2, characterized in that, The heat capacity analysis and calculation module determines the minimum water volume through the following steps: Based on the rated cooling capacity of the ground source heat pump unit The minimum start-stop time of the compressor and the supply and return water temperature difference of the air conditioning terminal system Calculate the minimum required heat capacity using the following formula. : ； According to the minimum heat capacity Specific heat capacity of water The density of water The minimum water volume is calculated according to the following formula. : 。 7. The small ground source heat pump system according to claim 2, characterized in that, The manifold parameter configuration module determines the inner diameter D and length L of the supply and return water manifolds according to the following volume constraint relationship: - ； in, Let be the internal volume of the terminal device; when solving, first calculate the pipe diameter with the pipe length fixed, and then adjust the pipe length if the requirements cannot be met.

8. The small ground source heat pump system according to claim 2, characterized in that, The hydraulic verification module is used to perform hydraulic verification on the inner diameter and length determined by the manifold parameter configuration module, including: Calculate the Reynolds number of the fluid in the supply and return water manifold based on the inner diameter and volumetric flow rate, and determine the flow regime based on the Reynolds number; Based on the determined flow regime, a method for calculating the friction resistance coefficient corresponding to the flow regime is selected to calculate the flow resistance of the most unfavorable loop in the air conditioning terminal system. If the flow resistance is greater than the head of the circulating pump, or the operating point of the circulating pump deviates from the high-efficiency range, the system returns to the manifold parameter configuration module to re-determine the inner diameter and length of the supply and return water manifolds until the flow resistance is not greater than the head of the circulating pump and the circulating pump operates in the high-efficiency range.

9. The small ground source heat pump system according to claim 8, characterized in that, In the hydraulic verification module, the Reynolds number Re is obtained according to the following formula: ； Where Q is the volumetric flow rate of the air conditioning terminal system, and D is the inner diameter of the supply and return water manifold. The kinematic viscosity of water; The criteria for determining the flow state are as follows: when Re < 2300, it is laminar flow; when 2300 ≤ Re ≤ 4000, it is a transition zone; and when Re > 4000, it is turbulent flow.

10. The small ground source heat pump system according to claim 9, characterized in that, The method for calculating the frictional resistance coefficient based on the flow regime determined by the judgment includes: If the flow regime is laminar, the frictional resistance coefficient is calculated according to the following formula: ； If the flow regime is turbulent, then the friction drag coefficient is calculated according to the Colbrook equation: ； in, This is the equivalent roughness of the pipe's inner wall. If the flow regime is a transition region, the frictional resistance coefficient is determined by interpolation.

11. The small ground source heat pump system according to claim 10, characterized in that, The friction drop in the flow resistance is calculated according to the Darcy-Weisbach formula, as follows: ； in, Where L is the friction resistance coefficient, L is the length of the supply and return water manifold, and D is the inner diameter of the supply and return water manifold. Let ρ be the density of water, and v be the average flow velocity across the pipe cross-section.

12. A design method for an air conditioning terminal system of a small ground source heat pump system according to any one of claims 1 to 11, characterized in that, Includes the following steps: S1: Determine the minimum heat capacity required by the air conditioning terminal system based on the rated cooling capacity of the ground source heat pump unit, the minimum start-stop time of the compressor, and the supply and return water temperature difference of the air conditioning terminal system. S2: Determine the required minimum water volume based on the minimum heat capacity, specific heat capacity of water, and density of water; S3: Using the minimum water volume as a design constraint, configure the inner diameter and length of the supply and return water manifolds in the air conditioning terminal system so that the sum of the internal volume of the supply and return water manifolds and the internal volume of the terminal equipment is not less than the minimum water volume; S4: Calculate the Reynolds number of the fluid in the supply and return water manifold after configuration, determine the flow state based on the Reynolds number, and select the corresponding friction resistance coefficient calculation method based on the determined flow state to calculate the flow resistance of the most unfavorable loop of the air conditioning terminal system. S5: Compare the flow resistance with the head of the circulating pump, and check whether the operating point of the circulating pump is in the high-efficiency range. If the flow resistance is not greater than the head of the circulating pump and the circulating pump is operating in the high-efficiency range, then determine the final values ​​of the inner diameter and length of the supply and return water manifold; otherwise, return to step S3 to reconfigure the inner diameter and length of the supply and return water manifold until the requirements are met.

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