**Abstract:** This paper presents and analyzes three application schemes for differential pressure control valves in a dual-pipe household heating system, while also discussing the principles behind selecting each scheme. It emphasizes that, under design conditions, the natural pressure head in a metered dual-pipe heating system should not be considered. Instead, indoor and outdoor systems should be treated differently. The study highlights the importance of maintaining proper pressure differentials to ensure the stable operation of thermostatic valves and prevent issues such as noise, oscillation, and reduced efficiency. Keywords: pressure control valve; household heat metering; dual-pipe heating system. **I. Overview** In a dual-pipe heating system with household metering, it is common to install thermostatic valves on each group of radiators to utilize free heat from appliances, lighting, and occupants. This leads to a variable flow system, where the pressure acting on the thermostatic valves changes with flow rate. When the actual pressure difference exceeds the valve’s capacity, noise may occur, especially when the room load is low. Frequent switching can cause oscillations, leading to wear and tear, and potentially affecting the performance of other temperature control valves. Therefore, in a well-designed system, the thermal power of the thermostatic valve must always be greater than or equal to 1, and the actual pressure difference should remain within its allowable range [1]. A differential pressure control valve, also known as a self-operated differential pressure control valve, is used in variable flow systems to maintain a constant pressure difference across a controlled loop. This ensures the normal operation of the regulating valve. In the context of a dual-pipe household heating system, the question arises: how should these valves be arranged? Three common configurations are typically considered: a. Installing the differential pressure control valve only at the building's heating inlet to regulate the pressure drop at this point. b. Placing the valve at the beginning of each riser in a two-pipe system to control the pressure difference of the riser. c. Locating the valve at the inlet of each household to maintain a constant indoor pressure. While these options are widely used, there is ongoing debate about which one is most suitable. Option 1 is the least costly but may not guarantee optimal performance, while Option 3 offers the best performance at a higher cost. Option 2 falls between the two. This paper provides an analysis of these three options, aiming to guide engineers in making informed design choices. It is important to note that the dual-pipe heating system discussed here includes both indoor and outdoor components. **II. Program Analysis** **1. Option 1: Differential Pressure Control Valve at the Building Heating Inlet** In this configuration, the differential pressure control valve is placed at the building’s heating inlet, controlling the pressure drop at that point. The total pressure difference acting on the household inlet (ΔPS) can be expressed as: ΔPS = ΔP1 + ΔP2 - ΔP3 Where: - ΔP1 is the pressure difference controlled by the valve at the heating inlet. - ΔP2 represents the natural pressure head due to water temperature differences. - ΔP3 is the resistance loss along the return pipe from the control point to the user’s inlet. Under design conditions, ΔP1 is a fixed value determined by the system’s most adverse loop. However, the natural pressure head (ΔP2) can vary depending on the floor level and temperature of the supply and return water. To ensure the thermostat valve operates correctly, ΔP2 should be taken as the minimum value during design calculations. This helps avoid situations where the actual pressure difference is lower than the designed value, leading to insufficient heating. Additionally, ΔP3 varies with flow and pipe length. During design, the maximum resistance loss is considered. However, in actual operation, the natural pressure head reduces the effective pressure difference, ensuring that the thermostat valve receives sufficient pressure to function properly. To maintain safe operation, the pressure difference at the household inlet (ΔPS) should not exceed 30 kPa. This ensures that the thermostat valve does not experience excessive pressure, which could lead to failure or inefficiency. **2. Option 2: Differential Pressure Control Valve on Each Common Riser** This option is suitable for a two-pipe system where the valve is installed at the start of each riser. Under design conditions, the natural pressure head is not considered, and the pressure difference (ΔP1) is set to match the resistance loss of the most adverse loop on the riser. Similar to Option 1, ΔP1 must be less than or equal to 30 - gH(ρh - ρg)/1000 kPa to ensure safe operation. If ΔP1 exceeds this limit, the system may not perform optimally, and the valve may not function as intended. **3. Option 3: Differential Pressure Control Valve at Each Household Inlet** For large-scale heating systems, this option is often preferred. Here, the differential pressure control valve is installed at each household inlet, ensuring a constant pressure difference for the indoor system. The pressure difference (ΔP1) should equal the total resistance loss of the most adverse indoor loop, including the heat meter and lock-up valve. To ensure safety, ΔP1 should not exceed 30 kPa. This setup minimizes fluctuations in pressure, improving the stability and efficiency of the thermostatic valves. **4. Indoor and Outdoor System Configurations** For indoor systems, it is recommended to use an iso-system to reduce the fluctuation of pressure differences across control valves. Similarly, for outdoor systems in Options 2 and 3, using an iso-system can help reduce capital costs by minimizing the resistance loss in the main pipes. **III. Conclusions** (1) Under design conditions, the natural pressure head in a metered dual-pipe heating system should not be considered. Indoor and outdoor systems should be designed separately. (2) When using Option 1, the control pressure difference (ΔP1) should equal the total resistance loss of the most adverse loop in the system, and must be less than or equal to 30 - gH(ρh - ρg)/1000 kPa. (3) For Option 2, the control pressure difference (ΔP1) should correspond to the resistance loss of the most adverse loop on the riser, and must also be less than or equal to 30 - gH(ρh - ρg)/1000 kPa. (4) Option 3 is ideal for large-scale systems. The control pressure difference (ΔP1) should equal the total resistance loss of the most adverse indoor loop, including the heat meter and lock-up valve, and must be less than or equal to 30 kPa. **References** 1. Gottfried Lerenat, Aubel, Ed., *Heating Control Technology*, Beijing: China Building Materials Industry Press, 1998 2. He Ping, Sun Gang, *Heat Engineering (New Version)*, Beijing: China Building Materials Industry Press, 1993 3. DBJ01-605-2000 *Technical Specifications for Design of New Central Heating Residential Household Heat Metering* (Beijing Standard) 4. DB29-26-2001 *Design Regulation for District Heating and Dwelling Heating* (Tianjin Standard)

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