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2026
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Optimization of Piping Systems and Energy-Saving Strategies for Chiller and Boiler Rooms
Anyone who has designed chilled and heated water plant rooms knows that equipment selection is only the first half of the job, Pipeline design is the decisive second half that determines whether a data center can operate efficiently. For the same chiller unit, a well‑designed piping layout can achieve an annual integrated COP of 5.8, whereas a poorly designed layout may yield only 4.6—a 20% difference in energy consumption, entirely attributable to the piping system.
Today’s article covers the design of data center piping. Layout principles, valve selection, pressure loss control, and energy-saving strategies We’ll comprehensively cover all four dimensions in one go, accompanied by a real-world case study of an 18,000 m² commercial complex, and conclude with seven key takeaways to help you avoid common pitfalls during construction and commissioning.
In a nutshell: The core objectives of data center piping design are “balanced resistance, controllable flow, maintenance isolation, and low‑loss, high efficiency”—in short, a well‑designed data center is one that achieves all 16 principles.
I. Three Fundamental Principles of Data Center Piping Layout
The layout of piping in the equipment room directly determines the stability of the hydraulic operating conditions. Clause 8.5.1 of GB 50736-2012 explicitly stipulates that “the number and configuration of chillers, pumps, and cooling towers shall meet the requirements for load‑changing and part‑load operation.” Translated into piping design, this boils down to three fundamental principles:
Principle 1: Selection Between Equal-Path and Unequal-Path Configurations
Recommended piping layout within the machine room (chiller → water pump → manifold) Same program Arrangement , ensuring that the flow resistance is uniform across all chillers. According to Clause 8.5.6 of GB 50736-2012, when the resistance difference among parallel loops in a system exceeds 15%, balancing valves shall be installed. In a data center where 3 to 4 chillers are connected in parallel, a series‑type piping arrangement can keep the resistance differences among loops within 5%, thereby fundamentally preventing uneven flow distribution.
The main pipeline to the terminal distribution network depends on its scale: For chillers with fewer than 3 units, use an unequal-length piping system + End balance valve , Four or more units must be on the same route. In practice, we’ve encountered too many projects in which four chillers are arranged with an unequal piping layout: the flow rate at the near‑end chiller exceeds the design value by 30%, while the flow rate at the far‑end chiller falls short of 70%, causing the COP to plummet.
Principle 2: Main Pipe Zoning and Valve Isolation
Each chiller must be equipped with inlet and outlet connections. Maintenance of butterfly valve + rubber flexible joint , ensuring that each chiller can be isolated for maintenance without affecting the operation of other units. The diameter of the main manifold (header/distribution pipe) is calculated based on the total flow rate, but a 10–15% margin should be provided.
A device is installed between the manifold and the distribution header. Bypass pipe+ Differential Pressure Bypass Valve The pipe diameter shall be 1/2 to 2/3 of the main pipe diameter. The differential-pressure bypass valve ensures that, when the terminal load decreases and the terminal valves partially close, the minimum flow rate on the chiller evaporator side remains no less than 60% of the rated flow (per Clause 8.5.9 of GB 50736-2012), thereby preventing the chiller from tripping due to low-flow protection.
Principle 3: Redundant Loop ( Cross-connection pipe )
For systems with two or more chillers, a bypass is installed between the inlet and outlet pipelines of the chillers. Bypass line , with a diameter identical to that of the main pipe. When a chiller is undergoing maintenance or failure, the chilled water can continue circulating through the bypass line, ensuring uninterrupted cooling supply. A normally closed butterfly valve is installed on the bypass line and is manually opened during maintenance.
II. Valve and Accessory Selection Matrix
The equipment room houses a wide variety of valves in large quantities; improper selection can lead to a sharp increase in pressure drop and difficulties during maintenance. The matrix below provides the most practical quick‑reference guide for valve selection in engineering projects:
Chiller inlet and outlet—Butterfly valves (wafer type)
For sizes DN200 and above, select a wafer‑type butterfly valve, which offers low flow resistance (Kv ≈ 0.1–0.3 when fully open), light weight, and low cost. Pair it with a rubber flexible joint to reduce vibration. Avoid gate valves—due to the compact space in the machine room, gate valves are 2–3 times taller than butterfly valves, leaving insufficient clearance for maintenance.
