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Branch Flow and Delta T Control

Branch Flow System

Large distributed systems, either as a building or part of a larger district system, need good delta T to operate effectively.

Application of the Energy Valve on every unit might not always be practical, and installation of the Energy Valves on the main risers or entry to the building for district cooling isn’t advisable, as Delta T Manager may starve individual units while trying to manage a whole building.

Schematic

The system shown in the figure, using Belimo Energy Valves™, provides the following advantageous functions:

  • The flow to the branch is monitored, and can be set to prevent overflow to the floor and also monitor the delta T
  • Energy on to each branch is monitored. This can be logged and alarmed if demand from any one branch increases dramatically
  • Flow through each terminal unit can now be verified using the flow meter attached to the Energy Valve, by opening them one at a time. Closing all valves will confirm if the valves are allowing water past when closed, or if a bypass valve is open
  • Full branch transparency (volumetric flow, temperatures, cooling/heating output, etc.) with data recording and Belimo Cloud connection

 



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Energy Valve



Common Issues in Terminal Unit Branches and How the Belimo Energy Valve™ addresses them

Larger buildings have complex distribution systems and are occupied, meaning that the retrofit of an Energy Valve on each terminal is impractical. However, lack of capacity at peak times or fines from district plant providers often drive building owners to look for a solution. The figure below shows a pressure dependent system with a single balancing valve. This is a typical contract installation of multiple low flow heating units, for example, used for underfloor heating.



Mechanical balancing valves only allow for a static balancing of the total flow to the floor, with unknown flow rates to each individual unit
This can be remedied by retrofitting Belimo Energy Valves™ to every branch. Monitoring the flow and delta T being supplied to a number of terminal units allows facilities teams to identify problem ‘passing units’ and bypasses left open. This focus improves efficiency quickly by offering a targeted approach to overcoming the issues being experienced. This involves replacing passing or stuck terminal valves with 'air bubble tight' zone valves, or closing a bypass valve that has been inadvertently left open.


Our need to operate more efficient buildings, drives the demand to check water flow rates not just once but multiple times during each season. Experience tells us tenant fit outs or changes to hydronic system adversely effect non-PI installations. However, even with PI valves installed, checking the identifying passing valves and open bypasses should remain a priority to keep delta T to an acceptable range.

By using an EV in the branch line, we are able to measure the total flow to the floor and also to each individual unit, if opened sequentially



With an EV, the branch flow can be measured when each valve is opened, allowing for verification


Ghost energy/passing/leakage is typically used to describe the process where water is unintentionally passing from the flow side to the return. A bypass is left open after maintenance or at axial valve leakage rates. These small rates quickly add up when a large number of them are applied. The rate at which these valves pass or leak is made worse over time by the accumulation of dirt on the seats of the valves.



An accidentally open bypass valve may not be discovered for weeks, months or even years

By using an EV in the branch line, we are able to measure the total flow to the floor and to each individual unit. You can ensure bypasses are closed and valves are not leaking. Should a number of terminal valves suffer from leakage, the characterised ball valve technology in the EV can be closed, hence providing a stop to the wastage when the branch is not in use.



With an EV, both leaking short-stroke valves or an open bypass can be clearly identified


Often, terminal units are statically balanced, which leads them to overflow and deliver low delta T when in part load. Valves may be allowing water past them when they should be closed. Sometimes, even a bypass left open can stay undetected, reducing the pressure and dragging the delta T down.



Low delta T syndrome

The Delta T Manager, integrated in the Belimo Energy Valve™, is a function that continuously measures the temperature spread. This information can either be used to raise an alarm while you are troubleshooting the branch, looking for passing/leaking valves or bypasses left open. Once the branch is performing as well as it can, you can enable Delta T Manager to limit overflows to the branch.



Delta T Manager

Success Story: Ludmillenstift hospital in Meppen/Germany

Intelligent Energy Valve solves longstanding hydraulics problems

The Ludmillenstift hospital in Meppen/Germany is renowned well beyond the local area for its standard of medical care, state-of-the-art diagnostic and therapeutic technology and its pleasant atmosphere. However, a large number of modernisations over the years, in the form of extensions or modifications, resulted in problems in the hospital's hydraulic distributor circuits. These have finally been rectified through the use of Belimo Energy Valves™.