Building Cooling System Design Solutions
Our organization has developed design documentation with fundamental solutions for the cooling supply of a multifunctional complex.
Cooling System Operation
Cooling System Project
The cooling system is designed to ensure the operation of ventilation and air conditioning systems in the buildings, as well as the stylobate section. The cooling system construction is performed in accordance with technical specifications.
The total capacity of the cooling system is 14.38 MW. The building cooling system is built on water-cooled chillers and cold storage units (26 units).
Chillers and Cold Storage Units
The chillers provide high-efficiency cooling with low energy consumption (coefficient EER 4.66 in standard mode).
Cold storage units are used to significantly reduce the load on chillers. For this project, the load directly on chillers due to the use of cold storage units will be 9 MW, with a total load on the cooling system of 14.78 MW. The cold storage units will provide additional power during daytime of approximately 5.5 MW. This corresponds to 44 MWh during their operation in daytime for 8 hours. The chillers and cold storage units are located in the refrigeration center.
Refrigeration Station
The refrigeration station operates 24/7 year-round.
A separate group of chillers operates in a special mode where coolant is prepared with negative temperature - first group: 6 units producing cold for cold storage units during night time to provide the ice volume necessary for cooling supply of air conditioning systems during daytime. During daytime, the same group of chillers but in normal mode works for consumers in parallel with cold storage units, where ice melting process occurs due to heat assimilation from building air conditioning systems. Coolant supply from cold storage units begins during peak loads when chiller capacity is insufficient.
A separate subsystem with three chillers (second group) operates 24/7 year-round for consumers where such mode is necessary - data center, server rooms, dispatch rooms, security posts, transformer substation premises.
The coolant in the circuit between chillers and cold storage units is a 20% propylene glycol solution, due to the need to ensure negative temperatures at the inlets to cold storage units.
All chillers are from the same manufacturer. Each chiller is equipped with several compressors. The manufacturer guarantees chiller operation without stopping if one compressor fails and during its dismantling and repair. Additionally, all chillers are of the same size and their connection scheme to pipelines allows transferring any chiller to either group. Cold storage units are provided in quantity of 22 units. This solution ensures equipment redundancy requirement of at least 83%.
Replacement of chiller and cold storage unit manufacturers is allowed while maintaining all necessary technical characteristics within acceptable limits.
The maximum number of simultaneously operating machines is 4 units. The maximum heat flow removed from condenser circuits is 10400 kW. Thus, for heat removal from chillers, closed evaporative cooling towers are used in quantity of 2 units with total cooling capacity of 9 MW. The cooling towers are located in a two-story engineering center room. The pump station for the chiller-cooling tower circuit and the pump station for the primary chiller-consumer circuit are located in the refrigeration center room in the building basement.
Due to the significant height of the serviced building section, a cascade scheme is used in the cooling system. The system is divided into three main cascades by installing intermediate water-to-water heat exchangers. Intermediate heat exchangers are installed on technical floors. Accordingly, shut-off and control valves, pumps and heat exchangers withstand operating pressure up to 25 bar according to manufacturer technical data. Each cascade of the cooling system has additional circuits that provide cooling supply to consumers located in separate fire compartments. Each cascade and circuit of the cooling system is equipped with a separate pump group located on corresponding technical floors.
Coolant Parameters
Chiller-cooling tower circuit: 40% aqueous propylene glycol solution with design temperatures for summer period and daytime operation: +33°C/+39°C;
Chiller-cold storage unit circuit: 20% aqueous propylene glycol solution with design temperatures for summer period and night operation: -8°C/-3°C;
At the output from refrigeration station - at the inlet to the first group of water-to-water heat exchangers:
Water with design temperatures for summer period and daytime operation +1...+3°C/+6...+8°C;
Further, when passing through the next intermediate heat exchanger, water temperature increases by 2°C or (in the upper part of the building) by 1°C, reaching at the last consumer value of +9°C/+14°C.
Cooling Consumers
The main consumers of cooling (chilled water) supplied by the cooling system are:
Supply and exhaust ventilation units located on technical floors of the building. In ventilation units, cooling and dehumidification of supply air occurs;
Local terminal units of air conditioning systems. In office premises of the building, chilled beams are used as terminal units, providing maximum comfort level - silent operation of beams, optimal air mobility in working zone. In public areas, fan coil units are used as terminal units. To ensure operability requirements, additional mixing units for regulating operating water temperature are built into circuits supplying chilled water to beams.
Cooling system pipelines with diameter 50mm and more are made of steel electric-welded pipes. Pipelines 40mm and less - cross-linked polyethylene pipes. Compensation of temperature deformations is ensured by pipeline turns.
Filling and draining of propylene glycol solution through storage tanks is carried out by separate pump stations located in refrigeration station premises. Propylene glycol is first poured from tank trucks into intermediate plastic containers. Containers are delivered from unloading area to refrigeration station premises where they are connected to corresponding filling pumps and water supply system. Propylene glycol in containers is diluted with water to required concentration. Then the obtained solution goes to corresponding pipeline system via filling pumps.
