Double pump based pressurization unit with water make-up and vacuum degassing
General:
The pressurization unit shall be complete package unit containing expansion vessel(s), buffer vessel, pumps, break tank and all controls, interlocks and ancillary equipment necessary to maintain the system static pressure in accordance with the operating conditions.
The whole unit shall be factory wired and shall be controlled via an integral control panel.
Expansion vessels shall be in accordance with EN 13831:2007 (BS 4814). Vessels shall be all welded steel construction and contain a butyl rubber bag.
Buffer vessel shall be in accordance with EN 13831:2007 (BS 4814). Vessel shall be welded steel construction and contain a butyl rubber bag or bladder enclosing a permanent pre-charged air cushion.
Each unit shall be provided with sufficient number and capacity of expansion vessels. These shall handle the full expansion volume of the system from normal cold fill or ambient conditions to normal working temperature and minimal water reserve in accordance with EN 12828 Appendix D.
The actual system water contents and the capacity of the expansion vessels, buffer vessel and break tank shall be calculated by the installer to achieve and accept the total system contraction/expansion volume of water.
The system pressure shall be maintained with the pressurisation pump within admission of ±0.2 bar. The buffer vessel shall be sized and correctly commissioned to prevent over frequent operation of the pumps.
The integral break tank shall be complete with a removable lid, inlet connection with supply pipe, overflow connection with discharge pipe, drain cock and outlet connection to the pump.
Duplicate direct-coupled pumps shall be provided comprising stainless steel casing with stainless steel impeller, stainless steel shaft, motor, mountings and fittings or as otherwise indicated.
Pumps shall be complete with drain plug and isolating valves.
Automatic changeover of the pumps shall be provided on pump failure. The changeover shall be remotely indicated. Provision shall be incorporated for periodic variation of the duty pump based on ‘hours run’ counter of the integral control panel. The over frequent starting of the duty pump shall be limited.
The system pressure shall be measured by analogue pressure sensor with
4-20 mA signal at the water side of the pressurization unit connection. The watercontent at the primary vessel shall be measured on one of the feet with load cell sensor.
Programmable high and low pressure signals/alarms shall be provided to interlock and shut off the boiler or chiller plant if the system operating limits are exceeded. A low-level alarm shall be provided on the break tank to stop the pump-set if the water level in the tank drops to a dangerous level.
A low and high level alarm shall be provided on the primary expansion vessel to respectively stop the pump-set or keep the spill valves shut if the water level in the expansion vessel drops or increases to dangerous levels.
Facilities for the transmission of the status of pumps, operating pressures and alarms from the unit to the main control panel or building management system, as indicated, shall be provided.
A safety valve shall be provided on closed systems with expansion vessels wherever required by BS 7074 Parts 1 and 2.
For initial system filling, a proprietary flexible hose system, complete with water stop valve, backflow prevention devices, braided hose, isolating valves, strainer etc. shall be provided and comply with Water Supply Regulations.
A pressure-step Vacuum degasser shall work with the Cyclonic principle and shall be integrated into the pressurization unit in order to remove air from a closed water system.
The pressurization control unit shall be selected according to manufacturer’s recommendations based on the system volume. Where a single unit cannot deal with the system volume separate multiple degassers shall be installed in parallel. The feed line to the vacuum degassing unit shall be provided with dirt separator.
The cyclonic based deaerator shall work on the basis of exposing part of the system water to a vacuum, this shall force all dissolved gases from the water. These gases shall then be expelled via an automatic air vent. Once the water sample has been deaerated it shall be fed back in to the main system. This cycle shall be repeated every 15 seconds to gradually remove all air from the system.
The pressure drop degasser shall be designed to free cooling systems from gas (air).Through a bypass, water will be degassed and sent back into the system. The system-side connection of the vessel shall be equipped with a valve that controls the flow to the device control. As this valve limits the flow a negative pressure shall be created in the vessel due to the suction effect of the pump. As a result, the water delivers its gas in the vessel. The gas accumulates in the center part of the vessel due to the cyclonic effect and forms large bubbles. If the solenoid valve shuts the pressure in the vessel shall rise which leads to the evacuation of the gases through a special valve located on the top of the vessel. This valve is designed in such a manner that air from the atmosphere cannot enter the vessel under any circumstances (sealed operation).