Pump outlet – Slow-closing check butterfly valve
A check valve must be installed at the pump outlet to prevent water hammer. A slow-closing butterfly check valve—providing both check and shut-off functions—is recommended, with a closing time adjustable between 5 and 15 seconds, effectively mitigating pressure fluctuations caused by water hammer.
Pump inlet – Y-type strainer
A Y‑type strainer must be installed at the pump inlet, with a mesh size of 20–40 mesh. The strainer’s pressure drop is an “invisible killer” of system pressure loss in the pump room: under normal operating conditions, a DN150 Y‑type strainer typically exhibits a pressure drop of about 2–3 kPa, but if the screen becomes clogged, the pressure drop can surge to over 20 kPa. During design, pressure gauges (or differential pressure gauges) must be installed upstream and downstream of the strainer; when the differential pressure exceeds 10 kPa, a cleaning alert should be triggered.
Manifold – static balancing valve + butterfly valve
Each branch line is equipped at its outlet with a butterfly valve (for maintenance isolation) and a static balancing valve (for initial commissioning and flow distribution). The balancing valve shall have a nominal diameter (DN) identical to that of the pipe, and its Kvs value shall be set to 1.3 times the design flow rate.
Quick selection formula: The Kvs value of a balancing valve is calculated as Kvs = G / √ΔP, where G is the design flow rate (m³/h) and ΔP is the pressure drop across the valve (MPa). When selecting a valve, the Kvs value should be taken as 1.3 times the calculated value to ensure that the valve opening remains within the 60%–80% range—too low will leave the valve nearly fully open with no control margin, while too high will result in an excessively small opening that is difficult to regulate precisely.
III. Pressure Loss Control and Pump Configuration Optimization
The pressure loss in the data center’s piping system directly determines the pump head, and for every 1-meter increase in pump head, annual electricity consumption rises by approximately 2–3%. The key to controlling pressure loss in the data center’s piping system is… "Short, straight, and smooth" Three words: route the piping along the shortest path, minimize bends, and ensure smooth transitions at diameter changes.
3.1 Estimation of Pressure Loss in Data Center Piping Systems
The total pressure loss of the chilled water piping in the computer room (including the chiller evaporator, piping, valves, and filters) is generally maintained at… 80~120 kPa (8~12 mH₂O). Where:
• Pressure drop across the chiller evaporator: 30–50 kPa (obtained from the manufacturer’s data sheet)
• Data center piping: 20–40 kPa along the run and at local points
• Valve (butterfly valve + check valve + balancing): 10–20 kPa
• Filter (normal operation): 2–5 kPa (can exceed 20 kPa when clogged)
3.2 Pump Configuration: Primary pump vs. secondary pump
Primary pump constant-flow system (Central chiller with constant flow on the chiller side and variable flow at the terminal units): Each chiller is paired with a single primary pump, which operates at a fixed speed. Flow at the terminals is regulated via two‑way valves, while a differential pressure bypass valve between the supply and return manifolds ensures a minimum flow rate on the chiller side. Applicable scenarios: projects with no more than three chillers and relatively stable terminal‑side load variations.
Secondary Pump Variable Flow System (Cooling‑side constant flow, terminal‑side variable flow): The primary pump operates at a fixed frequency to maintain constant flow on the cooling‑side, while the secondary pump uses variable frequency to track changes in terminal‑side load. Applicable scenarios: large‑scale projects with four or more chillers, where the supply‑return water loop radius exceeds 200 m or the elevation difference exceeds 30 m. Common secondary‑pump variable‑frequency control strategies include: End-Differential Pressure Control Method — A differential pressure sensor is installed at the most unfavorable terminal, and the secondary pump adjusts its speed via variable-frequency control based on this pressure difference.
Pump head calculation: H = H₁ + H₂ + H₃ + H₄
Where: H₁ = pressure loss across the chiller evaporator (m), H₂ = pressure loss in the machine room piping and valves (m), H₃ = pressure loss in the most unfavorable loop of the terminal network (m), H₄ = pressure loss across the terminal equipment (m).
Engineering experience: The combined value of H₁ and H₂ is typically 10–15 m, while H₃ and H₄ are determined based on hydraulic calculations for the piping network; the total head is generally 18–32 m.