Propylene glycol is not a toxic liquid.
The chillers are charged with refrigerant. A system of standard safety valves built into chillers and additional safety valves and pipelines made of annealed copper is provided.
Refrigerant is collected and discharged outside through pipelines made of annealed copper. The outlet of refrigerant vapor discharge pipe is brought out 2 meters above the roof level. Connection of each chiller is made at safety valve installation points through flexible insert in metal braid.
All refrigeration station premises are equipped with general ventilation systems. In general ventilation systems of refrigeration station, function of switching them to emergency operation mode is ensured.
Cooling System Automation
Each chiller is equipped with its own automation with microprocessor, has remote control capability through central control and management system, in addition remote parameter reading from chillers is provided through built-in digital interface.
The automation and dispatch system provides cooling system operation in winter and summer modes. Switching to summer/winter mode is carried out by dispatcher command.
Cooling system equipment operates in local, remote and automatic control modes. Transfer of system equipment to local control is carried out on control panel by manual/automatic switches. Operation in remote mode involves changing setpoints by operator from central dispatch station or from operator panel built into automation panel. In automatic mode, automation system executes algorithms embedded in it. Standard operation mode is automatic mode.
For monitoring refrigerant concentration in air of refrigeration station premises, installation of measurement sensors is provided. In case of refrigerant leaks, message is issued to automation system dispatch station.
The automation system must control:
- heat carrier parameters in characteristic points of system;
- environmental parameters;
- status of automatic switches, contactors, manual/automatic keys for pumps;
- position of motorized valves and gates by feedback signal from equipment.
For monitoring cooling system status, signals are transmitted to automation system dispatch station:
- status;
- coolant temperature at inlet and outlet of chillers.
The automation system for cooling section includes panels with controller equipment and sensors and does not include motor control panels, valves, gates and their actuators.
Cooling System Automation
Provides:
- management of chiller operation considering operation mode;
- maintaining constant pressure difference between supply and return mains for stabilizing operation of cooling consumers;
- monitoring chiller status;
- protection of circulation pumps from cavitation due to pressure drop in system;
- preliminary start of circulation pumps, performed automatically before chiller activation;
- stabilization of cooling liquid temperature supplied to chillers by managing performance of external circuit pumps smoothly using frequency regulator;
- operation of systems in full and partial load modes;
- remote activation of circulation through backup intermediate heat exchangers in case of coolant parameter loss;
- automatic regulation of coolant temperature supplied to consumers;
- automatic activation of makeup in case of pressure drop in system circuits;
- automatic activation of backup circulation pumps in case of failure of operating pumps;
- automatic activation of circulation through backup intermediate heat exchangers in case of heat carrier temperature drop below set value;
- monitoring temperature and pressure of supply and return coolant in all cooling system circuits;
- transmission of alarm signals via network.
Noise Protection Measures
To reduce vibration transmission from equipment to building load-bearing structures:
- pumps are installed on vibration-isolating supports;
- vibration-isolating inserts are used for connecting pipelines to pump nozzles;
- rigid embedding of pipelines in building walls is not allowed.
Hole sizes for pipeline passage through walls should ensure gap between surfaces of pipeline thermal insulation structure and building construction. Elastic waterproof materials should be used for gap sealing.
To reduce noise level, provide:
- additional wall cladding with soft sound-absorbing material filling;
- acoustic seam around premises perimeter filled with non-hardening latex mastic;
- door with increased sound insulation with solid filling, with threshold and tight seal around perimeter.
As measures to reduce noise from cooling tower fans, provide:
- use of anti-vibration compensators
- standard silencer
- installation of cooling towers on vibration supports.
Pipeline Corrosion Protection
For protection of cooling system pipelines from corrosion, pipelines are coated with primer in one layer and enamel in two layers. Roll-type thermal insulation and tubes - foamed rubber - are used as thermal insulation. This material has closed porous structure that prevents moisture penetration deep into thermal insulation, allowing to avoid vapor barrier.
Aluminum shells are used as protective covering layer.
Heat Removal Organization from Cooling Tower
Cooling towers are located in a two-story room where two external walls and roof represent ventilation grilles. Above this room is free space, below this room is foundation and ground. At external walls with grilles is free space.
When ventilation fans are activated, external air enters cooling tower through grilles in external walls. Parallel to this, above heat exchanger where propylene glycol circulates, water supply for irrigation is provided. Air flow directed from bottom to top catches water droplets, forming water mist from finely sprayed water. Further, gas-air mixture from water mist passes through heat exchanger where propylene glycol solution circulates. Since heat exchanger has higher temperature, instant moisture evaporation from heat exchanger surface occurs. Heated water vapor is removed through external louvered grilles in stylobate section roof, carrying away significant amount of thermal energy.
To reduce steaming, a dry heat exchanger is installed above, where propylene glycol circulates.