This process shall be interrupted regularly by closing the solenoid valve. Gases eliminated inside the pump can escape in this phase, a dry-run of the pump is avoided. Independent of the operating phase of the device, the control ensures that the pump shall run for a few seconds every 1 - 3 days. This prevents the pump from getting blocked.
Specification:
Pressure maintenance station should be pump based and should have a control unit with microprocessor control, colour touch screen display, Ethernet connection to the web, Mod-Bus connection to BMS systems, vacuum cyclonic degasser, water make-up, buffer vessel, primary vessel for expansion water volume and if required secondary vessel(s).
Control unit must have 2 pumps with time/load dependent switching, 2 spill valves, safety valve, degassing vessel, solenoid valve, break tank, feedback relays and microprocessor. The unit shall be mounted on a base plate and must be fully covered with a housing which protects all elements of the unit. Cooling version insulated against condensation.
An automatic function shall measure the gas content of the system and stop the degassing process if the gas content in the media is below a given level. A check must be performed every 24 h to verify that the gas content is still below the limit.
Control unit should guarantee highest precision where the pressure can varies only with ± 0.2 bar around the set point.
Pump should maintain smooth operation with pressure gradient controlled speed and highest system performance development, system protecting and minimised switching frequency operation with pressure gradient controlled pump speed that ensures highest performance development with self-optimized partial load operation, dynamic start/stop and controlled number of pump starts per hour.
Control unit should have a water make-up with contact meter and a break tank type AB according to EN1717, SVGW-tested.
Control unit should maintain degassing process in a special vessel with high vacuum on approx. atmospheric gas saturation, thus completely bubble-free water operation for getting rid of dissolved gases in the system.
Control unit should be CE-tested, according to the requirements of the European Directives PED/DEP 97/23/EC, 2004/108/EC, 2006/95/EC.
Microprocessor control should ensure an intelligent, secure system operation, self-optimizing with memory function.
Microprocessor control should have illuminated graphical colour touch screen display for the representation of all relevant parameters, with numeric and graphical display of the pressure and water level in the vessel.
Control unit shall withstand a maximum admissible system pressure.
Protective class of the control unit should be IP54.
Buffer vessel shall be provided to compensate for minor pressure changes and prevent frequent switching of the pump and the spill valve.
Vessels should be made-up from steel, welded and factory painted.
Vessels should be CE-tested, according to the requirements of the European Directives PED/DEP 97/23/EC.
A measuring foot to be used for content measurement, foot ring for upright assembly, including assembly kit for the water-side connection with 2 bar safety valve and ball valve for fast draining.
The vessel bag should be made up from airproof Isobutene-Isoprene Rubber (IIR) according to EN 13831 with reliable protection of the expansion water against the admission of oxygen.
The bag should be symmetrically suspended with volcanized O-ring sealing, little circumference, no wear.
The bag should be tested according to Pressure Equipment Directive with 5-years warrantee.
The bag should have the possibility to be vented at the top and drained at the bottom.
The bag must have surpassed the requirements of DIN 4807-T3 in order to insure long life cycle and extremely reliable operation.
Vessel should be suitable for temperatures between -10°C and 120°C with antifreeze capability up to 50 %.
Bag should be suitable for temperature between 5°C and 70°C.
Production and quality management shall be certified and monitored according to ISO 9001:2000.
The control panel shall display:
- System static pressure at the point of degasser connection
- Water content in the expansion vessels
- Operation mode (auto/standby)
- Collective alarm
- Pump status
- Solenoid valve status
- Water make-up status
Warranty:
The manufacturer shall warrant on supplied components for a period of 2 years from the date of dispatch.
Country of Origin:
The pressurization unit shall be manufactured in Europe. Certificates of origin shall be provided by valve manufacturer/supplier. The pressurization unit model shall have a CE certificate of conformity.