3.3 Variable-Frequency Group Control Strategy
Article 4.3.4 of GB 50189-2015 stipulates that “air-conditioning heating and cooling source systems shall be equipped with automatic control, and a centralized control scheme is recommended.” The core algorithm of centralized control is… Cooling Capacity – Number of Units – Three-Stage Inverter Interlock ：
① Cooling capacity calculation: Q = c × G × ΔT, with real-time measurement of the total flow rate and the supply‑return water temperature difference.
② Unit control: When the chiller’s load factor remains below 40% for 15 minutes, one unit is shut down; when the load factor exceeds 90% for 10 minutes, one additional unit is started.
③ Variable-frequency control: Secondary pump frequency = f_min + (f_max - f_min) × (ΔP_actual / ΔP_set), with a minimum frequency not less than 30 Hz.
IV. Four Key Strategies for Energy Conservation
Energy efficiency at the data center piping level hinges not on piling up equipment, but rather on… Leave appropriate interfaces for operational energy savings already during the piping design phase. . The following four strategies, ranked by return on investment:
Strategy 1: Large temperature difference, low flow rate (most effective)
Increasing the chilled water supply‑return temperature difference from 5°C (7/12°C) to 6–8°C (7/13°C or 6/14°C), while proportionally reducing the water flow rate, results in pump power consumption that is directly proportional to the cube of the flow rate (P ∝ G³). A 20% reduction in flow rate corresponds to a roughly 49% decrease in pump power. Clause 4.3.6 of GB 50189‑2015 encourages the adoption of large temperature‑difference designs. During piping system design, the pipe sizes for such high‑delta‑T systems can be reduced by one to two nominal sizes, thereby lowering initial capital costs.
Strategy 2: Free Cooling with Cooling Towers (Energy Savings During the Transition Season)
Install between the cooling tower supply and return piping and the chilled water supply and return piping. Plate heat exchanger bypass When the outdoor wet-bulb temperature falls below 10°C, the cooling tower directly produces chilled water, which is delivered to the terminal units via a plate heat exchanger, and the chiller is shut down. The piping system is designed with pre‑installed plate heat exchanger connections and valves, requiring minimal additional investment; in Shanghai, this approach can reduce chiller operating hours by approximately 800 to 1,200 hours annually.
Strategy 3: Condenser Heat Recovery (Year-Round Operation)
Install a three-way valve on the chilled-water outlet line of the chiller to divert a portion of the cooling water to a heat‑recovery plate heat exchanger, where it preheats domestic hot water or heating return water. Clause 4.3.7 of GB 50189‑2015 recommends “the use of condenser heat recovery technology.” During piping design, provide dedicated branch connections on the main chilled-water supply line for heat recovery; the recovered heat can account for 15% to 30% of the chiller’s condenser heat.
Strategy 4: Variable-frequency drive for pumps + group control (operational energy savings)
Variable-frequency secondary pumps, combined with chiller cluster control, can reduce pump energy consumption by 30% to 50% under partial-load conditions. The key lies in designing the piping system to accommodate the variable-frequency pumps. Independent differential pressure sensor interface — The sensor is installed at the most unfavorable terminal, with the signal cable routed back to the central control cabinet in the equipment room. In many projects, variable-frequency pumps are installed, but the differential pressure sensor is placed at the manifold in the equipment room, significantly compromising the effectiveness of the variable-frequency drive.
V. SVG: Piping System Diagram of the Chiller and Boiler Room
The diagram below illustrates a typical chiller‑pump system comprising three chillers, primary and secondary pumps, and a cooling tower, with key valves, pressure‑drop control points, and energy‑saving strategy integration locations clearly labeled.
▲ Parallel arrangement of three chillers · Decoupling of primary and secondary pumps · Differential pressure bypass · Free cooling via plate heat exchangers · Heat recovery integration
VI. Practical Example: 18,000 m² Commercial Complex
A commercial complex in Shanghai has a gross floor area of 18,000 m², with a summer cooling load of 1,620 kW (cooling design load of 90 W/m²) and a winter heating load of 720 kW. It is equipped with three 570-kW variable-speed centrifugal chillers—two in service and one on standby—designed for a large temperature difference of 7/13 °C (ΔT = 6 K).
