What are the requirements for vibration isolation measures during chiller installation? Key points for equipment foundation design and spring isolator selection
I am an HVAC expert. As the core cooling source equipment of an air-conditioning system, the operational vibration of chillers significantly affects the building structure, the acoustic environment of adjacent areas, and the service life of the equipment itself. Vibration isolation measures are a key link in ensuring long-term stable system operation and meeting noise control requirements; especially in buildings with high comfort requirements such as hotels and hospitals, they often determine the success or failure of the overall environmental quality. The following, combined with codes and engineering practice, elaborates in detail the vibration isolation requirements, equipment foundation design, and spring isolator selection key points for chiller installation.
**I. Core Requirements for Chiller Vibration Isolation Measures**
According to Article 10.3.2 of the Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings (GB 50736-2012) and Article 9.2.1 of the Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works (GB 50243-2016), large equipment such as chillers shall be provided with vibration-isolated foundations and shall meet the following general requirements:
1. **Selection of vibration isolation type**: Spring isolators or rubber isolation pads shall be preferred; for centrifugal or screw chillers with relatively large vibration, spring isolators must be used. Rubber isolation pads are only suitable for small units or temporary measures.
2. **Flexible treatment of connected piping**: Flexible joints (such as rubber flexible joints or metal bellows compensators) must be provided on the inlet and outlet piping of the unit, and the flexible joints shall be installed close to the unit side to prevent vibration from being transmitted to the building structure through the piping. Article 10.3.3 of GB 50736-2012 explicitly requires that "piping connected to equipment shall be provided with flexible connections."
3. **Isolation between unit and foundation**: It is strictly prohibited for chillers to be in direct rigid contact with the floor slab or ground; a vibration isolation layer shall be provided between the foundation and the structure.
**II. Key Points of Equipment Foundation Design**
The equipment foundation is the carrier of the vibration isolation system. During design, it shall be determined comprehensively in combination with unit weight, operating frequency, and building structure type (such as basement, floor slab, or roof):
1. **Foundation form**:
- **Concrete foundation**: A common practice is to use C20 or C25 concrete, with a foundation height generally not less than 200 mm, and the plan dimensions extending 100–200 mm beyond each side of the unit base. The foundation surface shall be flat, with an allowable levelness deviation not exceeding 2/1000.
- **Floating foundation**: Vibration isolation pads (such as rubber pads or glass wool boards) are laid beneath the concrete foundation, suitable for noise-sensitive locations (such as machine rooms below hotel guest rooms). For example, in a five-star hotel project, the chiller was located in a basement machine room directly below a banquet hall; 50 mm thick high-density glass wool boards were added beneath the foundation, and the measured floor slab vibration velocity was reduced by about 40%.
2. **Connection between foundation and structure**: The foundation shall be separated from the original structural floor slab or ground and supported by isolators. Article 9.2.2 of GB 50243-2016 emphasizes that "isolators shall be arranged evenly and the equipment shall be kept level."
3. **Load verification**: The total foundation load shall be calculated based on the unit weight (including the weight of the operating medium) and the dynamic load factor (generally 1.2–1.5) to ensure that the bearing capacity of the floor slab or roof structure meets the requirements. For example, in a data center project, the chiller weighed 8 t; the foundation was designed based on 1.5 times the dynamic load, and the structural discipline was commissioned to review the floor slab reinforcement.
**III. Key Points for Spring Isolator Selection**
Spring isolators are the core components of chiller vibration isolation; improper selection will lead to vibration isolation failure or even unit tilting. Key parameters include:
1. **Rated load and quantity**:
- The rated load of each isolator shall be the total unit weight (including foundation and medium) divided by the number of isolators, with a safety margin of 10%–20%. For example, for a unit weighing 10 t with 4 isolators, the rated load of each should preferably be 2.75–3 t (i.e., 10/4×1.1=2.75).
- The number of isolators is usually set according to the number of support points on the unit base, but uniform distribution must be ensured. Article 10.3.2 of GB 50736-2012 requires that "the number of isolators should not be less than 4."
2. **Natural frequency matching**:
- The natural frequency of the isolator shall be far lower than the unit operating frequency (usually 1/3–1/5 of the frequency corresponding to the compressor speed). For example, the operating frequency of a centrifugal chiller is about 50 Hz, and the natural frequency of the isolator should preferably be selected as 4–8 Hz; the same applies to screw units (speed about 3000 rpm, frequency 50 Hz).
- It can be calculated by the formula: natural frequency f=1/(2π)×√(k/m), where k is the spring stiffness and m is the load mass. In actual engineering, the matching parameters provided by the manufacturer shall be preferred.
3. **Damping ratio and stability**:
- Spring isolators shall have built-in damping materials (such as rubber or hydraulic damping), and the damping ratio is recommended to be ≥0.05 to prevent excessive amplitude during resonance. In a commercial complex project, undamped spring isolators were selected, and the amplitude at the instant of unit startup reached 5 mm, causing the pipe joint to rupture; this was later solved by replacing them with damped isolators.
4. **Installation height and restraint**:
- The installation height of the isolator should not exceed 1.5 times its diameter to avoid instability. At the same time, restraint devices shall be provided to prevent unit displacement or overturning. Article 9.2.3 of GB 50243-2016 requires that "isolators shall be provided with anti-displacement devices."
5. **Environmental adaptability**:
- For units installed outdoors, the isolators shall use anti-corrosion coatings (such as galvanized or stainless steel springs) to avoid stiffness changes caused by corrosion. For example, a coastal hotel project selected 316 stainless steel spring isolators, extending the service life to more than 15 years.
**IV. Actual Engineering Case**
Taking a super high-rise hotel project as an example, chillers (2 centrifugal units, each weighing 12 t) were installed in a machine room on basement level 2, directly below the presidential suite. The following measures were taken during design:
- The foundation adopted a floating type; the concrete foundation was 300 mm thick, with 100 mm thick rubber isolation pads laid beneath.
- Eight spring isolators were selected (per unit), with a rated load of 2 t each, a natural frequency of 5 Hz, and built-in damping.
- Double-sphere rubber flexible joints were used for pipe connections, and elastic supports and hangers were provided.
- After operation, actual measurements showed that the noise in the suite dropped from 45 dB(A) in the original scheme (without vibration isolation) to 28 dB(A), and the vibration velocity dropped from 3 mm/s to 0.2 mm/s, meeting the acoustic environment standard for five-star hotels.
**V. Summary**
The core of chiller vibration isolation measures lies in: the equipment foundation shall adopt a floating or vibration-isolated foundation design; spring isolator selection shall ensure matching of rated load, a natural frequency far lower than the unit operating frequency, and supporting flexible pipe connections. Negligence in any link (such as rigid foundation connection or insufficient isolator load) may lead to excessive vibration transmission, affecting building structural safety and occupant comfort. The above are reference opinions. The actual project situation still needs to be further comprehensively evaluated and implemented in combination with specific operating conditions, site conditions, and other factors.