Step 1: Chilled Water Flow Rate Calculation
G = Q / (c × ρ × ΔT) = 1620 / (4.186 × 1000 × 6) × 3600 = 232 m³/h
Flow rate per chiller = 232 / 2 = 116 m³/h (with 2 units in operation)
Step 2: Pipe Diameter Estimation (Velocity Method)
Main pipe (total flow rate 232 m³/h): d = 18.8 × √(232 / 1.5) = 18.8 × 12.44 = 234 mm → select DN250
Single chiller branch pipe (116 m³/h): d = 18.8 × √(116 / 1.8) = 18.8 × 8.03 = 151 mm → select DN150
Secondary pump discharge pipe (116 m³/h): d = 18.8 × √(116 / 2.0) = 18.8 × 7.62 = 143 mm → select DN150
Step 3: Pump Head Calculation
Primary pump head = Chiller evaporator (40 kPa = 4 m) + Chiller room piping and valves (50 kPa = 5 m) = 9 m → Select 12 m (including margin)
Secondary pump head = most unfavorable loop in the terminal piping network (120 kPa = 12 m) + terminal equipment (30 kPa = 3 m) + margin (10 kPa = 1 m) = 16 m → select 20 m (including margin)
Step 4: Energy-Saving Effect Estimation
Large temperature difference of 6 K vs. conventional 5 K: flow rate decreases by (6–5)/6 = 17%, and secondary pump power consumption is reduced by approximately 1 − (5/6)³ = 42%.
Annual electricity consumption of the secondary pump (conventional 5 kW): P = ρgH/η = 1000 × 9.8 × 0.0323 × 16 / 0.75 = 6.75 kW; annual energy consumption = 6.75 × 3000 h = 20,250 kWh.
Annual electricity consumption of the secondary pump (with a large temperature difference of 6 K and variable frequency): 6.75 × 0.58 = 3.92 kW; annual consumption = 3.92 × 3,000 h = 11,750 kWh.
Annual electricity savings: 8,500 kWh. At Shanghai’s commercial electricity rate of RMB 1.0 per kWh, this translates to annual savings of RMB 8,500. Additionally, free cooling provided by the plate heat exchanger saves approximately RMB 12,000 per year.
VII. 7 Tips to Avoid Common Pitfalls
Pit 1: The filter is not equipped with a differential pressure gauge. When the Y‑type filter becomes clogged, the pressure drop surges to over 20 kPa, and the pump’s head is insufficient, causing a sudden drop in flow rate—yet no one notices. During design, differential pressure gauges must be installed upstream and downstream of the filter, with an alarm triggered when the pressure difference exceeds 10 kPa.
Pit 2: The straight‑pipe length upstream of the pump is insufficient. A straight‑pipe section of at least 5D is required before the pump inlet; otherwise, vortexes at the inlet can induce cavitation. In practice, it is common to install the strainer directly adjacent to the pump inlet, with no straight‑pipe section in between.
Pit 3: The differential pressure bypass valve has been oversized. An excessively large valve diameter can cause a flow short‑circuit on the chiller side, leading to elevated supply water temperatures at the terminal units. The bypass valve should be sized based on 30–40% of the chiller’s rated flow rate, rather than being selected according to the main pipe diameter.
Pit 4: The differential pressure sensor for the variable-frequency pump is installed in the equipment room. The sensor should be located at the most unfavorable terminal—either on the rooftop or at the farthest AHU—since placement at the manifold would only measure the pressure difference on the equipment-room side and would fail to track changes in the terminal‑side load.
Pit 5: The cooling water pipes have not been insulated to prevent condensation. During the humid season, condensation forms on the pipe surfaces and drips, damaging electrical equipment and interior finishes. Cooling water pipes must also be insulated—using rubber‑plastic insulation with a thickness of 20–25 mm—particularly in sections that pass through electrical equipment rooms.
Pit 6: No automatic air vents are installed at the highest points of the piping. In the equipment room, certain sections of the piping—such as pipe runs spanning beams—lack air vents, resulting in air locks and unstable flow. An automatic air vent must be provided at every local high point.
Pit 7: Bypass piping was omitted. In systems with multiple chillers, no bypass lines were installed, causing the entire system to shut down if a single chiller failed. Bypass piping is extremely low‑cost—a short length of pipe and a butterfly valve—but it ensures system redundancy.
Summary
Data center piping design is the “last mile” of HVAC engineering and the stage that best showcases a designer’s expertise. Keep these four key words in mind: Tongcheng implements balanced distribution, selects valves to control pressure loss, decouples primary and secondary pumps to enable variable flow, and reduces energy consumption through large temperature differentials combined with free cooling. Once the piping is properly organized, the machine room naturally becomes more efficient.
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